NE

HUMAN ANATOMY

THE BODY AT WORK

CURIOUS QUESTIONS

Inside the
human heart

Explore
the human
skeleton

Structure
of the
ribcage

Breakdown of
the immune
system

How do we
speak and
sing?

OVER

200

ING
AMAZ
AMS
DIAGR

BOOK OF

THE

Tour the
lymphatic
system

HUMAN

How many
bones in the
human foot?

BODY

Guide to
essential
organs

Everything you need to know about the human body

Understand
the respiratory
system

Behind
the kidney
walls

Inside the
arteries
Complex
brain
functions

How did our

hands evolve?

Dissecting the
stomach
Muscle
anatomy
explained

PACKED FULL OF FASCINATING FACTS, IMAGES & ILLUSTRATIONS

WorldMags.net

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WorldMags.net
Welcome to
BOOK OF

THE

HUMAN

BODY

The human body is truly an amazing thing. Capable of awe-inspiring feats of

speed and agility, while being mind-blowing in complexity, our bodies are
unmatched by any other species on Earth. In this newly revised edition of
the Book of the Human Body, we explore our amazing anatomy in ne detail
before delving into the intricacies of the complex processes, functions and
systems that keep us going. We also explain the weirdest and most wonderful
bodily phenomena, from blushing to hiccuping, cramps to blisters. We
will tour the human body from head to toe, using anatomical illustrations,
amazing photography and authoritative explanations to teach you more. This
book will help you understand the wonder that is the human body and in no
time you will begin to see yourself in a whole new light!

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WorldMags.net

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WorldMags.net

BOOK OF

THE

HUMAN

BODY
Imagine Publishing Ltd
Richmond House
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Bournemouth
Dorset BH2 6EZ
 +44 (0) 1202 586200
Website: www.imagine-publishing.co.uk

Publishing Director
Aaron Asadi
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Ross Andrews
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Fiona Hudson
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Alexander Phoenix
Photographer
James Sheppard
Printed by
William Gibbons, 26 Planetary Road, Willenhall, West Midlands, WV13 3XT
Distributed in the UK, Eire & the Rest of the World by
Marketforce, Blue Fin Building, 110 Southwark Street, London, SE1 0SU
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Sydney, New South Wales 2000, Australia Tel +61 2 8667 5288
Disclaimer
The publisher cannot accept responsibility for any unsolicited material lost or damaged in the
post. All text and layout is the copyright of Imagine Publishing Ltd. Nothing in this bookazine may
be reproduced in whole or part without the written permission of the publisher. All copyrights are
recognised and used specifically for the purpose of criticism and review. Although the bookazine has
endeavoured to ensure all information is correct at time of print, prices and availability may change.
This bookazine is fully independent and not affiliated in any way with the companies mentioned herein.
How It Works Book of the Human Body Fourth Revised Edition 2015 Imagine Publishing Ltd

Part of the

bookazine series

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WorldMags.net

CONTENTS
064

Human anatomy

Urinary
system
explained

010 50 amazing body facts

018 Human cells
020 Inside a nucleus
021 What are stem cells?
022 Brain power
026 Vision and eyesight
028 How ears work
030 The tonsils
031 Vocal cords
032 All about teeth
034 Anatomy of the neck
036 The human skeleton

026

The power of
your brain

038 The spine

092
How do we
breathe?

040 How the body moves

042 How muscles work
044 Skin colour / Skin grafts
045 Under the skin
046 Heart attacks
047 Heart bypasses
048 The human kidneys
050 Kidney transplants
052 Vestigial organs
053 How the spleen works
054 How the liver works

The body at work

056 The small intestine

076 The science of sleep

058 The human ribcage

084 The blood-brain barrier

060 How the pancreas works

085 Pituitary gland up close

062 How your bladder works

086 Human digestion explained

064 The urinary system

088 Altitude sickness / Synapses

066 Inside the human stomach

089 Adrenaline

068 The human hand

090 Singing explained

070 Finger nails / Achilles tendon

092 Human respiration

071 Inside the knee

094 Dehydration / Sweating

072 How your feet work

095 Scar types

006

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Curious questions
142 Left or right brained?
144 Brain freeze
145 Runny nose / Comas
146 Sore throat / Ears pop /
Freckles

165
Cholesterol
explained

157

Correcting heart rhythms /

Salt / Adams apple

158 Seasickness / Rumbling

stomachs
159 Cravings
160 Feet smell / Knee-jerk
reaction
161 Blisters / Cramp

147 Memory / Toothpaste /

Epidurals

162 Brain control / Laughing

148 Blush / Caffeine / Fainting

163

149 Eyebrows / Earwax / Brain &

identity

164 Allergies / Eczema

150 72-hour deodorant /

Modern llings

165 Bruises / Water allergy /

Cholesterol

151

166 What are twins?

What powers cells?

Dandruff / Eye adjustment /

Distance the eye can see

152 Can we see thoughts?

168 Alveoli

154 How anaesthesia works

169 Migraines / Eyedrops

155

170 Paper cuts / Pins and

needles / Funny bones

Stomach ulcers / Mouth ulcers

156 Enzymes / Love

096 The immune system

171

100 Bone fracture healing

172 Raw meat / Inoculations /

Upper arm and leg

101 Making protein

173

102 The cell cycle

Aching muscles / Fat hormone

What causes insomnia?

104 Human pregnancy

174 Hair growth / Blonde hair

appearance

106 Embryo development

175

Wrinkles explained

108 How we taste / Taste buds

136

109 What is insulin?

The signs
of ageing

110 How do we smell?

111

Short term memory

112 White blood cells

114 The science of genetics
119 Burns
120 Circulatory system
122 How your blood works
126 Hormones
128 Tracheotomy surgery
129 Hayfever
130 Exploring the sensory system
134

Chickenpox

135

Why we cry

136

The ageing process revealed

100

Healing bone
fractures

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007

WorldMags.net
HUMAN
ANATOMY
024

010
50 fantastic
facts about
the body

SPL

How
we think

026
Inside the eye

021

068

Stem cells

The human
hand

010 50 amazing body facts

From head to toe

040 How the body moves

The types of joints explained

018 Human cells

How are they structured?

042 How muscles work

Muscle power revealed

020 Inside a nucleus

Dissecting a cells control centre

044 Skin colour / Skin grafts

Skin facts explained

021 What are stem cells?

Building block bring new life

031 Vocal cords

See how they help us talk

045 Under the skin

Anatomy of our largest organ

022 Brain power

About our most complex organ

032 All about teeth

Dental anatomy and more

046 Heart attacks

Why do they happen?

026 The science of vision

Inside the eye

034 Anatomy of the neck

Impressive anatomical design

047 Heart bypasses

How are blockages bypassed?

028 How ears work

Sound and balance explained

036 The human skeleton

A bounty of boney facts

048 Human kidneys

How do your kidneys function?

030 The tonsils

What are these eshy lumps?

038 The human spine

33 vertebrae explained

050 Kidney transplants

The bodys natural lters

008

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022

Understand
the nerves

024
How do
we smell?

058
The
human
ribcage

072
How do our
feet work?

046
Inside the heart

018
Cell structure
revealed
052 Vestigial organs
Are they really useless?
053 How the spleen works
Learn how it staves off infections
054 How the liver works
The ultimate multitasker
056 The small intestine
How does this organ work?

066 Inside the human stomach

How does this organ digest food?

058 The human ribcage

The protective function of the ribs

068 The human hand

Our most versatile body part

060 How the pancreas works

The bodys digestive workhorse

070 Finger nails / Achilles tendon

A look at ngernails and more

062 How your bladder works

Waste removal facts

071 Inside the knee

See how it allows us to walk

064 The urinary system

How we process waste

072 How your feet work

Feet facts and stats

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009

HUMAN
ANATOMY
WorldMags.net

Top 50 body facts

50

Amazing facts
about the
human
body
There are lots of medical
questions everybody wants
to ask but we just never
get the chance until now!
The human body is the most complex
organism we know and if humans tried
to build one articially, wed fail
abysmally. Theres more we dont
know about the body than we do know. This
includes many of the quirks and seemingly
useless traits that our species carry. However,
not all of these traits are as bizarre as they
may seem, and many have an evolutionary
tale behind them.
Asking these questions is only natural
but most of us are too embarrassed or
never get the opportunity so heres a
chance to clear up all those niggling
queries. Well take a head-to-toe tour
of the quirks of human biology,
looking at everything from tongue
rolling and why we are ticklish
through to pulled muscles
and why we dream.

010

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DID YOU KNOW? Useless body parts include the appendix, the coccyx and wisdom teeth

How do
we think?

What are thoughts? This question will

keep scientists, doctors and
philosophers busy for decades to
come. It all depends how you want to
dene the term thoughts. Scientists
may talk about synapse formation,
pattern recognition and cerebral
activation in response to a stimulus
(such as seeing an apple and
recognising it as such). Philosophers,
and also many scientists, will argue
that a network of neurons cannot
possibly explain the many thousands
of thoughts and emotions that we
must deal with. A sports doctor might
state that when you choose to run, you
activate a series of well-trodden
pathways that lead from your brain to
your muscles in less than a second.
There are some specics we do know
though such as which areas of your
brain are responsible for various types
of thoughts and decisions.

Pre-motor cortex

Frontal lobe
The frontal lobe is where your
personality is, and where your
thoughts and emotions form.
Removing this or damaging it can
alter your persona.

Primary motor cortex

The pre-motor cortex is where

some of your movements are
co-ordinated.

The primary motor cortex and the primary

somatosensory cortex are the areas which
receive sensory innervations and then
co-ordinate your whole range of movements.

Parietal lobe
The parietal lobe is responsible for
your complex sensory system.

Brocas
area

Primary auditory
complex

Brocas area is
where you form
complex words
and speech
patterns.

The primary auditory

complex is right next to
the ear and is where you
interpret sound waves
into meaningful
information.

Temporal lobe
The temporal lobe decides what to
do with sound information and also
combines it with visual data.

SPL

Occipital lobe
The occipital lobe is all
the way at the back, but
it interprets the light
signals in your eyes into
shapes and patterns.

Wernickes area
Wernickes area is where you interpret
the language you hear, and then you
will form a response via Brocas area.

Why can
some people
roll their
tongues but
others cant?

Dora Pete

In the
mornings,
do we wake up
or open our
eyes rst?
Sleep is a gift from nature, which is
more complex than you think. There
are ve stages of sleep which represent
the increasing depths of sleep when
youre suddenly wide awake and your
eyes spring open, its often a natural
awakening and youre coming out of
rapid eye movement (REM) sleep; you
may well remember your dreams. If
youre coming out of a different phase,
eg when your alarm clock goes off, it
will take longer and you might not
want to open your eyes straight away!

Do eyeballs
grow like the
rest of the body?

Only a small amount

hence why babies
appear so beautiful, as
their eyes are slightly
out of proportion and
so appear bigger.

Although were often taught in school that

tongue rolling is due to genes, the truth is
likely to be more complex. There is likely
to be an overlap of genetic factors and
environmental inuence. Studies on
families and twins have shown that it
cannot be a case of simple genetic
inheritance. Ask around the fact that
some people can learn to do it suggests
that in at least some people its
environmental (ie a learned behaviour)
rather than genetic (inborn).

Why do we ddle
4
subconsciously?
Im constantly
playing with my hair
This is a behavioural response
some people play with their hair
when theyre nervous or bored. For
the vast majority of people such
traits are perfectly normal. If they
begin to interfere with your life,
behavioural psychologists can help
but its extremely rare that youll
end up there.

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What is
a pulse?

When you feel your

own pulse, youre
feeling the direct
transmission of your
heartbeat down an
artery. You can feel a
pulse where you can
compress an artery
against a bone, eg
the radial artery at
the wrist. The
carotid artery can be
felt against the
vertebral body, but
beware: a) press too
hard and you can
faint, b) press both at
the same time and
youll cut off the
blood to your brain
and, as a protective
mechanism, youll
denitely faint!
011

HUMAN
ANATOMY
WorldMags.net

Top 50 body facts

The areas from 120 to 180
degrees are seen as 2D as
only one eye contributes, but
we dont really notice.

3D eld
Matt Willman

The central 120-degree

portion is the 3D part of
our vision as both eyes
contribute this is the part
we use the most.

11

How fast does

blood travel round
the human body?

What is
the point
of tonsils?

Your total circulating volume is about ve litres. Each

red blood cell within this has to go from your heart,
down the motorway-like arteries, through the
back-road capillary system, and then back through the
rush-hour veins to get back to your heart. The process
typically takes about a minute. When youre in a rush
and your heart rate shoots up, the time reduces as the
blood diverts from the less-important structures (eg
large bowel) to the more essential (eg muscles).

1. The most
important organ
SPL

The tonsils are collections of

lymphatic tissues which are
thought to help ght off
pathogens from the upper
respiratory tract. However,
they themselves can
sometimes become infected
leading to tonsillitis. The ones
you can see at the back of your
throat are just part of the ring
of tonsils. You wont miss them
if theyre taken out for
recurrent infections as the
rest of your immune system
will compensate.

The human eld of vision is just about 180

degrees. The central portion of this
(approximately 120 degrees) is binocular or
stereoscopic ie both eyes contribute,
allowing depth perception so that we can
see in 3D. The peripheral edges are
monocular, meaning that there is no
overlap from the other eye so we see in 2D.

12

Why do
we burp?

A burp is a natural
release of gas from
the stomach. This gas
has either been
swallowed or is the
result of something
youve ingested such
as a zzy drink. The
sound comes from the
vibration of the
oesophageal
sphincter at the
oesophago-gastric
junction, which is the
narrowest part of the
gastrointestinal tract.

2. Under pressure
Blood is moving fastest
and under the highest
pressure as it leaves the
heart and enters the
elastic aorta.

The brain has its own

special blood supply
arranged in a circle.

are
9What
lips for?

Lips are predominantly used as a tactile sensory organ,

typically for eating, but also for pleasure when kissing. They
are also used to help ne-tune our voices when we speak.

does it feel so weird when

10Why
you hit your funny bone?
Youre actually hitting the ulnar nerve as it wraps around the bony
prominence of the humerus bone, leading to a funny sensation.
Although not so funny as the brain interprets this sudden trauma
as pain to your forearm and ngers!

This massive vein sits

behind the aorta but is
no poor relation
without it, blood
wouldnt get back
to your heart.

3. The kidneys
These demand a massive
25 per cent of the blood
from each heart beat!

012

5. The
furthest point
These arteries and
veins are the furthest
away from your
heart, and blood flow
here is slow. As you
grow older, these
vessels are often the
first to get blocked by
fatty plaques.

Its different for everybody your

age, nutrition, health status, genes
and gender all play a role. In terms
of length, anywhere between
0.5-1 inch (1.2-2.5cm) a month
might be considered average,
but dont be surprised if youre
outside this range.

4. The inferior
vena cava

SP
L

ULNAR NERVE

13

How many
inches of
hair does the
average person
grow from their
head each year?

WorldMags.net

Frettie

Whats my
eld of vision
in degrees?

2D eld

5 TOP
FACTS

BODY
ROUNDUP

Emotions

Sneeze fast!

Red blood cells

Hard worker

Liquid

While great apes such as gorillas,

chimps and orang-utans use facial
expressions to show their
feelings, human beings are the
only animals known to cry as a
result of their emotions.

A sneeze is typically expelled at

around 161km/h (100mph).
Sneezing helps protect the body
by keeping the nose free of
bacteria and viruses. Theres a
video on our website.

Red blood cells also known

as erythrocytes live on
average for 120 days. There
are approximately 25 trillion
red blood cells in your body at
any given moment.

The heart beats on average

100,000 times per day. Of
course this will greatly vary
depending on your level of
activity and your
environmental conditions.

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Humans are made up of 70 per

cent water, which is essential
for body growth and repair. The
NHS suggests drinking 1.2
litres of water a day to avoid
growing dehydrated.

DID YOU KNOW? The average person breaks wind between 8-16 times per day

14

Why are
everyones
ngerprints
different?
Your ngerprints are ne ridges of
skin in the tips of your ngers and
toes. They are useful for improving
the detection of small vibrations
and to add friction for better grip.
No two ngerprints are the same
either on your hands or between
two people and thats down to
your unique set of genes.

15
Tristanb

Why do
we only
remember
some dreams?

16

Why, as we
get older,
does hair growth
become so erratic?

Dreams have fascinated humans

for thousands of years. Some
people think they are harmless
while others think they are vital to
our emotional wellbeing. Most
people have four to eight dreams
per night which are inuenced by
stress, anxiety and desires, but
they remember very few of them.
There is research to prove that if
you awake from the rapid eye
movement (REM) part of your sleep
cycle, youre likely to remember
your dreams more clearly.

DO MEN
HAVE NIPPLES?
20 WHY

Men and women are built from

the same template, and these
are just a remnant of a mans
early development.

WHATS THE
POINT OF
21
EYEBROWS?

17

Why do we all
have different
coloured hair?

Most of it is down to the genes that result

from when your parents come together to
make you. Some hair colours win out
(typically the dark ones) whereas some (eg
blonde) are less strong in the genetic race.

Is it possible to
18
keep your eyes
open when you sneeze?
Your eyes remain shut as a
defence mechanism to prevent
the spray and nasal bacteria
entering and infecting your
eyes. The urban myth that
your eyes will pop out if you
keep them open is unlikely
to happen but keeping
them shut will provide
some protection against
nasty bugs and viruses.

Biologically, eyebrows can

help to keep sweat and
rainwater from falling into
your eyes. More importantly in
humans, they are key aids to
non-verbal communication.

IS A
BELLY BUTTON?
22 WHAT
The umbilicus is where a
babys blood flows through to
get to the placenta to exchange
oxygen and nutrients with the
mothers blood. Once out, the
umbilical cord is clamped
several centimetres away from
the baby and left to fall off. No
one quite knows why youll get
an innie or an outie its
probably all just luck.

WHY DO
FINGERNAILS
23
GROW FASTER THAN
TOENAILS?

Hair follicles in different parts of your

body are programmed by your genes to
do different things, eg the follicles on
your arm produce hair much slower
than those on your head. Men can go
bald due to a combination of genes and
hormonal changes, which may not
happen in other areas (eg nasal hair).
Its different for everybody!

The longer the bone at the end

of a digit, the faster the growth
rate of the nail. However there
are many other influences too
nutrition, sun exposure,
activity, blood supply and
thats just to name a few.

19

What gives me
my personality?

Researchers have spent their whole lives trying to

answer this one. Your personality forms in the front
lobes of your brain, and there are clear personality
types. Most of it is your environment that is, your
upbringing, education, surroundings. However some
of it is genetic, although its unclear how much. The
strongest research in this comes from studying twins
what inuences one set of twins to grow up and be
best friends, yet in another pair, one might become a
professor and the other a murderer.

WorldMags.net

WHY DOES MY
ARM TINGLE
24
AND FEEL HEAVY IF I
FALL ASLEEP ON IT?
This happens because youre
compressing a nerve as youre
lying on your arm. There are
several nerves supplying the
skin of your arm and three
supplying your hand (the
radial, median and ulnar
nerves), so depending on
which part of your arm you lie
on, you might tingle in your
forearm, hand or fingers.

013

HUMAN
ANATOMY
WorldMags.net

Top 50 body facts

25

What makes some blood

groups incompatible while
others are universal?
Your blood type is determined by protein markers known as antigens on the surface of your
red blood cells. You can have A antigens, B antigens, or none in which case youre blood type
O. However, if you dont have the antigen, your antibodies will attack foreign blood. If youre
type A and youre given B, your antibodies attack the B antigens. However, if youre blood type
AB, you can safely receive any type. Those who are blood group O have no antigens so can give
blood to anyone, but they have antibodies to A and B so can only receive O back!

26

What is a pulled
muscle?

The hamstrings

Strain

These are a group of

three main muscles
which flex the knee.

A pulled muscle, or
strain, is a tear in a group
of muscle fibres as a
result of overstretching.

A
You have A antigens and B
antibodies. You can receive blood
groups A and O, but cant receive B.
You can donate to A and AB.

B
You have B antigens and A
antibodies. You can receive blood
groups B and O, but cant receive
A. You can donate to B and AB.

AB
You have A and B antigens and no
antibodies. You can receive blood
groups A, B, AB and O (universal
recipient), and can donate to AB.

O
Though warming up can help prevent
sprains, they can happen to anyone,
from walkers to marathon runners.
Pulled muscles are treated with RICE:
rest, ice, compression and elevation

SPL

SPL

You have no antigens but have A and B

antibodies. You can receive blood group
O, but cant receive A, B or AB and can
donate to all: A, B, AB and O.

What is the
appendix? Ive
28
heard it has no use

Why does
peoples
29
skin turn yellow

but can kill you

The heart is the most

efcient it extracts
80 per cent of the
oxygen from blood.
But the liver gets the
most blood 40 per
cent of the cardiac
output compared to
the kidneys, which
get 25 per cent, and
heart, which only
receives 5 per cent.
014

30

What
is the
gag reex?

if they contract
liver disease?

SPL

27

Which
organ
uses up the
most oxygen?

The appendix is useful in cows for

digesting grass and koala bears for
digesting eucalyptus koalas can have
a 4m (13ft)-long appendix! In humans,
however, the appendix has no useful
function and is a remnant of our
development. It typically measures
5-10cm (1.9-3.9in), but if it gets blocked it
can get inamed. If it isnt quickly
removed, the appendix can burst and
lead to widespread infection which can
be lethal.

This yellow discolouration of the skin

or the whites of the eyes is called
jaundice. Its due to a buildup of
bilirubin in your body, when normally
this is excreted in the urine (hence
why urine has a yellow tint). Diseases
such as hepatitis and gallstones can
lead to a buildup of bilirubin due to
altered physiological processes,
although there are many other causes.

3. Vagus nerve
The vagus nerve is stimulated,
leading to forceful contraction
of the stomach and diaphragm
to expel the object forwards.

1. Foreign bodies
This is a protective mechanism to prevent
food or foreign bodies entering the back of
the throat at times other than swallowing.

4. The gag
2. Soft palate
The soft palate (the fleshy part of the
mouth roof) is stimulated, sending signals
down the glossopharyngeal nerve.

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This forceful expulsion

leads to gagging, which
can develop into retching
and vomiting.

ANIMALS

FAST

1. Human
vs cheetah

TALL

While the world record

holder Usain Bolt can run it
in 9.58 seconds, a cheetah
can run 100m (328ft) in
just over six seconds.

2. Human
vs giraffe

3. Human
vs ea

HIGH

The average man in England

is 1.7m (5.5ft) tall. The
tallest man ever was 2.7m
(8.8ft). A giraffe can grow
up to 6m (19.7ft).

The mens outdoor high

jump world record is 2.45m
(less than twice the height
of a man). A ea can jump
up to 100 times its height.

WorldMags.net
Why dont eyelashes
32keep growing?
Wegmann

HEAD
HEAD
HUMANS VS

DID YOU KNOW? Your brain interprets pain from the rest of the body, but doesnt have any pain receptors itself

Loyna

shlomit g

Your eyelashes are formed from hair follicles, just like those on your
head, arms and body. Each follicle is genetically programmed to
function differently. Your eyelashes are programmed to grow to a
certain length and even re-grow if they fall out, but they wont grow
beyond a certain length, which is handy for seeing!

WHY DO
SOME PEOPLE
36
HAVE FRECKLES?

One side of the brain is

typically dominant over the
other. Since each hemisphere
of the brain controls the
opposite side (ie the left
controls the right side of your
body), right-handed people
have stronger left brain
hemispheres. Occasionally
youll nd an ambidextrous
person, where hemispheres
are co-dominant, and these
people are equally capable
with both right and left hands!

Could
we
34
survive on
vitamins
alone?

No, you need a diet

balanced in
carbohydrate,
protein, fat,
vitamins and
minerals to survive.
You cant cut one of
these and expect to
stay healthy.
However, its the
proportions of these
which keep us
healthy and t. You
can get these from
the ve major food
groups. Food charts
can help with this
balancing act.

35

Why do we get a
high temperature
when were ill?

The immune response leads to inammation and the release of

inammatory factors into your blood stream. These lead to an
increased heart rate and blood ow, which increases your core body
temperature as if your body is doing exercise. This can lead to
increased heat production and thus dehydration; for this reason, its
important to drink plenty of clear uids when youre feeling unwell.

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Klaus D. Peter, Wiehl, Germany

Light touches, by feathers, spiders, insects or other

humans, can stimulate ne nerve-endings in the skin
which send impulses to the somatosensory cortex in the
brain. Certain areas are more ticklish such as the feet
which may indicate that it is a defence mechanism
against unexpected predators. It is the unexpected
nature of this stimulus that means you can be tickled.
Although you can give yourself goosebumps through
light tickling, you cant make yourself laugh.

33

Jeinny Solis

31

Why are we
ticklish?

What
makes us
left-handed?

Freckles are concentrations of

the dark skin pigment melanin
in the skin. They typically
occur on the face and
shoulders, and are more
common in light-skinned
people. They are also a
well-recognised genetic trait
and become more dominant
during sun-exposure.

IS
A WART?
37 WHAT

Warts are small, rough, round

growths of the skin caused by
the human papilloma virus.
There are many different types
which can occur in different
parts of the body, and they can
be contagious. They commonly
occur on the hands, but can
also come up anywhere from
the genitals to the feet!

WHY DO I
TWITCH IN
38
MY SLEEP?
This is common and known in
the medical world as a
myoclonic twitch. Although
some researchers say these
twitches are associated with
stress or caffeine use, they are
likely to be a natural part of the
sleep process. If it happens to
you, its perfectly normal.

015

HUMAN
ANATOMY
WorldMags.net
3x SPL

Top 50 body facts

39

What triggers
the heart and
keeps it beating?
The heart keeps itself beating. The
sinoatrial node (SAN) is in the wall of the
right atrium of the heart, and is where the
heartbeat starts. These beats occur due to
changes in electrical currents as calcium,
sodium and potassium move across
membranes. The heart can beat at a rate of
60 beats per minute constantly if left alone.
However we often need it to go faster. The
sympathetic nervous system sends rapid
signals from the brain to stimulate the
heart to beat faster when we need it to in
ght or ight scenarios. If the SAN fails, a
pacemaker can send articial electrical
signals to keep the heart going.

The atria are the

low-pressure upper
chambers, and are the
first to contract, emptying
blood into the ventricles.

40

2. Ventricular systole

3. Ventricular diastole

The ventricles contract next,

and they send high-pressure
blood out into the aorta to
supply the body.

The heart is now relaxed and can

refill, ready for the next beat.

Why do bruises go
purple or yellow?

A bruise forms when capillaries under the skin leak and allow
blood to settle in the surrounding tissues. The haemoglobin in
red blood cells is broken down, and these by-products give a
dark yellow, brown or purple discolouration depending on the
volume of blood and colour of the overlying skin. Despite
popular belief, you cannot age a bruise different peoples
bruises change colour at different rates.

1. Damage to the
blood vessels
After trauma such as a fall,
the small capillaries are
torn and burst.

3. Discolouration
Haemoglobin is then
broken down into its
smaller components, which
are what give the dark
discolouration of a bruise.

2. Blood leaks
into the skin
Blood settles into the
tissues surrounding the
vessel. The pressure
from the bruise then
helps stem the bleeding.

What is
42
the little
triangle shape
on the side of
the ear?

David Benbennick

016

This is the tragus. It serves

no major function that we
know of, but it may help to
reect sounds into the ear
to improve hearing.

41

Why
does
cutting
onions make
us cry?

Denitions
Systole = contraction
Diastole = relaxation

Lali Masriera

1. Atrial systole

Onions make your eyes water due to their expulsion of

an irritant gas once cut. This occurs as when an onion
is cut with a knife, many of its internal cells are broken
down, allowing enzymes to break down amino acid
sulphoxides and generate sulphenic acids. These
sulphenic acids are then rearranged by another
enzyme and, as a direct consequence, synpropanethial-S-oxide gas is produced, which is volatile.
This volatile gas then diffuses in the air surrounding
the onion, eventually reaching the eyes of the cutter,
where it proceeds to activate sensory neurons and
create a stinging sensation. As such, the eyes then
follow protocol and generate tears from their tear
glands in order to dilute and remove the irritant.
Interestingly, the volatile gas generated by cutting
onions can be largely mitigated by submerging the
onion in water prior to or midway through cutting,
with the liquid absorbing much of the irritant.

43

When were
tired, why do
we get bags under
our eyes?

Blood doesnt circulate around your body as

efciently when youre asleep so excess water can
pool under the eyes, making them puffy. Fatigue,
nutrition, age and genes also cause bags.

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44

Why do
more
men go bald
than women?
Simple male pattern baldness is due
to a combination of genetic factors
and hormones. The most implicated
hormone is testosterone, which men
have high levels of but women have
low levels of, so they win (or lose?) in
this particular hormone contest!

The heart is amazing

DID YOU
KNOW?

It stimulates its own heartbeat, beats around 100,000 times a day and pumps
about 2,000 gallons of blood per day. Its also the most efcient of organs and
extracts the highest ratio of oxygen per unit of blood that it receives. The heart
has its own blood supply too that supplies its muscular wall.

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Why do some
48
hereditary
47
conditions skip a

DID YOU KNOW? The hyoid is the only bone that isnt connected to another bone it sits at the top of your neck

Why do we
get itchy?

Itching is caused by the release of a

transmitter called histamine from
mast cells which circulate in your body.
These cells are often released in
response to a stimulus, such as a bee
sting or an allergic reaction. They lead
to inammation and swelling, and
send impulses to the brain via nerves
which causes the desire to itch.

generation?

Genes work in pairs. Some genes are

recessive and if paired with a
dominant half, they wont shine
through. However, if two recessive
genes combine (one from your mother
and one from your father), the
recessive trait will show through.

49

45

Why do amputees
sometimes still
feel pain in their
amputated limbs?

Why do
we blink?

This is phantom limb pain and can range from a mild

annoyance to a debilitating pain. The brain can
sometimes struggle to adjust to the loss of a limb, and it
can still interpret the limb as being there. Since the
nerves have been cut, it interprets these new signals as
pain. There isnt a surgical cure as yet, though time and
special medications can help lessen the pain.

Blinking helps keep your eyes clean and moist. Blinking

spreads secretions from the tear glands (lacrimal uids)
over the surface of the eyeball, keeping it moist and also
sweeping away small particles such as dust.

50

Which muscle produces the

most powerful contraction
relative to its size?
The gluteus maximus is the largest muscle and forms the bulk of your buttock. The heart (cardiac muscle) is
the hardest-working muscle, as it is constantly beating and clearly can never take a break! However the
strongest muscle based on weight is the masseter. This is the muscle that clenches the jaw shut put a
nger over the lowest, outer part of your jaw and clench your teeth and youll feel it.

Myosin head

46

How come most

people have one foot
larger than the other?
Most peoples feet are different sizes in fact the two
halves of most peoples bodies are different! We all start
from one cell, but as the cells multiply, genes give them
varying characteristics.

Actin lament

Actin lament
is pulled

1. Taking the rst step

2. Preparation

Muscle contraction starts with an impulse received from the

nerves supplying the muscle an action potential. This
action potential causes calcium ions to flood across the
protein muscle fibres. The muscle fibres are formed from two
key proteins: actin and myosin.

The calcium binds to troponin which is a receptor on

the actin protein. This binding changes the shape of
tropomyosin, another protein which is bound to actin.
These shape changes lead to the opening of a series of
binding sites on the actin protein.

Cross bridge
detaches

3. Binding
Now the binding sites are free on actin, the myosin heads
forge strong bonds in these points. This leads to the
contraction of the newly formed protein complex; when all
of the proteins contract, the muscle bulk contracts.

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Energised myosin
head

4. Unbinding
When the energy runs out, the proteins lose their strong
bonds and disengage, and from there they return to
their original resting state.

017

HUMAN
ANATOMY
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Cells under the microscope

Cell structure
explained
Nucleus

There are around 75 trillion cells

in the human body, but what are
they and how do they work?
Cells are life and cells are
alive. You are here because
every cell inside your body
has a specic function and a
very specialised job to do. There are
many different types of cell, each one
working to keep the bodys various
systems operating. A single cell is the
smallest unit of living material in the
body capable of life. When grouped
together in layers or clusters, however,
cells with similar jobs to do form tissue,
such as skin or muscle. To keep these
cells working, there are thousands of
chemical reactions going on all the time.
All animal cells contain a nucleus,
which acts like a control hub telling the
cell what to do and contains the cells
genetic information (DNA). Most of the
material within a cell is a watery,
jelly-like substance called cytoplasm
(cyto means cell), which circulates
around the cell and is held in by a thin
external membrane, which consists of
two layers. Within the cytoplasm is a
variety of structures called organelles,
which all have different tasks, such as
manufacturing proteins the cells key
chemicals. One vital example of an
organelle is a ribosome; these numerous
structures can be found either oating
around in the cytoplasm or attached to
internal membranes. Ribosomes are
crucial in the production of proteins
from amino acids.
In turn, proteins are essential to
building your cells and carrying out the
biochemical reactions the body needs in
order to grow and develop and also to
repair itself and heal.

Ribosomes
These tiny structures make proteins and
can be found either floating in the
cytoplasm or attached like studs to the
endoplasmic reticulum, which is a conveyor
belt-like membrane that transports proteins
around the cell.

Endoplasmic reticulum
The groups of folded membranes (canals)
connecting the nucleus to the cytoplasm are
called the endoplasmic reticulum (ER). If
studded with ribosomes the ER is referred to
as rough ER; if not it is known as smooth
ER. Both help transport materials around the
cell but also have differing functions.

Smooth
endoplasmic
reticulum

Rough endoplasmic
reticulum (studded
with ribosomes)

Mitochondria
These organelles supply cells with the energy
necessary for them to carry out their functions.
The amount of energy used by a cell is measured
in molecules of adenosine triphosphate (ATP).
Mitochondria use the products of glucose
metabolism as fuel to produce the ATP.

018

The nucleus is the cells brain

or control centre. Inside the
nucleus is DNA information,
which explains how to make
the essential proteins needed
to run the cell.

Golgi body
Another organelle, the Golgi body is one
that processes and packages proteins,
including hormones and enzymes, for
transportation either in and around the
cell or out towards the membrane for
secretion outside the cell where it can
enter the bloodstream.

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Cell membrane
Surrounding and supporting
each cell is a plasma membrane
that controls everything that
enters and exits.

Super cells

DID YOU
KNOW?

Stem cells are self-renewing cells with the potential to become any other
type of cell in the body. Unlike regular cells, they do not have a specialisation,
such as nerve cells. Experts have discovered that adult stem cells can be
manipulated into other types with the potential to grow replacement organs.

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DID YOU KNOW? Bacteria are the simplest living cells and the most widespread life form on Earth

Cell anatomy

Types of human cell

Cytoplasm

So far around 200 different varieties of cell have been

identied, and they all have a very specic function to
perform. Discover the main types and what they do
NERVE CELLS
The cells that make up the nervous
system and the brain are nerve cells
or neurons. Electrical messages
pass between nerve cells along
long filaments called axons. To
cross the gaps between nerve
cells (the synapse) that electrical
signal is converted into a chemical
signal. These cells enable us to feel
sensations, such as pain, and they also
enable us to move.

Pore

FAT CELLS

BONE CELLS

SPL

The cells that make up bone matrix the hard

structure that makes bones strong consist of three
main types. Your bone mass is constantly changing
and reforming and each of the three bone cells plays its
part in this process. First the osteoblasts, which come
from bone marrow, build up bone mass and
structure. These cells then become
buried in the matrix at which
point they become known as
osteocytes. Osteocytes make
up around 90 per cent of the
cells in your skeleton and are
responsible for maintaining
the bone material. Finally,
while the osteoblasts add to
bone mass, osteoclasts are the
cells capable of dissolving bone
and changing its mass.

PHOTORECEPTOR CELLS

SPL

Science Photo Library

The cones and rods on the retina at

the back of the eye are known
as photoreceptor cells. These
contain light-sensitive
pigments that convert the
image that enters the eye
into nerve signals, which
the brain interprets as
pictures. The rods enable you
to perceive light, dark and
movement, while the cones
bring colour to your world.

SPL

LIVER CELLS
The cells in your liver are responsible
for regulating the composition of
your blood. These cells filter out
toxins as well as controlling fat,
sugar and amino acid levels.
Around 80 per cent of the livers
mass consists of hepatocytes,
which are the livers specialised
cells that are involved with the
production of proteins and bile.

MUSCLE CELLS

Lysosomes
This digestive enzyme breaks down
unwanted substances and worn-out
organelles that could harm the cell by
digesting the product and then
ejecting it outside the cell.

move. We can control skeletal muscles because they

are voluntary. Cardiac muscles, meanwhile, are
involuntary, which is fortunate because they
are used to keep your heart beating. Found in
the walls of the heart, these muscles create
their own stimuli to contract without input
from the brain. Smooth muscles, which are
pretty slow and also involuntary, make up
the linings of hollow structures such as blood
vessels and your digestive tract. Their
wave-like contraction aids the transport of blood
around the body and the digestion of food.

There are three types of muscle cell

skeletal, cardiac and smooth and
each differs depending on the
function it performs and its location
in the body. Skeletal muscles
contain long fibres that attach to
bone. When triggered by a nerve
signal, the muscle contracts and
pulls the bone with it, making you

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These cells also known as

adipocytes or lipocytes
make up your adipose
tissue, or body fat, which
can cushion, insulate
and protect the body.
This tissue is found
beneath your skin and
also surrounding your
other organs. The size of a fat
cell can increase or decrease
depending on the amount of
energy it stores. If we gain weight the cells fill with
more watery fat, and eventually the number of fat cells
will begin to increase. There are two types of adipose
tissue: white and brown. The white adipose tissue
stores energy and insulates the body by maintaining
body heat. The brown adipose tissue, on the other
hand, can actually create heat and isnt burned for
energy this is why animals are able to hibernate for
months on end without food.

EPITHELIAL CELLS
Epithelial cells make up the epithelial tissue that
lines and protects your organs
and constitute the primary
material of your skin.
These tissues form a
barrier between the
precious organs and
unwanted pathogens or
other fluids. As well as
covering your skin, youll
find epithelial cells inside
your nose, around your lungs
and in your mouth.
SPL

This is the jelly-like

substance made of
water, amino acids and
enzymes found inside
the cell membrane.
Within the cytoplasm are
organelles such as the
nucleus, mitochondria
and ribosomes, each of
which performs a specific
role, causing chemical
reactions in the
cytoplasm.

RED BLOOD CELLS

Unlike all the other cells in your
body, your red blood cells (also
known as erythrocytes) do
not contain a nucleus. You
are topped up with
around 25 trillion red
blood cells thats a third
of all your cells, making
them the most
common cell in
your body. Formed
in the bone marrow,
these cells are important
because they carry oxygen to all the
tissues in your body. Oxygen is carried in
haemoglobin, a pigmented protein that
gives blood cells their red colour.

019

HUMAN
ANATOMY
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Inside our cells

Inside a nucleus
Dissecting the control centre of a cell
Surrounded by cytoplasm, the
nucleus contains a cells DNA
and controls all of its functions
and processes such as movement
and reproduction.
There are two main types of cell: eukaryotic
and prokaryotic. Eukaryotic cells contain a
nucleus while prokaryotic do not. Some
eukaryotic cells have more than one nucleus
called multinucleate cells occurring when
fusion or division creates two or more nuclei.
At the heart of a nucleus youll nd the
nucleolus; this particular area is essential in
the formation of ribosomes. Ribosomes are

Central command
Take a peek at whats happening inside
the brain of a eukaryotic cell

1 Nuclear pore
These channels control the movement of molecules

responsible for making proteins out of amino

acids which take care of growth and repair.
Being so important, the nucleus is the most
protected part of the cell. In animal cells it is
always located near its centre and away from
the membrane to ensure it has the maximum
cushioning. As well as the jelly-like cytoplasm
around it, the nucleus itself is lled with
nucleoplasm, a viscous liquid which maintains
its structural integrity.
Conversely, in plant cells, the nucleus is more
sporadically placed. This is due to the larger
vacuole in a plant cell and the added protection
that is granted by a cell wall.

between the nucleus and cytoplasm.

2 Nuclear envelope
Acts as a wall to protect the DNA within the nucleus
and regulates cytoplasm access.

3 Nucleolus
Made up of protein and RNA, this is the heart of the
nucleus which manufactures ribosomes.

4 Nucleoplasm
This semi-liquid, semi-jelly material surrounds the
nucleolus and keeps the organelles structure.

5 Chromatin
Produces chromosomes and aids cell division by
condensing DNA molecules.

Nucleus in context

Explore the larger body that a

nucleus rules over and meet
its cellmates

3
5
Nucleus

Double membraned,

Made up of two separate

this produces energy for

entities, ribosomes make

the cell by breaking

proteins to be used both

down nutrients via

inside and outside the cell.

cellular respiration.

Golgi apparatus

020

Named after the Italian

Lysosome

biologist Camillo Golgi,

Small and spherical,

they create lysosomes

this organelle contains

and also organise the

digestive enzymes that

proteins for secretion.

attack invading bacteria.

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Prokaryotic cells are much more basic than

their eukaryotic counterparts. Up to 100 times
smaller and mainly comprising species of
bacteria, prokaryotic cells have fewer
functions than other cells, so they do not
require a nucleus to act as the control centre for
the organism.
Instead, these cells have their DNA moving
around the cell rather than being housed in a
nucleus. They have no chloroplasts, no
membrane-bound organelles and they dont
undertake cell division in the form of mitosis or
meiosis like eukaryotic cells do.
Prokaryotic cells divide asexually with DNA
molecules replicating themselves in a process
known as binary ssion.

Alamy

Mitochondrion
Ribosomes

How do cells
survive without
a nucleus?

WorldMags.net

A stem cell surrounded by

red blood cells. Soon it
could become one of them

What are stem cells?

Understand how these building blocks bring new life
Stem cells are incredibly
special because they
have the potential to
become any kind of cell
in the body, from red blood cells to
brain cells. They are essential to life
and growth, as they repair tissues
and replace dead cells. Skin, for
example, is constantly replenished
by skin stem cells.
Stem cells begin their life cycle as
generic, featureless cells that dont
contain tissue-specic structures,
such as the ability to carry oxygen.
Stem cells become specialised
through a process called
differentiation. This is triggered by
signals inside and outside the cell.
Internal signals come from strands
of DNA that carry information for all
cellular structures, while external
signals include chemicals from
nearby cells. Stem cells can
replicate many times known as

proliferation while others such as

nerve cells dont divide at all.
There are two stem cell types, as
Professor Paul Fairchild, co-director
of the Oxford Stem Cell Institute at
Oxford Martin School explains:
Adult stem cells are multipotent,
which means they are able to
produce numerous cells that are
loosely related, such as stem cells in
the bone marrow can generate cells
that make up the blood, he says. In
contrast, pluripotent stem cells,
found within developing embryos,
are able to make any one of the
estimated 210 cell types that make
up the human body.
This fascinating ability to
transform and divide has made
stem cells a rich source for medical
research. Once their true potential
has been harnessed, they could be
used to treat a huge range of
diseases and disabilities.

Cloning cells
Scientists can reprogram cells to
forget their current role and become
pluripotent cells indistinguishable
from early embryonic stem cells.
Induced pluripotent stem cells
(IPSCs) can be used to take on the
characteristics of nearby cells.
IPSCs are more reliable than stem
cells grown from a donated embryo
because the body is more likely to
accept self-generated cells. IPSCs can
treat degenerative conditions such as
Parkinsons disease and baldness,
which are caused by cells dying
without being replaced. The IPSCs ll
those gaps in order to restore the
bodys systems.
Professor Fairchild explains, by
deriving these cells from individuals
with rare conditions, we are able to
model the condition in the laboratory
and investigate the effects of new
drugs on that disease.

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021

The most fascinating organ of all

HUMAN
ANATOMY
WorldMags.net

The most fascinating organ of all

Your
brain
The human brain is the most
mysterious and complex
entity in the known universe

Its a computer, a thinking machine, a pink organ, and a vast

collection of neurons but how does it work? The human brain is
amazingly complex in fact, more complex than anything in the
known universe. The brain effortlessly consumes power, stores
memories, processes thoughts, and reacts to danger.
In some ways, the human brain is like a car engine. The fuel which could
be the sandwich you had for lunch or a sugar doughnut for breakfast causes
neurons to re in a logical sequence and to bond with other neurons. This
combination of neurons occurs incredibly fast, but the chain reaction might
help you compose a symphony or recall entire passages of a book, help you
pedal a bike or write an email to a friend.
Scientists are just beginning to understand how these brain
neurons work they have not gured out how they trigger a reaction
when you touch a hot stove, for example, or why you can re-generate
brain cells when you work out at the gym.
The connections inside a brain are very similar to the internet the
connections are constantly exchanging information. Yet, even the internet
is rather simplistic when compared to neurons. There are ten to 100 neurons,
and each one makes thousands of connections. This is how the brain
processes information, or determines how to move an arm and grip a surface.
These calculations, perceptions, memories, and reactions occur almost
instantaneously, and not just a few times per minute, but millions. According
to Jim Olds, research director with George Mason University, if the internet
were as complex as our solar system, then the brain would be as complex as
our galaxy. In other words, we have a lot to learn. Science has not given up
trying, and has made recent discoveries about how we adapt, learn new
information, and can actually increase brain capability.
In the most basic sense, our brain is the centre of all input and outputs in the
human body. Dr Paula Tallal, a co-director of neuroscience at Rutgers
University, says the brain is constantly processing sensory information even
from infancy. Its easiest to think of the brain in terms of inputs and outputs,
says Tallal. Inputs are sensory information, outputs are how our brain
organises that information and controls our motor systems.
Tallal says one of the primary functions of the brain is in learning to predict
what comes next. In her research for Scientic Learning, she has found that
young children enjoy having the same book read to them again and again
because that is how the brain registers acoustic cues that form into phonemes
(sounds) to become spoken words.
We learn to put things together so that they become smooth sequences,
she says. These smooth sequences are observable in the brain, interpreting

022

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Basal ganglia (unseen)

Regulates involuntary movements
such as posture and gait when we
walk, and also regulates tremors and
other irregularities. This is the
section of the brain where
Parkinsons Disease can develop.

Hypothalamus
Controls metabolic functions such as
body temperature, digestion,
breathing, blood pressure, thirst,
hunger, sexual drive, pain relays, and
also regulates some hormones.

Parts of
the brain

So what are the parts of the brain? According

to Olds, there are almost too many to count
perhaps a hundred or more, depending on
who you ask. However, there are some key
areas that control certain functions and store
thoughts and memories.

BIG BRAINS

LARGEST

Sperm whale
Marshmallow 2008

HEAD
HEAD

SMALLEST

Mouse lemur

LARGEST ON LAND

The smallest primate

brain is owned by the
pygmy mouse lemur of
Madagascar and
weighs in at just 0.004
pounds (2g).

The sperm whale has

evolved the largest brain
ever to exist on our
planet, weighing as
much as nine kilograms
or 20 pounds.

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Elephant
At 10.5 pounds
(4.78kg) its certainly a
big one. The brain of
the elephant makes up
less than 0.1 per cent of
its body weight.

DID YOU KNOW? The average human brain is 140mm wide x 167mm long x 93mm high
Cerebral cortex
The grey matter of the brain controls
cognition, motor activity, sensation, and
other higher level functions. Includes
the association areas which help
process information. These
association areas are what
distinguishes the human
brain from other brains.

Functions of the
cerebral cortex
Frontal lobe
Primarily controls senses
such as taste, hearing, and
smell. Association areas
might help us determine
language and the tone of
someones voice.

The cerebral cortex is the wrinkling

part of our brain that shows up when
you see pictures of the brain
Complex
movements
Skeletal movement

Parietal lobe
Where the brain senses
touch and anything that
interacts with the surface
of the skin, makes us
aware of the feelings
of our body and
where we are
in space.

Problem
solving

Touch and skin

sensations

Language
Receives
signals
from eyes
Analysis of
signal from eyes

Speech
Hearing

Prefrontal cortex
Executive functions such as complex
planning, memorising, social and verbal
skills, and anything that requires
advanced thinking and interactions. In
adults, helps us determine whether an
action makes sense or is dangerous.

Cerebellum
Consists of two cerebral
hemispheres that controls motor
activity, the planning of
movements, co-ordination, and
other body functions. This section
of the brain weighs about 200
grams (compared to 1,300 grams
for the main cortex).

Limbic system
The part of the brain
that controls intuitive
thinking, emotional
response, sense of
smell and taste.

Temporal lobe

PL
S

Analysis of
sounds

What distinguishes the human

brain the ability to process
and interpret what other parts
of the brain are hearing,
sensing, or tasting and
determine a response.

In a sense, the main function of

the brain is in ordering information
interpreting the outside world and
making sense of it
the outside world and making sense of it. The brain
is actually a series of interconnected
superhighways or pathways that move data from
one part of the body to another.
Tallal says another way to think about the brain
is by lower and upper areas. The spinal cord moves
information up to the brain stem, then up into the
cerebral cortex which controls thoughts and
memories. Interestingly, the brain really does work
like a powerful computer in determining not only
movements but registering memories that can be
quickly recalled.
According to Dr Robert Melillo, a neurologist
and the founder of the Brain Balance Centers
(www.brainbalancecenters.com), the brain
actually predetermines actions and calculates the
results about a half-second before performing

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them (or even faster in some cases). This means

that when you reach out to open a door, your
brain has already predetermined how to move
your elbow and clasp your hand around the door
handle maybe even simulated this movement
more than once, before you even actually perform
the action.
Another interesting aspect to the brain is that
there are some voluntary movements and some
involuntary. Some sections of the brain might
control a voluntary movement such as patting
your knee to a beat. Another section controls
involuntary movements, such as the gait of your
walk which is passed down from your parents.
Reexes, long-term memories, the pain reex
these are all aspects that are controlled by sections
in the brain.

023

HUMAN
ANATOMY
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Neurons, nerves and the spinal cord

Neuron
A neuron is a nerve cell in
the brain that can be
activated (usually by
glucose) to connect with
other neurons and form a
bond that triggers an
action in the brain.

Neurotransmitter
A neurotransmitter is the
electro-chemical circuit
that carries the signal from
one neuron to another
along the axon.

A thin synapse
A thin synapse
(measuring just a few
nanometres) between
the neurotransmitter,
carried along the axon in
the brain, forms the
electro-chemical
connection.

Neurons
explained
Neurons re like electrical circuits
Neurons are a kind of cell in the brain (humans have many cells in
the body, including fat cells, kidney cells, and gland cells). A neuron
is essentially like a hub that works with nearby neurons to generate
an electrical and chemical charge. Dr Likosky of the Swedish
Medical Institute says another way of thinking about neurons is
that they are like a basketball and the connections (called axons)
are like electrical wires that connect to other neurons. This creates
a kind of circuit in the human body. Tallal explained that input
from the ve senses in the body cause neurons to re.
The more often a collection of neurons are stimulated together
in time, the more likely they are to bind together and the easier and
easier it becomes for that pattern of neurons to re in synchrony as
well as sequentially, says Tallal.

Brain maps
DK Images

TrackVis generates unique maps of the brain

The brain - a fragile

organ that weighs
about 1,500 grams

TrackVis is a free program used by neurologists to see a map of the brain that shows
the bre connections. On every brain, these neural pathways help connect one part of
the brain to another so that a feeling you experience in one part of the brain can be
transmitted and processed by another part of the brain (one that may decide the touch
is harmful or pleasant). TrackVis uses fMRI readings on actual patients to generate the
colourful and eye-catching images. To construct the maps, the program can take
several hours to determine exactly how the bres are positioning in the brain.

What is my
brain like?
If you could hold it in your hand
In pictures, the human brain often looks pink and spongy.
According to Dr William Likosky, a neurologist at the Swedish
Medical Institute (www.swedish.org), the brain is actually
quite different from what most people think. Likosky
described the brain as being not unlike feta cheese in
appearance a fragile organ that weighs about 1,500 grams
and sags almost like a bag lled with water. In the skull, the
brain is highly protected and has hard tissue, but most of the
fatty tissue in the brain which helps pass chemicals and
other substances through membranes is considerably
more delicate.

024

The computers used to

generate the TrackVis
maps might use up to
1,000 graphics processors
that work in tandem to
process the data.

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5 TOP
FACTS

THE BRAIN

100,000 miles of
blood vessels

Headache not
in the brain?

The brain consists

of 60% fat

Your brain uses 20%

of power

The brain has trillions

of connections

There are a staggering

100,000 miles of blood
vessels in the brain, that is
enough to wrap around
Earth four times.

A headache actually occurs

in blood vessels around the
brain, not around the brain
itself. The brain cannot feel any
pain whatsoever.

Your brain is 60 per cent fat

which helps carry water and
protein through membranes to
brain cells, keeping everything
ticking over.

The brain is quite greedy; it

uses about 20 per cent of the
power in your body that is
generated from food
consumption and processing.

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The brain has trillions of

connections much
more than the internet,
and more than can
currently be counted.

DID YOU KNOW? The adult human brain weighs about 1.4kg (or three pounds)

Some nerve transmissions travel great

distances through the human body,
others travel short distances both use
a de-polarisation to create the circuit.
De-polarisation is like a wound-up
spring that releases stored energy once
it is triggered.

Nerves carry signals throughout the

body a chemical superhighway
Nerves are the transmission cables that carry brain waves in the
human body, says Sol Diamond, an assistant professor at the Thayer
School of Engineering at Dartmouth. According to Diamond, nerves
communicate these signals from one point to another, whether from
your toenail up to your brain or from the side of your head.

When many neurons are activated together

at the same time, the nerve is excited this
is when we might feel the sensation of
touch or a distinct smell.

Myelinated and
un-mylinated
Some nerves are myelinated
(or insulated) with fatty tissue
that appears white and forms a
slower connection over a
longer distance. Others are
un-myelinated and are
un-insulated. These nerves
travel shorter distances.

DK Images

How do
nerves
work?

Nerve triggers

Nerve transmissions

What does the

spinal cord do?
Spinal cord core

The spinal cord actually

is part of the brain and
plays a major role
Scientists have known for the
past 100 years or so that the
spinal cord is actually part of
the brain. According to
Melillo, while the brain has
grey matter on the outside
(protected by the skull) and
protected white matter on
the inside, the spinal cord is
the reverse: the grey matter is
inside the spinal cord and the
white matter is outside.

In the core of the spinal cord, grey matter

like the kind in the outer layer of the
brain is for processing nerve cells such
as touch, pain and movement.

Neuronal bre
tracts

Nerve root
Spinal nerve

Neurogenesis
According to Tallal, by repeating brain
activities such as memorisation and
pattern recognition, you can grow new
brain cells in the spinal cord and brain.

Grey matter cells

Grey matter cells in the spinal cord
cannot regenerate, which is why
people with a serious spinal cord injury
cannot recover over a period of time.
White matter cells can re-generate.

White matter cells

White matter cells in the spinal cord
carry the electro-chemical pulses up to
the brain. For example, when you are
kicked in the shin, you feel the pain in
the shin and your brain then tells you
to move your hand to cover that area.

Neuroplasticity
In the spinal cord and in the brain, cells
can rejuvenate over time when you
exercise and become strengthened. This
process is called neuroplasticity.

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025

HUMAN
ANATOMY
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How do we see?

Inside the
human eye
Uncovering one of the most complex
constructs in the natural world
The structure of the human eye is so
complex that its hard to believe that
its not the product of intelligent
design. But by looking at the eyes of
other animals, scientists have shown that it
evolved very gradually from a simple light-dark
sensor over the course of around 100 million
years. It functions in a very similar way to a
camera, with an opening through which the
light enters, a lens for focusing and a lightsensitive membrane at the back.
The amount of light that enters the eye is
controlled by the circular and radial muscles in
the iris, which contract and relax to alter the size

Fovea
This pit at the centre of the
back of the eye is rich in light
receptors and is responsible
for sharp central vision.

Optic nerve
Signals from the retina
travel to the brain via the
optic nerve, a bundle of
bres that exits through
the back of the eye.

of the pupil. The light rst passes

through a tough protective sheet
called the cornea, and then moves into
the lens. This adjustable structure
bends the light, focusing it down to a
point on the retina, at the back of the eye.
The retina is covered in millions of
light-sensitive receptors known as rods
and cones. Each receptor contains
pigment molecules, which change
shape when they are hit by light,
triggering an electrical message
that travels to the brain via the
optic nerve.

Blind spot
At the position where the
optic nerve leaves the eye,
there is no space for light
receptors, leaving a natural
blind spot in our vision.

Seeing in three dimensions

Each eye sees a slightly different image, allowing the brain to perceive depth
Our eyes are only able to produce two-dimensional images, but with some clever
processing, the brain is able to build these at pictures into a three-dimensional
view. Our eyes are positioned about ve centimetres (two inches) apart, so each sees
the world from a slightly different angle. The brain compares the two pictures,
using the differences to create the illusion of depth.

Individual image
Due to the positioning of our eyes,
when objects are closer than about
5.5m (18ft) away, each eye sees a
slightly different angle.

Combined image
The incoming signals from both
eyes are compared in the brain, and
the subtle differences are used to
create a three-dimensional image.

Try it for yourself

By holding your hand in front of
your face and closing one eye at a
time, it is easy to see the different
2D views perceived by each eye.

026

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Retina

Iris

The retina is covered in

receptors that detect light.
It is highly pigmented,
preventing the light from
scattering and ensuring a
crisp image.

This circular muscle

controls the size of
the pupil, allowing it
to be closed down in
bright light, or opened
wide in the dark.

HEAD
HEAD

AN EYE FOR SIZE

1. BIG

2. BIGGER

Tarsier

Ostrich

3. BIGGEST

Colossal squid

Ostriches are the largest

living birds and also have
the largest eyes of any
living land animal,
measuring an incredible
5cm (2in) in diameter.

The eyes of these tiny

primates are as big as
their brains, so as a
result, they have
developed extremely
good night vision.

Little is known about

these mysterious
creatures, but they have
eyes the size of footballs
the largest known in the
animal kingdom.

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DID YOU KNOW? 285 million people in the world are estimated to be visually impaired and 39 million of them are blind

Vision problems

Ciliary body
This tissue surrounds the
lens and contains the
muscles responsible for
changing its shape.

The most common problems

with our eyesight

Farsightedness (hyperopia)
If the eye is too short, the cornea is too at, or if
the lens sits too far back, incoming light is
focused behind the retina, making nearby
objects appear blurry, particularly in the dark.

Sclera
A tough white membrane
known as the sclera helps
to maintain the eyes
spherical shape.

Nearsightedness (myopia)
If the eye is too long, or the cornea and lens are
too curved, the light is focused before it hits the
back of the eye, and then starts to defocus
again as it reaches the retina, making distant
objects difcult to see.

Colour-blindness
This rare condition is often linked to a gene on
the X-chromosome and occurs more commonly
in men than in women. A defect in the cone
cells of the eye reduces the number of colours
that can be detected.

Protection
The eyes are shielded by several layers of protection.
They are almost completely encased in bone at the back
and insulated from shock by layers of muscle and
connective tissue. The front is kept moist with tears and
are constantly wiped by the blinking of the eyelids, while
the hairs of the eyebrows and eyelashes catch any debris
that might fall in.

Lachrymal gland
Tears are produced here
and wash across to the
inner corner of the eye,
helping to clean and
nourish the surface.

Cornea
Lens
The lens is responsible for
focusing the light, and can
change shape to
accommodate objects
near and far from the eye.

Pupil
The pupil is a hole that
allows light to reach
the back of the eye.

The pupil and iris are

covered in a tough,
transparent
membrane, which
provides protection
and contributes to
focusing the light.

Eyelashes
Eyebrows
The arch of the eyebrows
helps to keep sweat and
rain away from the eyes,
channelling it down the
sides of the face.

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Eyelashes not only catch

dust before it enters the
eye, they are also sensitive,
like whiskers, and the
slightest unexpected touch
triggers a protective blink.

027

HUMAN
ANATOMY
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How we process sounds

How
ears
work

Structure
of the ear
Auricle (pinna)
This is the visible part
of the outer ear that
collects sound wave
vibrations and directs
them into the ear.

Malleus
(hammer)
One of the three ossicles,
this hammer-shaped
bone connects to the
eardrum and moves with
every vibration bouncing
off the drum.

The human ear performs a

range of functions, sending
messages to the brain when a
sound is made while also
providing your body with a
sense of balance

The thing to remember when learning

about the human ear is that sound is all
about movement. When someone
speaks or bangs a drum or makes any
kind of movement, the air around them is
disturbed, creating a sound wave of alternating
high and low frequency. These waves are detected
by the ear and interpreted by the brain as words,
tunes or sounds.
Consisting of air-lled cavities, labyrinthine
uid-lled channels and highly sensitive cells, the
ear has external, middle and internal parts. The
outer ear consists of a skin-covered exible cartilage
ap called the auricle, or pinna. This feature is
shaped to gather sound waves and amplify them
before they enter the ear for processing and
transmission to the brain. The rst thing a sound
wave entering the ear encounters is the sheet of
tightly pulled tissue separating the outer and
middle ear. This tissue is the eardrum, or tympanic
membrane, and it vibrates as sound waves hit it.
Beyond the eardrum, in the air-lled cavity of the
middle ear, are three tiny bones called the ossicles.
These are the smallest bones in your entire body.
Sound vibrations hitting the eardrum pass to the
rst ossicle, the malleus (hammer). Next the waves
proceed along the incus (anvil) and then on to the
(stapes) stirrup. The stirrup presses against a thin
layer of tissue called the oval window, and this
membrane enables sound waves to enter the
uid-lled inner ear.
The inner ear is home to the cochlea, which
consists of watery ducts that channel the vibrations,
as ripples, along the cochleas spiraling tubes.
Running through the middle of the cochlea is the
organ of Corti, which is lined with minute sensory
hair cells that pick up on the vibrations and
generate nerve impulses that are sent to the brain as
electrical signals. The brain can interpret these
signals as sounds.

028

External acoustic
meatus (outer
ear canal)
This is the wax-lined tube
that channels sound
vibrations from the outer
pinna through the skull to
the eardrum.

Scala vestibuli
(vestibular canal)
Incoming vibrations travel
along the outer vestibular
canal of the cochlea.

Cochlear duct
The cochlear duct separates the
tympanic and vestibular canals.
The organ of Corti is found here.

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Tympanic membrane
(eardrum)
The slightly concave thin layer of skin
stretching across the ear canal and
separating the outer and middle ear.
Vibrations that hit the eardrum are
transmitted as movement to the
three ossicle bones.

5 TOP
FACTS
HUMAN EARS

Hearing range

Underwater hearing

Hearing loss

Wax essential

Making me dizzy

Human ears can hear sounds

with frequencies between 20Hz
and 20,000Hz. The ability to hear
frequencies above and below this
is linked to the size of the cells
and sensitivity.

Humans can hear much

higher-pitched sounds
(200,000Hz) when under water,
because we can hear with our
bones, bypassing the outer ear
and ossicles.

The most common causes of

hearing loss are ageing and
noise. As we age, our ability to
hear sounds with higher
frequencies deteriorates this is
known as presbycusis.

Wax cleans and lubricates the

outer auditory canal,
transporting dirt and dead
skin away from the ear. If
excessive wax is a problem,
consult your doctor.

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Inflammation of the inner ear due

to viral/bacterial conditions such as
labyrinthitis can cause dizziness
and nausea. When balance is
affected, sufferers may not be able
to walk or stand.

DID YOU KNOW? The eardrum needs to move less than the diameter of a hydrogen atom in order for us to perceive sound

Connected to the hammer, the

incus is the middle ossicle bone
and is shaped like an anvil.

Stapes (stirrup)
The stirrup is the third ossicle bone. It
attaches to the oval window at the
base of the cochlea. Movements
transferred from the outer ear to the
middle ear now continue their journey
through the fluid of the inner ear.

The vestibular system

Cochlea
A bony snail-shaped structure,
the cochlea receives vibrations
from the ossicles and
transforms them into electrical
signals that are transmitted to
the brain. There are three
fluid-filled channels the
vestibular canal, the tympanic
canal and the cochlea duct
within the spiral of the cochlea.

Inside the inner ear are the vestibule

and semicircular canals, which
feature sensory cells. From the
semicircular canals and
maculae, information about
which way the head is
moving is passed to
receptors, which send
electrical signals
to the brain as
nerve impulses.

Semicircular canal
These three loops positioned
at right angles to each other
are full of fluid that transports
sound vibrations to the crista.

Vestibular nerve
Sends information
about equilibrium from
the semicircular canals
to the brain.
DK Images

Incus (anvil)

Organ of Corti
The organ of Corti contains
rows of sensitive hair cells,
the tips of which are
embedded in the tectorial
membrane. When the
membrane vibrates, the hair
receptors pass information
through the cochlear nerve
to the brain.

Macula
Vestibule

A sensory area
covered in
tiny hairs.

Inside the fluid-filled

vestibules are two
chambers (the utricle
and saccule), both of
which contain a
structure called a
macula, which is
covered in sensory
hair cells.

Crista
Cochlear nerve

At the end of each semicircular canal

there are tiny hair-filled sensory receptors
called cristae.

Sends nerve impulses with

information about sounds from
the cochlea to the brain.

A sense of balance
The vestibular system functions to give
you a sense of which way your head is
pointing in relation to gravity. It enables
you to discern whether your head is
upright or not, as well as helping you to
maintain eye contact with stationary
objects while your head is turning.
Also located within the inner ear, but
less to do with sound and more
concerned with the movement of your
head, are the semicircular canals. Again
lled with uid, these looping ducts act
like internal accelerometers that can

detect acceleration (ie, movement of your

head) in three different directions due to
the positioning of the loops along
different planes. Like the organ of Corti,
the semicircular canals employ tiny hair
cells to sense movement. The canals are
connected to the auditory nerve at the
back of the brain.
Your sense of balance is so complex
that the area of your brain thats
dedicated to this one role involves the
same number of cells as the rest of your
brain cells put together.
The surfers semicircular canals
are as crucial as his feet when it
comes to staying on his board

Scala tympani
(tympanic canal)

Think of sounds as
movements, or
disturbances of air,
that create waves

Science Photo Library

The vestibular canal and this, the

tympanic canal, meet at the apex of
the cochlear spiral (the helicotrema).

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029

HUMAN
ANATOMY
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Your tonsils explained

What are
tonsils for?
What purpose do these fleshy lumps
in the back of our throats serve?

Tonsil
locations
Where you can nd
the three pairs of
tonsils in your head

030

Palatine tonsils

Lingual tonsils

Pharyngeal tonsils

These are the best-known pair

of tonsils, as theyre clearly
visible at the back of your throat.

The lingual tonsils are found at

the rear of your tongue one at
either side in your lower jaw.

These are otherwise known as

the adenoids and are located
at the back of the sinuses.

Lots of bed rest, uids

and pain relief like
paracetamol are all
recommended for
treating tonsillitis

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Tonsillitis in focus
Tonsillitis is caused by certain bacteria (eg
group A beta-haemolytic streptococci), and
sometimes viral infections, that result in a
sore and swollen throat, a fever, white spots at
the back of the throat and difculty
swallowing. Usually rest and antibiotics will
see it off, but occasionally the infection can
cause serious problems or reoccur very
frequently. In these cases, a tonsillectomy may
be considered,where the tonsils are removed.
The adenoids are less commonly infected
but, when they are, they become inamed,
obstruct breathing through the nose and
interfere with drainage from the sinuses,
which can lead to further infections. In
younger people, constant breathing through
the mouth can stress the facial bones and
cause deformities as they grow, which is why
children will sometimes have their adenoid
glands removed.

Thinkstock; DK Images

Tonsils are the small masses of esh

found in pairs at the back of the throats
of many mammals. In humans the word
is actually used to describe three sets of
this spongy lymphatic tissue: the lingual tonsils, the
pharyngeal tonsils and the more commonly
recognised palatine tonsils.
The palatine tonsils are the oval bits that hang
down from either side at the back of your throat you
can see them if you open your mouth wide in the
mirror. Although the full purpose of the palatine
tonsils isnt yet understood, because they produce
antibodies and because of their prominent position
in the throat, theyre thought to be the rst line of
defence against potential infection in both the
respiratory and digestive tracts.
The pharyngeal tonsils are also known as the
adenoids. These are found tucked away in the nasal
pharynx and serve a similar purpose to the palatine
tonsils but shrink in adulthood.
The lingual tonsils are found at the back of the
tongue towards the root and, if you poke your tongue
right out, you should spot them. These are drained
very efciently by mucous glands so they very rarely
get infected.

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DID YOU KNOW? The vocal cords remain open when you breathe, but close completely when you hold your breath

How do
humans
speak?
The vocal cords and larynx in particular
have evolved over time to enable humans to
produce a dramatic range of sounds in order
to communicate but how do they work?
Vocal cords, also known as
vocal folds, are situated in
the larynx, which is placed
at the top of the trachea.
They are layers of mucous membranes
that stretch across the larynx and control
how air is expelled from the lungs in
order to make certain sounds. The
primary usage of vocal cords within
humans is to communicate and it is
hypothesised that human vocal cords
actually developed to the extent we see
now to facilitate advanced levels of
communication in response to the
formation of social groupings during
phases of primate, and specically
human, evolution.

As air is expelled from the lungs, the

vocal folds vibrate and collide to produce
a range of sounds. The type of sound
emitted is effected by exactly how the
folds collide, move and stretch as air
passes over them. An individual
fundamental frequency (their standard
pitch) is determined by the length, size
and tension of their vocal cords.
Movement of the vocal folds is controlled
by the vagus nerve, and sound is then
further ne-tuned to form words and
sounds that we can recognise by the
larynx, tongue and lips. Fundamental
frequency in males averages at 125Hz,
and at 210Hz in females. Children have a
higher average pitch at around 300Hz.

Differences between male

and female vocal cords
Male voices are often much lower than
female voices. This is primarily due to
the different size of vocal folds present
in each sex, with males having larger
folds that create a lower pitched sound,
and females having smaller folds that
create a higher pitch sound. The
average size for male vocal cords are
between 17 and 25mm, and females
are normally between 12.5 and 17.5mm.
From the range in size, however, males
can be seen to have quite high pitch
voices, and females can have quite low
pitch voices.
The other major biological
difference that effects pitch is that
males generally have a larger vocal
tract, which can further lower the tone
of their voice independent of vocal
cord size. The pitch and tone of male

voices has been studied in relation to

sexual success, and individuals with
lower voices have been seen to be
more successful in reproduction. The
reason proposed for this is that a lower
tone voice may indicate a higher level
of testosterone present in a male.

The epiglottis stops food

entering the trachea

Tongue
This muscle, situated in the
mouth, can affect and
change sound as it travels up
from the vocal cords and out
through the mouth.

Trachea
The vocal cords are situated
at the top of the trachea,
which is where air from the
lungs travels up through
from the chest.

Vocal cords
These layers of mucous
membranes stretch across
the larynx and they open,
close and vibrate to produce
different sounds.

Epiglottis
This is a flap of skin that
shuts off the trachea when
an individual is swallowing
food. It stops food and liquids
going down the wrong way.

Vocal cords open when

breathing, but are pulled
together when speaking

Oesophagus
This tube, situated behind
the trachea, is where
food and liquid travels
down to the stomach.

Lips
Lips are essential for the
production of specific
sounds, like b or p.

Larynx
Known as the voice
box, this protects the trachea
and is heavily involved in
controlling pitch and volume.
The vocal cords are situated
within the larynx.

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031

HUMAN
ANATOMY
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Your teeth

The biological
structures that are so
versatile they enable us
to eat a well varied diet

All
about
teeth
The trouble
with teeth
Tooth decay, also often
known as dental caries,
affects the enamel and
dentine of a tooth, breaking
down tissue and creating
ssures in the enamel. Two
types of bacteria namely
Streptococcus mutans and
Lactobacillus are
responsible for tooth decay.
Tooth decay occurs after
repeated contact with acidproducing bacteria.
Environmental factors also
have a strong effect on dental
health. Sucrose, fructose and
glucose create large problems
within the mouth, and diet
can be an important factor in
maintaining good oral health.
The mouth contains an
enormous variety of bacteria,
which collects around the
teeth and gums. This is visible
in the form of a sticky white
substance called plaque.
Plaque is known as a biolm.
After eating, the bacteria in
the mouth metabolises sugar,
which subsequently attacks
the areas around the teeth.

032

The primary function of teeth

is to crunch and chew food.
For this reason, teeth are
made of strong substances
namely calcium, phosphorus and
various mineral salts. The main structure
of the tooth is dentine, which is itself
enclosed in a shiny substance called
enamel. This strong white coating is the
hardest material to be found in the
human body.
Humans have different types of teeth
that function in various ways. Incisors
tear at food, such as the residue found
on bones, while bicuspids have long
sharp structures that are also used for
ripping. Bicuspids tear and crush while
molars, which have a atter surface, grind
the food before swallowing. This aids
digestion. Because humans have a varied
array of teeth (called collective dentition)
we are able to eat a complex diet of both
meat and vegetables. Other species, such
as grazing animals, have specic types of
teeth. Cows, for example, have large at
teeth, which restrict them to a simple
grazing diet.
Teeth have many functions, in some
cases they aid hunting but they also have
strong psychological connotations. Both
animals and humans bare their teeth
when faced with an aggressive situation.
Teeth are the most enduring features of
the human body. Mammals are
described as diphyodont, which means
they develop two sets of teeth. In humans

the teeth rst appear at six months old

and are replaced by secondary teeth after
six or seven years. Some animals develop
only one set of teeth, while sharks, for
instance, grow a new set of teeth every
two weeks.
With humans, tooth loss can occur
through accident, gum disease or old age.

Enamel
The white, outer surface
of the tooth. This can be
clearly seen when
looking in the mouth.

From ancient times healers have sought

to treat and replace the teeth with false
ones. Examples of this practice can be
seen from ancient Egyptian times and
today, we see revolutionary new
techniques in the form of dental
implants, which are secured deep within
the bone of the jaw.

Pulp
The pulp nourishes the
dentine and keeps the
tooth healthy the pulp is
the soft tissue of the tooth,
which is protected by the
dentine and enamel.

Cementum
The root coating, it
protects the root
canal and the
nerves. It is
connected to the
jawbone through
collagen fibres.

Blood vessels
and nerves
The blood vessels
and nerves carry
important
nourishment to the
tooth and are
sensitive to
pressure and
temperature.

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Bone
The bone acts
as an
important
anchor for the
tooth and
keeps the root
secure within
the jawbone.

SMALL

A hippopotamus has an
enormous mouth that can
measure up to 1.2 metres
wide. They are equipped with
a pair of huge and very
dangerous incisors.

SHARP

2. Piranha
Piranha teeth are very small
but can be extremely sharp and
are often used by the local
populations of South America
to create a variety of tools
and weapons.

Keith Pomakis

1. Hippopotamus
Andrewself 08

ANIMAL TEETH

BIG

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ArtG 07

HEAD
HEAD

3. Hamster
A member of the rodent family,
the hamster has teeth that
grow continuously. They
therefore need to grind their
teeth on a hard substance to
prevent overgrowth.

DID YOU KNOW? The ancient Egyptians had severe problems with their teeth. They invented the worlds first dental bridge

Maxilla

Inside your
mouth

A layout of the upper area

of your mouth

Central incisors

The upper and lower areas of the mouth

are known as the maxilla and the
mandible. The upper area of the mouth
is attached to the skull bone and is often
called the upper arch of the mouth,
while the mandible is the v-shaped bone
that carries the lower set of teeth.

Lateral incisors

Canine teeth

Canine
1st bicuspid

Long, pointed teeth that are

used for holding and tearing at
the food within the mouth.

2nd bicuspid

Wisdom teeth
Usually appear between the
ages of 17 and 25, and often
erupt in a group of four.

1st molar

2nd molar

Science Photo Library

Science Photo Library

3rd molar or
wisdom tooth

Regular checkups help keep

teeth healthy

Tooth
anatomy
The tooth is a complex structure. The
enamel at the surface of the tooth is highly
visible while the dentine is a hard but
porous tissue found under the enamel.
The gums provide a secure hold for the
tooth, while the root is anchored right
into the jawbone. In the centre of the tooth
there is a substance called pulp which
contains nerves and blood vessels, the
pulp nourishes the dentine and keeps the
tooth healthy.
Tooth formation begins before birth.
Normally there are 20 primary teeth
(human baby teeth) and later, 28 to 32
permanent teeth, which includes the
wisdom teeth. Of the primary teeth, ten
are found in the maxilla (the upper jaw)
and ten in the mandible (lower jaw), while
the mature adult has 16 permanent teeth
in the maxilla and 16 in the mandible.

Eruption
of
teeth
The approximate
ages at which the
permanent teeth
begin to erupt

Age 6
First molar
Age 7
Central incisor

3rd molar or
wisdom tooth
2nd molar

Age 9
First premolar

1st molar
2nd premolar
1st premolar

Age 10
Second premolar

Canine

Age 11
Canine

Lateral incisors

Age 12
Second molar

Central incisors

Mandible

First and second

premolar teeth

A look inside your lower jawbone

Lateral and central incisors

Incisor comes from the Latin word to
cut, they are used to grip and bite.

The premolar or bicuspids are

located between the canine
and molar teeth. They are
used for chewing.

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Age 17 to 21
or not at all
Third molar
(wisdom teeth)
033

HUMAN
ANATOMY
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Neck anatomy

Anatomy of the neck

Explore one of the most complex and functional areas of the human body
The human neck is a perfect blend
of form and function. It has several
specic tasks (eg making it possible
to turn our heads to see), while
serving as a conduit for other vital activities (eg
connecting the mouth to the lungs).
The anatomical design of the neck would
impress modern engineers. The exibility of
the cervical spine allows your head to rotate,
ex and tilt many thousands of times a day.
The muscles and bones provide the strength
and exibility required, however the really
impressive design comes with the trachea,
oesophagus, spinal cord, myriad nerves and
the vital blood vessels. These structures must
all nd space and function perfectly at the same
time. They must also be able to maintain their
shape while the neck moves.
These structures are all highly adapted to
achieve their aims. The trachea is protected by
a ring of strong cartilage so it doesnt collapse,
while allowing enough exibility to move when
stretched. Above this, the larynx lets air move
over the vocal cords so we can speak. Farther
back, the oesophagus is a muscular tube which
food and drink pass through en route to the
stomach. Within the supporting bones of the
neck sits the spinal cord, which transmits the
vital nerves allowing us to move and feel. The
carotid arteries and jugular veins, meanwhile,
constantly carry blood to and from the brain.

Get it in the neck

We show the major features that are packed into
this junction between the head and torso

Sympathetic trunk

Cartilage

These special nerves run

alongside the spinal cord, and
control sweating, heart rate
and breathing, among other
vital functions.

This tough tissue

protects the delicate
airways behind,
including the larynx.

Vertebra
Phrenic nerve
These important
nerves come off the
third, fourth and fifth
neck vertebrae, and
innervate the
diaphragm, which
keeps you breathing
(without you having to
think about it).

These bones provide

support to prevent the neck
collapsing, hold up the skull
and protect the spinal
cord within.

How does the head

connect to the neck?
They are connected at the bottom of the skull
and at the top of the spinal column. The rst
vertebra is called the atlas and the second is
called the axis. Together these form a special
pivot joint that grants far more movement than
other vertebrae. The axis contains a bony
projection upwards, upon which the atlas
rotates, allowing the head to turn. The skull sits
on top of slightly attened areas of the atlas,
providing a safe platform for it to stabilise on,
and allowing for nodding motions. These bony
connections are reinforced with strong muscles,
adding further stability. Dont forget that this
amazing anatomical design still allows the vital
spinal cord to pass out of the brain. The cord sits
in the middle of the bony vertebrae, where it is
protected from bumps and knocks. It sends out
nerves at every level (starting right from the top)
granting control over most of the body.

034

Spinal cord
Shielded by the vertebrae,
the spinal cord sends
motor signals down nerves
and receives sensory
information from all
around the body.

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Larynx
Oesophagus
This pipe connects the
mouth to the stomach,
and is collapsed until
you swallow
something, when its
muscular walls stretch.

This serves two main

functions: to connect the
mouth to the trachea, and
to generate your voice.

Carotid artery
These arteries transmit
oxygenated blood from
the heart to the brain.
There are two of them
(right and left), in case one
becomes blocked.

HEAD
HEAD

1. LONG

LONG NECKS

2. LONGER

Human
The longest human neck
ever recorded was 40
centimetres (15.8 inches)
long. The average neck is
closer to 10-12 centimetres
(3.9-4.7 inches) in length.

Sauropod

3. LONGEST

Giraffe

These dinosaurs probably

had the longest necks of
all, with up to 19 vertebrae.
Extinction means they
dont win the prize as the
longest any more though.

The giraffe has the

longest neck of any land
animal today. However,
amazingly, it has the same
number of neck vertebrae
as we do seven.

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DID YOU KNOW? The hyoid bone at the front of the neck is the only one in the body not connected to another bone

The neck in context

Just say no

The human neck relies on a wide array of bones

and muscles for support, as we see here

The physiology that lets

us shake our heads

Atlas

Rotation

This section
articulates (moves)
around the odontoid
process which
projects through it.

The movement of
the atlas around
the odontoid peg
allows for rotation
of the skull above it.

Odontoid
process

Axis
In the spinal column, this
is the second vertebra,
which provides the
stability for the required
upwards bony projection.

This bony projection

is parallel with the
longitudinal axis
of the spine.

Sternocleidomastoid
Atlas

Turn your head left and feel the

right of your neck this is the
muscle doing the turning.

The first neck (cervical)

vertebra is what
permits the nodding
motion of the head.

Trapezius
When you shrug your
shoulders this broad
muscle tenses up
between your
shoulder and neck.

Axis

These vessels
drain blood
from the neck,
returning it to
the heart.

Cervical plexus
These nerves provide
sensation to the skin and
also control the fine
movements of the neck.

Spinal cord
Vertebrae create a
cage of bones to
protect the critical
spinal cord within.

Seventh cervical
vertebra
Splenius capitis

This is the bony

protuberance at the
bottom of your neck,
which you can feel;
doctors use it as a kind of
landmark so they can
locate the other vertebrae.

This muscle is an example

of one of the many
strap-like muscles which
control the multitude of
fine movements of the
head and neck.

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035

SPL; Thinkstock

Jugular vein

The second cervical

vertebra allows rotation
of the head. So when
youre shaking your head
to say no, you have got
this bone to thank.

HUMAN
ANATOMY
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Mandible

The human skeleton

How the
human
skeleton
works

Scapula

Sternum

Without a skeleton, we would not

be able to live. It is what gives us
our shape and structure and its
presence allows us to operate
on a daily basis. It also is a
fascinating evolutionary link
to all other living and
extinct vertebrates

The human skeleton is crucial

for us to live. It keeps our shape
and muscle attached to the
skeleton allows us the ability to
move around, while also protecting crucial
organs that we need to survive. Bones also
produce blood cells within bone marrow
and store minerals we need released on a
daily basis.
As a fully grown adult you will have
around 206 bones, but you are born with
over 270, which continue to grow,
strengthen and fuse after birth until
around 18 in females and 20 in males.
Human skeletons actually do vary between
sexes in structure also. One of the most
obvious areas is the pelvis as a female must
be able to give birth, and therefore hips are
comparatively shallower and wider. The
cranium also becomes more robust in
males due to heavy muscle attachment and
a males chin is often more prominent.
Female skeletons are generally more
delicate overall. However, although there
are several methods, sexing can be difcult
because of the level of variation we see
within the species.
Bones are made up of various different
elements. In utero, the skeleton takes
shape as cartilage, which then starts to
calcify and develop during gestation and
following birth. The primary element that

Collarbone

Carpals

4. Radius/Ulna
The radius and ulna are the bones
situated in the forearm. They
connect the wrist and the elbow.

5. Rib cage
This structure of many single rib bones creates a
protective barrier for organs situated in the chest
cavity. They join to the vertebrae in the spine at the
back of the body, and the sternum at the front.

makes up bone, osseous tissue, is

actually mineralised calcium
phosphate, but other forms of tissue such
as marrow, cartilage and blood vessels are
also contained in the overall structure.
Many individuals think that bones are
solid, but actually inner bone is porous and
full of little holes.
As we age, so do our bones. Even though
cells are constantly being replaced, and
therefore no cell in our body is more than
20 years old, they are not replaced with
perfect, brand-new cells. The cells contain
errors in their DNA and ultimately our
bones therefore weaken as we age.
Conditions such as arthritis and
osteoporosis can often be caused by ageing
and cause issues with weakening of bones
and reduced movement ability.

Patella

Tarsals
Phalanges

036

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HEAD
HEAD

SKELETONS

EXOSKELETONS

STRANGE SKELETONS

1. Snails
Exoskeletons are often
seen in animals. These are
bulky, tough outer layers
that protect the individual,
instead of the
endoskeletons we have.

2. Snake
The skeleton of a snake
is one of the strangest.
Because of how it moves,
it has more joints in the
body, primarily vertebrae,
and has no limbs.

NUMBERS OF
VERTEBRAE

3. Giraffe
Considering the size of a
giraffes neck, youd expect
it to have more cervical
vertebrae than a human,
but it only has seven the
same as us!

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DID YOU KNOW? Around five per cent of all animals have backbones and are therefore classified as vertebrates

Inside our
skeleton
How the human
skeleton works and
keeps us upright
1. Cranium
The cranium, also known as
the skull, is where the brain
and the majority of the
sensory organs are located.

2. Metacarpals
The long bones in the
hands are called
metacarpals, and are
the equivalent of
metatarsals in the
foot. Phalanges
located close to the
metacarpals make
up the fingers.

Breaking
bones

How
our joints work
The types of joints in our body explained
3. Skull sutures

1. Ball and socket joints

Both the hip and the shoulder joints are
ball and socket joints. The femur and
humerus have ball shaped endings, which
turn in a cavity to allow movement.

Whether its a complete break or

just a fracture, both can take time
to heal properly
If you simply fracture the bone, you may just need to keep it
straight and keep pressure off it until it heals. However, if
you break it into more than one piece, you may need metal
pins inserted into the bone to realign it or plates to cover the
break in order for it to heal properly. The bone heals by
producing new cells and tiny blood vessels where the
fracture or break has occurred and these then rejoin up. For
most breaks or fractures, a cast external to the body will be
put on around the bone to take pressure off the bone to
ensure that no more damage is done and the break can heal.

Although not generally

thought of as a joint, all the
cranial sutures present from
where bones have fused in
childhood are in fact
immoveable joints.

2. Vertebrae
Vertebrae fit together to
support the body and allow
bending movements. They
are joined by cartilage
and are classified as
semi-mobile joints.

The skull is actually

seven separate plates
when we are born,
which fuse together

Skull development
When we are born, many of our
bones are still somewhat soft and
are not yet fused this process
occurs later during our childhood

3. Vertebrae
There are three main kinds of
vertebrae (excluding the sacrum and
coccyx) cervical, thoracic and
lumbar. These vary in strength and
structure as they carry different
pressure within the spine.

The primary reasons for the cranium in particular not to be

fully fused at birth is to allow the skull to ex as the baby is
born and also to allow the extreme rate of growth that
occurs in the rst few years of childhood following birth.
The skull is actually in seven separate plates when we are
born and over the rst two years these pieces fuse together
slowly and ossify. The plates start suturing together early
on, but the anterior fontanel commonly known as the soft
spot will take around 18 months to fully heal. Some other
bones, such as the ve bones located in the sacrum, dont
fully fuse until late teens or early twenties, but the cranium
becomes fully fused by around age two.

6. Pelvis
This is the transitional joint between
the trunk of the body and the legs. It
is one of the key areas in which we
can see the skeletal differences
between the sexes.

7. Femur

4. Hinged joints

5. Gliding joints

6. Saddle joints

Both elbows and knees

are hinged joints. These
joints only allow limited
movement in one
direction. The bones fit
together and are moved
by muscles.

Some movement can

be allowed when flat
bones glide across
each other. The wrist
bones the carpals
operate like this,
moved by ligaments.

The only place we see

this joint in humans is
the thumb. Movement
is limited in rotation,
but the thumb can
move back, forward
and to the sides.

8. Fibula/Tibia
These two bones form the lower
leg bone and connect to the knee
joint and the foot.

3 skulls DK Images

This is the largest and longest single

bone in the body. It connects to the
pelvis with a ball and socket joint.

Baby
skull

Six year old

skull

Adult
skull

9. Metatarsals
These are the five long bones in
the foot that aid balance and
movement. Phalanges located
close to the metatarsals are the
bones which are present in toes.

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037

038

The human spine is made up of 33

vertebrae, 24 of which are articulated
(exible) and nine of which normally
become fused in maturity. They are
situated between the base of the skull to the pelvis,
where the spine trails off into the coccyx an
evolutionary remnant of a tail our ancestors would
have displayed.
The primary functions of the vertebrae that make
up the spine are to support the torso and head,
which protect vital nerves and the spinal cord and
allow the individual to move. By sitting closely
together, separated only by thin intervertebral discs
which work as ligaments and effectively form joints
between the bones, the vertebrae form a strong
pillar structure which holds the head up and allows
for the body to remain upright. It also produces a
base for ribs to attach to and to protect vital internal
organs in the human body.
Vertebrae are not all fused together because of the
need to move, and the vertebrae themselves are
grouped into ve types cervical, thoracic, lumbar,
sacral and coccygeal. The sacral vertebrae fuse
during maturity (childhood and teenage years) and
become solid bones towards the base of the spine.
The coccygeal vertebrae will fuse in some cases, but
studies have shown that often they actually remain
separate. Collectively they are referred to as the
coccyx (tail bone). The rest of the vertebrae remain
individual and discs between them allow them to
move in various directions without wearing the
bones down. The cervical vertebrae in the neck
allow particularly extensive movement, allowing
the head to move up and down and side to side. The
thoracic are far more static, with ties to the rib cage
resisting much movement. The lumbar vertebrae
allow modest side-to-side movement and rotation. A
particular feature of the spine is how it is actually
curved to allow distribution of the bodys weight, to
ensure no one vertebrae takes the full impact.

The human spine is

made up of 33
vertebrae, but how do
they support our
bodies while allowing
us such exibility?

This is the vertebrae

which connects the
spinal column with
the skull. It is named
atlas after the
legend of Atlas who
held the entire
world on
his shoulders.

C1 (atlas)

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These discs form a joint
between each vertebrae
and, effectively, work as
ligaments while also
serving as fantastic shock
absorbers. They facilitate
movement and stop the
bones rubbing together.

Intervertebral
discs

The thoracic vertebrae are the

intermediately sized vertebrae.
They increase in size as you
move down the spine, and they
supply facets for ribs to attach
to this is how they are
primarily distinguished.

Thoracic vertebrae

C2 is the pivot for C1 (atlas), and

nearly all movement for shaking
your head will occur at this joint
the atlanto-axial joint.

C2 (axis)

These are the smallest of

the articulating vertebrae,
and support the head and
neck. There are seven
vertebrae, with C1, C2 and
C7s structures quite
unique from the others.
They sit between the skull
and thoracic vertebrae.

Cervical
vertebrae

The human spinal cord is an immensely

complex structure made up of nerve cells
and a large amount of supporting,
protective tissue. It splits into 31 different
sections and stretches 43-45cm, down
from the brain to between the rst and
second lumbar vertebrae. Although more
commonly referred to in respect of the
brain, there is both white and grey matter
present in the centre of the spinal cord.
White matter contains axons tracts
surrounded by fats, and blood vessels to
protect them. The grey matter contains
more of the neural cell bodies, such as
dendrites, more axons and glial cells.
Spinal cord injuries are normally
caused by trauma. If the trauma causes
intervertebral discs and vertebrae to
break, they can pierce the spinal cord,
which can result in loss of feeling. Cord
severance may result in paralysis.

Spinal cords
and nerves

As you look at the human spine, you can

see some distinct curves. The primary
reasons for these are to help distribute
weight throughout the spine and support
aspects of the body. The curve most
familiar to us is the lumbar curve,
between the ribs and pelvis. This
develops when we start to walk at about
12-18 months and helps with weight
distribution during locomotion. Prior to
this we develop the cervical curve, which
allows us to support the weight of our
head at around three-four months, and
two smaller less-obvious curves in the
spine (the thoracic and pelvic curves) are
developed during gestation.

Spine curvature

The human spine

HUMAN
ANATOMY
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Science of the backbone

I
DK

8. Dorsal and
ventral roots

2. Epidural space

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This is the space between the pia

mater and the arachnoid mater,
which is filled with
cerebrospinal fluid.

This area that surrounds the grey

matter holds axon trails, but is
primarily made up of lipid tissue
(fats) and blood vessels.

11. White matter

L
SP

Coccyx (tailbone)
The coccyx can display between three and five
vertebrae. Theyre commonly thought to be fused,
but often are not. Although these vertebrae are a
vestigial remnant of a tail, they have several uses,
such as supporting weight when sitting.

SPL

The vertebrae
surround the
spinal cord,
which connects
the brain to the
nervous
system.

Skull

Neck
The bones
of the neck
(cervical
vertebrae)
are part of
the spine.

SURPRISING

6. Subarachnoid space

Within the horn-like shapes in

the centre of the spinal cord, sit
most of the important neural cell
bodies. They are protected in
many ways, including by the
white matter.

10. Grey matter

We have five sacral

vertebrae at birth, but by
maturity they will have fused
to form a solid bone, which
helps support the lumbar vertebrae
and connect the coccyx to the spine.

Sacral
vertebrae

DID YOU KNOW? Cartilage (intervertebral discs) actually makes up 25% of the spines length

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Some amphibians, such as

frogs, only have one neck
vertebrae! Their size and
structure means they dont
need the exibility that
most mammals need.

This thin, delicate layer sits

immediately next to the
spinal cord.

5. Pia mater

Named for its spider web

appearance, this is the second
layer of the tissue protection
provided for the spinal cord.

Humans have 31 pairs of spinal

nerves all aligned with
individual vertebrae, and
these communicate information
from around the body to the
spinal cord. They carry all
types of information motor,
sensory and so on and are
commonly referred to as mixed
spinal nerves.

2. Amphibians

4. Arachnoid mater

This is the tough outer layer of

tissue that protects the spinal
cord. The three layers of
protection between the
vertebrae and the spinal cord are
called the spinal meninges.

9. Spinal nerves

FEWEST

3. Dura mater

The skull is connected to the spine by the

atlanto-occipital joint, which is created by
C1 (atlas) and the occipital bone situated at
the base of the cranium (skull). This
unique vertebra has no body and
actually looks more like a ring than any
other vertebra. It sits at the top of the
cervical vertebrae and connects with the
occipital bone via an ellipsoidal joint,
allowing movement such as nodding or
rotation of the head. An ellipsoidal joint is
where an ovoid connection (in this case
the occipital bone) is placed into an
elliptical cavity (C1 vertebrae). The rest of
the cervical vertebrae also work to
support the weight of the head.

How is the skull

attached to the
spine?

With their long thin

necks, swans have 25
cervical vertebrae.
Such a high number
helps to ensure
maximum exibility.

These connect the spinal nerves

to the spinal cord, allowing
transition of information
between the brain and the body.

Four arteries, which form a

network called the Circle of
Willis, deliver oxygen-rich blood
to the brain. The brains
capillaries form a lining called
the blood-brain barrier, which
controls blood flow to the brain.

This is an immensely important

pathway for information to
transfer between the brain and
the bodys nervous system. It is
heavily protected by tissue and
vertebrae, as any damage to it
can be fatal.

Lumbar
vertebrae are the
largest of the
vertebrae and
the strongest,
primarily
because they
withstand the
largest
pressures.
Compared with
other vertebrae
they are more
compact, lacking
facets on the
sides of the
vertebrae.

Lumbar
vertebrae

Articulated vertebrae enable

maximum exibility

1. Swan

This is the space between the

outer protective tissue layer, dura
mater and the bone. It is filled
with adipose tissue (fat), while
also playing host to numerous
blood vessels.

7. Blood vessels

1. Spinal cord

CERVICAL
VERTEBRAE

2
MOST

Spinal column cross-section

s
ge
ma

10

11

HEAD
HEAD

3. Giraffe

Despite how incredibly

long giraffes necks are,
they only actually have
the same number of
cervical vertebrae as
humans just seven.

039

HUMAN
ANATOMY
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How the skeleton moves

Joints

Bone joints

Ball-andsocket joint

Pivot joint

The long bones of the legs

and arms both end in
ball-like protuberances,
which fit inside sockets in
the hip and shoulder,
giving these joints a wide
range of motion.

To turn the head from left to right,

the ring-shaped first vertebra
(known as the atlas) rotates
around a tiny spoke on the second
vertebra (known as the axis),
forming a pivot joint.

For individual bones to

function together, they
must be linked by joints
Some bones, like those in the
skull, do not need to move, and
are permanently fused
together with mineral sutures.
These xed joints provide maximum
stability. However, most bones need
exible linkages. In some parts of the
skeleton, partial exibility is sufcient, so
all that the bones require is a little
cushioning to prevent rubbing. The bones
are joined by a rigid, gel-like tissue known
as cartilage, which allows for a small range
of compression and stretching. These
types of joints are present where the ribs
meet the sternum, providing exibility
when breathing, and between the stacked
vertebrae of the spinal column, allowing it
to bend and ex without crushing the
spinal cord.
Most joints require a larger range of
movement. Covering the ends of the bones
in cartilage provides shock absorption, but
for them to move freely in a socket, the
cartilage must be lubricated to make it
slippery and wear-proof. At synovial joints,
the ends of the two bones are encased in a
capsule, covered on the inside by a
synovial membrane, which lls the joint
with synovial uid, allowing the bones to
slide smoothly past one another.
There are different types of synovial
joint, each with a different range of
motion. Ball-and-socket joints are used at
the shoulder and hip, and provide a wide
range of motion, allowing the curved
surface at the top end of each limb to slide
inside a cartilage covered cup. The knees
and elbows have hinge joints, which
interlock in one plane, allowing the joint to
open and close. For areas that need to be
exible, but do not need to move freely,
such as the feet and the palm of the hand,
gliding joints allow the bones to slide
small distances without rubbing.

Movements
The bones are joined
together with ligaments,
and muscles are attached
by tendons, allowing
different joints to be
moved in a variety of
different ways.

Basal joint

Ellipsoid joint

The thumb is joined to

the rest of the hand by
a bone called the
trapezium. It is shaped
like a saddle and
allows the thumb to
bend and pivot.

The bumps at the base of

the skull fit inside the ring
of the first vertebra,
allowing the head to tip
up, down and from side
to side.

Hinge joint
At joints like the knee and elbow, one
bone is grooved, while the other is
rounded, allowing the two to slot
together and move like a hinge.

Gliding joint
The joints between the carpal bones
of the hands and the tarsal bones of
the feet only allow limited
movement, enabling the bones to
slide past each other.

Hypermobility

Mobile

Semi-mobile

Fixed

Some people have particularly

exible joints and a much larger range
of motion. This is sometimes known
as being double jointed. It is thought
to result from the structure of the
collagen in the joints, the shape of the
end of the bones, and the tone of the
muscles around the joint.

The synovial joints are the most

mobile in the body. The ends of the
bones are linked by a capsule that
contains a uid lubricant, allowing
the bones to slide past one another.
Synovial joints come in different
types, including ball-and-socket,
hinge, and gliding.

Cartilaginous joints do not allow free

motion, but cushion smaller
movements. Instead of a lubricated
capsule, the bones are joined by
brous or hyaline cartilage. The
linkage acts as a shock absorber, so the
bones can move apart and together
over small distances.

Some bones do not need to move

relative to one another and are
permanently fused. For example the
cranium starts out as separate pieces,
allowing the foetal head to change
shape to t through the birth canal,
but fuses after birth to encase the
brain in a solid protective skull.

040

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STRANGE
BUT TRUE

What has more neck vertebrae,

a human or a giraffe?

NECK AND NECK

A Human B Giraffe C Same

Answer:
Amazingly, giraffes have just seven
vertebrae in their necks, the same as a
human being. But unlike us, their bones are
joined by ball-and-socket joints, allowing
them much more exibility.

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DID YOU KNOW? The bone marrow produces between two and three million new red blood cells every second

Why our joints crack

The synovial uid used to lubricate
the joints contains dissolved
gasses. The uid is sealed within a
capsule, so if the joint is stretched,
the capsule also stretches, creating
a vacuum as the pressure changes,
and pulling the gas out of solution
and into a bubble, which pops,
producing a cracking sound.

Muscle
The quadriceps muscle
group runs down the
front of the femur and
finishes in a tendon
attached to the knee cap.

Artery
The femoral artery
supplies blood to the
lower leg, and its
branches travel around
the knee joint and over
the patella.

Synovial membrane
The membrane surrounding the
interior of the joint produces a
lubricant called synovial fluid.

Knee cap
The patella prevents the
tendons at the front of the
leg from wearing away at
the joint.

External
ligaments
The joint is held
together by four
ligaments that
connect the femur
to the bones of the
lower leg.

Patellar ligament
The patellar ligament connects
the kneecap to both the
quadriceps in the thigh and the
tibia in the lower leg.

Ligament

Meniscus
Each of the bones is
capped with a
protective layer of
cartilage, preventing
friction and wear.

Cartilage

Fibula
The end of the fibula
(calf bone) has two
rounded bumps that
are separated by a
deep groove.

Capsule
Tibia
The rounded
ends of the fibula
fit in to two
concave slots at
the top of the
tibia (shin bone).

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Inside a joint

Synovial
membrane

Synovial joints prevent mobile areas of the skeleton from

grinding against one another as they move. The two bones
are loosely connected by strips of connective tissue called
tendons, and the two ends are encased in a capsule that is
lined by a synovial membrane. The bones are covered in
smooth cartilage to prevent abrasion and the membrane
produces a nourishing lubricant to ensure the joint is able
to move smoothly.

041

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Synovial uid

HUMAN
ANATOMY
WorldMags.net

Muscles explained

How do
muscles
work?
Muscles are essential for us to
operate on a daily basis, but how
are they structured and how do
they keep us moving

A muscle is a group of tissue bres that

contract and release to control
movements within the body. We have
three different types of muscles in our
bodies smooth muscle, cardiac muscle and
skeletal muscle.
Skeletal muscle, also known as striated muscle, is
what we would commonly perceive as muscle, this
being external muscles that are attached to the
skeleton, such as biceps and deltoids. These muscles
are connected to the skeleton with tendons. Cardiac
muscle concerns the heart, which is crucial as it
pumps blood around the body, supplying oxygen
and ultimately energy to muscles, which allows
them to operate. Smooth muscle, which is normally
sheet muscle, is primarily involved in muscle
contractions such as bladder control and
oesophagus movements. These are often referred to
as involuntary as we have little or no control over
these muscles actions.
Muscles control most functions within our
bodies; release of waste products, breathing,
seeing, eating and movement to name but a few.
Actual muscle structure is quite complex, and each
muscle is made up of numerous bres which work
together to give the muscle strength. Muscles
increase in effectiveness and strength through
exercise and growth and the main way this occurs
is through small damage caused by each repetition
of a muscle movement, which the body then repairs
and improves.
More than 640 muscles are actually present
across your entire body to enable your limbs to
work, control bodily functions and shape the body
as a whole.

6. Abdominal muscles
Abs are often built up by body
builders and support the body core.
They are also referred to as core
muscles and are important in
sports such as rowing and yoga.

7. Quadriceps
The large fleshy muscle
group covering the front
and sides of the thigh.

8. Gluteus maximus
The biggest muscle in the body,
this is primarily used to move
the thighs back and forth.

9. Hamstrings
Refers to one of the three
posterior thigh muscles, or to the
tendons that make up the borders
of the space behind the knee.

More than 300 individual

muscles are present
across your body to
enable your limbs to work
042

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HEAD
HEAD
HUMAN
MUSCLES

LARGEST MUSCLE

SMALLEST MUSCLE

1. Gluteus
maximus

2. Stapedius

STRONGEST MUSCLE

The smallest muscle in the

body is the stapedius,
which is situated in the
middle ear and helps move
the tiny bones which aide
our hearing.

The gluteus maximus, the

buttock, is the largest
muscle. It is a supercial
muscle that helps control
thigh movement.

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3. Masseter
muscle
This is very much dependant
on how you dene strength.
The masseter (jaw) muscle
can exert the highest direct
force on an object.

DID YOU KNOW? Skeletal muscles account for around 40 per cent of your total body mass
1. Deltoids

2. Trapezius

What affects our

muscle strength?

Large, superficial muscle at the

back of the neck and the upper
part of the thorax, or chest.

How strong we are is a combination

of nature and nurture

3. Pectoralis major

Muscle strength refers to the amount of force that a muscle

can produce, while operating at maximum capacity, in one
contraction. Size and structure of the muscle is important
for muscle strength, with strength being measured in
several ways. Consequently, it is hard to denitively state
which muscle is actually strongest.
We have two types of muscle bre one that supports
long, constant usage exerting low levels of pressure, and
one that supports brief, high levels of force. The latter is
used during anaerobic activity and these bres respond
better to muscle building.
Genetics can affect muscle strength, as can usage, diet
and exercise regimes. Contractions of muscles cause
injuries in the muscle bres and it is the healing of these
that actually create muscle strength as the injuries are
repaired and overall strengthen the muscle.

These muscles stretch across

the shoulders and aid lifting.

Commonly known as the pecs,

this group of muscles stretch
across the chest.

4. Biceps/triceps
These arm muscles work
together to lift the arm up and down.
Each one contracts, causing movement
in the opposite direction to the other.

5. Latissmus dorsi
Also referred to as the lats, these
muscles are again built up during
weight training and are used to
pull down objects from above.

Tendons attach muscles

such as biceps to bones,
allowing muscles to move
elements of our body

How does the

arm ex?
Biceps and triceps are a pair of muscles that work together
to move the arm up and down. As the bicep contracts, the
triceps will relax and stretch out and consequently the arm
will move upwards. When the arm needs to move down,
the opposite will occur with the triceps contracting and
the bicep relaxing and being forcibly stretched out by the
triceps. The bicep is so named a exor as it bends a joint,
and triceps would be the extensor as it straightens the joint
out. Neither of these muscles can push themselves straight,
they depend on the other to oppose their movements and
stretch them out. Many muscles therefore work in pairs,
so-called antagonistic muscles.

1. Tricep relaxes
2. Bicep contracts

3. Arm curls

1. Bicep relaxes

What are muscles made up of?

Muscles are made up of numerous cylindrical
bres, which work together to contract and
control parts of the body. Muscle bres are
bound together by the perimysium into small
bundles, which are then grouped together by
the epimysium to form the actual muscle.

Blood vessels and nerves also run through

the connective tissue to give energy to the
muscle and allow feedback to be sent to the
brain. Tendons attach muscles such as biceps
and triceps to bones, allowing muscles to
move elements of our body as we wish.

Epimysium

Blood vessel

The external layer that covers the

muscle overall and keeps the bundles
of muscle fibres together.

This provides oxygen and allows

the muscle to access energy for
muscle operation.

Perimysium
This layer groups
together muscle fibres
within the muscle.

Filaments
Myofibrils are constructed
of filaments, which are
made up of the proteins
actin and myosin.

Endomysium
Tendon

Myobril

These attach muscle to bones, which in

turn enables the muscles to move parts
of the body around (off image).

Located within the single muscle fibres,

myofibrils are bundles of actomyosin
filaments. They are crucial for contraction.

This layer surrounds

each singular muscle
fibre and keeps the
myofibril filaments
grouped together.

3. Arm extends
2. Tricep contracts

What is a pulled muscle,

and how does it happen?
They hurt like crazy so heres why
its important to warm up
A pulled muscle is basically a tear in muscle bres. Sudden
movements commonly cause pulled muscles, and often,
when an individual has not warmed up appropriately
before exercise or is unt, a tear can occur as the muscle is
not prepared for usage. The most common muscle to be
pulled is the hamstring,
Go run
which stretches from
get to the
the buttock to the knee. chopper!
A pulled muscle may
result in swelling and
pain can last for several
days before the bres
repair themselves. To
prevent pulling
muscles, warming up
is recommended
before any kind of
physical exertion.

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043

HUMAN
ANATOMY
WorldMags.net

Skin colour / Skin grafts

Skin colour
explained

Melanin and skin colour

Keratinocytes
These protective cells are produced
in the lower layers of the epidermis.
They take up the melanosomes
produced by the melanocytes.

What is melanin and how does

it affect the tone of our skin?
The light-absorbing pigment melanin is a
chemical substance that gives your skin its
natural colouring. Skin can vary from very dark
brown to almost completely white due to a
combination of your genes and inherited traits and the
amount of sunlight to which youre exposed.
Skin colour differs from person to person depending on
the concentration of melanin present in their skin and its
distribution throughout the skins layers. Basically, those
with less melanin have lighter skin, while those with more
of the pigment have darker skin. Melanin is produced by
specialised skin cells called melanocytes in the lower
layers of the epidermis and is contained inside a
melanosome by a very thin membrane.
Exposure to sunlight stimulates the production of
melanin granules. The melanosomes containing the
melanin then move out towards the skins protective
keratinocyte cells along branch cells called dendrites.
Melanin is then stored in the nuclei of the keratinocytes
where it acts as a natural protector against the effects of the
Suns ultraviolet rays. Keratinocytes make up the bulk
around 95 per cent of the outer layers of the skin and
form the barrier between the body and the outside world.
They take up melanin which can absorb cancer-causing UV
radiation so it doesnt get into the bodys internal tissues.

Surface

Keratinocytes

Basal skin cells manufactured in the

lower layers of the epidermis grow
through the skin to the surface, where
they are eventually sloughed away.

The keratinocytes of
lighter- skinned
people take up fewer
melanosomes.

DARK

Melanocyte

LIGHT

Dendrite

Melanocyte

Melanin is made in the melanocytes.

These branching cells pass
Those with lighter skin have fewer
People with darker skin, or those
melanin to keratinocytes.
dendrites in their lower layers and
who live in regions with greater
their melanocytes are
sunlight exposure, have more
also less active.
Melanosomes
Melanosomes
active melanocytes.
These packets of melanin release
The melanosomes in lighter skin
melanin granules into the keratinocytes.
release far fewer melanin granules.

How skin grafts work

Skin graft surgery

When our bodys largest organ is damaged,

sometimes it needs a helping hand to heal

044

Gauze
A sterile gauze
is applied while the
skin attaches and
a new blood
supply establishes.

Stitching
Small skin grafts
are stitched while
bigger areas
require stapling.

Donor skin
The donor skin is
removed and then
applied to the
injured area.
Alamy

Skin grafting is a medical procedure where a

portion of skin is removed and stitched onto
another part of the body. There are many
cosmetic and medical reasons why this
might be necessary: serious burns, surgery, tattoo
removal and some medical conditions (skin cancer or
diabetes, for example) might all necessitate skin grafting.
Autografts are skin grafts taken from the patients own
body, usually the buttocks, neck or back of the arm.
Depending on the size of the area that its removed from,
its then stitched or stapled closed again and the new
skin applied to the injured area. Allografts and
xenografts, meanwhile taken from other humans and
animals, respectively are temporary grafts.
But perhaps most interesting is the articial skin
called Integra, made of animal collagen that gives the
damaged part an organic scaffolding for new skin to
grow into. This is usually used in cases of extreme burns
where there isnt enough healthy skin for an autograft.

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5 TOP
FACTS
SKIN

Bacteria thrive
on human skin

You shed skin

every day!

Skin varies drastically

in thickness

As we age,
skin thins

We have billions
of sweat glands

Every square inch of an normal

humans skin has an average of
32 million bacteria on it no
matter how many baths or
showers you have a day!

Every 24 hours, you will lose

your uppermost layer of dead
skin cells, helping to keep your
skin fresh and clean and able
to breathe.

Skin is around 1mm thick on

your eyelids, but on your feet
this thickness increases to
3mm, giving you much more
protection where needed.

Skin thins over time and begins

to loosen, which is where
wrinkles come from, and why
people opt for plastic surgery
in later life.

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Each square inch of

healthy skin contains close
to 650 sweat glands, which
are essential for keeping
you cool.

DID YOU KNOW? All mammals have hair on their skin, including marine mammals which appear hairless

Under the skin

Find out more about the largest organ in your body
1. Epidermis
This is the top, protective layer. It
is waterproof and protects the
body against UV light, disease and
dehydration among other things.

3. Nerve ending
Situated within the dermis, nerve
endings allow us to sense temperature,
pain and pressure. This gives us
information on our environment and
stops us hurting ourselves.

5. Subcutaneous
tissue
The layer of fat found in the
hypodermis that is present to
prevent heat loss and protect
bone and muscle from
damage. It is also a reserve
energy source.

2. Dermis
The layer that nourishes and
helps maintain the epidermis,
the dermis houses hair
roots, nerve endings
and sweat glands.

DK Images

Our skin is the largest organ in our bodies with an

average individual skins surface area measuring
around two square metres and accounting for up
to 16 per cent of total body weight. It is made up of
three distinct layers. These are the epidermis, the dermis and
the hypodermis and they all have differing functions.
Humans are rare in that we can see these layers distinctly.
The epidermis is the top, waterproong layer. Alongside
helping to regulate temperature of the body, the epidermis
also protects against infection as it stops pathogens entering
the body. Although generally referred to as one layer, it is
actually made up of ve. The top layers are actually dead
keratin-lled cells which prevent water loss and provide
protection against the environment, but the lower levels,
where new skin cells are produced, are nourished by the
dermis. In other species, such as amphibians, the epidermis
consists of only live skin cells. In these cases, the skin is
generally permeable and actually may be a major
respiratory organ.
The dermis has the
connective tissue and nerve
endings, contains hair
follicles, sweat glands,
lymphatic and blood
vessels. The top layer of the
dermis is ridged and
interconnects securely
with the epidermis.
Although the
hypodermis is not actually
considered part of the
skin, its purpose is to
connect the upper layers
of skin to the bodys
underlying bone and
muscle. Blood vessels and
nerves pass through this
layer to the dermis. This
layer is also crucial for
temperature
regulation, as it
contains 50 per cent
of a healthy adults
body fat in
subcutaneous
tissue. These kinds of
layers are not often
seen in other species,
humans being one of few
that you can see the distinct
layers within the skin. Not only
does the skin offer protection for
muscle, bone and internal organs, but it is
our protective barrier against the
environment. Temperature regulation,
insulation, excretion of sweat and sensation are just a
few more functions of skin.

4. Pore
Used for temperature
regulation, this is
where sweat is
secreted to cool the
body down when it is
becoming too hot.

How your
skin works

The skin is made of many more

elements than most people imagine
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045

HUMAN
ANATOMY
WorldMags.net

Heart attacks explained

Heart attacks
A heart attack, also known as a
myocardial infarction, occurs
when a blockage stops blood
oxygenating the heart muscle. If
this is not corrected quickly, the muscle
tissue that is lacking oxygen can become
damaged, or indeed die. The scale of impact
on the individuals health after the attack is
dependant on how long the blockage occurs
for, what artery it affected and what
treatment was received. Following the
initial attack, heart failure or arrhythmias
can occur, both of which may prove fatal to
the victim. However, given the right
treatment many sufferers go on to make
good recoveries and can eventually return
to their normal activities.
The most common reason for heart
attacks worldwide in humans is the

What causes heart attacks and

how do they kill?

generation of coronary artery disease (CAD).

This is where arteries are constricted due to
plaque build-ups and this layer then
ruptures. Blood platelets make their way to
the site of rupture and start to form blood
clots. If these clots become too large, the
narrowed artery will block and a heart
attack occurs. Heart attacks can also be
caused by coronary artery spasms,
but these are rare.
Although some people
will be genetically
predisposed to heart
attacks, individuals
can reduce risk by
keeping their weight
down, watching what
they eat, not smoking and
exercising regularly.

1. Coronary arteries

4. Blockage occurs

These are the arteries that supply the heart

with blood. They are crucial to keeping the
heart working effectively.

Either through excess clotting or further deposit build-up, a

blockage can occur. This means blood flow cannot get through
at all and the lack of oxygen results in heart tissue dying.

Healthy
heart
muscle

Coronary artery
(supplies blood
and oxygen to
heart muscle)
Blocked
blood ow

Coronary
artery

Plaque
buildup in
artery

Blood clot
blocks
artery

3. Plaque rupture
Plaque becomes hardened as
it builds up, and it can rupture.
If it ruptures, platelets gather
to clot around the rupture,
which can cause a blockage
to occur.

Heart muscle

5. Dead tissue
Due to a lack of oxygen, some
sections of heart muscle can die off.
This can reduce effectiveness of the
muscle as a whole following recovery.

046

2. Plaque build-up
Dead heart muscle

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Plaque, made up of inflammatory cells,

proteins, fatty deposits and calcium,
narrows the artery and means that only
a reduced blood flow can get through.

5 TOP
FACTS

Risk scores

How much does it cost?

How much blood?

Beating heart bypass

New techniques

BYPASSES

Using complex mathematical

models, each individual patient is
given a risk of dying from the
operation, allowing them to make
a decision about how risky the
operation is.

The op is free on the NHS but in

the private sector it would cost
16,000-20,000
($23,300-$29,000). The price
varies with the risks and if its the
first surgery or a re-do.

On average, the heart beats 70

times per minute (about
100,000 times per day) which
pumps five litres of blood per
minute. Five per cent flows
through the coronary arteries.

A bypass can be performed

without stopping the heart,
using a special retractor. In a few
places, surgery has been
performed this way on patients
who are awake.

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New techniques include using

mini-incisions into the chest
and also the use of robots.
Small cameras are also used to
harvest the new vessels for the
bypass grafts.

DID YOU KNOW? The heart has four separate chambers, four valves to control blood flow and two main coronary arteries

Heart
bypass
What happens in surgery?

3. Bypassing
the heart
Blood is removed by pumping
it out of the body, oxygen is
added to it in a bypass machine
and the blood pumped back in.
This allows oxygenated blood
to continually flow while the
heart is stopped.

Bypass
graft
1. The problem

Aorta

Fatty plaques narrow and

eventually block the
coronary arteries,
preventing oxygen-rich
blood flowing to the
heart muscle.

4. Stopping
the heart
The aorta, the main
vessel out of the
heart, is clamped.
The heart is then
cooled and stopped
using a potassiumrich solution.

Plaque
blockage
Coronary
artery

6. Restarting
the heart
Once the new vessels
have been secured, the
aorta is unclamped
which washes the
potassium-rich solution
from the heart. The
patient is warmed and
the heart restarts.

2. Getting to
the heart
The chest is opened
through a cut down the
middle of the breastbone
(sternum). A special bone
saw is used to cut through
the sternum, which doesnt
damage the heart below.

5. Attaching the
new vessels
The new vessels are tested and
then sewn into place. The opening
is sewn to one of the large arteries
carrying oxygen-rich blood. The
end of the bypass graft is sewn
beyond the fatty plaque, allowing
blood to freely flow to the
affected heart muscles.

7. Closing
the chest
After making sure there is
no bleeding, thin metal
wires are used to hold the
two halves of the sternum
back together.

How heart
bypasses work
When too little blood is getting to the muscles of the heart, a
surgeon can bypass the blockages using the bodys own vessels
Although the heart pumps
oxygenated blood around the
body, the hearts muscular
walls need their own blood
supply. Oxygen-rich blood is delivered to
these tissues via small vessels on its
surface the coronary arteries. These
arteries can get narrowed or blocked up
with cholesterol causing fatty plaques
which slow blood ow. At times of
exercise, not enough blood gets to the
heart muscles, leading to pain due to lack

of oxygen angina. If a vessel becomes

completely blocked, no blood gets
through, causing a heart attack where
the heart muscle dies.
The rst way to treat this type of
coronary artery disease is with
medicines. Secondly, angioplasty can be
used, where narrowings within the
arteries are stretched using a balloon,
with or without placing a stent to keep
the vessel open. Finally, a heart bypass
operation is an option for some patients.

The surgeon uses healthy vessels from

other parts of the patients body to
bypass the blockage, allowing a new
route for blood to ow. This delivers
higher volumes of the oxygen-rich blood
to the heart muscles beyond the
blockage, preventing the pain.
Most bypasses are performed by
stopping the heart and using a heartlung bypass machine to deliver
oxygenated blood to the body. The new
vessels are then sewn into place.

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Bypass
grafts
The body has certain
vessels which it can do
without, and these act as
conduits for bypass
surgery. Commonly
used, the long saphenous
vein runs from the ankle
to the groin. A shallow
incision allows the vein to
be dissected away from
its surrounding tissue.
Other vessels often used
include small arteries
from behind the rib cage
(internal mammary
artery) or the arms
(radial artery).

Stopping
the
heart
Cardiopulmonary bypass
(where a machine takes
over the hearts pumping
action and the gas
exchange function of the
lungs) is established to
provide oxygenated
blood to the rest of the
body. Next, the heart is
stopped. This is achieved
using a potassium-rich
solution, pumped down
the coronary arteries.
This stops the heart
contracting. The surgeon
can now carefully attach
the fresh vessels to
bypass the blockages.

047

HUMAN
ANATOMY
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How your kidneys work

Kidney
function
How do your kidneys lter
waste from the blood to
keep you alive?

048

As blood enters the kidneys, it is passed

through a nephron, a tiny unit made up of
blood capillaries and a waste-transporting
tube. These work together to lter the blood,
returning clean blood to the heart and lungs
for re-oxygenation and recirculation and
removing waste to the bladder for excretion.

Renal cortex
This is one of two broad internal sections of the
kidney, the other being the renal medulla. The
renal tubules are situated here in the protrusions
that sit between the pyramids and secure the
cortex and medulla together.

Renal artery
This artery supplies the
kidney with blood that
is to be filtered.

Renal vein

Images

After waste has

been removed, the
clean blood is
passed out of the
kidney via the
renal vein.

DK

Kidneys are bean-shaped organs

situated halfway down the back
just under the ribcage, one on
each side of the body, and weigh
between 115 and 170 grams each, dependent
on the individuals sex and size. The left
kidney is commonly a little larger than the
right and due to the effectiveness of these
organs, individuals born with only one
kidney can survive with little or no adverse
health problems. Indeed, the body can
operate normally with a 30-40 per cent
decline in kidney function. This decline in
function would rarely even be noticeable
and shows just how effective the kidneys are
at ltering out waste products as well as
maintaining mineral levels and blood
pressure throughout the body. The kidneys
manage to control all of this by working with
other organs and glands across the body
such as the hypothalamus, which helps the
kidneys determine and control water levels
in the body.
Each day the kidneys will lter between
150 and 180 litres of blood, but only pass
around two litres of waste down the ureters
to the bladder for excretion. This waste
product is primarily urea a by-product of
protein being broken down for energy and
water, and its more commonly known as
urine. The kidneys lter the blood by
passing it through a small ltering unit
called a nephron. Each kidney has around
a million of these, which are made up of a
number of small blood capillaries, called
glomerulus, and a urine-collecting tube
called the renal tubule. The glomerulus sift
the normal cells and proteins from the blood
and then move the waste products into the
renal tubule, which transports urine down
into the bladder through the ureters.
Alongside this ltering process, the
kidneys also release three crucial hormones
(known as erythropoietin, renin and
calcitriol) which encourage red blood cell
production, aid regulation of blood pressure
and aid bone development and mineral
balance respectively.

Inside
your kidney

Ureter

Renal pelvis

Renal medulla

The tube that

transports the waste
products (urine) to
the bladder following
blood filtration.

This funnel-like structure is

how urine travels out of the
kidney and forms the top part
of the ureter, which takes
urine down to the bladder.

The kidneys inner section, where blood is

filtered after passing through numerous
arterioles. Its split into sections called
pyramids and each human kidney will
normally have seven of these.

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Renal
capsule
The kidneys fibrous outer
edge, which provides
protection for the
kidneys internal fibres.

DID YOU
KNOW?

Two for the price of one

We are thought to have two kidneys because they are so crucial to our survival,
the second is purely a back up. Having two organs obviously increases our
chances of survival and reproductive fitness.

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DID YOU KNOW? Useless body parts include the appendix, the coccyx and wisdom teeth

Nephrons the ltration

units of the kidney
Proximal tubule
Nephrons are the units which lter all blood that passes
through the kidneys. There are around a million in each
kidney, situated in the renal medullas pyramid structures. As
well as ltering waste, nephrons regulate water and mineral
salt by recirculating what is needed and excreting the rest.

Links Bowmans capsule

and the loop of Henle,
and will selectively
reabsorb minerals from
the filtrate produced by
Bowmans capsule.

Collecting
duct system
Although not
technically part of the
nephron, this collects all
waste product filtered
by the nephrons and
facilitates its removal
from the kidneys.

Glomerulus
High pressure in the
glomerulus, caused by it
draining into an arteriole
instead of a venule,
forces fluids and soluble
materials out of the
capillary and into
Bowmans capsule.

Bowmans
capsule

The glomerulus
This group of capillaries is the rst step of
ltration and a crucial aspect of a nephron.
As blood enters the kidneys via the renal
artery, it is passed down through a series of
arterioles which eventually lead to the
glomerulus. This is unusual, as instead of
draining into a venule (which would lead
back to a vein) it drains back into an
arteriole, which creates much higher
pressure than normally seen in capillaries,
which in turn forces soluble materials
and uids out of the capillaries. This process
is known as ultraltration and is the rst
step in ltration of the blood. These then
pass through the Bowmans capsule
(also know as the glomerular capsule) for
further ltration.

Afferent arteriole

Proximal tubule

This arteriole supplies the

blood to the glomerulus
for filtration.

Where reabsorption of
minerals from the
filtrate from Bowmans
capsule will occur.

Also known as the

glomerular capsule, this
filters the fluid that has
been expelled from the
glomerulus. Resulting
filtrate is passed along
the nephron and
will eventually make
up urine.

Glomerulus
This mass of
capillaries is the
glomerulus.

Distal
convoluted
tubule
Partly responsible
for the regulation of
minerals in the
blood, linking to the
collecting duct
system. Unwanted
minerals are
excreted from
the nephron.

This artery supplies the

kidney with blood. The
blood travels through
this, into arterioles as you
travel into the kidney,
until the blood reaches
the glomerulus.

Renal vein
This removes blood that has
been filtered from the kidney.

Renal tubule
The loop of Henle controls the mineral and
water concentration levels within the kidney
to aid filtration of fluids as necessary. It also
controls urine concentration.

This arteriole is how

blood leaves the
glomerulus following
ultrafiltration.

Bowmans
capsule
This is the surrounding
capsule that will filter
the filtrate produced by
the glomerulus.

What is urine and what

is it made of?

Renal artery

Loop of Henle

Efferent arteriole

Made up of three parts, the proximal

tubule, the loop of Henle and the distal
convoluted tubule. They remove waste
and reabsorb minerals from the filtrate
passed on from Bowmans capsule.

Urine is made up of a range of organic

compounds such as proteins and
hormones, inorganic salts and
numerous metabolites. These
by-products are often rich in nitrogen
and need to be removed from the blood
stream through urination. The pH-level
of urine is typically around neutral
(pH7) but varies depending on diet,
hydration levels and physical tness.
The colour of urine is also determined
by these factors, with dark-yellow urine
indicating dehydration and greenish
urine being indicative of excessive
asparagus consumption.

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94% water

6% other organic
compounds

049

HUMAN
ANATOMY
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Kidney transplants

Kidney transplants
The kidneys are the bodys natural lters. You can survive
on just one, but when that fails you may need a transplant
Transplanting organs is a
complex process, although
it can give a new lease of life
to recipients. The kidney is
the most frequently transplanted
organ, both in the UK and around the
world. However, there is a discrepancy
between the number of patients
waiting for a transplant and the number
of available organs; only around one
third of those waiting per year receive

their transplant. The number of

patients registered for a kidney
transplant increases each year, and has
risen by 50 per cent since 2000.
Kidney transplants come from two
main sources: the living and the
recently deceased. If a healthy,
compatible family member is willing to
donate a kidney, they can survive with
just one remaining kidney. In other
cases, someone elses tragedy is

someone elses fortune. For those who

are declared brain-dead, the beating
heart will keep the kidneys perfused
until they are ready to be removed. In
some patients, the ventilator will be
switched off and its a race against time
to harvest organs. Either way, consent
from the family is needed, even at such
an emotional and pressurised time.
When a suitable organ becomes
available, it is matched via a national

register to a suitable recipient. A

retrieval team from a central
transplant unit (of which there are 20
based around the UK) will go to
whichever hospital the donor is in. They
will remove the organs, while the
recipient is being prepared in the base
hospital. During the tricky operation,
the new kidney is plumbed into the
pelvis, leaving the old, non-functioning
ones in-situ.

How to perform a kidney transplant

Transplanting a kidney is
a case of careful and
clever plumbing. The rst
step is to harvest the
donor kidney, and then
its a dash to transplant
the new kidney into the
recipient. When the
brain-dead donor is
transferred to the
operating theatre for
organ harvest, they are
treated with the same
care and respect as if they
were still alive. When
consent has been given
for multiple organ
harvest, a cut is made
from the top of the chest
to the bottom of the
pelvis. The heart and
lungs are retrieved rst,
followed by the
abdominal organs.

1. The donor

2. Out with the old?

3. Into the pelvis

The donor kidney is harvested, including enough length of

artery, vein and ureter (which carries urine to the bladder)
to allow tension-free implantation into the recipient.

As long as theres no question

of cancer, the original kidneys
are left in place.

An incision is made in the

lower part of the abdomen to
gain access into the pelvis.

7. Whats that
lump?
The new kidney can
be felt underneath
the scar in the
recipient. These
patients are often
recruited to medical
student exams .

8. Catheter
A catheter is left
in-situ for a short
while, so that the
urine output of the
new kidney can be
measured exactly.

The renal artery and vein

are connected to the
corresponding iliac artery
and vein in the recipients
body. Holes (arteriotomies)
are created in the main
arteries, and the kidneys
vessels are anastomosed
(a surgical join between
two tubes using sutures).

050

4. Make space!

6. The nal link

The surgeon will create space in the pelvis, and identify the large
vessels which run from the heart to the leg (the iliac arteries and
veins). The new kidneys vessels vwill be connected to these.

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The ureter, which drains urine from the kidney, is

connected to the bladder. This allows the kidney to
function in the same way as one of the original kidneys.

Science Photo Library

5. Plumbing it in

5TOP
FACTS

Pioneers

The organ gap

Which other organs?

Through the keyhole

Do something about it

TRANSPLANTS

The very first kidney transplant

to take place in the UK was
performed in Edinburgh, 1960.
Here a surgeon transplanted a
kidney from a 49-year-old into
his twin brother.

Around 7,000 people in the

United Kingdom last year
were waiting for organ
transplants, but only around
2,300 kidney transplants
actually took place.

Organs that can be

transplanted include kidneys,
livers, hearts, lungs, the
pancreas and intestines; tissues
include bones, heart valves,
skin and corneas.

When removing a kidney from a

living donor, the most modern
centres use keyhole surgery
(laparoscopy) to do it this
leads to smaller scars, less pain
and faster recovery.

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You can register to

become an organ donor
at www.organdonation.
nhs.uk dont forget to
talk to your loved ones
about it.

DID YOU KNOW? Of the millions of people in the UK suffering from kidney disease, 50,000 will suffer end-stage renal failure

Who is
suitable?
Of the several million people in
the UK with kidney disease, only
around 50,000 will develop
end-stage renal failure (ESRF). For
these people, dialysis or kidney
transplantation are the only
options. Kidney damage from
diabetes is the most common
cause of transplantation. Other
causes include damage from high
blood pressure, chronic kidney
scarring (chronic pyelonephritis)
and polycystic kidney disease
(the normal kidney tissue is
replaced with multiple cysts);
many other less common causes
exist also.
Patients must be selected
carefully due to the scarcity of
organs. Those with widespread
cancer, severely calcied arteries,
persistent substance abuse and
unstable mental problems mean
that transplants are likely to fail
and so these patients are
unsuitable to receive a precious
kidney transplant.

Patients are
monitored for
the rest of
their lives

Patient 2

From patient 1
family member

From patient 2
family member

Antibody
If the antigens are too dissimilar, the hosts existing
immune system thinks the new kidney is a foreign invader
and attacks it with antibodies, leading to rejection.

Antigens
Antigens from the recipient kidneys ABO
blood group and HLA system should be as
close a match to the donors as possible.

When things go wrong

Kidneys need to be carefully matched to suitable donors, or rejection of the new organ
will set in fast. Rejection occurs when the host bodys natural antibodies think the
new tissue is a foreign invader and attacks; careful pre-operative matching helps limit
the degree of this attack. The most important match is via the ABO blood group type
the blood group must match or rejection is fast and aggressive. Next, the bodys HLA
(human leukocyte antigen) system should be a close a match as possible, although it
doesnt need to be perfect. Incorrect matches here can lead to rejection over longer
periods of time. After the operation, patients are started on anti-rejection medicines
which suppress the hosts immune system (immunosuppressants such as Tacrolimus,
Azathioprine or Prednisolone). Patients are monitored for the rest of their lives for
signs of rejection. These immunosuppressants arent without their risks since they
suppress the bodys natural defences, the risks of infections and cancers are higher.

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Science Photo Library

CO
M
PA
TI
BL
E

Patient 1

NON-COMPATIBLE

Patient 1 needs a new kidney but their

family member isnt compatible.
Patient 2 also needs a kidney and has
an incompatible family member as
well. However, patient 2s relation is
compatible with patient 1 and vice
versa. The surgeon arranges a swap
a paired transplant. A longer line of
patients and family members
swapping compatible kidneys can be
arranged a daisy-chain transplant.
A good Samaritan donor, who isnt
related to any of the recipients, can
start the process. This rst recipients
family member will subsequently
donate to someone else a domino
transplant effect which can go on for
several cycles.

NON-COMPATIBLE

Domino
transplants

Time is always of
the essence

Pack
carefully!
The transport of harvested organs
is time critical the sooner the
surgeon can put them into the
recipient the better. As soon as
blood stops owing to the
harvested tissue, the lack of oxygen
damages these cells, which is
called ischaemia. The retrieval
team have a few tricks up their
sleeves to maximise the viability of
the precious cargo they carry.
In the operating theatre, just
before they remove the harvested
kidney, it is ushed clean of blood
with a special cold, nutrient-rich
solution. Once removed, it is
quickly put in a sterile container
with ice. The most modern
technique is to use a cold perfusion
machine instead of ice, which
pumps a cooled solution through
the kidney and improves its lasting
power. While hearts and lungs can
only last around four hours,
kidneys can last 24-48 hours.
Transfer of the affected organ is
done via the fastest method
possible; this often involves using
helicopters or police escorts.
All of these methods prolong the
preservation time of the kidney,
although once plugged back in, it
can take a few days for the kidney
to start working properly
(especially if harvested from a nonheart-beating donor).

051

HUMAN
ANATOMY
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Vestigial organs

Useless body parts

Why have humans and other animals stopped using certain
organs and functions which were once crucial for survival?
much as other creatures; some of our physical
attributes and behavioural responses are
functional in other animals, but they do not
seem to be of any benet to us. These
evolutionary remnants that no longer serve any
purpose are called vestigial organs, though this
can apply as much to behaviour and other body
structures as it does to actual organs.
Evolution has also adapted some existing
features to help us in new ways, in a process
known as exaptation. For example, birds wings
not only help them to y but keep them warm
too. These changes may take thousands of years
to develop, and in some cases the original role
is eventually eliminated altogether.

Appendicitis in focus
What happens when your appendix gets inamed?

Surgery

Progression

During surgery to remove

the appendix, the surgeon
ties off the base to prevent
bowel contents leaking, and
removes the whole
appendix organ.

The inflammation can

lead to perforation of the
appendix and
inflammation of the
surrounding tissues. The
pain then worsens and
then localises to the
lower right-hand side of
the abdomen.

Blockage
A blockage, caused by either a
tiny piece of waste or swollen
lymphatic tissue in the bowel
wall, causes appendix swelling.

Evolutions
leftovers

Appendix

The best known of the

vestigial organs, the
appendix is used in animals
to help digest cellulose found
in grass, but in humans it
serves no clear function now.

Tailbone

Goosebumps

The hard bone at the

bottom of your spine,
the coccyx, is a remnant
of our evolutionary
ancestors tail. It has no
function in humans, but you
could break it if you fall over.

Animals use body hair for

insulation from the cold, by
trapping a warm layer of air
around the body. Each hair
can stand on end when its
own tiny muscle contracts,
but as human beings have
lost most of their body hair, a
jumper is more effective.

The eshy red fold found

in the corner of your eye
used to be a transparent
inner eyelid, which is
still present in both
reptiles and birds.

5
Inammation

SPL

Beyond the blockage, inflammation

sets in, which causes intense
abdominal pain.

052

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Plica semilunaris

Wisdom teeth

These teeth emerge

during our late teens in each
corner of the gums. Our
ancestors used them to help
chew dense plant matter, but
they have no function today,
but can cause a lot of pain.

SPL; Thinkstock

Charles Darwin is one of historys

most famous naturalists. Living in
the 19th Century, he became
celebrated for his theories on
evolution. In his seminal work On The Origin Of
Species he described how similar animals were
likely to be related by common ancestors,
rather than be completely unrelated. As
subsequent generations are born, traits and
features that did not bring a survival benet to
that species were eliminated. That, in a
nutshell, is the theory of evolution.
As a consequence, some organs and traits left
in the body lose their function and are no longer
used. This applies to modern human beings as

THE
STATS
THE SPLEEN

7.6 x 12.7 x 2.5cm

TOTAL
TOTAL
WHITE PULP 25%
RED PULP 75%
SIZE

200g
~5%

WEIGHT
PERCENTAGE OF
CARDIAC OUTPUT
IT RECEIVES

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DID YOU KNOW? Around 15 per cent of us have an extra spleen a small sphere close to but separate from the principal organ

How the spleen works

Perhaps not as well known as famous organs like the heart,
the spleen serves vital functions that help keep us healthy
The spleens main functions are to remove old
blood cells and ght off infection. Red blood cells
have an average life span of 120 days. Most are
created from the marrow of long bones, such as
the femur. When theyre old, its the spleens job to identify
them, lter them out and then break them down. The smaller
particles are then sent back into the bloodstream, and either
recycled or excreted from other parts of the body. This takes
place in the red pulp, which are blood vessel-rich areas of the
spleen that make up about three-quarters of its structure.
The remainder is called white pulp, which are areas lled
with different types of immune cell (such as lymphocytes).
They lter out and destroy foreign pathogens, which have
invaded the body and are circulating in the blood. The white
pulp breaks them down into smaller, harmless particles.
The spleen is surrounded by a thin, fragile capsule and so is
prone to injury. It sits beneath the lower ribs on the left-hand
side of your body, which affords it some protection, but car
crashes, major sports impacts and knife wounds can all
rupture the organ. In the most serious cases, blood loss can
endanger the persons life, and in these situations it needs to
be removed by a surgeon. Since this reduces the bodys ability
to ght infections, some people will need to take antibiotics to
boost their immunity for the rest of their lives.

Inside the spleen

We take you on a tour of the
major features in this oftenoverlooked organ

Hilum
The entrance to the spleen,
this is where the splenic artery
divides into smaller branches
and the splenic vein is formed
from its tributaries.

Splenic artery

Location
The spleen sits underneath the
9th, 10th and 11th ribs (below
the diaphragm) on the
left-hand side of the body,
which provides it with some
protection against knocks.

Splenic vein
The waste products
from filtration and
pathogen digestion
are returned to the main
circulation via this vein
for disposal.

The spleen receives a blood

supply via this artery,
which arises from a branch
of the aorta called the
coeliac trunk.

The immune system

Spleen

Adenoids

One of the master co-ordinators

that staves off infections and
filters old red blood cells. It
contains a number of
lymphocytes that recognise and
destroy invading pathogens
present in the blood as it flows
through the spleen.

These are part of the tonsillar

system that are only present in
children up until the age of five;
in adults they have disappeared.
They add an extra layer of
defence in our early years.

Bone marrow

A small organ that sits just above

the heart and behind the
sternum. It teaches
T-lymphocytes to identify and
destroy specific foreign bodies.
Its development is directly
related to hormones in the body
so its only present until puberty
ends; adults dont need one.

This forms the central, flexible

part of our long bones (eg femur).
Bone marrow is essential as it
produces our key circulating
cells, including red blood cells,
white blood cells and platelets.
The white blood cells mature
into different types (eg
lymphocytes and neutrophils),
which serve as the basis of the
human immune system.

Tonsils

Lymph nodes

These are masses of lymphoid

tissue at the back of the throat
and can be seen when the mouth
is wide open. They form the first
line of defence against inhaled
foreign pathogens, although
they can become infected
themselves, causing tonsillitis.

These are small (about 1cm/

0.4in) spherical nodes that are
packed with macrophages and
lymphocytes to defend against
foreign agents. These are often
linked in chains and are
prevalent around the head,
neck, axillae (armpits) and groin.

Thymus

Alamy

Although the red blood that flows through our bodies gets all the
glory, the transparent lymphatic fluid is equally important. It has its
own body-wide network which follows blood vessel flow closely and
allows for the transport of digested fats, immune cells and more

White pulp
Making up roughly a
quarter of the spleen,
the white pulp is
where white blood
cells identify and
destroy any type of
invading pathogens.

Red pulp
Forming approximately
three-quarters of the
spleen, the red pulp is
where red blood cells are
filtered and broken down.

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Splenic capsule
The capsule provides some
protection, but its thin
and relatively weak. Strong
blows or knife wounds can
easily rupture it and lead to
life-threatening bleeding.

Sinusoid
Similar to those found in the
liver, these capillaries allow
for the easy passage of
large cells into the splenic
tissue for processing.

053

HUMAN
ANATOMY
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The liver explained

How the liver works

The human liver is the
ultimate multitasker
it performs many
different functions
all at the same time
without you
even asking

The liver is the largest internal organ in

the human body and, amazingly, has over 500
different functions. In fact, it is the second
most complex organ after the brain and is
intrinsically involved in almost every aspect of the bodys
metabolic processes.
The livers main functions are energy production,
removal of harmful substances and the production of
crucial proteins. These tasks are carried out within liver
cells, called hepatocytes, which sit in complex
arrangements to maximise their overall efciency.

The liver is the bodys main powerhouse, producing

and storing glucose as a key energy source. It is also
responsible for breaking down complex fat molecules and
building them up into cholesterol and triglycerides, which
the body needs but in excess are bad. The liver makes
many complex proteins, including clotting factors which
are vital in arresting bleeding. Bile, which helps digest fat
in the intestines, is produced in the liver and stored in the
adjacent gallbladder.
The liver also plays a key role in detoxifying the blood.
Waste products, toxins and drugs are processed here into

The hepatobiliary
region
Two halves
The liver is anatomically split
into two halves: left and right.
There are four lobes, and the
right lobe is the largest.

Eight segments

The gallbladder

Functionally, there are

eight segments of the
liver, which are based
upon the distribution
of veins draining
these segments.

The gallbladder and liver

are intimately related. Bile,
which helps digest fat, is
produced in the liver and
stored in the gallbladder.

The common bile duct

This duct is small, but vital in
the human body. It carries bile
from the liver and gallbladder
into the duodenum where it
helps digest fat.

Feel your liver

Take a deep breath in and feel
just under the right lower
edge of your ribs in some
people the lower edge of the
liver can be felt.

The portal triad

The common bile duct,
hepatic artery and
hepatic portal vein form
the portal triad, which
are the vital inflows and
outflows for this liver.

Digestion
The biggest organ
The liver is the largest of
the internal organs, sitting in the
right upper quadrant of the abdomen,
just under the rib cage and attached to
the underside of the diaphragm.

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Once nutrients from food have

been absorbed in the small
intestine, they are transported
to the liver via the hepatic
portal vein (not shown here)
for energy production.

5 TOP
FACTS
LIVER

Ice cold liver

Liver transplants

Maximising numbers

Largest organ in the body

Greek mythology

Polar bear liver is an incredibly

rich source of vitamin A
so much so that Arctic
explorers have actually died
from eating it, as it can cause
extreme vitamin A poisoning.

In the UK 600-700 liver

transplants are performed
each year. The donor liver
can be preserved in a solution
for up to 24 hours before it
is transplanted.

Ways around the shortage of

donor livers include splitting an
adult liver in half and giving it to
two children, and live-donor
transplantation (a portion of a
relatives liver is transplanted).

The liver is the largest internal

organ in the human body and in
most animals bodies too. It
typically has the same shape as
a humans, except in snakes
where it is elongated.

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Wise Titan Prometheus

was chained for eternity to a
rock in the Caucasus, where
an eagle would eat at his liver
and each day the liver would
be renewed!

DID YOU KNOW? The liver can regenerate itself. If up to 75 per cent of the liver is removed, it can grow back to restore itself
forms which are easier for the rest of the body to use or
excrete. The liver also breaks down old blood cells,
produces antibodies to ght infection and recycles
hormones such as adrenaline. Numerous essential
vitamins and minerals are stored in the liver: vitamins A,
D, E and K, iron and copper.
Such a complex organ is also unfortunately prone to
diseases. Cancers (most often metastatic from other
sources), infections (hepatitis) and cirrhosis (a form of
brosis often caused by excess alcohol consumption) are
just some of those which can affect the liver.

The liver also breaks

down old blood cells
and recycles hormones
such as adrenaline

A high demand organ

The liver deals with a massive amount of blood.
It is unique because it has two blood supplies. 75
per cent of this comes directly from the
intestines (via the hepatic portal vein) which
carries nutrients from digestion, which the liver
processes and turns into energy. The rest comes
from the heart, via the hepatic artery (which

branches from the aorta), carrying oxygen which

the liver needs to produce this energy. The blood
ows in tiny passages in between the liver cells
where the many metabolic functions occur. The
blood then leaves the liver via the hepatic veins
to ow into the biggest vein in the body the
inferior vena cava.

Liver lobules

The functional unit which

performs the livers tasks

3. Sinusoids

Science Photo Library

These blood filled

channels are lined by
hepatocytes and provide
the site of transfer of
molecules between blood
and liver cells.

The liver is considered a chemical factory, as it

forms large complex molecules from smaller
ones brought to it from the gut via the blood
1. The lobule
stream. The functional unit of the liver is the
This arrangement of blood
lobule these are hexagonal-shaped
vessels, bile ducts and
hepatocytes form the
structures comprising of blood vessels
functional unit of the liver.
and sinusoids. Sinusoids are the
specialised areas where blood
comes into contact with the
2. The hepatocyte
hepatocytes, where the livers
These highly active cells
biological processes take place.
perform all of the livers
key metabolic tasks.

4. Kupffer cells
9. Central vein
Blood from sinusoids, now
containing all of its new
molecules, flows into
central veins which then
flow into larger hepatic
veins. These drain into
the heart via the
inferior vena cava.

5. Hepatic
artery branch
Blood from here supplies
oxygen to hepatocytes and
carries metabolic waste
which the liver extracts.

Stony
Gallstones are
common but
usually dont cause
problems.

The gallbladder
Bile, a dark green slimy liquid, is produced in the
hepatocytes and helps to digest fat. It is stored in a
reservoir which sits on the under-surface of the liver,
to be used when needed. This reservoir is called the
gallbladder. Stones can form in the gallbladder
(gallstones) and are very common, although most
dont cause problems. In 2009, just under 60,000
gallbladders were removed from patients within the
NHS making it one of the most common operations
performed; over 90 per cent of these are removed via
keyhole surgery. Most patients do very well without
their gallbladder and dont notice any changes at all.

These specialised cells sit

within the sinusoids and
destroy any bacteria which
are contaminating blood.

6. Bile duct
Bile, which helps digest fat, is
made in hepatocytes and
secreted into bile ducts. It then
flows into the gallbladder for
storage before being
secreted into
the duodenum.

7. Portal vein
8. The portal triad
The hepatic artery, portal vein and bile duct are known as
the portal triad. These sit at the edges of the liver lobule
and are the main entry and exit routes for the liver.

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This vein carries nutrient-rich blood

directly from the intestines, which
flows into sinusoids for conversion
into energy within hepatocytes.

055

HUMAN
ANATOMY
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How the small intestine works

The surface area of the

small intestine is huge
in fact, rolled at it would
cover a tennis court!

Structure of the
small intestine
Examine the anatomy of this vital
organ in the human digestive tract

Lumen
This is the space inside the
small intestine in which the
food travels to be digested
and absorbed.

Exploring the
small intestine
Crucial for getting the nutrients we need from the
food we eat, how does this digestive organ work?
The small intestine is one of the
most important elements of our
digestive system, which enables us
to process food and absorb
nutrients. On average, it sits at a little over six
metres (19.7 feet) long with a diameter of 2.5-3
centimetres (1-1.2 inches), and its made up of
three distinctive parts: the duodenum,
jejunum and the ileum.
The duodenum connects the small intestine
to the stomach and is the key place for further
enzyme breakdown, following the stomach

056

turning food into an amino acid state. While

the duodenum is very important in breaking
food down, using bile and enzymes from the
gallbladder, liver and pancreas, it is the
shortest element of the small bowel, only
averaging about 30 centimetres (11.8 inches).
The jejunum follows the duodenum and its
primary function is to encourage absorption of
carbohydrates and proteins by passing the
broken-down food molecules through an area
with a large surface area so they can enter the
bloodstream. Villi small nger-like structures

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Mucosa
The internal lining of the
small intestine where the
plicae circulares (mucosal
folds) and villi are situated.

Mucosal folds
These line the small
intestine to increase
surface area and help
push the food on its way
by creating a valve-like
structure, stopping food
travelling backwards.

Submucosa
This supports the mucosa
and connects it to the layers
of muscle (muscularis) that
make up the exterior of the
small intestine.

and mucosal folds line the passage and

increase the surface area dramatically to aid
this process. The ileum is the nal section of
the small bowel and serves to catch nutrients
that may have been missed, as well as
absorbing vitamin B12 and bile salts.
Peristalsis is the movement used by the small
intestine to push the food through to the large
bowel, where waste matter is stored for a short
period then disposed of via the colon. This
process is generated by a series of muscles
which make up the organs outer wall.

THE
STATS
SMALL BOWEL

IT TAKES FOOD
6m DIAMETER 2.5-3cm TIME
TO PASS THROUGH 1-4 hours
2 AMOUNT OF BODYS
SURFACE
NUMBER OF VILLI
AREA 250m NUTRIENT ABSORPTION 90% PER SQUARE MM 10-40

LENGTH

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DID YOU KNOW? The small intestine is actually longer than the large intestine, but is so called because of its narrower diameter

Serosa
This protective outer layer stops
the small intestine from being
damaged by other organs.

What exactly are nutrients?

There are three main types of nutrient that we process in the body:
lipids (fats), carbohydrates and proteins. These three groups of
molecules are broken down into sugars, starches, fats and smaller,
simpler molecule elements, which we can absorb through the
small intestine walls and that then travel in the bloodstream to our
muscles and other areas of the body that require energy or to be
repaired. We also need to consume and absorb vitamins and
minerals that we cant synthesise within the body, eg vitamin B12
(prevalent in meat and sh).

Fat

Carbohydrate

Protein
Nutrients
Nutrients move through
the tube-like organ to be
diffused into the body,
mainly via the bloodstream.

Blood vessels
These sit close to the
small intestine to
allow easy diffusion
of nutrients into the
bloodstream.

What role do these little nger-like

protrusions play in the bowel?

Villi

Longitudinal
muscle layer
Circular
muscle layer

This contracts and extends

to help transport food with
the circular muscle layer.

Villi are tiny nger-like

structures that sit all over
the mucosa. They help
increase the surface area
massively, alongside the
mucosal folds.

A closer look at villi

Epithelium
(epithelial cells)
These individual cells that
sit in the mucosa layer
are where individual
microvilli extend from.

Lacteal
Mucosa
The lining of the small
intestine on which
villi are located.

The lacteal is a
lymphatic capillary
that absorbs nutrients
that cant pass directly
into the bloodstream.

This works in partnership

with the longitudinal
muscle layer to push the
food down via a process
called peristalsis.

Microvilli

Corbis; Thinkstock

These are a mini version

of villi and sit on villis
individual epithelial cells.

Capillary bed
These absorb simple
sugars and amino acids as
they pass through the
epithelial tissue of the villi.

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057

HUMAN
ANATOMY
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Human ribcage formation

Inside the thoracic cavity

It may not look like it at rst glance,
but there are more than two dozen
bones that make up the ribcage

Clavicle
Also known as the
collarbone, this pair of
long bones is a support
between the sternum
and the shoulder blades.

True ribs
Rib pairs one through
seven attach to the
sternum directly via
a piece of cartilage.

The human
ribcage
Ribs are not merely armour for the organs
inside our torsos, as we reveal here
The ribcage also known as the
thoracic cage or thoracic basket is
easily thought of as just a
framework protecting your lungs,
heart and other major organs. Although that is
one key function, the ribcage does so much
more. It provides vital support as part of the
skeleton and, simply put, breathing wouldnt
be possible without it.
All this means that the ribcage has to be
exible. The conical structure isnt just a rigid
system of bone its both bone and cartilage.
The cage comprises 24 ribs, joining in the back
to the 12 vertebrae making up the middle of the
spinal column. The cartilage portions of the
ribs meet in the front at the long, at threebone plate called the sternum (breastbone). Or

058

False ribs
Rib pairs eight through
ten connect to the
sternum via a structure
made of cartilage linked
to the seventh true rib.

rather, most of them do. Rib pairs one through

seven are called true ribs because they attach
directly to the sternum. Rib pairs eight through
ten attach indirectly through other cartilage
structures, so theyre referred to as false ribs.
The nal two pairs the oating ribs hang
unattached to the sternum.
Rib fractures are a common and very painful
injury, with the middle ribs the most likely
ones to get broken. A fractured rib can be very
dangerous, because a sharp piece could pierce
the heart or lungs. Theres also a condition
called ail chest, in which several ribs break
and detach from the cage, which can even be
fatal. But otherwise theres not much you can
do to mend a fractured rib other than keep it
stabilised, resting and giving it time to heal.

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What are hiccups?

Hiccupping known medically as singultus, or
synchronous diaphragmatic utter (SDF) is an
involuntary spasm of the diaphragm that can
happen for a number of reasons. Short-term
causes include eating or drinking too quickly, a
sudden change in body temperature or shock.
However, some researchers have suggested
that hiccupping in premature babies who tend
to hiccup much more than full-term babies is
due to their underdeveloped lungs. It could be an
evolutionary leftover, since hiccupping in humans
is similar to the way that amphibians gulp water
and air into their gills to breathe.

5 TOP
FACTS
RIBCAGE TRIVIA

Flexible cage

Endless ribs

In normal adults, the ribcage

expands by three to five
centimetres (1.2 to two inches)
when you inhale. In an average
breath at rest, we take in about
500 millilitres (0.9 pints) of air.

Fractures

Snakes can have up to 400

vertebrae, with all but the tail
vertebrae having a pair of ribs.
Each rib is attached to a belly
scale which is a key part of
how snakes slither.

The seventh and the tenth ribs

are the ones most likely to get
broken in humans, while the
first pair is rarely fractured
because of its location behind
the clavicle.

Sunken chest

Tasty ribs

Pectus excavatum is a
congenital deformity caused by
abnormal growth of the ribcage,
resulting in a caved-in
appearance that can also affect
the heart and lungs.

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Large carnivores, such as lions,

often head towards the
ribcages of their kills first to
devour both the rib meat and
rich organs, like the heart,
which are encased within.

DID YOU KNOW? The condition known as flail chest is fatal in almost 50 per cent of cases

Manubrium
This broadest and thickest part
of the sternum connects with
the clavicles and the cartilage
for the rst pair of ribs.

Breathe in,
breathe out
Consciously take in a breath, and think about the
fact that there are ten different muscle groups
working together to make it happen. The
muscles that move the ribcage itself are the
intercostal muscles. They are each attached to
the ribs and run between them. As you inhale,
the external intercostals raise the ribs and
sternum so your lungs can expand, while your
diaphragm lowers and attens. The internal
intercostals lower the ribcage when you exhale.
This forces the lungs to compress and release air
(working in tandem with seven other muscles). If
you breathe out gently, its a passive process
that doesnt require much ribcage movement.

Inhalation
Sternal angle
This is the angle formed by
the joint between the
manubrium and the body,
often used as a sort of
landmark by physicians.

As you inhale, the

intercostal muscles
contract to expand
and lift the ribcage.

Contraction
The diaphragm contracts by
moving downward, allowing
the lungs to ll with air.

Body
The main body of the
sternum (breastbone) is
almost at, with three
ridges running across its
surface and cavities for the
cartilage attaching to rib
pairs three through seven.

Floating ribs
(not shown)
Pairs 11-12 are only attached
to the vertebrae, not the
sternum, so are often called
the oating, or free, ribs.

Xiphoid process
This extension from the
sternum starts as cartilage,
but hardens to bone and
fuses to the rest of the
breastbone in adulthood.

Ribs in other animals

ribs overlap one another with hook-like
structures called uncinate processes,
which add strength. Frogs dont
have any ribs, while turtles eight rib
pairs are fused to the shell. A snakes
ribcage, meanwhile, runs the length
of its body and can comprise hundreds
of pairs of ribs. Despite the variations
in appearance, ribcages all serve the
same basic functions for the
most part: to provide support and
protection to the rest of the body.

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Exhalation
The intercostal muscles
relax as we exhale,
compressing and
lowering the ribcage.

Relaxation
The diaphragm relaxes,
moving upward to force
air out of the lungs.

059

Thinkstock

Most vertebrates (ie animals with

backbones) have a ribcage of sorts
however, ribcages can be very
different depending on the creature.
For example, dogs and cats have 13
pairs of ribs as opposed to our 12.
Marsupials have fewer ribs than
humans, and some of those are so tiny
they arent much more than knobs of
bone sticking out from the vertebrae.
Once you get into other vertebrates,
the differences are even greater. Birds

HUMAN
ANATOMY
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The pancreas up-close

How the pancreas works

Learn how the workhorse of the digestive system helps
to break down food and control our blood sugar levels
The pancreas is a pivotal organ
within the digestive system. It sits
inside the abdomen, behind the
stomach and the large bowel,
adjacent to the spleen. In humans, it has a head,
neck, body and tail. It is connected to the rst
section of the small intestine, the duodenum,
by the pancreatic duct, and to the bloodstream
via a rich network of vessels. When it comes to
the function of the pancreas, it is best to think
about the two types of cell it contains:
endocrine and exocrine.
The endocrine pancreas is made up of
clusters of cells called islets of Langerhans,
which in total contain approximately 1 million
cells and are responsible for producing
hormones. These cells include alpha cells,
which secrete glucagon, and beta cells which
generate insulin. These two hormones have
opposite effects on blood sugar levels
throughout the body: glucagon increases
glucose levels, while insulin decreases them.
The cells here are all in contact with
capillaries, so hormones which are produced
can be fed directly into the bloodstream.
Insulin secretion is under the control of a
negative-feedback loop; high blood sugar leads
to insulin secretion, which then lowers blood
sugar with subsequent suppression of insulin.
Disorders of these cells (and thus alterations of
hormone levels) can lead to many conditions,
including diabetes. The islets of Langerhans are
also responsible for producing other hormones,
like somatostatin, which governs nutrient
absorption among other things.
The exocrine pancreas, meanwhile, is
responsible for secreting digestive enzymes.
Cells are arranged in clusters called acini,
which ow into the central pancreatic duct.
This leads into the duodenum part of the
small bowel to come into contact with and aid
in the digestion of food. The enzymes secreted
include proteases (to digest protein), lipases (for
fat) and amylase (for sugar/starch). Secretion of
these enzymes is controlled by a series of
hormones, which are released from the
stomach and duodenum in response to the
stretch from the presence of food.

060

Anatomy of the pancreas

It might not be the biggest organ but the pancreas is a key
facilitator of how we absorb nutrients and stay energised

Pancreatic duct
Within the pancreas, the digestive
enzymes are secreted into
the pancreatic duct,
which joins onto
the common
bile duct.

Common bile duct

The pancreatic enzymes are
mixed with bile from the
gallbladder, which is all sent
through the common bile
duct into the duodenum.

Duodenum
The pancreas empties
its digestive enzymes
into the rst part of
the small intestine.

Head of the
pancreas
The head needs to be
removed if its affected by
cancer, via a complex
operation that involves the
resection of many other
adjacent structures.

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Body of the
pancreas
The central body sits
on top of the main
artery to the spleen.

KEY
DATES
PANCREATIC PAST

336 BCE 1st century CE

The Greek anatomist
who will first discover
the pancreas
Herophilus is born.

The name pancreas is given,

meaning all flesh, as its
believed to serve solely as a
cushioning, protective fat pad.

1642

1889

The pancreatic duct is

German scientists remove
found in Padua, Italy. It is the pancreas in a dog and
named after its discoverer: induce diabetes, proving
the duct of Wirsung.
an irrefutable link.

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1966
The first modern human
pancreatic transplant is
performed in the USA on a
28-year-old female patient.

DID YOU KNOW? In the UK, 80 per cent of acute pancreatitis cases are caused by gallstones or excessive alcohol ingestion

Tail of the pancreas

This is the end portion of
the organ and is positioned
close to the spleen.

What brings on diabetes?

Diabetes is a condition where a
person has higher blood sugar than
normal. It is either caused by a
failure of the pancreas to produce
insulin (ie type 1, or insulindependent diabetes mellitus), or
resistance of the bodys cells to
insulin present in the circulation (ie
type 2, or non-insulin-dependent
diabetes mellitus). There are also

other disorders of the pancreas.

Inammation of the organ (ie acute
pancreatitis) causes severe pain in
the upper abdomen, forcing most
people to attend the emergency
department as it can be life
threatening. In contrast, cancer of
the pancreas causes gradually
worsening pain which can often be
mistaken for other ailments.

Beta cells
It is the beta cells
within the islets of
Langerhans which
control glucose
levels and amount
of insulin secretion.

Insulin released
The vesicle releases its
stored insulin into the
blood capillaries
through exocytosis.

Blood supply
The pancreas derives its blood
supply from a variety of sources,
including vessels running to the
stomach and spleen.

High glucose
When the levels of
glucose within the
bloodstream are high,
the glucose wants to
move down its diffusion
gradient into the cells.

Calcium
effects
The calcium
causes the
vesicles that
store insulin to
move towards
the cell wall.

Every vertebrate animal has a pancreas of some form,

meaning they are all susceptible to diabetes too. The
arrangement, however, varies from creature to creature. In
humans, the pancreas is most often a single structure that sits
at the back of the abdomen. In other animals, the arrangement
varies from two or three masses of tissue scattered around
the abdomen, to tissue interspersed within the connective
tissue between the bowels, to small collections of tissue within
the bowel mucosal wall itself. One of the other key differences
is the number of ducts that connect the pancreas to the bowel.
In most humans theres only one duct, but occasionally there
may be two or three and sometimes even more. In other
animals, the number is much more variable. However, the
function is largely similar, where the pancreas secretes
digestive enzymes and hormones to control blood sugar levels.

GLUT2

Depolarisation

This is a glucosetransporting channel,

which facilitates the
uptake of glucose
into the cells.

The metabolism of glucose

leads to changes in the
polarity of the cell wall
and an increase in the
number of potassium ions.

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Calcium channels
Changes in potassium
levels cause voltage-gated
calcium channels to open in
the cell wall, and calcium
ions to ow into the cell.

061

Corbis; Sleyman Habib

Does the pancreas vary in

humans and animals?

HUMAN
ANATOMY
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Thinkstock

The human bladder

When youve got to
go, youve got to go
but really our bodies
are reacting to our
bladders direction

THE COMPLETE
URINARY SYSTEM
Kidneys
The kidneys
turn unwanted
substances in the
blood into urine.

Ureters
Ureters carry
urine from
the kidneys to
the bladder.

How your
bladder works

Urethra
The urethra runs
from the bottom
of the bladder to
the outside world.

Bladder

The bladder is one of the key organs in the urinary

system and it stores urine following production by
the kidneys until the body can release it.
Urine is a waste substance produced by the
kidneys as they lter our blood of toxins and other unneeded
elements. Up to 150 litres (40 gallons) of blood are ltered per day
by your kidneys, but only around two litres (0.5 gallons) of waste
actually pass down the ureters to the bladder.
Urine travels down the ureters and through the ureter valves,
which attach each tube to the organ and prevent any liquid
passing back. The bladder walls, controlled by the detrusor
muscles, relax as urine enters and allow the organ to ll. When

SPL

As a key part of the urinary system, the bladder

is crucial to removing waste from your body

the bladder becomes full, or nearly full, the nerves in the

bladder communicate with the brain, which in turn induces an
urge to urinate. This sensation will get stronger if you do not go
creating the bursting for a wee feeling that you can
occasionally experience. When ready to urinate, both the
internal and external sphincters relax and the detrusor muscles
in the bladder wall contract in order to generate pressure,
forcing urine to pass down the urethra and exit the body.
As well as telling you when you need to pass uid, the urinary
system also helps to maintain the mineral and salt balance in
your body. For instance, when salts and minerals are too highly
concentrated, you feel thirst to regain the balance.

This muscular
bag generally
holds around a
pint of urine.

Incontinence explained
For the bladder to work correctly,
several areas within it must all function
properly. It is most commonly the
failure of one of these features that
leads to incontinence.
A common type of urinary
incontinence is urge incontinence. This
is when an individual feels a sudden
compulsion to urinate and will release

062

urine without control. It is often caused

by involuntary spasms by the detrusor
muscles which can be a result of either
nervous system problems or infections.
Another type is stress incontinence,
caused when the external sphincter or
pelvic oor muscles are damaged. This
means urine can accidentally escape,
especially if the pelvic oor is under

pressure (eg while coughing, laughing

or sneezing). This kind of incontinence
is most common in the elderly.
One modern remedy is a preventative
implant that has been developed to
replace post-event incontinence pads.
This comes in the form of a collagenbased substance injected around the
urethra in order to support it.

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5 TOP
FACTS
BLADDERS

Urethras all the same?

Womens urethras are much

shorter than mens due to
differing genitalia. Women are
consequently far more likely to
get bladder/urine infections
because of this.

Getting the urge

The urge to urinate normally

comes when the bladder
reaches between 25-50% of
full volume to avoid reaching
100% when involuntary
urination will occur.

Duration

Can you drink urine?

Urine can stay in the bladder

for anywhere between one to
eight hours before excretion.
The time it remains there will
vary depending on the amount
of liquid consumed.

How to keep healthy

Of course, this would not

generally be recommended in
normal circumstances, but
yes, urine is completely sterile
it contains no bacteria,
viruses or fungi.

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Its advised to drink around 1- 1.5

litres (2.1-3.1 pints) of water a
day. This will keep the urinary
system working most effectively.
We lose more water than this
but obtain some from food.

DID YOU KNOW? Everyones bladder differs slightly in size. The average maximum capacity is between 600-800ml (1.3-1.7pt)

Inside
the bladder
How this organ acts as the middleman between
your kidneys and excretion

FULL
BLADDER

Bladder wall
(detrusor
muscles)
Ureters
These tubes link the kidneys
and the bladder, transporting
the urine for disposal.

Ureter valves
These sit at the end of
the ureters and let
urine pass into the
bladder without letting
it flow back.

The detrusor muscles

make up a layer of the
bladder wall. These
muscles cause the wall
to relax and extend as
urine enters, while
nerves situated in the
wall measure how full
the bladder is and will
signal to the brain
when to urinate.

Internal
urethral sphincter
The internal sphincter is
controlled by the body. It
stays closed to stop urine
passing out of the body.

External urethral
sphincter
(distal sphincter)

Pelvic oor muscles

These hold the bladder in place,
and sit around the urethra
stopping unintended urination.

This sphincter is controlled

by the individual, and they
control whether to open or
close the valve.

What is
urine made
up of?
A human bladder usually holds around
350 millilitres (0.7 pints) of urine, though
male bladders can typically hold slightly
more than those of females. Urine is
made up of urea, the waste by-product
the body forms while breaking down
protein across the body. The kidneys will
lter this out and pass it with extra water
to the bladder for expulsion. Other waste
products produced or consumed by the
body that pass through the kidneys will
also exit the body via this route.
Typically, urine is made up of 95 per cent
water and 5 per cent dissolved or
suspended solids including urea, plus
chloride, sodium and potassium ions.

URINE
CONTENTS
Uric acid
0.6g
Bicarbonate
ions
1.2g
Creatinine
2.7g
Potassium ions
3.2g
Sodium ions
4.1g

EMPTYING
BLADDER

Chloride ions
6.6g

Bladder wall
(controlled by
detrusor
muscles)

Internal urethral
sphincter

These muscles contract

to force the urine out
of the bladder.

External urethral
sphincter
(distal sphincter)
This also relaxes for the urine
to exit the body.

Urea
25.5g

2x DK Images

This relaxes when the

body is ready to expel
the waste liquid.

Urethra
Urine travels down this
passageway to leave the body.

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063

HUMAN
ANATOMY
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Human urinary system

The urinary
system
explained

Kidneys
This is where liquids are
filtered and nutrients are
absorbed before urine
exits into the ureters.

Every day the body produces waste

products that enter the bloodstream
but how do we get rid of them?
The human urinary systems
primary function is to remove
by-products which remain in
the blood after the body has
metabolised food. The process is made up
of several different key features. Generally,
this system consists of two kidneys, two
ureters, the bladder, two sphincter
muscles (one internal, one external) and a
urethra and these work alongside the
intestines, lungs and skin, all of which
excrete waste products from the body.
The abdominal aorta is an important
artery to the system as this feeds the renal
artery and vein, which supply the kidneys
with blood. This blood is ltered by the
kidneys to remove waste products, such as
urea which is formed through amino acid
metabolism. Through communication
with other areas of the body, such as the
hypothalamus, the kidneys also control

water levels in the body, sodium and

potassium levels among other electrolytes,
blood pressure, pH of the blood and are
also involved in red blood cell production
through the creation and release of the
hormone erythropoietin. Consequently,
they are absolutely crucial to optimum
body operation.
After blood has been ltered by the
kidneys, the waste products then travel
down the ureters to the bladder. The
bladders walls expand out to hold the
urine until the body can excrete the waste
out through the urethra. The internal and
external sphincters then control the
release of urine.
Generally, a human will produce
approximately 2.5-3 litres of urine a day,
although this can vary dramatically
dependant on external factors such as
water consumption.

Ureter
These tubes link the
kidneys and the bladder.

Inferior vena cava

This carries deoxygenated
blood back from the kidneys
to the right aorta of the heart.

Abdominal aorta
This artery supplies blood
to the kidneys, via the renal
artery and vein. This blood
is then cleansed by
the kidneys.

Bladder
This is where urine
gathers after being
passed down the
ureters from
the kidneys.

Generally, a human will produce

2.5-3 litres of urine a day
How do the kidneys work?
The kidneys will have around 150-180 litres of blood to lter per day, but only pass around
two litres of waste down the ureters to the bladder for excretion, therefore the kidneys
return much of this blood, minus most of the waste products, to the heart for reoxygenation and recirculation around the body.
The way the kidneys do this is to pass the blood through a small ltering unit called a
nephron. Each kidney has around a million of these, which are made up of a number of
small blood capillaries and a tube called the renal tubule. The blood capillaries sift the
normal cells and proteins from the blood for recirculation and then direct the waste
products into the renal tubule. This waste, which will primarily consist of urea, mixes with
water and forms urine as it passes through the renal tubule and then into the ureter on its
way to the bladder.

064

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THE
STATS
URINARY SYSTEM

CAPACITY 400600ml
Human st BLADDER
TIME URINES
BLOOD FILTERED
150180 litres
IN BLADDER 1-8hrs PER DAY
AVERAGE SIZE
OF KIDNEY

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DID YOU KNOW? On average, you make the same amount of urine in the day as in the night

How do we store waste until

were ready to expel it?
The bladder stores waste products by allowing the urine to enter
through the ureter valves, which attach the ureter to the bladder.
The walls relax as urine enters and this allows the bladder to
stretch. When the bladder becomes full, the nerves in the bladder
communicate with the brain and cause the individual to feel the
urge to urinate. The internal and external sphincters will then
relax, allowing urine to pass down the urethra.

Bladder
lls

Why do we
get thirsty?

1. Ureters
These tubes connect to the kidneys and urine
flows down to the bladder through them.

2. Internal urethral sphincter

This remains closed to ensure urine does
not escape unexpectedly.

Maintaining the balance between the

minerals and salts in our body and water is
very important. When this is out of balance,
the body tells us to consume more liquids to
redress this imbalance in order for the body
to continue operating effectively.
This craving, or thirst, can be caused by
too high a concentration of salts in the body,
or by the water volume in the body dropping
too low for optimal operation. Avoiding
dehydration is important as long term
dehydration can cause renal failure, among
other conditions.

3. External
urethral
sphincter
This secondary
sphincter also
remains closed
to ensure no
urine escapes.

4. Ureter valves

The human
urinary
system

These valves are situated

at the end of the ureters
and let urine in.

Bladder
empties

5. Bladder walls
(controlled by
detrusor muscles)
The detrusor muscles in the wall of
the bladder relax to allow expansion
of the bladder as necessary.

1. Internal urethral sphincter

This relaxes when the body is ready to expel
the waste.

2. External
urethral sphincter

Renal artery and vein

This also relaxes for the urine

to exit the body.

This supplies blood to the kidneys

in order for them to operate, and
then removes deoxygenated blood
after use by the kidneys.

Pelvis
The bladder sits in the pelvis,
and the urethra passes through
it for urine to exit the body.

Urethra

DK Images

The urethra is the tube

that urine travels
through to exit the body.

3. Bladder
walls
(controlled
by detrusor
muscles)
These muscles
contract to force
the urine out of
the bladder.

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4. Urethra
Urine travels down this
passageway to exit the body.

065

HUMAN
ANATOMY
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The human stomach

Inside the human stomach

Discover how this amazing digestive organ stretches, churns and holds
corrosive acid to break down our food, all without getting damaged
The stomachs major role is as a
reservoir for food; it allows large
meals to be consumed in one sitting
before being gradually emptied into
the small intestine. A combination of acid,
protein-digesting enzymes and vigorous
churning action breaks the stomach contents
down into an easier-to-process liquid form,
preparing food for absorption in the bowels.
In its resting state, the stomach is contracted
and the internal surface of the organ folds into
characteristic ridges, or rugae. When we start
eating, however, the stomach begins to distend;

the rugae atten, allowing the stomach to

expand, and the outer muscles relax. The
stomach can accommodate about a litre (1.8
pints) of food without discomfort.
The expansion of the stomach activates
stretch receptors, which trigger nerve
signalling that results in increased acid
production and powerful muscle contractions
to mix and churn the contents. Gastric acid
causes proteins in the food to unravel, allowing
access by the enzyme pepsin, which breaks
down protein. The presence of partially
digested proteins stimulates enteroendocrine

Lining under the microscope

The stomach is much more than just a storage bag. Take
a look at its complex microanatomy now

cells (G-cells) to make the hormone gastrin,

which encourages even more acid production.
The stomach empties its contents into the
small intestine through the pyloric sphincter.
Liquids pass through the sphincter easily, but
solids must be smaller than one to two
millimetres (0.04-0.08 inches) in diameter
before they will t. Anything larger is reuxed
backwards into the main chamber for further
churning and enzymatic breakdown. It takes
about two hours for half a meal to pass into the
small intestine and the process is generally
complete within four to ve hours.

Chief cell (yellow)

Chief cells make pepsinogen; at the low pH
in the stomach it becomes the digestive
enzyme pepsin, which deconstructs protein.

Gastric pits

Mucous cell

The entire surface of the

stomach is covered in tiny
holes, which lead to the
glands that produce mucus,
acid and enzymes.

These cells secrete alkaline

mucus to protect the
stomach lining from damage
by stomach acid.

Mucosa
G-cell (pink)
Also known as
enteroendocrine cells,
these produce hormones
like gastrin, which regulate
acid production and
stomach contraction.

Submucosa

Muscularis

Muscle layers
Parietal cell (blue)

The stomach has three layers

of muscle running in different
orientations. These produce
the co-ordinated contraction
required to mix food.

These cells produce hydrochloric

acid, which kills off microorganisms, unravels proteins and
activates digestive enzymes.

066

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THE
STATS
GASTRIC FIGURES

ACID
pH LEVEL 2.5
PRODUCED
50ml GASTRIC
2 litres/day AVERAGE
EMPTYING
CAPACITY 1-4 litres TIME
4-5hrs LENGTH 25cm

VOLUME
WHEN EMPTY

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DID YOU KNOW? Stomach rumbling, also known as borborygmus, is actually the noise of air movement in the intestines

Fundus

Gastric anatomy
This major organ in the digestive system has several distinct
regions with different functions, as we highlight here

The top portion of the

stomach curves up and
allows gases created
during digestion to
be collected.

Cardia
The oesophagus empties into
the stomach at the cardia. This
region makes lots of mucus,
but little acid or enzymes.

Pyloric sphincter
The pyloric sphincter is a strong
ring of muscle that regulates the
passage of food from the
stomach to the bowels.

Antrum
The antrum contains cells that
can stimulate or shut off acid
production, regulating the pH
level of the stomach.

Body
Also called the corpus, this
is the largest part of the
stomach and is responsible
for storing food as gastric
juices are introduced.

Small intestine
Pancreas
Large intestine

The bottom of the stomach

is located in front of the
pancreas, although the two
arent directly connected.

Why doesnt it
digest itself?
Your stomach is full of corrosive acid and
enzymes capable of breaking down protein if
left unprotected the stomach lining would
quickly be destroyed. To prevent this from
occurring, the cells lining the stomach wall
produce carbohydrate-rich mucus, which forms
a slippery, gel-like barrier. The mucus contains
bicarbonate, which is alkaline and buffers the pH
at the surface of the stomach lining, preventing
damage by acid. For added protection, the
protein-digesting enzyme pepsin is created from
a zymogen (the enzyme in its inactive form)
pepsinogen; it only becomes active when it
comes into contact with acid, a safe distance
away from the cells that manufacture it.

The large intestine curls

around and rests just below
the stomach in the abdomen.

Produced by parietal
cells in the stomach
lining, gastric acid has a
pH level of 1.5 to 3.5

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Vomit reex
step-by-step
Vomiting is the forceful expulsion
of the stomach contents up the
oesophagus and out of the mouth.
Its the result of three co-ordinated
stages. First, a deep breath is
drawn and the body closes the
glottis, covering the entrance to
the lungs. The diaphragm then
contracts, lowering pressure in the
thorax to open up the oesophagus.
At the same time, the muscles of
the abdominal wall contract,
which squeezes the stomach. The
combined shifts in pressure both
inside and outside the stomach
forces any contents upwards.

067

Thinkstock

The stomach empties into

the first section of the small
intestine: the duodenum.

HUMAN
ANATOMY
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How do our hands work?

The human hand is an important

feature of the human body,
which allows individuals to
manipulate their surroundings
and also to gather large amounts of data from
the environment that the individual is
situated within. A hand is generally dened
as the terminal aspect of the human arm,
which consists of prehensile digits, an
opposable thumb, and a wrist and palm.
Although many other animals have similar
structures, only primates and a limited
number of other vertebrates can be said to
have a hand due to the need for an
opposable thumb to be present and the
degree of extra articulation that the human
hand can achieve. Due to this extra
articulation, humans have developed ne
motor skills allowing for much increased
control in this limb. Consequently we see
improved ability to grasp and grip items and
development of skills such as writing.
A normal human hand is made up of ve
digits, the palm and wrist. It consists of 27
bones, tendons, muscles and nerves, with
each ngertip of each digit containing
numerous nerve endings making the hand a
crucial area for gathering information from
the environment using one of mans most
crucial ve senses: touch. Muscles interact
together with tendons to allow ngers to
bend, straighten, point and, in the case of the
thumb, rotate. However, the hand is an area
that sees many injuries due to the number of
ways we use it, one in ten injuries in A&E
being hand related, and there are also
several disorders that can affect the hand
development in the womb, such as
polydactyly, where an individual is born
with extra digits, which are often in perfect
working order.

068

The human hand

We take our hands for granted, but they are
actually quite complex and have been
crucial in our evolution

Bones in
the hand
The human hand contains 27
bones, and these divide up into
three distinct groups: the
carpals, metacarpals and
phalanges. These also then
further break down into three:
the proximal phalanges,
intermediate phalanges and
distal phalanges. Eight bones
are situated in the wrist and
these are collectively called
the carpals. The metacarpals,
which are situated in the palm
of the hand account for a
further ve out of the 27, and
each nger has three
phalanges, the thumb has two.
Intrinsic muscles and tendons
interact to control movement of
the digits and hand, and attach
to extrinsic muscles that
extend further up into the arm,
which ex the digits.

Distal phalanges
A distal phalange (fingertip) is situated
at the end of each finger. Deep flexors
attach to this bone to allow for
maximum movement.

Intermediate
phalanges
This is where the
superficial flexors attach
via tendons to allow the
digit to bend.

Proximal
phalanges
Each finger has three
phalanges, and this phalange
joins the intermediate to its
respective metacarpal.

Metacarpals
These five bones make up the
palm, and each one aligns
with one of the hands digits.

Carpals
The carpals (scaphoid, triquetral, trapezium,
trapezoid, lunate, hamate, capitate and
pisiform) sit between the ulna and radius
and the metacarpals.

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SAFER

Having recovered from a

few earlier blunders, the
Brazilian keeper is now
considered one of the best.

2. Gianluigi
Buffon
Named the Serie A
Goalkeeper of the Year a
record nine times, this is
one guy it would be hard
to put one past.

SAFEST
Juan Fernndez

SAFE HANDS

1. Julio Cesar
Soares de
Espindola

Olaf Nordwch

SAFE
Agncia Brasil

HEAD
HEAD

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3. Iker Casillas
Fernandez
Voted best goalie in the
world by the International
Federation of Football
History and Statistics for
two years running.

DID YOU KNOW? Skin is attached to tendons and so when you bend you fingers back, dimples appear on the back of your hand

Muscles and other structures

The movements and articulations of the hand and
by the digits are controlled by tendons and two
muscle groups situated within the hand and wrist.
These are the extrinsic and intrinsic muscle groups,
so named as the extrinsics are attached to muscles
which extend into the forearm, whereas the
intrinsics are situated within the hand and wrist.
The exors and extensors, which make up the
extrinsic muscles, use either exclusively tendons to
attach to digits they control (exors) or a more

Opposable
thumbs

complex mix of tendons and intrinsic muscles to

operate (extensors). These muscles will contract in
order to cause digit movement, and exors and
extensors work in a pair to complement each to
straighten and bend digits. The intrinsic muscles
are responsible for aiding extrinsic muscle action
and other movements in the digits and have three
distinct groups; the thenar and hypothenar
(referring to the thumb and little nger
respectively), the interossei and the lumbrical.

Increased articulation of
the thumb has been
heralded as a key
factor in human
evolution. It allowed
for increased grip
and control, and for
tool use to develop
among human
ancestors as well as other
primates. This has later also facilitated
major cultural advances, such as writing. Alongside
the four other exible digits, the opposable thumb
makes the human hand one of the most dexterous in
the world. A thumb can only be classied as
opposable when it can be brought opposite to the
other digits.

Thenar space
Thenar refers to the thumb,
and this space is situated
between the first digit and
thumb. One of the deep
flexors (extrinsic muscle) is
located in here.

Interossei
muscle
(intrinsic)
This interossei muscle sits
between metacarpal
bones and will unite with
tendons to allow extension
using extrinsic muscles.

This nerve stretches

down the forearm into
the hand and allows for
sensory information
to be passed from
hand to brain.

Arteries, veins
and nerves
These supply fresh
oxygenated blood (and
take away deoxygenated
blood) to hand muscles.

Hypothenar
muscle (intrinsic)
re
do
r2

00
8

Hypothenar refers to the little

finger and this muscle group is one
of the intrinsic muscles.

W
ilf

Extrinsic muscles are so

called because they are
primarily situated outside
the hand, the body of the
muscles situated along the
underside or front of the
forearm. This body of
muscles actually breaks
down into two quite distinct
groups: the exors and the
extensors. The exors run
alongside the underside of
the arm and allow for the
bending of the digits,
whereas the extensor
muscles main purpose is the
reverse this action, to
straighten the digits. There
are both deep and supercial
exors and extensors, and
which are used at any one
time depends on the digit to
be moved.

The most common theory for why some individuals

are left handed is that of the disappearing twin. This
supposes that the left-handed individual was
actually one of a set of twins, but that in the early
stages of development the other, right handed, twin
died. However, its been found that dominance of one
hand is directly linked with hemisphere dominance
in the brain, as in many other paired organs.
Individuals who somehow damage their dominant
hand for extended periods of time can actually
change to use the other hand, proving the impact and
importance of environment and extent to which
humans can adapt.

Forearm
muscles

Left handed
or right
handed?

Ulnar nerve

Insertion of exor tendon

This is where the tendon attaches the
flexor muscle to the finger bones to
allow articulation.

Mid palmar space

Tendons and intrinsic muscles
primarily inhabit this space
within the hand.

Tendons and
intrinsics
These attach the
flexor muscles to the
phalanges, and facilitate
bending. Tendons also
interact with the intrinsics
and extensors in the wrist,
palm and forearm to
straighten the digits.

Science photo library

Thenars

Supercial exors

Deep exors

The intrinsic group of

muscles is used to flex the
thumb and control its
sideways movement.

The other flexor that acts on

the digits is the superior flexor,
which attaches to the
intermediate phalanges.

The digits have two extrinsic flexors that

allow them to bend, the deep flexor and
the superficial. The deep flexor attaches
to the distal phalanges.

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Extensors
Extensors on the back of
the forearm straighten the
digits. Divided into six
sections, their connection
to the digits is complex.

069

HUMAN
ANATOMY
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Achilles tendon / Fingernails

What are our

ngernails
made of?
And how are they formed?

Fingernails are made of a tough protein called keratin (from the

Greek word Kera, meaning horn). Keratin is also what animals
hooves and horns are made from. Most animals have a
supportive bone structure in their horns, although rhinoceros
horns are made completely of keratin compacted together. The only other
biological material which has a similar toughness to keratinised tissue is
chitin, the main component of exoskeletons belonging to arthropods. The
half-moon shape that you can see at the bottom of your nail (apart from
maybe your little nger) is called the lanula. This is a group of cells that
produce keratin and other living cells. As these living cells are pushed
forward by newer cells, they die and merge with the keratin to become
keritinised. They then become attened, stiff and known as your ngernails.

The half-moon shape that you

can see at the bottom of your
nail is called the lanula

What does
the Achilles
tendon do?
Is it really a weak spot and how
important is it?
This tendon, the strongest in your body, connects the calf muscles to
the heel. When everything is ne, it pulls the back of the foot up
when the calf muscles contract. This way, your heel raises and your
weight goes to your toes.
It enables us to do such things as sprinting, hopping or jumping. It also stores
elastic energy to do these tasks more efciently. Biological anthropologists
believe all this was very important for the way we evolved to run around on two
legs and survive.
The Achilles tendon is seemingly named thus after the mythological Greek
character of Achilles, who during the Trojan War - made famous by Homers epic
poem The Illiad - is shot by a poisoned arrow in his unprotected heel - hence the
common phrase describing a persons weak point.

070

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Inside
the knee

Quadriceps
The quadriceps, made up
of four muscles,
are on the front of the
thigh and help to
straighten the leg.

How do our knee joints

allow us to walk and run?
The knee is the largest and
also one of the most complex
joints in the body, allowing
us bipedal humans to move
around and get from point A to point B.
Three different bones meet at the knee
joint and work together to allow for
movement and protection. At the top of
the knee is the lower part of the
thighbone (femur). This rotates on top of
the shinbone (tibia) and the kneecap
(patella), the latter of which moves in a
groove between the femur and tibia.
Cartilage within the knee cushions it
from shock caused by motion, while
ligaments prevent damage occurring to
the joint in case of unusual or erratic
motion. Muscles running from the hip
down to the knee joint are responsible
for working the knee joint and allowing
our legs to bend, stretch, and ultimately
allowing us to walk, run and skip.

Hamstrings
Hamstring muscles running
from the thigh to the knee joint
are responsible for bending
the leg at the knee.

Femur

S
cie
nce
Ph
oto
L

ibr
ar y

This bone runs from the hip to

the knee joint. It is the thickest
and the longest bone in the
human body.

Cartilage
The point at which the three
bones meet is covered in tough,
elastic articular cartilage,
allowing smooth movement of
the joint and absorbing shock.

The knee
structure

How does everything work in

tandem to allow for movement?

Synovial membrane
The soft tissue at the centre of the
knee joint contains synovial fluid,
providing lubrication for the
moving knee.

Patella

Ligaments

This bone slides at the front of

the femur and tibia as the knee
moves, protecting the knee and
giving the muscles leverage.

These elastic bands of tissue

connect the bones together
and provide stability and
strength to the knee joint.

Menisci
The three bones are separated
with two discs of connective
tissue called menisci, also
acting as shock absorbers and
enhancing stability.

Tendons
These tough cords of tissue
attach muscle to bone, so that
the muscles can bend and
straighten the leg as required.

Tibia
This bone connects the knee to
the ankle, running parallel to the
thinner fibula bone.

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The patella, seen

separated above, is also
known as the kneecap

071

HUMAN
ANATOMY
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Anatomy of the foot

How do your
feet work?
Feet are immensely complex structures,
yet we put huge amounts of pressure on
them every day. How do they cope?

DK

Images

A sprained ankle is the most common type of soft tissue

injury. The severity of the sprain can depend on how you
sprained the ankle, and a minor sprain will generally
consist of a stretched or only partially torn ligament.
However, more severe sprains can cause the ligament
to tear completely, or even force a piece of bone to
break off.
Generally a sprain happens
when you lose balance or slip,
and the foot bends inwards
towards the other leg. This then
overstretches the ligaments
and causes the damage. Over
a quarter of all sporting
injuries are sprains
of the ankle.

072

Terminal aspects of the foot

that aid balance by grasping
onto the ground. They are the
equivalent of fingers in the
foot structure.

Muscles including the extensor

digitorum brevis muscle
Muscles within the foot help the foot lift and
articulate as necessary. The extensor digitorum
brevis muscle sits on the top of the foot, and
helps flex digits two-four on the foot.

Blood vessels
These supply blood to the foot,
facilitating muscle operation by
supplying energy and oxygen and
removing deoxygenated blood.

Ligaments
Ligaments support the
tendons and help to form the
arches of the foot, spreading
weight across it.

Tendons (extensor digitorum

longus, among others)
Fibrous bands of tissue which connect
muscles to bones. They can withstand a lot
of tension and link various aspects of the
foot, facilitating movement.

Tibia
The larger and stronger of the lower
leg bones, this links the knee and the
ankle bones of the foot.

Fibula
This bone sits alongside the tibia, also
linking the knee and the ankle.

The structure
of the foot
and how the
elements
work together
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Images

What happens when

you sprain your ankle?

Toes

DK

The human foot and ankle is crucial for locomotion

and is one of the most complex structures of the
human body. This intricate structure is made
up of no less than 26 bones, 20 muscles, 33
joints although only 20 are articulated as well as numerous
tendons and ligaments. Tendons connect the muscles to the
bones and facilitate movement of the foot, while ligaments hold
the tendons in place and help the foot move up and down to
initiate walking. Arches in the foot are formed by ligaments,
muscles and foot bones and help to distribute weight, as well as
making it easier for the foot to operate efciently when walking
and running. It is due to the unique structure of the foot and the
way it distributes pressure throughout all aspects that it can
withstand constant pressure throughout the day.
One of the other crucial functions of the foot is to aid balance,
and toes are a crucial aspect of this. The big toe in particular
helps in this area, as we can grip the ground with it if we feel we
are losing balance.
The skin, nerves and blood vessels make up the rest of the
foot, helping to hold the shape and also supplying it with all the
necessary minerals, oxygen and energy to help keep it moving
easily and constantly.

5 TOP
FACTS

Bunions

Athletes foot

Warts

Ingrown toenails

Achilles tendonitis

FOOT AILMENTS

This is an enlargement of the skin

or tissue around the big toe.
Formation is often attributed to
ill-fitting shoes, though its
suspected that genetics is the
root problem.

A fungal infection thats often

transmitted in areas where
people walk around barefoot,
this develops when the skin is
not properly dried and aired. It
displays as flaky, itchy skin.

Warts are small, benign

lumps of skin, which appear
following exposure to a
virus most commonly
the human papillomavirus
2 and 7.

Ingrown toenails are a form of

nail disease where the nail
grows into either side of the
nail bed. Infection can often
occur if it is not caught and
treated early.

WorldMags.net

This is the inflammation

of the Achilles tendon,
which occurs prior to the
rupture of the tendon,
and is commonly seen
in athletes.

DID YOU KNOW? In a lifetime, a person will walk the equivalent of four times around the globe more than 100,000 miles!

How do
we walk?

4. Leg swing
The lower leg will
then swing at the
knee, under the body,
to be placed in front
of the stationary,
weight- bearing foot.

Human gait is the term to describe how we

walk. This gait will vary between each
person, but the basics are the same

2. Weight transfer
The weight will transfer fully
to the foot still in contact
with the ground, normally
with a slight leaning
movement of the body.

3. Foot lift
After weight has
transferred and the
individual feels
balanced, the ball of
the first foot will then
lift off the ground,
raising the thigh.

The structure of the foot

enables us to stay balanced

6. Repeat
process

5. Heel
placement

1. Heel lift

The heel will normally be

the part of the foot thats
placed first, and weight
will start to transfer back
onto this foot as it hits
the ground.

The first step of walking is for

the foot to be lifted off the
ground. The knee will raise and
the calf muscle and Achilles
tendon, situated on the back of
the leg, will contract to allow
the heel to lift off the ground.

The process is
then repeated with
the other foot. During
normal walking or
running, one foot will
start to lift as the other
starts to come into
contact with the ground.

Bones of the foot

Distal
phalanges

Proximal
phalanges

The bones which

sit at the far end
of the foot and
make up the tips
of the toes.

These bones link the

metatarsals and the
distal phalanges and
stretch from the
base of the toes.

Metatarsals
The five, long bones that are
the metatarsals are located
between the tarsal bones
and the phalanges. These
are the equivalent of the
metacarpals in the hand.

Cuneiforms
bones (three)
Three bones that fuse
together during bone
development and sit
between the metatarsals
and the talus.

Navicular
This bone, which is
so named due
to its resemblance
to a boat, articulates
with the three
cuneiform bones.

A baby is born with 22

out of a total 26 bones in each foot

DK Images

Cuboid

Talus

Calcaneus

One of five irregular bones

(cuboid, navicular and three
cuneiform bones) which make
up the arches of the foot.
These help with shock
absorption in locomotion.

The talus is the

second largest
bone of the foot,
and it makes up
the lower part of
the ankle joint.

This bone
constitutes the
heel and is crucial
for walking. It is
the largest bone
in the foot.

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THE
BODY
AT WORK

129

100
How our
bones heal

Hayfever
explained

076 The science of sleep

Understand why we sleep

100 Healing bone fractures

How broken bones are mended

119 Burns
The causes and effects of burns

084 The blood-brain barrier

What important role does it play?

101 Making protein

How are they manufactured?

120 Circulatory system

How blood gets transported

085 Pituitary gland up close

The master gland explored

102 The cell cycle

Inside a vital process

122 How your blood works

The miraculous uid analysed

086 Human digestion explained

The digestion process revealed

104 Human pregnancy

The different stages explained

126 Hormones
Understand the human
endocrine system

088 Altitude sickness / Synapses

What causes altitude sickness?

106 Embryo development

How a foetus evolves

089 Adrenaline
How this hormone affects us

108 How we taste / Taste buds

The way we sense avours

090 Singing explained

How do we sing?

109 Insulin
Why do we need insulin?

092 Human respiration

The lungs explained

110 How do we smell

Understand the sense of smell

094 Dehydration / Sweating

Why we sweat and using uids

111

095 Scar types

How different scar types form

112 White blood cells

How infection is fought

096 The immune system

Combating viruses

114 The science of genetics

How genes dene who we are

074

Short term memory

How do we retain information?

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128 Tracheotomy surgery

Behind the scenes of a life-saving
medical procedure
129 Hayfever
Why do people suffer?
130 Exploring the sensory system
How we experience the world
134

Chickenpox
How harmful can it really be?

135

Why do we cry?
The different types of tears

136

Ageing
The side effects of the ageing
process revealed

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114
Alamy

DNA
explored

126
The role of
hormones

135
Why do
we cry?

102

Thinkstock

The cell cycle

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Tracheotomy
surgery

Corbis

128
DK Images

The cell damage

from viruses
causes diseases

075

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BODY AT WORK

What happens when we sleep?

The science of

Sleep

Unravelling the mysteries behind insomnia, sleepwalking, dreams and more

There have been many ideas and theories

proposed about why humans sleep, from a way to
rest after the days activities or a method for saving
energy, to simply a way to ll time until we can be
doing something useful. But all of these ideas are
somewhat awed. The body repairs itself just as well
when we are sitting quietly, we only save around 100
calories a night by sleeping, and we wouldnt need to
catch up on sleep during the day if it were just to ll
empty time at night.
One of the major problems with sleep deprivation
is a resulting decline in cognitive ability our brains
just dont work properly without sleep. We will nd
ourselves struggling with memory, learning,

We spend around a third of

our lives sleeping. It is vital to
our survival, but despite years of
research, scientists still arent
entirely sure why we do it. The urge to sleep is
all-consuming, and if we are deprived of it, we will
eventually slip into slumber even if the situation is
life-threatening.
Sleep is common to mammals, birds and reptiles
and has been conserved through evolution, despite
preventing us from performing tasks such as eating,
reproducing and raising young. It is as important as
food and, without it, rats will die within two or three
weeks the same period it takes to die of starvation.

076

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5 TOP
FACTS

MOST COMMON
DREAMS

Falling

Flying

One of the most common

dreams is falling, but the danger
is not as real as it seems. We
often wake up before we hit the
ground in our dreams, but if we
dont we will come to no harm.

Taking exams

Some dreamers can take control

of their dream experience, a
phenomenon known as lucid
dreaming. Once you realise you are
dreaming you can start to enjoy
strange new sensations like flying.

Adults often continue to

dream about exams long after
they have left school, and
experience the same kinds of
anxious feelings that they did
when they were younger.

Being chased

Death

The fight or flight response is

hard-wired into our brains, and
another common dream theme
is being chased. The pursuer
can be anything from a familiar
face to a mythical monster.

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Dreams about the death of a

loved one can be distressing,
but there is absolutely no
evidence to suggest humans
are capable of predicting the
future in their dreams.

DID YOU KNOW? Marine mammals sleep with just half of their brain at a time, allowing them to surface for air

Theories of why we sleep

Energy
conservation
We save around 100 calories per night
by sleeping; metabolic rate drops, the
digestive system is less active, heart
and breathing rates slow, and body
temperature drops. However, the
calorie-saving equates to just one cup
of milk, which from an evolutionary
perspective does not seem worth the
accompanying vulnerability.

Restoration
One of the major problems with sleep
deprivation is a decline in cognitive
function, accompanied by a drop in
mood, and there is mounting evidence
that sleep is involved in restoring the
brain. However, there is little evidence
to suggest that the body undergoes
more repair during sleep compared to
rest or relaxation.

Evolutionary
protection

Memory
consolidation

An early idea about the purpose of sleep

is that it is a protective adaptation to fill
time. For example, prey animals with
night vision might sleep during the day to
avoid being spotted by predators.
However, this theory cannot explain
why sleep-deprived people fall asleep in
the middle of the day.

planning and reasoning. A lack of sleep can have

severe effects on our mood and performance of
everyday tasks, ranging from irritability, through to
long term problems such as an increased risk of
heart disease and even a higher incidence of road
trafc accidents.
Sleep can be divided into two broad stages:
non-rapid eye movement (NREM), and rapid eye
movement (REM) sleep. The vast majority of our
sleep (around 75 to 80 per cent) is NREM,
characterised by electrical patterns in the brain
known as sleep spindles and high, slow delta
waves. This is the time when we sleep the deepest.
Without NREM sleep, our ability to form declarative

One of the strongest theories regarding

sleep is that it helps with consolidation
of memory. The brain is bombarded
with more information during the day
than it is possible to remember, so sleep
is used to sort through this information
and selectively practise parts that need
to be stored.

memories, such as learning to associate pairs of

words, can be seriously impaired. Deep sleep is
important for transferring short-term memories into
long-term storage. Deep sleep is also the time of peak
growth hormone release in the body, which is
important for cell reproduction and repair.
The purpose of REM sleep is unclear, with the
effects of REM sleep deprivation proving less severe
than NREM deprivation; for the rst two weeks
humans report little in the way of ill effects. REM
sleep is the period during the night when we have
our most vivid dreams, but people dream during
both NREM and REM sleep. One curiosity is that
during NREM sleep, dreams tend to be more concept-

based, whereas REM sleep dreams are more vivid

and emotional.
Some scientists argue that REM sleep allows our
brains a safe place to practice dealing with situations
or emotions that we might not encounter during our
daily lives. During REM sleep our muscles are
temporarily paralysed, preventing us acting out
these emotions. Others think that it might be a way
to unlearn memories, or to process unwanted
feelings or emotions. Each of these ideas has its
aws, and no one knows the real answer.
Over the next few pages we will delve into the
science of sleep and attempt to make sense of the
mysteries of the sleeping brain.

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077

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BODY AT WORK

What happens when we sleep?

The sleep cycle

During the night, you cycle through ve separate stages of sleep every 90 to 110 minutes
The ve stages of sleep can be distinguished by
changes in the electrical activity in your brain,
measured by electroencephalogram (EEG). The rst
stage begins with drowsiness as you drift in and out
of consciousness, and is followed by light sleep and

then by two stages of deep sleep. Your brain activity

starts to slow down, your breathing, heart rate and
temperature drop, and you become progressively
more difcult to wake up. Finally, your brain perks
up again, resuming activity that looks much more

like wakefulness, and you enter rapid eye movement

(REM) sleep the time when your most vivid dreams
occur. This cycle happens several times throughout
the night, and each time, the period of REM sleep
grows longer.

How much 30%

time is spent
in each sleep
stage?

20%

Other
stages

Growth
hormone
release
After you fall asleep,
the pituitary gland
ramps up its
production of
growth hormone.

REM sleep

50%
Stage 2
sleep

Low temperature
Body temperature falls just
before you fall asleep, and is
maintained at a lower level
throughout the night.

Limited
movement
Muscle tone drops
during sleep, but you
still change position,
tossing and turning.

Different when
dreaming
During REM sleep, your
heart rate rises, but your
larger muscles are
paralysed. This mean just
your fingers, toes and eyes
twitch as you dream.

Slow breathing
As you fall into deeper and
deeper sleep, your breathing
becomes slower and more rhythmic
and your heart rate drops.

Stages of sleep
Not all sleep is the same. There are five separate stages, divided by brain activity

 JFKRQBP

 JFKRQBP

 JFKRQBP

1 Drowsiness

2 Light sleep

3 Moderate sleep

During the first stage of sleep you are just drifting off;
your eyelids are heavy and your head starts to drop.
During this drowsy period, you are easily woken and
your brain is still quite active. The electrical activity on
an electroencephalogram (EEG) monitor starts to slow
down, and the cortical waves become taller and
spikier. As the sleep cycle repeats during the night, you
re-enter this drowsy half-awake, half-asleep stage.

After a few minutes, your brain activity slows further,

and you descend into light sleep. On the EEG monitor,
this stage is characterised by further slowing in the
waves, with an increase in their size and short one- or
two-second bursts of activity known as sleep
spindles. By the time you are in the second phase of
sleep, your eyes stop moving, but you can still be
woken quite easily.

As you start to enter this third stage, your sleep

spindles stop, showing that your brain has entered
moderate sleep. This is then followed by deep sleep.
The trace on the EEG slows still further as your brain
produces delta waves with occasional spikes of
smaller, faster waves in between. As you progress
through stage-three sleep, you become much more
difficult to wake up.

078

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HEAD
HEAD

1. SLEEPY

2. SLEEPIER

Tokyo, Japan

3. SLEEPIEST

Moscow,
Russia

According to data collected

by the Jawbone UP tness
tracker in 2014, Tokyo is the
city that sleeps the least,
averaging just ve hours
and 44 minutes each night.

People living in the famous

Russian capital sleep in
late, rising at 8:08am on
average after six hours
and 42 minutes of sleep.

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SLEEPLESS IN

Melbourne,
Australia
The residents of the
Australian city of
Melbourne clock an average
of six hours and 58 minutes
of sleep every night.

DID YOU KNOW? Sleeping in at the weekends causes social jet lag and makes it more difficult to get up on Monday morning

WAKE

Dreaming versus deep sleep

REM

First
cycle

Second
cycle

Third
cycle

Fourth
cycle

Fifth
cycle

Deep sleep

Dreaming (REM)

STAGE 1
STAGE 2
STAGE 3
STAGE 4

The brain is a power-hungry organ; it

makes up only two per cent of the total
mass of the body, but it uses an
enormous 25 per cent of the total energy
supply. The question is, how does it get
rid of waste? The Nedergaard Lab at
the University of Rochester in New
York thinks sleep might be a time to
clean the brain. The rest of the
body relies on the lymphatic
drainage system to help remove
waste products, but the brain is a
protected area, and these vessels
do not extend upward into the
head. Instead, your central nervous
system is bathed in a clear liquid
called cerebrospinal uid (CSF), into
which waste can be dissolved for
removal. During the day, it remains
on the outside, but the labs research
has shown that, during sleep, gaps
open up between brain cells and the
uid rushes in, following paths along
the outside of blood vessels, sweeping
through every corner of the brain and
helping to clear out toxic molecules.

 JFKRQBP

 JFKRQBP

4 Deep sleep

5 REM sleep

There is some debate as to whether sleep stages three

and four are really separate, or whether they are part
of the same phase of sleep. Stage four is the deepest
stage of all, and during this time you are extremely
hard to wake. The EEG shows tall, slow waves known
as delta waves; your muscles will relax and your
breathing becomes slow and rhythmic, which can lead
to snoring.

After deep sleep, your brain starts to perk up and its

electrical activity starts to resemble the waking brain.
This is the period of the night when most dreams
happen. Your muscles are temporarily paralysed, and
your eyes dart around, giving it the name rapid eye
movement (REM) sleep. You cycle through the stages of
sleep about every 90 minutes, experiencing between
three and five dream periods each night.

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Wide awake

Deep sleep

The red areas in this scan

show areas of activity in the
waking human brain, while
the blue areas represent
areas of inactivity.

During the later stages of

NREM sleep, the brain is less
active, shown here by the
cool blue and purple colours
that dominate the scan.

REM (dream) sleep

Light sleep

When dreaming, the human

brain shows a lot of activity,
displaying similar red
patterns of activity to the
waking brain.

In the first stages of NREM

sleep, the brain is less active
than when awake, but you
remain alert and easy to
wake up.

Sleep deprivation

NREM sleep

The sleep-deprived brain

looks similar to the brain
during NREM sleep, showing
patterns of inactivity.

As you descend through the

four stages of NREM sleep,
your brain becomes
progressively less active.

079

Science Photo Library; Alamy; Thinkstock

Brain activity

Clearing
the mind

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BODY AT WORK

What happens when we sleep?

Sleep
disorders
There are over 100 different
disorders that can get in the way
of a good nights sleep
Sleep is necessary for our health, so disruptions to
the quality or quantity of our sleep can have a
serious negative impact on daily life, affecting both
physical health and mental wellbeing.
Sleep disorders fall into four main categories:
difculty falling asleep, difculty staying awake,
trouble sticking to a regular sleep pattern and
abnormal sleep behaviours. Struggling with falling
asleep or staying asleep is known as insomnia, and
is one of the most familiar sleep disorders; around a
third of the population will experience it during
their lifetime. Difculty staying awake, or
hypersomnia, is less common. The best-known
example is narcolepsy, which is when sufferers
experience excessive daytime sleepiness,
accompanied by uncontrollable short periods of
sleep during the day. Trouble sticking to a regular
sleeping pattern can either be caused by external
disruption to normal day-to-day rhythms, for
example by jet lag or shift work. It can also be the
result of an internal problem with the part of the
brain responsible for setting the body clock.
Abnormal sleep behaviours include problems like
night terrors, sleepwalking and REM-sleep
behaviour disorder. Night terrors and sleepwalking
most commonly affect children, and tend to resolve
themselves with age, but other sleep behaviours
persist into adulthood. In REM-sleep behaviour
disorder, the normal muscle paralysis that
accompanies dreaming fails, and people begin to act
out their dreams.
Treatment for different sleep disorders varies
depending on the particular problem, and can be as
simple as making the bedroom environment more
conducive to restful sleep.

Sleepwalking

Sleepwalkers can perform complicated

actions while in deep NREM sleep

Sleepwalking affects between one

and 15 per cent of the population,
and is much more common in
children than in adults, tending to
happen less and less after the age
of 11 or 12. Sleepwalkers might just
sit up in their bed, but can
sometimes perform complex
behaviours, such as walking,
getting dressed, cooking, or even
driving a car. Although
sleepwalkers seem to be acting
out their dreams, sleepwalking
tends to occur during the
deep-sleep phase of NREM sleep
and not during REM sleep.

Sleep apnoea
Sleep apnoea is a dangerous sleep disorder. It is
when the walls of the airways relax so much
during the night that breathing is interrupted for
ten seconds or more, restricting the supply of
oxygen to the brain. The lack of oxygen initiates a

protective response, pulling the sufferer out of

deep sleep to protect them from damage. This can
cause people to wake up, but often it will just put
them into a different sleep stage, interrupting their
rest and causing feelings of tiredness the next day.

Loud breathing

Waking up

Lack of oxygen

People suffering with sleep apnoea

often snore, gasp and breathe
loudly as they struggle for air
during the night.

The low oxygen level in the blood

triggers the brain to wake up in an
attempt to fix the obstruction.

If the airway is obstructed for

ten seconds or more, the
amount of oxygen reaching
the brain drops.

Muscle collapse
The muscles supporting
the tongue, tonsils and
soft palate relax during
sleep, causing the throat
to narrow.

Treatment for
different sleep
disorders varies
A continuous
positive airway
pressure (CPAP)
machine pumps
air into a
close-fitting mask,
preventing the
airway from
collapsing

080

Risk factors
Sleep apnoea is much more
common in patients who are
overweight, male and over
the age of 40. Smoking,
alcohol and sleeping pills also
increase the risk.

Warning signs
Reduced airow
Soft-tissue collapse reduces the amount
of air entering the lungs or obstructing
the airways completely.

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People may not know they have sleep

apnoea, but warning signs include
daytime sleepiness, headaches and
night sweats.

RECORD
BREAKERS

GETTING SOME
SHUT-EYE

20
WorldMags.net
hours Sleepiest animal
a day

The little brown bat is the sleepiest animal on the planet, spending a massive 20 hours
every day snoozing. The koala is a close rival, sleeping for over 14 hours every day.

DID YOU KNOW? After 24 hours without sleep your cognition is at the same level as a person with a blood alcohol content of 0.10%

Narcolepsy
Narcolepsy is a chronic condition
that causes people to suddenly fall
asleep during the daytime. In the
United States, it affects one in every
3,000 people. Narcoleptics report
excessive daytime sleepiness,
accompanied by a lack of energy
and impaired ability to concentrate.
They fall asleep involuntarily for
periods lasting just a few seconds at
a time, and some can continue to
perform tasks such as writing,
walking, or even driving during
these microsleeps. In 70 per cent of
cases, narcolepsy is accompanied
by cataplexy, where the muscles go
limp and become difcult to control.
It has been linked to low levels of the
neurotransmitter hypocretin,
which is responsible for promoting
wakefulness in the brain.

People with narcolepsy fall

asleep involuntarily
during the day

Insomnia

Insomniacs have difculty falling

asleep or staying asleep. Sufferers can
wake up during the night, wake up
unusually early in the morning, and
report feeling tired and drained
during the day. Stress is thought to be
one of the major causes of this sleep
disruption, but it is also associated
with mental health problems like
depression, anxiety and psychosis,
and with underlying medical
conditions ranging from lung
problems to hormone imbalances.
After underlying causes have been
ruled out, management of insomnia
generally involves improving sleep
hygiene by sticking to regular sleep
patterns, avoiding caffeine in the
evening and keeping the bedroom free
from light and noise at night.

One in three people in the UK will

experience insomnia in their lifetime

Sleep studies
The most common type of sleep
study is a polysomnogram (PSG),
which is an overnight test
performed in a specialist sleep
facility. Electrodes are placed on the
chin, scalp and eyelids to monitor
brain activity and eye movement,
while pads are placed on the chest
to track heart rate and breathing.
Blood pressure is also monitored
throughout the night, and the
amount of oxygen in the
bloodstream can be tracked using a
device worn on the nger. The
equipment monitors how long it
takes a patient to fall asleep, and
then to follow their brains and
bodies as they move through each
of the ve sleep stages.

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BSIP SA / Alamy

Electrodes monitor brain activity,

eye movement, heart rate and
breathing in sleep studies

081

THEWorldMags.net
BODY AT WORK

What happens when we sleep?

How to get a good nights sleep

Understanding your biological clock is the key to a healthy nights sleep
Your body is driven by an internal
circadian master clock known as
the suprachiasmatic nucleus,
which is set on a time scale of
roughly 24 hours. This biological
clock is set by sunlight; blue light
hits special receptors in your eyes,
which feed back to the master
clock and on to the pineal gland.
This suppresses the production of
the sleep hormone melatonin and
tells your brain that it is time to
wake up.
Disruptions in light exposure can
play havoc with your sleep, so it is
important to ensure that your
bedroom is as dark as possible.
Many electronic devices produce
enough light to reset your biological
clock, and using backlit screens late

at night can confuse your brain,

preventing the production of
melatonin and delaying your sleep.
Ensuring you see sunlight in the
morning can help to keep your
circadian clock in line, and sticking
to a regular sleep schedule, even at
the weekends, helps to keep this
rhythm regular.
Another important factor in a
good nights sleep is winding down
before bed. Stimulants like
caffeine and nicotine keep your
brain alert and can seriously
disrupt your sleep. Even
depressants like alcohol can have a
negative effect; even though it
calms the brain, it interferes with
normal sleep cycles, preventing
proper deep and REM sleep.

The blue light from televisions, mobile phones and

computer screens disrupts your circadian rhythm

The dangers of sleep deprivation

Lack of sleep doesnt just make you tired it can have dangerous unseen effects

IMPAIRED JUDGEMENT

Sleep deprivation impacts your visual working

memory, making it hard to distinguish between
relevant and irrelevant stimuli, affecting emotional
intelligence, behaviour and stress management.

INCREASED ACCIDENTS

In the USA it is estimated that 100,000 road accidents

each year are the result of driver fatigue, and over a
third of drivers have admitted to falling asleep behind
the wheel.

082

WEIGHT GAIN

Sleep deprivation affects the levels of hormones

involved in regulating appetite. Levels of leptin (the
hormone that tells you how much stored fat you have)
drop, and levels of the hunger hormone ghrelin rise.

MOOD DISORDERS

Mental health problems are linked to sleep disorders,

and sleep deprivation can play havoc with
neurotransmitters in the brain, mimicking the
symptoms of depression, anxiety and mania.

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RAISED BLOOD PRESSURE

Poor sleep can raise blood pressure, and in the long

term is associated with an increased risk of diseases
such as coronary heart disease and stroke. This danger
is increased in people with sleep apnoea.

HALLUCINATIONS

Severe sleep deprivation can lead to hallucinations

seeing things that arent really there. In rare cases , it
can lead to temporary psychosis or symptoms that
resemble paranoid schizophrenia.

STRANGE
BUT TRUE

Who holds the world record for

the longest time without sleep?

STAYING AWAKE

A Randy Gardner B Barack Obama C No one

Answer:
Randy Gardner used to hold the ofcial world record,
set at 264 hours (11 days) in 1964, but today no one
is able to claim the title. The Guinness Book of World
Records scrapped it in 1989 because trying to break
the record is considered too dangerous.

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DID YOU KNOW? Sleep deprivation was found to have played a significant role in the nuclear meltdown at Chernobyl in 1986

Sleep myths debunked SLEEP STATS

The science behind ve of the most common myths
relating to sleep

What are the most common

sleeping positions?

Counting sheep
helps you sleep

41%
15%
Foetus
Log

This myth was put to the test by the University of Oxford,

who challenged insomniacs to either count sheep,
imagine a relaxing scene, or do nothing as they tried to
fall asleep. When they imagined a relaxing scene, the
participants fell asleep an average of 20
minutes earlier than when they tried
either of the other two methods.

Yawning
wakes you up
Yawning has long been associated with
tiredness and was fabled to provide more
oxygen to a sleepy brain, but this is not the
case. New research suggests that we actually
yawn to cool our brains down, using a deep
intake of breath to keep the brain running at
its optimal temperature.

Teenagers
are lazy

8%
Soldier

7%

Freefaller

How does sleep

time vary with
age?

13%
Yearner
5%

Starsh

16 hours
INFANTS

9 hours
TEENS

7 hours
ADULTS

What keeps the

UK up at night?

Sleep habits start to change just before puberty,

and between the ages of ten and 25, people need
around nine hours of sleep every night. Teens can
also experience a shift in their circadian rhythm,
called sleep phase delay, pushing back their
natural bedtime by around two hours, and
encouraging them to sleep in.

67% 36%
13%
34% 19%
Noise
Partner Temperature
Light

Discomfort

Many people have heard that waking a sleepwalker might kill

them, but there is little truth behind these tales. Waking a
sleepwalker can leave them confused and disorientated, but
the act of sleepwalking in itself can be much more dangerous.
Gently guiding a sleepwalker back to their bed is
the safest option, but waking them carefully
shouldnt do any harm.

Canada

UK

7h03

6h49

USA

6h22

Japan

6h31
Mexico

7h06

What do
people
dream
about?

Cheese gives
you nightmares
The British Cheese Board conducted a study in an
attempt to debunk this myth by feeding 20g (0.7oz) of
cheese to 200 volunteers every night for a week and
asking them to record their dreams. There were no
nightmares, but strangely 75 per cent of men and 85 per
cent of the women who ate Stilton reported vivid dreams.

Germany

7h01
Other

14%

Sadness,
apprehension,
anger

65%
Happiness
& excitement

20%
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Sex

1%
083

Thinkstock; Dreamstime

You should never wake

a sleepwalker

Which country
sleeps the longest?

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BODY AT WORK

The blood-brain barrier

What is the bloodbrain barrier?

How does this gateway control the molecules
that pass from the blood into the brain

Crossing the BBB

The endothelial lining of the blood-brain barrier
loves lipids (fatty molecules), but it hates
particles with high electrical charges (ions) and
large substances. Thus the ideal substance is
small, rich in lipids and has a low electrical
charge. Barbiturates are such an example, as they
freely ow across the blood-brain barrier to
suppress brain function; they act as sedatives and
antidepressants. However this free movement
comes with risks too much of it will accumulate
and slow the brain to a point where you can lose
consciousness and even stop breathing.

084

Breaking down the barrier

This built-in gateway is the main line of
defence for the central nervous system

Just passing through

Some ions are transported
out of the blood cells and
into the astrocytes, and then
out of the astrocytes and
into neurons in the brain.

Lipophilic
Substances rich in
lipids can diffuse
across the barrier
with relative ease.

Astrocyte
These numerous
star-shaped cells provide
biochemical support to the
endothelial cells, and also
play an important role in
transportation and repair.

Special transport
Active and passive
transporters across this
membrane can overcome
some of these problems,
and be manipulated to
deliver medications to
the correct place.

Highly charged
Highly charged ions are
repelled, meaning that
some medications are
ineffective in the brain.

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A tight squeeze
The tiny gaps between
cells regulate the size
and type of particle that
are able to t through.

Thinkstock; SPL

The blood-brain barrier (BBB) is an

essential group of cells that line the
blood vessels in the central nervous
system (brain and spinal cord).
They allow passage of materials between the
clear uid surrounding the brain (cerebrospinal
uid) and the red blood cells in arteries, veins
and capillaries. The key advantage of having
such a barrier is that it prevents large microorganisms passing into the brain and causing
infections. While infections in other areas are
common (such as after a cut nger, or mild chest
infections), those affecting the brain are much
rarer. However when they do occur (eg
meningitis), they are potentially life
threatening as they are very difcult to treat.
The tight junctions between cells regulate
the size and type of particle that pass between
them, including oxygen molecules, carbon
dioxide molecules, nutrients and hormones.
Since its so effective, it also stops medications
from entering the brain (such as certain
antibiotics), so while they are effective in the
rest of the body, they are ineffective in this vital
organ. Overcoming this is a major aim of
doctors in the next decade, and the battle has
already started. Manipulating the blood-brain
barriers natural transport mechanisms and
delivering drugs within nanoparticles to
squeeze through the tight junctions are just
two examples of the modern techniques that
are under development. -

RECORD
BREAKERS
TALL TALE

TALLEST MAN IN HISTORY

2.72m
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At 2.72 metres (eight foot, 11.1 inches) Robert Wadlow is the tallest man
on record. A sufferer of gigantism, he was 0.9 metres (three feet) taller
than his father. Sadly, he was only 22 when he died in 1940.

DID YOU KNOW? In fish, the intermediate lobe controls skin colour change, while birds have no intermediate lobe at all

Pituitary gland up close

What does this hormone factory do and why couldnt we live without it?

Gigantism in focus
The pituitary gland also produces growth
hormone, which in adults controls the amount
of muscle and fat in the body and plays a key
role in the immune system. In children, of
course, growth hormone has a very noticeable
effect in increasing height and bulk until
adulthood. However, sometimes the pituitary
gland becomes hyperactive often as a result of
a benign tumour and produces excess growth
hormone. In these cases, a person can grow to a
far-beyond-average height, with hands, feet and
facial features growing proportionally. While this
might not seem so bad, gigantism is nearly
always accompanied by other health issues,
such as skeletal problems, severe headaches
and more life-threatening conditions like heart
disorders. If diagnosed early, treatment such as
drugs that inhibit growth hormone production
and surgical removal of the tumour can help
avert the more serious conditions of gigantism.

The master gland in context

Where does this vitally important hormone
manufacturer sit within the human brain?

Hypothalamus
The secretion of hormones
from the pituitary gland is
directly controlled by this
part of the brain, which
links the nervous and
endocrine systems.

Pituitary stalk
This is what connects
the pituitary lobes to
the hypothalamus.

Posterior lobe
This doesnt produce any
hormones itself, but
stores and releases some,
like ADH, made elsewhere
in the hypothalamus.

Capillaries
Hormones are exchanged
between the anterior lobe
and the hypothalamus via
a network of capillaries.

Anterior lobe
Subdivided into three
parts, including the thin
intermediate lobe, this
produces seven kinds
of hormone which each
target specific organs.

Thyroid
One of the largest
endocrine glands that
regulates metabolism
is in turn regulated by
the pituitary gland.
Alamy

The pea-sized pituitary gland is

found at the base of the brain, close
to the hypothalamus. It looks a
relatively insignicant part of the
brain, but it plays a role in many vital systems.
Often referred to as the master gland, it not
only releases hormones that control various
functions, but it also prompts the activity of
other glands like the ovaries and testes.
The pituitary gland comprises three sections
called lobes: the anterior, the posterior and the
intermediate the latter of which is considered
part of the anterior lobe in humans. These work
together with the hypothalamus, which
monitors hormones in the blood and stimulates
the pituitary gland to produce/release the
appropriate hormone(s) if levels fall too low.
The anterior lobe produces seven important
hormones, which include those that regulate
growth and reproduction. Adrenocorticotropic
hormone (ACTH) targets the adrenal glands to
produce cortisol and controls metabolism,
while luteinising hormone triggers ovulation in
women and stimulates testosterone production
in men. The posterior lobe, meanwhile, doesnt
generate any hormones itself, but stores two:
antidiuretic hormone (ADH), which decreases
urine production by making the kidneys return
more water to the blood, and oxytocin, which
tells the uterus to contract during childbirth
and also prompts milk production.

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085

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BODY AT WORK

Human digestive system

Human
digestion
How does food get
turned into energy?
The digestive system is a group of organs that
process food into energy that the human body
can use to operate. It is an immensely complex
system that stretches all the way between the
mouth and the anus.
Primary organs that make up the system are the mouth,
oesophagus, stomach, small intestine, large intestine and the
anus. Each organ has a different function so that the maximum
amount of energy is gained from the food, and the waste can
be safely expelled from the body. Secondary organs, such as
the liver, pancreas and gall bladder, aid the digestive process
alongside mucosa cells, which line all hollow organs and
produce a secretion which helps the food pass smoothly
through them. Muscle contractions called peristalsis also help
to push the food throughout the system.
The whole digestive process starts when food is taken into
the body through the mouth. Mastication (chewing) breaks
down the food into smaller pieces and saliva starts to break
starch in these pieces of food into simpler sugars as they are
swallowed and move into the oesophagus. Once the food has
passed through the oesophagus, it passes into the stomach. It
can be stored in the stomach for up to four hours.
The stomach will eventually mix the food with the digestive
juices that it produces, which will break down the food further
into simpler molecules. These molecules then move into the
small intestine slowly, where the nal stage of chemical
breakdown occurs through exposure to juices and enzymes
released from the pancreas, liver and glands in the small
intestine. All the nutrients are then absorbed through the
intestinal walls and transported around the body through the
blood stream.
After all nutrients have been absorbed from food through the
small intestine, resulting waste material, including bre and
old mucosa cells, is then pushed into the large intestine where it
will remain until expelled by a bowel movement.

Nutrients are then

absorbed through the
intestinal walls and
transported around
the body
086

Large intestine
The colon, as the large
intestine is also known, is
where waste material will
be stored until expelled
from the digestive system
through the rectum.

Small intestine
Nutrients that have been
released from food are
absorbed into the blood
stream so they can be
transported to where they are
needed in the body through
the small intestine wall.
Further breaking down occurs
here with enzymes from the
liver and pancreas.

How
your
body
digests
food
Many different organs
are involved in the
digestion process

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Rectum
This is where waste
material (faeces) exits
the digestive system.

5 TOP
FACTS

Complete digestion
takes time!

Some food
for thought

The stomach can

hold two litres

We use pints of
saliva a day!

Enzyme production
declines through age

DIGESTION

Generally, it can take between

24 and 72 hours for the food
you eat to be fully digested,
meaning youre constantly
digesting food!

An average human male will

consume approximately 50
tons of food during his lifetime.
Thats the equivalent of ten
African elephants.

The stomach will normally

feel full when it reaches a
capacity of one litre, but
ultimately it can stretch up
to two litres.

Up to four pints of saliva can be

produced by an individual each
day and it helps to digest food
and protect teeth and tissue
inside the mouth.

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Enzymes are crucial for

digestion, but as we age,
enzyme production reduces at
70 a person may produce half
what they did at 20.

DID YOU KNOW? The human digestive system is between 20 to 30 feet long!
Mouth

Oesophagus
The oesophagus passes the food
into the stomach. At this stage, it
has been broken down through
mastication and saliva will be
breaking down starch.

Oesophageal
sphincter
This is the control
valve for letting food
into the stomach.

DK Images

This is where food enters the body and first gets broken into
more manageable pieces. Saliva is produced in the glands
and starts to break down starch in the food.

How does our

stomach work?
The stomach is one of the most crucial
organs within the digestive system

Corpus body
This is where stomach
acid is situated,
consequently it is
where food is broken
down into molecules
that the small intestine
can then process.

Mucosa
These cells line all of the
stomach to aid movement of
food throughout the organ.

Stomach

Duodenum

This is where food is broken

down to smaller molecules
which can then be passed into
the small intestine. Stomach
acid and enzymes produced
by the stomach aid this.

The area at the top of the

small intestine, this is
where most chemical
breakdown occurs.

The stomachs function is to break down food

into simple molecules before it moves into
the small intestine where nutrients are
absorbed. The organ actually splits into four
distinct parts, all of which have different
functions. The uppermost section is the
cardia, where food is rst stored, the fundus
is the area above the corpus body, which
makes up the main area of the stomach
where food is mixed with stomach acid. The
nal section is the antrum, containing the
pyloric sphincter, which is in control of
emptying the stomach contents into the
small intestine. Food is passed down into the
stomach by mucosa and peristalsis through
the oesophageal sphincter, and then mixed
in the stomach with acids and juices by
muscle contractions.

How the
intestine works
The intestine is a crucial
part of the digestive
system that is heavily
involved in breaking
down and absorbing
nutrients released from
ingested food

Rectum

Villi
These cells are shaped like fingers
and line the small intestine to increase
surface area for nutrient absorption.

DK Images

This is where
waste is stored
briefly until it
is expelled by
the body.

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The intestine splits into two distinct parts,

the small intestine and the large intestine.
The small intestine is where the food goes
through nal stages of digestion and
nutrients are absorbed into the blood stream,
the large intestine is where waste is stored
until expelled through the anus. Both the
small and large intestines can be further
divided into sections, the duodenum,
jejunum and ileum are the three distinct
sections of the small intestine and the
cecum, colon and rectum are the sections of
the large intestine. As well as storing waste,
the large intestine removes water and salt
from the waste before it is expelled. Muscle
contractions and mucosa are essential for the
intestine to work properly, and we see a
variation of mucosa, called villi, present in
the lower intestine.

087

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BODY AT WORK

Altitude sickness / Synapses

What causes
altitude sickness?

High altitude sickness can have a

severe physical effect on the
human body. Descending to
lower altitudes is the only way to
ease symptoms

Discover the effects that dizzying heights can have on

the human body
Adventurous explorers can spend
months training prior to scaling
mountain peaks, but regardless of
tness level, high altitudes can take its
toll on the human body.
Between around 1,524 and 3,505 metres (5,000 and
11,500 feet) above sea level is considered high
altitude. At this level, most travellers will start to feel
the effects of high altitude sickness as they attempt
to acclimatise to the change in atmosphere that
happens at this height.
The most common symptom is shortness of
breath, which is due to a lack of atmospheric
pressure. At these heights, air molecules are more

dispersed, so less oxygen can be inhaled. In order to

compensate, your heart rate will increase and the
body will produce more red blood cells, making it
easier to transport oxygen around the body.
The low humidity levels at high altitude can also
cause moisture in the skin and lungs to evaporate
quicker, so dehydration is a real threat. Your face,
legs and feet may start to swell as the body attempts
to retain uid by holding more water and sodium in
the kidneys.
Difculty sleeping is also common, and symptoms
of high altitude sickness can get progressively worse
the higher you climb, including mood changes,
headaches, dizziness, nausea and loss of appetite.

How does a synapse work?

Neuron
As well as a long extension
called the axon, each neuron
has multiple branch-like
extensions called dendrites,
which take in nerve messages
from other neurons.

Neurotransmitter molecules

The sending nerve cell

contains a nucleus, which
holds the cells genes and
controls its functions.

When the nerve signal reaches the synapse, it

is converted into neurotransmitters, which are
the chemicals that bind to the receptor nerve
cell, causing an electrical impulse.

Axon
The nerve signals travel in
one direction along the axon
to the synaptic knob at the
end of the axon.

Nerve impulse
A nerve impulse is initiated
when a stimulus (change in
the internal or external
environment) alters the
electrical properties of the
neuron membranes.

Ions
The flow of these charged
particles is the basis of
the propagation of a
nerve impulse.

Trillions of neurons carry messages around

the body, but how do they pass them on?
The nervous system involves a complex collection of nerve cells
called neurons. Nerve messages can travel along individual
neurons as electrical nerve impulses caused by the movement of
lots of electrically charged ion particles. In order to cross the
minuscule gaps between two neurons, the nerve message must be converted
into a chemical message capable of jumping the gap. These tiny gaps between
neurons are called synapses, forming the main contact zone between two
neurons. Each neuron consists of a cell body and branching structures known
as axons and dendrites. Dendrites are responsible for taking information in via
receptors, while axons transmit information away by passing electrical signals
across the synapse from one neuron to another.

088

Vesicle
This is the tiny membrane that stores
neurotransmitter molecules. The vesicles travel
from the sending neuron to the synapse, where
they fuse with the presynaptic membrane and
release the neurotransmitters.

Presynaptic
membrane
Synaptic cleft
Postsynaptic
membrane
The cell membranes of
the sending neuron
(presynaptic membrane)
and the receiving neuron
(post-synaptic
membrane) are separated
by a fluid-filled gap called
the synaptic cleft.

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Ongoing message
Once the neurotransmitters
cross the gap between the two
neurons, ion channels in the
receiving neuron open allowing
the positive ions to flow into the
receiving neuron.

DK Images

Dendrite

5 TOP
FACTS

ADRENLINE

Welcome to the world

When you need to breathe

And relaaax

Amino what now?

Fight or ight

A babys stress level during

birth is high and, as a result,
their adrenaline level is also
very high at this time. This
subsides post birth back down
to normal levels.

Due to its blood-vesselconstricting properties, adrenaline

is also used to treat breathing
difficulties associated with
anaphylactic shock caused by
allergic reactions.

After stressful situations, its

often a good idea to physically
work off the adrenaline in your
body so it doesnt stay in your
system, keeping you awake at
night, for example.

Adrenaline can be obtained from

animals or synthesised in the lab.
The chemical name for it is
aminohydroxyphenylpropionic
acid, which is represented with the
chemical formula C9H13NO3.

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Adrenaline

Medulla

Discover the science behind your bodys

amazing chemical coping mechanism
Nestling on a layer of fat
located just above each
of your kidneys are the
bodys adrenal glands.
Around 8cm long, the adrenal glands
produce hormones that affect your
bodys consumption of energy as well
as your stress responses.
Adrenal glands consist of two main
layers of hormone-secreting cells: the
outer cortex and the inner medulla.
While the cortex produces energybalancing hormones, the medulla
produces a chemical called
epinephrine, which we know better

Cortex

At the core of the

adrenal gland, the
adrenal medulla
produces, stores and
releases adrenaline.

At the edge of the adrenal gland, the

cortex produces steroid hormones that
include cortisol (for balancing blood sugar
and carb metabolism) and aldosterone
(for balancing the bodys salts and water).

Kidney

as adrenaline. Identied in 1900,

adrenaline is a fast-acting hormone
that helps the body deal with
unexpected stresses not to mention
high levels of excitement by upping
your heart rate and the ow of blood
to your muscles.
The effect of this is that your blood
vessels and air passages dilate,
meaning that more blood passes to
the muscles and more oxygen gets to
the lungs quicker, temporarily
improving the bodys physical
performance and potentially saving
your life.

Adrenaline is a fast-acting
hormone that helps the
body deal with stresses

The saying fight or flight is

associated with adrenaline because
when were stressed we produce the
hormone in order that we can either
get ready to defend ourselves or
make a run for it.

The organ that

filters waste
from the blood.

Fat
Each adrenal
gland is protected
by a layer of fat.

Your
adrenal glands

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BODY AT WORK

Singing explained

The process
behind singing
How do some people manage to hit all
the right notes?
From belting out ballads like Mariah
Carey to crooning along to Frank
Sinatra, singing is an ability we all
possess. We may not all be
talented enough to reach the top of the
charts, but we can all produce some sort of
tune, which all stems from a clever little
organ in the neck.
Also known as the voice box, the
larynx is your own complex musical
instrument. It contains vocal folds,
better known as vocal cords, which
vibrate to produce your voice, but the
type of sound created depends on a
number of factors.
The amount of air forced out of the
lungs controls the volume, so a greater
exhale of breath will generate a louder
sound, while the pitch is determined
by how fast your vocal folds vibrate. A
slower vibration will produce a lower
note and a faster vibration will produce a
higher note. It works in a similar way to the
strings on a guitar, with the speed of the
vibration inuenced by the physical
characteristics of the strings. For example, the
thicker and longer the guitar strings, the slower
they vibrate when plucked, thus producing a
low-pitched note. Similarly, the thicker or longer
your vocal folds, the lower the sound theyll produce
when vibrating. This is why men, who typically have
thicker and longer vocal folds than women, also have
deeper voices.
While you may not have control over the size of your
vocal folds, you can control their tightness, which also
affects pitch. Muscles in your larynx create tension on
your vocal folds, and can tighten them so they vibrate
faster and produce a higher note, or loosen them to
vibrate slower and produce a lower note. Learning how
to control these muscles, and therefore your pitch, is

Where does your

voice come from?
The mechanisms that enable
you to produce sounds

Sound waves
The vibrating vocal folds modulate
the flow of air from the lungs, which
travels out through the mouth to be
interpreted as sound by the ears.

Sounding words
The vibrations are formed into
words, or lyrics, by movements
of the tongue, cheeks and lips.

Also known as
the voice box, the
larynx is your
own complex
musical
instrument
090

Rush of air
When air is expelled from the
lungs it rushes up the trachea
to the larynx, or voice box,
which contains the vocal folds.

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DID YOU KNOW? Singing causes the brain to release pleasure-inducing endorphins and the stress-relieving hormone oxytocin

Why are some people naturally good

at singing?
No matter how much practice you have or
how good your vocal coach is, theres no
guarantee that youll be able to win
Eurovision. The fact is some people are just
born with a naturally great singing voice. The
shape and size of their vocal folds plays a part
in this, but so do the measurements of their
mouth, throat and nasal cavities. These are
the bodys natural resonators, meaning they
can help enhance the tone and intensity of

Speaking and singing

When you speak or sing, the muscles in your
larynx cause the vocal folds to close.

Sometimes a
great singing
voice is all down
to genetics

the voice. This is what creates the distinctive

nasal tone of some country music stars and
the more breathy voice of Marilyn Monroe, for
example. You may not be able to control the
natural tone of your voice, but you can adjust
the style by making use of particular
resonance chambers in your body. For
example, if you want your voice to have an
airy quality, try directing the vibrations
toward the back of your mouth.

With a bit of
practice every
day, anyone
can become a
good singer

Vocal folds
When a burst of air forces the vocal folds open,
the pressure behind them decreases, causing
them to close again.

Breathing
When you breathe, the vocal folds open up to
let the air in and out unobstructed.

How can I become a better

singer?

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Science Photo Library

Air pressure
As the air pressure builds up again behind the folds,
they reopen. This process repeats several times a
second to vibrate the vocal folds.

Anyone can become a better singer with the right training

and enough practice. The problem for most bad singers is
the inability to imitate the correct notes. Perceiving the
notes isnt the problem, because this is how they recognise
tunes in the rst place, but when it comes to controlling the
tension of the vocal cords to match the same pitch, they
often struggle. This is simply a case of poor wiring in the
brain, but with plenty of practice the brain can be
reprogrammed to give the larynx muscles the correct
instructions to produce the right sounds. For many people,
inefcient breathing can also hinder their ability to carry a
tune. However, by training themselves to breathe by
moving their diaphragm not their chest and shoulders
they can prevent their vocal folds from tightening when
they inhale and air from being forced out too quickly when
they exhale, thus having better control over their voice.

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BODY AT WORK

How we breathe

Human
respiration
Respiration is crucial to an organisms
survival. The process of respiration is the
transportation of oxygen from the air that
surrounds us into the tissue cells of our
body so that energy can be broken down
The primary organs used
for respiration in humans
are the lungs. Humans
have two lungs, with the
left lung being divided into two lobes
and the right into three. Lungs have
between 300500 million alveoli,
which is where gas exchange occurs.
Respiration of oxygen breaks into
four main stages: ventilation,
pulmonary gas exchange, gas
transportation and peripheral gas
exchange. Each stage is crucial in
getting oxygen to the bodys tissue,
and removing carbon dioxide.
Ventilation and gas transportation
need energy to occur, as the
diaphragm and the heart are used to
facilitate these actions, whereas gas
exchanging is passive. As air is drawn
into the lungs at a rate of between 1020 breaths per minute while resting,
through either your mouth or nose by
diaphragm contraction, and travels
through the pharynx, then the
larynx, down the trachea, and into
one of the two main bronchial tubes.
Mucus and cilia keep the lungs clean
by catching dirt particles and
sweeping them up the trachea.
When air reaches the lungs, oxygen
is diffused into the bloodstream
through the alveoli and carbon
dioxide is diffused from the blood
into the lungs to be exhaled. Diffusion
of gases occurs because of differing
pressures in the lungs and blood. This
is also the same when oxygen
diffuses into tissue around the body.
When blood has been oxygenated by
the lungs, it is transferred around the
body to where it is most needed in the
bloodstream. If the body is

092

exercising, the breathing rate

increases and, consequently, so does
the heart rate to ensure that oxygen
reaches tissues that need it. Oxygen is
then used to break down glucose to
provide energy for the body. This
happens in the mitochondria of cells.
Carbon dioxide is one of the waste
products of this, which is why we get
a build up of this gas in our body that
needs to be transported back into the
lungs to be exhaled.
The body can also respire
anaerobically, but this produces far
less energy and instead of producing
co2 as a byproduct, lactic acid is
produced. The body then takes time
to break this down after exertion has
nished as the body has a so-called
oxygen debt.

1. Nasal passage/
oral cavity
These areas are where air
enters into the body so that
oxygen can be transported into
and around the body to where
its needed. Carbon dioxide
also exits through these areas.

5. Alveoli
The alveoli are tiny little sacs which are situated
at the end of tubes inside the lungs and are in
direct contact with blood. Oxygen and carbon
dioxide transfer to and from the blood stream
through the alveoli.

Pulmonary
artery

How our
lungs
work
Lungs are the major

Pulmonary
vein

respiratory organ in humans

Capillary beds

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5 TOP
FACTS
LUNGS

Lung capacity
varies hugely

The right lung

is bigger

We have excess
lung capacity

Alveoli have massive

surface area

We breathe 11,000
litres of air per day

Dependant on sex and body

size, alongside external
factors such as altitude, lung
capacity ranges between
4,000 and 6,000cm3.

Interestingly, the left lung is

slightly smaller than the right in
the human body because the left
lung has to make room for the
heart to fit in.

On average, humans only use

about one-eighth of the
capacity of our lungs for each
breath so we have a large
reserve volume.

If one persons entire

alveoli were laid out they would
have the surface area of about 70cm2
thats roughly the size of half a
tennis court!

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On average, one individual will

breathe in 11,000 litres of air in
any given day. If they exercise
heavily during that day, this will
increase further.

DID YOU KNOW? Trained free-divers can hold their breath underwater for up to nine minutes

Air is pulled into the

body through the nasal
passages and then
passes into the trachea.

The intake of oxygen into the body is complex

Breathing is not something that we have to
think about, and indeed is controlled by muscle
contractions in our body. Breathing is
controlled by the diaphragm, which contracts
and expands on a regular, constant basis.
When it contracts, the diaphragm pulls air into
the lungs by a vacuum-like effect. The lungs
expand to ll the enlarged chest cavity
and air is pulled right through
the maze of tubes that
make up the
lungs to

the alveoli at the ends, which are the nal

branching. The chest will be seen to rise
because of this lung expansion. Alveoli are
surrounded by blood vessels, and oxygen and
carbon dioxide are then interchanged at this
point between the lungs and the blood. Carbon
dioxide removed from the blood stream
and air that was breathed in but not
used is then expelled from the lungs
by diaphragm expansion. Lungs
deate back to a reduced size
when breathing out.

Lungs
Deoxygenated blood
arrives back at the
lungs, where another
gas exchange occurs at
the alveoli. Carbon
dioxide is removed and
oxygen is placed back
into the blood.

4. Bronchial tubes
These tubes lead to either the
left or the right lung. Air passes
through these tubes into the
lungs, where they pass
through progressively smaller
and smaller tubes until they
reach the alveoli.

6. Ribs
These provide protection
for the lungs and other
internal organs situated
in the chest cavity.

DK Images

3. Trachea

How do we breathe?

Chest cavity
This is the space that
is protected by the
ribs, where the lungs
and heart are
situated. The space
changes as the
diaphragm moves.

Diaphragm
This is a sheet of muscle situated
at the bottom of the rib cage
which contracts and expands to
draw air into the lungs.

Heart
The heart pumps oxygenated
blood away from the lungs,
around the body to tissue,
where oxygen is needed to
break down glucose
into a usable form
of energy.

Rib cage
This is the bone
structure which
protects the organs.
The rib cage can
move slightly to
allow for lung
expansion.

Tissue
Oxygen arrives
where energy is
needed, and a gas
exchange of
oxygen and carbon
dioxide occurs so
that aerobic
respiration can
occur within cells.

DK Images

This is part of both

the respiratory and
digestive system. A flap
of connective tissue
called the epiglottis
closes over the trachea
to stop choking when
an individual takes food
into their body.

DK Images

2. Pharynx

Why do we need oxygen?

We need oxygen to live as it is crucial for the release
of energy within the body
Although we can release energy through
anaerobic respiration temporarily, this method
is inefcient and creates an oxygen debt that
the body must repay after excess exercise or
exertion has ceased. If oxygen supply is cut off for

more than a few minutes, an individual will die.

Oxygen is pumped around the body to be used
in cells that need to break down glucose so that
energy is provided for the tissue. The equation
that illustrates this is:

C6H12O6+6O2 = 6CO2+6H2O + energy

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BODY AT WORK
Science Photo Library

Sweating / Dehydration

Pore

Skin

Sweat is
released directly
into the dermis
via the secretary
duct, which then
filters through
the skins pores
to the surface.

Once the sweat is on the skins

surface, its absorbed moisture
evaporates, transferring the
heat into the atmosphere.

Beads of sweat from the pores in

human skin, taken with a
scanning electron microscope

Why do we sweat?
Sweat is produced by dedicated sweat
glands, and is a mechanism used
primarily by the body to reduce its
internal temperature. There are two
types of sweat gland in the human body, the
eccrine gland and the apocrine gland. The former
regulates body temperature, and is the primary
source of excreted sweat, with the latter only
secreting under emotional stresses, rather than
those involved with body dehydration.
Eccrine sweat glands are controlled by the
sympathetic nervous system and, when the

internal temperature of the body rises, they secrete

a salty, water-based substance to the skins surface.
This liquid then cools the skin and the body
through evaporation, storing and then transferring
excess heat into the atmosphere.
Both the eccrine and apocrine sweat glands only
appear in mammals and, if active over the majority
of the animals body, act as the primary
thermoregulatory device. Certain mammals such
as dogs, cats and sheep only have eccrine glands in
specic areas such as paws and lips warranting
the need to pant to control their temperature.

Dehydration

Too much H2O?

Hydration is all about nding the perfect
balance. Too much hydration can be
harmful as well as too little; this is
known as water intoxication. If too
much liquid is in your body, nutrients
such as electrolytes and sodium are
diluted and the body suffers. Your cells
bloat and expand and can even burst,
and it can be fatal if untreated. The best
treatment is to take on IV uids
containing electrolytes.

094

Secretary part

Nerve bres

This is where the

Deliver messages to
majority of the glands
glands to produce
secretary cells can
sweat when the body
be located.
temperature rises.

Secreted sweat
travels up to the
skin via this duct.

How does a lack of water vary from mild to fatal?

Thirst is triggered by a
concentration of particles
in the blood, indicating a
need to hydrate.

1%

Mild

2%

Moderate

3%

Dizziness

Dry skin

Other symptoms
at this level
include fatigue, a
dry mouth and
constipation.

Headaches

4%
5%

Dehydration levels

and sugar levels going haywire.

Enzymatic activity is slowed, toxins
accumulate more easily and your
breathing can even become more
difcult as the lungs are having to
work harder.
Babies and the elderly are most
susceptible as their bodies are not as
resilient as others. It has been
recommended to have eight glasses
of water or two litres a day. More
recent research is undecided as to
how much is exactly needed.

Secretary
duct

Dangers of dehydration

What happens if we dont

drink enough?
Just by breathing,
sweating and urinating,
the average person loses
ten cups of water a day.
With H2O making up as much as 75
per cent of our body, dehydration is a
frequent risk. Water is integral in
maintaining our systems and it
performs limitless functions.
Essentially, dehydration strikes
when your body takes in less uid
than it loses. The mineral balance in
your body becomes upset with salt

DK Images

As your doctor may tell you, its glandular

Fever

Severe

Racing pulse

Lack of sweat

6%
Dehydration is
now so severe
that IV fluid
replacement
is necessary.

7%
8%
9%
10%
11%
12%

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Fatal

Delirium

Other symptoms
include sunken eyes,
low blood pressure
and dark urine.

Loss of
consciousness

Here symptoms
become much more
extreme and
cognitive abilities
may also suffer.

Risk of heat exhaustion or

heat stroke is prevalent
and can even be fatal.

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Why does skin scar?

Scars are made up of the same proteins as normal skin, so why
do they look so different?
Scars are a natural part of the healing
process, with most of us having some
form of them on our body. The reason
why scars look different compared to
normal skin stems from their proteins composition.
Normal skin benets from a weaved protein
structure, whereas the proteins in scars are aligned
in one direction. This results in a different
appearance compared to normal, healthy skin. Scars
are smoother due to a lack of sweat glands and hair
follicles, so they can often become itchy. There are
also a number of different types of scar that can

form. The most common is a at scar these tend to

initially be dark and raised, but will fade and atten
over time as the scar matures. A hypertrophic scar
can be identied by its red appearance and elevated
nature. This scar type typically forms when the
dermis is damaged, and this can become itchy and
painful over time.
Keloid scars are by far the most extreme scar type
when compared to the others. Unlike most scars,
they extend beyond the connes of the original
injury and are formed due to excessive scar tissue
being produced. Keloid scars are raised above the

surrounding skin, and are hard, shiny and hairless.

The reason behind why keloids form is poorly
understood, but it is known that people with darker
skin tones are more likely to form keloids.
Pitted scars are generally formed from acne or
chicken pox, and tend to be numerous in areas
where these conditions were prevalent. Scar
contractures, meanwhile, usually form after a burn,
and are caused by the skin shrinking and tightening.
The severity of these kinds of scars can depend on
their bodily location; if they form around a joint they
can lead to movement being restricted.

Epithelial cells

Newly formed scar

Clotting occurs due to a combination of

proteins in the blood, which help a scab to
form, protecting the wound from infection.

By rapidly multiplying, the

epithelial cells fill in over the
newly formed granulation tissue.

Once the newly formed epithelium

thickens, the area contracts and forms
a scar on the skins surface.

illustration by Nicholas Forder

Clotting

Inammatory chemicals

White blood cells

Granulation tissue

Scar tissue

The body recognises that it has sustained

an injury, and white blood cells release
inflammatory chemicals to help protect
the area.

To help fight off potential

infection, white blood cells
seep into the area and flock
to the wound.

The new granulation tissue

replaces the clotted blood, and
helps restore the blood supply to
the damaged area.

Once fully formed, this tissue is known as scar

tissue. Due to excessive collagen production this
tissue often lacks in flexibility, which can lead to pain
and dysfunction.

Scars cannot be stopped from forming, but there are

various treatments available to help reduce their
appearance. Silicone gels or sheets have been shown to
effectively minimise scar formation and are often used
when people have been burnt. These must be applied or
worn throughout the scars maturation phase to maximise
their efcacy. Corticosteroid injections can be used to
reduce any inammation (swelling) around the scar and to
atten it as well. A riskier treatment for scars is surgery.

This can be used to change the shape of the scar, however

there is a risk of worsened scarring if unsuccessful.
There are also certain steps that can be taken to help
reduce the risk of an unsightly scar forming from an
injury. By cleaning dirt and dead tissue away from the
wound, you are increasing the chance that the scar will
form neatly. It is also vital that you dont pick or scratch the
scar, as this will slow down its formation, resulting in a
more obvious appearance.

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A neat, even scar is the best

you can hope for even with
todays technology

Dreamstime

Can scars be treated?

095

THEWorldMags.net
BODY AT WORK

Human immune system

How your immune

system works

Physical
defences

Your body is locked in a constant

war against a viscous army
Its true: while youre sitting around
watching TV, trillions of foreign invaders
are launching a full scale assault on the
trillions of cells that constitute you.
Collectively known as pathogens, these attackers
include bacteria, single-celled creatures that live to
eat and reproduce; protists, larger single-cell
organisms; viruses, packets of genetic information

096

that take over host cells and replicate inside them;

and fungi, a type of plant life.
Bacteria and viruses are by far the very worst
offenders. Dangerous bacteria release toxins in the
body that cause diseases such as E. coli, anthrax, and
the black plague. The cell damage from viruses causes
measles, the u and the common cold, among
numerous other diseases.

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Human anatomy subscribes to the notion

that good fences make good neighbours.
Your skin, made up of tightly packed cells
and an antibacterial oil coating, keeps
most pathogens from ever setting foot in
body. Your bodys openings are wellfortied too. Pathogens that you inhale
face a wall of mucus-covered membranes
in your respiratory tract, optimised to
trap germs. Pathogens that you digest end
up soaking in a bath of potent stomach
acid. Tears ush pathogens out of your
eyes, dousing bacteria with a harsh
enzyme for good measure.

Just about everything in our environment is

teeming with these microscopic intruders... including
you. The bacteria in your stomach alone outnumber
all the cells in your body, ten-to-one. Yet, your scrappy
microscopic soldiers usually win the day against
pathogens, through a combination of sturdy barriers,
brute force, and superior battleeld intelligence,
collectively dubbed the immune system.

5 TOP
FACTS
IMMUNE SYSTEM

The cure can

sometimes hurt

Immunity soldiers
are everywhere

You can borrow

immunity

It deals with internal

troubles, too

It has trouble with

change

Sneezing, coughing, a sore throat

and fever are all common means
of expelling pathogens. So nom
matter how annoying they are,
each one is necessary.

A single drop of blood contains

around 375,000 white blood
cells and blood constitutes for
seven per cent of your total
body weight.

Antibodies in breast milk give

babies temporary immunity
from diseases their mother is
immune to, preventing
infancy infection.

In addition to fighting
pathogens, T-cells fight the
bodys own cancerous cells and
some cancer therapies boost
the number of T-cells.

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Unfortunately you cannot

develop immunity to the
flu and common cold
because the viruses are
always mutating.

DID YOU KNOW? Dr Karl Landsteiner first identified the major human blood groups A, B, AB and O in 1901

The adaptive immune system

Fighting the good ght, and white blood cells are
right on the front line
When a pathogen is tough, wily,
or numerous enough to survive
non-specic defences, its up to
the adaptive immune system to
clean up the mess. The key forces
in the adaptive immune system
are white blood cells called
lymphocytes. Unlike their
macrophage cousins,
lymphocytes are engineered to
attack only one specic type of
pathogen. There are two types of
lymphocytes: B-cells and T-cells.
These cells join the action
when macrophages pass along
information about the invading
pathogen, through chemical
messages called interleukins.
After engulng a pathogen, a
macrophage communicates
details about the pathogens
antigens telltale molecules that
characterise a particular
pathogen. Based on this
information, the immune system
identies specic B-cells and
T-cells equipped to recognise and
battle the pathogen. Once they
are successfully identied, these
cells rapidly reproduce,
assembling an army of cells that
are ready and equipped to take
down the attacker.

Non-specic
defences

As good as your physical defence system is, pathogens

do creep past it regularly. Your body initially responds
with counterattacks known as non-specic defences,
so named because they dont target a specic type
of pathogen.
After a breech bacteria rushing in through a cut, for
example cells release chemicals called inammatory
mediators. This triggers the chief non-specic defence,
known as inammation. Within minutes of a breach,
your blood vessels dilate, allowing blood and other uid
to ow into the tissue around the cut.
The rush of uid in inammation carries various types
of white blood cells, which get to work destroying
intruders. The biggest and toughest of the bunch are
macrophages, white blood cells with an insatiable
appetite for foreign particles. When a macrophage detects
a bacteriums telltale chemical trail, it grabs the intruder,
engulfs it, takes it apart with chemical enzymes, and
spits out the indigestible parts. A single macrophage can
swallow up about 100 bacteria before its own digestive
chemicals destroy it from within.

The B-cells ood your body

with antibodies, molecules that
either disarm a specic pathogen
or bind to it, marking it as a target
for other white blood cells. When
T-cells nd their target, they lock
on and release toxic chemicals
that will destroy it. T-cells are
especially adept at destroying
your bodys cells that are infected
with a virus.
This entire process takes
several days to get going and may
take even longer to conclude. All
the while, the raging battle can
make you feel terrible.
Fortunately, the immune
system is engineered to
learn from the past. While
your body is producing new
B-cells and T-cells to ght the
pathogens, it also produces
memory cells copies of the
B-cells and T-cells, which stay in
the system after the pathogen is
defeated. The next time that
pathogen shows up in your body,
these memory cells help launch a
counter-attack much more
quickly. Your body can wipe out
the invaders before any infection
takes hold. In other words, you
develop immunity.
Vaccines accomplish the same
thing by giving you just enough
pathogen exposure for you to
develop memory cells, but not
enough to make you sick.

2. Bacterium antigen
These distinctive molecules allow your
immune system to recognise that the
bacterium is something other than a body cell.

4. Engulfed
bacterium
During the initial
inflammation reaction,
a macrophage engulfs
the bacterium.

3. Macrophage

1. Bacterium

These white blood

cells engulf and digest
any pathogens they
come across.

Any bacteria that enter

your body have
characteristic antigens
on their surface.

7. Nonmatching B-cells
Other B-cells, engineered to
attack other pathogens,
dont recognise
the antigen.

5. Presented
bacterium antigen
After engulfing the bacterium, the
macrophage presents the
bacteriums distinctive antigens,
communicating the presence of
the specific pathogen to B-cells.

6. Matching B-cell

9. Memory cell

The specific B-cell that

recognises the antigen, and
can help defeat the pathogen,
receives the message.

The matching B-cell also

replicates to produce
memory cells, which will
rapidly produce copies of
itself if the specific
bacteria ever returns.

How B-cells
attack
B-cells target and
destroy specific bacteria
and other invaders
11. Phagocyte
White blood cells
called phagocytes
recognise the antibody
marker, engulf the
bacteria, and
digest them.

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10. Antibodies
The plasma cells release
antibodies, which
disable the bacteria by
latching on to their
antigens. The antibodies
also mark the bacteria
for destruction.

8. Plasma cell
The matching B-cell
replicates itself,
creating many
plasma cells to fight
all the bacteria of this
type in the body.

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BODY AT WORK

Human immune system

1. Tonsils

Your tonsils can help

ght bacteria

Ed Uthman, MD

Lymphoid tissue loaded with

lymphocytes, which attack
bacteria that get into the body
through your nose or mouth.

Klem 2007

2. Left subclavian vein

One of two large veins that serve
as the re-entry point for lymph
returning to the bloodstream.

6. Lymph
node cluster

3. Right lymphatic duct

Passageway leading from lymph vessels
to the right subclavian vein.

Who watches the

watchmen?
The immune system is a powerful set of
defences, so when it malfunctions, it
can do as much harm as a disease.
Allergies are the result of an overzealous
immune system. In response to
something relatively benign, like
pollen, the immune system triggers
excessive measures to expel the
pathogen. On the extreme end, allergies
may cause anaphylactic shock, a
potentially deadly drop in blood
pressure, sometimes accompanied by
breathing difculty and loss of
consciousness. In autoimmune
disorders such as rheumatoid arthritis,
the immune system fails to recognise
the bodys own cells and attacks them.

In an allergic reaction, the body may resort to

sneezing to expel a fairly harmless pathogen

098

4. Right subclavian vein

The second of the two subclavian
veins, this one taking the opposite
path to its twin.

7. Left
lymphatic duct

5. Spleen

Passageway leading from

lymph vessels to the left
subclavian vein.

An organ that houses white

blood cells that attack
pathogens in the
bodys bloodstream.

8. Thymus gland
Organ that provides area for
lymphocytes produced by bone
marrow to mature into
specialised T-cells.

9. Thoracic duct
The largest lymph vessel
in the body.

11. Peyers patch

Nodules of lymphoid tissue supporting
white blood cells that battle pathogens
in the intestinal tract.

10. Lymph vessels

12. Bone marrow

Lymph collects in tiny capillaries,

which expand into larger vessels.
Skeletal muscles move lymph
through these vessels, back into
the bloodstream.

The site of all white blood

cell production.

The
lymphatic
system

Lymph
nodes
explained

The lymphatic system is a network of

organs and vessels that collects lymph
uid that has drained from the
bloodstream into bodily tissues and
returns it to your bloodstream. It also
plays a key role in your immune
system, ltering pathogens from
lymph and providing a home-base for
disease-ghting lymphocytes.

Your immune system depends

on these .04-1-inch swellings to
ght all manner of pathogens.
As lymph makes its way
through a network of bres in
the node, white blood cells
lter it, destroying any
pathogens they nd.

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Lymph nodes
lter out
pathogens moving
through your
lymph vessels

DK Images

Disorders of
the immune
system

Located along lymph vessels

throughout the body, lymph nodes
filter lymph as it makes its way back
into the bloodstream.

MOST DEADLY

National Photo Company

HEAD
HEAD

1. Inuenza

MOST CONTAGIOUS

The u kills hundreds of

thousands of people in a
good year. And every
once in a while, a virulent
form can take out tens of
millions of people.

2. Measles

MOST COMMON

One person infected with

measles will spread the virus
to just about every
unvaccinated person they
encounter. Luckily, the
vaccine is very effective.

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GERMS AND
VIRUSES

3. Tuberculosis
Excavated Ancient Egyptian
mummies show signs of
tuberculosis, and the disease
is still thriving today. Around
2 billion people around the
world are infected.

DID YOU KNOW? In 2008, approximately 33 million people worldwide were living with HIV or AIDS

Know your
enemy:

1. Flagella

3. Capsule

Flagella swish
for movement

Protects the
inner contents

2. Pili
The pili anchor to
cell surfaces

Bacteria
Bacteria are the smallest and, by far, the most populous form of life
on Earth. Right now, there are trillions of the single-celled creatures
crawling on and in you. In fact, they constitute about four pounds of
your total body weight. To the left is a look at bacteria anatomy

What is HIV

and how does it affect the

immune system?
4. Nucleoid
The nucleoid contains
genetic material

6. Cell wall
Provides structural
integrity

The human immunodeciency virus (HIV) is a retrovirus (a virus

carrying ribonucleic acid, or RNA as its known), transmitted
through bodily uids. Like other deadly viruses, HIV invades
cells and multiplies rapidly inside. Specically, HIV infects cells
with CD4 molecules on their surface, which includes infectionghting helper T-cells. HIV destroys the host cell, and the virus
copies go on to infect other cells. As the virus destroys helper
T-cells, it steadily weakens the immune system. If enough
T-cells are lost, the body becomes highly susceptible to a range
of infections, a condition known as acquired immune deciency
syndrome (AIDS).

8. Cytoplasm
Home of all material
outside the nucleoid

5. Ribosomes
These help with protein
manufacturing

7. Cell membrane
The cells interior barrier

Inside these
microorganisms
1

Major points of the lymph node

3
2

1. Outgoing lymph
vessel

10

7. Sinus

The vessel that carries

filtered lymph out of the
lymph node

5
11

2. Valve
A structure that prevents
lymph from flowing back
into the lymph node

3. Vein

4. Artery

8. Incoming lymph
vessel
A vessel that carries lymph
into the lymph node
The T-cells, B-cells and
natural killer cells that
fight infection

10. Germinal centre

Divides the lymph node

into individual cells

This is the site of

lymphocyte multiplication
and maturation

6. Capsule

11. Macrophage

5. Reticular bres

A channel that slows the

flow of lymph, giving
macrophages the
opportunity to destroy any
detected pathogens

9. Lymphocyte

Passageway for blood

leaving the lymph node
Supply of incoming blood
for the lymph node

Bacteria
anatomy

The protective, shielding

fibres that surround the
lymph node

Large white blood cells that

engulf and destroy any
detected pathogens

Scanning electron micrograph of HIV-1 budding (in green) from cultured

lymphocyte. This image has been coloured to highlight the most
important features. Multiple round bumps on the cell surface represent
sites of assembly and budding of virions.

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BODY AT WORK

Mending bones

Bone fracture
healing process
Learn how your body mends broken bones
If a bone has too much pressure put
on it, there is a chance it will break.
Your body has ways of repairing
these breaks, but it takes time and
care. There are different kinds of break, ranging
from a hairline fracture to a fully shattered
bone, but they all mend in a similar way.
As a bone breaks, the blood vessels are also
severed. Blood leaks out and forms a clot called
a fracture haematoma. This stops blood ow to
the area and also helps keep both pieces of bone
aligned, ready for healing.
The body then makes brous cells and
cartilage, which reinforce the bond and
strengthen it. This creates a callus, which is
essentially a weakened bone. Over time, the
callus builds up and the two parts of the bone

gradually fuse together, like a bridge being

constructed from either side of a river until both
ends meet in the middle.
Once both sections of bone are connected
again, specialised cells called osteoblasts enter to
produce bone cells. These new cells replace the
callus, returning the bone to its original shape.
Much like repairing a broken toy with glue,
the bone needs to be kept straight and steady
for the fusion to happen correctly. This is why
doctors will put a cast on the broken bone. The
cast provides essential support, protection and
stability, ensuring the broken bone doesnt
move. A cast will generally stay on for a few
weeks until the bond has become strong
enough, but it could take months for a properly
set bone to fully recover.

All-star cast
Most breaks on an arm or a leg will have a plaster
cast put on them to prevent the bone from
setting at a wonky angle or not setting at all.
It will generally be made from plaster of Paris.
This is a mixture of water and gypsum that sets
really hard once it has dried. The broken bone is
bandaged and the wet mixture is applied to the
gauze. Once it has dried then it should provide
safety and stability for the bone.
Fibreglass is an increasingly common cast
material. As with the plaster cast, the broken
bone is bandaged up. Next, another bandage,
made of breglass and layered with resin, is
soaked in water. This makes it exible enough to
be wrapped around the bone before it hardens as
it dries. This is much lighter than a plaster cast
and the outer layer is waterproof.

The stages of bone repair

Marrow
Internal callus
(brous tissue
and cartilage)

New
blood
vessels

Healed
fracture

Hard
bone
callus

Ruptured
blood
vessels

Blood ow
improves

External
callus
Blood clot

Tissue growth

Remodelling

When a bone breaks, the blood vessels

that run through the bone are severed.
The blood forms a clot to align the bones.
This creates a solid yet weak structure to
prepare for mending. The clot also cuts off
blood ow to the edges of the broken bone,
so these cells die.

A few days later, the blood clot called the fracture

haematoma is gradually replaced by tougher
tissue, which becomes a soft callus. Fibrous tissue
and cartilage are produced that begin to bridge the
gap between the fractured ends. New blood vessels
begin to form and the callus usually lasts around
three weeks.

Bone-forming cells called osteoblasts work in

teams to build a new bone, creating a more solid
structure called a hard bone callus. It takes several
months to ll the cavity with harder bone,
strengthened by nutrients like calcium and
phosphorus. However, it may take longer for the
bone to be completely healed.

100

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Thinkstock

Blood
clot
forms

5 TOP
FACTS
PROTEIN

Pokmon

Protein from food

Speedy Pokmon character

Pikachu had a protein named
after it in 2008. The protein,
pikachurin, is used in kinetic
vision, which, aptly, is the
detection of fast objects.

We get protein from meat,

fish, eggs, nuts and dairy
products. We digest the
proteins into amino acids,
which we later use to replace
these proteins in our bodies.

Protein we need

Biuret test

Your body makes thousands

of proteins every day. For each
1kg you weigh, you typically
require 1g of protein. So daily a
70kg man must manufacture
70g of protein for his needs.

Genome studies

The Biuret test is a chemical

form of analysis that is used to
measure the amount of
protein that is present in food.
It works out protein levels by
analysing the peptide bonds.

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From studies into the human

genomes sequenced so far, it
has been discovered that the
body contains over 2 million
proteins, coded by just
20,000-25,000 genes.

DID YOU KNOW? Around half of your bodys non-water mass is made up of proteins

Protein production

1. Cell

Protein is generated in the nucleus of a cell using genetic

coding information held within our DNA. To produce
protein, DNA unravels to allow messenger RNA (or mRNA) to
copy it and form a template. This template is translated by
ribosomes into amino acids, which then line up to form a
protein. Parts of DNA code will
serve as punctuation, telling
the ribosome when to start
and stop, and some parts
will instruct the cell how
frequently it must produce
the specic protein.

The body is made up of millions

of cells, none of which could
survive without protein, for
repair and replacement.

6. mRNA

5. DNA

This type of genetic acid

forms a template based on
DNA sequences, which is
then used to produce amino
acids by the ribosome.

7. Ribosome
This is the protein-making
machine in the cell. It uses
mRNA templates to synthesise
the specific protein needed.

DNA (deoxyribonucleic
acid) holds the information
necessary for amino acid
and ultimately protein
production in the letter
sequence in its structure.

8. Amino acid

9. Protein
Proteins are made up of long chains of
amino acids. Each protein has a specific
function which suits its role and is
crucial to our bodies being able to
operate effectively.

3. Chromosome
2. Nucleus
This is the control centre of
the cell where all important
genetic data is stored.

Most human cells have a set of

46 chromosomes and these
contain our genetic information
which, among other things,
instructs the cell which protein
to make and also how.

How do we make protein?

Proteins are the building blocks of the human body,
but how do we go about manufacturing them?
Proteins are large complex molecules made up of a
chain of amino acids. Every cell in our body needs
protein to stay alive as it is necessary for tissue
repair and replacing dead cells.
They have many other functions as well as aiding cell repair
and production including forming antibodies to help ght off
disease, forming enzymes which speed up or trigger chemical
reactions and co-ordinating processes within the body (via
hormone regulation, for instance). Proteins also provide
support for cells and form structural elements of the body, such
as nails and teeth, as well as facilitating the transportation of
some small molecules around various systems.
We build proteins using information encoded in our genetic
code. DNA code utilises groups of three letters (a mix of A, G, C

and T) and these short sequences, which are known as triplets

or codons, then code mRNA templates; these templates are
translated by cell ribosomes into amino acids.
Each protein is made up of hundreds of thousands of amino
acids, which are in long chains. There are 20 different types of
amino acid that can be combined to build a protein and it is the
sequence of amino acids that determines each proteins unique
three-dimensional structure and its function.
However, not all amino acids can be made by the body. The
ones that need to be consumed via our diet are called essential
amino acids. If possible, the body will also conserve energy by
using amino acids from food rather than producing them itself.
Protein deciency can cause diseases such as kwashiorkor, a
form of malnutrition common in poverty-stricken areas.

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4. Nucleosomes
These are balls formed of
DNA strands and histones
(spool-like proteins) which
sit inside chromosomes.

Why are
amino acids
important?
Amino acids are vital to
our bodies being able to
operate as they are the
building blocks of
proteins. Each type of
amino acid performs a
different job, which aids
protein activity in the
body and determines the
proteins primary
function(s). Without these,
proteins would not be
able to help the body with
movement, defence
against disease,
processing food or
co-ordinating general
growth and development.
There are nine
essential amino acids for
humans that must be
absorbed from external
protein sources (eg meat/
sh) as they cannot be
synthesised by the body.
Without the required
amount of amino acids,
the body can really suffer.

101

SPL

These small molecules

combine in specific string
sequences to generate the
different types of protein.

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BODY AT WORK

Cell division explained

The cell cycle

Inside one of the bodys most vital processes
The continuous cycle of cell
division and growth is essential
to all life on Earth. Without it, no
organism on the planet would be
able to reproduce or develop. The cell cycle
consists of three main stages: interphase,
mitosis and cytokinesis.
During interphase, the cell expands and
makes the new proteins and organelles it will
need for division. It then makes copies of its
chromosomes, doubling the amount of DNA in
the cell and ensuring the conditions are right to
begin the next phase.
In mitosis, the membrane surrounding the
nucleus breaks down, exposing the
chromosomes, which are pulled to opposite
sides of the cell by tiny spindle bres. A new
nuclear envelope then forms around the
chromosomes at each end of the cell. During
cytokinesis the cytoplasm splits in half to
create two daughter cells, each with their own
nucleus and organelles.
The cycle is managed by regulating enzymes
known as CDKs . These act as a checkpoint
between the phases of division, giving the
signal for the next stage in the cycle to begin.
The cell cycle of prokaryotic cells (those
without a nucleus) is slightly different. Bacteria
and other prokaryotes divide via a process
called binary ssion, in which the cell
duplicates its genetic material before doubling
in size and splitting in two. Meiosis is another
type of cell division and is concerned with
sexual reproduction as opposed to the asexual
organic growth of tissue in mitosis.

Cancer and the cycle

If the cell cycle goes wrong, cancerous
tumours are a possible consequence. It all
depends on the levels of proteins in the cycle. A
protein called p53 halts the process if DNA is
damaged. This provides time for the protein to
repair the DNA as the cells are then killed off
and the cycle begins anew. On the rare
occasions this process fails, cells can
reproduce at a rapid rate and tumours can
form. Chemo- and radiotherapy work by
destroying these mutated cells. A p53 mutation
is the most frequent one leading to cancer. An
extreme case is Li Fraumeni syndrome, where
a genetic defect in p53 leads to a high
frequency of cancer in those affected.

102

Cell duplication
Explore the key stages of mitosis now

Prophase

Prometaphase

Metaphase

Anaphase

Chromosomes
condense, becoming
thicker and shorter.
Sister chromatids form
when the chromosomes
replicate themselves.

The nuclear envelope

breaks down and spindle
bres extend from
either side of the cell to
attach to the middle of
each chromatid.

In this phase, all the

spindle bres are
attached and the
chromosomes are
arranged in a line along
the equator of the cell.

Now, the spindle bres

pull the chromosomes
apart, with the
chromatids moving to
opposite ends or poles
of the cell.

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STRANGE
BUT TRUE

APPETITE FOR SELFDESTRUCTION

What is apoptosis?
A Another type of cell division
B Programmed cell death
C A new type of soft drink

Answer:
Essentially a cell committing suicide, apoptosis is a
controlled biological system that kills off unneeded
or excess cells. One example is the removal of
webbing in between your ngers and toes before
you are born.

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DID YOU KNOW? A common theory is that every living cell is descended from a single ancestral cell from 3-4bn years ago

Every step of the cell

division cycle is vital for life
as we know it

An experts view
Paul Nurse, Nobel Prize winner and director of the Francis Crick Institute, chats
about cell cycle

What is mitosis?
Mitosis describes what happens near the end of the
cycle. The replicated chromosomes are separated
from each other into opposite ends of the cell just
before the cell divides.
What are the different parts of the cycle?
The other major part occurs before mitosis and is the
process in which the DNA that makes up the
chromosomes replicates itself. This is called the
S-phase or DNA synthetic phase [which is part of
interphase]. The S-phase replicates and mitosis
separates and divides.
What is the difference between mitosis and
meiosis and does cell division occur in both?
Meiosis is usually considered to be the mitotic full
cycle and also leads towards cell reproduction.
However, in meiosis there are two M-phases or
divisions so the number of DNA and chromosomes
are halved. Meiosis uses gametes for fertilisation in
diploid cells in animal and plants.
Does it occur in eukaryotic or prokaryotic cells?
Only in eukaryotic cells. In prokaryotic cells there is a
cell cycle but it is not mitosis. This [process] is
simply the copying of DNA and then a much less
obvious separation of the copied DNA into the two
divided cells.
Why did you use yeast in your experiments?
Yeast is a very simple eukaryote, which reproduces
in much the same way as more complex cells in us. It
only has 5,000 genes compared to our 25,000. It
simplies cell division so is extremely convenient to
study. Its got fantastic genetics and genomics,
which allow you to investigate complicated
processes like the cell cycle.

Telophase

Cytokinesis

The two new sets of

chromosomes form
groups at each pole and
a new envelope forms
around each as the
spindle disappears.

The cytoplasm divides

and two or more
daughter cells are
produced. Mitosis and
the cell cycle have now
reached their end.

Why do skin cells divide so quickly and nerve

cells so slowly?
Cells change at varying rates and some nerve cells
barely divide at all. This is one reason why it is
difcult to regenerate the nervous system when it
becomes damaged. Because the body has to deal
with cuts and abrasions, it is much easier to get skin
cells to divide.
What is tissue culture and why is it important?
It is simply a way of growing cells from animals and
plants in test tubes. They will divide under these
circumstances so you can study the cell cycle away
from the complexities of an animal or plant.
What are the differences between plant and
animal cell cycles?
Fundamentally, not very much. They both undergo
the same processes but are subject to different
overall controls.
What is proteolysis and how does that
mechanism help the cell cycle?
It is a biochemical mechanism that breaks down
protein. It takes away certain proteins as part of a
regulatory system for a variety of biological process
such as the cell cycle. It is used at the end of the
cycle to destroy excess protein and prepare for the
next cycle.
You discovered CDK (Cyclin-dependent kinase).
How do they contribute to the cell cycle?
CDK is a type of enzyme and my research group was
involved in discovering that they were the major
regulators in the cycle. CDK brings about the S-phase
and mitosis and controls them.
How can the cycle help understand potential
cures for cancer?
To understand cancer, you have to be able to
understand the cell cycle. Crudely blocking the cell
cycle is a problem as a therapy as our body is full of
other cells that have to divide.

Dreamstime; BBC; Thinkstock; Dr. Cecil Fox; Corbis

What is the cell cycle?

The cell is the basic unit of life for all living things.
One of its many properties is the ability to reproduce.
The cell cycle is a series of processes that occur
between the birth of the cell and its division into two.

Paul Nurse is also the

former director of Cancer
Research UK and president
of the Royal Society

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103

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BODY AT WORK

Human pregnancy explained

Human pregnancy
Nine months of change and growth

Weight gain

BI
RT
H
AT
BA
BY
HE

ST
(FO ORA
R B GE
RE OF
AS FAT
TFE
ED
ING
)

4.0
kg

LA
RG
ER

BR
EA
ST
S

E
UT
OF

At first, it is a collection of embryonic

cells no bigger than a pinhead

0.8k
g SURRO AM
UND NIOTIC
ING T
0.7
HE FFLUID
ETUS
kg
T
E
LUM
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OD
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tiredness, lower-back pain, heartburn, increased appetite and muscle cramps, as well as
the enlargement of her breasts and stretch marks. Her blood sugar levels, heart rate and
breathing also increase to cope with the growing demands of the fetus.
As the date of labour approaches, the mother feels sudden contractions known as
Braxton-Hicks, and the neck of her uterus begins to soften and thin out. Meanwhile, the
lungs of the fetus ll with surfactant. This substance enables the lungs to soften, making
them able to inate when it takes its rst breath of air. Finally, chemical signals from the
fetus trigger the uterus to go into labour.

(These figures vary according to several factors

including the age, race, diet and the
pre-pregnancy weight and size of the person)

3.
3k
gT

Pregnancy is a unique period in a womans life that brings about physical and
emotional changes. When it occurs, there is an intricate change in the
balance of the oestrogen and progesterone hormones, which causes the
cessation of menstruation and allows the conditions in the uterus (womb) to
become suitable for the growth of the fetus. The lining of the uterus, rather than being
discharged, thickens and enables the development of the baby.
At rst, it is a collection of embryonic cells no bigger than a pinhead. By week four the
embryo forms the brain, spinal cord and heart inside the newly uid-lled amniotic sac.
Protected by this cushion of uid, it becomes recognisably human and enters the fetal
stage by week eight.
Many demands are put on the mothers body and she is likely to experience sickness,

The average woman gains 12.5kg

during pregnancy. This consists of

FIRST TRIMESTER (012 weeks)

SECOND TRIMESTER (1327 weeks)

This begins after the last menstrual period, when an egg is

released and fertilised. It takes about nine weeks for the
resulting embryo to develop into a fetus. During this period,
the mother will be prone to sickness and mood swings due to
hormonal changes.

The fetus grows rapidly and its organs

mature. By week 20 its movements can
be felt. At week 24 it can suck its thumb
and hiccup, and can live independently
of the mother with medical support.

Head
Face begins to
look human and
the brain is
developing rapidly.

Week 9

Heart

Week 16

All the internal

organs are formed
and the heart is able
to pump blood
around its body.

HE
PL
AC
EN
TA

Hair and teeth

At 16 weeks, fine hair
(lanugo) grows over the fetal
body. By 20 weeks, teeth
start forming in the jaw and
hair grows.

Movement
By week 16 the eyes
can move and the
whole fetus makes vigorous
movements.

Sound and light

The fetus will respond to
light and is able to hear
sounds such as the
mothers voice.

4 x trimester images Science Photo Library

Vernix
By 20 weeks, this
white, waxy
substance covers
the skin,
protecting it from
the surrounding
amniotic fluid.

Movement

Weight

Fetus moves around

to encourage muscle
development.

Week 16: 140g

Week 20: 340g

Weight
10g

104

Length
5.5cm

Length
Week 16: 18cm
Week 20: 25cm

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Sweating
An increase in
blood circulation
causes mother to
sweat more.

The female seahorse

deposits her eggs in the
pouch of the male seahorse.
He fertilises the eggs and
carries them for the full
term of three weeks.

JUST PLAIN WEIRD

2. Komodo
dragons
Female komodo dragons
can give birth to male
babies without fertilisation
from a male partner. This is
known as parthenogenesis.

3. Spotted hyenas
Female spotted hyenas have
genitalia like a penis. It
stretches to allow the insertion
of the male penis during
copulation, and stretches again
when giving birth through it.

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Midori 07

ANIMAL
PREGNANCIES

VIRGIN BIRTH

1. Seahorses

BudgieKiller 05

MEN ONLY
Joanne Merriam 05

HEAD
HEAD

DID YOU KNOW? 200 extra calories a day are needed in mid-pregnancy, which is 10 per cent more than the usual

The placenta
The placenta is an essential interface between
the mother and fetus. When mature it is a 22cm
diameter, at oval shape with a 2.5cm bulge in
the centre. The three intertwined blood
vessels from the cord radiate from the centre
to the edges of the placenta. Like tree roots,
these villous structures penetrate the
placenta and link to 15 to 20 lobes on
the maternal surface.
The ve major functions of the
placenta deal with respiration,
nutrition, excretion of waste
products, bacterial protection
and the production of hormones.

Whartons jelly
The umbilical blood vessels are coated with
this jelly-like substance and protected by a
tough yet flexible outer membrane.

Placenta body
Is firmly attached to the inside
of the mothers uterus.

Maternal surface
Blood from the mother is absorbed and
transferred to the fetal surface.

Fetal surface
Blood vessels radiate out from the umbilical
cord and penetrate the placenta. The surface
is covered with the thin amnion membrane.

Umbilical cord
Consists of three blood vessels. Two carry carbon
dioxide and waste from the fetus, the other supplies
oxygen and nutrients from the mother.

Science Photo Library

THIRD TRIMESTER (2840 weeks)

Breathlessness
The increased size of
the fetus by 24 weeks
causes compression of
rib cage and discomfort
for mother.

Week 24

Movement
By the 28th week,
due to less room in
uterus, the fetus will
wriggle if it feels
uncomfortable.

Now almost at full term, the fetus can recognise and

respond to sounds and changes in light. Fat begins
to be stored under the skin and the lungs are the
very last organs to mature.

Week 32

Hands
The fetus can move
its hands to touch
its umbilical cord at
24 weeks.

The three
intertwined
blood vessels
radiate from
the centre to
the edges of
the plancenta

Position
By 28 weeks, the
uterus has risen to a
position between
the navel and the
breastbone.

Under pressure
Pressure on the diaphragm and
other organs causes indigestion and
heartburn in the mother. She will
find it difficult to eat a lot.

Position
Weight
Week 24: 650g
Week 28: 1,250g

Length
Week 24: 34cm
Week 28: 38cm

Head positions itself downwards, in

preparation for labour.

Head
The head
can move
at 28 weeks
and the eyes
can open
and see.

Weight
1,500g

Length
41cm

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Sleep patterns
Fetus will sleep and wake in
20-minute cycles.

105

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BODY AT WORK

From fertilisation to foetus

Week 5

How does an
embryo develop?

Pharyngeal arches that develop in the

face, jaws, throat and neck appear
between the head and body. A
complex network of nerves and blood
vessels are developing. The embryos
eyes have formed and the ears are
becoming visible. The spleen and
pancreas are beginning to develop in
the central part of the gut. The thymus
and parathyroid glands develop from
the third pharyngeal arch. The arms
and legs begin to emerge
as paddle-shaped buds.

Discover how a fertilised egg transforms into

an embryo and eventually a new human being
After fertilisation, the single-celled zygote splits
into two, then the two cells double to four, four
to eight and so on. The journey along the
fallopian tube is quite slow, while growth
continues. On its way, the zygote divides to
make a clump of 32 cells, known as the morula stage. If the
early embryo splits into two clumps before this, it may
develop into identical twins. Every cell in the morula could
still become part of the growing embryo.
By the time the womb cavity is reached, the cell cluster
becomes hollow and lled with uid. It is now referred to as
the blastocyst, which is an embryo that has reached the stage

where it has two different cell types. The surface cells, or outer
coat, will become, among other things, the placenta that
nourishes the baby; the inner cells, known as the inner cell
mass, will become the foetus itself. On contact, the blastocyst
burrows into the uterine wall for nourishment in a process
known as implantation. Blastocyst formation usually occurs
on the fth day after fertilisation.
The embryonic stage begins in the fth week. From weeks
ve to eight, development is rapid, as major organs and
systems begin to emerge. At this time, the rst bone cells will
also appear. By the end of the eighth week, the embryo is
known as a foetus and increasingly looks like a mini human.

Fertilisation and IVF explained

Natural fertilisation takes place via sexual
intercourse. An egg, or ovum, is released by an
ovary and is fertilised by a sperm. Fertilisation
occurs when the sperm and egg unite in one of the
females Fallopian tubes. The fertilised egg, known
as a single-celled zygote, then travels to the uterus,

where it implants into the uterine lining. In vitro

fertilisation (IVF) is a form of assisted reproductive
technology, where the sperm nucleus is combined
with an egg cell in a lab. The resultant embryo is
manually introduced to the uterus, where it
develops in the same way as a natural conception.

Ovulated egg
The sperm cells are
chemically attracted to the
egg and attach themselves
in an attempt to break
through the outer coat.

Uterus (womb)
The whole process from ejaculation to
fertilisation can take less than an hour. If a
woman has an average 28-day menstrual
cycle, fertilisation is counted as having taken
place around day 14, not on day one.

Ovary
A woman usually has two tubes and
two ovaries, one either side of her
uterus. Every month one of the
ovaries releases an egg, which
passes slowly along its Fallopian
tube towards the womb.

Fallopian tube
Fertilised egg
Only one sperm will be
successful. The egg will
then lose its attraction,
harden its outer shell and
the other sperm will let
go. If eggs are not
fertilised within 12 hours
of release, they die.

If a woman has sexual

intercourse during the
days of her monthly cycle,
just before or after an egg
has been released from
the ovary, a sperm cell
from her partner could
travel to the Fallopian tube
and fertilise the ovum.

In vitro (in glass)

IVF is the process by which eggs are
removed from the ovaries and mixed
with sperm in a laboratory culture dish.
Fertilisation takes place in this dish.

106

Sperm
During sexual intercourse, millions of sperm are
ejaculated into the vagina, with only thousands
surviving to make the journey to meet the egg.

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Week 3
At the start of week 3 a groove will
form towards what will become the
tail end of the embryo; this is the
primitive streak. A new layer of tissue
the mesoderm will develop from
the primitive streak. The spinal cord,
kidneys and major tissues will all grow
from this. Cells from the ectodermal
tissue create the neural fold and plate,
the first stages in the development of
the nervous system. The neural
groove will go on to form the spine.

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DID YOU KNOW? In 2009, almost two per cent of all babies born in the UK were conceived as a result of IVF

Journey of an embryo
The first eight weeks is an immense time of change for a just-conceived human

Week 7
The embryos eyelids begin to form from a single
membrane that remains fused for several days. At
this stage in development, the limb muscles are
beginning to form. The chest cavity will be
separated from the abdominal cavity by a band of
muscles; this will later develop into the diaphragm.

Week 8
Between the fourth and eighth
weeks, the brain has grown so
rapidly that the head is extremely
large in proportion to the rest of the
body. The gonads, or sex glands, will
now start to develop into ovaries or
testes. The elbows, fingers, knees
and toes are really taking shape.
Inside the chest cavity, the lungs are
developing too. At the end of the
eight-week period, the embryo
becomes a foetus.

Week 6
42 tissue blocks have formed along the embryos
back and the development of the backbone, ribs and
muscles of the torso begins. The length of the embryo is
now 7-8mm (0.3in) . The embryos heart has established a
regular rhythm and the stomach is in place. Ears, nose,
fingers and toes are just beginning to appear.

Week 4
The kidneys are forming from mesodermal tissue and the mouth is
emerging. A basic spinal cord and gut now run from the head to the tail.
The head and tail fold downward into a curve as a result of the embryo
developing more rapidly from the front. The heart tube bends into a U
shape and blood begins to circulate around the body.

Week 2

Week 1
Within one week of conception, the
fertilised egg, known as a blastocyst, will
make its way to the uterus. Within days the
cells will arrange themselves into two
masses: the outer coat will become the
placenta, while the inner cell mass
becomes the foetus. All being well, the
developing embryo will settle into the folds
of the womb lining.

What is amniotic uid?

The amniotic sac is a bag of uid in
the uterus, where the unborn baby
develops. Its lled with a colourless
uid mainly made of water that
helps to cushion the foetus and
provides uids which enable the baby
to breathe and swallow. The uid also
guards against infection to either the
foetus or the uterus. Amniotic uid
plays a vital role in the development
of internal organs, such as the lungs
and kidneys; it also maintains a
constant temperature. The amniotic
sac starts to form and ll with uid
within days of conception.

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The body of this foetus is really taking

shape, safe within the amniotic sac

3x SPL

The inner cells of the embryo divide into two

layers: the ectoderm and the endoderm. The
tissues and organs of the body will eventually
develop from these. The amniotic sac, which
will soon form a protective bubble around the
embryo, also starts to develop. The embryo,
now completely embedded in the womb,
is a disc-shaped mass of cells,
measuring roughly 0.2mm
(0.008in) in diameter.

107

TASTE

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BODY AT WORK

What happens when we sleep?

How do taste
buds work?
Discover how we distinguish
between avours
Taste buds are sensory organs that are found in the little
bumps (or papillae) on the tongue. The tongue contains
about 8,000 taste buds and theyre replaced
approximately every two weeks. Sensitive microscopic
hairs on the taste buds (microvilli) pick up dissolved chemicals from
food and send electrical signals to the brain that distinguishes between
ve different tastes: sweet, bitter, savoury (umami), salty and sour.
Varying sensitivity to these tastes occurs across the whole of the tongue.
But taste buds alone cannot tell us the exact avour of food. Other
factors such as smell, spiciness, temperature and texture also
contribute to the eventual taste. So if you hold your nose while you eat
then your brain wont get the full taste story!

The ve basic
human
tastes
Building an in-depth map of the tongue
There is general agreement that humans have ve basic tastes,
although the fth taste primary has only been recently ofcially
recognised. Sweetness, bitterness, sourness and saltiness were
joined by savouriness in 2002. Several other sensations that the
tongue can recognise have been identied but are not classied as tastes.
Sweetness is associated primarily with simple carbohydrates of which sugar is
one of the most common. The way sweetness is detected is complex and only
recently has the current model of multiple binding sites between the receptors
and sweet substance itself been proposed and accepted. A sweet taste infers that
the substance is high in energy and studies have shown that newborns in
particular, who need a high calorie intake to grow, demonstrate a preference for
sugar concentrations sweeter than lactose, which is found in breast milk.
Bitterness can be detected in very low levels and is generally perceived to be an
unpleasant or sharp taste. Many toxic substances in nature are known to be bitter
and there is an argument proposed by evolutionary scientists that bitterness
sensitivity is an evolutionary defence mechanism. Humans, however, have now
developed various techniques to make previous inedible bitter substances edible
through reducing their toxicity, often through cooking.
The taste of saltiness is produced by the presence of sodium ions, or other
closely related alkali metal ions. Potassium and lithium produce a similar taste as
they are most closely related to sodium.
Sourness detects acidity. The way we measure the degree of sourness is through
rating sour substances against dilute hydrochloric. The mechanism involved in
detecting sourness is similar to saltiness in that taste is caused by a concentration
of ions in this case hydrogen ions. Savouriness is the newest of the recognised
basic tastes and the taste is produced by fermented or aged foods. Glutamate is a
common compound that can cause this taste and consequently savouriness is
considered fundamental to Eastern cuisine.

108

Factors such as smell,

spiciness and texture also
contribute to taste
Taste qualities are found in all areas of
the tongue, although some regions are
more sensitive than others.

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Your taste buds have

very tiny, sensitive hairs
called microvilli which
send messages to your
brain about how
something tastes.

WorldMags.net

The importance
of insulin
The hormone that controls your blood sugar levels

When you eat, your digestive

system breaks down the food and
passes its nutrients into your
bloodstream. These nutrients
include glucose (sugar), but high levels of
glucose in your blood can be damaging and
even fatal. To keep these levels low, your
pancreas produces insulin to help cells absorb
the glucose so they can use it as energy. As well
as helping fat and muscle cells to absorb
glucose, insulin helps your liver hold on to any

Injecting insulin
There are two main types of diabetes. Type 1
occurs when the pancreas does not produce
any insulin, and Type 2 occurs when the
pancreas doesnt produce enough insulin or if
the bodys cells do not react to the insulin being
produced. Although there is no cure for
diabetes, people with Type 1 can control the
systems by regularly injecting themselves with
insulin or using a pump that constantly sends
insulin into their blood at a rate they control.
They also need to monitor their blood sugar
levels by pricking their nger and placing a
drop of blood on the testing strip of a blood
glucose meter. Doing this before and after
meals will help them adjust their insulin
injections and diet accordingly. People with
Type 2 diabetes can control their symptoms by
eating a healthy, balanced diet and exercising
more regularly, but may need injections if their
condition progresses.

The pancreas produces

insulin for the body to
be able to absorb glucose

excess glucose in your body so that it can

release it when it is needed, such as between
meals, when exercising or if your blood sugar
level is too low.
If your body fails to produce any or enough
insulin, or if your cells become resistant to the
hormone, this results in a condition known as
diabetes. It increases your blood sugar level and
you can develop hyperglycaemia. To try to get
rid of the excess glucose in your blood, your
body will pass it in your urine. But it will also

take more
water with it,
leading to an
increase in frequency and
volume of urination and an increase in thirst. If
left untreated, it can lead to a condition called
diabetic ketoacidosis, where the body breaks
down fats and proteins for energy instead of
sugars, resulting in a build-up of ketones (acids)
in the blood. This can lead to unconsciousness
and even death.

Insulin
in action
How the bodys cells absorb glucose for energy
Glucose absorbed
The insulin stimulates
glucose transporter
molecules to move to the
outer membrane, allowing
the cell to absorb glucose.

Insulin produced
When the concentration of
glucose in the blood increases,
the beta cells of the islets of
Langerhans in the pancreas
produce insulin.

Insulin attaches
Insulin binds to the insulin
receptors on the outer
membrane of the bodys fat
and muscle cells.

Insulin can be injected into the abdomen, upper

arm, upper buttocks or outer thigh

In fat-tissue cells, glucose

increases the uptake of fatty
acids to create the storage
form of fat.

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Muscle cells
(myocytes)
In muscle-tissue cells,
glucose is stored as
glycogen, which is broken
down to supply the muscles
with energy when needed.

109

Thinkstock

Fat cells
(adipocytes)

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BODY AT WORK

The sense of smell

How do
we smell?

Olfactory bulb
This area of the brain is where signals are
processed and smell is perceived. Other
animals have a much larger area as they
can perceive wider ranges of smells and
use their sense of smell more.

The ability to smell is one of our

most crucial senses and can
inuence the food we eat and
the people we date
Smell, or olfaction to use the
proper terminology, is a very
direct sense, in that we
actually breathe in
microscopic bits of the substance that
we smell. These hit the olfactory
epithelium, a mucus membrane in the
nasal cavity, which contains millions
of olfactory receptor neuron cells. Each of
these sensory cells is covered in small
hair-like structures, called cilia, which react to
the odour and send signals to the olfactory nerve,
which relays this information to the brain so it is then
perceived as smell. Humans can recognise around
10,000 different odours and no two individuals can
sense anything exactly the same.

1 Women smell better

Consistently, women out-perform

men in smelling ability tests, and
research has shown that women can
recognise the scent of their baby
only days after birth.

2 Smell affects taste

The human nose is actually the

main organ involved in perceiving
taste. Taste buds can only
distinguish sweet, sour, bitter and
salt, everything else perceived
comes from smell!

people cant
smell better
3 Blind
Its a common myth that blind
people can smell better than the
sighted. However, this has never
been proven and most studies
refute the fact.

smelling ability
doesnt improve
4 Your
after childhood
At about eight years old, our sense
of smell reaches its full potential.
However, this ability reduces as
you age.

of smell
improves throughout
5 Sense
the day
When you first wake up, your sense
of smell is far less acute than it is in
the evening.

110

The olfactory nerves pass

information about the particles
sensed in the nasal cavity to the
brain, where these signals are
perceived as a certain smell.

Nasal cavity
This is where air and
microscopic molecules of
substances we are to smell
enter. Air is pulled into this
area to pass through into the
lungs by the bodys
diaphragm movements.

Olfactory epithelium
This is where the olfactory
nerve cells are located. In a
human, this area is around
10cm squared.

Cells that smell

The patch of sensory cells located in the nasal
cavity are made up of several different parts
Mucosa
Mucosa lines the epithelium inside the nasal cavity and catches the
odour particles to be sensed by the receptor neuron cells.

Olfactory receptor neuron cells

These are odour-sensitive cells that are stimulated by the
cilia. They then send messages through to the brain.

Olfactory cilia
These sense the particles in air. There are 8-20 of these
on each olfactory nerve cell which line the epithelium.

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Chabacano, 2007

5 TOP
FACTS
SMELL

Olfactory nerves

RECORD
BREAKERS
CARD COUNTING

59
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PACKS OF CARDS MEMORISED

In 2007, David Farrow broke the world record for the most decks of playing
cards memorised in a single sighting, recalling a total of 3,068 cards.

DID YOU KNOW? Short-term memories are often stored as audio, which is why we repeat things we want to remember in our head

Short-term
memory
Find out how the brain decides what to
remember and what to forget
As you read this, you store the words
at the beginning of each sentence in
your short-term memory while you
work your way through to the end,
enabling you to understand the text.
At the same time, you are probably ignoring the
feeling of the glossy pages against your skin as you
hold the magazine.
Short-term memory acts somewhat like a
gatekeeper between incoming sensory
information and long-term storage. You are
constantly bombarded by information, and the
incoming traces from your sensory receptors last
for just fractions of a second before they are lost.
You dont have time to process all of it, so shortterm memory allows you to pass small amounts of

important information in a temporary loop while

your brain decides what to do with it.
Short-term memory has two major limitations.
The rst is that you can only store a small amount
of information, and the second is that the memory
decays over time. If you pay attention, your
short-term memory can hold around four chunks
of new information for between ten and 20
seconds, but if you are distracted, you will rapidly
forget it all.
Rehearsing the information inside your head
effectively resets the timer and restarts the
memory loop, allowing you to extend this time. A
part of the brain called the hippocampus then
decides which bits are important enough commit
to longer-term storage, and which to forget.

Making memories
Find out how incoming visual information
becomes memory

Extending your
short-term memory
You can hold four items of information in your
memory for around ten seconds without trying, but
memorising a sheet of 20 words can prove
challenging. Your short-term memory has its
limitations, but you can improve it with a few
simple tricks.
Instead of overloading your memory by trying to
memorise them one-by-one, divide the images into
linked chunks, for example, ofce objects or things
that y. Categorising the words like this helps by
tapping into your long-term memory, which
mainly stores linked concepts and is triggered by
cues and associations.
Short-term memory tends to be encoded
verbally, and you might nd yourself repeating the
names of the items in the pictures inside your head
in order to help with recall, but you can improve
still further if you take advantage of visual
encoding. By creating a scene inside your head and
visiting each item in turn, you start to remember
the words more easily.

Occipital lobe

Processing

The occipital lobes process

incoming visual information.

The incoming signals

from the eyes are
passed to the occipital
lobes for processing.

Storage

Thalamus

Short-term memories are rapidly turned into

long-term memories that can last days, weeks
or even a lifetime.

The thalamus is
involved in attention
and the early stages
of short-term
memory formation.

Prefrontal cortex
This part of the brain has a
crucial role in coordinating
short-term memory and in
rehearsing information.

In order to transfer information

from sensory memory to
short-term memory you need to
be paying active attention.

Input
Incoming information
is stored for less than
a second in your
sensory memory.

Transfer
Incoming signals from all
of the sensory systems
are passed in to the
hippocampus, where
they are combined as a
single experience.

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Hippocampus
This region of the
brain is involved in
transferring
short-term
memories into
long-term storage.

Thinkstock; Science Photo Library

Attention

Long-term
memories
Memories are stored
throughout the cortex as
groups of nerve cells that
fire together in
coordinated patterns.

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BODY AT WORK

Blood cells explained

How do white
blood cells work?

One of the bodys main defences against infection and

foreign pathogens, how do these cells protect our bodies?
White blood cells, or leukocytes, are
Types of leukocyte
the bodys primary form of defence
against disease. When the body is
invaded by a pathogen of any kind, the
white blood cells attack in a variety of ways; some
produce antibodies, while others surround and
ultimately devour the pathogens whole.
In total, there are ve types of white blood cell
(WBC), and each cell works in a different way to
ght a variety of threats. These ve cells sit in two
groupings: the granulocytes and the
agranulocytes. The groups are determined based
on whether a cell has granules in the cytoplasm.
These granules are digestive enzymes that help
break down pathogens. Neutrophils, eosinophils
and basophils are all granulocytes, the enzymes
in which also give them a distinct colouration
which the agranulocytes do not have.
As the most common WBC, neutrophils make up
between 55 and 70 per cent of the white blood cells
in a normal healthy individual, with the other four
types (eosinophils, basophils, monocytes and
lymphocytes) making up the rest. Neutrophils are
the primary responders to infection, actively
moving to the site of infection following a call from
mast cells after a pathogen is initially discovered.
They consume bacteria and fungus that has
broken through the bodys barriers in a process
called phagocytosis.
Lymphocytes the second-most common kind
of leukocyte possess three types of defence cells:
B cells, T cells and natural killer cells. B cells
release antibodies and activate T cells, while T
cells attack diseases such as viruses and tumours
when directed, and regulatory T cells ensure the
immune system returns to normal after an attack.
Natural killer cells, meanwhile, aid T cell response
by also attacking virus-infected and tumour cells,
which lack a marker known as MHC.
The remaining types of leukocyte release
chemicals such as histamine, preparing the body
for future infection, as well as attacking other
causes of illness like parasites.

Natural killer cells

aid T cell response
by also attacking
virus-infected and
tumour cells
112

Different kinds of WBC have different roles, which

complement one another to defend the body

Lymphocyte
These release antibodies
as well as attack virus and
tumour cells through three
differing types of cell. As a
group, they are some of
the longest lived of the
white blood cells with the
memory cells surviving for
years to allow the body to
defend itself if repeat
attacks occur.

Eosinophil
Eosinophils are the white
blood cells that primarily
deal with parasitic
infections. They also have
a role in allergic reactions.
They make up a fairly small
percentage of the total
white blood cells in our
body about 2.3 per cent.

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Monocyte
Monocytes help prepare us
for another infection by
presenting pathogens to the
body, so that antibodies can
be created. Later in their life,
monocytes move from the
bloodstream into tissue,
and then evolve into
macrophages which can
conduct phagocytosis.

THE
STATS
LEUKOCYTES

DIAMETER 80mm
6 MACROPHAGE
BLOOD
BACTERIA CONSUMED
COMPOSITION 1% BY EACH NEUTROPHIL 5-20
NEUTROPHIL
LIFETIME (HOURS)

4 in 1,000
NUMBER OF WBCS IN
A DROP OF BLOOD
7,000
WBCS WHICH
ARE BASOPHILS

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DID YOU KNOW? WBCs have colour but appear white when blood is put through a centrifuge, hence their group name

White blood cells at work

The body has various outer defences against infection, including the
external barrier of the skin, but what happens when this is breached?

Skin breach

Mast cells

WBCs arrive

A foreign object breaks

through the skin,
introducing bacteria (shown
in green) into the body.

Mast cells release cytokines

and then WBCs are called
into action to ensure the
infection does not spread.

Macrophages move to the

site via the bloodstream to
start defending against
invading bacteria.

Macrophages
consume bacteria
Bacteria are absorbed into
cytoplasm and broken
down by the macrophages.

Healing
Following removal of the
bacteria, the body will start
to heal the break in the skin
to prevent further infection.

A microscopic illustration
of a neutrophil the most
abundant WBC

Basophil
Basophils are involved in
allergic response via
releasing histamine and
heparin into the
bloodstream. Their
functions are not fully
known and they only
account for 0.4 per cent of
the bodys white blood
cells. Their granules
appear blue when viewed
under a microscope.

Neutrophils are the most

common of the leukocytes.
They have a short life span
so need to be constantly
produced by the bone
marrow. Their granules
appear pink and the cell
has multi-lobed nuclei
which make them easily
differentiated from other
types of white blood cell.

If the immune system stops working properly,

we are at risk of becoming ill. However,
another problem is if the immune system
actually goes into overdrive and starts
attacking the individuals cells, mistaking them
for pathogens. There are a large number of
autoimmune ailments seen across the world,
such as Crohns disease, psoriasis, lupus and
some cases of arthritis, as well as a large
number of diseases that are suspected to
have autoimmune roots.

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We can often treat these conditions with

immunosuppressants, which deactivate
elements of the immune system to stop the
body attacking itself. However, there are
drawbacks with this treatment as, if the
person exposes themselves to another
pathogen, they would not have the normal
white blood cell response. Consequently, the
individual is less likely to be able to ght
normally low-risk infections and, depending on
the pathogen, they can even be fatal.

113

SPL; Thinkstock

A faulty immune system

Neutrophil

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BODY AT WORK

Understanding our genes

GENETICS
From inheritance to genetic diseases, what secrets are hidden
in our genes and how do they determine who we are?

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RECORD
BREAKERS
GIANT GENOME

THE LONGEST GENOME

150bn
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An ordinary-looking white ower, Paris japonica, has the

longest known genome with 150 billion base pairs. If
stretched out it would measure over 91 metres (300 feet)!

DID YOU KNOW? If all 46 human chromosomes were stitched together and stretched they would measure nearly 2m (6.6ft)

Genes dene who we are. They are

the basic unit of heredity, each
containing a coded set of
instructions to make a protein.
Humans have an estimated 20,500 genes,
varying in length from a few hundred to more
than 2 million base pairs. They affect all
aspects of our physiology, providing the code
that determines our physical appearance, the
biochemical reactions that occur inside our
cells and even, many argue, our personalities.
Every individual has two copies of every gene
one inherited from each parent. Within the
population there are several alleles of each
gene that is, different forms of the same code,
with a number of minor alterations in the
sequence. These alleles perform the same
underlying function, but it is the subtle
differences that make each of us unique.
Inside each of our cells (except red blood
cells) is a nucleus, the core which contains our
genetic information: deoxyribonucleic acid
(DNA). DNA is a four-letter code made up of
bases: adenine (A), guanine (G), cytosine (C) and
thymine (T). As molecular biologist Francis
Crick once put it, DNA makes RNA, RNA makes
protein and proteins make us. Our genes are
stored in groups of several thousand on 23 pairs
of chromosomes in the nucleus, so when a cell
needs to use one particular gene, it makes a
temporary copy of the sequence in the form of

How is our genetic code stored?

Genetic information is coded into DNA using just four
nucleobases: A, C, G and T
Chromosome
Humans have 46
chromosomes 23 pairs
containing around
20,500 genes.

Nucleus
Surrounded by a doublethickness membrane, the
nucleus contains the genetic
information of the cell.

Double stranded
DNA has two complementary strands
one forms a template to make the
other, allowing accurate replication.

Base pairs
The bases of DNA
are always found
in pairs: adenine
pairs with thymine,
and guanine pairs
with cytosine.

Double helix
DNA is arranged in a double helix
shape, with the bases forming the
ladder-like rungs in the centre.

DNAs chemical structure

Nucleotide

We put deoxyribonucleic acid under the microscope

DNA is a polymer made up of

building blocks called nucleotides.

Phosphate
Phosphate groups
link the sugars of
adjacent nucleotides
together, forming a
phosphate backbone.

Hydrogen bond
Two bases interact with
each other by hydrogen
bonds (weak electrostatic
interactions that hold the
strands of DNA together).

A
Nucleobase

Sugar
Each base is attached
to a five-carbon sugar
called deoxyribose.

Each nucleotide contains a

base, which can be one of four:
adenine (A), thymine (T),
guanine (G) or cytosine (C).

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BODY AT WORK

Understanding our genes

ribonucleic acid (RNA). This copy contains all of
the information required to make a protein
the building blocks of the human body.
The Human Genome Project aimed to map
the entire human genome; this map is
effectively a blueprint for making a human.
Using the information hidden within our
genetic code, scientists have been able to
identify genes that contribute to various
diseases. By logging common genetic variation
in the human population, researchers have
been able to identify over 1,800 diseaseassociated genes, affecting illnesses ranging
from breast cancer to Alzheimers. The
underlying genetic inuences that affect
complex diseases like heart disease are not yet

The Human
Genome
Project
The Human Genome Project, an
initiative to map the sequence of
the entire human genetic code,
began in 1990 and was completed
in 2003. The 3.3-billion base pair
sequence was broken into
sections of around 150,000 base
pairs in length and the sequence
for each identied. These were
then joined and used to map the
information on to chromosomes
to determine which genes were
found on each and in what order.
The genome map (right) shows a
human chromosome compared
with other animals; the colours
are a heat map demonstrating
areas where genetic information
has been conserved through
evolution (the more fragmented
the pattern, the more differences
there are in the genetic code).

fully understood, but having the genome

available to study is making the task of
identifying genetic risk factors much easier.
Interestingly, the Human Genome Project
discovered we have far fewer genes than rst
predicted; in fact, only two per cent of our
genome codes for proteins. The remainder of
the DNA is known as non-coding and serves
other functions. In many human genes are
non-coding regions called introns, and
between genes there is intergenic DNA. One
proposed function is that these sequences act
as a buffer to protect the important genetic
information from mutation. Other non-coding
DNA acts as switches, helping the cell to turn
genes on and off at the right times.

Genetic mutations are the source of variation

in all organisms. Most genetic mutation occurs
as the DNA is being copied, when cells prepare
to divide. The molecular machinery responsible
for duplicating DNA is prone to errors, and often
makes mistakes, resulting in changes to the
DNA sequence. These can be as simple as
accidentally substituting one base for another
(eg A for G), or can be much larger errors, like
adding or deleting bases. Cells have repair
machinery to correct errors as they occur, and
even to kill the cell if it makes a big mistake, but
despite this some errors still slip through.
Throughout your life you will acquire many
mutations in your cells. Many of these are
completely harmless, either occurring in

Mapping the human genome

How does our genetic makeup compare to that of
other creatures?
Zebrash
Divergence between fish and
mammals occurred very early
in evolution, so similarities in
our genes are very
fragmented.

Chicken
Despite the fact
that we are not
closely related to
birds, the chicken
still has regions of
DNA that are quite
similar to ours.

Human
This ring represents
the genes on a
human chromosome,
with the numbers
providing a
representation
of scale.

Dog
Some regions of the
canine genome are
very different to ours,
but the pink bands
show an area that has
been conserved.

Rat
The mouse and rat genomes
have similar patterns,
demonstrating these rodents
close evolutionary relationship.

Chimpanzee
One of our closest living
relatives the solid bands
demonstrate we share a
great deal of genetic
information (ie 98 per cent).

Mouse
There is less in common between
human and mouse (90 per cent),
but we are sufficiently similar that
mice make a good scientific model
for studying human disease.

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KEY
DATES
GENETICS HISTORY

1865

1905

1953

1983

2003

Gregor Mendel, the father of

modern genetics, observes
patterns of genetic inheritance
in peas grown in his garden.

William Bateson is the first

person to use the term
genetics to describe the study
of biological inheritance.

Francis Crick (right) and

James Watson reveal the
double helix structure of
DNA using X-rays.

Polymerase chain reaction

(PCR) is invented, enabling
small DNA samples to be
amplified for testing.

Completion of the
Human Genome Project
provides access to the
human DNA blueprint.

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DID YOU KNOW? Humans share 98 per cent genetic similarity with chimpanzees but just seven per cent with E coli

non-coding regions of DNA, or changing the

gene so nominally that the protein is virtually
unaffected. However, some mutations do lead
to disease (see When genes go wrong box).
If mutations are introduced into the sperm
and egg cells they can be passed on to the next
generation. However, not all mutations are bad,
and this process of randomly introduced
changes in the DNA sequence provides the
biological underpinning that supports Darwins
theory of evolution. This is most easily observed
in animals. Take, for example, the peppered
moth. Before the Industrial Revolution the
majority of these moths had white wings,
enabling them to hide against light-coloured
trees and lichens. However, a minority had a

mutant gene, which gave them black wings;

this made them an easy target for predators and
kept their numbers low. When factories began
to cover the trees in soot, however, the lightcoloured moths struggled to hide themselves
against the newly blackened environment, so
black moths ourished. They survived much
longer, enabling them to pass on their mutation
to their offspring and altering the gene pool.
It is easy to see how a genetic change like the
one that occurred in the peppered moth could
give an advantage to a species, but what about
genetic diseases? Even these can work to our
advantage. A good example is sickle cell
anaemia a genetic disorder thats quite
common in the African population.

Using genetics to
convict criminals

A single nucleotide mutation causes

haemoglobin, the protein involved in binding
oxygen in red blood cells, to misfold. Instead of
forming its proper shape, the haemoglobin
clumps together, causing red blood cells to
deform. They then have trouble tting through
narrow capillaries and often become damaged
or destroyed. However, this genetic mutation
persists in the population because it has a
protective effect against malaria. The malaria
parasite spends part of its life cycle inside red
blood cells and, when sickle cells rupture, it
prevents the parasite from reproducing.
Individuals with one copy of the sickle cell gene
and one copy of the healthy haemoglobin gene
have few symptoms of sickle cell anaemia,

Why do we look
like our parents?

Forensic scientists can use traces of DNA to

identify individuals involved in criminal activity.
Only about 0.1 per cent of the genome differs
between individuals, so rather than sequencing
the entire genome, scientists take 13 DNA
regions that are known to vary between
different people in order to create a DNA
ngerprint. In each of these regions there are
two to 13 nucleotides in a repeating pattern
hundreds of bases long the length varies
between individuals. Small pieces of DNA
referred to as probes are used to identify
these repeats and the length of each is
determined by a technique called polymerase
chain reaction (PCR). The odds that two people
will have exactly the same 13-region prole is
thought to be one in a billion or even less, so if
all 13 regions are found to be a match then
scientists can be fairly condent that they can
tie a person to a crime scene.

Its a common misconception that we inherit

entire features from our parents eg You have
your fathers eyes. Actually inheritance is much
more complicated several genes work together
to create traits in physical appearance; even eye
colour isnt just down to one gene that codes for
blue, brown or green, etc. The combinations of
genes from both of our parents create a mixture of
their traits. However, there are some examples of
single genes that do dictate an obvious physical
characteristic all on their own. These are known as
Mendelian traits, after the scientist Gregor Mendel
who studied genetic inheritance in peas in the
1800s. One such trait is albinism the absence of
pigment in the skin, hair and eyes due to a defect
in the protein that makes melanin.

Carrier parents
Carrier children
Two out of four will be
carriers, like their parents,
with one normal and one
faulty gene.

Each parent carries the

albinism gene (dark pink), but
they have one normal gene
(light pink), so they are able
to make melanin.

Gametes
Each child inherits one
gene from the mother and
one from the father.

Healthy child
One in four children will
receive one healthy gene
from the father and one
from the mother.

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Affected child
One in four children will
receive two copies of the
faulty gene and as a
result will be unable to
produce melanin.

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BODY AT WORK

Understanding our genes

but are protected from malaria too, allowing
them to pass the gene on to their children.
Genetics is a complex and rapidly evolving
eld and more information about the function
of DNA is being discovered all the time. It is now
known that environmental inuences can alter
the way that DNA is packaged in the cell,
restricting access to some genes and altering
protein expression patterns. Known as
epigenetics, these modications do not actually
alter the underlying DNA sequence, but
regulate how it is accessed and used by the cell.
Epigenetic changes can be passed on from one
cell to its offspring, and thus provide an
additional mechanism by which genetic
information can be modied across generations
of humans.

Repairing faulty genes

We reveal how donated cells can be used to mend any
damaged genes within the human body

Target gene
The healthy gene is
isolated from the DNA
of the donor individual.

Packaging
The gene is
packaged into a
delivery vector,
like a virus, to
help it get inside
the target cell.

Fertilised egg
A fertilised human egg is a
source of undifferentiated
stem cells, which can
become any type of cell.

Transduction
Embryonic
stem cells

The new gene is introduced

into the stem cells produced
by the fertilised egg.

The fertilised egg

becomes a blastocyst,
which contains
undifferentiated
embryonic stem cells.

When our genes

go wrong
Cancer is not just the result of one or two genetic
mutations in fact, it takes a whole series of
mistakes for a tumour to form. Cells contain
oncogenes and tumour suppressor genes, whose
healthy function is to tell the cell when it should
and should not divide. If these become damaged,
the cell cannot switch off its cell division
programme and it will keep making copies of
itself indenitely. Each time a cell divides there is
a risk that it will make a mistake when copying its
DNA, and gradually the cell makes more and more
errors, accumulating mutations that allow the
tumour to progress into malignant cancer.

Differentiation
Chemical signals are
added to the stem cells to
force them to differentiate
into the desired cell type,
eg liver cells.

Transplant
The new cells are transplanted
into the recipient, carrying with
them the healthy gene.

Tumour-associated
genes
Genes normally involved in
regulating cell behaviour can
go on to cause cancer if they
become mutated.

118

Mutagens

Localised

Invasion

Metastasis

Environmental factors, or
mutagens such as radiation
and chemicals can cause
damage to the DNA, leading to
mutations in key genes.

Cancer usually starts with just

one or a few mutated cells;
these begin to divide
uncontrollably in their local
area creating a tumour.

As the tumour grows in

size it starts to invade
the surrounding area,
taking over
neighbouring tissues.

Further mutations allow cells

of the tumour to break free and
enter the bloodstream. From
here they can be distributed
throughout the body.

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SPL; Alamy; Thinkstock

How tumours develop

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DID YOU KNOW? Approximately 300,000 people die from burns each year worldwide

What happens when

we burn ourselves?
Burns range from irritating to life-threatening
learn about the different types now
Most people associate burns with
ames, but they have many other
causes. A burn is medically dened
as coagulative destruction of skin,
meaning any energy source can cause one. This
energy damages underlying skin proteins and
fat cells, causing breaks in the skin.
Burns are generally classied by their depth.
First-degree (supercial) burns leave painful,

red skin, but without large blisters. Only the

epidermis is damaged, so regrowth is fast.
Second-degree burns (partial thickness) can be
either supercial or deep. The skin usually
blisters and can be very painful. The dermis
layer is also damaged so regrowth is slow, taking
several weeks or even months. In third-degree
burns (full thickness) the skin is left white or
pale, with no blistering and little to no sensation.

The basal growth layer is destroyed so no new

skin can grow.
Even minor burns can cause problems if not
treated properly. The rst priority is to stop the
burning process; cold running water is often the
best rst treatment. Infection, dehydration and
protein loss are all problems that occur next,
which our resilient skin can solve itself if the
injury isnt too severe.

How burns are measured

Classied by their depth, each burn case requires unique treatment

1
5
2

1 The skin
Your skin is vital to your wellbeing. It has multiple
important functions, including temperature control,
sensation and appearance.

3 First-degree burn

5 Blisters

Only the uppermost skin layers (known as the epidermis)

are affected, but the burn is painful, leaving the area red,
raw and tender to the touch.

Blisters appear when the epidermis separates from the

dermis, and are especially common in rst and
second-degree burns.

2 Basal layer

4 Second-degree burn

6 Third-degree burn

This layer is the key to regeneration, as new skin cells

grow from here. If undamaged, regrowth occurs without
any need for medical assistance.

These partial-thickness burns affect the upper or deep

dermal layers, and like rst-degree burns hurt a lot
because the nerve endings remain active.

Deep burns destroy the basal layer and nerve endings, so

they are painless. Regrowth will not occur alone, so skin
grafts are needed.
A second-degree burn will

Four major causes of burns

heal itself over time but

Chemical

Radiation

Electrical

Heat can come from

a ame or friction
(known as dry
burns), hot liquids
(known as wet
burns) or contact
with hot surfaces.

Alkalis burn for hours,

whereas acids are
short-lived. These
require no heat to
cause a burn, and can
take time to develop
after skin contact.

Ionising radiation
burns can be cover the
body due to exposure.
Sunburn is a common
type of radiation burn,
caused by exposure to
UV in sunlight.

These often cause

deep burns that heal
slowly. A small skin
defect may mask
underlying damage,
which can extend
throughout the body.

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probably leave scars

Thinkstock

Thermal

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BODY AT WORK

Blood vessels

Arteries and veins form the plumbing system that carries

blood around the body. Find out more about the circular
journey it takes...
The network of blood vessels in the
human body must cope with different
volumes of blood travelling at different
pressures. These blood vessels come
in a multitude of different sizes and
shapes, from the large, elastic aorta down to very
tiny, one-cell-thick capillaries.
Blood is the ultimate multitasker. It carries oxygen
for various tissues to use, nutrients to provide
energy, removes waste products and even helps you
warm up or cool down. It also carries vital clotting

Connective
tissue

factors which stop us bleeding. Blood comes in just

two varieties; oxygen-rich (oxygenated) blood is
what the body uses for energy, and is bright red.
After it has been used, this oxygen-depleted
(deoxygenated) blood is returned for recycling and is
dark red (not blue, as is often thought).
Blood is carried in vessels, of which there are
two main different types arteries and veins.
Arteries carry blood away from the heart and deal
with high pressures, and so have strong elastic
walls. Veins carry blood back towards the heart and
deal with lower pressures, so have thinner walls.

Ed Uthman, MD

Inside the
circulatory
system

Most of the amyloid

consisted of acellular pink
globules that effaced and
expanded the node, but
this image shows the
characteristic involvement
of blood vessel walls

Tiny capillaries connect arteries and veins together,

like small back-roads connecting motorways to
dual carriageways.
Arteries and veins are constructed differently to
cope with the varying pressures, but work in
tandem to ensure that the blood reaches its nal
destination. However, sometimes things go wrong,
lead to certain medical problems: varicose veins
from failing valves; deep vein thrombosis from
blood clots blocking the deep venous system; heart
attacks from blocked arteries; and lastly lifethreatening aneurysms from weak artery walls.

Capillary wall
Elastic layer
Muscle

Cell nucleus

Inner lining

Outer
protective
layer
Valve

Muscle layer

How do veins
work?

Arteries under
pressure!

Connecting it
all together

Veins carry low pressure blood. They contain

numerous one-way valves which stop
backwards ow of blood, which can occur
when pressure falls in-between heartbeats.
Blood ows through these valves towards the
heart but cannot pass back through them in
the other direction. Valves can fail over time,
especially in the legs. This leads to saggy,
unsightly veins, known as varicose veins.

Arteries cope with all of the pressure

generated by the heart and deliver oxygen-rich
blood to where it needs to be 24 hours a day.
The walls of arteries contain elastic muscles,
allowing them to stretch and contract to cope
with the wide changes in pressure generated
from the heart. Since the pressure is high,
valves are unnecessary, unlike the lowpressure venous system.

Capillaries are the tiny vessels which connect

small arteries and veins together. Their walls
are only one cell thick, so this is the perfect
place to trade substances with surrounding
tissues. Red blood cells within these
capillaries trade water, oxygen, carbon
dioxide, nutrients, waste and even heat.
Because these vessels are only one cell wide,
the cells have to line up to pass through.

120

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DID YOU KNOW? Vascular surgeons can bypass blocked arteries using either the patients own veins or synthetic grafts
Arteries
All arteries carry blood away
from the heart. They carry
oxygenated blood, except
for the pulmonary artery,
which carries deoxygenated
blood to the lungs.

A game of two halves

HEAD AND
ARMS

Lungs
In the lungs, carbon dioxide
is expelled from the body
and is swapped for fresh
oxygen from the air. This
oxygen-rich blood takes on
a bright red colour.

Aorta

Plasma carries all

of the different
types of cells

The aorta is an artery which

carries oxygenated blood to the
body; it is the largest blood
vessel in the body and copes
with the highest pressure blood.

LUNG

LUNG

HEART
The left side

Veins
All veins carry blood
to the heart. They
carry deoxygenated
blood, except for
the pulmonary vein,
which carries
oxygenated blood
back to the heart.

body tissues (the systemic circulation).

The right side of the heart pumps
deoxygenated blood towards the lungs, so
it can pick up new oxygen molecules to be
used again (the pulmonary circulation).

In human beings, the heart is a double

pump, meaning that there are two sides
to the circulatory system. The left side of
the heart pumps oxygen and nutrient-rich
blood to the brain, vital organs and other

The left side of the heart

pumps oxygenated blood
for the body to use. It
pumps directly into
arteries towards the brain
and other body tissues.

LIVER

Whats in
blood?
Its only the iron in red blood cells which
make blood red take these cells away and
what youre left with is a watery yellowish
solution called plasma. Plasma carries all
of the different types of cells and also
contains sugars, fats, proteins and salts.
The main cell types are red blood cells
(formed from iron and haemoglobin, which
carries oxygen around the body), white
blood cells (which ght infection from
bacteria, viruses and fungi) and platelets
(tiny cell fragments which stop bleeding by
forming clots at the sites of any damage).

Blood vessels
Different shapes and sizes
Capillary sphincter muscles

The right
side
The right side of the
heart pumps
deoxygenated
blood to the lungs,
where blood
exchanges carbon
dioxide for
fresh oxygen.

KIDNEY

These tiny muscles can open and close,

which can decrease or increase blood flow
through a capillary bed. When muscles
exercise, these muscles relax and blood
flow into the muscle increases.

Capillary bed
This is the capillary network that
connects the two systems. Here,
exchange of various substances
occurs with surrounding tissues,
through the one-cell thick walls.

Venule

Capillaries
Tiny capillaries connect
arteries and veins
together. They allow
exchange of oxygen,
nutrients and waste in the
bodys organs and tissues.

TRUNK
AND LEGS

Arteriole
Vein

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Artery
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BODY AT WORK

A look inside your blood

How your
blood works
The science behind the miraculous uid
that feeds, heals and ghts for your life
White blood cells
White blood cells, or leukocytes, are
the immune systems best weapon,
searching out and destroying
bacteria and producing antibodies
against viruses. There are five
different types of white blood cells,
all with distinct functions.

Platelet
When activated, these sticky cell
fragments are essential to the
clotting process. Platelets adhere to a
wound opening to stem the flow of
blood, then they team with a protein
called fibrinogen to weave tiny
threads that trap blood cells.

Red blood cell

Known as erythrocytes, red blood
cells are the bodys delivery service,
shuttling oxygen from the lungs to
living cells throughout the body and
returning carbon dioxide as waste.

Blood vessel wall

Granulocyte

Arteries and veins are composed of three

tissue layers, a combination of elastic
tissue, connective tissue and smooth
muscle fibres that contract under signals
from the sympathetic nervous system.

The most numerous type of white

blood cell, granulocytes patrol the
bloodstream destroying invading
bacteria by engulfing and digesting
them, often dying in the process.

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DK Images

HEAD
HEAD

LANDMARK
BLOOD EVENTS

1. Discovery of
veins and arteries

2. First blood
transfusion

3. Discovery of
blood types

In 300 BC, Greek anatomist

Herophilus of Chalcedon gured
out that arteries and veins
not only carry blood, but are
distinct pathways.

After a century of animalhuman blood transfusions,

James Blundell performed the
rst recorded human-to-human
transfusion in 1818.

In 1901, Austrian physician

Karl Landsteiner was the rst
to identify three basic blood
groups, revolutionising the
success of blood transfusions.

1818 - first human-tohuman transfusion

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DID YOU KNOW? If you took all of the blood vessels out of your body and laid them end to end, they would stretch for 160,000km
Monocyte

Components
of blood

The largest type of white blood cell, monocytes are born in bone
marrow, then circulate through the blood stream before maturing
into macrophages, predatory immune system cells that live in
organ tissue and bone.

Blood is a mix of solids and liquids, a blend of highly specialised

cells and particles suspended in a protein-rich uid called
plasma. Red blood cells dominate the mix, carrying oxygen to
living tissue and returning carbon dioxide to the lungs. For
every 600 red blood cells, there is a single white blood cell, of
which there are ve different kinds. Cell fragments called
platelets use their irregular surface to cling to vessel walls and
initiate the clotting process.

54%
Plasma
1%
White blood
cellls and
platelets

45%
Red blood
cells
Bone marrow contributes
four per cent of a persons
total weight

Bobjgalindo

Plasma
Composed of 92 per cent water, plasma is
the protein-salt solution in which blood
cells and particles travel through the
bloodstream. Plasma helps regulate
mineral exchange and pH, and carries the
proteins necessary for clotting.

Red blood cells are so numerous

because they perform the most
essential function of blood
Blood is the river of life. It
feeds oxygen and
essential nutrients to
living cells and carries
away waste. It transports the foot
soldiers of the immune system, white
blood cells, which seek out and
destroy invading bacteria and
parasites. And it speeds platelets to
the site of injury or tissue damage,
triggering the bodys miraculous
process of self-repair.
Blood looks like a thick,
homogenous uid, but its more like a

watery current of plasma a strawcoloured, protein-rich uid carrying

billions of microscopic solids
consisting of red blood cells, white
blood cells and cell fragments called
platelets. The distribution is far from
equal. Over half of blood is plasma,
45 per cent is red blood cells and a
tiny fragment, less than one per cent,
is composed of white blood cells
and platelets.
Red blood cells are so numerous
because they perform the most
essential function of blood, which is to

deliver oxygen to every cell in the

body and carry away carbon dioxide.
As an adult, all of your red blood cells
are produced in red bone marrow, the
spongy tissue in the bulbous ends of
long bones and at the centre of at
bones like hips and ribs. In the
marrow, red blood cells start out as
undifferentiated stem cells called
hemocytoblasts. If the body detects a
minuscule drop in oxygen carrying
capacity, a hormone is released from
the kidneys that triggers the stem cells
to become red blood cells. Because red

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blood cells only live 120 days, the

supply must be continuously
replenished; roughly 2 million red
blood cells are born every second.
A mature red blood cell has no
nucleus. The nucleus is spit out during
the nal stages of the cells two-day
development before taking on the
shape of a concave, doughnut-like
disc. Like all cells, red blood cells are
mostly water, but 97 per cent of their
solid matter is haemoglobin, a
complex protein that carries four
atoms of iron. Those iron atoms have

123

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BODY AT WORK

A look inside your blood

Waste product
of blood cell

1. Born in the bones

2. One life to live

When the body detects a low oxygen

carrying capacity, hormones released from
the kidney trigger the production of new
red blood cells inside red bone marrow.

Mature red blood cells,

also known as
erythrocytes, are
stripped of their nucleus
in the final stages of
development, meaning
they cant divide
to replicate.

6. Reuse and recycle

As for the globin and other cellular
membranes, everything is
converted back into basic amino
acids, some of which will be used
to create more red blood cells.

Waste
excreted
from body

Life cycle of
red blood cells
Every second, roughly 2 million red blood cells decay and die. The
body is keenly sensitive to blood hypoxia reduced oxygen
carrying capacity and triggers the kidney to release a hormone
called erythropoietin. The hormone stimulates the production of
more red blood cells in bone marrow. Red blood cells enter the
bloodstream and circulate for 120 days before they begin to
degenerate and are swallowed up by roving macrophages in the
liver, spleen and lymph nodes. The macrophages extract iron from
the haemoglobin in the red blood cells and release it back into the
bloodstream, where it binds to a protein that carries it back to the
bone marrow, ready to be recycled in fresh red blood cells.

5. Iron ions
In the belly of Kupffer cells,
haemoglobin molecules are split into
heme and globin. Heme is broken
down further into bile and iron ions,
some of which are carried back and
stored in bone marrow.

3. In circulation

4. Ingestion

Red blood cells pass from

the bone marrow into the
bloodstream, where they
circulate for around 120 days.

Specialised white blood cells in the liver and

spleen called Kupffer cells prey on dying red blood
cells, ingesting them whole and breaking them
down into reusable components.

the ability to form loose, reversible

bonds with both oxygen and carbon
dioxide think of them as weak
magnets making red blood cells such
an effective transport system for
respiratory gasses. Haemoglobin,
which turns bright red when
oxygenated, is what gives blood its
characteristic colour.
To provide oxygen to every living
cell, red blood cells must be pumped
through the bodys circulatory system.
The right side of the heart pumps
CO2-heavy blood into the lungs, where
it releases its waste gasses and picks
up oxygen. The left side of the heart
then pumps the freshly oxygenated
blood out into the body through a
system of arteries and capillaries,
some as narrow as a single cell. As the

124

red blood cells release their oxygen,

they pick up carbon dioxide
molecules, then course through the
veins back toward the heart, where
they are pumped back into the lungs
to exhale the excess CO2 and collect
some more precious O2.
White blood cells are greatly
outnumbered by red blood cells, but
they are critical to the function of the
immune system. Most white blood
cells are also produced in red bone
marrow, but white blood cells unlike
red blood cells come in ve different
varieties, each with its own
specialised immune function. The
rst three varieties, collectively called
granulocytes, engulf and digest
bacteria and parasites, and play a role
in allergic reactions. Lymphocytes,

another type of white blood cell,

produce anti-bodies that build up our
immunity to repeat intruders. And
monocytes, the largest of the white
blood cells, enter organ tissue and
become macrophages, microbes that
ingest bad bacteria and help break
down dead red blood cells into
reusable parts.
Platelets arent cells at all, but
fragments of much larger stem cells
found in bone marrow. In their resting
state, they look like smooth oval
plates, but when activated to form a
clot they take on an irregular form
with many protruding arms called
pseudopods. This shape helps them
stick to blood vessel walls and to each
other, forming a physical barrier
around wound sites. With the help of

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proteins and clotting factors found in

plasma, platelets weave a mesh of
brin that stems blood loss and
triggers the formation of new collagen
and skin cells.
But even these three functions of
blood oxygen supplier, immune
system defender and wound healer
only begin to scratch the surface of the
critical role of blood in each and every
bodily process. When blood circulates
through the small intestine, it absorbs
sugars from digested food, which are
transported to the liver to be stored as
energy. When blood passes through
the kidneys, it is scrubbed of excess
urea and salts, waste that will leave
the body as urine. The proteins
transport vitamins, hormones,
enzymes, sugar and electrolytes.

THE
STATS
BLOOD

PUMPED BY
7% BLOOD
7,000 litres
HEART PER DAY
BLOOD IN
RED BLOOD CELLS
HUMAN BODY 5 litres
MADE EVERY SECOND 2 million

BLOOD PERCENTAGE
OF BODY WEIGHT

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DID YOU KNOW? Until the 23rd week of foetal development, red blood cells are produced in the liver, not red bone marrow

Haemophilia
This rare genetic blood disorder severely inhibits the
clotting mechanism of blood, causing excessive
bleeding, internal bruising and joint problems. Platelets
are essential to the clotting and healing process,
producing threads of fibrin with help from proteins in
the bloodstream called clotting factors. People who
suffer from haemophilia almost exclusively males are
missing one of those clotting factors, making it difficult to
seal off blood vessels after even minor injuries.

Platelets weave
a mesh of fibrin
that stems blood
loss

Thalassemia
Another rare blood disorder affecting 100,000
newborns worldwide each year, thalassemia
inhibits the production of haemoglobin, leading
to severe anaemia. People who are born with the
most serious form of the disease, also called
Cooleys anaemia, suffer from enlarged hearts,
livers and spleens, and brittle bones. The most
effective treatment is frequent blood
transfusions, although a few lucky patients have
been cured through bone marrow transplants
from perfectly matching donors.

Hemochromatosis
Sickle cell anaemia
Anaemia is the name for any blood disorder that results
in a dangerously low red blood cell count. In sickle cell
anaemia, which afflicts one out of every 625 children of
African descent, red blood cells elongate into a sickle
shape after releasing their oxygen. The sickle-shaped
cells die prematurely, leading to anaemia, or sometimes
lodge in blood vessels, causing terrible pain and even
organ damage. Interestingly, people who carry only one
gene for sickle cell anaemia are immune to malaria.

One of the most common genetic

blood disorders, hemochromatosis is
the medical term for iron overload,
in which your body absorbs and
stores too much iron from food.
Severity varies wildly,
and many people experience few
symptoms, but others suffer
serious liver damage or
scarring (cirrhosis), irregular
heartbeat, diabetes and even heart
failure. Symptoms can be aggravated
by taking too much vitamin C.

Blood
disorders

Blood is a delicate balancing act, with

the body constantly regulating
oxygen ow, iron content and clotting
ability. Unfortunately, there are
several genetic conditions and
chronic illnesses that can disturb
the balance, sometimes with
deadly consequences.

Deep vein thrombosis

Left to right: a red blood cell,

platelet and white blood cell

Thrombosis is the medical term for any blood clot that is

large enough to block a blood vessel. When a blood clot
forms in the large, deep veins of the upper thigh, its
called deep vein thrombosis. If such a clot breaks free, it
can circulate through the bloodstream, pass through
the heart and become lodged in arteries in the lung,
causing a pulmonary embolism. Such a blockage can
severely damage portions of the lungs, and multiple
embolisms can even be fatal.

Science Photo Library

Blood and healing

Think of blood as the bodys
emergency response team to an
injury. Platelets emit signals that
encourage blood vessels to
contract, stemming blood loss.
The platelets then collect around
the wound, reacting with a
protein in plasma to form brin, a
tissue that weaves into a mesh.
Blood ow returns and white
blood cells begin their hunt for
bacteria. Fibroblasts create beds
of fresh collagen and capillaries
to fuel skin cell growth. The scab
begins to contract, pulling the
growing skin cells closer together
until damaged tissue is replaced.

More than a one-trick pony, your blood

is a vital cog in the healing process

STAGE 1

STAGE 2

STAGE 3

STAGE 4

INJURY

HAEMOSTASIS

INFLAMMATORY STAGE

PROLIFERATIVE STAGE

When the skin surface is cut, torn

or scraped deeply enough, blood
seeps from broken blood vessels to
fill the wound. To stem the flow of
bleeding, the blood vessels around
the wound constrict.

Activated platelets aggregate

around the surface of the wound,
stimulating vasoconstriction.
Platelets react with a protein in
plasma to form fibrin, a web-like
mesh of stringy tissue.

Once the wound is capped with a

drying clot, blood vessels open up
again, releasing plasma and white
blood cells into the damaged
tissue. Macrophages digest
harmful bacteria and dead cells.

Fibroblasts lay fresh layers of

collagen inside the wound and
capillaries begin to supply blood
for the forming of new skin cells.
Fibrin strands and collagen pull
the sides of the wound together.

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BODY AT WORK

Controlling the human body

Hormones

Hypothalamus
Releases hormones to the
pituitary gland to promote
its production and
secretion of hormones to
the rest of the body.

How the human endocrine system

develops and controls the human body
The glands in the endocrine system
use chemicals called hormones to
communicate with and control the
cells and organs in our bodies.
They are ductless glands that secrete different
types of hormone directly into the bloodstream
and target specic organs.
The target organs contain hormone
receptors that respond to the chemical
instructions supplied by the hormone. There
are 50 different types of hormone in the body
and they consist of three basic types: peptides,
amines and steroids.
Steroids include the testosterone hormone.
This is secreted by the cortex of the adrenal
gland, the male and female reproductive
organs and by the placenta in pregnant

women. The majority of hormones are peptides

that consist of short chains of amino acids.
They are secreted by the pituitary and
parathyroid glands. Amine hormones are
secreted by the thyroid and adrenal medulla
and are related to the ght or ight response.
The changes that are caused by the
endocrine system act more slowly than the
nervous system as they regulate growth,
moods, metabolism, reproductive processes
and a relatively constant stable internal
environment for the body (homeostasis). The
pituitary, thyroid and adrenal glands combine
to form the major elements of the bodys
endocrine system along with various other
elements such as the male testes, the female
ovaries and the pancreas.

Pituitary gland
Releases hormones to
the male and female
reproductive organs
and to the adrenal
glands. Stimulates
growth in childhood and
maintains adult bone
and muscle mass.

Pineal gland
Secretes melatonin, which
controls sleep patterns and
controls the production of
hormones related to the
reproductive organs.

Amine hormones are secreted by the

thyroid and adrenal medulla

Medulla
Cortex

Is part of the immune

system. It produces
thymosins that control
the behaviour of white
blood T-cells.

Thymus

Image

We have two adrenal glands that are positioned on top of both

kidneys. The triangular-shaped glands each consist of a twocentimetre thick outer cortex that produces steroid hormones,
which include testosterone, cortisol and aldosterone.
The ellipsoid shaped, inner part of the gland is known as the
medulla, which produces noradrenaline and adrenaline. These
hormones increase the heart rate, and the bodys levels of oxygen
and glucose while reducing non-essential body functions.
The adrenal gland is known as the ght or ight gland as it
controls how we respond to stressful situations, and prepares the
body for the demands of either ghting or running away as fast as
you can. Prolonged stress over-loads this gland and causes illness.

DK

Adrenal gland

The
endocrine
system

Adrenal glands
Controls the burning of
protein and fat, and
regulates blood pressure.
The medulla secretes
adrenaline to stimulate the
fight or flight response.

Kidney

Male testes
These two glands produce
testosterone that is
responsible for sperm
production, muscle and
bone mass and sex drive.

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DID YOU KNOW? When you are excited the hypothalamus and pituitary gland release opiate-like endorphins

Hypothalamus

Pituitary gland

Hypothalamus
neurons

The pea-sized pituitary gland is a major

endocrine gland that works under the
control of the hypothalamus. The two
organs inside the brain work in concert and
mediate feedback loops in the endocrine
system to maintain control and stability
within the body.
The pituitary gland features an anterior
(front) lobe and a posterior (rear) lobe. The
anterior lobe secretes growth hormones
that stimulate the development of the
muscles and bones; it also stimulates the
development of ovarian follicles in the
female ovary. In males, it stimulates the

These synthesise and

send hormones to the
posterior lobe.

Portal veins
Hormones from the
hypothalamus are
carried to the
anterior lobe
through these veins.

Anterior lobe
Posterior lobe

Thyroid and parathyroids

Parathyroid
Works in combination
with the thyroid to
control levels of calcium.

Thyroid cartilage
(Adams apple)

The two lobes of the thyroid sit on each side of the

windpipe and are linked together by the isthmus that
runs in front of the windpipe. It stimulates the amount
of body oxygen and energy consumption, thereby
keeping the metabolic rate of the body at the current
levels to keep you healthy and active.
The hypothalamus and the anterior pituitary gland
are in overall control of the thyroid and they respond to
changes in the body by either suppressing or increasing
thyroid stimulating hormones. Overactive thyroids
cause excessive sweating, weight loss and sensitivity to
heat, whereas underactive thyroids cause sensitivity to
hot and cold, baldness and weight gain. The thyroid can
swell during puberty and pregnancy or due to viral
infections or lack of iodine in a persons diet.
The four small parathyroids regulate the calcium
levels in the body; it releases hormones when calcium
levels are low. If the level of calcium is too high the
thyroid releases calcitonin to reduce it. Therefore, the
thyroid and parathyroids work in tandem.

Thyroid
Important for maintaining
the metabolism of the
body. It releases T3 and
T4 hormones to control
the breakdown of food
and store it, or release it
as energy.

production of sperm cells. The posterior

lobe stores vasopressin and oxytocin that
is supplied by the hypothalamus.
Vasopressin allows the retention of water in
the kidneys and suppresses the need to
excrete urine. It also raises blood pressure
by contracting the blood vessels in the heart
and lungs.
Oxytocin inuences the dilation of the
cervix before giving birth and the
contraction of the uterus after birth. The
lactation of the mammary glands are
stimulated by oxytocin when mothers begin
to breastfeed.

FRONT

REAR

Right
lobe
Left
lobe
Isthmus

Trachea
(windpipe)
Parathyroids

Pancreas
Maintains healthy
blood sugar levels in
the blood stream.

Female ovaries
Are stimulated by
hormones from the
pituitary gland and
control the
menstrual cycle.

Pancreatic cells

Islets of
Langerhans

The pancreas is positioned in the abdominal cavity above the small

intestine. It consists of two types of cell, the exocrine cells that do not
secrete their output into the bloodstream but the endocrine cells do.
The endocrine cells are contained in clusters called the islets of
Langerhans. They number approximately 1 million cells and
are only one or two per cent of the total number of cells in
the pancreas. There are four types of endocrine cells in
the pancreas. The beta cells secrete insulin and the
alpha cells secrete glucagon, both of which
stimulate the production of blood sugar (glucose)
in the body. If the Beta cells die or are destroyed
it causes type 1 diabetes, which is fatal unless
treated with insulin injections.
The other two cells are the gamma and
delta cells. The former reduces appetite
and the latter reduces the absorption of food
in the intestine.

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Red blood
cells

Acinar cells
These secrete
digestive enzymes
to the intestine.

Duct cells
Secrete bicarbonate
to the intestine.

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BODY AT WORK

Tracheotomies

Tracheotomy surgery
Discover the science and tech behind this life-saving procedure
If the upper airway is blocked, by
trauma, cancer or inammation, an
alternative route must be found for
air to enter the lungs.
Planned tracheotomies are performed under
general anaesthesia or sedation. The neck is
extended backwards to allow the surgeon to
easily identify the structures in the throat and
to make an accurate incision (see diagram).
First, a vertical cut is made in the skin, below
the tracheal cartilage, and the underlying
muscle and blood vessels are carefully moved
out of the way to expose the trachea.
The trachea is normally held open by
C-shaped rings of cartilage, which prevent the
airway from collapsing. A hole is made between
the third and fourth rings, allowing the surgeon
access to the airway without disrupting the
cartilage supports. A tracheotomy tube is then
inserted into the airway and secured to the
neck. If the tracheal opening is going to be a
permanent feature rather than temporary then
a piece of cartilage may be removed to allow the
tube to sit more comfortably.
The vocal cords sit just behind the tracheal
cartilage, above the tracheotomy incision site,
but in order to talk, air must be able to pass
through the vocal cords to make them vibrate.
Some tracheotomy tubes contain unidirectional
valves, enabling the patient to breathe in
through the tube and out through their mouth,
which provides good air supply to the lungs,
without hampering speech.
If the patient is unable to breathe unaided, a
ventilator may be attached to mechanically
move air in and out of the lungs.

Anatomy of a tracheotomy
The trachea is surrounded by a mineeld of major
blood vessels, nerves, glands and muscles

Thyroid cartilage
Larynx
The vocal cords sit
behind the thyroid
cartilage, above the
point of the incision.

The surgeon uses the

prominent Adams apple as
a marker to locate the best
incision site on the neck.

Oesophagus
The oesophagus lies
behind the trachea, so the
surgeon must take care
not to puncture through
from one to the other.

Cartilage ring

Trachea

The trachea is held open

by stiff C-shaped rings
made of cartilage.

The trachea connects the

lungs to the mouth and
nose; a tracheotomy
bypasses them to grant
direct access to the lungs.

Carotid artery
Large arteries supplying blood
to the brain and face run up
either side of the trachea.

Stoma
A temporary or
permanent tube is
inserted into the
trachea through an
incision between the
rings of cartilage.

Thyroid
The thyroid gland,
responsible for making
numerous hormones,
sits just beneath the
tracheotomy site.

Have you got a pen?

128

Flanges
The outer portion of
the tube has flanged
edges, which means it
can be securely taped
to the neck.

Corbis

A tracheotomy is a complex procedure, so in

life-threatening, emergency situations a faster
procedure known as a cricothyrotomy (also
called cricothyroidotomy) may be performed.
A higher incision is made just below the thyroid
cartilage (Adams apple) and then through the
cricothyroid membrane, directly into the trachea.
It is possible to perform this procedure with a
sharp instrument and any hollow tube, such as a
straw or a ballpoint pen case. However, nding
the correct location to make the incision is
challenging, and without medical training there
is great risk of damaging major blood vessels,
the oesophagus or the vocal cords.

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STRANGE
BUT TRUE

Where did hay fever get

its name?

MISLEADING NAME

A Hay allergy B Harvesting C Doctors name

Answer:
The term hay fever has nothing to do with hay, and
everything to do with trees, grasses and ragweed.
The name came about because symptoms would
strike during hay-harvesting season, when these
pollens would be rife.

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DID YOU KNOW? Allergic diseases, including asthma, are the fifth most common chronic disease in all ages

When hay fever attacks

When summer strikes, why do some of us suffer?
We trample on lawns and mow them
down, but eventually grass gets
revenge. Its pollen causes many of us to
suffer from hay fever, and so do trees,
weeds and even some fruit.
Despite being smaller than the tip of a pin,
pollen is carried by the wind and lodges in the
nasal lining tissues and throat, where it can cause
an allergic reaction. This is when the body
mistakenly thinks it has been invaded by a threat,
such as a virus.
To ght back, the body produces a type of
antibody known as immunoglobulin E (IgE) in
response to the allergen, causing nasal passages to
become inamed, producing more mucus. This is
designed to help ush out the allergens but can

lead to other symptoms such as headaches or

coughing caused by mucus dripping down the
back of the throat from the nose.
People genetically predisposed to hay fever are
called atopics. Hay fever usually develops during
childhood or teenage years, but adults can get it
too. This is likely to follow repeated contact with a
substance that your immune system perceives as a
threat. No one knows for sure why hay fever starts
affecting someone at the point in time it does.
Hay-fever sufferers are in trouble when the
pollen count reaches 50 pollen grains per cubic
metre of air. Youll experience it worse in the
morning when plants release their pollen.
Allergens collect in the air on humid days and
during storms, but rain clears the pollen.

Pollen forecast

Why do we get a runny nose?

Allergy in numbers
15%: Of UK population get
hay fever
40%: Risk if one parent suffers
80%: Risk if both parents suffer

95 per cent of hay-fever sufferers are

allergic to grass pollen. Close
windows on dry, windy days.

TREE POLLEN (MARCH-MAY)

Affects 25 per cent of sufferers and
instigators include ash, birch, beech,
willow and oak. Cut back branches in
the garden to reduce pollen.

WEED POLLEN (SUMMER EARLY AUTUMN)

In the USA, ragweed is the biggest
culprit. One plant can spew out
millions of pollen grains daily.

Too much histamine

Histamine irritates the upper
respiratory passages, making
them swell and produce the
typical hay fever symptoms.
Histamine makes your mucus
membranes work over time,
producing enough mucus to
ush the pollen out.

An inside look at how pollen can

affect us

The statistics

GRASS POLLEN
(MAY-JULY)

Airborne pollen
Fine dusty pollen is carried
by the wind and inhaled
through the nasal passage.
People with a genetic
disposition to hay fever,
known as atopics, will have
an allergic reaction.

95%: Of hay-fever sufferers are

allergic to grass pollen
1 in 5: Affected by hay fever

Antibodies

21 million: UK adults suffer

from one or more
type of allergy

The pollen protein triggers

your immune system,
which creates thousands
of antibodies. The
antibodies attach
themselves to mast cells,
which release histamine
a substance the body
produces to ght infection.

Protein problem
Proteins on the surface of the
pollen grain irritate and
iname the cells that line your
mouth, nose, eyes and throat.
The bodys immune system
treats the pollen like a virus
and takes action to expel it.

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BODY AT WORK

The sensory system

Ears feed sounds to
the brain but also
control balance

9,000 taste
buds over the
tongue and
throat

About 100 million

photoreceptors per eye

We can process
over 10,000
different smells

Touch is the first

sense to develop
in the womb

Exploring the
sensory system
The complex senses of the human body and how they interact is vital to
the way we live day to day

The sensory system is what enables us

to experience the world. It can also
warn us of danger, trigger memories
and protect us from damaging stimuli,
such as hot surfaces. The sensory system is highly
developed, with many components detecting both
physical and emotional properties of the
environment. For example, it can interpret
chemical molecules in the air into smells, moving
molecules of sound into noises and pressure
placed on the skin into touch. Indeed, some of our
senses are so nely tuned they allow reactions
within milliseconds of detecting a new sensation.
The ve classic senses are sight, hearing, smell,
taste and touch. We need senses not only to
interpret the world around us, but also to function
within it. Our senses enable us to modify our
movements and thoughts, and sometimes they
directly feed signals into muscles. The sensory
nervous system that lies behind this is made up of
receptors, nerves and dedicated parts of the brain.

130

There are thousands of different stimuli that can

trigger our senses, including light, heat, chemicals
in food and pressure. These stimulus modalities
are then detected by specialised receptors, which
convert them into sensations such as hot and cold,
tastes, images and touch. The incredible receptors
like the eyes, ears, nose, tongue and skin have
adapted over time to work seamlessly together
and without having to be actively switched on.
However, sometimes the sensory system can go
wrong. There are hundreds of diseases of the
senses, which can have both minor effects, or a
life-changing impact. For example, a blocked ear
can affect your balance, or a cold your ability to
smell but these things dont last for long.
In contrast, say, after a car accident severing the
spinal cord, the damage can be permanent. There
are some very specic problems that the sensory
system can bring as well. After an amputation, the
brain can still detect signals from the nerves that
used to connect to the lost limb. These sensations

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can cause excruciating pain; this particular

condition is known as phantom limb syndrome.
However the sensory system is able to adapt to
change, with the loss of one often leading to others
being heightened. Our senses normally function to
gently inhibit each other in order to moderate
individual sensations. The loss of sight from
blindness is thought to lead to strengthening of
signals from the ears, nose and tongue. Having
said this, its certainly not universal among the
blind, being more common in people who have
been blind since a young age or from birth.
Similarly, some people who listen to music like to
close their eyes, as they claim the loss of visual
input can enhance the audio experience.
Although the human sensory system is well
developed, many animals out-perform us. For
example, dogs can hear much higher-pitched
sounds, while sharks have a far better sense of
smell in fact, they can sniff out a single drop of
blood in a million drops of water!

STRANGE
BUT TRUE

Which creatures can have

up to a hundred eyes?

SIGHT TO BEHOLD

A Scallops B Spiders C Peacocks

Answer:
Scallops are an underwater mollusc that
amazingly can have as many as 100 eyes!
Although they cant create as clear a picture as
our eyes, they can detect enough light and
movement to warn them of oncoming predators.

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DID YOU KNOW? Taste and smell are closely linked. To test this, pinch your nose as you eat something and it will taste bland

Bodys messengers
The sensory system is formed from neurons. These are
specialised nerve cells which transmit signals from one
end to the other for example, from your skin to your
brain. They are excitable, meaning that when
stimulated to a certain electrical/chemical threshold
they will re a signal. There are many different types,
and they can interconnect to affect each others signals.

Retinal neuron

Olfactory neuron

These retinal bipolar cells are found in

the eye, transmitting light signals from
the rods and cones (where light is
detected) to the ganglion cells, which
send impulses into the brain.

The many fine dendritic arms

of the olfactory cell line the
inner surface of the nasal
cavity and detect thousands of
different smells, or odorants.

Purkinje cell
These are the largest neurons
in the brain and their many
dendritic arms form multiple
connections. They can both
excite and inhibit movement.

Motor neuron
These fire impulses
from the brain to the bodys
muscles, causing contraction
and thus movement. They
have lots of extensions (ie
they are multipolar) to
spread the message rapidly.

Unipolar neuron

Anaxonic neuron
Found within the retina of
the eye, these cells lack an
axon (nerve fibre) and
allow rapid modification of
light signals to and from
bipolar cells.

Pyramidal neuron
These neurons have a
triangular cell body, and
were thus named after
pyramids. They help
to connect motor
neurons together.

These sensory neurons

transduce a physical
stimulus (for example, when
you are touched) into an
electrical impulse.

How do we smell?

Olfactory nerve

Find out how our nose

and brain work together
to distinguish scents

New signals are rapidly

transmitted via the
olfactory nerve to the brain,
which collates the data
with sight and taste.

Olfactory bulb
Containing many types of
cell, olfactory neurons
branch out of here through
the cribriform plate below.

Olfactory neuron
These neurons are highly
adapted to detect a wide
range of different odours.

Cribriform plate
A bony layer of the skull
with many tiny holes,
which allow the fibres of
the olfactory nerves to
pass from nose to brain.

Olfactory
epithelium
Lining the nasal cavity,
this layer contains the
long extensions of the
olfactory neurons and is
where chemical
molecules in air trigger
an electric impulse.

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Total recall
Have you ever smelt something that
transported you back in time? This is known
as the Madeleine effect because the writer
Marcel Proust once described how the scent
of a madeleine cake suddenly evoked strong
memories and emotions from his childhood.
The opposite type of recall is voluntary
memory, where you actively try and
remember a certain event. Involuntary
memories are intertwined with emotion and
so are often the more intense of the two.
Younger children under the age of ten have
stronger involuntary memory capabilities
than older people, which is why these
memories thrust you back to childhood. Older
children use voluntary memory more often,
eg when revising for exams.

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BODY AT WORK

The sensory system

Key nerves
These transmit vital sensory
information to our brain while also
sending motor function signals all
around the body
Olfactory nerve
Starting in the nose, this nerve
converts chemical molecules
into electrical signals that are
interpreted as distinct odours
via chemoreceptors.

Understanding
lightning reexes

Optic nerve
The optic nerves convert light signals
into electrical impulses, which are
interpreted in the occipital lobe at the
back of the brain. The resulting image
is seen upside down and back to front,
but the brain reorients the image.

Have you ever felt something scorching hot or

freezing cold, and pulled your hand away without
even thinking about it? This reaction is a reex.
Your reexes are the most vital and fastest of all
your senses. They are carried out by the many
reex arcs located throughout the body.
For example, a temperature-detecting nerve in
your nger connects to a motor nerve in your
spine, which travels straight to your biceps,
creating a circular arc of nerves. By only having
two nerves in the circuit, the speed of the reex
is as fast as possible. A third nerve transmits the
sensation to the brain, so you know whats
happened, but this nerve doesnt interfere with
the arc; its for your information only. There are
other reex arcs located within your joints, so
that, say, if your knee gives way or you suddenly
lose balance, you can compensate quickly.

1. Touch receptor
When a touch receptor is
activated, information about the
stimulus is sent to the spinal cord.
Reflex actions, which dont
involve the brain, produce rapid
reactions to dangerous stimuli.

Eye movements

Trigeminal nerve

The trochlear, abducent

and oculomotor nerves
control the eye muscles
and so the direction in
which we look.

This nerve is an example of a

mechanoreceptor, as it fires when
your face is touched. It is split into
three parts, covering the top, middle
and bottom thirds of your face.

Facial and
trigeminal motors
The motor parts of these
nerves control the muscles of
facial expression (for
example, when you smile),
and the muscles of the
jaw to help you chew.

2. Signal sent
to spine

3. Motor neurons
feed back

When sensory nerve

endings fire,
information passes
through nerve fibres
to the spinal cord.

The signals trigger motor

neurons that initiate their
own impulses that feed back
to the muscle, telling it to
move the body part.

132

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5 TOP
FACTS
HUMAN SENSES

A matter of taste

There are about 9,000 taste

buds on the tongue and throat.
These convert chemicals found
in saliva into electrical signals,
split into five tastes: sweet, salt,
sour, bitter and umami.

Smell vs sight

Sensitive skin

Odours offer better memory

recall than visual cues, as smell
is tied to emotion. Looking at
an old photograph can trigger
memory, but a smell can evoke
how you felt at the time.

Human skin contains over half

a million sensory receptors.
These are of the highest
concentration in the fingertips,
the ends of the toes and lips,
where theyre most needed.

Upside down

Staying steady

The images formed in the

occipital cortex are upside
down, before the brain flips
them. However babies start
by seeing upside down, until
the brain learns to adapt.

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Ears do more than detect

sound. The fluid and fine hairs
in the inner ear maintain
balance. If you spin round and
stop, this fluid is still moving
which is why we get dizzy.

DID YOU KNOW? The three smallest bones in the human body the hammer, anvil and stirrup are located in the middle ear

Intermediate nerve
This is a small part of the larger
facial nerve. It provides the key
sensation to the forward part of
the tongue to help during eating.

Crossed senses
Vestibulocochlear
nerve
This nerve provides
sensation to the inner part
of the ear.

Glossopharyngeal motor
The motor part of this nerve controls
the pharynx, helping us
to speak and breathe normally.

Synaesthesia is a fascinating, if yet completely

understood, condition. In some people, two or
more of the ve senses become completely
linked so when a single sensation is triggered, all
the linked sensations are activated too. For
example, the letter A might always appear red,
or seeing the number 1 might trigger the taste
of apples. Sights take on smells, a conversation
can take on tastes and music can feel textured.
People with synaesthesia certainly dont
consider it to be a disorder or a disease. In fact,
many do not think what they sense is unusual,
and they couldnt imagine living without it. It
often runs in families and may be more common
than we think. More information about the
condition is available from the UK Synaesthesia
Association (www.uksynaesthesia.com).
5 5
5
5 5
5 5
5
5
5 5

5
5
5 5
5
5 5
5
5 5
2
5
5 5 5
2 5
5 5
2 2
5
5
5
5
5

5
5
2 5
5
5
5
2
2
5 2 2 2
5

Non-synaesthetes
struggle to identify a
triangle of 2s among a
eld of number 5s.

5
5
2
2
5

But a synaesthete who

sees 2s as red and 5s
as green can quickly
pick out the triangle.

A patients sense of
proprioception is being put
to the test here

Vagus nerve
The vagus nerve is spread all
around the body. It is a mixed
sensory and motor nerve, and
is responsible for controlling all
of the functions we dont think
about like our heartbeat.

Vagus motor
This portion of the vagus
nerve can slow the
heartbeat and breathing
rate, or increase the
speed of digestion.

Accessory nerve
The hypoglossal nerve
This nerve controls the
movements of the tongue.

Connecting the muscles of the neck

to the brain, this nerve lets us turn
our heads from side to side.

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Our sense of balance and the position of our

bodies in space are sensations we rarely think
about and so are sometimes thought of as a
sixth sense. There is a whole science behind
them though, and they are collectively called
proprioception. There are nerves located
throughout the musculoskeletal system (for
example, within your muscles, tendons,
ligaments and joints) whose job it is to send
information on balance and posture back to the
brain. The brain then interprets this information
rapidly and sends instructions back to the
muscles to allow for ne adjustments in balance.
Since you dont have to think about it and you
cant switch it off, you dont know how vital
these systems are until theyre damaged. Sadly
some medical conditions, including strokes, can
affect our sense of proprioception, making it
difcult to stand, walk, talk and move our limbs.

133

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Is there really a
sixth sense?

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BODY AT WORK

Chickenpox

Understanding
chickenpox
Discover the biology behind the infamous childhood
ailment and why it never really goes away
Chickenpox is a strain of the
Varicella zoster virus, which many
of us have experienced during our
youth. Most prominent in children,
the virus is contracted through coughing and
sneezing or transferred on shared objects,
which makes schools a prime location.
The most famous symptom is the appearance
of small itchy red spots, which vary in size from
10-20 millimetres (0.4-0.8 inches) across. The
extent can vary but in most cases they cover the

face, arms, legs, stomach and back. These

develop into uid-lled blisters and are often
accompanied by a fever. The blisters burst, scab
over and fall off within a few days, but new
waves of spots can emerge to replace them; it
usually takes one to two weeks for the body to
regain control. Chickenpox is rarely serious but
it is important not to interfere with the scabs as
infection can make it more severe.
A vaccine is only offered in extreme
circumstances when an individual may have a

weak immune system or be particularly

vulnerable to the disease.
After the outbreak, chickenpox doesnt
disappear entirely. The disease lies in a
dormant state within the body as your immune
system keeps it under wraps. The infection can
break out again later and reappear as shingles.
A rash builds up on a certain point of the body
and the symptoms return, most commonly in
people over 50. On average, three in every 1,000
people contract shingles in the UK each year.

When chickenpox strikes back

Grown-up
chickenpox

Get under the skin to see how shingles can catch the body unawares

Blisters emerge
Start of the illness

Blisters become visible and

The virus inltrates the

inamed rashes appear on

skin and causes

all affected areas.

inammation and a
burning sensation.

Dont scratch!
The blisters then
harden into scabs and
fall off. Scratching at
the spots makes the

Low immunity

healing process slower.

The Varicella virus

becomes active
when the immune

Future effects

system is weak,

In around 10-20 per

overcoming the

cent of people who

bodys natural

have shingles, the

defences.

nerve bres become

90 per cent of adults are immune

if theyve had the disease as a
child but it still affects adults and
teenagers. If you develop
chickenpox at a later age, all the
symptoms are more severe, with
more chronic pain, headaches and
sore throats; therefore, there is
greater need for treatment, such
as pain relief and soothing creams.
The disease tends to affect
adults more dramatically as it can
now mutate into a variety of other
strains, such as shingles or, in
extreme cases, lead to
encephalitis, postherpetic
neuralgia or pneumonia. However,
the chances of this happening are
only around ten per cent.

lead to postherpetic

Once the immune system regains

neuralgia (nerve pain).

Deaths from chickenpox

control, the virus retreats and lies

have reduced dramatically

dormant in the bodys nervous

in the last 25 years

system, but it can return later.

134

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Alamy; Thinkstock

damaged which can

Dormancy

5 TOP
FACTS

Runny noses

Hush, little baby

Onion weeping

Crocodile tears

Darwins discovery

CRYING

If you find that your nose runs a

lot when you cry, it is because
excess tears are running from
your eyes, down your tear ducts
and into your nose, causing
those tearful sniffles.

Babies typically cry for about

one to three hours per day. This
can be for a variety of reasons,
because theyre hungry, thirsty,
tired, scared or have just been to
the toilet.

Syn-propanethial-S-oxide is
created by an enzyme in a cut
onion. When it evaporates, this
compound irritates our lacrimal
glands and tears are triggered in
order to dilute it.

While crocodiles are known for

looking teary as they eat food
theyve just caught, they arent
sad. The tears merely lubricate
their eyes when they spend time
out of the water.

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There is a condition called the

PseudoBulbar Affect (PBA) in
which people cry or laugh
uncontrollably. First described by
Charles Darwin it is often the result
of brain injuries.

DID YOU KNOW? The average person will produce 140-280g (5-10oz) of basal tears per day to keep the eyes moist

Why do we cry?
Find out how our tears have been helping to
protect us since the dawn of time
brought about whether through
happiness, sadness or pain the
brains cerebrum is aware that you
are undergoing a strong emotional
reaction to a stimulus. The
endocrine system releases a set of
hormones to the lacrimal gland,
which secretes liquid onto the eye.
Excess water can escapes down
the nose, via the tear ducts.
Studies of tears have shown
there is a biochemical reason
for emotional crying. While
reex tears are 98 per cent
water, emotional tears contain
several chemicals, including
adrenocorticotropic hormones
present in times of stress, and leucineenkephalin an endorphin that releases pain
and improves your mood. Therefore, crying
appears to be a way of releasing
hormones and toxins that build
up during times of
intense emotion.

The lacrimal
system

Battle of
the sexes

1 Lacrimal gland
This gland receives the
message from the cerebrum to
produce tears.

2 Cornea
Tears help protect the surface
of the eye.

3 Tear ducts
This is where the water flows to. If
theres too much, it flows down
the face.

3
4

4 Runny nose
Tears that flow through the tear
ducts go down a nasal passage,
which is what
causes a runny nose.

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While there is a stereotype

that women are tearier
than men, there is some
science to explain the
reasons behind this. Studies
have shown that women cry
about four times as often as
men and, while there are
cultural factors to be taken
into consideration, there are
biological factors too.
Until their adolescent
years, boys and girls cry
fairly equally. As testosterone
levels rise in boys, they are
more likely to get angry
than upset. Meanwhile,
girls gain increased
oestrogen levels, which
modies endorphin
production, often leading
to more emotional responses
to stimuli.

135

SPL; Thinkstock

Whether its a sad lm, a joyous

reunion or simply that youve just
banged your knee on a coffee table,
everyone has cried at some point in
their life. But why have we evolved to do it?
Theres a theory that it stems right back as far
as our pre-evolved days, where tears streaming
down our primitive eyes and blurring our
vision was a sign of surrender, proving that we
meant our aggressor no harm.
But moving on to the present day, the science
shows that there are a number of sound
biological reasons for tearing up.
There are reex tears, the stream caused by
getting smoke or sulphenic acid from a
chopped onion into your eye. When this
happens, sensory nerves in your cornea send a
signal to the brain that the eyes need
protecting. The brain then releases hormones
into the lacrimal glands located behind the
eyelid, which produces tears to provide a layer
of protection and to water down the irritant.
However, the more common form of crying is
the emotional kind. When strong emotions are

THEWorldMags.net
BODY AT WORK

Science Photo Library

Old age explained

The ageing
process

What happens to the

human body as we age?

The whys of ageing, at its most basic

level, seem simple: over the course of
our lives, our bodies simply wear out. Or
thats what weve been led to believe,
anyway. Scientists who study gerontology, or the
process of ageing, dont yet have a denitive answer
as to why we age. There are two schools of thought.
The wear-and-tear concept meaning our cells are
used up over time that many people subscribe to is
just one example of an error theory.
Proponents of the error theory believe that
random external events cause damage that builds
up in our bodies over the course of our lifetime until

136 | How It Works

our cells can no longer function. Free radicals

unstable oxygen molecules that are a natural
by-product of cell function can build up and bond
to other cells. As a result, DNA can be damaged. They
may also result in protein cross-linking, or
glycosylation, a phenomenon by which protein
molecules in our bodies inappropriately bond
together. They arent as elastic and dont move or
break down like theyre supposed to.
Theres some evidence for this theory wrinkles,
for example, are caused by a breakdown of collagen,
a type of protein found in the skin. Protein crosslinking may also be responsible for a lot of

WorldMags.net

inrmities associated with ageing that have to do

with stiffening or hardening of tissues, such as
atherosclerosis.
Cells can also mutate on a genetic level due to
environmental or other factors. Problems with
mitochondria, structures that provide energy inside
cells, can cause cells to die as well as diseases
associated with old age such as Alzheimers disease.
Another group of theories puts forth the idea that
our life spans are predetermined or programmed.
One scenario suggests that the biological clock is
set by both our neuroendocrine system, which
produces hormones, and our immune system. The

5 TOP
FACTS

Grey hair

Wrinkles

Missing teeth

Loss of eyesight

Loss of hearing

SIGNS OF AGEING

When your hair turns grey has

a lot to do with your genetics,
but the loss of melanin
associated with grey hair is
due to older age.

The loss of skin elasticity also

ages us through the creation of
wrinkles, although in some
cases it can be prevented or at
least slowed down.

Enamel on our teeth wears

down over time and
maintaining dental hygiene
becomes more difficult,
resulting in tooth loss.

With ageing can come a number

of vision problems that can
cause a loss of sight, including
cataracts, glaucoma and
macular degeneration.

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Age-related hearing loss can

be caused by everything from
environmental factors to a
degeneration of the fine hair
cells in the cochlea.

DID YOU KNOW? The process of ageing by a living system, or organism, is known as organismal senescence

Younger

Epidermis
The skin is kept smooth by
the proteins collagen and
elastin, which break down
and lose their stretch over
time, causing wrinkles.

Shaft
The hair shaft itself is
composed of keratin, a
fibrous protein.

Each hair follicle in our heads

contains melanin a pigment that
gives our hair its colour. Over time the
melanin production decreases and
unpigmented hair begins to grow

Hair bulb
Hair root

The bulb is at the base of

the root. It contains the
follicle, which forms a
socket for the hair.

The root comprises three layers

the outer root, the inner root
and the bulb which gives hair
its structure and rigidity.

Papilla
This specialised cell is fed by
the bloodstream and is
responsible for the growth
of new hairs, and their
number of pigment cells.

Subcutaneous fat layer

As we age, the fat pads under the skin
diminish and cause skin and muscle to sag.

hypothalamus in the brain sends

messages via hormones to the pituitary
gland, which in turn stimulates or
restricts hormone secretions by the
thyroid, adrenal glands, ovaries and
even the testicles.
Over time this complex system does
not function as efciently, leading to
everything from problems sleeping to
menopause (which is a normal part of
ageing for women, but can lead to
additional health problems).
Different types of cells in the
immune system decline in number as
we age and do not function as well. Some
scientists point to the fact that the overall
risk of contracting cancers goes up as we
get older; younger, more efcient
immune systems may have been able to
fend them off.
Or it could all simply be genetic. That
is, our DNA tells our bodies when life is at
an end. There does seem to be a genetic
component to ageing among most
animals they have predictable life
spans. Women also tend to live longer
than men. If your parents lived a long
time, you are more likely to do so
yourself. One group of genes, known as
the longevity assurance gene, ha been
determined to inuence life span. If you
inherit the helpful version then you are
more likely to have a longer life.
Although our genes play a part in our
life span, obviously they can be
inuenced or changed. Otherwise, wed
still be living to the ripe old age of 30

Signs of
ageing

Older
instead of 80 (the average life span in
developed countries). Most researchers
believe that ageing is a complex process
that no single theory can explain its a
combination of our genes, our biological
functions and environmental factors.
We tend to focus more on the visible
signs of ageing at rst, like wrinkles and
grey hairs, and these changes are prime
examples of how complicated the
process can be. Weve already talked a
bit about the cause of wrinkles: the
connective tissues collagen and elastin,
that keep skin looking smooth, both
break down over time. Without the rm
connections underneath, the skin sags.
Many people lose fat deposits in their
faces, and the skins oil production
decreases. Many of these things have a
genetic component, but outside factors
such as exposure to ultraviolet radiation
and smoking both cause wrinkles and
sags faster. The Suns rays break down
connective tissues, while smoking
causes blood vessels to contract.
Grey hair is caused by a loss of
melanin, the pigment that is responsible
for our hair colour. Only recently have
scientists learned that melanin
production gets interrupted when
hydrogen peroxide levels in the body
increase over time. Other proteins found
in hair cells that are responsible for
regrowth diminish over time too. Unlike
with wrinkles, however, there isnt much
you can do to avoid going grey other than
dye your hair. Genetics do appear to play

Cortex

Science Photo Library

What looks like spots and

wrinkles is actually a number of
changes going on under the skin

Going grey

Hair colour is
determined through
the cortex, which is
part of the shaft of
visible hair.

Greying
A reduction in
melanin production
causes hair to grey.

Hair loss
A full head of hair
will thin as the
autoimmune system
attacks the follicles.

Wrinkles
These develop
as collagen and
skin cells begin
to deteriorate.

Hearing loss
Skin tone
Decreased
subcutaneous fat
and elastic tissues
cause sagging.

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The sensory hair cells in the

cochlea deteriorate,
causing age-related hearing
loss, known as presbycusis.
Gonzalo Haro

Ageing skin

Age spot
Sun damage, as well as
the ageing process in
general, can cause
clumps of melanin to
concentrate into spots.

137

THEWorldMags.net
BODY AT WORK

Old age explained

corresponding decrease in growth

factors (hormones or proteins that
stimulate cell growth). Loss of tone in
muscles such as the anal sphincter
and the bladder can cause one of the
most embarrassing signs of ageing for
many people: incontinence.
The ageing brain is still very
mysterious compared with what we
know about the rest of the human
body. It was once thought that
age-related issues such as memory
loss had to do with a decrease in
neurons. Now, however, researchers
believe that unless you have a specic
disease that damages neurons,
complex chemical processes are
more likely to blame. For example,
the brains of people with Alzheimers
disease tend to have deposits of
brous proteins called amyloids. The
exact cause remains unknown,
although one current theory is that
the amyloids manage to get into the
brain because the system that
regulates the exchange of blood in
the brain, known as the blood-brain
barrier, malfunctions.
What is arguably most fascinating
about the ageing process is that its
different for everyone and its
unpredictable in so many ways.
Thanks to the advances being made
in medicine, were learning more
every day about not only what causes
the most unpleasant signs of ageing,
but also what we can possibly do to
counteract them.

The seven
stages of man
What are the principal
stages of the visible
human ageing process
throughout our lives?

Bone
loss
A condition that affects ageing bones
Osteoporosis is a degenerative bone disease that results in lower bone density,
which makes the bones weak and fragile. The risk of falling as well as breaking
bones increases as the disease worsens. It is caused by a loss of the minerals that
make up bone, such as calcium. There is a genetic factor, and the decrease of sex
hormones in both genders increase the likelihood of developing osteoporosis.

SPL

a part, though. If your parents went

grey at a young age, it is likely that you
will too.
The internal signs of ageing are
more serious, health-wise, than the
external ones. When and how they
occur are also based on a wide
variety of factors. Some gerontologists
like to generalise that some parts of
the body get harder as we age, while
others get softer, but everything is
interconnected. As we mentioned
before, arteries get harder due to a
buildup of plaque. The heart builds
up pressure because it has to work
more to pump blood through the
harder, narrower blood vessels,
which results in high blood pressure.
Other muscles, like the lungs, get
harder due to calcium deposits.
These can be caused by hormonal
changes or from having serious
infections such as tuberculosis.
Meanwhile, hormonal changes
cause calcium to leech from the
bones, making them soft and brittle
and reducing their density. Known as
osteoporosis, this loss means that
were at a greater risk of breaking
bones. Sarcopenia, or loss of muscle
mass, is another soft sign of ageing.
Muscles contain special cells called
satellites, a form of stem cell. These
cells are responsible for muscle
growth as well as regeneration when
theres some form of damage. These
cells gradually become less procient
over time, possibly due to a

1. Healthy bone

2. Bone with osteoporosis

Healthy bones contain tight,

strong structures and are able to
easily bear body weight in
most circumstances.

Bones with osteoporosis have

gapped, porous structures. They
are fragile and can fracture easily,
as well as lead to falls.

3. Puberty

5. Adulthood

This growth spurt

indicates the start
of sexual maturity.
Girls tend to reach
puberty two years
earlier than boys.

Muscles are
developed and
strong. Organs are
fully functional.

1. Infancy
The completely
dependent infant
experiences rapid
physical growth.

138 | How It Works

2. Childhood

4. Young adulthood

Tissue, muscle and

bone then grow
gradually until puberty.

A period of increasing
physical maturity and body
development.

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6. Late adulthood
After middle age tissues
begin to deteriorate and
weaken, while hair loses
its pigmentation.

HEAD
HEAD

DRASTIC

1. Nutritional
changes

2. Hormone
therapy

MORE DRASTIC

Antioxidants such as vitamin E

and calorie-restrictive diets
have both been shown to
extend life span, but not
without potential health risks.

3. Plastic
surgery

MOST DRASTIC

The use of hormones such

as human growth hormone
to combat signs of ageing,
such as decreased muscle
mass, is very controversial.

The visible signs of ageing

can be combated
temporarily through
surgery and other
cosmetic procedures.

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WAYS TO
BEAT AGEING

DID YOU KNOW? Ageing changes can be universal (happen to most people) or probabilistic (only occur in some people)

Life expectancy
around the world

5
2

1
6

4
7
3

All of the senses decline as we age. Hearing declines

because the structures in the ear break down over
time. Damage to the auditory nerve, which relays the
signal to the brain, may also be to blame. Vision also
lessens because older eyes are less responsive,
sharp or sensitive. The eye muscles can also become
less responsive, resulting in a loss of peripheral
vision and a narrower depth of eld. Taste and smell
both decrease with age as well. The 9,000 tastebuds
with which we are born decrease over the course of
our lives. Smell may diminish due to a loss of nerve
endings in the nose. Decreased blood ow to the
areas of the brain and nervous system that receive
touch information may be responsible for a loss of
sensations like pain, cold, heat and vibration. The
brain itself gets smaller over time and chemical
processes (as well as a lack of stimulation) result in
age-related complaints such as memory loss.

Science Photo Libra

ry

A more elderly
appearance results
from wrinkles, hair
loss and decreased
muscle tone.

Asia has nearly every range of life

expectancy within its borders.

2. North America
Canadians have a slightly higher
life expectancy than Americans.

Japan is the Asian country with

the highest average life
expectancy on the continent.

3. South America

7. Indonesia

The largest country has one of

the lowest life expectancies.

Indonesia is roughly on a par

with much of Asia.

4. Africa

8. Australia and
New Zealand

6. Japan

These industrialised countries

have an 80+ life expectancy.

Cataracts
1. Normal lens
In a person with a normal
lens, light from an image
passes through the lens and
is projected onto the tissue at
the back of the eye called the
retina. The retina changes
the image to a nerve signal
and transmits it to the brain,
where it is processed.

2. Lens with
cataract
If protein clumps onto the
lens (due to wear and tear or
diseases like diabetes), it can
create a cloudy area known
as a cataract. Light is
diffused through the lens to
the retina, resulting in a
blurry image.

Science Photo Library

The senses

7. Old age

5. Asia

Much of Europe enjoys a

healthy life expectancy of more
than 72 years.

Most of Africa, being

undeveloped, has much lower
life expectancy.

Slowing down the

ageing process
Although ageing itself is inevitable (at least currently),
theres a lot that we can do to slow down the ageing
process. Visible signs of ageing like wrinkles can be
diminished by avoiding Sun exposure and other risk
factors like smoking. Internal signs of ageing can all be
combated to some extent by lifestyle changes. Weightbearing exercises such as weight-lifting, for example,
have been shown to help maintain bone density and
stave off osteoporosis. Aerobic exercise like walking or
cycling can prevent weight gain which leads to
numerous diseases and conditions that age us as well
as improve cardiovascular health. Diet also plays a part
in ageing a balanced one can not only reduce the risk of
diseases like type two diabetes but also keep our
immune systems operating at their peak for longer.
Some researchers treat ageing like a disease. To that
end, stem-cell treatments and even cryogenics are
looked to as a potential cure. But at what cost? Others
feel that we werent meant to live forever and should
focus on ways to age comfortably.

SPL

80+
77.5-80
75-77.5
72.5-75
70-72.5
67.5-70
65-67.5
60-65
55-60
50-55
45-50
40-45
0-40

1. Europe

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There are a number of

ways to slow down
the ageing process

139

WorldMags.net
CURIOUS
QUESTIONS

168
What do
alveoli do?

151
Powering
cells

144
173

Brain freeze
explained

Alamy

SPL

145
What makes
your nose run?

Thinkstock

How do we
know how
much to
eat?

142 Left or right brained?

The truth behind thinking

150 72-hour deodorant /

Modern llings
How do we combat body odour?

144 Brain freeze

Why do we feel this cold pain?

151

145 Runny nose /Coma

What makes your nose run?
146 Sore throat / Ears pop /
Freckles
Why do your ears pop?
147 Memory / Toothpaste /
Epidurals
What is a memory?
148 Blushing / Caffeine / Fainting
The telltale signs of blushing
149 Eyebrows / Earwax / Self
Do we need eyebrows?
140

What powers your cells?

Inside the mitochondria

152 Can we see thoughts?

Is this science or a myth?
154 How anaesthesia works
The drug that stops pain signals
155

Stomach ulcers /
Mouth ulcers
How do ulcers form?

156 Enzymes / Love

Love as a chemical reaction
157

Correcting heart rhythms /

Salt / Adams apple
Is salt bad for your heart?

WorldMags.net

158 Seasickness /
Rumbling stomachs
Explaining seasickness
159 Cravings
Why do we crave avours?
160 Feet smell / Knee-jerk
reaction
What makes feet smell?
161 Blisters / Cramp
What causes blisters to appear?
162 Brain control / Laughing
Do our brains control us?

WorldMags.net
160

166

The kneejerk reaction

explained

What causes
twins?

147
Understand
epidurals

162
Do our
brains
control us?

145

SPL

Why does
your nose
run?

Dandruff / Eye adjustment /

Distance the eye can see
Revealing how dandruff forms

164 Allergies / Eczema

Why do some people suffer?
165 Bruises / Water allergy /
Cholesterol
How are bruises caused?

170 Paper cuts / Pins and

needles / Funny bones
Why do paper cuts hurt so
much?
171

Aching muscles /
Fat hormone
What causes muscle ache?

172 Raw meat / Inoculations /

Upper arm and leg
Should we eat raw meat?

166 What are twins?

What causes twins to be born?

173

168 How do alveoli help

you breathe?
Inside your lungs

174 Hair growth / Blonde hair

Our hair explained

169 Migraines / Eye drops

Discover how migraines strike

175

164
Allergies explained

What causes insomnia?

Suffering sleepless nights?
Thinkstock

163

Wrinkles explained
What causes this sign of aging?

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141

CURIOUS
QUESTIONS
WorldMags.net

How we think

Left or right brained?

Actually, youre neither. Discover the truth behind the way we think
Its true that the different sides of
the brain perform different tasks,
but do these anatomical
asymmetries really dene our
personalities? Some psychologists argue that
creative, artistic individuals have a more
developed right hemisphere, while analytical,
logical people rely more heavily on the left side
of the brain, but so far, the evidence for this
two-sided split has been lacking.
In a study published in the journal PLOS ONE,
a team at the University of Utah attempted to
answer the question. They divided the brain up
into 7,000 regions and analysed the fMRI scans

of over 1,000 people, in order to determine

whether the networks on one side of the brain
were stronger than the networks on the other.
Despite the popularity of the left versus right
brain myth, the team found no difference in the
strength of the networks in each hemisphere,
or in the amount we use either side of our
brains. Instead, they showed that the brain is
more like a network of computers. Local nerves
can communicate more efciently than distant
ones, so instead of sending every signal across
from one hemisphere of the brain to the other,
neurones that need to be in constant
communication tend to develop into organised

Examining the human brain

What do the different parts of the brain
actually do?
Brocas area
(speech)

Parietal lobe
(pressure, taste)
The parietal lobes handle
sensory information and
are involved in spatial
awareness and navigation.

local hubs, each responsible for a different

set of functions.
Hubs with related functions cluster
together, preferentially developing on the
same side of the brain, and allowing the nerves
to communicate rapidly on a local scale. One
example is language processing in most
people, the regions of the brain involved in
speech, communication and verbal reasoning
are all located on the left-hand side.
Some areas of the brain are less symmetrical
than others, but both hemispheres are used
relatively equally. There is nothing to say you
cant be a brilliant scientist and a great artist.

Occipital lobe
(vision)
Incoming information
from the eyes is
processed at the
back of the brain in
the visual cortex.

Brocas area is responsible

for the ability to speak and
is almost always found on
the left side of the brain.

Frontal lobe
(planning,
problem solving)
At the front of each
hemisphere is a frontal
lobe, the left side is more
heavily involved in speech
and verbal reasoning,
while the right side
handles attention.

Auditory cortex
(hearing)
The auditory cortex is
responsible for processing
information from the ears
and can be found on both
sides of the brain, in the
temporal lobes.

Temporal lobe
(hearing, facial
recognition, memory)

Wernickes area
(speech
processing)

The temporal lobes are

involved in language
processing and visual memory.

142

The region of the brain

responsible for speech
processing is found on
the left-hand side.

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NERVE IMPULSE SPEED

100 metres
per second

1.4kg

MASS

SYNAPSES

>100

86
trillion
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billion

BRAINY NUMBERS

NEURONS

THE
STATS

20% OXYGEN
USAGE

POWER
CONSUMPTION

20W

DID YOU KNOW? It is a myth that we only use ten per cent of our brains; even at rest, almost all brain regions are active

Give your brain a

fun workout

Boost your memory

Look at this list of items for one minute,

then cover the page and see how many you
can remember:

It took 82,944
computer processors
40 minutes to simulate
just one second of
human brain activity,
its that powerful

A microscopic image of
the brains extremely
complex neural network

Myth-taken identity
The left vs right brain personality myth is actually
based on Nobel Prize-winning science. In the
1940s, a radical treatment for epilepsy was trialled;
doctors severed the corpus callosum of a small
number of patients, effectively splitting their brains
in two. If a patient was shown an object in their
right eld of view, they had no difculty naming it,
but if they were shown the same object from the

left, they couldnt describe it. Speech and language

are processed on the left side of the brain, but the
information from the left eye is processed on the
right. The patients were unable to say what they
saw, but they could draw it. Psychologists
wondered whether the differences between the
two hemispheres could create two distinctive
personality types, left-brained and right-brained.

9e_d

Telephone

Grape

Duck

FejWje

F_bbemYWi[

Key

Teacup

Bicycle

F[dY_b

Match

Table

Difcult? Try again, but this time, make up a

story in your head, linking the objects
together in a narrative.

,
ned
pture were
u
Duck
ther ps
e
opened his teacurywher
front door
eve
to nd his
table

TO DO:

Left

Right

BANG
Planner

Impulsive

Rational

?!@#
Emotional

You get the idea. Make it as silly as you like;

strange things are much more memorable
than the mundane.

Slow brain ageing

Learning a new language is one of the

best ways to keep your brain active. Here are
four new ways to say hello:

Precise

Intuitive

Logical

Feb_i^0




9p[iY

(che-sh-ch)


Hkii_Wd0


PZhWlijlk`






pZhW^#ijleeo


7 hWX_Y0





CWh^WXW
(mar-ha-ba)


ImW^_b_0


>k`WcXe
(hud-yambo)

Corbis; Thinkstock

Creative

Problem solving

Spiritual

Dog lovers

Cat lovers

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143

CURIOUS
QUESTIONS
WorldMags.net

Brain freeze

What is brain
freeze?
That intense pain you sometimes get when
you eat ice cream too fast is technically
called sphenopalatine ganglioneuralgia,
and its related to migraine headaches
The pain of a brain freeze, also know as an ice cream headache, comes from
your bodys natural reaction to cold. When your body senses cold, it wants
to conserve heat. One of the steps it takes to accomplish this is constricting
the blood vessels near your skin. With less blood owing near your skin,
less heat is carried away from your core, keeping you nice and warm.
The same thing happens when something really cold hits the back of your mouth.
The blood vessels in your palate constrict rapidly. When the cold goes away (because
you swallowed the ice cream or cold beverage), they rapidly dilate back to their
standard, normal state.
This is harmless, but a major facial nerve called the trigeminal lies close to your
palate and this nerve interprets the constriction/dilation process as pain. The location
of the trigeminal nerve can cause the pain to seem like its coming from your forehead.
Doctors believe this same misinterpretation of blood vessel constriction/dilation is the
cause of the intense pain of a migraine headache.

A major
facial nerve
called the
trigeminal
lies close to
your palate

The Ophthalmic branch

carries sensory messages
from the eyeball, tear gland,
upper nose, upper eyelid,
forehead, and scalp.

The Mandibular branch

carries sensory signals
from the skin, teeth and
gums of the lower jaw, as
well as tongue, chin, lower
lip and skin of the
temporal region.

The Maxillary branch carries

sensory messages from the
skin, gums and teeth of the
upper jaw, cheek, upper lip,
lower nose and lower eyelid.

The trigeminal facial nerve

is positioned very close to
the palate. This nerve
interprets palate blood
vessel constriction and
dilation as pain.

144

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WorldMags.net
What makes your nose run?
Discover what is going on inside a blocked nose and why it gets runny when were ill
It surprises many people but the main
culprit responsible for a blocked and
runny nose is typically not excess
mucus but swelling and inammation.
If the nose becomes infected, or an allergic
reaction is triggered, the immune system produces
large quantities of chemical messengers that cause
the local blood vessels in the lining of the nose to
dilate. This enables more white blood cells to enter
the area, helping to combat the infection, but it also
causes the blood vessels to become leaky, allowing
uid to build up in the tissues.
Decongestant medicine contains a chemical thats
similar to adrenaline, which causes the blood
vessels to constrict, stopping them from leaking.

Goblet cell

Cilia

Mucus

Tiny hair-like
structures move
mucus towards the
back of the throat so
that it can be
swallowed.

The glycoproteins that

make up mucus dissolve in
water, forming a gel-like
substance that traps debris.
The more water, the runnier
the mucus.

Epithelial cells

The lining of the nose

has many mucusproducing goblet cells.

The nose is lined

by epithelial cells,
covered in cilia.

Connective
tissue
Beneath the cells
lining the nose is a
layer of connective
tissue that is rich
in blood vessels.

Macrophage

Blood vessels

Cells of the immune

system produce chemical
mediators like histamine,
which cause local blood
vessels to become leaky.

Inflammatory chemical signals

cause blood vessels to dilate,
allowing water to seep into the
tissues, diluting the mucus and
making it runny.

How is a person brought

out of a coma?
When we talk about bringing
someone out of a coma, we are
referencing medically induced
comas. A patient with a
traumatic brain injury is
deliberately put into a deep
state of unconsciousness in
order to reduce swelling and
allow the brain to rest. When
the brain is injured,
it becomes inamed. The
swelling damages the brain
because it is squashed inside
the skull.

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Doctors induce the coma

using a controlled dose of
drugs. To bring the person out
of the coma, they simply stop
the treatment. Bringing the
patient out of the coma doesnt
wake them immediately. They
gradually regain consciousness
over days, weeks or longer.
Some people make a full
recovery, others need
rehabilitation or lifetime care
and others may remain
unaware of their surroundings.

145

CURIOUS
QUESTIONS
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Ears popping / Sore throats / Freckles

Thinkstock

Why do our ears

pop on planes?
The eardrum is a thin membrane that helps to transmit sound. Air
pressure is exerted on both sides of the eardrum; with the
surrounding atmospheric pressure pushing it inwards while air
being delivered via a tube between the back of your nose and the
eardrum pushes it outwards. This tube is called the Eustachian tube, when
you swallow ot opens and a small bubble of air is able to move causing a pop.
Rapid altitude changes in planes make the pop much more noticeable
due to bigger differences in pressure. Air pressure decreases as a plane
ascends; hence air must exit the Eustachian tubes to equalise these pressures,
again causing a pop. Conversely, as a plane descends, the air pressure starts
to increase; therefore the Eustachian tubes must open to allow through more
air in order to equalise the pressure again, causing another pop.

What are freckles?

Freckles are clusters of the pigment melanin. It is
produced by melanocytes deep in the skin, with greater
concentrations giving rise to darker skin tones, and
hence, ethnicity. Melanin protects the skin against
harmful ultraviolet sunlight, but is also found in other locations
around the body,. Freckles are mostly genetically inherited, but not
always. They become more prominent during sunlight exposure,
as the melanocytes are triggered to increase production of melanin,
leading to a darker complexion. People with freckles generally have
pale skin tones, and if they stay in the Sun for too long they can
damage their skin cells, leading to skin cancers like melanoma.

Rapid altitude
changes make
the pop much
more noticeable

Honey and lemon can be

drank warm as a comfort
remedy when suffering
from a sore throat or cold,
and is a popular drink with many
who are feeling unwell. The idea is
that honey coats the throat and
therefore any inamed areas will be
protected by a layer of honey, while
at the same time soothing painful

146

areas. This means it will be less

painful when these areas come into
contact with other surfaces when you
eat or swallow.
Lemon also helps to settle the
stomach too, as it contains acid,
which can be particularly helpful
when experiencing an upset stomach
from the effects of a cold or other
digestion-related illness.

WorldMags.net

Thinkstock

Why does hot honey

and lemon help your
throat when its sore?

WorldMags.net
What is an epidural?
The science behind blocking pain explained

What is a
memory?
Memory is the brains
ability to recall
information from the past
and it generally falls into
three categories sensory, short-term
and long-term.
Look at this page then close your
eyes and try to remember what it
looks like. Your ability to recall what
this page looks like is an example of
your sensory memory. Depending on
whether or not this page is important
to you will be the determining factor
in how likely it is that it will get passed
on to your short-term memory.
Can you remember the last thing
you did before reading this? That is
your short-term memory and is a bit
like a temporary storage facility where
the less-important stuff can decay,
whereas the more important stuff can
end up in the long-term memory.
Our senses are constantly being
bombarded with information.
Electrical and chemical signals travel
from our eyes, ears, nose, touch and
taste receptors and the brain then
makes sense of these signals. When
we remember something, our brain
reres the same neural pathways
along which the original information
travelled. You are almost reliving the
experience by remembering it.

An epidural (meaning above

the dura) is a form of local
anaesthetic used to
completely block pain while
a patient remains conscious. It involves
the careful insertion of a ne needle
deep into an area of the spine between
two vertebrae of the lower back.
This cavity is called the epidural
space. Anaesthetic medication is
injected into this cavity to relieve pain
or numb an area of the body by reducing
sensation and blocking the nerve roots
that transmit signals to the brain.
The resulting anaesthetic medication
causes a warm feeling and numbness
leading to the area being fully
anaesthetised after about 20 minutes.
Depending on the length of the
procedure, a top-up may be required.
This form of pain relief has been used
widely for many years, particularly
post-surgery and during childbirth.

1. Epidural space
The outer part of the
spinal canal, this cavity is
typically about 7mm
(0.8in) wide in adults.

6. Processing
Anaesthetic in the blood is ltered
out by theliver and kidneys, then
leaves the body in urine. The effects
usually wear off a couple of hours
after the initial injection.

Liver
Kidney
Ureter

2. Epidural needle
After sterilising the area, a
needle is inserted into the
interspinous ligament until
there is no more
resistance to the injection
of air or saline solution.

Bladder

3. Anaesthetic
Through a ne catheter in the
needle, anaesthetic is carefully
introduced to the space
surrounding the spinal dura.

4. Absorption
5. Radicular arteries

Over about 20 minutes

the anaesthetic
medication is broken
down and absorbed into
the local fatty tissues.

The anterior and posterior radicular

arteries run with the ventral and
dorsal nerve roots, respectively,
which are blocked by the drug.

How does toothpaste for

sensitive teeth work?
Imagine just one of your teeth. It has two
primary sections: the crown located above
the gum line and the root below it. The
crown comprises the following layers from
top to bottom: enamel, dentine and the pulp gum.
Nerves branch from the root to the pulp gum. The
dentine runs to the root and contains a large number of
tubules or microscopic pores, which run from the
outside of the tooth right to the nerve in the pulp gum.
People with sensitive teeth experience pain when
their teeth are exposed to something hot, cold or when
pressure is applied. Their layer of enamel may be

thinner and they may have a receded gum line

exposing more dentine. Therefore, the enamel and
gums offer less protection and, as such, this is what
makes their teeth sensitive.
Sensitive toothpaste works by either numbing tooth
sensitivity, or by blocking the tubules in the dentine.
Those that numb usually contain potassium nitrate,
which calms the nerve of the tooth. The toothpastes
that block the tubules in the dentine usually contain a
chemical called strontium chloride. Repeated use
builds up a strong barrier by plugging the tubules more
and more.

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147

CURIOUS
QUESTIONS
WorldMags.net

Caffeine / Blushing / Fainting

Why and how

do we blush?
Blushing occurs when an excess of blood
ows into the small blood vessels just
under the surface of the skin. Facial skin
has more capillary loops and vessels, and
vessels are nearer the surface so blushing is most
visible on the cheeks, but may be seen across the
whole face. The small muscles in the vessels are
controlled by the nervous system.
Blushing can be affected by factors such as heat,
illness, medicines, alcohol, spicy foods, allergic
reactions and emotions. If you feel guilty, angry,
excited or embarrassed, you will involuntarily
release adrenaline, which sends the automatic
nervous system into overdrive. Your breathing will
increase, heart rate quicken, pupils dilate, blood will
be redirected from your digestive system to your
muscles, and you blush because your blood vessels
dilate to improve oxygen ow around the body; this
is all to prepare you for a ght or ight situation. The
psychology of blushing remains elusive; some
scientists even believe we have evolved to display
our emotions, to act as a public apology.

Red glow
Cheeks turn red while blushing
due to blood vessels being near
the skins surface.

Nervousness
Being embarrassed releases
adrenaline, which stimulates
the nervous system.

Blushing can
be affected by
heat, illness,
medicines and
spicy foods

What makes
caffeine so
addictive?

What makes
us faint?
Fainting, or syncope, is a
temporary loss of consciousness
due to a lack of oxygen to the
brain. It is preceded by dizziness,
nausea, sweating and blurred vision.
The most common cause is
overstimulation of the bodys vagus nerve.
Possible triggers of this include intense
stress and pain, standing up for long periods
or exposure to something unpleasant.
Severe coughing, exercise and even
urinating can sometimes produce a similar
response. Overstimulation of the vagus
nerve results in dilation of the bodys blood
vessels and a reduction of the heart rate.
These two changes together mean that the
body struggles to pump blood up to the
brain against gravity. A lack of blood to the
brain means there is not enough oxygen for
it to function properly and fainting occurs.

When we are awake the naturally

occurring brain chemical adenosine
is drawn to fast moving receptors in
the brain. As adenosine attaches to
the receptors it slows them down, which causes us
to feel sleepy.
The receptor cells confuse caffeine for
adenosine cells and as such willingly bond to it.
The action doesnt slow down the receptors
movement as adenosine would and as the space is
usurped they are unable to sense adenosine so the
cells speed up, increasing neuron ring in the
brain. The pituary gland interprets this as a ght
or ight scenario so releases hormones to alert the
adrenal glands to produce adrenaline. This results
in dilated pupils, a racing heart and an increase in
blood pressure. The liver also releases sugar into
the bloodstream for an instant energy boost.

148 | How It Works

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2. Instant
coffee
The level of caffeine present
in instant coffee was not
much more with an average
of 54mg of caffeine per
regular serving.

MOST CAFFEINE

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3. Ground
coffee
Ground coffee, however,
contains the most caffeine.
The mean level was 105mg,
in some cases ranging as
high as 254mg per serving.

Science Photo Library

CAFFEINATED
DRINKS

MORE CAFFEINE

1. Tea
In a survey by the
Food Standards
Agency, the mean
amount of caffeine
found in tea was
40mg per cup.

Image author: Pleple2000, 2008

SOME CAFFEINE

Image author: Naama Ym, 2005

HEAD
HEAD

Where is the self

in the brain?

What is
earwax?
Earwax is a substance that can be
found in the ear canal of humans
and other mammals. Medically it
is referred to as cerumen and
consists of dead skin, hair and water-soluble
secretions from the outer ear canal. It serves
several functions one of which is as an
antibacterial, self-cleaning lubricant. Excess
cerumen usually nds its way out of the ear
canal through the washing of hair and jaw
movement. Occasionally it can collect and get
compacted which can lead to tinnitus.

Why do we have eyebrows?

Eyebrows are very important for diverting
moisture, such as salty sweat, away from our
eyes due to their distinctive arch shape.
This would obviously be useful for
allowing us to see clearly if it was raining or if

we were sweating a lot. It is quite easy

to see how this could have had an
evolutionary advantage in terms of
escaping predators. Sweat also causes
irritation in the eyes.

Until recently, neuroscientists had thought it

fanciful to speculate about the physical substrates
of such high-level phenomena as consciousness
and the self, but recent advances in functional
neuroimaging are enabling us to make signicant in-roads into
these questions. Researchers have identied a core brain
network, the default-mode network, which accounts for much
of the brains metabolism and appears to support a background
level of consciousness, of the sort associated with daydreaming or mind-wandering. Crucially, the default-mode
network becomes especially activated during self-judgments,
as well as other high-level, species-specic behaviours such as
taking another persons point of view, or thinking outside of the
moment to contemplate the past or future. The default-mode
network decreases in activity and connectivity during states of
reduced consciousness such as sleep or anaesthesia, and is
known to exist only in a primitive form in infants and lower
primates. Using functional magnetic resonance imaging
(fMRI), we recently found that the psychedelic drug, psilocybin,
the active component of magic mushrooms, also decreases
activity and connectivity in the default-mode network in a
manner that correlates with loss of self, or ego-disintegration.

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149

CURIOUS
QUESTIONS
WorldMags.net

72-hour deodorants / Fillings

How 72-hour deodorants work

Discover the chemistry that helps us combat body odour for up to days at a time
Deodorants prevent
the odour associated
with sweating, either
by masking it, or by
killing the bacteria responsible. To
make the effects last longer, the
active ingredients are sometimes
encased within microcapsules. As
the capsules take up water from
sweat they burst, releasing
deodorising chemicals. By
including capsules of a variety of
sizes, each requiring a different
amount of water to burst, the
duration can be extended.

Most deodorants also contain

antiperspirants, which prevent
sweating from occurring at all.
These are usually aluminiumbased compounds. The aluminium
is taken up by the cells that line the
openings of the ducts that carry
sweat to the surface of the skin.
As the aluminium moves into
the cells, it takes water with it,
causing the cells to swell and
closing off the ducts. Depending on
the type of aluminium compound
used, the effect will last for
different lengths of time.

Antiperspirants
cause cells to swell
and the ducts to close
up, preventing
sweating altogether

Modern llings
Composite resins are replacing traditional
metal llings, but what are they made of?
Curing

Layering

A light is used to trigger a

chemical reaction within
the resin, causing the
material to harden.

The liquid composite resin is

applied in layers. After each
layer, the composite is cured.

Composite resin
Finishing touches
A piece of carbon paper is used
to test whether the bite lines
up properly, and the filling is
smoothed down accordingly.

Dental composites are

made from a resin matrix
that contains inorganic
materials, such as silica,
for durability.

Acid
Primer
A priming agent is brushed
onto the prepared tooth
surface to enable the filling
to adhere properly.

Decay

Traditional silver-coloured amalgam llings are

made from mixed metals, and are often
comprised of around 50 per cent mercury.
Historical evidence suggests that this type of
lling has been in use since around 650 A.D, and
despite the advances in composite materials, the
amalgam lling is still in use to this day.
There has been much controversy over the
biological safety of amalgam llings though, and
concerns have been raised regarding mercury
released into the body, as well as into the
environment. However, as it stands, no causal
link between health complaints and amalgam
llings has been proven. In fact, they still provide
some advantages over composite llings, and
require signicantly less repair and replacement.
Amalgam llings
require much less
upkeep than their
composite counterparts

A controlled amount of acid

is applied to the drilled tooth
to generate micro-holes for
the filling to bind to.

Base
In deeper fillings, a cement
base made from glass
ionomer or zinc phosphate is
added to insulate the nerve
from temperature changes.

Thinkstock; SPL

The decayed portion of the

tooth is removed using a
high-speed drill; this
generates a solid platform
for the filling to stick to.

150 | How It Works

Is metal bad?

WorldMags.net

STRANGE
BUT TRUE

Who do you inherit

mitochondria from?

INHERITED AT BIRTH

A Father B Mother C Grandparent

Answer:
The DNA within mitochondria is only from your
mothers egg. The corresponding DNA from your
fathers sperm is destroyed after fertilisation. This
means researchers can track back unchanged
maternal inheritance lines many hundreds of years.

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DID YOU KNOW? Mitochondrial disease occurs when mitochondria malfunction there is a huge variety of symptoms

What powers your cells?

Discover how mitochondria produce all the energy your body needs
maintain life - by controlling Krebs Cycle which
is the set of reactions that produce ATP.
Mitochondria are found in nearly every cell
in your body. They are found in most eukaryotic
cells, which have nucleus and other organelles
bound by a cell membrane. This means cells
without these features, such as red blood cells,
dont contain mitochondria. Their numbers
also vary based on the individual cell types,
with high-energy cells, like heart cells,
containing many thousands. Mitochondria are
vital for most life human beings, animals and
plants all have them, although bacteria dont.

Inside the mitochondria

Take a tour of the cells energy factory
ATP synthesis
ATP is the basic energy unit of the cell
and is produced by ATP synthase
enzymes on the inner membrane at its
interaction with the matrix.

Mitochondrial DNA
Mitochondria have their
own DNA and can divide to
produce copies.

They are deeply linked with evolution of all

life. It is believed mitochondria formed over a
billion years ago from two different cells, where
the larger cell enveloped the other. The outer
cell became dependent on the inner one for
energy, while the inner cell was reliant on the
outer one for protection.
This inner cell evolved to become a
mitochondrion, and the outer cells evolved to
form building blocks for larger cell structures.
This process is known as the endosymbiotic
theory, which is Ancient Greek for living
together within.

Phospholipid
bilayer
Every mitochondria has
a double-layered
surface composed of
phosphates and lipids.

Mitochondria produce
fuel for everyday
activities such as
exercise

Outer membrane
The outer membrane contains
large gateway proteins, which
control passage of substances
through the cell wall.

Inner membrane
This layer contains the
key proteins that
regulate energy
production inside the
mitochondria, including
ATP synthase.

Inter-membrane
space
This contains proteins
and ions that control
what is able to pass in
and out of the organelle
via concentration
gradients and ion pumps.

Cristae
The many folds of the
inner membrane
increase the surface
area, allowing greater
energy production for
high-activity cells.

Matrix
The mitochondrial matrix
contains the enzymes, ribosomes
and DNA, which are essential to
allowing the complex energyproducing reactions to occur.

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How many are

in a cell?
The number of mitochondria in a
cell depends on how active that
particular cell is and how much
energy it requires to function. As a
general rule, they can either be low
energy without a single
mitochondrion, or high energy with
thousands per cell. Examples of
high-energy cells are heart muscles
or the busy liver cells, which are
active even when youre asleep,
and are packed with mitochondria
to keep functioning. If you train
your muscles at the gym, those
cells will develop more
mitochondria as an adaptive
mechanism to help provide energy.

151

SPL

Mitochondria are known as the

batteries of cells because they use
food to make energy. Muscle bres
need energy for us to move and
brain cells need power to communicate with the
rest of the body. They generate energy, called
adenosine triphosphate (ATP), by combining
oxygen with food molecules like glucose.
However, mitochondria are true biological
multi-taskers, as they are also involved with
signalling between cells, cell growth and the
cell cycle. Theyperform all of these functions by
regulating metabolism - the processes that

CURIOUS
QUESTIONS
WorldMags.net

Mind reading

Is it possible
to see our
thoughts?

This CT scan of the brain has fused

PET images over it, showing activity
of different regions when the patient
is exposed to a range of stimuli

This DTI view of the

brain uses the high
water content in
neurons to show ne
structure and activity

brain. It has also led to benets for imaging

other diseases in other parts of the body,
including several forms of cancer.
These advanced imaging techniques
include scans to produce images of the
anatomical structure of the brain, and
interpretation of energy patterns to
determine activity or abnormalities.
Scientists have started to ascertain which
parts of the brain function as we form
different thoughts and experience different
emotions. This means we are very much on
the brink of seeing our own thoughts.

SPL

At its most simple level, the brain

is a series of interconnecting
neurons that relay electrical
signals between one another.
They are all or none transmitters as, like a
computer, they either transmit a signal (like a
binary 1) or do not (0). Different neurons are
receptive to different stimuli, such as light,
touch and pain. The complex activity of these
neurons is then interpreted by various parts
of the brain into useful information. For
example, light images from the eye are
relayed via the optic nerve to the occipital
cortex located in the back of the skull, for
interpretation of the scene in front of you.
The generation and interpretation of
thoughts is a more complex and less well
understood process. In fact, it is a science of its
own, where there are many denitions of
what a thought is, and of what denes
consciousness. In an effort to better dene
these, doctors, scientists and psychologists
have turned to novel imaging techniques to
better understand the function of our minds.
Research into understanding brain activity
and function has led to some of the most
advanced imaging techniques available. This
has helped to treat conditions such as
Alzheimers dementia, epilepsy and stroke,
as well as mental illnesses where there is not
necessarily a physical problem within the

SPL

The brain is perhaps the most vital of

the bodys vital organs, yet in many
ways its also the least understood

How can we view the brain?

152

Magnetic resonance
imaging (MRI)

This combines multiple X-rays

to see the bones of the skull
and soft tissue of the brain. Its
the most common scan used
after trauma, to detect injuries
to blood vessels and swelling.
However, it can only give a
snapshot of the structure so
cant capture our thoughts.

MRI uses strong magnetic

elds to align the protons in
water molecules in various
body parts. When used in
the brain, it allows intricate
anatomical detail to be
visualised. It has formed the
basis of novel techniques to
visualise thought processes.

Oliver Stollmann

Computed
tomography (CT)

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Functional MRI (fMRI)

This form of MRI uses bloodoxygen-level-dependent
(BOLD) contrast, followed by a
strong magnetic eld, to detect
tiny changes in oxygen-rich
and oxygen-poor blood. By
showing pictures to invoke
certain emotions, fMRI can
reveal which areas are active
during particular thoughts.

 Thierry Geoffroy

1. HEAD TRAUMA

2. BRAIN TUMOURS

CT scan
Fast and easily accessible
24 hours a day, these
scans can identify
life-threatening bleeding
within the skull for
neurosurgeons to stop.

Marvin 101

HEAD
HEAD

3. ALZHEIMERS

3D MRI
These 3D scans show intricate
anatomical details of brain
tumours, particularly in relation to
the surrounding structures. This
enables doctors to determine if
they can be safely removed or not.

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BRAIN SCANS

PET scan
This functional imaging
is allowing researchers
to test novel drugs and
treatments to prevent
progression of this
serious brain disorder.

DID YOU KNOW? CT scanning of the brain was invented in the early-Seventies

Picking apart the brain

The sensory and

motor cortexes

The frontal lobes

The pre- and post-central gyri

receive the sensory information
from the body and then dispatch
orders to the muscles, in the form of
signals through motor neurons.

The frontal lobes of the folded

cerebral cortex take care of
thought, reasoning, decisions and
memories. This area is believed to
be largely responsible for our
individual personalities.

The occipital cortex

In the posterior fossa of the skull,
this cortex receives impulses from
the optic nerves to form images.
These images are in
fact seen upside down, but this
area enables them to be
interpreted the right way up.

The brainstem

The cerebellum

Formed from the midbrain,

pons and medulla oblongata,
the brainstem maintains the
vital functions without us
having to think about them.
These include respiration and
heart function; any damage
to it leads to rapid death.

SPL

Alamy

The cerebellum is responsible

for fine movements and
co-ordination. Without it, we
couldnt write, type, play
musical instruments or
perform any task that requires
precise actions.

The pituitary gland

Imaging
Alzheimers

This tiny gland is responsible

for hormone production
throughout the body, which
can thus indirectly affect our
emotions and behaviours.

Diffusion tensor
imaging (DTI)

Positron emission
tomography (PET)

This MRI variant relies on the

direction of water diffusion
within tissue. When a magnetic
gradient is applied, the water
aligns and, when the eld is
removed, the water diffuses
according to a tissues internal
structure. This allows a 3D
image of activity to be built up.

This bleeding-edge technology

detects gamma rays emitted
from biologically active tissues
based on glucose. It can pick
up unusual biological activity,
such as that from cancer. There
have been recent advances to
combine PET with CT or MRI to
obtain lots of data quickly.

WorldMags.net

Alzheimers disease is a potentially

debilitating condition, which can lead
to severe dementia. The ability to
diagnose it accurately and early on has
driven the need for modern imaging
techniques. The above image shows a
PET scan. The right-hand side of the
image (as you look at it) shows a normal
brain, with a good volume and activity
range. On the left-hand side is a patient
affected by Alzheimers. The brain is
shrunken with fewer folds, and a lower
range of activity biologically speaking,
there are far fewer neurons ring.

153

CURIOUS
QUESTIONS
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Anaesthesia

How anaesthesia works

By interfering with nerve transmission these special drugs stop

pain signals from reaching the brain during operations
The body under
general anaesthetic
What happens to various parts of
the body when were put under?

Brain activity
Electroencephalograms (EEGs)
show that the electrical
activity in the brain drops to a
state deeper than sleep,
mimicking a coma.

Nil by mouth
General anaesthetics suppress
the gag reflex and can cause
vomiting, so to prevent
choking patients must not eat
before an operation.

Heart rate
The circulatory system is
slowed by anaesthetic, so
heart rate, blood pressure
and blood oxygen are all
continuously monitored.

Pain neurons
Unlike with local
anaesthetic, pain
neurons still fire under
general anaesthesia,
but the brain does
not process the
signals properly.

Comfortably numb
If large areas need to be anaesthetised while the
patient is still awake, local anaesthetics can be
injected around bundles of nerves. By preventing
transmission through a section of a large nerve,
the signals from all of the smaller nerves that
feed into it cant reach the brain. For example,
injecting anaesthetic around the maxillary nerve
will not only generate numbness in the roof of
the mouth and all of the teeth on that side, but
will stop nerve transmission from the nose and
sinuses too. Local anaesthetics can also be
injected into the epidural space in the spinal
canal. This prevents nerve transmission through
the spinal roots, blocking the transmission of
information to the brain. The epidural procedure
is often used to mollify pain during childbirth.

154

Airway
Loss of consciousness and
muscle relaxation suppress
breathing and prevent
coughing, so a tube and
ventilator are used to
maintain the airway.

Nausea
Many anaesthetics
cause nausea. Often
antiemetic drugs that
prevent vomiting are
given after surgery.

Muscle relaxation
A muscle relaxant is often
administered with the
anaesthetic; this causes
paralysis and enables lower
doses of anaesthetic to be used.

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Getty

Anaesthetics are a form of drug widely

used to prevent pain associated with
surgery. They fall into two main
categories: local and general. Local
anaesthetics can be either applied directly to the
skin or injected. They are used to numb small areas
without affecting consciousness, so the patient will
remain awake throughout a procedure.
Local anaesthetics provide a short-term blockade
of nerve transmission, preventing sensory neurons
from sending pain signals to the brain. Information
is transmitted along nerves by the movement of
sodium ions down a carefully maintained
electrochemical gradient. Local anaesthetics cut
off sodium channels, preventing the ions from
travelling through the membrane and stopping
electrical signals travelling along the nerve.
Local anaesthesia isnt specic to pain nerves, so it
will also stop information passing from the brain to
the muscles, causing temporary paralysis.
General anaesthetics, meanwhile, are inhaled
and injected medications that act on the central
nervous system (brain and spinal cord) to induce a
temporary coma, causing unconsciousness, muscle
relaxation, pain relief and amnesia.
Its not known for sure how general anaesthetics
shut down the brain, but there are several proposed
mechanisms. Many general anaesthetics dissolve in
fats and are thought to interfere with the lipid
membrane that surrounds nerve cells in the brain.
They also disrupt neurotransmitter receptors,
altering transmission of the chemical signals that let
nerve cells communicate with one another.

Memory
General anaesthetic affects
the ability to form memories;
the patient doesnt remember
the operation and often wont
recall coming to either.

KEY
DATES
STOMACH ULCERS

1900s
Stress and diet are blamed
for stomach ulcers. Patients
are prescribed rest and
bland food, like oatmeal.

1970

1982

Stomach acid is proposed as Two Australian scientists

the cause of gastric ulcers show that H pylori causes
and antacid treatment is
stomach ulcers, but some
introduced to counter it.
are sceptical to begin with.

1996

2005

The first antibiotics are Barry Marshall and Robin

approved for treatment Warren are awarded a
of the infection that
joint Nobel prize for
causes stomach ulcers.
their 1982 discovery.

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DID YOU KNOW? The scientists who revealed bacteria caused gastric ulcers had to drink their own experiment to prove it!

What causes stomach ulcers?

Originally thought to be the result of stress, we now know that bacteria are the culprits
Normally a thick layer of
alkaline mucus
effectively protects the
cells lining the stomach
from the low pH of stomach acid. If
this mucus becomes disrupted,
however, acid comes into contact
with the organs lining, damaging
the cells and resulting in an ulcer.
Around 60 per cent of stomach
ulcers are caused by inammation
due to chronic infection by the
bacterium Helicobacter pylori.
Bacterial by-products damage the
cells lining the stomach, causing a
breakdown of the top layers of tissue.
Non-steroidal anti-inammatory
drugs (NSAIDs), like ibuprofen and
aspirin, also cause stomach ulcers in
large doses. They disrupt the
enzymes responsible for mucus
production, diminishing the
protective barrier.

An ulcer in the making

Gastrin

Once bacteria breach the stomach lining, it can no

longer protect itself from its acidic contents

Neutralising
stomach
acid

Helicobacter pylori
Bacteria burrow through the mucus
in the stomach to escape damage
by acid. They stick to the cells of the
interior lining.

H pylori break down

urea to make
ammonia. This is
used to produce
bicarbonate to
neutralise
dangerous
stomach acid.

The inflammatory
response increases
production of the
hormone gastrin. This in
turn stimulates the
formation of more
stomach acid.

Damage

Enzymes
H pylori produce proteases
and phospholipases
enzymes that damage the
proteins and cell
membranes of the
stomach cells.

Ammonia
The ammonia made by
the bacteria as a defence
against acid damages the
cells lining the stomach,
causing inflammation.

As the cells become

damaged a wound opens
up in the stomach wall. If this
becomes deep enough it can
perforate blood vessels
causing bleeding.

Why do we sometimes
get mouth ulcers?

Alamy

Ulcers are small lesions usually

triggered by physical damage to the
inside of the mouth, for example
biting your cheek accidentally,
eating sharp food or brushing your
teeth. They are very rarely
contagious and usually heal within
ten days. Recurrent ulcers have a
variety of causes, the most common
being stress and hormonal changes.

In other cases, recurrent ulcers may

be symptomatic of conditions
including B12 or iron deciencies,
gastrointestinal diseases or
immunosuppressant diseases such
as HIV. Ulcers are sometimes
triggered by sensitivity to certain
foods including strawberries,
almonds, tomatoes, cheese,
chocolate and coffee.

They are rarely contagious

and usually heal in ten days

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155

CURIOUS
QUESTIONS
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Love as a chemical reaction

Why do we feel love?

The hormones and chemicals that cause us to fall
head over heels
7. Nucleus accumbens

8. Deactivate prefrontal cortex

The nucleus accumbens then pushes the prefrontal
cortex for action, but it deactivates, suspending
feelings of criticism and doubt.

The secretion of dopamine stimulates

the nucleus accumbens, an area of the
brain that plays a vital role in addiction.

3. Prefrontal cortex
Messages are then sent to the
prefrontal cortex, the brains
decision-making centre, where it
judges if the potential romantic
partner is a good match.

6. Hormone levels
As dopamine levels increase,
levels of serotonin, the
hormone responsible for mood
and appetite, decrease,
causing feelings of obsession.

2. Hippocampus
The hippocampus, the
memory forming area of
the brain, records this
pleasant experience
making you want to seek it
out again.

5. Norepinephrine
Norepinephrine, another
neurotransmitter similar to
adrenalin, is also released,
which gets your heart racing
and causes you to sweat.

9. Deactivate
amygdala
The amygdala also deactivates,
reducing the ability to feel fear
and stress and creating a more
happy, carefree attitude.

1. Amygdala

4. Hypothalamus

When you see

someone you like, the
amygdala, the area of
the brain responsible
for emotions,
recognises it as a
positive experience.

If the attraction is there,

the prefrontal cortex
stimulates the
hypothalamus, which
releases the
neurotransmitter
dopamine, causing feeling
of ecstasy.

How do enzymes keep you alive?

Enzymes increase the speed of
reactions that take place inside cells
by lowering the energy-activation
requirement for molecular
reactions. Molecules need to react with each
other to reproduce, but our bodies provide
neither the heat nor the pressure required for
these reactions.
Each cell contains thousands of enzymes,
which are amino acid strings rolled up into a ball
called a globular protein. Each enzyme contains
a gap called an active site into which a molecule
can t. Once inside the crack, the molecule

156 | How It Works

which becomes known as a substrate

undergoes a reaction such as dividing or merging
with another molecule without having to expel
energy in a collision with another molecule. The
enzyme releases it and oats on within the cells
cytoplasm. The molecule and active site need to
match up perfectly in order for the sped-up
reaction to take place. For example, a lactose
molecule would t into a lactase enzymes active
site, but not that of a maltase enzyme.
Interestingly enough, enzymes dont get used
up in the process, so they can theoretically
continue to speed up reactions indenitely.

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Enzymes such as
trypsin work to help
break down
proteins

Thinkstock

The proteins that speed up your bodys chemical reactions

WorldMags.net
Correcting heart rhythms
How can a little electricity be used to x a heart thats beating off-kilter?
8. Low energy

3. Timing the shock

Resetting an abnormal
heart beat uses fairly
low-energy shocks of just
50-200 joules.

The heart is vulnerable when it

is between beats, so to prevent
a cardiac arrest, the shock is
timed to coincide with the
pumping of the ventricles.

6. Natural pacemaker
The heart has its own internal
pacemaker known as the sinoatrial
node. Delivering a small electric
shock to this resynchronises the
organs natural electrical activity.

5. Electric shocks
Low-energy electric shocks
are delivered to the heart
through the electrodes.

BEFORE CARDIOVERSION
4. Arrhythmia
If the heart beats too fast, or
at an irregular pace, it
becomes unable to
effectively pump blood
around the body.

1. Paddles
Two metallic plates are
placed on the patients
chest across the heart.

Atrial brillation

AFTER CARDIOVERSION
7. Cardioversion
machine

2. Conductive gel
A saltwater-based gel is
used so the current can
travel from the electrodes
and through the skin.

Whys salt
bad for
the heart?
Simply put, too much salt is bad for
you as it increases the demand on
your heart to pump blood around the
body. This is because when you eat
salt it causes the body to retain
increased quantities of water, which
increases your blood pressure, and
this places more strain on your heart.
As such, most doctors recommend
moderating daily salt intake.

The machine records the

electrical activity of the
heart and calculates the
electric shocks required
to restore the organ to
its normal rhythm.

Normal ECG

Do women have
Adams apples?
You may not realise, but actually everyone has an
Adams apple, but mens are usually easier to see in
their throat. Its a bump on the neck that moves
when you swallow, named after the biblical Adam.
Supposedly, its a chunk of the Garden of Edens forbidden fruit
stuck in his descendants throats, but its actually a bump on the
thyroid cartilage surrounding the voice box. Thyroid cartilage is
shield-shaped and the Adams apple is the bit at the front.
Why do mens Adams apples stick out more? This is partly
because they have bonier necks, but it is also because their
larynxes grow differently from womens during puberty to
accommodate their longer, thicker vocal cords, which give them
deeper voices.

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157

CURIOUS
QUESTIONS
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Rumbling stomach / Seasickness

What causes
a rumbling
stomach?

Oesophagus
This muscular pipe
connects the throat
to the stomach.

Discover how the small

intestine is really to blame
Waves of involuntary muscle
contractions called peristalsis churn
the food we eat to soften it and
transport it through the digestive
system. The contractions are caused by strong
muscles in the oesophagus wall, which take just
ten seconds to push food down to the stomach.
Muscles in the stomach churn food and gastric
juices to break it down further.
Then, after four hours, the semi-digested
liqueed food moves on to the small intestine
where yet more powerful muscle contractions
force the food down through the intestines bends
and folds. This is where the rumbling occurs. Air
from gaseous foods or that swallowed when we eat
often due to talking or inhaling through the nose
while chewing food also ends up in the small
intestine, and its this combination of liquid and
gas in a small space that causes the gurgling noise.
Rumbling is louder the less food present in the
small intestine, which is partly why people
associate rumbling tummies with hunger. The
other reason is that although the stomach may be
clear, the brain still triggers peristalsis at regular
intervals to rid the intestines of any remaining
food. This creates a hollow feeling that causes you
to feel hungry.

After four
hours, the semidigested liquefied
food moves to the
small intestine

Stomach
Food is churned and
mixed with gastric
juices to help it to
break down.

Lungs

Small intestine
Here, liquid food
combined with trapped
gases can make for some
embarrassing noises.

Liver

Large intestine
Food passes from the
small intestine to the
large intestine where
it is turned into faeces.

Rectum

No, theyre not altitude sickness is a collection

of symptoms brought on when youre suddenly
exposed to a high-altitude environment with
lower air pressure so less oxygen enters our body.
The symptoms can include a headache, fatigue,
dizziness and nausea.
Seasickness, on the other hand, is a more
general feeling of nausea thats thought to be
caused when your brain and senses get mixed

158

signals about a moving environment for

instance, when your eyes tell you that your
immediate surroundings (such as a ships
cabin) are still as a rock, while your sense of
balance (and your stomach!) tells you something
quite different.
This is the reason why closing your eyes or
taking a turn out on deck will often help, as it
reconciles the two opposing sensations.

Thinkstock

Are seasickness and altitude

sickness the same thing?

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This vast network of 100 million neurones

constantly samples the ingested food,
relaying this information to the brain

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How do cravings work?

Is a child destined to develop a taste for all things sweet?
Hunger and cravings are two very
different things. While one is about
survival, the other satises the nagging
need for something sugary. Its believed
we all develop a taste for sweetness in infancy. This
stems from the predominant sweet taste of our
mothers milk; when we taste it, the brains reward
centres light up, causing us to derive pleasure from
this experience. As we continue to consume our
mothers milk this pleasure is reinforced, which
could explain how our sugar cravings originate.

Our mothers diet can inuence our preferences

for certain foods. Scientists have found that avours
are transmitted from mother to baby via the
amniotic uid surrounding the foetus in the womb.
Once born, the probability of the child disliking the
avours they have already experienced is reduced.
Our gut also plays a large role in cravings. The gut
contains an almost separate autonomous system
that governs the digestion lining. This vast network
of 100 million neurones constantly samples the
ingested food, relaying this information to the brain.

People commonly
crave the sweet
taste and
melt-in-the-mouth
texture of chocolate

This endless conversation can cause our appetite

and cravings to change. The gut bacteria are also
heavily involved; when they break down large
quantities of bre, they produce a specic compound
that is sent to the brain, triggering it to feel full and
satised from the recently ingested meal.
So should we consider cravings as a sign of food
addiction? Although high-sugar and high-fat foods
exhibit some of the hallmarks of addiction, the
consensus is that its actually the behaviour around
eating these foods that we are addicted to.

Tricking our
senses
Does a spoons colour change the way yoghurt
tastes? In reality it doesnt, but the colour of
cutlery can alter how you think something
tastes. A recent study fed a group of volunteers
the same yoghurt using a white and a black
spoon. The results showed that the yoghurt was
perceived to taste sweeter on the white spoon.
Altering the spoons weight was then tested.
The lighter spoons caused the participants to
feel the yoghurt was denser and more
luxurious. Scientists are unsure what
mechanism causes these bizarre results, and
want to carry out further research into why we
make these associations.

Can the latest technology stop cravings?

Ghrelin is the bodys hunger-inducing
hormone. By using a ghrelin antagonist, scientists
aim to suppress this hormones activity, stopping
cravings from ever materialising. This research
has implications for cravings of other substances
too. Scientists have hypothesised that due to the
similarities between this system and that
responsible for craving nicotine and alcohol, it
may be possible to switch off these cravings as
well as those related to food.

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Science Museum; Thinkstoc

One of the most recent inventions is a microchip

that aims to control cravings, developed by Kings
College Londons Centre for Bio-Inspired
Technology. Once implanted in the body, the chip
will use electrodes to monitor the signals that are
consistently passing between the gut and the
brain. By listening to the communication
between the two organs, the microchip will be
able to recognise signals for cravings and alter
these before they reach the brain.

159

CURIOUS
QUESTIONS
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Knee-jerk reactions / Feet smell

What causes
the knee-jerk
reaction?

Why do
feet smell?
Producing up to a pint of
sweat each day, no wonder
your feet get a bit whiffy

Why does your leg kick out when the doctor taps
just below your knee?
Doctors often test the knee-jerk, or patellar reex, to look for potential neurological
problems. Lightly tapping your patellar tendon just below the kneecap stretches the
femoral nerve located in your thigh, which in turn causes your thigh muscle
(quadriceps) to contract and the lower leg to extend. When struck, impulses travel
along a pathway in the dorsal root ganglion, a bundle of nerves in the L4 level of the spinal cord.
Reex actions are performed independently of the brain. This allows them to happen almost
instantaneously within about 50 milliseconds in the case of the knee-jerk reex. This reex
helps you to maintain balance and posture when you walk, without having to think about every
step you take.

The knee-jerk step-by-step

1. Quadriceps and hamstring muscles
The knee-jerk reflex means that the quadriceps muscles
contract at the same time the hamstring muscle relaxes.

3. Interneuron
The interneuron provides a
connection between the
sensory and motor neurons.

Sweat actually keeps the skin of our

feet moist and exible to cope with the
constantly changing pressure when
we walk. Without this moisture the
skin would dry and crack, and walking would
become extremely painful. Despite the huge
number of glands (250,000 per foot) and amount of
sweat that comes from our feet, remember its still
just salt and water. The odour comes from the
bacteria that live on human skin which, while
unsettling, are perfectly natural. Our socks are a
dark, moist-infested feast for them, as they eat
sweat and dead skin. It is the waste products they
excrete from this consumption that are what
smells bad. The more the bacteria eat the worse
our feet smell. To keep the smell down, make sure
you change your socks and let your shoes air for 24
hours if you can. Also, wash your feet and spray
them with antiperspirant!

4. Motor neuron
The motor, or efferent
neuron, carries the nerve
impulse to the muscles.

5. Spinal cord
Sensory neuron
Motor neuron
Interneuron

2. Sensory neuron
The sensory, or afferent
neuron, receives an impulse
from the femoral nerve.

The spinal cord has both grey

matter, which contains nerve cell
bodies, and white matter, which
contains the nerve fibres.

Reflex actions are performed

independently of the brain
160

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The wonderful smell of

freshly cut grass, daisies
and feet

WorldMags.net

DID YOU KNOW? Writers cramp occurs in the hands and lower arms but is actually a form of dystonia, a neurological condition
Blisters shouldnt be
burst as they are the
bodys way of protecting
deeper skin layers

Cramp
explained
Why do our muscles tense up?

What
are
blisters?
Why do burns cause bubbles to develop
below the surface of the skin?

Though our skin is an

amazing protector against
the elements, it can become
damaged by such factors as
heat, cold, friction, chemicals, light,
electricity and radiation, all of which
burn the skin. A blister is the resulting
injury that develops in the upper layers
of the skin as a result of such burns.
The most common example of a
blister, which weve no doubt all
experienced at some time, is due to the
repeated friction caused by the material
of a pair of shoes rubbing against, and
irritating, the skin. The resulting water
blister is a kind of plasma-lled bubble
that appears just below the top layers of
your skin. The plasma, or serum which
is a component of your blood is
released by the damaged tissue cells

SPL

Blister caused by
second-degree burns

and lls the spaces between the layers

of skin to cushion the underlying skin
and protect it from further damage. As
more and more serum pours into the
space, the skin begins to inate under
the pressure, forming a small balloon
full of the serous liquid. Given time to
heal, the skin will reabsorb the plasma
after about 24 hours.
Similarly, a blood blister is a variation
of the same injury where the skin has
been forcefully pinched or crushed but
not pierced, causing small blood vessels
to rupture, leaking blood into the skin.
All blisters can be tender but should
never be popped to drain the uid as
this leaves the underlying skin
unprotected and invites infection into
the open wound.

Cramp is an involuntary contraction of a muscle, often in

a limb such as the leg, that can cause pain and
discomfort for seconds, minutes or, in extreme cases, for
several hours. They are most common after or during
exercise, coinciding with low blood sugar levels, dehydration and a
high loss of salt from sweating. Although the full range of causes is
something of a mystery due to limited research in the area, cramp is
believed to be the result of muscle fatigue. If a muscle has been
shortened through prolonged use, but is repeatedly stimulated, it
isnt able to properly relax. A reex arc from the central nervous
system to the muscle informs it to continue contracting when it is not
necessary, leading to a painful spasm known as cramp as the muscle
continually attempts to contract. This is why athletes pushed beyond
their limits, such as football players who have to play extra time in a
match, will often experience this condition.

Rest
At rest the calf
muscle is in its
relaxed position.

Stretch
When the leg is
bent or stretched
the calf muscle
will contract, and
then relax when
it is not.

Plasma
Serum is released by the damaged
tissues into the upper skin layers to
prevent further damage below in the
epidermal layer. It also aids the
healing process, which is why you
should avoid popping your blisters.

Duration

Skin

Any generated
cramp usually lasts
for a few seconds,
however some
severe cases can
last hours.

When any type of burn is

experienced, the overlying skin
expands as it receives the protective
plasma/serum.

Cramp
Prolonged
stretching of the
leg prevents the
calf muscle from
relaxing, which can
lead to cramp.

Damage
This particular example of a blister burn
has caused damage to the keratinocytes
in the skin. Second-degree burns are
most often caused when the skin comes
into contact with a hot surface, such as
an iron or boiling water, or even after
exposure to excessive sunlight.

Fluid reabsorbed
After a day or so the serum will be
absorbed back into the body and the
raised skin layers will dry out and flake
off in their own time.

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CURIOUS
QUESTIONS
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Brain control / Laughing

Do we control our brains or

do our brains control us?
An experiment at the Max Planck Institute, Berlin, in 2008
showed that when you decide to move your hand, the decision
can be seen in your brain, with an MRI scanner, before you are
aware you have made a decision. The delay is around six
seconds. During that time, your mind is made up but your consciousness
doesnt acknowledge the decision until your hand moves. One
interpretation of this is that your consciousness the thing you think of as
you is just a passenger inside a deterministic automaton. Your
unconscious brain and your body get on with running your life, and only
report back to your conscious mind to preserve a sense of free will. But its
just as valid to say that when you make a decision, theres always
background processing going on, which the conscious mind ignores for
convenience. In the same way, your eye projects an upside-down image
onto your retina, but your unconscious brain turns it the right way around.

Gelotology is the study

of laughter and its
effects on the
human body

What happens
when we laugh?
Which muscles react when we nd
something funny and why is
laughter so hard to fake?

Alamy

Laughing can
sometimes be
completely involuntary
and involves a complex
series of muscles, which is why its so
difcult to fake and also why an
active effort is required to suppress
laughter in moments of sudden
hilarity at inopportune moments.
In the face, the zygomaticus major
and minor anchor at the cheekbones
and stretch down towards the jaw to

pull the facial expression upward;

on top of this, the zygomaticus major
also pulls the upper lip upward
and outward.
The sound of our laugh is
produced by the same mechanisms
which are used for coughing and
speaking: namely, the lungs and the
larynx. When were breathing
normally, air from the lungs passes
freely through the completely open
vocal cords in the larynx. When they
close, air cannot pass, however
when theyre partially open, they
generate some form of sound.
Laughter is the result when we
exhale while the vocal cords close,
with the respiratory muscles
periodically activating to produce
the characteristic rhythmic sound
of laughing.
The risorius muscle is used to
smile, but affects a smaller portion
of the face and is easier to control
than the zygomatic muscles. As a
result, the risorius is more often
used to feign amusement, hence
why fake laughter is easy to detect
by other humans.

Laughter is produced by the same mechanisms

used for coughing and speaking
162 | How It Works

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WorldMags.net

Dust, water vapour and pollution in the air will rarely let you see more than
20 kilometres, even on a clear day. Often, the curvature of the Earth gets in
the way rst eg at sea level, the horizon is only 4.8km away. On the top of Mt
Everest, you could theoretically see for 339km, but in practice cloud gets in
the way. For a truly unobstructed view, look up. On a clear night, you can see the
Andromeda galaxy with the naked eye, which is 2.25 million light years away.

What is dandruff?
Dandruff is when dead skin cells fall off the scalp. This
is normal, as our skin is always being renewed. About
half the population of the world suffers from an
excessive amount of this shedding, which can be
triggered by things like temperature or the increased activity of a
microorganism that normally lives in everyones skin, known as
malassezia globosa. Dandruff is not contagious and there are many
treatments available, the most common is specialised shampoo.
Horoporo

What is the maximum

distance the human
eye can see?

Our line of sight can be impeded by

many things, from pollution to the
curvature of the Earth

Why do eyes
take a while to
adjust to dark?
At the back of the eye on the retina, there
are two types of photoreceptors (cells
which detect light). Cones deal with
colour and ne detail and act in bright
light, while rods deal with vision in low-light
situations. In the rst few minutes of moving into a
dark room, cones are responsible for vision but
provide a poor picture. Once the rods become more
active, they take over and create a much better
picture in poor light. Once you move back into light,
the rods are reset and so dark-adaption will take a
few moments again. Soldiers are trained to close or
cover one eye at night when moving in and out of a
bright room, or when using a torch, to protect their
night vision. Once back in the dark, they reopen the
closed eye with the rods still working and, as a
result, maintain good vision. This allows them to
keep operating in a potentially hostile environment
at peak operational efciency. Give it a try next time
you get up in the middle of the night, it may help you
avoid tripping over in the dark.

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CURIOUS
QUESTIONS
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Thinkstock

Allergies / Eczema

Why do some people

have allergies and
some dont?
Allergies can be caused by two things: host and
environmental factors. Host is if you inherit an allergy or are
likely to get it due to your age, sex or racial group.
Environmental factors can include things such as pollution,
epidemic diseases and diet. People who are likely to develop allergies
have a condition known as atopy. Atopy is not an illness but an
inherited feature, which makes individuals more likely to develop an
allergic disorder. Atopy tends to run in families.
The reason why atopic people have a tendency to develop allergic
disorders is because they have the ability to produce the allergy
antibody called Immunoglobulin E or IgE when they come into
contact with a particular substance. However, not everyone who has
inherited the tendency to be atopic will develop an allergic disorder.

People who are likely

to develop allergies
have a condition known
as atopy

Eczema explained

The histamine increase

can cause itching,
leading to open sores

What causes the skin to react to otherwise harmless material?

164 | How It Works

Under the skin

What happens inside the body when eczema flares up?

Ceramides
The membranes of skin cells contain waxy lipids
to prevent moisture evaporation, but these are
often deficient in eczema.

Allergen
entry route

Allergen
Eczema is commonly triggered
by the same things as many
allergies anything from pet
hair to certain types of food.

The cells of the skin are

normally tightly bound
together to prevent
contaminants from
entering the body, but in
eczema there are gaps.

Water loss
The skin is less able
to retain water,
leading to dryness
and irritation.

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Inammatory
response
The immune system
produces a response to
allergens beneath the skin,
leading to redness, itching
and also inflammation.

Alamy; J Kadavoor; Thinkstock

Eczema is a broad term for a

range of skin conditions, but
the most common form is
atopic dermatitis. People with
this condition have very reactive skin,
which mounts an inammatory response
when in contact with irritants and
allergens. Mast cells release histamine,
which can lead to itching and scratching,
forming sores open to infection.
There is thought to be a genetic
element to the disease and a gene
involved in retaining water in the skin
has been identied as a potential
contributor, but there are many factors.
Eczema can be treated with steroids,
which suppress immune system
activity, dampening the inammation
so skin can heal. In serious cases,
immunosuppressant drugs used to
prevent transplant rejection can
actually be used to weaken the immune
system so it no longer causes
inammation in the skin.

WorldMags.net
Why do
bruises go
purple?
Sometimes we trip over or hurt
ourselves in other ways. When it
happens some of our blood vessels
break, blood piles up under our skin
and we can see this as a bruise. These nasty
things have the familiar black and blue or
purple appearance in the beginning but
gradually change into different colours.
The purple colour is given by haemoglobin, a
protein that carries the oxygen in our red blood
cells. Our body reacts to this with some white
blood cells called phagocytes eating up the
materials in the bruise. As the phagocytes
degrade the haemoglobin, they turn it into other
molecules. Different molecules show different
colours and the bruise will change colour with
time to green, yellow and brown. When
everything has been cleared up by your
immune system the bruise disappears and
youre ready to bump into something else.

Is it possible for humans to

have an allergy to water?
A rare condition called aquagenic
urticaria is often referred to as an
allergy to water. The symptoms of
aquagenic urticaria are painful but
generally not fatal. Contact with watercontaining substances can bring out sore hives
on the surface of the skin, cause a burning
sensation and induce headaches. Because saliva

The purple is given

by haemoglobin
Artery wall
Wear and tear comes
with age, and a diet high
in saturated fat can lead
to fatty buildup on
artery walls.

contains water, the condition hinders intimacy.

Death could occur when water is swallowed if
the throat swells up, blocking the airway. The
root cause is unknown. One hypothesis is that
H2O generates a toxic compound in the outer
layers of the skin, prompting the release of
histamines. Reactions can sometimes be
controlled with antihistamines.

Aquagenic urticaria mainly

occurs in women and can affect
parts, or the whole, of the body

Is cholesterol
bad for you?

Plaque
Artery walls thicken with
further deposits of
cholesterol and connective
tissue, which can lead
to a deadly blockage.

Is this substance as evil as we hear?

Cholesterol is a fatty molecule in the blood and, generally
speaking, having too much is bad: it can stick to the walls of
your arteries and increase the risk of heart disease. Most
foods, with the exception of offal, eggs and shellsh, dont
contain any cholesterol, but many contain saturated fats, which are
turned into cholesterol by the liver. However, cholesterol itself isnt
unhealthy in fact, you wouldnt be able to live without it. The body uses
cholesterol as a kind of padding, coating the outer membranes of all our
cells and insulating nerve bres, helping signals travel properly to and
from the brain. Its also a fundamental part of the endocrine system, as
all steroid hormones (eg oestrogen) are synthesised from cholesterol.
Importantly, a good, balanced diet and regular exercise can keep
cholesterol easily within a healthy range for most people.

Restriction of blood flow in

the arteries can lead to angina,
strokes and heart attacks.

SPL

Blood

Cholesterol itself isnt

unhealthy in fact, you
wouldnt be able to live
without it

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165

CURIOUS
QUESTIONS
WorldMags.net

Twins

Monozygotic twins
are a rarity

What
are twins?

Twins are becoming more prevalent due to medical

developments, but how and why do they occur?

The number of twins, or multiples,

being born is actually on the rise
due to the increase in use of fertility
treatments such as IVF as people
wait longer to have children. The number of
twins surviving early births is also increasing
due to improved medical knowledge.
However, twins are still a relatively rare
occurrence making up only around two per
cent of the living worlds population. Within
this, monozygotic twins (from one ovum) make
up around eight per cent with dizygotic (from
two ovum) seen to be far more common.
While there is no known reason for
the occurrence of the split of the ovum that
causes monozygotic twins, the chances of
having twins is thought to be affected by
several different factors. It is believed twins
run in the family, often seeming to skip
generations, while the age, weight, height, race
and even diet of the mother are thought to

166

potentially impact the chances of conceiving

dizygotic twins. Also, if the mother is going
through fertility treatments, she is much more
likely to become pregnant with multiples.
It will become apparent quite early on that a
mother is carrying twins as this is often picked
up during early ultrasound scans. There can be
other indications such as increased weight gain
or extreme fatigue. Although twins are often
born entirely healthy and go on to develop
without problems later in life due to medical
advances, twins can be premature and smaller
than single births due to space constrictions
within the womb during development.

Strange, but
true

It is believed twins
run in the family,
often seeming to
skip generations
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There are many stories of identical twins being

separated at birth and then growing up to lead
very similar lives. One example described in the
1980 January edition of Readers Digest tells of
two twins separated at birth, both named James,
who both pursued law-enforcement training and
had a talent for carpentry. One named his son
James Alan, and the other named his James Allan
and both named their dogs Toy. There were also
the Mowforth twins, two identical brothers who
lived 80 miles apart in the UK, dying of exactly the
same symptoms on the same night within hours of
each other.

5 TOP
FACTS

MULTIPLE BIRTHS

12 foetus world record

Nonuplets exist

Race affects conception

Most children

Quad gestation

Although sadly this pregnancy

did not reach full term and no
babies survived, a woman in
Argentina was observed to have
12 foetuses inside her womb
from natural conception.

A Malaysian mother gave birth

to five boys and four girls in
March 1999 none survived
over six hours. Another set of
nonuplets suffered a similar fate
in Sydney in 1971.

With regard to DZ twins, there

is seen to be a higher
prevalence of these twins in
black Africans, and a lower
incidence than to be expected
in Oriental mothers.

The highest recorded number

of children had by one woman
is the first wife of Feodor
Vassilyev, who lived in the
1700s. She gave birth to an
incredible 69 children.

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With regard to quadruplets,

the average gestation period is
just 32 weeks thats eight
weeks shorter than usual,
primarily due to the size
restriction of the womb.

DID YOU KNOW? Female monozygotic twins are more common due to the increased likelihood of male mortality in the womb

Multiple pregnancies,
multiple problems?
There are many difculties with twin
pregnancies mainly due to the limited size
of the mothers womb. Multiple pregnancies
rarely reach full term due to these limits,
twins averaging at around 37 weeks. Also,
because of the lack of space and eggs splitting
in the womb, further complications such as
conjoined twins can occur. Conjoined twins
can be a problem dependant on where

Placenta
Provides a metabolic
interchange between
the twins and mother.

theyre joined. If it is by a vital organ or bone

structure, one or both may die following birth
as they grow or during an operation to
separate them.
It is also suspected that as many as one in
eight pregnancies may have started out as a
potential multiple birth, but one or more of the
foetuses does not progress through
development to full term.

Twins inside
the womb
Uterine wall
The protective wall
of the uterus.

Amniotic sac
A thin-walled sac that
surrounds the fetus
during pregnancy.

Formation of
identical and
fraternal twins
Monozygotic (MZ), or identical, twins are formed by the
egg splitting soon after fertilisation, and from those
identical split groups of cells, two separate foetuses will
start to grow. Monozygotic twins are therefore genetically
identical and will be the same sex, except when mutations
or very rare syndromes occur during gestation. No reason
is known for the occurrence of the split of the ovum, and
the father has no inuence over whether identical twins
are produced.
Dizygotic (DZ) twins, however, are produced when the
females ovaries release two ovum and both are fertilised
and implanted in the womb wall. They can be known as
fraternal twins as genetically they are likely to only be as
similar as siblings. They will also have separate placentas,
where MZ twins will share one, as they are entirely
separate to each other they are just sharing the womb
during gestation. This kind of twin is far more common.

Monozygotic

2. Fertilised
egg splits

1. Sperm
fertilises egg
In MZ twins, only one
egg and one sperm
are involved.

At some point very

early on, the fertilised
egg will split and two
separate foetuses will
start to form. These
will be genetically
identical.

Umbilical cord
A rope-like cord
connecting the fetus
to the placenta.

Cervix

Genetically
identical, but why
do twins differ?
From studying identical, monozygotic twins,
we can attempt to decipher the level of impact
environment has on an individual and the
inuence genes have. As the genetics of the
individuals would be identical, we can say
that differences displayed between two
MZ twins are likely to be down to
environmental inuences.
Some of the most interesting studies look at
twins that have been separated at birth, often
when individuals have been adopted by

Dizygotic

The lower part of the

uterus that projects
into the vagina.

different parents. Often we see a similar IQ

and personality displayed, whether or not
they grow up together, but even these and
other lifestyle choices can vary dependant
on environment.
Ultimately, it is hard to draw rm
conclusions from twin studies as they will be
an unrepresentatively small sample within a
much larger population and we often nd that
both environment and genetics interact to
inuence an individuals development.

4. Separate
eggs
continue
to develop
In DZ twins, both
foetuses will
continue to develop
independently to
each other.

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3. Sperm
fertilise
separate
eggs
In DZ twins, two
separate eggs are
fertilised by
different sperm.
These will implant
independently in
the mothers
womb wall,
commonly on
opposite sides.

167

CURIOUS
QUESTIONS
WorldMags.net

Alveoli anatomy

How do alveoli
help you breathe?
The lungs are lled with tiny
balloon-like sacs that keep you alive
blocks of each are the tiny alveolus. They are
the nal point of the respiratory tract, as the
bronchi break down into smaller and smaller
tubes, leading to the alveoli, which are grouped
together and look like microscopic bunches of
grapes. Around the alveoli is the epithelial layer
which is amazingly only a single cell thick
and this is surrounded by extremely small
blood vessels called capillaries. It is here that
vital gas exchange takes place between the
fresh air in the lungs and the deoxygenated

Alveoli anatomy
How alveoli enable gas exchange

blood within the capillary venous system on

the other side of the epithelial layer.
The alveoli of the lungs have evolved to
become specialised structures, maximising
their efciency. Their walls are extremely thin
and yet very sturdy. Pulmonary surfactant is a
thin liquid layer made from lipids and proteins
that coats of all the alveoli, reduces their
surface tension and prevents them crumpling
when we breathe out. Without them, the lungs
would collapse.

Type I pneumocytes

Breathe in,
breathe out

These large, attened cells form

95 per cent of the surface area of
an alveolus, and are the very thin
diffusion barriers for gases.

Type II
pneumocytes
These thicker cells form
the remaining surface area
of the alveoli. They secrete
surfactant, which prevents
the thin alveoli collapsing.

Oxygenated blood
The freshly oxygenated
blood is taken away by
capillaries and enters the
left side of the heart,
to be pumped
through the body.

One cell thick

Deoxygenated
blood arrives

The alveolus wall is just

one cell thick, separated
from the blood capillaries
by an equally thin
basement membrane.

The capillary veins bring

deoxygenated blood from the
right side of the heart, which
has been used by the body
and now contains toxic CO2.

168

Macrophages
These are defence
cells that digest
bacteria and particles
present in air, or that
have escaped from the
blood capillaries.

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The alveoli function to allow gas

exchange, but since theyre so
small, they cant move new air
inside and out from the body
without help. Thats what your
respiratory muscles and ribs do,
hence why your chest moves as
you breathe. The diaphragm,
which sits below your heart and
lungs but above your abdominal
organs, is the main muscle of
respiration. When it contracts, the
normally dome-shaped diaphragm
attens and the space within the
chest cavity expands. This
reduces the pressure compared to
the outside atmosphere, so air
rushes in. When the diaphragm
relaxes, it returns to its dome
shape, the pressure within the
chest increases and the old air
now full of expired carbon dioxide
is forced out again. The muscles
between the ribs (called
intercostal muscles) are used
when forceful respiration is
required, such as during exercise
Try taking a deep breath and
observe how both your chest
expands to reduce the pressure!

DK Images; Thinkstock

Gas exchange occurs in the lungs,

where toxic gases (carbon dioxide)
are exchanged for fresh air with its
unused oxygen content. Of all the
processes in the body that keep us functioning
and alive, this is the most important. Without it,
we would quickly become unconscious through
accumulation of carbon dioxide within the
bloodstream, which would poison the brain.
The two lungs (left and right) are made up of
several lobes, and the fundamental building

5 TOP
FACTS
IN YOUR EYES

Blue eyes

Blinking

People with blue eyes all

share a common ancestor. A
genetic mutation about
10,000 years ago gave
someone blue eyes, when
everyone elses were brown.

Sight

Your eyes will blink around

15-20 times per minute and
it last for around 100
milliseconds. You also blink
more when talking than
when reading.

Tears

Technically, you see with

your brain and not your
eyes. Poor vision sometimes
stems from problems with
the visual cortex of the brain
and not the eye itself.

Measurements

Tears are not only an

emotional response; they
also help prevent your eyes
from drying up and get rid
of any irritating particles
that could cause damage.

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On average, a human eyeball

is around 2.5cm (1in) in
diameter and weighs as
little as 7.5g (0.25oz). A
giant squids eyeball is ten
times as big as a humans.

DID YOU KNOW? SAD is more common in women and people between the ages of 15 and 55

How do dilating eye

drops work?
Discover how they are used to diagnose and treat eye conditions
Sight is one our most important
senses, so maintaining good eye
health is absolutely essential.
However, eyesight problems can be
difcult to detect or treat on the surface, so
specialist eye doctors will often use dilating
eye drops in order to get a better look inside the
eye at the lens, retina and optic nerve.
The drops contain the active ingredient
atropine, which works by temporarily relaxing
the muscle that constricts the pupil, enabling it
to remain enlarged for a longer period of time
so a thorough examination can be performed.
Some dilating eye drops also relax the muscle
that focuses the lens inside the eye, which
allows an eye doctor or optometrist to measure
a prescription for young children who cant
perform traditional reading tests.
Dilating eye drops are not only used to help
perform procedures, they may also be
administered after treatment, as they can
prevent scar tissue from forming. They are also
occasionally prescribed to children with
lazy-eye conditions, as they will temporarily
blur vision in the strong eye, causing the brain
to use and strengthen the weaker eye.

Before and after

A better look inside the eye
Contracted pupil
A contracted pupil will appear much
smaller and let less light into the
eye, which makes it difcult to see
the retina and optic nerve inside.

Dilated pupil
Dilating eye drops will
temporarily paralyse the
muscle that constricts
the pupil, which means
the pupil will remain
dilated for much longer.

Our eyes need good

care to stay healthy

Ray of light
The size of the pupil will determine
how much light enters the eye.
Dilated pupils let in more light, which
means you can see a larger portion
of the retina and optic nerve.

Optic nerve

Retina

The lens

The optic nerve carries

electrical impulses from
the retina to the brain,
which then interprets them
as visual images.

This light-sensitive tissue

converts incoming light
into electrical impulses.
These impulses are then
sent to the optic nerve.

It is positioned behind the pupil

and helps focus light onto the
retina. Some dilating eye drops
relax the muscle around it to
prevent the lens from focusing.

Why do we get migraines?

Discover how these mega-headaches strike
Those who suffer from
migraines know they are
a constant concern as
they are liable to strike
at any time. Essentially, a migraine
is an intense pain at the front or on
one side of the head. This usually
takes the form of a heavy throbbing
sensation and can last as little as an
hour or two and up to a few days.
Other symptoms of a migraine
include increased sensitivity to
light, sound and smell, so isolation
in a dark and quiet room often
brings relief. Nausea and vomiting is

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also often reported, with pain

sometimes subsiding after the
sufferer has been sick.
It is thought that migraines occur
when levels of serotonin in the brain
drop rapidly. This causes blood
vessels in the cortex to narrow,
which is caused by the brain
spasming. The blood vessels widen
again in response, causing the
intense headache. Emotional
upheaval is often cited as a cause for
the drop in serotonin in the brain, as
is a diet in which blood-sugar levels
rise and fall dramatically.

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How It Works | 169

CURIOUS
QUESTIONS
WorldMags.net

Pins and needles / Burns / Funny bones

What are pins

and needles?

Pins and
needles is the
result of nerves
that have been
prevented from
sending signals
ring all at once

The numb sensation of your leg

going to sleep isnt caused by
cutting off the blood circulation.
Its the pressure on the nerves that
is responsible. This squeezes the insulating
sheath around the nerve and shorts it out,
blocking nerve transmission. When pressure
is released, the nerves downstream from the
pinch point suddenly all begin ring at once.
This jumble of unco-ordinated signals is a
mixture of pain and touch, hot and cold all
mixed together, which is why its excruciating.

This squeezes the

insulating sheath
around the nerve
and shorts it out

Thinkstock

Thinkstock

Why do
paper
cuts hurt
so much?

170 | How It Works

Paper can cut your skin

as it is incredibly thin
and, if you were to look
at it under a highpowered microscope, it has
serrated edges. Critically though, a
sheet of loose paper is far too soft
and exible to exert enough
pressure to pierce the skin, hence
why they are not a more frequent
occurrence. However, if the paper
is xed in place maybe by being
sandwiched within a pack of
paper a sheet can become stiff
enough to attain skin-cutting
pressure. Paper cuts are so painful
once inicted as they stimulate a
large number of pain receptors
nociceptors send nerve signals to
the spinal cord and brain in a
very small area due to the
razor-type incision. Because paper
cuts tend not to be deep, bleeding
is limited, leaving pain receptors
open to the environment.

Are there other funny

bones in the body?
The term funny bone is misleading
because it refers to the painful sensation
you experience when you trap your ulnar
nerve between the skin and the bones of
the elbow joint. This happens in the so-called cubital
tunnel, which directs the nerve over the elbow but has
little padding to protect against external impacts. The
ulnar nerve takes its name from the ulna bone, which is
one of two bones that runs from the wrist to the elbow;
the other is the radial bone, or radius.
No other joint in the human skeleton combines these
conditions and duplicates the this erroneously named
reaction so we only have one funny bone.

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WorldMags.net
Why do our muscles ache?
Learn what causes stiffness and pain in our muscles for days after exercise

The leptin (LEP)

gene was originally
discovered when a
random mutation
occurred in mice,
making them put
on weight

Weight lifting and the body

What happens to your biceps when you pump iron?
Pain
The soreness associated
with exercise is the result of
repetitive stretching of
contracted muscles.

Bending
Normally when the biceps
muscle group contracts it
shortens, pulling the forearm
towards the shoulder.

Straightening

Stretching

As the arm straightens out, the

biceps are stretched, but the
weight is still pulling down on the
hand, so the muscles remain partly
contracted to support it.

As the muscle tries to contract,

the weight pulls in the opposite
direction, causing microscopic
tears within the muscle cells.

The fat hormone

Discover how the body manages to
keep track of its energy reserves
In order to know how much food to eat, the human body needs a
way of assessing how much energy it currently has in storage.
Leptin more commonly known as the fat hormone essentially
acts as our internal fuel gauge. It is made by fat cells and tells the
brain how much fat the body contains, and whether the supplies are
increasing or being used up.
Food intake is regulated by a small region of the brain called the
hypothalamus. When fat stores run low and leptin levels drop, the
hypothalamus stimulates appetite in an attempt to increase food intake and
regain lost energy. When leptin levels are high, appetite is suppressed,
reducing food intake and encouraging the body to burn up fuel.
It was originally thought that leptin could be used as a treatment for
obesity. However, although it is an important regulator of food intake, our
appetite is affected by many other factors, from how full the stomach is to an
individuals emotional state or their food preferences. For this reason, its
possible to override the leptin message and gain weight even when fat stores
are sufcient.

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171

Alamy

Normally, when our muscles contract

they shorten and bulge, much like a
bodybuilders biceps. However, if the
muscle happens to be stretched as it
contracts it can cause microscopic damage.
The quadriceps muscle group located on the
front of the thigh is involved in extending the
knee joint, and usually contracts and shortens to
straighten the leg. However, when walking
down a steep slope, say, the quadriceps contract
to support your body weight as you step
forward, but as the knee bends, the muscles are
pulled in the opposite direction. This tension
results in tiny tears in the muscle and this is the
reason that downhill running causes so much
delayed-onset pain.
At the microscopic level, a muscle is made up
of billions of stacked sarcomeres, containing
molecular ratchets that pull against one another
to generate mechanical force. If the muscle is
taut as it tries to contract, the sarcomeres get
pulled out of line, causing microscopic damage.
The muscle becomes inamed and lls with
uid, causing stiffness and activating pain
receptors hence that achy feeling you get after
unfamiliar exercise.

CURIOUS
QUESTIONS
WorldMags.net

Bones / Raw meat / Inoculations

Why shouldnt
Why do the
we eat raw
upper arm
meat?
and upper
leg have only
one bone?

Mark Wolfe

How do
inoculations
work?
The terms inoculation and vaccination are
used interchangeably. They involve
introducing a foreign substance (antigens) into
the body, causing antibody production. These
can either be dead, made less harmful, or just contain
certain bits that cause disease.
White blood cells called B lymphocytes recognise these
antigens, and produce antibodies to neutralise them.
After the initial encounter, a group of B lymphocytes are
made called memory cells, which produce antibodies
faster if exposed to the same antigen again.

They involve introducing

antigens into the body
172 | How It Works

Thinkstock

The makeup of the

human skeleton is a
fantastic display of
evolution that has left us
with the ability to perform
incredibly complex tasks without
even thinking about them. There
are several different types of joint
between bones in your body, which
reect their function; some are
strong and allow little movement,
others are weak but allow free
movement. The forearm and lower
leg have two bones, which form
plane joints at the wrist and ankle.
This type of joint allows for a range
of ne movements, including gliding
and rotation. The hinge joints at
your elbows and knees allow for less
lateral movement, but they are
strong. Shoulders and hips, though,
are ball-and-socket joints, which
allow for a wide range of motion.

Meat can harbour many different bacteria, viruses

and even parasites. Cooking meat properly
destroys them, making meat much safer for
consumption. Bacteria and viruses can make you
ill, while parasites can grow inside your gut and even migrate
to your brain. Food poisoning is a very serious business and
by not cooking meat thoroughly, you are greatly increasing
your chances of getting something nasty. People quite often
eat raw meat such as steak tartare, but it requires extra care
in the preparation. Besides safety, cooking meat also makes it
taste better. By cooking meat and other foods, humans can
get much more energy than from chewing raw food alone.

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HEAD
HEAD

LONGEST-SLEEPING
MAMMALS

1. SHORTEST

2. AVERAGE

Giraffe

Human

Giraffes require less

sleep than any other
mammal, typically
getting 20-30
minutes per day for
ve minutes at a time.

3. LONGEST

The amount of sleep

we need varies from
person to person,
but we typically
require about eight
hours per night.

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Koala
Koalas are some of
the heaviest
sleepers, clocking
up approximately
15 hours of
snoozing per day.

DID YOU KNOW? Light affects the sleeping pattern of blind people, as ganglion cells are different from those that allow us to see

What causes
insomnia?
Why checking your phone before bed could
be spoiling your sleep

Laughter is
produced by the
same coughing

Light sensitivity
The ganglion layer

How light affects your ability to sleep

The retina of the eye contains a

layer of photosensitive ganglion
cells, which contain a
photopigment melanopsin, called
the ganglion layer.

Pineal gland
The suprachiasmatic
nucleus sends
information from the
photosensitive
ganglion cells to
the pineal gland,
located in the
epithalamus
section of
the brain.

Light
sensitivity
Unlike the other
photoreceptors in the
eye, photosensitive
ganglion cells
contribute little to
vision, but they are
sensitive to light.

Melatonin
Suprachiasmatic nucleus

Optic nerve

The suprachiasmatic nucleus is a tiny

area of neurons, located in the
hypothalamus area of the brain, which
controls circadian rhythms.

The photosensitive ganglion cells have

long fibres that connect to the optic
nerve and eventually reach the
suprachiasmatic nucleus.

When the photosensitive ganglion

cells detect darkness, a message is
sent to the pineal gland to produce
melatonin, a hormone that can
cause drowsiness.
Art Agency

Most of us experience insomnia at some

point in our lives, nding it difcult to
drift off and stay asleep, despite having
plenty of opportunity to. Typical causes
of insomnia include stress and anxiety, but did you
know that your gadgets could be to blame, too?
Our sleepiness and wakefulness throughout the
day and night is regulated by our circadian rhythm.
This is essentially our body clock, creating physical,
mental and behavioural changes that occur in our
bodies over a roughly 24-hour cycle. Circadian
rhythms are found in most living things, including
animals, plants and many tiny microbes, and they
are created by natural factors in the body. However,
they also respond to signals from the environment,
such as light, so that we remain in sync with the
Earths rotation.
All forms of light, both natural and articial, affect
our body clock, as when the photosensitive retinal
ganglion cells in our eyes detect light, they send this
information to the suprachiasmatic nucleus (SCN)
the group of nerves in the brain that control
circadian rhythms. When light is detected, the SCN
will delay the production of melatonin, a hormone
that sends us to sleep. However, the retinal ganglion
cells have been found to be particularly sensitive to
the blue light with a short wavelength of 480
nanometres emitted by most computer, smartphone
and tablet screens. Exposure to a lot of this type of
light in the hours before we go to bed has been
proven to suppress melatonin levels, making it
difcult for us to get to sleep.

Blocking blue light

The best way to reduce your
exposure to blue light is to avoid
staring at a screen within two hours
prior to going to bed. Instead,
illuminate the room with the
warmer, longer-wavelength light
from regular incandescent bulbs or
even candles. However, if you just
cant resist staring at your computer

or phone before bed, there are ways

that you can do so and still get a good
nights sleep. Wearing special
glasses with amber-coloured lenses
will lter out blue, low-wavelength
light, allowing you to stare at your
screen for as long as you like.
Companies such as Uvex (uvexsafety.co.uk) make blue-blocking

glasses and goggles in a range of

styles. Alternatively, you could use
computer software such as f.lux
(justgetux.com) and smartphone
apps such as Twilight (play.google.
com) that automatically adjusts your
screen to lter out blue light between
sunset and sunrise, replacing it with
a softer red light.

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Filter out blue

light with a pair
of amber-tinted
glasses

173

CURIOUS
QUESTIONS
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Hair growth / Blonde hair

Why does blonde

hair look darker
when its wet?
Dry blonde hair has a rough, tiled surface something like sh
scales. When light rays hit these scales, they bounce off in all
directions. Some of the light reaches your eyes and makes the
hair look brighter; its like shining a torch on the hair.
When you wash your hair, a thin lm of water forms around each bre.
Light rays pass into the lm of water, bounce around inside, and theres
a chance theyll get absorbed by the hair. Since the light gets trapped
inside the water, less of it reaches your eyes, so the hair actually appears
lot darker.

Thinkstock

A thin film of water forms

around each fibre

How quickly does

human hair grow?
Human hair grows on average 1.25 centimetres (0.5 inches)
per month, which is equivalent to about 15 centimetres
(six inches) per year. There are several variables that can
affect hairs growth rate such as age, health and genetics.
Each hair grows in three stages, the rst being the anagen phase
where most growth occurs. The longer your hair remains in this stage
dictates how long and quickly it develops; this can last between two
and eight years and is followed by the catagen (transitional) and
telogen (resting) phases. Hair growth rates vary across different areas
of the head, with that on the crown growing the fastest.

Each hair grows in three

stages, the first being the
anagen phase where most
growth occurs
174 | How It Works

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How do wrinkles form?

Discover how the bodys largest organ loses its elasticity over time
Wrinkles are an inevitable part of
the natural ageing process and
there are two types. Dynamic
wrinkles develop due to repeated
muscle movements, such as smile lines
around the mouth, and static wrinkles are
caused by environmental factors, lifestyle
habits and the ageing process. Static wrinkles
are visible even when your face is at rest and
often deepen over time. They are caused by a
loss of skin elasticity, fat and collagen.
The skin itself is made up of three separate
layers. The epidermis layer on the surface is
made up of dead skin cells and protects the
body from outside elements such as water
and sunlight. Beneath this layer is the
dermis, which is responsible for the skins
strength and elasticity, because its rich in
collagen and elastin bres. The base layer,
known as the hypodermis, is where you nd
the fat cells that give the skin its plump
youthful appearance.
Over time, wrinkles will start to form on
both the epidermis and dermis layers. As we
age, our skin cells take longer to divide, which
means the skin repairs at a much slower rate
than when its young. As a result of this, the
dermis layer will begin to thin out, and ne
lines start to form on the epidermis due to a
loss of moisture.
Eventually, collagen and elastin will break
down in the dermis layer, which reduces
support so the skin is unable to ping back as
quickly when stretched. Fat will also begin to
deplete in the hypodermis layer, causing the
skin to sag and appear much less plump.

Wrinkles are
caused by a loss
of collagen, fat
and elasticity in
the skin

What causes wrinkles?

The beauty industry makes millions of
pounds every year with products that
promise to slow down the ageing
process and vanquish already visible
lines and wrinkles.
Unfortunately, wrinkles are
unavoidable as we age, but their
development can be slowed to some
extent with a few preventative
measures. Exposure to sunlight is in
fact most detrimental to your skin, as
ultraviolet rays can break down
collagen and elastin bres in the dermis

layer, which leads to the skin losing its

strength and elasticity. So keeping your
skin suitably covered and protected
with a high-factor sun cream will help
to protect it from the effects of harmful
ultraviolet radiation.
Genetic factors, stress and repeated
facial expressions can also play a part in
how quickly wrinkles form, while
ditching bad habits such as smoking,
which reduces blood supply to the skin,
will also help delay the onset of ne
lines and wrinkles.

The ageing process

A closer look at how wrinkles form in the skin
Younger skin

Older skin
Deep wrinkles

Holding moisture

Fine lines start to develop

due to a lack of moisture
before eventually deepening
as the dermis layer weakens.

Youthful skin is softer and

smoother because it holds
much more moisture in the
epidermis layer than that of
older skin .

Less collagen
and elastin

Dermis layer
The dermis layer provides
support and gives skin its
elasticity as its packed full
of elastin fibres and
collagen.

Over time, collagen and

elastin fibres diminish in
the dermis layer, which
lessens support for the
epidermis, causing skin
to wrinkle.

Plump appearance

Loss of fat

Fat cells are stored in the

hypodermis layer and are
responsible for plumping up
younger skin.

As we age, skin will start to sag

as fat depletes in the
hypodermis layer.

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175

tr Sp
ia ec
l o ia
ff l
er

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HUMAN ANATOMY
How are
hormones
produced?

THE BODY AT WORK

CURIOUS QUESTIONS

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Blocked arteries
explained

Human
respiration

BOOK OF

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HUMAN

BODY

The structure
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Explore liver
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What makes
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Human anatomy

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How taste
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The lining of
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and behaviours

Curious questions

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