Nutrition in Humans
Sites for food digestion
mouth cavity
stomach
duodenum
ileum
Types of
Digestion
Mechanical Chemical
Mechanical
digestion
bread
Increases the surface area
for chemical digestion
Digestion in mouth cavity
Mechanical Chemical
Bread
2 Saliva
Mastication Teeth
contains
1 Starch + H2O
Saliva Bolus Amylase
3
Increase the S.A.
for chemical digestion
+ Saliva Maltose
Saliva
Amylase Water
Starch Maltose Lubricates the food, so Moistens dry food
it can be swallowed
easily
Swallowing
Nasal cavity
Soft palate
bolu
s
Epiglottis
Trachea Oesophagus
Position of different structures
during swallowing
2
Soft palate is
raised prevent food
from going up
3 Trachea is
closed by
epiglottis
1 Tongue is
raised Bolus enters
4 oesophagus
Peristalsis
Wave action
Circular muscle
contracts
X
Longitudinal muscle
Circular muscle
These two muscles contract
& relax alternately
Digestion in stomach
Closed during
physical digestion
Circular muscle
Longitudinal muscle
Closed during
physical digestion
The churning movement of the stomach
sphincters
open
Digestion in
stomach
Mechanical Chemical
Feature Adaptation Feature Adaptation
Food is 1. Protease Protein Peptides
Strong muscle
contraction churned up
to form
chyme
to increase
surface area
for enzyme
to act on
Wall of Stomach
Mucus-secreting gland Gastric gland
Feature Adaptation Feature Adaptation
• Protects the wall 1. Protease
Mucus Protein Peptides
2. Acid * Provides an acidic
from being medium for enzymes
• Lubrication
digested
* Kills germs
Digestion in Duodenum
2
Digestion in Duodenum
Bile
contains Pancreatic juice
three juices Intestinal juice
from
gall bladder
Bile
from
pancreas
Duodenum
Pancreatic juice
Intestinal juice
Ileum
Liver, bile and gall bladder
Bile which is stored
in the gall bladder
Produces
Liver the bile is then
discharged into
the duodenum
Gall
bladder
Bile Composition
Bile salt Bile pigment
(green in colour)
emulsified
NaHCO3
Oil Oil
Products of
droplets
Increase S.A. for latter chemical digestion breakdown of
haemoglobins
Emulsification No enzyme in bile
Mechanical digestion Bile is an alkaline fluid
Pancreas
The pancreatic juice Pancreatic
is discharged into the
juice
duodenum
Produces
Pancreas
Pancreatic
Composition juice
Pancreatic Protease Lipase NaHCO3
amylase
Protein Peptides Fatty
Starch Oil droplets
Maltose acids
Peptides Amino acids
+
Glycerol
Pancreatic juice is an alkaline fluid
3 Duodenum Ileum
4
from
gall bladder
intestine
from
pancreas
Duodenum
small
Intestinal juice
Ileum
3 Duodenum 4 Ileum
Intestinal
Composition
juice
Intestinal Intestinal
protease carbohydrases
Peptides Amino acids
Disaccharides Monosaccharides
Maltose Glucose
which neutralises
the acid in chyme
Bile 1
Contains
Pancreatic hydrogencarbonate
juice
2
Intestinal which provides an
alkaline medium for
juice the enzymes
Summary
Starch
Salivary Gland
Amylase
Pancreas
Maltose
Intestinal
Carbohydrase Gland
Glucose
Protein
Gastric Gland
Proteases
Pancreas
Peptides
Pancreas
Proteases
Intestinal Gland
Amino Acids
Oil
Bile salt Liver
Oil droplets
Lipase Pancreas
Fatty Acids
+
Glycerol
Summary
Process Structure involved
Mechanical Chewing :Large food By
Digestion teeth
is broken into
smaller pieces
ChurningLarge
: food By
is broken into strong muscle
smaller pieces
By
Oil
Emulsification :is broken bile salt
into oil droplets
Chemical By
Digestion enzymes
All digested Large intestine
food will be
absorbed in
the small
intestine
Undigested
remains
Large intestine
3
No function in human Colon
But in herbivores,
Reduced in size caecum & appendix
are longer.
2 They play an 4
Caecum important roleRectum
in
1
digestion of cellulose.
Appendix
Digestion – completed in small intestine
Before digestion After digestion
Protein Amino Acids
Fat Fatty Acids & glycerol
Starch Glucose
Absorption
Absorption
1. Stomach e.g. water, alcohol
2. Ileum (most important site for food
absorption)
Absorption in ileum
Wall of ileum
ileum
Absorption in ileum
Wall of ileum
Finger-like structure called
villus
Villus / villi
Increases
the surface
area for
absorption
Finger-like structure called
villus
Villus
1 Epithelium
2 Blood
capillaries
3 Lacteal
Villus
1 Epithelium (very thin)
Digested is one-cell
food thick
shorten the
distance for
diffusion of
digested food
Villus
Blood
2 capillaries
Transport the
absorbed food
Maintain a steep
conc. gradient to
enhance the rate
of diffusion
Villus
Absorb & transport
fat molecules in
digested food
3 Lacteal
Absorption in villus
Blood capillary
Epithelial cell Lacteal
Absorption in villus
Blood capillary
By diffusion &
active transport
Pass into the
capillaries Epithelial cell Lacteal
100 units
ileum glucose
90 … 50 40 0
blood
vessel 0 10 … 50 60 100
Movement of Movement of
molecules from low
molecules from
conc. to high conc.
high conc. to using energy from
low conc. respiration
Diffusion Active Transport
Absorption in villus
Blood capillary
By diffusion &
active transport 2
1
2
Enter the lacteal &
recombine to fat
molecules
Epithelial cell Lacteal
Summary
Structural features Adaptation of ileum
Wall of ileum is highly
folded & To increase surface area for
has numerous villi food absorption
To shorten distance for
diffusion
One-cell thick epithelium
Lacteal is surrounded by a
network of blood capillaries
To transport absorbed
food
heart
hepatic vein
cells
aorta
the
ort l
sp se
fat tran ves
to ph
Glucose, amino acids,
lym
fat etc. carried by aorta
to all tissue cells
liver
hep e um
atic il
por
tal v
ein
Assimilation - the used up of digested
food by cells
Amino acids protein
(for growth & repair)
Glucose energy source
Fat energy source
cell
heart
hepatic vein Blood glucose = 100 units
Blood amino acid =90 units
1. Excess glucose converted aorta
to glycogen
2. Excess amino acids sel he
es tt
deaminated to form v or
h
p nsp
urea lym tra
to t
fa
liver
hep e um Excess fat molecules
atic il
por are stored around
tal v
ein internal organs & under
After a diet
the skin
Blood glucose = 200 units
Blood amino acid =120 units
Large intestine
3
Colon
2 4
Caecum Rectum
1
Appendix 5
Anus
3
Colon
absorbs water
& minerals
but most of the
water in the gut is
absorbed in the
small intestine
3
Colon
absorbs water
If & minerals
leads to
diarrhoea
& results in dehydration &
excessive loss of ions
Egestion
Undigested
food Removal of
Dead bacteria
semi- undigested or
unabsorbed food
Living bacteria solid
Bile pigment
faeces
Water
Dead cells from
digestive system temporarily
Secretions of stored in
the alimentary
canal 9
Rectum
Egestion
Constipation Removal of
undigested or
unabsorbed
difficult to semi-
remove food
solid If you do not
the faeces faeces have dietary
become harder fibers
faeces stay
longer in the
excess water is which would
large intestine
absorbed stimulate
peristalsis
Functions of liver
4. Storage of
vitamin A & D,
iron & glycogen
3. Bile
2. Deamination
secretion
6. Detoxification
1. Blood glucose
5. Production
level regulation
of heat,
plasma protein
