CAPE Biology Unit 2

Study Notes
Topics:

1: Photosynthesis
2: Respiration
3: Energy Flow and Nutrient Cycling
4: The Uptake and Transport of Water and Minerals
5: Circulatory System in Mammals
6: The Hormone System and Homeostasis
7: The Kidney and Excretion
8: The Human Nervous System
9: Health and Diseases
10: Immunology
11: Social and Preventative Medicine

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1. Photosynthesis

Photosynthesis

Photosynthesis is essentially the reverse of respiration. It is usually simplified to:

carbon dioxide + water (+ light energy) = glucose + oxygen

But again this simplification hides numerous separate steps. To understand photosynthesis
in detail we can break it up into 2 stages:

Light  
light-dependent reactions light-indepdendent reactions
(thylakoid membrane) (stroma)
Water Hydrogen Glucose
H2O H C6H12O6
O2 ADP + Pi ATP CO2 ATP ADP + Pi

• The light-dependent reactions use light energy to split water and make some ATP and
energetic hydrogen atoms. This stage takes place within the thylakoid membranes of
chloroplasts, and is very much like the respiratory chain, only in reverse.
• The light-independent reactions don’t need light, but do need the products of the light-
dependent stage (ATP and H), so they stop in the absence of light. This stage takes place
in the stroma of the chloroplasts and involves the fixation of carbon dioxide and the
synthesis of glucose.

We shall see that there are many similarities between outer membrane
photosynthesis and respiration, and even the same inner membrane
enzymes are used in some steps. thylakoid membrane

thylakoid lumen
Chloroplasts
granum (thylakoid stack)
Photosynthesis takes place entirely within stalked particles
chloroplasts. Like mitochondria, chloroplasts have a (ATP synthase)
double membrane, but in addition chloroplasts have a stroma
third membrane called the thylakoid membrane. This starch grain
is folded into thin vesicles (the thylakoids), enclosing
small spaces called the thylakoid lumen. The

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thylakoid vesicles are often layered in stacks called grana. The thylakoid membrane contains
the same ATP synthase particles found in mitochondria. Chloroplasts also contain DNA,
tRNA and ribososomes, and they often store the products of photosynthesis as starch grains
and lipid droplets.

Chlorophyll is a fairly small molecule (not a protein) with a structure similar to haem, but with
a magnesium atom instead of iron. Chlorophyll and the other pigments are arranged in
complexes with proteins, called photosystems. Each photosystem contains some 200
chlorophyll molecules and 50 molecules of accessory pigments, together with several protein
molecules (including enzymes) and lipids. These photosystems are located in the thylakoid
membranes and they hold the light-absorbing pigments in the best position to maximise the
absorbance of photons of light. The chloroplasts of green plants have two kinds of
photosystem called photosystem I (PSI) and photosystem II (PSII). These absorb light at
different wavelengths and have slightly different jobs in the light dependent reactions of
photosynthesis.

Light Dependent Reactions

In the light dependent reactions, chlorophyll converts sunlight energy into chemical energy
(ATP and NADPH)
ATP: Adenosine Triphosphate NADPH: Nicotinamide adenine dinucleotide phosphate
The analogy is with solar cells converting sunlight into electricity which can do work.

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In photosynthesis the electrons are picked up by electron transport systems which use the
energy in the electrons to make an energy carrying compound called ATP and a second
compound, NADPH.
Pigments in Chloroplasts
Photons - light is composed of energy called a photon. Photons have wavelengths, the
longer the wavelength, the less energy stored. When light (photons) strike an object, they
may be absorbed, reflected, or transmitted (pass thru). Reflected light gives an object its
color. Absorbed light provides the energy to drive chemical reactions.
Chlorophyll - absorbs violet, blue and red light (reflects green) - The TWO most common
Types of Chlorophylls are designated Chlorophyll a and Chlorophyll b.
Carotenoids - absorb blue and green light (reflect yellow, orange, or red). Carotenoids are
visible in the fall, when plants stop producing chlorophyll; leaves take on a yellow/red color
Phycocyanins - absorb green and yellow light (reflect blue or purple)
Xanthophyll - type of carotenoid that reflects yellow light (seen in the autumn)
Steps of the Light Reactions

The light reactions occur in several steps, all of which take place in the thylakoid membrane,
as shown in Figure above.

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Step 1: Units of sunlight, called photons, strike a molecule of chlorophyll in photosystem II of
the thylakoid membrane. The light energy is absorbed by two electrons (2 e-) in the
chlorophyll molecule, giving them enough energy to leave the molecule.
Step 2: At the same time, enzymes in the thylakoid membrane use light energy to split apart
a water molecule. This produces:
• two electrons (2 e-). These electrons replace the two electrons that were lost from
the chlorophyll molecule in Step 1.
• an atom of oxygen (O). This atom combines with another oxygen atom to produce a
molecule of oxygen gas (O2), which is released as a waste product.
• two hydrogen ions (2H+). The hydrogen ions, which are positively charged, are
released inside the membrane in the thylakoid interior space.
Step 3: The two excited electrons from Step 1 contain a great deal of energy, so, like hot
potatoes, they need something to carry them. They are carried by a series of electron-
transport molecules, which make up an electron transport chain. The two electrons are
passed from molecule to molecule down the chain. As this happens, their energy is captured
and used to pump more hydrogen ions into the thylakoid interior space.
Step 4: When the two electrons reach photosystem I, they are no longer excited. Their
energy has been captured and used, and they need more energy. They get energy from
light, which is absorbed by chlorophyll in photosystem I. Then, the two re-energized
electrons pass down another electron transport chain.
Step 5: Enzymes in the thylakoid membrane transfer the newly re-energized electrons to a
compound called NADP+. Along with a hydrogen ion, this produces the energy-carrying
molecule NADPH. This molecule is needed to make glucose in the Calvin cycle.
Step 6: By now, there is a greater concentration of hydrogen ions—and positive charge—in
the thylakoid interior space. This difference in concentration and charge creates what is
called a chemiosmotic gradient. It causes hydrogen ions to flow back across the thylakoid
membrane to the stroma, where their concentration is lower. Like water flowing through a
hole in a dam, the hydrogen ions have energy as they flow down the chemiosmotic gradient.
The enzyme ATP synthase acts as a channel protein and helps the ions cross the
membrane. ATP synthase also uses their energy to add a phosphate group (Pi) to a
molecule of ADP, producing a molecule of ATP. The energy in ATP is needed for the Calvin
cycle.

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The Light-Independent Reactions
The light-independent, or carbon-fixing
reactions, of photosynthesis take place in the
stroma of the chloroplasts and comprise
another cyclic pathway, called the Calvin
Cycle. The Calvin cycle is a metabolic pathway
found in the stroma of the chloroplast in which
carbon enters in the form of CO2 and leaves in
the form of sugar.

The Calvin Cycle involves the fixation and

reduction of Carbon. The Steps:

1. CO2 combines with the phosphorylated 5-

carbon sugar ribulose bisphosphate
2. This reaction is catalyzed by the enzyme ribulose bisphosphate carboxylase oxygenase
(RUBISCO an enzyme which can fairly claim to be the most abundant protein on earth)
3. The resulting 6-carbon compound breaks down into two molecules of 3-phosphoglyceric
acid (PGA)
4. The PGA molecules are further phosphorylated (by ATP) and are reduced (by NADPH)
to form phosphoglyceraldehyde (G3P, also called PGAL)
5. Phosphoglyceraldehyde serves as the starting material for the synthesis of glucose and
fructose, or it can be used to make more RuBP.
6. Glucose and fructose make the disaccharide sucrose, which travels in solution to other
parts of the plant (e.g., fruit, roots) or is used in the synthesis of the polysaccharides
starch and cellulose

Factors Affecting Photosynthesis

Light Intensity
Low light intensity lowers the rate of photosynthesis. As the intensity is increased the rate
also increases. However, after reaching an intensity of 10,000 lux (lux is the unit for
measuring light intensity) there is no effect on the rate. Very high intensity may, in fact, slow
down the rate as it bleaches the chlorophyll. Normal sunlight (usually with an intensity of
about 100,000 lux) is quite sufficient for a normal rate of photosynthesis.

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Carbon Dioxide Concentration
In the atmosphere, the concentration of carbon dioxide ranges from .03 to .04 %. However, it
is found that 0.1% of carbon dioxide in the atmosphere increases the rate of photosynthesis
significantly. This is achieved in the greenhouses which are enclosed chambers where plants
are grown under controlled conditions. The concentration is increased by installing gas
burners which liberate carbon dioxide as the gas burns. Crops like tomatoes, lettuce are
successfully grown in the greenhouses. These greenhouse crops are found to be bigger and
better-yielding than their counterparts growing in natural conditions.
The following graph shows how different concentrations affect the rate of photosynthesis.

Temperature
An optimum temperature ranging from 25oC to 35oC is
required for a good rate. At temperatures around 0oC
the enzymes stop working and at very high
temperatures the enzymes are denatured. Since both
the stages of photosynthesis require enzyme activity,
the temperature has an affect on the rate of
photosynthesis.

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Chlorophyll Concentration
The concentration of chlorophyll affects the rate of reaction as they absorb the light energy
without which the reactions cannot proceed. Lack of chlorophyll or deficiency of chlorophyll
results in chlorosis or yellowing of leaves. It can occur due to disease, mineral deficiency or
the natural process of aging (senescence). Lack of iron, magnesium, nitrogen and light affect
the formation of chlorophyll and thereby causes chlorosis.
Water
Water is an essential factor in photosynthesis. The effect of water can be understood by
studying the yield of crops which is the direct result of photosynthetic activity. It is found that
even slight deficiency of water results in significant reduction in the crop yield. The lack of
water not only limits the amount of water but also the quantity of carbon dioxide. This is
because in response to drying the leaves close their stomata in order to conserve water
being lost as water vapour through them.

Practice questions
1. What colour photon is reflected by photosynthetic organisms containing chlrophyll a
and b?
a) violet b) blue c) green d) red

2. What is the substrate for photolysis in plants?

a) H2S b) H2O c) O2 d) (b) and (c)

3. When does the process of splitting water to release hydrogen ions, electrons, and
oxygen occur?
a)during the light reactions b)during the Calvin cycle
c)during carbon fixation d)both (b) and (c)

4. When a molecule of water is split, what is the fate of the oxygen atoms from the water?
a)it is released as carbon dioxide (CO2) b)it is released as oxygen gas (O2)
c)it is released as water (H2O) d)it is incorporated into glucose (C6H12O6)

5. When does the process of incorporating the carbon of carbon dioxide into
carbohydrates occur?
a)during the light reactions b)during the Calvin cycle
c)during carbon fixation d)both (b) and (c)

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6. What is the term for an individual flattened membrane-bound sac in the chloroplast?
a) granum b) stroma c) thylakoid d) lamella

7. What do the proteins plastocyanin (Pc) and plastoquinone (Q) have in common?
a) they are electron acceptors of photosystems
b) they receive electrons and move to transfer them within the thylakoid membrane
c) they allow H+ ions to pass across the membrane
d) they are found in both chloroplasts and mitochondria

8. What is the final electron acceptor in non-cyclic phosphorylation?

a) NADP+ b) oxygen c) H2O d) P680

9. In what phase of photosynthesis are the products of the light reactions used?
a) during the light reactions b) during photolysis
c) during the Calvin cycle d) during the synthesis of ATP

10. Where do the surplus H+ ions flow to cause ATP synthase to make ATP?
a) matrix to thylakoid space b) stroma to thylakoid space
c) thylakoid space to stroma d) stroma to cytoplasm

11. Where in the chloroplast does the Calvin cycle occur?

a) stroma b) thylakoid space c) thylakoid membrane d) cytoplasm

12. What is the name of the large enzyme that catalyzes the carbon fixation reaction of the
Calvin cycle?
a) ATP synthase b) glyceraldehyde carboxylase
c) ribulose phosphate carboxylase d) rubisco

13. Define photosynthesis.

14. What materials are required for photosynthesis? What is produced?
15. Write the overall reaction for photosynthesis.
16. Describe what happens during the cyclic phosphorylation of photosystem I. How does
the transfer of electrons lead to the synthesis of ATP?
17. Describe the reactions of carbon fixation or the Calvin cycle. What enzyme catalyzes
the reaction? What are the products of the reaction?

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2. Respiration
Metabolism refers to all the chemical reactions taking place in a cell. There are thousands of
these in a typical cell, and to make them easier to understand, biochemists arrange them into
metabolic pathways. The intermediates in these metabolic pathways are called metabolites.
• Reactions that release energy (usually breakdown reactions) are called catabolic reactions
(e.g. respiration)
• Reactions that use up energy (usually synthetic reactions) are called anabolic reactions
(e.g. photosynthesis).
Photosynthesis and respiration are the reverse of each other, and you couldn’t have one
without the other. The net result of all the photosynthesis and respiration by living organisms
is the conversion of light energy to heat energy.
Cellular Respiration
The equation for cellular respiration is usually simplified to:
glucose + oxygen → carbon dioxide + water (+ energy)
But in fact respiration is a complex metabolic pathway, comprising at least 30 separate
steps. To understand respiration in detail we can break it up into 3 stages:
  →
Glycolysis Krebs Cycle Respiratory Chain
(cytoplasm) (mitochondrial (inner mitochondrial
Glucose Pyruvate matrix) Hydrogen membrane) Water
C6H12O6 C3H4O3 H H2O
CO2 O2 ADP + Pi ATP

Before we look at these stages in detail, there are a few points from this summary.
• The different stages of respiration take place in different parts of the cell. This allows the
cell to keep the various metabolites separate, and to control the
outer membrane
stages more easily. inner membrane
• As we saw in module 3, the energy released by respiration is
christa (fold)
in the form of ATP.
• Since this summarises so many separate steps (often matrix

+ - stalked particles
involving H and OH ions from the solvent water), it is (ATP synthase)
meaningless to try to balance the summary equation.
• The release of carbon dioxide takes place before oxygen is ribosomes
involved. It is therefore not true to say that respiration turns
DNA
oxygen into carbon dioxide; it is more correct to say that
respiration turns glucose into carbon dioxide, and oxygen into water.

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• Stage 1 (glycolysis) is anaerobic respiration, while stages 2 and 3 are the aerobic stages.

Much of respiration takes place in the mitochondria. Mitochondria have a double membrane:
the outer membrane contains many protein channels called porins, which let almost any
small molecule through; while the inner membrane is more normal and is impermeable to
most materials. The inner membrane is highly folded into folds called christae, giving a larger
surface area. The electron microscope reveals blobs on the inner membrane, which were
originally called stalked particles. These have now been identified as the enzyme complex
that synthesises ATP, and is more correctly called ATP synthase (more later). The space
inside the inner membrane is called the matrix, and is where the Krebs cycle takes place.
The matrix also contains DNA, tRNA and ribosomes, and some genes are replicated and
expressed here.

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Details of Respiration

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Glycolysis - occurs in the cell cytoplasm in both aerobic and anaerobic conditions.
1. Glucose is phosphorylated twice, i.e. ATP is used to add a phosphate group to glucose.
This makes the glucose more reactive, allowing it to be broken down. A six carbon (6C)
phosphorylated sugar is produced called hexose bisphosphate.
2. The hexose bisphosphate is converted into two molecules of a 3C sugar phosphate
called Triose Phosphate (TP)
3. Hydrogen is removed from each of the TP molecules, i.e. the TP molecules are oxidised.
The hydrogen is passed to NAD, a coenzyme which, by definition, is said to be reduced.
Remember - any substance that gains oxygen or loses hydrogen or electrons is said to
be oxidised. Any substance that loses oxygen or gains hydrogen or electrons is said to
be reduced. The enzymes which remove hydrogen from substances are called
dehydrogenases. The hydrogen atoms picked up by NAD are used to generate four
molecules of ATP. The removal of hydrogen from TP produces pyruvic acid also called
pyruvate (PA).
The Link Reaction - occurs only if oxygen is available.
4. PA enters the mitochondrion
5. Carbon dioxide and hydrogen are removed from the PA by decarboxylase and
dehydrogenase enzymes respectively. The PA is combined with coenzyme A (CoA) to
form a 2C compound called acetylcoenzyme A (AcCoA).

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Kreb's Cycle - only occurs if oxygen is available.

6. AcCoA (2C) is combined with oxaloacetate (4C) to form citrate (6C). Citrate enters the
Kreb’s cycle. This involves a series of decarboxylation and dehydrogenation reactions.
7. The carbon dioxide is released. The hydrogen which is removed is passed to coenzymes
such as NAD and FAD (i.e. the coenzymes are reduced).
8. 2ATP molecules are generated directly in the Kreb’s cycle.
9. Eventually the 4C compound (oxaloacetate) is regenerated. This then combines with
more AcCoA and the whole cycle begins again.

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The electron transfer chain - only occurs if oxygen is available.

10. NADH molecules bind to Complex I and release their hydrogen atoms as protons (H +)
and electrons (e-). The NAD molecules then returns to the Krebs Cycle to collect more
hydrogen. FADH binds to complex II rather than complex I to release its hydrogen.
11. The electrons are passed down the chain of proteins complexes from I to IV, each
complex binding electrons more tightly than the previous one. In complexes I, II and IV
the electrons give up some of their energy, which is then used to pump protons across
the inner mitochondrial membrane by active transport through the complexes. Altogether
10 protons are pumped across the membrane for every hydrogen from NADH (or 6
protons for FADH).
12. In complex IV the electrons are combined with protons and molecular oxygen to form
water, the final end-product of respiration. The oxygen diffused in from the tissue fluid,
crossing the cell and mitochondrial membranes by lipid diffusion. Oxygen is only involved

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 at the very last stage of respiration as the final electron acceptor, but without the whole
respiratory chain stops.

13. The energy of the electrons is now stored in the form of a proton gradient across the
inner mitochondrial membrane. It’s a bit like using energy to pump water uphill into a high
reservoir, where it is stored as potential energy. And just as the potential energy in the
water can be used to generate electricity in a hydroelectric power station, so the energy
in the proton gradient can be used to generate ATP in the ATP synthase enzyme. The
ATP synthase enzyme has a proton channel through it, and as the protons “fall down”
this channel their energy is used to make ATP, spinning the globular head as they go. It
takes 4 protons to synthesise 1 ATP molecule.
This method of storing energy by creating a protons gradient across a membrane is
called chemiosmosis, and was discovered by Peter Mitchell in the 1960s, for which work
he got a Nobel prize in 1978. Some poisons act by making proton channels in
mitochondrial membranes, so giving an alternative route for protons and stopping the
synthesis of ATP. This also happens naturally in the brown fat tissue of new-born babies
and hibernating mammals: respiration takes place, but no ATP is made, with the energy
being turned into heat instead.

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How Much ATP is Made in Respiration?

Other substances can also be

used to make ATP. Triglycerides
are broken down to fatty acids and
glycerol, both of which enter the
Krebs Cycle. A typical triglyceride
might make 50 acetyl CoA
molecules, yielding 500 ATP
molecules. Fats are a very good
energy store, yielding 2.5 times as
much ATP per g dry mass as
carbohydrates. Proteins are not
normally used to make ATP, but in
times of starvation they can be broken down and used in respiration. They are first broken
down to amino acids, which are converted into pyruvate and Krebs Cycle metabolites and
then used to make ATP.

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Anaerobic Respiration
When oxygen is not available to serve
as the final electron acceptor, the
electron transport system is unable to
function. Electrons are not passed down
the cytochrome system, and both
FADH2 and NADH are unable to release
electrons. If the carrier molecules
cannot be returned to their oxidized
state, they are unable to accept new
electrons. The entire aerobic pathway
will shut down.The cell does have an
alternative system which will allow glycolysis to continue despite the lack of oxygen.
Anaerobic fermentation will remove hydrogens and electrons from NADH and will remove the
end product pyruvate. Together, these actions will allow glycolysis to continue.
Two different anaerobic fermentation pathways are known. Alcoholic fermentation is
common in bacteria and yeast cells. In alcoholic fermentation, pyruvate is first
decarboxylated to yield a 2-carbon substance acetaldehyde. Acetaldehyde is then reduced
as hydrogens are transferred from NADH to acetaldehyde to produce ethyl alcohol. Once the
NAD has been oxidized, glycolysis can continue.
The same result is reached by animal cells through the process of lactic acid fermentation.
Here pyruvate is used as the direct acceptor of the hydrogens removed from NADH. The end
product is a molecule of lactic acid. Lactic acid [or lactate] is a common by-product of
anaerobic respiration in muscle cells. The steps of anaerobic fermentation do not themselves
produce any additional ATP. Their sole value is that, by permitting the continued glycolytic
activity, they allow at least some energy to be recovered in the absence of oxygen.

Practice Questions

1. Which of the following is not a product of fermentation?

A) CO2 B) O C) ethanol D) lactate

2. What substance is produced by the oxidation of pyruvate and feeds into the citric acid
cycle?
A) pyruvate B) glucose C) acetyl-CoA D) O2

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3. In aerobic cellular respiration, which generates more ATP, substrate-level
phosphorylation or chemiosmosis?
A) substrate-level phosphorylation B) chemiosmosis
C) both generate the same amount of ATP D) neither generates any ATP

4. What role does O2 play in aerobic respiration?

A) it plays no role
B) it combines with acetyl-CoA at the start of the Krebs cycle
C) it is given off as a by-product during the oxidation of pyruvate
D) it combines with H2O to help drive the formation of ATP
E) it is the final electron acceptor at the end of the electron transport chain

5. During aerobic respiration, FADH2 is produced in

A) glycolysis B) the oxidation of pyruvate
C) the Krebs cycle D) fermentation

6. NADH is produced during

A) glycolysis B) the oxidation of pyruvate
C) the Krebs cycle D) all of the above

7. During what stage of cellular respiration is the most ATP synthesized?

A) glycolysis B)oxidation of pyruvate C)Krebs cycle D) chemiosmosis

8. What substance is regenerated by fermentation?

A)O2 B)NAD+ C)acetyl-CoA D)ATP

9. During chemiosmosis in aerobic respiration, protons are pumped

A) out of the cell
B) out of the mitochondria into the cell cytoplasm
C) out of the mitochondrial matrix into the outer compartment of the mitochondria
D) out of the cell cytoplasm into the matrix of the mitochondria

10. Oxidizing which of the following substances yields the most energy?
A)proteins B)glucose C)fatty acids D)alcohol

11. Draw glycolysis.

Tell how many carbon atoms are present in glucose and in pyruvate.

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 List the kinds of high-energy molecules are produced and tell how many.

12. Draw the reaction that forms Acetyl CoA .

13. Draw the Krebs cycle.

Tell how many carbon atoms are present in each of the compounds produced by the
Krebs cycle.
List the kinds of high-energy molecules are produced and tell how many are produced
during one turn of the cycle.

14. How many ATP are produced by the complete oxidative breakdown of one glucose
molecule?

15. Where does chemiosmotic phosphorylation occur?

16. The electron transport chain pumps what kind of ions into the intermembrane space?

17. Name the ultimate electron acceptor in aerobic respiration.

18. Glycolysis depends on a continuous supply of what molecule?

19. What is the end product of fermentation?

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3. Energy Flow and Nutrient Cycling

Ecosystems

Ecology is the study of living organisms and their environment. Its aim it to explain why
organisms live where they do. To do this ecologists study ecosystems; areas that can vary
in size from a pond to the whole planet.

Ecosystem: A reasonably self-contained area together with all its living organisms.
Habitat: The physical or abiotic part of an ecosystem, i.e. a defined area with
specific characteristics where the organisms live, e.g. oak forest, deep
sea, sand dune, rocky shore, moorland, hedgerow, garden pond, etc.
Community: The living or biotic part of an ecosystem, i.e. all the organisms of all the
different species living in one habitat.
Biotic: Any living or biological factor.
Abiotic: Any non-living or physical factor.
Population: The members of the same species living in one habitat.
Ecological niche: A niche is the sum total of an organism's use of biotic and abiotic
resources in its environment, how it "fits into" an ecosystem: A niche
may apply to species, populations or even individuals.
Energy and Matter
Before studying ecosystems, it is important to appreciate the difference between energy and
matter. Energy and matter are quite different things and cannot be inter-converted.
• Energy comes in many different forms (such as heat, light, chemical, potential, kinetic, etc.)
which can be inter-converted, but energy can never be created, destroyed or used up. If
we talk about energy being “lost”, we usually mean as heat, which is radiated out into
space. Energy is constantly arriving on earth from the sun, and is constantly leaving the
earth as heat, but the total amount of energy on the earth is constant.
• Matter comes in three states (solid, liquid and gas) and again, cannot be created or
destroyed. The total amount of matter on the Earth is constant. Matter (and especially the
biochemicals found in living organisms) can contain stored chemical energy, so a cow
contains biomass (matter) as well as chemical energy stored in its biomass.

All living organisms need energy and matter from their environment. Matter is needed to
make new cells (growth) and to create now organisms (reproduction), while energy is

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needed to drive all the chemical and physical processes of life, such as biosynthesis, active
transport and movement.

Food Chains and Webs

The many relationships between the members of a community in an ecosystem can be

described by food chains and webs. Each stage in a food chain is called a trophic level, and
the arrows represent the flow of energy and matter through the food chain. Food chains
always start with photosynthetic producers (plants, algae, plankton and photosynthetic
bacteria) because, uniquely, producers are able to extract both energy and matter from the
abiotic environment (energy from the sun, and 98% of their matter from carbon dioxide in the
air, with the remaining 2% from water and minerals in soil). All other living organisms get
both their energy and matter by eating other organisms.

Although this represents a “typical” food chain, e.g.

grass ---> grasshopper --> mouse ---> snake ---> hawk
with producers being eaten by animal consumers, different organisms use a large range of
feeding strategies (other than consuming), leading to a range of different types of food chain.
Some of these strategies are defined below, together with other terms associated with food
chains. The real world, of course, is more complicated than a simple food chain. While many
organisms do specialize in their diets (anteaters come to mind as a specialist), other
organisms do not. Hawks don't limit their diets to snakes, snakes eat things other than mice,

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mice eat grass as well as grasshoppers, and so on. A more realistic depiction of who eats
whom is called a food web; an example is shown. It is when we have a picture of a food web
in front of us that the definition of food chain makes more sense. We can now see that a food
web consists of interlocking food chains, and that the only way to untangle the chains is to
traceback along a given food chain to its source.
Producer: An organism that produces food from carbon dioxide and water using
photosynthesis. Can be plant, algae, plankton or bacteria.
Consumer: An animal that eats other organisms
Herbivore: A consumer that eats plants (= primary consumer).
Carnivore: A consumer that eats other animals (= secondary consumer).
Omnivore: A consumer that eats plants or animals.
Autotroph: An organism that manufactures its own food (= producer)
Heterotroph: An organism that obtains its energy and mass from other organisms
(=consumers + decomposers)
Predator: An animal that hunts and kills animals for food.
Prey: An animal that is hunted and killed for food.
Scavenger: An animal that eats dead animals, but doesn't kill them
Detritus: Dead and waste matter that is not eaten by consumers
Decomposer: An organism that consumes detritus (= detrivores + saprophytes)
Detrivore: An animal that eats detritus.
Saprophyte: A microbe (bacterium or fungus) that lives on detritus.
Symbiosis: Organisms living together in a close relationship (= parasitism,
mutualism, pathogen).
Mutualism: Two organisms living together for mutual benefit.
Commensalism: Relationship in which only one organism benefits

So food chains need not end with a consumer, and need not even start with a producer, e.g.:

Primary Top Scavenger

Producer
Consumer Consumer

Detritus Decomposer Consumer Parasite

In ecology, energy flow (calorific flow) refers to the flow of energy through a food chain.

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In following energy flow in an ecosystem, ecologists seek to quantify the relative importance
of different component species and feeding relationships.

A general energy flow scenario follows:

* Energy is taken up from the sun by the autotrophs, the so called primary producers, like
green plants which transform it to glucose and ATP by photosynthesis.
* The primary consumers eating these autotrophs are herbivores. They extract most of the
energy stored in the plant through digestion, and transform it into the form of energy they
need. A part of the energy received by the herbivore is converted to bodily heat, which is
radiated away and lost from the system.
* Carnivores feed on the herbivores, recovering their energy for themselves. Again some
energy is lost from the system.
* Other carnivores prey on those carnivores, and most of the energy is passed along,
while some is again lost.

The energy is passed on from trophic level to trophic level and each time some (about 90%)
of the energy is lost. So the top consumer of a food chain receives the least energy. This
loss of energy at each level limits typical food chains to only 4-6 links.

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Energy Flow in Ecosystems

Three things can happen to the energy taken in by the organisms in a trophic level:
• It can be passed on to the biomass of the next trophic level in the food chain when the
organism is eaten.
• It can become stored in detritus. This energy is passed on to decomposers when the
detritus decays.
• It can be converted to heat energy by inefficient chemical reactions, radiated by warm
bodies, or in friction due to movement. The heat energy is lost to the surroundings, and
cannot be regained by living organisms. These three fates are shown in this energy flow
diagram:

Eventually all the energy that enters the

ecosystem will be converted to heat,
which is lost to space.

Material Cycles in Ecosystems

Matter cycles between the biotic
environment and in the abiotic
environment. Simple inorganic
molecules (such as CO2, N2 and H2O)
are assimilated (or fixed) from the
abiotic environment by producers and
microbes, and built into complex
organic molecules (such as
carbohydrates, proteins and lipids).
These organic molecules are passed
through food chains and eventually
returned to the abiotic environment
again as simple inorganic molecules by
decomposers. Without either
producers or decomposers there
would be no nutrient cycling and no life.

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The simple inorganic molecules are often referred to as nutrients. Nutrients can be grouped
as: major nutrients (molecules containing the elements C, H and O, comprising >99% of
biomass); macronutrients (molecules containing elements such as N, S, P, K, Ca and Mg,
comprising 0.5% of biomass); and micronutrients or trace elements (0.1% of biomass).
Macronutrients and micronutrients are collectively called minerals. While the major nutrients
are obviously needed in the largest amounts, the growth of producers is usually limited by
the availability of minerals such as nitrate and phosphate.
There are two groups of decomposers:
• Detrivores are animals that eat detritus (such as earthworms and woodlice). They digest
much of the material, but like all animals are unable to digest the cellulose and lignin in
plant cell walls. They break such plant tissue into much smaller pieces with a larger
surface area making it more accessible to the saprophytes. They also assist saprophytes
by excreting useful minerals such as urea, and by aerating the soil.
• Saprophytes (or decomposers) are microbes (fungi and bacteria) that live on detritus. They
digest it by extracellular digestion, and then absorb the soluble nutrients. Given time, they
can completely break down any organic matter (including cellulose and lignin) to inorganic
matter such as carbon dioxide, water and mineral ions.
Detailed material cycles can be constructed for elements such as carbon, nitrogen, oxygen
or sulphur, or for compounds such as water, but they all have the same basic pattern as the
diagram above. We shall only study the nitrogen cycles in detail.
Ecological Pyramids
In general as you go up a food chain the size of the individual increases and the number of
individuals decrease. These sorts of observations can be displayed in ecological pyramids,
which are used to quantify food chains. There are three kinds:
The Pyramid of Energy
Conversions efficiencies are always much less than 100%. At each link in a food chain, a
substantial portion of the sun's energy - originally trapped by a photosynthesizing autotroph -
is dissipated back to the environment (ultimately as heat). Thus it follows that the total
amount of energy stored in the bodies of a given population is dependent on its trophic level.
For example, the total amount of energy in a population of toads must necessarily be far less
than that in the insects on which they feed. The insects, in turn, have only a fraction of the
energy stored in the plants on which they feed. This decrease in the total available energy at
each higher trophic level is called the pyramid of energy. The figure represents net
production at each trophic level expressed in kcal/m2/yr.

26
The Pyramid of Biomass
How does one measure the amount of energy in a population? Since all organisms are made
of roughly the same organic molecules in similar proportions, a measure of their dry weight is
a rough measure of the energy they contain. A census of the population, multiplied by the
weight of an average individual in it, gives an estimate of the weight of the population. This is
called the biomass (or standing crop). This, too, diminishes with the distance along the
food chain from the autotrophs which make the organic molecules in the first place. Analysis
of various ecosystems indicates that those with squat biomass pyramids (with conversion
efficiencies between one trophic level and the next averaging 10% or better) are less likely to
be disrupted by physical or biotic changes than those with tall, skinny pyramids (having
conversion efficiencies less than 10%).
The Pyramid of Numbers
Small animals are more numerous than larger ones. This graph shows the pyramid of
numbers resulting when a census of the populations of autotrophs, herbivores, and two
levels of carnivores was taken on an acre of grassland. The pyramid arises because;
• Each species is limited in its total biomass by its trophic level.

27
 • So, if the size of the individuals at a given trophic level is small, their numbers can be
large and vice versa.
• Predators are usually larger than their prey.
• Occupying a higher trophic level, their biomass must be smaller.
• Hence, the number of individuals in the predator population is much smaller than that
in the prey population.
Since the shape of the pyramid is dependent on the number of individuals at each level the
overall shape may not represent a classic pyramid (see below)

Nutrient cycling
Plants need nutrients from the soil to grow, just like people need food. Soil nutrients mostly
come from the breakdown of mineral-bearing rocks and from organic matter, which comes
from the decomposition of plants and animals. The nutrients that plants get from the soil are
stored in all plant tissues, such as leaves, stems and flowers. When these tissues fall to the
ground they start to break down, and together with decomposing dead insects, dead animals
and animal feces, they are eventually re-incorporated into the soil by rainfall and
earthworms. There, the organic matter is further broken down and slowly transformed to
become nutrients that are available to growing plants (and the cycle continues).

28
The Nitrogen Cycle

29
Microbes are involved at most stages of the nitrogen cycle:
Nitrogen Fixation. 78% of the atmosphere is nitrogen gas (N2), but this is inert and can’t be
used by plants or animals. Nitrogen fixing bacteria (Rhizobium) reduce nitrogen gas to
+
ammonia (N2 + 6H  2NH3), which dissolves to form ammonium ions ( NH 4 ). This process
uses the enzyme nitrogenase and ATP as a source of energy. The nitrogen-fixing bacteria
may be free-living in soil or water, or they may live in colonies inside the cells of root nodules
of leguminous plants such as clover or peas. This is an example of mutualism as the plants
gain a source of useful nitrogen from the bacteria, while the bacteria gain carbohydrates and
protection from the plants. Nitrogen gas can also be fixed to ammonia by humans using the
Haber process, and a small amount of nitrogen is fixed to nitrate by lightning.
Nitrification. Nitrifying bacteria can oxidise ammonia to nitrate in two stages: first forming
+
( )
nitrite ions using bactewria e.g. Nitrosomonas NH 4 → NO2 then forming nitrate ions
-

( -
2
-
3 )
using bacteriae.g. Nitrobacter NO → NO . These are chemosynthetic bacteria, which
means they use the energy released by nitrification to live, instead of using respiration.
Plants can only take up nitrogen in the form of nitrate.
Denitrification. The anaerobic denitrifying bacteria e.g. Pseudomonas convert nitrate to N2
and NOx, which is then lost to the air. This represents a constant loss of “useful” nitrogen
from soil, and explains why nitrogen fixation by the nitrifying bacteria and fertilisers are so
important.
Ammonification. Microbial saprophytes break down proteins in detritus to form ammonia in
two stages: first they digest proteins to amino acids using extracellular protease enzymes,
then they remove the amino groups from amino acids using deaminase enzymes.
Importance of bacteria in nitrogen cycle
• Some of these talented bacteria interlive with legumes such as beans: these take
nitrogen out of the air in soils.
• Other bacteria live freely in the soil, processing manures and urine, and also helping
to decompose dead plants and animals.
• A third kind of bacteria lives in the soil and changes "fixed" nitrogen into nitrates,
which plants can use. Without these nitrifying bacteria, agricultural fertilizers do not
work.

30
Practice questions

1. In an energy pyramid, the bottom level represents:

a. consumers b. producer c. scavengers d. decomposers

2. An ecosystem is made up of:

a. living things only b. physical environment only
c. living things and the physical environment d. living things and decaying matter

3. An example of a biotic factor in a forest ecosystem is:

a. waterfall b. cliff c. a tree d. a rock

4. Both consumers and producers are a source of food for:

a. scavengers b. decomposers c. carnivores d. herbivores

5. How is a food web model different from a food chain?

a. in a web, energy moves from an organism to only one other.
b. in a web, energy may move to many organisms from one.
c. in a web, an organism gets energy from one source.
d. in a web, an organism receives less energy than in a chain.

6. A ‘habitat’ is:
a. a place to buy furniture and furnishings
b. the same as an ecosystem
c. a particular area inhabited by plants and animals
d. the number of different organisms living in a specific area

7. ‘Biodiversity’ is described as:

a. the range of different species in an environment
b. the seasonal and daily changes in an environment
c. the way species differ from one another
d. the influence of physical factors on an environment

7. In the 1960’s myxomatosis was ‘accidentally’ released killing approximately 90% of

rabbits in the uk. What happened in the food chain below?
Carrots → rabbits → foxes
a. the number of carrots increased b. the number of foxes increased
c. the number of carrots decreased and the number of foxes increased
d. the number of carrots increased and the number of foxes decreased

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9. Which of these are not competed for by plants?
a. light b. minerals c. warmth d. water

10. A symbiotic relationship exists between two organisms of different species. If only one
organism benefits from the relationship and the other is not harmed, the relationship is
called
a.commensalistic b.mutualistic c.parasitic d.saprophytic

11. Describe the three different types of ecological pyramid?

12. How do light, temperature, and soil composition affect an ecosystem's capacity to
support life?

13. How is nitrogen recycled in nature?

Ecological Systems biodiversity and conservation

Components of an Ecosystem
You are already familiar with the parts of an ecosystem. You have learned about climate and
soils from past lectures. From this course and from general knowledge, you have a basic
understanding of the diversity of plants and animals, and how plants and animals and
microbes obtain water, nutrients, and food. We can clarify the parts of an ecosystem by
listing them under the headings "abiotic" and "biotic".

ABIOTIC COMPONENTS BIOTIC COMPONENTS

Sunlight Primary producers
Temperature Herbivores
Precipitation Carnivores
Water or moisture Omnivores
Soil or water chemistry (e.g., P, NH4+) Detritivores
etc. etc.
All of these vary over space/time
By and large, this set of environmental factors is important almost everywhere, in all
ecosystems.
Usually, biological communities include the "functional groupings" shown above. A
functional group is a biological category composed of organisms that perform mostly the

32
same kind of function in the system; for example, all the photosynthetic plants or primary
producers form a functional group. Membership in the functional group does not depend very
much on who the actual players (species) happen to be, only on what function they perform
in the ecosystem.
Controls on Ecosystem Function
Now that we have learned something about how ecosystems are put together and how
materials and energy flow through ecosystems, we can better address the question of "what
controls ecosystem function"? There are two dominant theories of the control of ecosystems.
The first, called bottom-up control, states that it is the nutrient supply to the primary
producers that ultimately controls how ecosystems function. If the nutrient supply is
increased, the resulting increase in production of autotrophs is propagated through the food
web and all of the other trophic levels will respond to the increased availability of food
(energy and materials will cycle faster).
The second theory, called top-down control, states that predation and grazing by higher
trophic levels on lower trophic levels ultimately controls ecosystem function. For example, if
you have an increase in predators, that increase will result in fewer grazers, and that
decrease in grazers will result in turn in more primary producers because fewer of them are
being eaten by the grazers. Thus the control of population numbers and overall productivity
"cascades" from the top levels of the food chain down to the bottom trophic levels.
So, which theory is correct? Well, as is often the case when there is a clear dichotomy to
choose from, the answer lies somewhere in the middle. There is evidence from many
ecosystem studies that BOTH controls are operating to some degree, but that NEITHER
control is complete. For example, the "top-down" effect is often very strong at trophic levels
near to the top predators, but the control weakens as you move further down the food chain.
Similarly, the "bottom-up" effect of adding nutrients usually stimulates primary production, but
the stimulation of secondary production further up the food chain is less strong or is absent.
Ecosystem review Coral reef
LOCATION: Coral reefs are generally found in clear, tropical oceans. Coral reefs form in
waters from the surface to about 150 feet deep because they need sunlight to survive. The
three types of reefs include fringing reefs, barrier reefs, and atolls. Fringing reefs occur along
shorelines of continents and islands and are commonly found in Hawaii and the Caribbean.
Barrier reefs are found farther offshore than fringing reefs, they occur most often in the Indo-
Pacific and Caribbean. Atolls are a series of low coral islands surrounding a central lagoon,
frequently found in the Indo-Pacific. The largest reef in the world, the Great Barrier Reef in

33
Australia is longer than 1200 miles. That’s longer than the distance between Seattle, WA and
Los Angeles, CA!
HABITAT: Coral reefs need water that is between 68-82° F, which is often located along the
eastern shores of land. Reefs usually develop in areas that have a lot of wave action
because the waves bring in food, nutrients and oxygen to the reef. Waves also prevent
sediment from falling on the reef. Reefs need calcium from the water to grow, which is more
often available in shallow warm waters.
PLANTS: The sun is the source of energy for the coral reef ecosystem. Plant plankton, called
phytoplankton; algae; and other plants convert light energy into chemical energy through
photosynthesis. As animals eat the plants and other animals, energy is passed on through
the food chain. Reef building corals work together with microscopic algae, called
zooxanthellae that live in their tissue. The zooxanthellae provide oxygen and food to the
coral through photosynthesis. The coral polyp gives the algae a home, and the carbon
dioxide it needs through respiration. Besides zooxanthellae, algae and sea grasses are the
main types of plants in the coral reef ecosystem. These plants give food and oxygen to the
animals that live on the reef. Sea grasses are especially important because they provide
shelter for juvenile reef animals like conch and lobster.

ANIMALS: Did you know that there can be as many different types of fish in two acres of
coral reef in Southeast Asia as there are species of birds on the entire continent of North
America? Shocking, isn’t it? Coral reefs only make up about 1% of the ocean floor, but they
house nearly 25% of life in the ocean. Animals use coral reefs either as a stopping point, like
an oasis, as they travel the deep blue sea, or they live as residents at the reef. The corals
themselves are the most abundant animal on the reef. They are tiny organisms are called
polyps, that attach themselves to the hard reef and live there forever. The reef is like a giant
apartment building in New York City and the coral polyps live together in each apartment.
Corals are closely related to sea anemones and sea jellies, and use their tentacles for
defense and to capture their prey. Corals can be a variety of colors, white, red, pink, green,
blue, orange and purple, due to natural pigments and the zooxanthellae in their tissues.
Other animals that live on the coral reef include sea urchins, sponges, sea stars, worms, fish,
sharks, rays, lobster, shrimp, octopus, snails and many more. Many of these animals work
together as a team like the coral polyp and zooxanthellae. This teamwork is called
symbiosis. One example of symbiosis on the reef is the anemone fish and sea anemone.
The sea anemone’s tentacles provide protection and safety for the fish and their eggs, while
the fish protects the anemone from predators, such as butterfly fish. Sometimes anemone
fish even remove parasites from their home anemone.

34
PEOPLE AND CORAL REEFS: Coral reef ecosystems are important for many reasons.
They remove and recycle carbon dioxide, which is a gas that contributes to global warming.
Reefs protect land from harsh weather by absorbing the impact from strong waves and
storms. Reefs provide food, for example, lobster and conch. Coral reefs are also a huge
tourist attraction. Coral reefs are a big source of biodiversity, without the reef, many of these
plants and animals would die. Some people think coral reefs may provide important
medicines for people. For example, some coral skeletons can be used by humans as a bone
substitute in reconstructive bone surgery. Coral reefs are also a useful educational tool.
People can learn more about biomes and ecosystems, and the interrelationship between
organisms and their environment by studying coral reefs.
Coral reefs are being destroyed at an alarming rate. It is estimated that we have already lost
10% of the worlds reefs, and scientists say that in the next 50 years many of the coral reefs
on Earth will be gone. This destruction is often connected with human activity: pollution,
sewage, erosion, irresponsible fishing, poor tourism practices, and global warming. There
are some simple things that you can do to help coral reefs. Don’t put chemicals down your
drain or on your lawn, instead use biodegradable products. Even though you may be far from
a coral reef ecosystem, these products end up in the watershed and may eventually pollute
waters that support coral. Conserve water. The less water you use, the less runoff and
wastewater eventually find their way into our oceans. Visit a coral reef! Many vacation spots
have beautiful coral reefs. When you go, hire local guides, this way you’ll learn about the reef
from the people who know it best. When you visit a coral reef, treat it with care, do not touch
or step on the corals.

Biodiversity and conservation

Key Definitions
Biodiversity – this is the total number of different species living in a defined area,
ecosystem or biome. It is also possible to consider the biodiversity of the earth.
Endangered species – any species whose numbers have become so low that they are
unlikely to be maintained by normal rates of reproduction and are in danger of becoming
extinct.
Biomes are the major regional groupings of plants and animals discernible at a global scale.
Their distribution patterns are strongly correlated with regional climate patterns and identified
according to the climax vegetation type.

35
Biomass – refers to all biological matter in an ecosystem . This means that only 30% of the
weight of any creature is counted, the rest being water.
Biodiversity – The biodiversity of the planet is the result of evolution. In any ecosystem,
there is a huge interdependence between species and it is clear that biodiversity is essential
to maintain ecological balance and stability. Another part of biodiversity is the extent of
genetic diversity with species and populations. Such genetic diversity is also essential for the
stability and survival of a species.
The Need to maintain Biodiversity
Biodiversity is in decline – mostly as a result of a variety of man’s activities. It is now well
understood that it is important to try and halt this decline – indeed, conservation measures
are needed, not only to halt the decline, but to try and restore as much biodiversity as
possible. The need to maintain biodiversity may be considered in terms of biological reasons
or reasons from a human perspective:
Biological reasons
As mentioned above, it is essential that biodiversity is maintained if ecosystems (and the
whole planet) are to remain ecologically balanced and stable. In addition, evolution has
resulted in diverse gene pools within populations – the maintenance of these gene pools and
the genetic diversity of species is extremely important if species are to be prevented from
becoming extinct.
Human reasons
Other species of animals and plants provide an important resource for humans. These may
be
• For use in agriculture, either as potential food supplies or to be crossed with existing
agricultural species to improve features, such as yield, hardiness or disease resistance.
• To provide possible medicines
• To encourage tourism in some countries - ecotourism
• From an ethical point of view, if human activity has been largely responsible for the
decline in biodiversity, then humans have an obligation to reverse this decline. Equally, it
is important to try and maintain the current level of biodiversity for future generations.
Reasons why species have become endangered
In African ecology, the elephant is regarded as a keystone species. In 1930 there were
estimated to be 5 – 10 million African elephants. By 1979 the number was reduced to 1.3
million and when it was officially added to the endangered list in 1989,

36
the numbers had fallen to around 600,000 - less than 10% of its numbers earlier in the
twentieth century in numbers:
• Habitat loss – elephants eat a great deal and need a large amount of habitat. During the
twentieth century, the human population of Africa has increased massively and, as a result,
humans and elephants have become competitors for living space. The forest and savannah
habitats of the elephant have been reduced as humans have used timber for fuel and
building and land for growing crops and grazing livestock.
• When humans and elephants live in close proximity, various problems arise – elephants
raid crops and, on occasion, will rampage through villages. Farmers and other residents
regard them as something of a pest and shoot them.
• Hunting – this has been a major cause of the decline in elephant numbers. Elephants
became prized trophies for big-game hunters and, more recently, they have been killed for
their ivory tusks. Ivory is easily caved and regarded as a beautiful material – most of the
ivory carving in the world takes place in Japan and other countries in Asia. At one stage,
ivory was more expensive than gold – indeed, it became known as ‘white gold’. Hunting
continues for the global ‘bushmeat’
• Poaching – it is no longer legal to hunt elephants in most African countries. However, the
high prices paid for ivory meant that elephants continued to be killed by poachers. At its
peak, the poachers became highly organised, using automatic weapons, vehicles and even
planes to herd and kill huge numbers at a time. The biggest elephants were usually targeted
(because they have the largest tusks) which meant that it was generally the adults that were
killed, leaving young elephants without any adults to learn from. As a result, the social
structure of the elephant populations broke down and many of the elephant groups left were
leaderless juveniles.
Methods of protecting endangered species
Ex-situ methods (Ex-situ methods refer to methods of conservation that occur outside of the
natural habitat of the animal)
• Zoos
One way of protecting endangered species of animals is to capture some from the wild and
place them in captivity. In this way, it is possible to make sure that they are well fed,
protected from predators and disease and isolated from other potential problems which might
be encountered in their natural habitat. If such animals are simply placed in zoos, the zoo is
really acting as an ‘ark’ and little is actually being achieved in terms of maintaining or
increasing populations in the wild. If the animals will breed in captivity, then it is possible to

37
maintain or even increase numbers. If such captive-bred individuals can be returned to their
natural habitat, then it might be possible to increase numbers in the wild, thereby preventing
the endangered from becoming extinct. Captive breeding has a number of advantages:
• it is possible to monitor the health of the mother and the development of the fetus during
the pregnancy.
• sperm and eggs can be obtained from the captive individuals
• these can be stored in a frozen form
• it allows the possibility of artificial insemination
• also in-vitro fertilisation
• fertilised embryos may be implanted in surrogate mothers (which might even be of
different species)
• there is the possibility of international co-operation and the transfer of breeding
individuals between different zoos
• it allows the keeping of breeding records and the genetic relatedness of captive
individuals

Although some species of animals have been bred successfully in captivity and released
back into the wild, with other species this has not been straightforward and a number of
problems have been encountered. It has been found that some species simply do not breed
successfully in captivity, whilst, in some cases, there have been problems in releasing
animals that have bred in captivity.

Captive Breeding
There are a number of reasons why animals do not always breed successfully when in
captivity:

1 They are no longer living in their natural habitat

2 The conditions experienced in captivity can cause stress and behavioural changes

3 The stress can disrupt normal reproductive cycles and breeding behaviour

4 They often have little choice of mate and may reject the chosen mate Release of captive-
bred individuals into the wild Problems which reduce the success rate of releasing
captive-bred individuals include:
1 Habitat destruction (usually as a result of man’s activities) might mean that there is
very little suitable habitat available in which to release the animals

38
 2 Having been in captivity, animals might not find it easy to move around in their
natural habitat
3 It may not be easy for them to find enough food – especially if they have been used
to being fed in captivity
4 They may not be able to communicate with other members of their species in the
wild and may not integrate into social groups
5 They may be susceptible to diseases in the wild. Some of these problems are being
overcome by making sure that conditions within zoos are as close to the natural
habitat of the species as possible. Contact with humans is kept to an absolute
minimum and individuals can be ‘acclimatised’ in cages before they are actually
released into their natural habitat.

• Botanic gardens
Endangered species of plants can be grown in botanic gardens. Clearly, it is possible to
create ideal growing conditions – either outdoors or in glasshouses, when it is possible to
control very carefully the growing conditions. This applies to the availability of light, nutrients,
water and the atmospheric conditions. Within such botanic gardens, it is also possible to
propagate endangered species – either by growing from seed or by some means of
vegetative propagation, such as cuttings. Techniques of tissue culture also allow large
numbers to be produced very quickly. This allows the possibility of re-introducing
endangered species of plants into their natural habitat.
Seed banks
Many plants produce seeds which are very long-lived and large numbers can be stored in a
relatively small space. Such a collection of seeds is referred to as a seed bank. The life span
of such seeds can be extended if they are kept in carefully controlled conditions – especially
in an atmosphere of low oxygen levels, moisture and temperature. Given that the seeds will
contain all the genetic material of any given species, it also means that the gene pool of that
species is being maintained. Clearly, if the seeds of endangered species are stored in this
way, such seeds can be germinated at any time and plants can be grown in Botanic gardens
or restored to the wild. Some species produce seeds which have a limited longevity (e.g.
cocoa, rubber, coconut) – keeping their seeds in seed banks is not possible. Such plants
would need to be maintained in botanic gardens.
Sperm bank or cryobank is a facility that collects and stores sperm mainly from sperm
donors, primarily for the purpose of achieving pregnancies through third party reproduction,
notably by artificial insemination. Sperm can be store for years without significant damage
however attempts to store embryos is not a successful .The zona pelucida surrounding the

39
embryo is susceptible to freezing damage also the DNA of the embryos is also susceptible to
freezing damage.
In-situ methods (In-situ methods refer to methods of conservation that occur within the
natural habitat of the animal)
• National Parks (and other protected areas)
Many countries have designated areas, such as National Parks, which are set up to
conserve rare / endangered species and maintain important habitats. Often, legislation is
passed to ensure that such areas are protected under the law. The ways in which National
Parks protect their resident species include:
1. Wardens, rangers and volunteers can be used to patrol the parks
2. Access by humans can be restricted – often footpaths are created and maintained to
avoid interference with wildlife habitats
3. Agricultural activities can be strictly controlled – traditional farming methods can be
encouraged
4. Industrial activities and mining can be limited and controlled
5. The building of roads, dwellings and other developments can be strictly controlled
6. Visitor Centres can be established to educate the general public in the importance of
conservation within the Park – and elsewhere
Wildlife can be protected directly e.g. 24 hour surveillance of nests / breeding sites In
addition to National Parks (which usually occupy large areas of land), different countries can
also create other categories of conservation areas if they contain species or habitats which
need some form of protection
Endangered Species Jamaican Iguana
The Jamaican Iguana belongs to the subfamily
Iguaninae, within the family of Iguanid lizards
comprising 31 species. Many of these lizards attain very
large body size and all feed predominantly on plants.
The genus Cyclura has eight species and is restricted
to the northern part of the Caribbean. The Jamaican
Iguana is endemic to Jamaica and reaches a body
length of up to 150cm. or more, making it the islands
largest native land animal.

40
It was believed extinct since a remnant population on Goat Island, off Jamaica's south coast,
disappeared in the 1940's. However, a carcass of one was discovered in the Jamaica's
Hellshire Hills in 1970. Then in June 1990 a hunter and his dog cornered a male specimen
which was brought to Hope Zoo. As a result, the Jamaican Iguana Research and
Conservation Group was founded. Supported by large numbers of volunteers, some 7500
man hours were spent methodically surveying the forest. Animals heard and seen provided
estimates of at least 15 iguanas surviving in the area and the very first photographs of
Jamaican iguanas were taken in the wild.
The Hellshire Hill's, which represent an outstanding example of unspoilt dry limestone forest,
are located west of Kingston, froming a peninisula which measures abou 10 x 15km. The
area where most sightings have been made is some 4 kilometers long, much of which forms
a steep sided natural crater.
Two nesting sites were identified. There is very little or no soil covering the deeply fissured
limestone substrate, the thick vegatation seemingly growing out of little more than bare rock.
Opportunities for a burrowing lizard of the size of this iguana to dig and lay its egges are,
therefore, few and far between.
As field observations record a predominantly ageing population, it is almost certain that most
iguanas succumb during infancy, probably to the ubiquitous mongoose. A program of
collecting up eggs and hatchlings was quickly implemented and after two years up to 80
young iguana are growing up in the safety of Hope Zoo, Jamaica. These animals will be
used as stock for captive breeding and for release back into the wild, having attained a size
beyond the scope of mongoose predation.
Apart from the mongoose, other threats to the iguana are posed from feral pigs and dogs,
and by disturbance from charcoal burning. The greatest threat however, would undoubtedly
be the developement of the area for human settlements. The Natural Resources
Conservation Authority is endeavouring to protect the area in perpetuity.
Species Diversity
a. Definition - the measure of the number of different species represented in an ecosystem
b. Highest in a mature ecosystems over an immature ecosystems
c. Highest in complex ecosystems over simple ecosystems
d. Simple ecosystems have very low species diversity
(1) Vulnerable to disruption or destruction

41
 (2) Lowest in monocultures (wheat field)
e. HIGH SPECIES DIVERSITY is the name of the game
(1) High species diversity ecosystems are stable and complex
(2) High species diversity ecosystems have many paths through the food web
(3) Low species diversity ecosystems have few paths through the food web

Practice questions

1. What is biodiversity?
a. A variety of cars b. The variety of species in an area
c. A variety of health foods d. None of the above

2. Species diversity includes ______.

a. the number of populations of a single species
b. the number of species in the world
c. the number of species in a region d. b and c e.all of the above

3. Biodiversity _______.
a.is defined as the sum total of all organisms in an area
b.takes into account the diversity of populations
c.takes into account the diversity of genes
d.takes into account the diversity of communities e.all of the above

4. What is the value of genetic diversity for a given species?

a. Genetic diversity provides more types of partners for better selection in mating.
b. Genetic diversity provides more opportunities for mating with other species.
c. Species with more genetic diversity have better chances of surviving, because their
built-in variation better enables them to cope with environmental change.
d. The value of genes is for maintaining compatibility within a static environment.
e. There is no value of genetic diversity for species, only for populations.

5. What is the value of biodiversity to humanity?

a. Biodiversity provides valuable ecosystem services free of charge.
b. Biodiversity enhances food security.
c. Biodiversity provides traditional medicines and high-tech pharmaceutical products.

42
 d. Biodiversity provides economic benefits through tourism and recreation.
e. All of the above.

6. The greatest loss of biodiversity is caused by

A) competition with introduced species. B) habitat alteration.
C) pollution. D) hunting. E) overgrazing by domestic animals.

7. Buying an item made from material from an endangered species

A) keeps some poor peasant from starving to death.
B) has no relevance to protecting the species.
C) contributes toward its extinction.
D) shows esteem for the species. E) shows good taste.

8. The preservation of wild species has an economic value because

A) wild plants may be used as a genetic bank for cultivated species.
B) ecotourism generates large amounts of money.
C) Americans have spent over $100 billion dollars on wildlife related activities in a
single year.
D) wild plants may be used to create lifesaving medications. E) all of the above

9. A species introduced into an area from somewhere else is called a/an ________
species.
A) wild B) natural C) exotic D) native E) none of the above

10. The region of the world where more living species live than any other place is the
A) grassland. B) deciduous forest. C) temperate rain forest.
D) tropical rain forest. E) coral reefs.

11. Extinction is a natural process that occurred long before humans ever evolved. Why
should we be so concerned about extinction now?

43
4. The Uptake and Transport of Water and Minerals

Stem Structure

• Epidermis. One cell thick. In young plants the epidermis cells may secrete a waterproof
cuticle, and in older plants the epidermis may be absent, replaced by bark.
• Cortex. Composed of various “packing” cells, to give young plants strength and flexibility,
and are the source of plant fibres such as sisal and hemp.
• Vascular Tissue. This contains the phloem and xylem tissue, which grow out from the
cambium. In dicot plants (the broad-leafed plants), the vascular tissue is arranged in vascular
bundles, with phloem on the outside and xylem on the inside. In older plants the xylem
bundles fuse together to form the bulk of the stem.

44
• Pith. The central region of a stem, used for food storage in young plants. It may be absent
in older plants (i.e. they’re hollow).

Root Structure
•Epidermis. A single layer of
cells often with long extensions
called root hairs, which increase
the surface area enormously. A
single plant may have 1010 root
hairs.
•Cortex. A thick layer of packing
cells often containing stored
starch.
•Endodermis. A single layer of
tightly-packed cells containing a
waterproof layer called the
casparian strip. This prevents the
movement of water between the cells.
•Pericycle. A layer of undifferentiated meristematic (growing) cells.
•Vascular Tissue. This contains xylem and phloem cells, which are continuous with the
stem vascular bundles. The arrangement is different, and the xylem usually forms a star
shape with 2-6 arms.

45
Transport Systems in Plants
Plants don’t have a circulatory system like animals, but they do have a sophisticated
transport system for carrying water and dissolved solutes to different parts of the plant, often
over large distances.
Xylem Tissue
Xylem tissue is composed of dead cells joined together to form long empty tubes. Different
kinds of cells form wide and narrow tubes, and the end cells walls are either full of holes, or
are absent completely. Before death the cells form thick cell walls containing lignin, which is
often laid down in rings or helices, giving these cells a very characteristic appearance under
the microscope. Lignin makes the xylem vessels very strong, so that they don’t collapse
under pressure, and they also make woody stems strong.
Phloem
Phloem is the living tissue that carries organic nutrients (known as photosynthate),
particularly sucrose, a sugar, to all parts of the plant where needed. In losing their nuclei,

46
sieve tube members lack the molecular control mechanisms most living cells possess.
Nucleated cells adjacent to sieve tube members appear to take over the control of cellular
functions within these phloem transport cells. These nucleated cells are appropriately called
companion cells. Sieve plates are specialized areas where materials flow through tiny pores
from one sieve tube member to another. When phloem is damaged or torn, callose seals off
these areas to prevent loss of cell sap. Most phloem cells are parenchyma cell types.
Sometimes phloem tissues contain sclerenchyma fibers for support.

Mineral uptake in plants

This is the process in which minerals enter the cellular material, typically following the same
pathway as water. The most normal entrance portal for mineral uptake is through plant
roots.(Roots, 2005) Some mineral ions diffuse in-between the cells. In contrast to water,
some minerals are actively taken up by plant cells. Mineral nutrient concentration in roots
may be 10,000 times more than in surrounding soil. During transport throughout a plant,
minerals can exit xylem and enter cells that require them. Mineral ions cross plasma
membranes by a chemiosmotic mechanism. Plants absorb minerals in ionic form: nitrate
(NO3−), phosphate (HPO4−) and potassium ions (K+); all have difficulty crossing a charged
plasma membrane. It has long been known plants expend energy to actively take up and
concentrate mineral ions. Proton pump hydrolyzes ATP to transport H+ ions out of cell; this
sets up an electrochemical gradient that causes positive ions to flow into cells. Negative ions
are carried across the plasma membrane in conjunction with H+ ions as H+ ions diffuse down
their concentration gradient.

Water Transport in Plants

Vast amounts of water pass through plants. A large tree can use water at a rate of 1 dm³
min-1. Only 1% of this water is used by the plant cells for photosynthesis and turgor, and the
remaining 99% evaporates from the leaves and is lost to the atmosphere. This evaporation
from leaves is called transpiration.
The movement of water through a plant can be split into three sections: through the roots,
stem and leaves:

47
1. Movement through the Roots
cell wall
cytoplasm
vacuole

soil particles

epidermis endodermis xylem

root hair cortex pericycle

symplast pathway (cytoplasms)

aoplast pathway (cell walls)

Water moves through the root by two paths:

• The Symplast pathway consists of the living cytoplasms of the cells in the root (10%).
Water is absorbed into the root hair cells by osmosis, since the cells have a lower
water potential that the water in the soil. Water then diffuses from the epidermis
through the root to the xylem down a water potential gradient. The cytoplasms of all the
cells in the root are connected by plasmodesmata through holes in the cell walls, so
there are no further membranes to cross until the water reaches the xylem, and so no
further osmosis.

48
• The Apoplast pathway consists of the cell walls between cells (90%). The cell walls are
quite thick and very open, so water can easily diffuse through cell walls without having
to cross any cell membranes by osmosis. However the apoplast pathway stops at the
endodermis because of the waterproof casparian strip, which seals the cell walls. At
this point water has to cross the cell membrane by osmosis and enter the symplast.
This allows the plant to have some control over the uptake of water into the xylem.

49
 The uptake of water by osmosis actually produces a force that pushes water up the
xylem. This force is called root pressure, which can be measured by placing a
manometer over a cut stem, and is of the order of 100 kPa (about 1 atmosphere). This
helps to push the water a few centimetres up short and young stems, but is nowhere
near enough pressure to force water up a long stem or a tree. Root pressure is the
cause of guttation, sometimes seen on wet mornings, when drops of water are forced
out of the ends of leaves.
2. Movement through the Stem
The xylem vessels form continuous pipes from the roots to the leaves. Water can move
up through these pipes at a rate of 8m h-1, and can reach a height of over 100m. Since
the xylem vessels are dead, open tubes, no osmosis can occur within them. The driving
force for the movement is transpiration in the leaves. This causes low pressure in the
leaves, so water is sucked up the stem to replace the lost water. The column of water in
the xylem vessels is therefore under tension (a stretching force). Fortunately water has a
high tensile strength due to the tendency of water molecules to stick together by
hydrogen bonding (cohesion), so the water column does not break under the tension
force. This mechanism of pulling water up a stem is sometimes called the cohesion-
tension mechanism.
The very strong lignin walls of the xylem vessels stops them collapsing under the suction
pressure, but in fact the xylem vessels (and even whole stems and trunks) do shrink
slightly during the day when transpiration is maximum.
3. Movement through the Leaves
The xylem vessels ramify in the
leaves to form a branching system of
fine vessels called leaf veins. Water
diffuses from the xylem vessels in
the veins through the adjacent cells
down its water potential gradient. As
in the roots, it uses the symplast
pathway through the living cytoplasm
and the apoplast pathway through
the non-living cell walls. Water
evaporates from the spongy cells
into the sub-stomatal air space, and
diffuses out through the stomata.

50
Evaporation is endothermic and is driven by solar energy, which is therefore the ultimate
source of energy for all the water movements in plants:
energy water water water water water
from vapour diffuses sucked diffuses diffuses
sun diffuses out of up through into root
out of leaf xylem xylem root from soil

water low low low low

evaporates  in pressure  in  in
from leaf in xylem root root
spongy cells cells cortex epidermis
Factors affecting Transpiration
The rate of transpiration can be measured in the lab using a potometer (“drinking meter”):
speed of movement of air bubble (mm/s)

leafy x cross-sectional area of capillary tube (mm2)

shoot = rate of water uptake (mm3/s)

reservoir
ruler

water
capillary air
tube bubble reservoir

A potometer actually measures the rate of water uptake by the cut stem, not the rate of
transpiration; and these two are not always the same. During the day plants often transpire
more water than they take up (i.e. they lose water and may wilt), and during the night plants
may take up more water than they transpire (i.e. they store water and become turgid). The
difference can be important for a large tree, but for a small shoot in a potometer the
difference is usually trivial and can be ignored.
The potometer can be used to investigate how various environmental factors affect the rate
of transpiration.

51
• Light. Light stimulates the stomata to open allowing gas exchange for photosynthesis,
and as a side effect this also increases transpiration. This is a problem for some plants
as they may lose water during the day and wilt.
• Temperature. High temperature increases the rate of evaporation of water from the
spongy cells, and reduces air humidity, so transpiration increases.
• Humidity. High humidity means a higher water potential in the air, so a lower water
potential gradient between the leaf and the air, so less evaporation.
• Air movements. Wind blows away saturated air from around stomata, replacing it with
drier air, so increasing the water potential gradient and increasing transpiration.
Many plants are able to control their stomata, and if they are losing too much water and their
cells are wilting, they can close their stomata, reducing transpiration and water loss. So long
periods of light, heat, or dry air could result in a decrease in transpiration when the stomata
close.
Mineral Ion transport in Plants
Ions are absorbed from the soil by both passive and active transport. Specific ion pumps in
the membranes of root hair cells pump ions from the soil into the cytoplasms of the epidermis
cells. Two lines of evidence indicate that active transport is being used:
• The concentrations of ions inside root cells are up to 100 times greater than in the soil, so
they are being transported up their concentration gradient.
• If respiratory inhibitors such as cyanide are applied to living roots, ion uptake is greatly
reduced, since there is no ATP being made to drive the membrane pumps. Any remaining
uptake must be passive.
The active uptake of ions is partly responsible for the water potential gradient in roots, and
therefore for the uptake of water by osmosis.
Ions diffuse down their concentration gradient from the epidermis to the xylem. They travel
up the xylem by mass flow as the water is pulled up the stem (in other words they are simply
carried up in the flow of the xylem solution). In the leaves they are selectively absorbed into
the surrounding cells by membrane pumps.

52
Solute Transport in Plants
The phloem contains a very concentrated solution of dissolved solutes, mainly sucrose, but
also other sugars, amino acids, and other metabolites. This solution is called the sap, and
the transport of solutes in the phloem is called translocation.
Unlike the water in the xylem, the contents of the phloem can move both up and down a
plant stem, often simultaneously. It helps to identify where the sugar is being transported
from (the source), and where to (the sink).
• During the summer sugar is mostly transported from the leaves, where it is made by
photosynthesis (the source) to the roots, where it is stored (the sink).
• During the spring, sugar is often transported from the underground root store (the source)
to the growing leaf buds (the sink).
• Flowers and young buds are not photosynthetic, so sugars can also be transported from
leaves or roots (the source) to flowers or buds (sinks).
Surprisingly, the exact mechanism of sugar transport in the phloem is not known, but it is
certainly far too fast to be simple diffusion. The main mechanism is thought to be the mass
flow of fluid up the xylem and down the phloem, carrying dissolved solutes with it. Plants
don’t have hearts, so the mass flow is driven by a combination of active transport (energy
from ATP) and evaporation (energy from the sun). This is called the mass flow theory, and it
works like this:

1. Sucrose produced by photosynthesis is actively pumped into the phloem vessels by the
companion cells.
2. This decreases the water potential in the leaf phloem, so water diffuses from the
neighbouring xylem vessels by osmosis.
3. This is increases the hydrostatic pressure in the phloem, so water and dissolved solutes
are forced downwards to relieve the pressure. This is mass flow: the flow of water
together with its dissolved solutes due to a force.
4. In the roots the solutes are removed from the phloem by active transport into the cells of
the root.
5. At the same time, ions are being pumped into the xylem from the soil by active transport,
reducing the water potential in the xylem.
6. The xylem now has a lower water potential than the phloem, so water diffuses by
osmosis from the phloem to the xylem.
7. Water and its dissolved ions are pulled up the xylem by tension from the leaves. This is
also mass flow.

53
 phloem xylem
1 2 evaporates
leaf cells
(source)

3 7 movement of sucrose
movement of water
movement of ions

root cells soil

(sink)
4 6 5

54
This mass-flow certainly occurs, and it explains the fast speed of solute translocation.
However there must be additional processes, since mass flow does not explain how different
solutes can move at different speeds or even in different directions in the phloem. One
significant process is cytoplasmic streaming: the active transport of molecules and small
organelles around cells on the cytoskeleton.
Evidence backing up the Mass Flow
1) The conc. of sucrose in sieve tubes has been tested and seen to be greater at the
sources than the sinks
2) There have also been observed hydrostatic pressure differences
3) Rate off transport in the sieve tubes is faster than simple diffusion
4) The number of mitochondria present in the companion cells is much greater than would
be expected
Problems with the mass flow theory
1) It raises the question of why there is cytoplasm - as mass flow would be easier without it
(the ans to this is perhaps to prevent it becoming a feeding ground for microorganisms if
damaged)
2) The largest problem is that it fails to show how substances flow in 2 different directions.
Translocation Experiments
1. Ringing Experiments

If the phloem is punctured with a hollow phloem xylem

tube then the sap oozes out, showing
that there is high pressure (compression) if phloem is
inside the phloem (this is how maple punctured sap
syrup is tapped). If the xylem is oozes out
punctured then air is sucked in, showing
stem
that there is low pressure (tension) inside if xylem is
the xylem. This illustrates the main punctured air
difference between transport in xylem is sucked in
and phloem: Water is pulled up in the
xylem, sap is pushed down in the
phloem.

55
Since the phloem vessels are outside the
xylem vessels, they can be selectively leave
removed by cutting a ring in a stem just for a
deep enough to cut the phloem but not week
the xylem. After a week there is a
swelling above the ring, reduced growth ring of
below the ring and the leaves are bark and
unaffected. This was early evidence that phloem
sugars were transported downwards in removed
the phloem.
2. Radioactive Tracer Experiments
Radioactive isotopes can be used trace precisely where different compounds are being
transported from and to, as well as measuring the rate of transport. The radioactivity can be
traced using photographic film (an autoradiograph) or a GM tube. This technique can be
used to trace sugars, ions or even water.
In a typical experiment a plant is grown in the lab and one leaf is exposed for a short time to
carbon dioxide containing the radioactive isotope 14C. This 14CO2 will be taken up by
photosynthesis and the 14C incorporated into glucose and then sucrose. The plant is then
frozen in liquid nitrogen to kill and fix it quickly, and placed onto photographic film in the dark.
The resulting autoradiograph shows the location of compounds containing 14C.

This experiment shows that organic compounds (presumably sugars) are transported
downwards from the leaf to the roots. More sophisticated experiments using fluorescently
labelled compounds can locate the compound specifically to the phloem cells.

The movement of water through a plant is called the transpiration stream. This pathway
begins at the root epidermis and continues symplastically and apoplastically to the
endodermis. The path continues in the vascular cylinder of the root. The water and mineral
solution accumulated by the endodermal transport proteins is conducted up the xylem of the
root, the stem, and the leaf. In the leaf the solution coats the mesophyll cells apoplastically,
evaporates into the gas spaces between the cells, and escapes the leaf through the stomata
and into the atmosphere. Thus water passes through (trans-) the plant and exits by small
pores (-spira-) in this process (-tion). Transpiration is supported by four critical factors.

Root pressure pushes water up the xylem, the influx of water into roots is not uniform along
the length of a root. However, the important point here is that the endodermis has transport

56
proteins that allow the root to accumulate ions by active transport. This burns much sugar
(note drop in ψ as you compare across the endodermis above) but importantly produces a
more concentrated solution of mineral inside the vascular cylinder of the root. Water follows
the flow of minerals osmotically and this can develop pressure inside the vascular cylinder if
the transpiration rate is slow (weather is humid, cloudy, cool). The pressure that develops at
the bottom of the column of xylem can push water up that column. The photo below shows
this nicely; a severed shoot often exudes a drop of liquid from the xylem. The total pressure
that roots can provide this way is about 0.05 to 0.5 MPa depending on weather conditions.
This amount of pressure in a xylem tracheid might permit a push to a few meters up a
shoot...but no more.

Root pressure is also sometimes visible on leaves. Under conditions of high humidity, cool
temperature, and low light exposure root pressure can push xylem fluids through leaf
mesophyll and out some larger pores in the leaves called hydathodes. Thus on a cool
morning as you walk across the grass you notice a drop of liquid on the tip of each blade.
You may have thought this was dew, but because it is on the upward pointing tip, you realize
that this cannot be so. A test of solutes would demonstrate that this is xylem sap, not
condensed humidity! The process by which this exudes is called guttation and it is driven by
root pressure. Parking your car under certain species of trees can leave some nasty "water
spots" on your wax job. Again, if this were dew, the pure condensation would not leave a
mineral spot behind; this is xylem sap that dries, leaving a mineral deposit.

Capillarity allows water to climb up the xylem

We have already discussed this in a previous lecture. Again the amount of climb that is
possible in a tracheid of normal diameter is perhaps a meter up the plant. This capillarity is a
function of adhesion of the liquid to the cell wall of the xylem, and cohesion of the water
molecules to each other.

Cohesion in the column of water prevents cavitation The column of water in the xylem
extends from the root xylem, through the stem xylem, and up into the leaf xylem. This
column must be unbroken for water to be able to continue to flow. As water is drawn up a tall
tree, the tensile strength of water is needed to keep the column intact. Fortunately the
cohesion of water molecules provides this tensile strength. In addition, some trees have
evolved an anti-cavitation device: bordered pits. Along the side walls of the cells in the xylem
these pits permit water to enter or exit the column based upon pressure and so on. The pit
membrane is really a primary cell wall that is reasonably flexible. As pressure changes occur

57
in a tracheid, the membrane can respond by closing the border on the pit or opening the
border on the pit. The plug for the border is called the torus.

Evaporation from the leaves pulls water up the xylem Evaporation from the intercellular
spaces in the leaf into the atmosphere is a strong pull that removes water from the top of the
column of water in the xylem. This process generates sufficient force to lift the column of
water up against the gravity vector in tall trees.
Practice questions
1. High root pressure can cause water to be lost by leaves through the process of
A)respiration b)regurgitation c)transpiration d)guttation e)translocation

2. The reason that a column of water in a tall tree does not sink because of its weight is
A)the formation of hydrogen bonds with the plants vessels
B)bubbles form that are too large to be transported
C)the presence of strong ion concentrations near the top of the tree
D)the venturi effect of air flowing through stomata
E)the tensile strength of a column of water.

3. The opening of the stomata is effected by all of the following except

A)oxygen concentration b)temperature c)light d)carbon dioxide concentration

4. In plants, water rises beyond the point supported by the atmospheric pressure mostly
because of
A)capillarity b)gravity c)evaporation d)active transport e)the proton pump

5. The combination of pressure potential and solute potential is

a)water potential b)transpiration potential c)field potential
d)stem potential e)osmotic potential

6. Scientists take advantage of _______________ in studying translocation by phloem.

A)ants b)aphids c)bees d)butterflies e)termites

7. Which of these is not a reason why plants need a transport system?

a. They can't rely on diffusion alone b. Too active
c. Small surface area to volume ratio d. Multicellular

8. Xylem tissue doesn't carry...

58
 A. Water b. Inorganic substances c. Organic nutrient

9. The distribution of the xylem and phloem in the stem is like:

A. Xylem in the middle and phloem outside
B. Seperate vascular bundles around a medulla C. Forming a central midribi

10. Root hair cells absorb mineral ions using

A. Active transport b. Diffusion c. Osmosis

11. Differentiate between the following:

(a) diffusion and osmosis (b) transpiration and evaporation
(c) osmotic pressure and osmotic potential (d) imbibition and diffusion
(e) apoplast and symplast pathways of movement of water in plants.
(f) guttation and transpiration.

12. Describe transpiration pull model of water transport in plants. What are the factors
influencing transpiration? How is it useful to plants?

13. What essential role does the root endodermis play during mineral absorption in plants?

59
5. Circulatory System in Mammals

Human Circulatory System

Small organisms don’t have a bloodstream, but instead rely on the simple diffusion of
materials for transport around their cells. This is OK for single cells, but it would take days for
molecules to diffuse through a large animal, so most animals have a circulatory system with
a pump to transport materials quickly around their bodies. This is an example of a mass flow
system, which means the transport of substances in the flow of a fluid (as opposed to
diffusion, which is the random motion of molecules in a stationary fluid). The transport of
materials in the xylem and phloem of plants is another example of mass flow. Mass flow
systems work together with the specialised exchange systems (such as lungs, gills and
leaves).

Humans have a double circulatory system with a 4-chambered heart. In humans the right
side of the heart pumps blood to the lungs only and is called the pulmonary circulation, while
the left side of the heart pumps blood to the rest of the body – the systemic circulation. Until
then people assumed that blood ebbed and flowed through the same tubes, because they
hadn't seen capillaries.

The Heart
The human heart has four
chambers: two thin-walled atria
on top, which receive blood,
and two thick-walled ventricles
underneath, which pump blood.
Veins carry blood into the atria
and arteries carry blood away
from the ventricles. Between
the atria and the ventricles are
atrioventricular valves, which
prevent back-flow of blood from
the ventricles to the atria. The
left valve has two flaps and is
called the bicuspid (or mitral)
valve, while the right valve has
3 flaps and is called the

60
tricuspid valve. The valves are held in place by valve tendons (“heart strings”) attached to
papillary muscles, which contract at the same time as the ventricles, holding the vales
closed. There are also two semi-lunar valves in the arteries (the only examples of valves in
arteries) called the pulmonary and aortic valves.
The left and right halves of the heart are separated by the inter-ventricular septum. The walls
of the right ventricle are 3 times thinner than on the left and it produces less force and
pressure in the blood. This is partly because the blood has less far to go (the lungs are right
next to the heart), but also because a lower pressure in the pulmonary circulation means that
less fluid passes from the capillaries to the alveoli.
The heart is made of cardiac muscle, composed of cells called myocytes. When myocytes
receive an electrical impulse they contract together, causing a heartbeat. Since myocytes are
constantly active, they have a great requirement for oxygen, so are fed by numerous
capillaries from two coronary arteries. These arise from the aorta as it leaves the heart.
Blood returns via the coronary sinus, which drains directly into the right atrium.
The Cardiac Cycle
When the cardiac muscle contracts the volume in the chamber decrease, so the pressure in
the chamber increases, so the blood is forced out. Cardiac muscle contracts between 60-100
times per minute when you are at rest, pumping around 75 cm³ of blood from each ventricle
each beat (the stroke volume). It does this continuously for up to 100 years. There is a
complicated sequence of events at each heartbeat called the cardiac cycle.
Cardiac muscle is myogenic, which means that it can contract on its own, without needing
nerve impulses. Contractions are initiated within the heart by the sino-atrial node (SAN, or
pacemaker) in the right atrium. This
extraordinary tissue acts as a clock and
contracts spontaneously and rhythmically
about once a second, even when
surgically removed from the heart.
The cardiac cycle has three stages:
1. Atrial Systole (pronounced sis-toe-
lay). The SAN contracts and transmits
electrical impulses throughout the
atria, which both contract, pumping
blood into the ventricles. The
ventricles are electrically insulated

61
 from the atria, so they do not contract at this time.
2. Ventricular Systole. The electrical impulse passes to the ventricles via the
atrioventricular node (AVN), the bundle of His and the Purkinje fibres. These are
specialised fibres that do not contract but pass the electrical impulse to the base of the
ventricles, with a short but important delay of about 0.1s. The ventricles therefore contract
shortly after the atria, from the bottom up, squeezing blood upwards into the arteries. The
blood can't go into the atria because of the atrioventricular valves, which are forced shut
with a loud "lub".
3. Diastole. The atria and the ventricles relax, while the atria fill with blood. The semilunar
valves in the arteries close as the arterial blood pushes against them, making a "dup"
sound.
The pressure changes
show most clearly what is
happening in each
chamber. Blood flows
because of pressure
differences, and it always
flows from a high
pressure to a low
pressure, if it can. So
during atrial systole the
atria contract, making the
atrium pressure higher
than the ventricle
pressure, so blood flows
from the atrium to the
ventricle. The artery
pressure is higher still, but
blood can’t flow from the
artery back into the heart
due to the semi-lunar
valves. The valves are
largely passive: they open when blood flows through them the right way and close when
blood tries to flow through them the wrong way.

62
The PCG (or phonocardiogram) is a recording of the sounds the heart makes. The cardiac
muscle itself is silent and the sounds are made by the valves closing. The first sound (lub) is
the atrioventricular valves closing and the second (dub) is the semi-lunar valves closing.
The ECG (or electrocardiogram) is a recording of the electrical activity of the heart. There
are characteristic waves of electrical activity marking each phase of the cardiac cycle.
Changes in these ECG waves can be used to help diagnose problems with the heart
Blood pressure: The blood pressure is the pressure of the blood within the arteries. It is
produced primarily by the contraction of the heart muscle. Its measurement is recorded by
two numbers. The first (systolic pressure) is measured after the heart contracts and is
highest. The second (diastolic pressure) is measured before the heart contracts
The pulse rate is a measurement of the heart rate, or the number of times the heart beats
per minute. As the heart pushes blood through the arteries, the arteries expand and contract
with the flow of the blood. Taking a pulse not only measures the heart rate, but also can
indicate the following: heart rhythm and strength of the pulse
Factors affecting blood pressure
Exercise: Regular exercise, along with an active lifestyle, may decrease blood pressure. To
significantly reduce the risk of developing high blood pressure, it is recommended that adults
participate in 150 minutes a week of cardiovascular exercise such as walking, cycling and
swimming. Increasing daily activity by walking to and from class and work (rather than taking
the bus) and walking up and down stairs (versus riding the elevator), will also contribute to
an active, healthy lifestyle.
Nutrition: Research has shown that diet affects the development of high blood pressure
(hypertension). The DASH (Dietary Approaches to Stop Hypertension) eating plan is
recommended if your blood pressure is high or if you are at risk for high blood pressure.
DASH is a combination diet that is low in fat and rich in fruits and vegetables. It is low in
cholesterol and saturated fat, high in dietary fiber, potassium, calcium and magnesium and
moderately high in protein.
Alcohol: Alcohol is a drug, and regular over-consumption can raise blood pressure
dramatically, as well as cause an elevation upon withdrawal. Try to limit alcohol to twice a
week and drink only 1-2 servings (equivalent to two four-ounce glasses of wine, two eight-
ounce glasses of beer or two shots of spirits). Also, remember that alcohol intake can be a
factor in weight gain. The current recommendation is to limit alcohol intake to no more than
two drinks per day for most men and no more than one drink per day for women and lighter-
weight persons.

63
Stress: The effects of stress can vary, but long-term, chronic stress appears to raise blood
pressure. Various relaxation techniques such as deep breathing, progressive relaxation,
massage and psychological therapy can help to manage stress and help lower stress-
induced blood pressure elevations.
Smoking: Smoking is the third leading cause of death in the United States. Smoking causes
peripheral vascular disease (narrowing of the vessels that carry blood to the legs and arms),
as well as hardening of the arteries. These conditions clearly can lead to heart disease and
stroke and are contributing factors in high blood pressure. Don't start smoking and if you do
smoke, seek assistance with quitting.
Cardiac Output: Stroke Volume• Affect of stroke volume on blood pressure.• If less blood
is ejected from the heart with each beat, then blood pressure will be lower because there will
be less blood pressing against the vessel walls.• Blood volume affects end diastolic volume
and therefore stroke volume• With decreased stroke volume, due to decreased venous
return, volume there is a decreased cardiac output and a decreased blood pressure• With
increased stroke volume, due to increased venous return and/or increased contractility, there
is an increased cardiac output and increased blood pressure.
Vessel Elasticity • besides peripheral resistance, blood vessel elasticity also affects blood
pressure. • A healthy elastic artery expands, absorbing the shock of systolic pressure. The
elastic recoil of the vessel then maintains the continued flow of blood during diastole. • When
an individual has arteriosclerosis, arteries become calcified and rigid, so they can't expand
when the pulse wave of systolic pressure passes through them. Thus the walls of the artery
experience higher pressures and become weaker and weaker.
Blood Volume Analogy: Hoses • Blood volume affects blood pressure. • When there is a
greater volume of fluid, more fluid presses against the walls of the arteries resulting in a
greater pressure. • When there is less volume there is less pressure.
Blood vessels
Blood circulates in a series of different kinds of blood vessels as it circulates round the body.
Each kind of vessel is adapted to its function. Both arteries and veins are composed of three
layers the tunica adventitia which is a fibrous outer layer containing collagen and
connective tissue, the tunica media which is thick and contains elastic fibres and smooth
muscles in arteries but is thin in veins and the tunica intima which consists of the layer of
endothelial cells lining the lumen.

64
 Veins and Venules Capillaries Arteries and Arterioles
collagen& base m en tmemb rane collagen&
connectivetissue (collagen ) connectivetissue
sm oothm uscle end otheliumcell sm oothm uscle
&elastictissue &elastictissue
sem ilunarvalve
lum en(blood) redb
loodce
ll lumen(blood)
0.1-20mm 8µm 0.1-10mm

Function is to allow exchange Function is to carry blood

Function is to carry blood
of materials between the blood from the heart to the
from tissues to the heart
and the tissues tissues
Thick walls with smooth
Very thin, permeable walls,
Thin walls, mainly collagen, elastic layers to resist high
only one cell thick to allow
since blood at low pressure pressure and muscle layer
exchange of materials
to aid pumping
Large lumen to reduce Very small lumen. Blood cells
Small lumen
resistance to flow. must distort to pass through.
Many valves to prevent back- No valves (except in
No valves
flow heart)
Blood pressure falls in
Blood at low pressure Blood at high pressure
capillaries.
Blood usually oxygenated
Blood changes from
Blood usually deoxygenated (except in pulmonary
oxygenated to deoxygenated
(except in pulmonary vein) artery)
(except in lungs)

Arteries carry blood from the heart to every tissue in the body. They have thick, elastic walls
to withstand the high pressure of blood from the heart. The arteries close to the heart are
particularly elastic and expand during systole and recoil again during diastole, helping to
even out the pulsating blood flow. The smaller arteries and arterioles are more muscular and
can contract (vasoconstriction) to close off the capillary beds to which they lead; or relax
(vasodilation) to open up the capillary bed. These changes are happening constantly under
the involuntary control of the medulla in the brain, and are most obvious in the capillary beds
of the skin, causing the skin to change colour from pink (skin arterioles dilated) to blue (skin
arterioles constricted). There is not enough blood to fill all the body’s capillaries, and at any
given time up to 20% of the capillary beds are closed off.

65
Veins carry blood from every tissue in the body to the heart. The blood has lost almost all its
pressure in the capillaries, so it is at low pressure inside veins and moving slowly. Veins
therefore don’t need thick walls and they have a larger lumen than arteries, to reduce the
resistance to flow. They also have semi-lunar valves to stop the blood flowing backwards. It
is particularly difficult for blood to flow upwards through the legs to heart, and the flow is
helped by contractions of the leg and abdominal muscles:
leg
vein
valve stops
back-flow
leg
muscles

relaxed leg muscles contracted leg muscles relaxed leg muscles

slow flow blood forced upwards blood sucked upwards
The body relies on constant contraction of these muscles to get the blood back to the heart,
and this explains why soldiers standing still on parade for long periods can faint, and why
sitting still on a long flight can cause swelling of the ankles and Deep Vein Thrombosis (DVT
or “economy class syndrome”), where small blood clots collect in the legs.
Capillaries are where the transported substances actually enter and leave the blood. No
exchange of materials takes place in the arteries and veins, whose walls are too thick and

66
impermeable. Capillaries are very narrow and thin-walled, but there are a vast number of
them (108 m in one adult!), so they have a huge surface area : volume ratio, helping rapid
diffusion of substances between blood and cells. Capillaries are arranged in networks called
capillary beds feeding a group of cells, and no cell in the body is more than 2 cells away from
a capillary.
artery capillary bed vein

arteriole venule

cells
smooth
muscle sphincters
bypass vessel

Tissue Fluid
These substances are all exchanged between the blood and the cells in capillary beds.
Substances do not actually move directly between the blood and the cell: they first diffuse
into the tissue fluid that surrounds all cells, and then diffuse from there to the cells.
capillary

cells
 →
tissue 
fluid


 lymph vessel

1. At the arterial end of the capillary bed the blood is still at high hydrostatic pressure, so
blood plasma is squeezed out through the permeable walls of the capillary. Cells and
proteins are too big to leave the capillary, so they remain in the blood.
2. This fluid now forms tissue fluid surrounding the cells. Materials are exchanged
between the tissue fluid and the cells by all four methods of transport across a cell
membrane. Gases and lipid-soluble substances (such as steroids) cross by lipid

67
 diffusion; water crosses by osmosis, ions cross by facilitated diffusion; and glucose and
amino acids cross by active transport.
3. At the venous end of the capillary bed the blood is at low pressure, since it has lost so
much plasma. Water returns to the blood by osmosis since the blood has a low water
potential. Solutes (such as carbon dioxide, urea, salts, etc) enter the blood by diffusion,
down their concentration gradients.
4. Not all the plasma that left the blood returns to it, so there is excess tissue fluid. This
excess drains into lymph vessels, which are found in all capillary beds. Lymph vessels
have very thin walls, like capillaries, and tissue fluid can easily diffuse inside, forming
lymph.

The Pulse: The rhythmic contraction and expansion of an artery due to the surge of blood
from the beat of the heart. The pulse is most often measured by feeling the arteries of the
wrist. There is also a pulse, although far weaker, in veins
Transport of Oxygen
Oxygen is carried in red blood cells bound to the
protein haemoglobin. A red blood cell contains
about 300 million haemoglobin molecules and there
are 5 million red blood cells per cm³ of blood. The
result of this is that blood can carry up to 20%
oxygen, whereas pure water can only carry 1%.
The haemoglobin molecule consists of four
polypeptide chains, with a haem prosthetic group at
the centre of each chain. Each haem group
contains one iron atom, and one oxygen molecule
binds to each iron atom. So one haemoglobin
molecule can bind up to four oxygen molecules.
A sample of blood can therefore be in any state from completely deoxygenated (0%
saturated) to fully oxygenated (100% saturated). Since deoxyhaemoglobin and
oxyhaemoglobin are different colours, it is easy to measure the % saturation of a sample of
blood in a colorimeter. As the chemical equation shows, oxygen drives the reaction to the
right, so the more oxygen there is in the surroundings, the more saturated the haemoglobin
will be. This relation is shown in the oxygen dissociation curve:

68
 The concentration of oxygen in the
surroundings can be measured as a % (there’s
about 20% oxygen in air), but it’s more correct
to measure it as a partial pressure (PO2,
measured in kPa). Luckily, since the pressure
of one atmosphere is about 100 kPa, the
actual values for PO2 and % O2 are the same
(e.g. 12% O2 has a PO2 of 12 kPa). The graph
is read by starting with an oxygen
concentration in the environment surrounding
the blood capillaries on the horizontal axis,
then reading off the state of the haemoglobin in
the blood that results from the vertical axis.

This curve has an S (or sigmoid) shape, and

shows several features that help in the
transport of oxygen in the blood:
• In the alveoli of the lungs oxygen is constantly being brought in by ventilation, so its
concentration is kept high, at around 14 kPa. As blood passes through the capillaries
surrounding the alveoli the haemoglobin binds oxygen to become almost 100%
saturated. Even if the alveolar oxygen concentration falls a little the haemoglobin stays
saturated because the curve is flat here.
• In tissues, like muscle, liver or brain, oxygen is used by respiration, so is low, typically
about 4 kPa. At this PO2 the haemoglobin is only 50% saturated, so it unloads about half
its oxygen (i.e. from about 100% saturated to about 50% saturated) to the cells, which
use it for respiration.
• In tissues that are respiring quickly, such as contracting muscle cells, the PO2 drops
even lower, to about 2 kPa, so the haemoglobin saturation drops to about 10%, so
almost 90% of the oxygen is unloaded, providing more oxygen for the muscle cells.
• Actively-respiring tissues also produce a lot of CO2, which dissolves in tissue fluid to
make carbonic acid and so lowers the pH. The chemical equation above shows that
hydrogen ions drive the reaction to the left, so low pH reduces the % saturation of
haemoglobin at any PO2. This is shown on the graph by the dotted line, which is lower
than the normal dissociation curve. This downward shift is called the Bohr effect. The
Bohr Effect facilitates oxygen transport as hemoglobin binds to oxygen in the lungs, but
then releases it in the tissues, particularly those tissues in most need of oxygen. When a

69
 tissue's metabolic rate increases, its CO2 production increases. The CO2 is quickly
converted into bicarbonate molecules and acidic protons by the enzyme carbonic
anhydrase: CO2+ H2O H+ + HCO3−. This causes the pH of the tissue to decrease, and
so increases the dissociation of oxygen from hemoglobin to the tissue, allowing the
tissue to obtain enough oxygen to meet its demands (and raise its blood pH).The
dissociation curve shifts to the right when carbon dioxide or hydrogen ion concentration
is increased. This facilitates increased oxygen dumping. This makes sense because
increased CO2 concentration and lactic acid build-up occur when the muscles need more
oxygen. Changing hemoglobin's oxygen affinity is the body's way of adapting quickly to
this problem.
It is important to remember that oxygen can only diffuse in and out of the blood from
capillaries, which are permeable. Blood in arteries and veins is “sealed in”, so no oxygen can
enter or leave the blood whatever the external conditions. So as haemoglobin travels from
the lungs to a capillary bed in a body tissue and back to the lungs, it “switches” from one
position on the dissociation curve to another position, without experiencing the intermediate
stages of the curve.

Practice questions
1. What is the purpose of the circulatory system?
a. to supply oxygen to the body’s cells b. to supply nutrients to the body’s cells
c. to transport hormones and cellular waste products d. to fight germs
e. all of the above

2. What type of blood vessel carries blood away from the heart (usually oxygenated)?
a. artery b. capillary c. vein d. alveoli e. lymphatic vessel

3. What type of vessel carries the blood towards the heart (usually deoxygenated blood)?
a. artery b. capillary c. vein d. alveoli e. lymphatic vessel

4. What is the structure and location of the capillaries?

a. thin walled, flattened shape; which carry blood from the heart.
b. walls are a single layer of cells which carry blood between arteries and veins.
c. thick muscular walls, which carry blood away from the heart.
d. thin walled, which carry blood to the heart.
e. thick walled and moves blood through the heart only

70
5. What is the largest artery in the body?
a. aflective artery b. carotid artery c. aorta d. asitrocolic artery e. alveoli

6. What type of circulation describes the movement of blood between the heart and the
lungs?
a. pulmonary b. systemic c. cardiac d. bronchi e. none of the above

7. How many chambers are there in the human heart?

a. one b. two c. three d. four e. five

8. Blood travels through which of the following organs?

a. kidneys b. liver c. lungs d. heart e. all of the above

9. What is the leading cause of death in United States?

a. heart cancer b. broken hearts c. leukemia d. heart disease e. murder

10. High blood pressure is another name for ____________.

a. hypertension b. stroke c. arteries d. inferior vena cava e. hyperglycemia

11. What builds up in the blood vessels that could cause a heart attack?
a. stress b. tar c. plaque d. cells e. glue

12. Another name for ‘hardening of the arteries’ is:

a. heart attack b. hypertension c. atherosclerosis d. Cancer e. Hodgkin’s

13. What can happen when the coronary artery leading to the brain gets ‘clogged’?
a. stroke b. lymphoma c. leukemia d. arthritis e. anemia

14. What kind of diet causes heart disease?

a. vegetables b. fruits c. saturated fat d. proteins e. carbohydrates

15. How can you prevent a stroke or heart attack?

a. don't smoke b. don’t drink

16. Describe the flow of blood through the heart.

17. What would happen if the blood vessel supplying the heart muscle was blocked?
18. What else is contained in plasma apart from cells?
19. Where are blood cells made? 20. How is the heartbeat regulated?

71
6. The Hormone System and Homeostasis
Humans have two complementary control systems that they can use to respond to their
environment: the nervous system and the endocrine (hormonal) system. We’ll now look
briefly at the hormone system.
Hormones are secreted by glands into the blood stream. There are two kinds of glands:
• Exocrine glands secrete chemicals to the outside, or to body cavities, usually through
ducts (tubes). E.g. sweat glands, mammary glands, digestive glands.
• Endocrine glands do not have ducts but secrete chemicals directly into the tissue fluid
whence they diffuse into the blood stream. E.g. thyroid gland, pituitary gland, adrenal
gland. The hormone-secreting glands are all endocrine glands.
Gland Hormone Target organ Function

Pineal gland melatonin many biological clock

Pituitary gland FSH ovaries menstrual cycle

LH ovaries menstrual cycle
ADH* kidneys water homeostasis
growth hormone many stimulates cell division
oxytocin uterus birth contractions
prolactin mammary glands milk production

Thyroid gland thyroxine* liver metabolic rate

Adrenal glands adrenaline* many fight or flight

cortisol many anti-stress

Pancreas insulin* liver glucose homeostasis

glucagon* liver glucose homeostasis

Ovaries oestrogen uterus menstrual cycle

progesterone uterus menstrual cycle

Testes testosterone many male characteristics

Once a hormone has diffused into the blood stream it is carried all round the body to all
organs. However, it only affects certain target organs, which can respond to it. These target
organs have specific receptor molecules in their cells to which the hormone binds. These

72
receptors are protein molecules, and they form specific hormone-receptor complexes, very
much like enzyme-substrate complexes. Cells without the specific receptor will just ignore a
hormone. The hormone-receptor complex can affect almost any aspect of a cell’s function,
including metabolism, transport, protein synthesis, cell division or cell death.

There are three different ways in which a hormone can affect cell function:
Some hormones Some hormones release a The steroid hormones
affect the permeability of “second messenger” inside the are lipid-soluble so can
the cell membrane. They cell. They bind to a receptor on easily pass through
bind to a receptor on the the membrane, which then membranes by lipid
membrane, which then activates an enzyme in the diffusion. They diffuse to the
activates a transporter, membrane, which catalyses nucleus, where the bind to a
so substances can enter the production of a chemical in receptor, which activates
or leave the cell. (E.g. the cytoplasm, which affects protein synthesis.
insulin stimulates various aspects of the cell. (E.g. testosterone stimulates
glucose uptake.) (E.g. adrenaline stimulates spermatogenesis.)
glycogen breakdown.)
hormone
hormone molecule
hormone molecule
molecule cytoplasm
transporter membrane
receptor enzyme
membrane nucleus
receptor S P
Protein
receptor synthesis

So in most cases, the hormone does not enter the cell. The effect of a hormone is
determined not by the hormone itself, but by the receptor in the target cell. So the same
hormone can have different effects in different target cells.

Comparison of Nervous and Hormone Systems

Nervous System Hormone System
Transmitted by specific neurone cells Transmitted by the circulatory system
Effect localised by neurone anatomy Effect localised by target cell receptors
Fast-acting (ms–s) Slow-acting (mins–days)
Short-lived response Long-lived response

73
The two systems work closely together: endocrine glands are usually controlled by the
nervous system, and a response to a stimulus often involves both systems.

Excretion and Homeostasis

Excretion means the removal of waste products from cells. There are five important
excretory organs in humans:

• Skin excretes sweat, containing water, ions and urea

• Lungs excrete carbon dioxide and water
• Liver excretes bile, containing bile pigments, cholesterol and mineral ions
• Gut excretes mucosa cells, water and bile in faeces. (The bulk of faeces comprises
plant fibre and bacterial cells, which have never been absorbed into the body,
so are not excreted but egested.)
• Kidneys excrete urine, containing urea, mineral ions, water and other “foreign” chemicals
from the blood.

This section is mainly concerned with the excretion of nitrogenous waste as urea. The body
cannot store protein in the way it can store carbohydrate and fat, so it cannot keep excess
amino acids. The “carbon skeleton” of the amino acids can be used in respiration, but the
nitrogenous amino group must be excreted.
Amino Acid Metabolism
Amino acid metabolism takes place in the liver, and consists of three stages:
1. Transamination
In this reaction an amino group is transferred from an amino acid to a keto acid, to form a
different amino acid.
Amino acid 1 + Keto acid 2 → Keto acid 1 + Amino acid 2
In this way scarce amino acids can be made from abundant ones. In adult humans only 11 of
the 20 amino acids can be made by transamination. The others are called essential amino
acids, and they must be supplied in the diet.
2. Deamination
In this reaction an amino group is removed from an amino acid to form ammonia and a keto
acid. The most common example is glutamate deamination:

74
 COOH COOH

CH2 CH2
CH2 CH2
NAD NADH
NH2— CH— COOH + H2O NH3 + O=CH— COOH
glutamate ammonia -ketoglutarate

This reaction is catalysed by the enzyme glutamate dehydrogenase. Most other amino acids
are first transaminated to from glutamate, which is then deaminated. The NADH produced is
used in the respiratory chain; the α -ketoglutarate enters the Krebs cycle; and the ammonia
is converted to urea in the urea cycle.

3. Urea Synthesis
In this reaction ammonia is converted to urea, ready for excretion by the kidney.
3ATP 3ADP + 3Pi H2N
2NH3 + CO2 C=O + H2O
H2N
ammonia
urea
Ammonia is highly toxic, due to the reversal of the glutamate dehydrogenase reaction that
would use up all the α -ketoglutarate and so stop the Krebs cycle. Urea is less toxic than
ammonia, so it is safer to have in the bloodstream. The disadvantage is that it “costs” 3 ATP
molecules to make one urea molecule. This is not in fact a single reaction, but is a summary
of another cyclic pathway, called the urea cycle (or orthnthine cycle). It was the first cyclic
pathway
Homeostasis
Homeostasis literally means “same state” and it refers to the process of keeping the internal
body environment in a steady state. The importance of this cannot be over-stressed, and a
great deal of the hormone system and autonomic nervous system is dedicated to
homeostasis. In module 3 we saw how the breathing and heart rates were maintained. Here
we shall look at three more examples of homeostasis in detail: temperature, blood glucose
and blood water.
All homeostatic mechanisms use negative feedback to maintain a constant value (called the
set point). Negative feedback means that whenever a change occurs in a system, the
change automatically causes a corrective mechanism to start, which reverses the original
change and brings the system back to normal. It also means that the bigger then change the

75
bigger the corrective mechanism. Negative feedback applies to electronic circuits and central
heating systems as well as to biological systems.
effector reverses
factor to be controlled

change (negative
disturbance feedback)

time
set point
change
detected
overshoot-
new disturbance

So in a system controlled by negative feedback the level is never maintained perfectly, but
constantly oscillates about the set point. An efficient homeostatic system minimises the size
of the oscillations.

Blood Glucose Homeostasis

Glucose is the transport carbohydrate in animals, and its concentration in the blood affects
every cell in the body. Its concentration is therefore strictly controlled within the range
80-100 mg 100cm-3, and very low level (hypoglycaemia) or very high levels (hyperglycaemia)
are both serious and can lead to death.
Blood glucose concentration is controlled by the pancreas. The pancreas has glucose
receptor cells, which monitor the concentration of glucose in the blood, and it also has
endocrine cells (called the islets of Langerhans), which secrete hormones. The α cells
secrete the hormone glucagon, while the β cells secrete the hormone insulin. These two
hormones are antagonistic, and have opposite effects on blood glucose:
• insulin stimulates the uptake of glucose by cells for respiration, and in the liver it stimulates
the conversion of glucose to glycogen (glycogenesis). It therefore decreases blood
glucose.
• glucagon stimulates the breakdown of glycogen to glucose in the liver (glycogenolysis),
and in extreme cases it can also stimulate the synthesis of glucose from pyruvate. It
therefore increases blood glucose.

76
 glucagon insulin
stimulates stimulates

gluconeogenesis glycogenesis

Puruvate Glucose Glycogen

glycolysis glycogenolysis

insulin glucagon
stimulates stimulates

After a meal, glucose is absorbed from the gut into the hepatic portal vein, increasing the
blood glucose concentration. This is detected by the pancreas, which secretes insulin from
its β cells in response. Insulin causes glucose to be taken up by the liver and converted to
glycogen. This reduces blood glucose, which causes the pancreas to stop secreting insulin.
If the glucose level falls too far, the pancreas detects this and releases glucagon from its α
cells. Glucagon causes the liver to break down some of its glycogen store to glucose, which
diffuses into the blood. This increases blood glucose, which causes the pancreas to stop
producing glucagon.

These negative feedback loops continue all day, as shown in this graph:
140
blood glucose concentration (mg 100cm-3)

120

100
insulin glucagon insulin glucagon insulin set
point
glucose absorbed

glucose→glycogen

glucose→glycogen

glucose absorbed
glycogen→glucose

80

60

40 meal
meal

20

0
7am 8am 9am 10am 11am 12am 1pm 2pm

77
Diabetes Mellitus
Diabetes is a disease caused by a failure of glucose homeostasis. There are two forms of
the disease. In insulin-dependent diabetes (also known as type 1 or early-onset diabetes)
there is a severe insulin deficiency due to autoimmune killing of β cells (possibly due to a
virus). In non insulin-dependent diabetes (also known as type 2 or late-onset diabetes)
insulin is produced, but the insulin receptors in the target cells don’t work, so insulin has no
effect. In both cases there is a very high blood glucose concentration after a meal, so the
active transport pumps in the proximal convoluted tubule of the kidney can’t reabsorb it all
from the kidney filtrate, so much of the glucose is excreted in urine (diabetes mellitus means
“sweet fountain”). This leads to the symptoms of diabetes:
• high thirst due to osmosis of water from cells to the blood, which has a low water potential.
• copious urine production due to excess water in blood.
• poor vision due to osmotic loss of water from the eye lens.
• tiredness due to loss of glucose in urine and poor uptake of glucose by liver and muscle
cells.
• muscle wasting due to gluconeogenesis caused by increased glucagon.
Diabetes can be treated by injections with insulin or by careful diet. Until the discovery of
insulin in 1922 by Banting and Best, diabetes was an untreatable, fatal disease.
Diabetes insipidus is a condition where excess urine is excreted caused by the sufferers
inability to produce ADH and promote the retention of water.
The homeostatic maintenance of internal bodily conditions within tolerable limits is one
fundamental characteristic of living things. In order for an organism's life systems to function
properly, the tissues and cells require appropriate conditions. Homeostasis depends on the
dynamic action and interaction of a number of body systems.[1] Factors such as temperature,
salinity, acidity, plus nutrient and waste balances all affect a complex organism's ability to
sustain life.
With regard to any given life system parameter, an organism may be a conformer or a
regulator. Regulators try to maintain the parameter at a constant level over possibly wide
ambient environmental variations. On the other hand, conformers allow the environment to
determine the parameter. For instance, endothermic animals maintain a constant body
temperature, while ectothermic animals exhibit wide body temperature variation.
This is not to say that conformers don't have behavioural adaptations allowing them to exert
some control over a given parameter. For instance, reptiles often rest on sun-heated rocks in
the morning to raise their body temperature. Likewise, regulators' behaviors may contribute

78
to their internal stability: The same sun-baked rock may host a ground squirrel, also basking
in the morning sun.
An advantage of homeostatic regulation is that it allows an organism to function effectively in
a broad range of environmental conditions. For example, ectotherms tend to become
sluggish at low temperatures, while a co-located endotherm may be fully active. That thermal
stability comes at a price since an automatic regulation system requires additional energy.
One reason snakes may eat only once a week is that they use much less energy to maintain
homeostasis.
Control Mechanisms
All homeostatic control mechanisms have at least three interdependent components for the
variable being regulated: The receptor is the sensing component that monitors and responds
to changes in the environment. When the receptor senses a stimulus, it sends information to
a control center, the component that sets the range at which a variable is maintained. The
control center determines an appropriate response to the stimulus. The result of that
response feeds to the receptor, either enhancing it with positive feedback or depressing it
with negative feedback [2]
Feedback Mechanisms
Negative feedback
The body's homeostatically cultivated systems are maintained by negative feedback
mechanisms, sometimes called negative feedback loops. In negative feedback, any change
or deviation from the normal range of function is opposed, or resisted. The change or
deviation in the controlled value initiates responses that bring the function of the organ or
structure back to within the normal range.
Negative feedback loops have been compared to a thermostatically controlled temperature in
a house, where the internal temperature is monitored by a temperature-sensitive gauge in
the thermostat. If it is cold outside, eventually the internal temperature of the house drops,
as cold air seeps in through the walls. When the temperature drops below the point at which
the thermostat is set, the thermostat turns on the furnace. As the temperature within the
house rises, the thermostat again senses this change and turns off the furnace when the
internal temperature reaches the pre-set point.
Negative feedback loops require a receptor, a control center, and an effector. A receptor is
the structure that monitors internal conditions. For instance, the human body has receptors in
the blood vessels that monitor the pH of the blood. The blood vessels contain receptors that

79
measure the resistance of blood flow against the vessel walls, thus monitoring blood
pressure. Receptors sense changes in function and initiate the body's homeostatic response.
These receptors are connected to a control center that integrates the information fed to it by
the receptors. In most homeostatic mechanisms, the control center is the brain. When the
brain receives information about a change or deviation in the body's internal conditions, it
sends out signals along nerves. These signals prompt the changes in function that correct
the deviation and bring the internal conditions back to the normal range.
Positive Feedback Mechanisms
Positive feedback mechanisms are designed to accelerate or enhance the output created by
a stimulus that has already been activated. Unlike negative feedback mechanisms that
initiate to maintain or regulate physiological functions within a set and narrow range, the
positive feedback mechanisms are designed to push levels out of normal ranges. To achieve
this purpose, a series of events initiates a cascading process that builds to increase the
effect of the stimulus. This process can be beneficial but is rarely used by the body due to
risks of the acceleration becoming uncontrollable.
One bodily positive feedback example event is blood platelet accumulation which in turn
causes blood clotting in response to a break or tear in the lining of blood vessels. Another
example is the release of oxytocin to intensify the contractions that take place during
childbirth.
Positive feedback can also be harmful. An example being when you have a fever it causes a
positive feedback within homeostasis that pushes the temperature continually higher. Body
temperature can reach extremes of 45ºC (113ºF), at which cellular proteins denature,
causing the active site in proteins to change, thus causing metabolism stop and ultimately
resulting in death.

Fruit Ripening

When the fruit is full size but it

is green and immature...
events must now happen to
cause it to ripen so that it is
attractive and rewarding for
an animal to carry it
off...dispersing the seeds.

80
In the diagram above on the left is an unripe fruit. It is hard, green, sour, has no smell, is
mealy (starch present), and so on. Sometimes we crave such a combination of
characteristics...a 'Granny Smith' apple has many of those. Such fruits are similar to celery or
other vegetables, and so are not appealing at other times.
The way fruits ripen is that there is commonly a ripening signal...a burst of ethylene
production. Ethylene is a simple hydrocarbon gas (H2C=CH2) that ripening fruits make and
shed into the atmosphere. Sometimes a wound will cause rapid ethylene production...thus
picking a fruit will sometimes signal it to ripen...as will an infection of bacteria or fungi on the
fruit. This ethylene signal causes developmental changes that result in fruit ripening.
Ethylene also affects many other plant functions such as: abscission of leaves, fruits, and
flower petals; drooping of leaves; sprouting of potato buds; seed germination;
New enzymes are made because of the ethylene signal. These include hydrolases to help
break down chemicals inside the fruits, amylases to accelerate hydrolysis of starch into
sugar, pectinases to catalyze degradation of pectin (the glue between cells), and so on.
Ethylene apparently "turns on" the genes that are then transcribed and translated to make
these enzymes. The enzymes then catalyze reactions to alter the characteristics of the fruit.
The action of the enzymes causes the ripening responses. Chlorophyll is broken down and
sometimes new pigments are made so that the fruit skin changes color from green to red,
yellow, or blue. Acids are broken down so that the fruit changes from sour to neutral. The
degradation of starch by amylase produces sugar. This reduces the mealy (floury) quality
and increases juiciness (by osmosis, a process we will study later). The breakdown of pectin,
thanks to pectinase, between the fruit cells unglues them so they can slip past each other.
Those results in a softer fruit...at extreme, pectin losses may make a fruit "pithy". Also
enzymes break down large organic molecules into smaller ones that can be volatile
(evaporate into the air) and we can detect as an aroma.
If you think of this process in apples, the ethylene signal causes the fruit to change from
green to yellow, from hard to soft, from mealy to juicy, from tart to sweet, from odorless to
fragrant.
How can you assist fruit ripening? First let me tell you that bananas are shipped to the US as
hard, green, sour, unripened fruits. They ship better that way. They arrive into a distributor's
warehouse without bruises. The bananas are put in a room and gassed with ethylene. They
all begin to ripen. You buy them at the store and within a few days the ripening process is so
rapid that the bananas are "over the hill" before you can eat them all.

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Fruit Abscission
The fruit-ripening process described above, also occurs in a layer of cells in the pedicel near
the point of attachment to the stem of the plant. This layer of cells in the pedicel is often
called the abscission zone because this layer will eventually separate and the fruit will drop
from the plant.
Just as the cells inside the fruit, the cells in this cross sectional layer in the pedicel get the
ethylene signal from the ripening fruit. Reception of the signal causes new enzymes to be
made. The cells "ripen" and pectinases unglue the cells of the abscission zone. When the
cells have weak-enough connections, the weight of the fruit will cause it to fall from the plant.
In this way then, the ripening process is used for a second function in the plant...to make the
fruit drop from the tree so an animal can pick it up and carry it off to disperse seeds. Plants
are modular organisms, and use the same genetic and physiological processes for different
processes in the various modules.

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7. The Kidney and Excretion
The kidney
Kidneys have two main functions.
1. They are excretory organs, removing nitrogenous and other waste from the body. 2. They
play an important part in maintaining a constant internal environment by helping to regulate
pH, water and sodium ion concentrations in the blood and tissues. This Factsheet will focus
on the role of the kidney in excretion and osmoregulation.
Excretion
Surplus nitrogen-containing compounds such as amino acids have to be broken down in the
body because they are toxic and are then excreted as ammonia, urea or uric acid (Table 1).
Some important biological properties of these three substances are summarised in Table 2.

83
From this you can work out that:
· Freshwater fish excrete ammonia. Although it is very poisonous, fish are surrounded by
large amounts of water so the ammonia can easily be diluted to safe levels.
· Mammals excrete nitrogen mainly as urea. Urea requires more energy in the form of ATP
for its production but is much less toxic than ammonia and fairly soluble. It therefore does
not require large amounts of water to remove it from the body.
· Birds excrete nitrogen mainly as uric acid. Flight demands a low body mass. Removing
nitrogenous waste as uric acid means that large amounts of water are not required.
Insects also excrete uric acid. As they are so small, they are very prone to water loss so
it is important that they do not lose large amounts of water in excreting nitrogenous
waste.

Basic kidney structureThe basic structure of the mammalian kidney is shown in Figure 1.
Each kidney contains a million coiled tubes called nephrons and it is in the nephron that
urine formation occurs. Each nephron is divided into a number of distinct regions with
particular functions labelled A, B, C (Figure 2).

84
85
A. Ultrafiltration.
The Bowman's capsule contains a dense capillary network called the glomerulus. Blood
flows into these capillaries through a wide afferent arteiole and leaves through a narrower
efferent arteriole. The blood pressure inside these capillaries is high because:
1. The renal artery contains blood at very high pressure which enters the glomerulus via the
short afferent arteriole.
2. The efferent arteriole has a smaller diameter than the afferent arteriole. The high pressure
forces small molecules such as water, glucose, amino acids, sodium chloride and urea
through the filter i.e. from the blood in the glomerular capsule across the basement
membrane of the Bowman's capsule and into the nephron. This type of high-pressure
filtration is known as ultrafiltration. The fluid formed in this way is called glomerular filtrate.
Large molecules such as plasma proteins and blood cells do not pass through the filter
because they are too big.
Blood plasma is separated from the filtrate by two rows of cells, the lining cells of the
capillary and the podocytes which make up the inner layer of the capsule. The capillaries
have pores in their walls which the molecules in the plasma are able to pass directly through.
The small molecules then pass through the basement membrane and once through this, they
can pass between the processes of the podocyte directly into the cavity of the renal capsule.
The actual filter is just the basement membrane and this is extremely thin.
B. Selective reabsorption in the proximal convoluted tubule

86
The filtrate contains toxic substances such as urea which it is necessary to remove from the
body but it also contains substances such as glucose which are required by the body. The
function of the proximal convoluted tubule is to reabsorb these useful substances (Figure 5).

87
1. Glucose diffuses into the cells which line the proximal convoluted tubule. Microvilli
increase the surface area for efficient absorption.
2. The glucose is actively transported out of the cells into the intercellular spaces.
Mitochondria supply the necessary ATP.
3. Once in the intercellular spaces, the glucose diffuses through the walls of the
capillaries and is transported away by the blood.
4. Active transport of glucose out of the tubule cells maintains a concentration gradient so
more glucose is able to diffuse out of the tubule fluid.
Similar mechanisms result in the reabsorption of many of the amino acids and up to 90% of
the sodium ions from the tubule fluid. The removal of all these soluble substances results in
an osmotic gradient between the fluid in the tubule and the cells which line it. Water is
therefore drawn out of the tubule fluid by osmosis, and passes into blood. This process is
responsible for 85-90% of water reabsorption in the Nephron. It is only the remaining 10-15%
which is regulated in the loop of Henle and collecting duct.

88
C. Osmoregulation (Figure 6)
The ability to produce concentrated urine is important in allowing terrestrial mammals to
conserve water. The loop of Henle and the collecting duct form a system known as a
countercurrent multiplier whose function is to remove water from the fluid in the tubule and
produce a concentrated urine.
1. Na+ and Cl- ions are actively pumped out of the ascending limb. The ions accumulate in
the interstitial fluid. This lowers the water potential of the interstitial fluid. The tendency is
for water to osmotically follow the Na+ and Cl- ions but it cannot since most of the
ascending limb is impermeable to water.
2. Water is drawn out of the descending limb and into the interstitial fluids by osmosis. This
makes the fluid in the descending limb more and more concentrated.

89
3. By the time the fluid in the descending limb has reached the bottom of the limb, it has
lost a lot of water and is very concentrated. The fluid surrounding the bottom of the loop -
in the medulla of the kidney – is also very concentrated because of the accumulation of
Na+ and Cl- ions. The direction of the concentration gradient is shown by the arrow.
4. The fluid then enters the ascending limb. As it moves up the ascending limb, sodium ions
are actively pumped out of it.
5. This makes the fluid at the top of the ascending limb very dilute again.
6. The fluid then empties into collecting ducts which pass through the very concentrated
medullary region.
7. Under the influence of the hormone ADH, the wall of the collecting duct becomes
permeable to water which is therefore osmotically drawn out of the collecting duct and
into the blood capillaries in the region.
8. By drawing water out of the fluid in the collecting duct, a very concentrated urine can be
produced. By regulating the permeability of the collecting duct (via ADH), the amount of
water in the blood and the concentration of the urine can be controlled.

What controls ADH?

The osmotic concentration of the blood is monitored by osmoreceptors in the

hypothalamus. Blood pressure is monitored by baroreceptors which are widely dispersed
throughout the circulatory system. Both types of receptor can send impulses to the posterior
pituitary gland to start/stop ADH release. If too much water is lost from the body:
1. The volume of blood plasma falls, its osmotic concentration therefore increases and
blood pressure falls.
2. Osmoreceptor and baroreceptors detect these changes and an impulse is sent to the
posterior pituitary gland.
3. ADH is released.
4. ADH increases the permeability to water of the collecting duct and the distal convoluted
tubule.
5. More water is therefore drawn out of the collecting duct and distal convoluted tubule back
into the blood. This restores the volume and pressure of the blood and reduces its
osmotic concentration.
6. The stimulus to the posterior pituitary is switched off. If the osmotic concentration of the
blood falls or if blood pressure increases, less ADH is released, less water is reabsorbed,
resulting in a large volume of dilute urine. This restores the osmotic concentration and
pressure of the blood.

90
Protein in the urine (kidney): although healthy people do pass small amounts of protein in
the urine normally, above a certain level suggests that there may be damage to the filter
mechanism (the glomeruli) or inflammation. A second source of protein in urine is blood that
may come from any part of the kidney or urinary pathway. High levels of protein in the urine
may therefore be due to diseases of the kidney such as glomerulonephritis. It may also be
due to general illnesses that also affect the kidney as in high blood pressure or heart failure.
Infections of the renal pathway
Diabetic nephropathy:Diabetic nephropathy is the kidney disease that occurs as a result of
diabetes. It is a leading cause of kidney failure in Europe and the USA. After many years of
diabetes the delicate filtering system in the kidney becomes destroyed, initially becoming
leaky to large blood proteins such as albumin which are then lost in urine. This is more likely
to occur if the blood sugar is poorly controlled.
1. It begins with a tiny amount of protein appearing in the urine - this is called
microalbuminuria. The kidney function may well be normal at this point.
2. Over 10-15 years proteinuria increases, and nephrotic syndrome may develop
3. With the development of proteinuria, the kidneys' ability to remove poisons from the
blood deteriorates such that 5-10 years later the kidneys are almost completely unable to
remove these poisons from the blood.
4. This is called "end-stage renal disease" (ESRD), and, unless treated, the poisons can
build up to fatal levels.

The Course of Kidney Disease: Diabetic kidney disease takes many years to develop. In
some people, the filtering function of the kidneys is actually higher than normal in the first few
years of their diabetes. Over several years, people who are developing kidney disease will
have small amounts of the blood protein albumin begin to leak into their urine. This first stage
of CKD is called microalbuminuria. The kidney’s filtration function usually remains normal
during this period. As the disease progresses, more albumin leaks into the urine. This stage
may be called macroalbuminuria or proteinuria. As the amount of albumin in the urine
increases, the kidneys’ filtering function usually begins to drop. The body retains various
wastes as filtration falls. As kidney damage develops, blood pressure often rises as well.
Overall, kidney damage rarely occurs in the first 10 years of diabetes, and usually 15 to 25
years will pass before kidney failure occurs. For people who live with diabetes for more than
25 years without any signs of kidney failure, the risk of ever developing it decreases.

91
Urea Cycle
The urea cycle consists of five reactions - two mitochondrial and three cytosolic. The cycle
converts two amino groups, one from NH4+ and one from Asp, and a carbon atom from
HCO3-, to relatively nontoxic excretion product, urea, at the cost of four "high-energy"
phosphate bonds (3 ATP hydrolyzed to 2 ADP and one AMP). Orn is the carrier of these
carbon and nitrogen atoms.

Practice questions

1. Where does active transport occur?

A. In the proximal tubules of the kidney. B. In the distal tubules of the kidney.
C. In the loops of Henle of the kidney. D. In the collecting ducts.

2. Which of these components of blood would pass from the blood into the initial filtrate in
the glomerulus?
A. Water B. Glucose C. Urea D. Proteins E. Red blood cells

92
3. The proximal tubule causes what change in the volume of the filtrate?
A. Increase. B. Decrease. C. No significant change.

4. The proximal tubule causes what change in the osmolarity of the filtrate.
A. Increase. B. Decrease. C. No significant change.

5. The proximal tubule causes what change in the urea concentration of the filtrate.
(Think carefully!)
A. Increase. B. Decrease. C. No significant change.

6. The descending limb of the loop of Henle causes what change in the volume of the
filtrate.
A. Increase. B. Decrease. C. No significant change.

7. The descending limb of the loop of Henle causes what change in the osmolarity of the
filtrate.
A. Increase. B. Decrease. C. No significant change.

8. The descending limb of the loop of Henle causes a significant change in the urea
concentration of the filtrate.
A. True. B. False.

9. How does urea leave the filtrate in the collecting duct?

A. Simple diffusion.B. Facilitated diffusion.
C. Active transport. D. It doesn’t; the collecting duct isn’t permeable to urea.

10. How does water leave the filtrate in the descending limb of the loop of Henle?
A. Simple diffusion. B. Facilitated diffusion.
C. Active transport. D. It doesn’t; the descending limb isn’t permeable to water.

11. How does Na+ leave the filtrate in the ascending limb of the loop of Henle?
A. Simple diffusion. B. Facilitated diffusion.
C. Active transport. D. It doesn’t; the ascending limb isn’t permeable to Na+.

12. How does Cl- leave the filtrate in the ascending limb of the loop of Henle?
A. Simple diffusion. B. Facilitated diffusion.
C. Active transport. D. It doesn’t; the ascending limb isn’t permeable to Cl-.

93
8.: The Human Nervous System

Humans, like all living organisms, can respond to their environment. Humans have two
complimentary control systems to do this: the nervous system and the endocrine (hormonal)
system. We’ll look at the endocrine system later, but first we’ll look at the nervous system.
The human nervous system controls everything from breathing and producing digestive
enzymes, to memory and intelligence.

Nerve Cells

The nervous system composed of nerve cells, or neurones:

A neurone has a cell body with extensions leading off it. Numerous dendrons and dendrites
provide a large surface area for connecting with other neurones, and carry nerve impulses
towards the cell body. A single long axon carries the nerve impulse away from the cell body.

94
The axon is only 10µm in diameter but can be up to 4m in length in a large animal (a piece of
spaghetti the same shape would be 400m long)! Most neurones have many companion cells
called Schwann cells, which wrap their cell membrane around the axon many times in a
spiral to form a thick insulating lipid layer called the myelin sheath. Nerve impulse can be
passed from the axon of one neurone to the dendron of another at a synapse. A nerve is a
discrete bundle of several thousand neurone axons.

Humans have three types of neurone:

• Sensory neurones have long axons and transmit nerve impulses from sensory receptors all
over the body to the central nervous system.
• Motor neurones
also have long
axons and transmit
nerve impulses from
the central nervous
system to effectors
(muscles and
glands) all over the
body.

• Interneurones (also
called connector
neurones or relay
neurones) are
usually much
smaller cells, with
many
interconnections.

95
The Reflex Arc
The three types of neurones are arranged in circuits and networks, the simplest of which is
the reflex arc.
In a simple reflex arc, such as the knee jerk, a stimulus is detected by a receptor cell, which
synapses with a sensory neurone. The sensory neurone carries the impulse from site of the
stimulus to the central nervous system (the brain or spinal cord), where it synapses with an
interneurone. The interneurone synapses with a motor neurone, which carries the nerve
impulse out to an effector, such as a muscle, which responds by contracting.

Reflex arc can also be represented by a simple flow diagram:

sensory motor
Stimulus Receptor neurone Coordinator neurone Effector Response
external stimuli cell or organ Brain or spinal cord muscles or movement, secretion,
internal stimuli (interneurones) glands behaviour

The Organisation of the Human Nervous System

The human nervous system is far more complex than a simple reflex arc, although the same
stages still apply. The organisation of the human nervous system is shown in this diagram:

Human Nervous System

Central Nervous System (CNS) Peripheral Nervous System (PNS)

Brain and spinal cord Everything else
Interneurons Sensory & motor neurons

Somatic Nervous System Autonomic Nervous System

Voluntary Involuntary
Input from sense organs Input from internal receptors
Output to skeletal muscles Output to smooth muscles & glands

Sympathetic Motor System Parasympathetic Motor System

"fight or flight" responses relaxing responses
Neurotransmitter: noradrenaline Neurotrasmitter: acetylcholine
"Adrenergic System" "Cholinergic System"

96
It is easy to forget that much of the human nervous system is concerned with routine,
involuntary jobs, such as homeostasis, digestion, posture, breathing, etc. This is the job of
the autonomic nervous system, and its motor functions are split into two divisions, with
anatomically distinct neurones. Most body organs are innervated by two separate sets of
motor neurones; one from the sympathetic system and one from the parasympathetic
system. These neurones have opposite (or antagonistic) effects. In general the sympathetic
system stimulates the “fight or flight” responses to threatening situations, while the
parasympathetic system relaxes the body. The details are listed in this table:

Organ Sympathetic System Parasympathetic System

Eye Dilates pupil Constricts pupil
Tear glands No effect Stimulates tear secretion
Salivary glands Inhibits saliva production Stimulates saliva production
Lungs Dilates bronchi Constricts bronchi
Heart Speeds up heart rate Slows down heart rate
Gut Inhibits peristalsis Stimulates peristalsis
Liver Stimulates glucose production Stimulates bile production
Bladder Inhibits urination Stimulates urination

The Nerve Impulse

Neurones and muscle cells are electrically excitable cells, which mean that they can transmit
electrical nerve impulses. These impulses are due to events in the cell membrane, so to
understand the nerve impulse we need to revise some properties of cell membranes.
The Membrane Potential
All animal cell membranes contain a protein pump called the Na+K+ATPase. This uses the
energy from ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2
potassium ions in. If this was to continue unchecked there would be no sodium or potassium
ions left to pump, but there are also sodium and potassium ion channels in the membrane.
These channels are normally closed, but even when closed, they “leak”, allowing sodium
ions to leak in and potassium ions to leak out, down their respective concentration gradients.

97
 3Na+
outside +
cell
Na Na+K+ATPase K
membrane

inside closed closed -

(leak) ATP ADP+Pi (leak)
2K+
The combination of the Na+K+ATPase pump and the leak channels cause a stable imbalance
of Na+ and K+ ions across the membrane. This imbalance causes a potential difference
across all animal cell membranes, called the membrane potential. The membrane potential is
always negative inside the cell, and varies in size from –20 to –200 mV in different cells and
species. The Na+K+ATPase is thought to have evolved as an osmoregulator to keep the
internal water potential high and so stop water entering animal cells and bursting them. Plant
cells don’t need this as they have strong cells walls to prevent bursting.
The Action Potential
In nerve and muscle cells the membranes are electrically excitable, which means that they
can change their membrane potential, and this is the basis of the nerve impulse. The sodium
and potassium channels in these cells are voltage-gated, which means that they can open
and close depending on the voltage across the membrane.
The nature of the nerve impulse was discovered by Hodgkin, Huxley and Katz in Plymouth in
the 1940s, for which work they received a Nobel prize in 1963. They used squid giant
neurones, whose axons are almost 1mm in diameter, big enough to insert wire electrodes so
that they could measure the potential difference across the cell membrane. In a typical
experiment they would apply an electrical pulse at one end of an axon and measure the
voltage changes at the other end, using an oscilloscope:
The normal membrane potential of these nerve cells is –70mV (inside the axon), and since
this potential can change in nerve cells it is called the resting potential. When a stimulating
pulse was applied a brief reversal of the membrane potential, lasting about a millisecond,
was recorded. This brief reversal is called the action potential:
The action potential has 2 phases called depolarisation and repolarisation.

98
1. Depolarisation. the membrane
potential changes .The voltage-gated out
open -
ion channels can detect this change,
and when the potential reaches – Na
30mV the sodium channels open for K
0.5ms. The causes sodium ions to
rush in, making the inside of the cell in
closed
more positive. This phase is referred
+
(leak) +
to as a depolarisation since the Na
normal voltage polarity (negative
inside) is reversed (becomes positive
inside).

99
2. Repolarisation. When the K+
membrane potential reaches 0V, the
out
+
potassium channels open for 0.5ms,
causing potassium ions to rush out,
making the inside more negative Na K
again. Since this restores the original
polarity, it is called repolarisation. in
closed open
(leak) -
+ +
The Na K ATPase pump runs continuously, restoring the resting concentrations of sodium
and potassium ions.

How do Nerve Impulses Start?

In the squid experiments the action potential was initiated by the stimulating electrodes. In
living cells they are started by receptor cells. These all contain special sodium channels that
are not voltage-gated, but instead are gated by the appropriate stimulus (directly or
indirectly). For example chemical-gated sodium channels in tongue taste receptor cells open
when a certain chemical in food binds to them; mechanically-gated ion channels in the hair
cells of the inner ear open when they are distorted by sound vibrations; and so on. In each
case the correct stimulus causes the sodium channel to open; which causes sodium ions to
flow into the cell; which causes a depolarisation of the membrane potential, which affects the
voltage-gated sodium channels nearby and starts an action potential.
How are Nerve Impulses Propagated?
Once an action potential has started it is moved (propagated) along an axon automatically.
The local reversal of the membrane potential is detected by the surrounding voltage-gated
ion channels, which open when the potential changes enough.
direction of
nerve impulse just opened next to
- refactory open Na+ channels

membrane
+ + - - + +
- - + + - -
axon
membrane - - + + - -
+ + - - + +
resting action resting
potential potential potential
The ion channels have two other features that help the nerve impulse work effectively:

100
• After an ion channel has opened, it needs a “rest period” before it can open again. This is
called the refractory period, and lasts about 2 ms. This means that, although the action
potential affects all other ion channels nearby, the upstream ion channels cannot open
again since they are in their refractory period, so only the downstream channels open,
causing the action potential to move one-way along the axon.
• The ion channels are either open or closed; there is no half-way position. This means that
the action potential always reaches +40mV as it moves along an axon, and it is never
attenuated (reduced) by long axons. In other word the action potential is all-or-nothing.

How Fast are Nerve Impulses?

Action potentials can travel along axons at speeds of 0.1-100 m/s. This means that nerve
impulses can get from one part of a body to another in a few milliseconds, which allows for
fast responses to stimuli. (Impulses are much slower than electrical currents in wires, which
travel at close to the speed of light, 3x108 m/s.) The speed is affected by 3 factors:
• Temperature. The higher the temperature, the faster the speed. So homoeothermic (warm-
blooded) animals have faster responses than poikilothermic (cold-blooded) ones.
• Axon diameter. The larger the diameter, the faster the speed. So marine invertebrates,
who live at temperatures close to 0°C, have developed thick axons to speed up their
responses. This explains why squid have their giant axons.
• Myelin sheath. Only vertebrates have a myelin sheath surrounding their neurones. The
voltage-gated ion channels are found only at the nodes of Ranvier, and between the nodes
the myelin sheath acts as a good electrical insulator. The action potential can therefore
jump large distances from node to node (1mm), a process that is called saltatory
propagation. This increases the speed of propagation dramatically, so while nerve
impulses in unmyelinated neurones have a maximum speed of around 1 m/s, in myelinated
neurones they travel at 100 m/s.

direction of
nerve impulse

+ - - +
- + + -
+ - - +
myelin node of Ranvier
sheath -ions channels here only

101
Saltatory conduction
Saltatory conduction (from the Latin saltare, to hop or leap) is a means by which action
potentials are transmitted along myelinated nerve fibers. Because the cytoplasm of the axon
is electrically conductive, and because the myelin inhibits charge leakage through the
membrane, depolarization at one node of Ranvier is sufficient to elevate the voltage at a
neighboring node to the threshold for action potential initiation. Thus in myelinated axons,
action potentials do not propagate as waves, but recur at successive nodes and in effect
"hop" along the axon, by which process they travel faster than they would otherwise. This
process is outlined as the charge will passively spread to the next node of Ranvier to
depolarize it to threshold which will then trigger an action potential in this region which will
then passively spread to the next node and so on. This phenomenon was discovered by Ichiji
Tasaki[1][2] and Andrew Huxley[3] and their colleagues.
Apart from increasing the speed of the nerve impulse, the myelin sheath helps in reducing
energy expenditure as the area of depolarization and hence the amount of sodium/potassium
ions that need to be pumped to bring the concentration back to normal, is decreased.
Saltatory conduction had been found exclusively in the myelinated nerve fibers of
vertebrates, but was later discovered in a pair of medial myelinated giant fibers of Penaeus
orientalis (chinensie) and Penaeus japonicus [4][5][6], as well as a median giant fiber of an
earthworm[7]. Saltatory conduction has also been found in the small- and medium-sized
myelinated fibers of Penaeus shrimp[8].

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Synapses
The junction between two neurones is called a synapse. An action potential cannot cross the
synaptic cleft between neurones, and instead the nerve impulse is carried by chemicals
called neurotransmitters. These chemicals are made by the cell that is sending the impulse
(the pre-synaptic neurone) and stored in synaptic vesicles at the end of the axon.The
synapse prevents the movement of impulses back towards the receptor. The cell that is
receiving the nerve impulse (the post-synaptic neurone) has chemical-gated ion channels in
its membrane, called neuroreceptors. These have specific binding sites for the
neurotransmitters.

1. At the end of the pre-synaptic neurone there are voltage-gated calcium channels. When
an action potential reaches the synapse these channels open, causing calcium ions to
flow into the cell.

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2. These calcium ions cause the synaptic vesicles to fuse with the cell membrane, releasing
their contents (the neurotransmitter chemicals) by exocytosis.
3. The neurotransmitters diffuse across the synaptic cleft.
4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing
the channels to open. In the example shown these are sodium channels, so sodium ions
flow in.
5. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an
action potential.
6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for
example the enzyme acetylcholinesterase breaks down the neurotransmitter
acetylcholine. The breakdown products are absorbed by the pre-synaptic neurone by
endocytosis and used to re-synthesise more neurotransmitter, using energy from the
mitochondria. This stops the synapse being permanently on.

Cholinergic synapse A synapse is cholinergic if it uses acetylcholine as its

neurotransmitter. Cholinergic means "related to the neurotransmitter acetylcholine". The
parasympathetic nervous system is entirely cholinergic. A substance is cholinergic if it is
capable of producing, altering, or releasing acetylcholine. A cholinergic, also known as a
cholinergic agent or a parasympathomimetic, is any chemical which functions to enhance the
effects mediated by acetylcholine in the central nervous system, the peripheral nervous
system, or both. These include acetylcholine's precursors and cofactors, acetylcholine
receptor agonists (such as muscarine and nicotine), as well as cholinergic enzymes such as
the anticholinesterases.

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9. Health and Diseases
Mental health
Mental health is a concept that refers to a human individual's emotional and psychological
well-being. defines mental health as "A state of emotional and psychological well-being in
which an individual is able to use his or her cognitive and emotional capabilities, function in
society, and meet the ordinary demands of everyday life."
According to the World Health Organization, there is no one "official" definition of mental
health. Cultural differences, subjective assessments, and competing professional theories all
affect how "mental health" is defined. In general, most experts agree that "mental health" and
"mental illness" are not opposites. In other words, the absence of a recognized mental
disorder is not necessarily an indicator of mental health.
One way to think about mental health is by looking at how effectively and successfully a
person functions. Feeling capable and competent; being able to handle normal levels of
stress, maintain satisfying relationships, and lead an independent life; and being able to
"bounce back," or recover from difficult situations, are all signs of mental health.
Physical health
Physical health is the overall condition of a living organism at a given time, the soundness of
the body, freedom from disease or abnormality, and the condition of optimal well-being.
People want to function as designed, but environmental forces can attack the body or the
person may have genetic malfunctions. The main concern in health is preventing injury and
healing damage caused by injuries and biological attacks.
Emotional and social health
Children take their first significant steps toward socialization and peer interaction when they
begin to engage in cooperative play at around age four. Their social development will
progress throughout childhood and adolescence as they develop friendships, start to be
influenced by their peers, and begin to show interest in the opposite sex.
Factors which can have a negative impact on the emotional and social well-being of children
include:

• Violence. Bullying can cause serious damage to a child's sense of self-esteem and
personal safety, as can experiences with school violence.
• Family turmoil. Divorce, death, and other life-changing events that alter the family
dynamic can have a serious impact on a child. Even a positive event such as the

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 birth of a sibling or a move to a new city and school can put emotional strain on a
child.
• Stress. The pressure to perform well academically and in extracurricular activities
such as sports can be over-whelming to some children.
• Peer pressure. Although it can have a positive impact, peer pressure is often a
source of significant stress for children. This is particularly true in adolescence when
"fitting in" seems all-important.
• Drugs and alcohol. Curiosity is intrinsic to childhood, and over 30% of children have
experimented with alcohol by age 13. Open communication with children that sets
forth parental expectations about drug and alcohol use is essential.
• Negative sexual experiences. Sexual abuse and assault can emotionally scar a child
and instill negative feelings about sexuality and relationships.

Causes and symptoms

Childhood health problems may be congenital (i.e., present at birth) or acquired through
infection, immune system deficiency, or another disease process. They may also be caused
by physical trauma (e.g., a car accident or a playground fall) or a toxic substance (e.g., an
allergen, drug, or poisonous chemical), or triggered by genetic or environmental factors.
Physical and mental health problems in childhood can cause a wide spectrum of symptoms.
However, the following behaviors frequently signify a larger emotional, social, or mental
disturbance:

• signs of alcohol and drug use

• falling grades
• lack of interest in activities that were previously enjoyable to the child
• excessive anxiety
• persistent, prolonged depression
• withdrawal from friends and family
• violence
• temper tantrums or inappropriate displays of anger
• self-inflicted injury
• bizarre behavior and/or speech
• trouble with the police
• sexual promiscuity
• suicide attempts

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The causes of developmental disorders and delays and learning disabilities are not always
fully understood. Pervasive developmental disorder (PDD) and autistic spectrum disorder
(more commonly known as autism) are characterized by unresponsiveness and severe
impairments in one or more of the following areas:

• Social interaction. Autistic children are often unaware of acceptable social behavior and
are withdrawn and socially isolated. They frequently do not like physical contact.
• Communication and language. A child with autism or PDD may not speak or may display
limited or immature language skills.
• Behavior. Autistic or PDD children may have difficulty dealing with anger, can be self-
injurious, and may display obsessive behavior.

Mental illnesses are medical conditions that disrupt a person’s thinking, feeling, mood,
ability to relate to others, and daily functioning. Just as diabetes is a disorder of the
pancreas, mental illnesses are medical conditions that often result in a diminished capacity
for coping with the ordinary demands of life.
Serious mental illnesses include major depression, schizophrenia, bipolar disorder,
obsessive compulsive disorder (OCD), panic disorder, post traumatic stress disorder
(PTSD), and borderline personality disorder. The good news about mental illness is that
recovery is possible.
Mental illnesses can affect persons of any age, race, religion, or income. Mental illnesses are
not the result of personal weakness, lack of character, or poor upbringing. Mental illnesses
are treatable. Most people diagnosed with a serious mental illness can experience relief from
their symptoms by actively participating in an individual treatment plan.
In addition to medication treatment, psychosocial treatment such as cognitive behavioral
therapy, interpersonal therapy, peer support groups, and other community services can also
be components of a treatment plan and that assist with recovery. The availability of
transportation, diet, exercise, sleep, friends, and meaningful paid or volunteer activities
contribute to overall health and wellness, including mental illness recovery.

Here are some important facts about mental illness and recovery:

• Mental illnesses are biologically based brain disorders. They cannot be overcome
through "will power" and are not related to a person's "character" or intelligence.
• Mental disorders fall along a continuum of severity. Even though mental disorders are
widespread in the population, the main burden of illness is concentrated in a much

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 smaller proportion — about 6 percent, or 1 in 17 Americans — who suffer from a serious
mental illness. It is estimated that mental illness affects 1 in 5 families in America.
• The World Health Organization has reported that four of the 10 leading causes of
disability in the US and other developed countries are mental disorders. By 2020, Major
Depressive illness will be the leading cause of disability in the world for women and
children.
• Mental illnesses usually strike individuals in the prime of their lives, often during
adolescence and young adulthood. All ages are susceptible, but the young and the old
are especially vulnerable.
• Without treatment the consequences of mental illness for the individual and society are
staggering: unnecessary disability, unemployment, substance abuse, homelessness,
inappropriate incarceration, suicide and wasted lives; The economic cost of untreated
mental illness is more than 100 billion dollars each year in the United States.
• The best treatments for serious mental illnesses today are highly effective; between 70
and 90 percent of individuals have significant reduction of symptoms and improved
quality of life with a combination of pharmacological and psychosocial treatments and
supports.
• With appropriate effective medication and a wide range of services tailored to their
needs, most people who live with serious mental illnesses can significantly reduce the
impact of their illness and find a satisfying measure of achievement and independence. A
key concept is to develop expertise in developing strategies to manage the illness
process.
• Early identification and treatment is of vital importance; By ensuring access to the
treatment and recovery supports that are proven effective, recovery is accelerated and
the further harm related to the course of illness is minimized.
• Stigma erodes confidence that mental disorders are real, treatable health conditions. We
have allowed stigma and a now unwarranted sense of hopelessness to erect attitudinal,
structural and financial barriers to effective treatment and recovery. It is time to take
these barriers down.

Physical Disease
A disease is an abnormal condition of an organism that impairs bodily functions. In human
beings, "disease" is often used more broadly to refer to any condition that causes discomfort,
dysfunction, distress, social problems, and/or death to the person afflicted, or similar
problems for those in contact with the person. In this broader sense, it sometimes includes
injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors,

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and atypical variations of structure and function, while in other contexts and for other
purposes these may be considered distinguishable categories.
While many diseases are biological processes with observable alterations of organ function
or structure, others primarily involve alterations of behavior.
Classifying a condition as a disease is a social act of valuation, and may change the social
status of the person with the condition (the patient). Some conditions (known as culture-
bound syndromes) are only recognized as diseases within a particular culture. Sometimes
the categorizaton of a condition as a disease is controversial within the culture.
Inherited Disease

Disease resulting from the effect of having

defective genes. These diseases are inherited
because genetic material is accurately copied
before being passed onto the offspring from a
parent. However, they can also arise as a
result of a sudden change in the DNA known
as a mutation. Common examples of inherited
diseases in humans are cystic fibrosis, sickle-
cell anaemia, polydactyly, and Huntingdon's
disease. Downs syndrome is an example of a
disease arising from mutation, but which is not
inherited.
Cystic fibrosis, sickle-cell anaemia, polydactyly, and Huntingdon's disease are all each the
result of a single defective gene. Down's syndrome, however, is usually the result of having
an extra chromosome containing thousands of genes. In polydactyly (extra fingers) and
Huntingdon's disease (physical and mental degeneration) the diseases show dominance –
this means that inheriting a single defective gene will result in the disease. Cystic fibrosis
(viscous secretions, especially in the lungs) is recessive, which means that two defective
genes have to be inherited for the disease to occur.
In sickle-cell anaemia people who inherit a single defective gene are normal most of the
time, but can show anaemia from time to time. However, if a person inherits two defective
genes, they show severe illness. This defective gene exhibits incomplete dominance. The
gene for sickle-cell anaemia is more common than would be expected considering the
anaemia it causes. It is more common than expected because inheritance of a single

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defective gene makes the person partly immune to malaria, so natural selection favours
these individuals where malaria is common.
Down Syndrome, chromosomal disorder occurring in about 1 out of every 800 births.
People with Down syndrome may have mild to severe learning disabilities and physical
symptoms that include a small skull, extra folds of skin under the eyes, a flattened nose
bridge, and a large, protruding tongue. Muscle tone throughout the body is usually low. The
condition was formerly known as “mongolism” because the features of people with Down
syndrome were thought to resemble those of Mongolian Asians. This term is now considered
offensive and inappropriate and is no longer used.
Down syndrome results when a person inherits all or part of an extra copy of chromosome
21. This can occur in a variety of ways, the causes of which are unknown. The most common
chromosomal abnormality that produces Down syndrome (accounting for about 95 percent of
all cases) is Trisomy 21, a defect in which an extra, third copy of chromosome 21 is present
in every cell in the body. The risk of Trisomy 21 is directly related to the age of the mother.
The number of Down syndrome births is relatively low for 18-year-old mothers—about 1 in
2100 births. In the later childbearing years the risk increases significantly—from 1 in 1000
births for 30-year-old women to 1 in 100 births for 40-year-old women.
There is no cure for Down syndrome. However, prenatal tests are available to identify
foetuses with the disorder. The American College of Obstetricians and Gynaecologists
recommends that the so-called triple-screen blood test be offered to all pregnant women.
This test measures the levels of three chemicals in the blood of the pregnant woman to
indicate the baby's risk of Down syndrome. If the risk is high, amniocentesis, a procedure for
removing a sample of the amniotic fluid surrounding the foetus, is administered to confirm
the findings from the blood tests. Foetal cells are present in their fluid and can be checked
for the presence of the chromosomal disorder.
People with Down syndrome are subject to a variety of medical conditions. Heart
abnormalities that may require surgery are present in about half of all Down syndrome
cases. Thyroid problems (underproduction or overproduction of thyroid hormones) affect 10
to 20 percent of people with Down syndrome, but these problems respond well to treatment.
The risk of acute leukaemia is somewhat increased, although treatment is successful in the
majority of cases.
Cystic Fibrosis, (disorder caused by a single recessive autosomal gene) in which the
exocrine glands secrete abnormally thick mucus, leading to obstruction of the pancreas and
chronic infections of the lungs, which generally cause death in childhood or early adulthood.
Some mildly affected patients may survive longer. No cure for the disease has yet been

110
found. Patients with pancreatic insufficiency can take pancreatic enzymes with meals. Those
with respiratory infections are treated with antibiotics, with aerosols that relieve constriction
of the airways, and by physical therapy to help them cough up the obstructing secretions.
Intestinal obstruction, which occurs primarily in infancy (meconium ileus), may require
surgery. Trials are currently under way to use the recombinant human enzyme DNAse to
liquify the thick mucus. The use of gene therapy to treat cystic fibrosis is also in the
experimental stage.
Cystic fibrosis is the most common inherited fatal disease of Caucasians, occurring about
once in every 2500 births. Its occurrence in African Americans is much lower—about one in
every 17,000 births. If both parents carry the gene responsible for the disease, they have a
one-in-four chance of having an affected child. In 1989, the gene responsible for cystic
fibrosis was identified on chromosome 7. Since that time more than 200 different mutations
in the cystic fibrosis gene have been described, and tests have been developed to detect the
most common alterations. These tests can identify unaffected carriers of the disorder.
Infectious disease
An infectious disease is a clinically evident disease resulting from the presence of
pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular
parasites, and aberrant proteins known as prions. These pathogens are able to cause
disease in animals and/or plants.
Infectious pathologies are usually qualified as contagious diseases (also called
communicable diseases) due to their potentiality of transmission from one person or species
to another. Transmission of an infectious disease may occur through one or more of diverse
pathways including physical contact with infected individuals. These infecting agents may
also be transmitted through liquids, food, body fluids, contaminated objects, airborne
inhalation, or through vector-borne spread. The term infectivity describes the ability of an
organism to enter, survive and multiply in the host, while the infectiousness of a disease
indicates the comparative ease with which the disease is transmitted to other hosts.[3] An
infection however, is not synonymous with an infectious disease, as an infection may not
cause important clinical symptoms or impair host function.
Chronic disease
Chronic disease simply means persistent or recurring disease, usually affecting a person for
three months or longer. A chronic disease is generally one that is hereditary or one that is
the result of factors such as poor diet and living conditions, using tobacco or other harmful
substances, or a sedentary lifestyle. Such a disease is not typically contracted from another
person by contagion, because most chronic illnesses are not caused by infection. The term

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chronic disease commonly applies to conditions that can be treated but not necessarily
cured.
There are different types of chronic disease from A to Z. From Alzheimer's, arthritis and
asthma to "zoonoses," chronic diseases are many and varied. Zoonoses are diseases that
are passed to humans by animals, such as avian flu. Endometriosis, chronic fatigue
syndrome, tetanus, different types of cancers, lyme disease, chronic ear infection and even
obesity are considered chronic diseases.
A chronic disease often requires extensive care by a healthcare provider with the
cooperation of the patient in learning and practicing methods of rehabilitation. While
healthcare providers offer different courses of treatment to lessen the effects of symptoms
caused by chronic disease, most chronic illnesses cannot be cured completely. Frequently
the result is a lifetime of discomfort, doctor's visits, medical tests, medications, therapies and
sometimes surgeries.
Deficiency disease
Deficiency Diseases, disorders caused by lack of specific essential substances such as
vitamins, minerals, or amino acids. More broadly, the term applies to conditions in which the
essential substances are present but not absorbed, or in which the organism fails to produce
a natural and essential substance (see Hormone). Such diseases as beriberi, scurvy,
pellagra, and rickets are caused by lack of particular vitamins, and recovery is dramatically
prompt when adequate quantities of the vitamins are supplied in the diet. Certain types of
anemia may be caused by a dietary lack of iron in usable form. At least ten amino acids, ten
minerals, and ten vitamins are indispensable nutritional elements in the human diet, and the
absence of any one causes a specific deficiency disease
Self inflicted diseases
Self inflicted diseases are causes partially or completely by the actions of the sufferer. A
clear example of this is alcoholism since the alcohol must be consciously imbibed. The
drunkenness liver cancer and other consequences of alcoholism can therefore be said to be
self inflicted.
Diabetes
Diabetes is a chronic disease that occurs when the pancreas does not produce enough
insulin, or when the body cannot effectively use the insulin it produces. Hyperglycaemia, or
raised blood sugar, is a common effect of uncontrolled diabetes and over time leads to
serious damage to many of the body's systems, especially the nerves and blood vessels.

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Diabetes causes about 5% of all deaths globally each year.
80% of people with diabetes live in low and middle income countries. Most people with
diabetes in low and middle income countries are middle-aged (45-64), not elderly (65+).
Diabetes deaths are likely to increase by more than 50% in the next 10 years without urgent
action.
Type 1 Diabetes is autoimmune disease that affects 0.3% on average. It is result of
destruction of beta cells due to aggressive nature of cells present in the body. Researchers
believe that some of the Etiology and Risk factors which may trigger type 1 diabetes may
be genetic, poor diet (malnutrition) and environment (virus affecting pancreas). Secondly, in
most of the cases diabetes occurs because there is abnormal secretion of some hormones
in blood which act as antagonists to insulin. Example- Adrenocortical hormone, Adrenaline
hormone and Thyroid hormone.
Type 2 Diabetes is also called non insulin-dependent diabetes mellitus (NIDDM) or adult-
onset diabetes. It occurs when the body produces enough insulin but cannot utilize it
effectively. This type of diabetes usually develops in middle age. A general observation says
that about 90-95 % of people with suffering with diabetes are type 2; about 80 percent are
overweight. It is more common among people who are older; obese; have a family history of
diabetes; have had gestational diabetes. There are number of risk factors found to be
responsible for type 2 diabetes, the more the Etiology and Risk factors carried by an
individual the higher the risk for developing the diabetes.
Causes of Diabetes
Diabetes mellitus occurs when the pancreas doesn't make enough or any of the hormone
insulin, or when the insulin produced doesn't work effectively. In diabetes, this causes the
level of glucose in the blood to be too high.
In Type 1 diabetes the cells in the pancreas that make insulin are destroyed, causing a
severe lack of insulin. This is thought to be the result of the body attacking and destroying its
own cells in the pancreas - known as an autoimmune reaction.
It's not clear why this happens, but a number of explanations and possible triggers of this
reaction have been proposed. These include:
infection with a specific virus or bacteria;
exposure to food-borne chemical toxins; and

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exposure as a very young infant to cow's milk, where an as yet unidentified component of
this triggers the autoimmune reaction in the body.
However, these are only hypotheses and are by no means proven causes.
Type 2 diabetes is believed to develop when:
the receptors on cells in the body that normally respond to the action of insulin fail to be
stimulated by it - this is known as insulin resistance. In response to this more insulin may be
produced, and this over-production exhausts the insulin-manufacturing cells in the pancreas;
there is simply insufficient insulin available; and
the insulin that is available may be abnormal and therefore doesn't work properly.
The following risk factors increase the chances of someone developing Type 2 diabetes:
Increasing age;
obesity; and
Physical inactivity.
Rarer causes of diabetes include:
Certain medicines;
pregnancy (gestational diabetes); and
any illness or disease that damages the pancreas and affects its ability to produce insulin
e.g. pancreatitis.
What doesn't cause diabetes
It's important to also be aware of the different myths that over the years have arisen about
the causes of diabetes.
Eating sweets or the wrong kind of food does not cause diabetes. However, it may cause
obesity and this is associated with people developing Type 2 diabetes.
Stress does not cause diabetes, although it may be a trigger for the body turning on itself as
in the case of Type 1 diabetes. It does, however, make the symptoms worse for those who
already have diabetes.

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Cancer
The search for cause(s) of cancer has been going on for centuries. Early researchers said
that cancer was a natural result of aging. As cells degenerated, it was believed that some
simply became malignant. Others said cancer was hereditary, and investigations into
genetics began. Then some began to consider chemical links while still others questioned
whether viruses or bacteria were at fault. Finally, the "irritation" theory became popular, and
researchers began trying to identify irritants - such as tobacco and coal tar - that would
cause cancer in laboratory animals. Ultimately, though, cancer experts were forced to
confront the fact that although all these factors might be involved, none of them invariably
cause cancer. Not every animal or person exposed to an irritant or a particular chemical in
the laboratory developed cancer, nor did all elderly people or everyone with a family history
of cancer get it. As a result, scientists had to abandon the theory that cancer had a single
cause However, despite the fact that there is yet no absolute agreement among the cancer
research community in terms of what actually causes cancer, scientists are certain that
many factors can be linked to cancer. These factors, including many other possible causes
of cancer suggested by cancer researchers, are believed to be "cancer risk factors." These
risk factors include eating habits, lifestyle, living or working environments, genetics, and
many others. Following are some major cancer risk factors identified by researchers with the
support of scientific statistics:
Smoking
Cigarette smoking alone is directly related to at least one-third of all cancer deaths annually
in the United States. Cigarette smoking is the most significant cause of lung cancer and the
leading cause of lung cancer death in both men and women. Smoking is also responsible for
most cancers of the larynx, oral cavity, and esophagus. In addition, it is highly associated
with the development of, and deaths from bladder, kidney, pancreatic, and cervical cancers.
Tobacco smoke contains thousands of chemical agents, including 60 substances that are
known to cause cancer (carcinogens).
The health risks with cigarette smoking are not limited to smokers. Exposure to
environmental tobacco smoke significantly increases a nonsmoker's risk of developing lung
cancer. Environmental tobacco smoke is the smoke that nonsmokers are exposed to when
they share air space with someone who is smoking.
Diet
The life style factor that has received the most attention in recent years is diet. Evidence
suggests that about one-third of the cancer deaths each year that occur in the United States
are related to dietary factors. These include types of food, preparation methods, portion size,

115
variety, and overall caloric balance. A high-fat diet has been associated with an increased
risk for cancer of the prostate, endometrium, and colon and rectum. It is believed that a high-
fat diet is a cancer promoter, with numerous theories to explain the effects of excess fat. For
instance, excess fat seems to be involved in the production of free radicals, which play a role
in many types of cancer. A high-fat diet also increases the flow of bile acids into the intestine,
which can promote colon cancer.
Study results suggest that certain food additives, as well as preparation methods, can either
cause or promote cancer. Even some so-called natural methods of preserving foods are not
considered safe. For example, pickled, cured, and smoked products appear to promote
stomach cancer, possibly due to nitrites used in curing as well as to other compounds
produced during smoking and pickling. The decrease in gastric cancer incidence is largely
due to modern refrigeration and a reduction in pickled, cured, and smoked food products.
Genetics
By definition, cancer is really a disease of genes. Genes are very small molecules in our
cells, which determine almost everything in our body. Genes that control the genetics and
heredity of each cell are strung like beads on a necklace along the cell's DNA in the cell
nucleus. In a benign or malignant tumor, several of the genes regulating these processes are
abnormal (mutated). Abnormal genes may be inherited or damaged by carcinogens, viruses,
errors in cell division, and as yet unknown factors. A number of the most common cancers,
including breast, colon, ovarian, and uterine cancer, recur generation after generation in
some families. In addition, certain genetic factors may predispose those affected to specific
cancers. A few rare cancers, such as the eye cancer, retinoblastoma, and a type of colon
cancer, have been linked to specific genes that can be tracked within a family.
Although it is helpful to know the role that our genetic heritage may play as a possible cause
of cancer, scientists believe that environmental influences and our behaviors may outweigh
the risks inherent in our family tree.
Viruses
Viruses can help to cause some cancers. But this does not mean that these cancers can be
caught like an infection. What happens is that the virus can cause genetic changes in cells
that make them more likely to become cancerous.
These cancers and viruses are linked
• Cervical cancer and the genital wart virus, HPV
• Primary liver cancer and the Hepatitis B virus
• T cell leukaemia in adults and the Human T cell leukaemia virus

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There will be people with primary liver cancer and with T cell leukaemia who haven't had the
related virus. But infection may increase their risk of getting that particular cancer. With
cervical cancer, scientists now believe that everyone with an invasive cervical cancer will
have had an HPV infection beforehand.
Many people can be infected with a cancer-causing virus, and never get cancer. The virus
only causes cancer in certain situations. Many women get a high risk HPV infection, but
never develop cervical cancer. Another example is Epstein-Barr virus (EBV). These are
some facts about this common virus

• Most people are infected with EBV

• People who catch it late get glandular fever but this does not cause cancer
• In sub-Saharan Africa, EBV infection and repeated attacks of malaria together cause a
cancer called Burkitt's lymphoma that affects children
• In China, EBV infection (together with other unknown factors) causes naso-pharyngeal
cancer
• In AIDs patients and transplant patients EBV can cause lymphoma

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Cancer in the Caribbean

Age-standardized cancer incidence and mortality rates in the Caribbean and US, per
100,000
Colorec Lung
Breast Cervix Prostat Colorecta
tal Incide
Inciden Inciden e Lung l Stomach
Inciden nce/
Populat c ce Inciden Incidence/ Incidence Incidence/
ce/ Mortal
ion e/Morta /Mortal ce/ Mortality / Mortality
Mortalit ity
lity ity Mortali Male Mortality Male
y Femal
Female Female ty Male Male
Female e
US 134.4/2 48.9/4 173.8/3
8.9/2.8 46/17.4 77.8/76.3 62.1/24.8 12.3/6.3
SEER 6.4 0.9 0.3
Bahama 54.4/21. 16.7/6. 5.1/4. 65.3/35
14.7/8.9 21.2/19.7 15.2/8.6 16.5/12.4
s 5 2 8 .6
Barbad 62.5/25. 24.9/9. 18.5/11. 3.3/3. 99.7/55
15.3/14.4 24.1/14.9 21.5/17.1
os 4 4 1 0 .3
31.2/14. 20.2/8. 17.0/13. 16.3/1 28.2/26
Cuba 40.0/38.0 13.4/10.7 7.1/6.9
6 3 5 6.2 .4
Domini
can 36.1/11. 30.8/17 9.3/9. 85.3/42
12.3/6.8 18.6/18.5 11.6/6.5 13.4/10.4
Republi 5 .3 2 .2
c
87.3/48 0.5/0. 38.1/20
Haiti 4.4/2.0 7.5/4.8 11.0/10.1 11.3/7.3 28.8/25.1
.1 4 .0
Jamaic 43.5/18. 31.2/12 6.0/5. 42.4/22
12.0/7.3 24.1/22.1 14.3/8.6 26.2/20.0
a 3 .2 5 .4
Trinida
51.1/20. 27.1/10 4.6/4. 60.5/32
d and 16.0/9.7 14.3/13.2 14.8/8.5 11.3/8.7
6 .7 3 .3
Tobago

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General statistics and prevalence
At the end of 2007, an estimated 230,000 people were living with HIV and AIDS in the
Caribbean. Some 20,000 people were newly infected during 2007, and there were 14,000
deaths due to AIDS.
In two countries in this region - the Bahamas and Haiti - more than 2% of the adult
population is living with HIV. Higher prevalence rates are found only in sub-Saharan Africa,
making the Caribbean the second-most affected region in the world. Half of adults living with
the virus are women.
AIDS is now one of the leading causes of death in some of these countries, with Haiti being
the worst affected. An estimated 7,500 lives are lost each year to AIDS in Haiti, and
thousands of children have been orphaned by the epidemic.
Trends and transmission routes
Overall, the main route of HIV transmission in the Caribbean is heterosexual sex. Much of
this transmission is associated with commercial sex, but the virus is also spreading in the
general population, especially in Haiti. Sex between men is also a major factor in some
countries' epidemics. Cultural and behavioural patterns (such as early initiation of sexual
acts, and taboos related to sex and sexuality), gender inequalities, lack of confidentiality,
stigmatization and economic need are some of the factors influencing vulnerability to HIV
and AIDS in the Caribbean.
Haiti's HIV prevalence levels have been very high since the late 1980s. Although the rate
among pregnant women fell between 1996 and 2004, it has since remained stable. With very
low condom use among young people, and about 60% of the population under 24, much
scope exists for renewed growth in Haiti's mainly heterosexually-transmitted epidemic. On
the other side of Hispaniola Island, in the Dominican Republic, HIV prevalence declined
slightly between 2002 and 2007, possibly because of prevention efforts that encouraged
people to have fewer sexual partners and increase condom use.
Responding to the crisis
Since countries in the Caribbean face common problems, and resources are limited, the
need for a co-ordinated response to HIV and AIDS has long been recognised. The Pan
Caribbean Partnership Against HIV/AIDS (PANCAP) was established in 2001, with the aim
of preventing the spread of HIV and alleviating the suffering it causes across the Caribbean.
PANCAP has brought together governments, non-governmental organisations, private sector
groups, faith-based organisation and donor agencies to co-ordinate both prevention and
treatment efforts Some strong responses have been formed on a local level, too: most

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nations have developed National AIDS Commissions, strategic plans, legislation and HIV-
related programmes and services. 12 13
However, since most countries in the region are limited by poor public infrastructure and
fragile economies, acting out these responses has been difficult. Political leadership has also
been varied. Many Caribbean islands are heavily dependent on tourism, and in some areas
officials are reluctant to draw attention to the problem of AIDS for fear that this might
discourage visitors. 14 This is exactly what happened to Haiti in the early 1980s, when it was
established that a number of early cases of HIV in the United States had occurred among
Haitian immigrants. Since AIDS had only recently emerged, people were quick to associate
this new problem with Haiti:
HIV Prevention in the Caribbean
Numerous different approaches have been taken to preventing HIV in the Caribbean. Some
programmes have achieved significant success, but the barriers of poverty and insufficient
resources continue to limit HIV prevention throughout the region. 18
It is difficult to give an overall assessment of how successful HIV prevention has been in the
Caribbean, but the examples below give an indication of the achievements that have been
made in certain areas.
Voluntary counselling and testing
In general, experts recommend that testing for HIV should occur with the consent of
individuals involved, and should be complimented by counselling. Most countries in the
Caribbean have opened voluntary counselling and testing (VCT) centres, and international
agencies such as USAID and the Global Fund to Fight AIDS, Tuberculosis and Malaria have
provided grants to expand such services in a number of countries. 19 20
In the past, Cuba adopted the controversial approach of adopting mandatory testing among
certain groups, such as pregnant women, hospital patients and prison inmates. If found HIV
positive, individuals were taken to sanatoriums, where they were provided with care and
support while their sexual partners were traced. The rules have relaxed in recent years: it is
no longer compulsory for HIV positive people to stay at sanatoriums following an eight week
probationary period, and testing is now generally voluntary, with the exceptions of blood
donors and prisoners. 21
Although Cuba’s approach has been questionable in terms of human rights, it has certainly
worked – infection rates have remained exceptionally low. Additionally, reports suggest that
the sanatoriums are far from the restrictive institutions that people have sometimes portrayed

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them to be. Even now that it is not compulsory, many HIV positive people choose to remain
at the sanatoriums due to the quality of care and support that they receive. 22
Providing condoms and information
In Haiti, the Foundation for Reproductive Health and Family Education (FOSREF, a non-
profit organization established in 1989) has provided basic training on reproductive health,
including HIV and AIDS, to 500 teachers, 6,500 young workers, and 30,000 young
volunteers who disseminate information to their peers. As a result, a large number of people
are now using condoms, and there is evidence of sexual behaviour change and reductions in
HIV prevalence where the program has been carried out. In 2006, FOSREF was awarded a
United Nations Population Award for its work. 23
Haiti has seen a general decline in HIV prevalence since the mid-1990s, although this drop
has been more pronounced in urban areas than rural ones (some of which have seen little
change). HIV prevalence is still alarmingly high, though, and there are indications that
condom use is decreasing and that young Haitians are becoming sexually active at an earlier
age. It is therefore vital that prevention campaigns are sustained and strengthened. 24
On the other side of the Hispaniola Island, HIV prevalence has also receded in the
Dominican Republic. This decline is largely attributed to effective prevention campaigns,
which have encouraged people to use condoms and reduce their number of sexual partners.
25 In the capital city of Santo Domingo, sustained efforts to promote consistent condom use

and safer sexual behaviour among sex workers and their clients have been linked to
decreasing HIV prevalence among pregnant women. 26
Condom use is still stigmatised in many parts of the Caribbean. Many people are often too
embarrassed to buy condoms from shops, and even to use them with their partners:
Preventing mother-to-child-transmission
Most countries in the Caribbean have taken steps to prevent mother-to-child-transmission of
HIV. Cuba’s mother-to-child-transmission programme is one of the most effective in the
world; all pregnant women are tested for HIV, and those that test positive are provided with
antiretroviral drugs to reduce the risk of transmission. This scheme has helped to keep the
total number of HIV-positive babies below 100. In Barbados and the Bahamas, a
combination of increased voluntary counselling and testing services and improved access to
antiretroviral drugs has helped to significantly reduce the rate of mother-to-child-
transmission.

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Media campaigns
In 2005, television and radio broadcasters in the Caribbean united to form the Broadcast
Media Partnership on HIV/AIDS. This was followed by the announcement in August 2006
that a group of international donors - the Henry J. Kaiser Family Foundation, the Ford
Foundation and the Elton John AIDS Foundation – would provide US$1 million to initiate the
project. Participating broadcasters have promised that 12 minutes of airtime every day will be
dedicated HIV/AIDS related programming, and that this coverage will include news,
documentaries, dramas and other formats.
"This is the first time broadcasters have come together to combat a social problem. We have
a unique opportunity to leverage the communication power of our media platforms to raise
awareness, fight stigma and intolerance, and support people already living with [HIV].”
- Allyson Leacock, general manager of the Caribbean Broadcasting Corporation (CBC)
Some programmes have already been aired, and a website has been established. It is
expected that the partnership will become fully operational during 2007. In 2002, ministers
from several Caribbean countries convened in Havana, Cuba, to agree upon a commitment
to HIV/AIDS education:
"We, the Ministers of Education of the Caribbean… recognize that education is integral to the
fight against AIDS, and that the disease will not be overcome without the full involvement of
the education sector."
- Havana Commitment of Caribbean Ministers of Education, November 2002 - 33
But while political commitment is seemingly in place, poverty and a lack of resources have
generally hindered progress. Many children have no access to school education, particularly
in rural areas, which are often acutely affected by HIV. 34 Cuba is the only Caribbean country
that has made sex education mandatory at all levels of teaching, from preschool to
university. 35

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AIDS treatment in the Caribbean
Estimated number of Number of people
ARV Coverage,
Country people in need of receiving ARVs,
December 2006
ARVs, 2006 December 2006
Cuba 1,500 3,000 >95%
Suriname 740 700 93%
Barbados 710 600 87%
Guyana 2,500 2,000 72%
Jamaica 4,500 2,500 56%
Trinidad and
5,700 3,000 45%
Tobago
Haiti 22,000 9,000 39%

Provision of antiretrovirals
Countries in this region are making efforts to slow the epidemic and to limit its impact, most
obviously through their efforts to provide antiretroviral drugs. In 2002, the Pan Caribbean
Partnership against HIV/AIDS signed an agreement with six pharmaceutical companies to
provide access to cheaper antiretroviral drugs. Progress since then has been uneven, partly
due to wide differences in drug prices.
Access to antiretroviral therapy is provided to all those in need in Cuba, and Barbados is
close to this goal. However in Trinidad and Tobago, only 58% of those in need of treatment
for AIDS were receiving it at the end of 2007, and rates in the four other large countries were
even lower.
AVERT.org features further discussion of treatment and other issues connected with HIV &
AIDS in the Caribbean, and information about universal access to AIDS treatment.

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Estimated HIV/AIDS prevalence and deaths due to AIDS, end 2007

Living with HIV/AIDS

Deaths due to
Country Adult (15-49) AIDS during 2007
All people
rate %
Bahamas 6,200 3.0 <200
Barbados 2,200 1.2 <100
Cuba 6,200 0.1 <100
Dominican Republic 62,000 1.1 3,900
Haiti 120,000 2.2 7,500
Jamaica 27,000 1.6 1,400
Trinidad and Tobago 14,000 1.5 <1,000
It should be noted that the above figures are estimates and are made with a large degree of
uncertainty. For example, the number of people living with HIV in Haiti is estimated as being
between 100,000 and 140,000, and the figure for Cuba lies in the range 3,600 to 12,000.
Economic Impact of AIDS
The magnitude of the pandemic in the poorest regions of the world has attracted the
attention of the international community because of its potential global effects in a scenario
of fragile stability worldwide.
In some of the countries hit hardest by HIV/AIDS, in southern Africa, life expectancy for
children born in 2000 was as much as 30 years less than it was before the disease became
a pandemic.
It is clear that this factor is going to be reflected in the macroeconomic indicators of those
countries. The World Bank estimates that with a prevalence (number of cases in relation to
total population) of HIV/AIDS at 20 percent in 1999, South Africa's gross domestic product
(GDP) will be 17 percent less in the year 2010 than it would have been without the presence
of the deadly virus.
But this grim situation is even worse if we take a look at the individual households affected
by the disease.
In Africa alone, more than 12 million children have lost their parents to the pandemic. For
millions more families, HIV/AIDS means a dramatic reduction of income because it generally
affects the economically active members of the household.

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In Latin America, though the disease has not reached the emergency levels seen on the
African continent, the number of new cases is growing rapidly, particularly in Central America
and the Caribbean.
A study conducted by the University of the West Indies predicts that by the year 2005 the
GDP of Jamaica will drop 6.4 percent and that of Trinidad and Tobago will fall 4.2 percent as
a consequence of HIV/AIDS. The economic result: a decline in savings and investment, with
rising unemployment in key sectors like agriculture and manufacturing.
But even before the impact of the pandemic is felt in national economic indicators, HIV/AIDS
represents a heavy burden for public finances, particularly for the health sector.
In some Caribbean countries, HIV/AIDS patients occupy as many as 25 percent of available
hospital beds.

In Brazil, with a population of 162 million, the government spent more than 300 million dollars
last year on HIV/AIDS drugs alone. Costa Rica designates seven million dollars annually for
the same purpose, though the incidence of the virus is relatively low in this country of 3.5
million.

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Human Immunodeficiency Viruses overview

There are two of them:

HIV-1 — the cause of AIDS in the Western Hemisphere and in Europe
HIV-2 — the major cause of AIDS in Africa and Southeast Asia.
They are retroviruses.
HIV can only enter cells that express the transmembrane protein CD4 found on helper T
cells and a second "coreceptor" on these cells:
Strains of HIV (designated "R5") bind the coreceptor CCR5. These are the strains that are
most infectious.
Strains of HIV (designated "X4") bind the coreceptor CXCR4.
Both strains usually coexist in an ongoing infection with X4 tending to dominate in the final
stages of AIDS.
The virion binds to both CD4 and either coreceptor with molecules on its surface called
glycoprotein 120 (gp120).
This binding triggers an allosteric change in a second molecule, called glycoprotein 41
(gp41), which penetrates the host plasma membrane allowing the virion to get inside.
When HIV infects a cell

• its molecules of reverse

transcriptase and integrase are
carried into the cell attached to the
viral RNA molecules.
• The reverse transcriptase
synthesizes DNA copies of the RNA.
• These enter the nucleus where the
integrase catalyzes their insertion
into the DNA of the host's
chromosomes.
• The HIV DNA is transcribed into
fresh RNA molecules which reenter
the cytosol where

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 o some are translated by host ribosomes.

The env gene is translated into molecules of the envelope protein (gp160).
Proteases of the host cell then cut gp160 into

▪ gp120 which sits on the surface of the virions (and is the target of most of the vaccines
currently being tested).
▪ gp41, a transmembrane protein associated with gp120.
▪ the gag and pol genes are translated into a single protein molecule which is cleaved by
the viral protease into
▪ 6 different capsid proteins
▪ the protease
▪ reverse transcriptase
▪ the integrase
o other RNA molecules become incorporated into fresh virus particles

Disease Transmission

HIV is present in body fluids

• especially blood and semen
• especially in the early and late phases of the disease

Breaks or abrasions in mucous membranes and skin allow the virus in.
In North America, transmission occurs primarily

• between men when one ejaculates into the rectum (or mouth — the adenoids and
tonsils are filled with dendritic cells) of the other
• among intravenous drug users who share needles
• in women who are the sexual partners of bisexual men or i.v. drug users
• in the newborn babies of these women
• in recipients of infected blood or blood products. This last category accounted for a
devastating epidemic among hemophiliacs in the 1980s who unknowingly used HIV-
contaminated preparations of factor VIII. In some areas, 90% or more of the
hemophiliacs developed AIDS.

That risk, and the risk from blood transfusions, is now virtually zero because

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o all donated blood is now tested to see if the donor has been infected with HIV (as well
as some other viruses);
o plasma-derived preparations of factors 8 and 9 are now treated with heat and/or
solvents to destroy any viruses that might be present;
o recombinant factor 8 and recombinant factor 9 made by genetic engineering are
now available.

Disease Progression
Infection by HIV produces three phases of disease:

• an early phase that

o lasts about 2 weeks
o is accompanied by fever, aches, and other flu-like symptoms
o is accompanied by high levels of virus in the blood.
• a middle phase with these features:
o lasts for months or even years
o produces few, if any, symptoms
o The patient's blood contains few viruses, but contains antibodies to the virus. These
antibodies are the basis of the most common test for HIV infection.
o Continuous infection, death, and replacement of CD4+ T cells. The T cells are probably
killed by the patient's CD8+ cytotoxic T cells (CTL). Some may die from apoptosis.
• It is the late phase that is called AIDS. It has these features:
o A rapid decline in the number of CD4+ T cells. When these drop below about 400 per µl
(normal is >1000), the patients immunity is sufficiently weakened that opportunistic
infections begin. These are infections caused by organisms that ordinarily do not cause
disease symptoms in immunocompetent people. They include:
▪ viruses, e.g., herpes simplex, herpes varicella-zoster, Epstein-Barr virus (EBV)
▪ bacteria, e.g., Mycobacterium tuberculosis
▪ fungi, e.g. Candida albicans (the cause of "thrush"), Pneumocystis jirovecii (causes
pneumonia)
▪ protozoans, e.g., Microsporidia

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o When the CD4+ count drops below 200 per µl, opportunistic infections become more
severe and cancer (e.g., lymphoma, Kaposi's sarcoma) may develop. These usually kill
the patient within a year or so.

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10. Immunology
Specific immune response
Specific immune response occurs when a particular antigen passes the body’s passive
defenses. It involves cells and proteins within the blood and lymph that attach, disarm,
destroy and remove foreign bodies. The specific system gives a highly effective, long
lasting immunity against anything the body recognise as foreign. It responds to specific
microorganisms and enhances the activity of the non-specific system.
The central feature of the specific immune system is the ability to distinguish between self
and non-self. Every cell has complex molecules (proteins and glycoproteins) on its surface
membrane which act as recognition devices and have specific shapes. These molecules are
called antigens or immunoglobins. The immune system is usually tolerant to the body’s
own antigens (self antigens) and does not attack against them. However, breakdown of the
recognition system can lead to autoimmune disease such as AIDS and rheumatoid arthritis,
which result in self-destruction of body parts.
When a foreign organism (bacteria, viruses or even another person’s cells) enters the body,
the foreign antigens on the invading cells activate an immune response. The foreign
antigens are called non-self antigens. The immune system produces antibodies and
specialised cells that attempt to destroy foreign cells and particles that have entered the
body. There are two types of responses: Humoral(antibody) response (involving B cells)
and cell mediated immunity (involving T cells).

Humoral (antibody-mediated) Response - B-cells

The humoral immune response is initiated by an activation phase. This is where
macrophages (white blood cells) engulf and digest microbes (including their antigens)
through a process of called phagocytosis. Some of the digested antigens are then displayed
on the surfaces of the macrophages (called epitopes). This display provides other cells of
the immune system with an opportunity to recognise the invader and become activated. This
is called antigen presentation.
• During antigen presentation the macrophage selects T-helper cells and B-cells that
have membrane receptors that are complementary in shape to the antigens
exposed. This is known as clonal selection.

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 • T-helper cells (Th cells – see cell mediated response) recognise and bind to the
displayed antigens. This then initiates the next phase of the humoral response (B
and T cells).
• In the next phase, called the effector phase, activated Th cells trigger specific B-
cells to proliferate and release antibodies. These antibodies bind to the invader and
fight infection.
The effector phase involves specific lymphocytes (white blood cells) that mature in the bone
marrow. These are called B lymphocytes (B-cells). B-cells can produce a specific
antibody in response to a particular antigen. An antibody is a type of globular protein that
reacts with a specific antigen.

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When a B cell meets an antigen it will divide through mitosis and after several generations
will differentiate into plasma cells. All plasma cells are formed from one type of B cell and
will secrete the same antibody. Plasma B-cells can synthesise and secrete up to 2000
antibody molecules per second! The antibodies produced circulate in the blood and lymph
or secrete antibodies onto the surfaces of mucous membranes, such as those found lining
the lungs.
Different antibodies work in different ways:
• agglutination makes pathogens clump together
• antitoxins neutralise the toxins produced by bacteria
• lysis digests the bacterial membrane, killing the bacterium
• opsonisation coats the pathogen in protein that identifies them as foreign cells.
When confronted with an antigen for the first time, B cells produce memory cells as well as
plasma cells; this is called the primary response. The primary response is usually slow,
taking days or even weeks to recruit enough plasma cells to bring an infection under control.
However, when a second invasion occurs, the response is quicker. Memory cells are
involved in the secondary response and stick to and destroy antigens
Cell Mediated Response - T Cells The cell-mediated response involves cells that are
specific to the antigens on the invading pathogens. The cells involved are lymphocytes,
called T cells, which mature in the thymus. In the thymus the T cells develop surface
receptors called T-cell receptors where they become ‘programmed’ for the antigen of their
specific enemy. Many different kinds of T cells are produced which recognise, attach and
destroy infected, mutant or ‘foreign’ cells. After encountering a specific foreign antigen, T
cells reproduce rapidly, however they do not produce antibodies like B cells.
Macrophages that have ingested foreign material carry some of the foreign antigen on their
surface. The macrophages then carry the foreign cells to the T helper (Th) and T killer (Tk)
cells in the lymph nodes, spleen and blood.

• The Helper T-cells, Th (as the name would suggest, help other cells of the immune
system) recognise the non-self antigen (from the foreign cells) that the macrophages
display on their outer surface. The Th recognise the antigens and stimulate B cells
to proliferate - B cells will not reproduce and form plasma cells with out assistance
from helper T cells.

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 • T helper cells also secrete proteins (interlukin and lymphokines) that stimulate other
B and T cells to divide, where some of the cells become effector cells and memory
T cells.
o Lymphokines stimulate macrophages to engulf invading cells.
o The interlukin can stimulate cytotoxic T cells (Tc)
• Cytotoxic (killer) T cells attacks body cells that have been infected by virus,
bacteria or fungus.
o A Tc cell identifies its antigen, where in this case a viral protein coat is left
outside the infected cell, and kills the infected cell before the virus has time to
replicate.
o Tc cells kill the infected cells by secreting proteins (perforin) that punch holes
in the membrane of the cell, and the contents ooze out.
o Tc cells cannot kill isolated virus particles, as they need the viral antigen
before they become activated.

• Natural killer (Nk) cells have the same response as Tc cells, however they may
attack tumor and other cancerous cells.
• Once the Th and Tc cells are activated, they divide many times, where some of the
cells become effector T cells, and others as memory cells, where they migrate to
the lymph nodes to be activated quickly upon a second invasion.
Another type of T-cells is the T-suppressor cells, Ts – These play an important role in
regulating that action of the lymphocytes, where they can help prevent the immune system
overreacting to a stimulus.
When the B and T cells develop in the bone marrow and thymus (respectively), they enter
the blood stream, then leave it, and move around the body in the lymphatic system.
The immune system contains a number of lymphoid tissues and organs, such as the spleen,
tonsils, and lymphnodes; these are connected to a network of vessels (similar to that of the
blood).
The lymphatic vessels contain lymph, which drains from nearby tissues. Memory B and T
cells circulate in the lymph, ready to react with their antigen. Antigens that enter the body
are carried by the macrophages to a lymphatic organ, where there is a high concentration of
white blood cells, such as Th and Tc cells.
If you have an infection, you may have noticed that your glands (lymph nodes) may be
swollen and sore, indicating that you have an infection of some kind Natural passive
immunity - Antibodies made in one individual are passed into another individual of the same

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species. This only affords temporary protection, for, as the antibodies do their job, or are
broken down by the body's natural processes, their number diminishes and protection is
slowly lost. For example, antibodies from a mother can cross the placenta and enter her
foetus. In this way they provide protection for the baby until its own immune system is fully
functional. Passive immunity may also be conferred by colostrum (the mother’s first milk),
from which antibodies are absorbed from the intestines of the baby.
Acquired passive immunity - Here, antibodies which have been made in one individual
are extracted and then injected into the blood of another individual which may, or may not,
be of the same species. For example, specific antibodies used for combating tetanus and
hepatitis B are cultured in horses and later injected into Man. They act to prevent tetanus
and hepatitis respectively. This type of immunity is again short-lived – a matter of weeks
only.

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 Flow chart of immune response involving B and T cells

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Types of immunity:
Natural active immunity - The
body manufactures its own
antibodies when exposed to an
infectious agent. Since memory
cells produced on exposure to the
first infection are able to stimulate
the production of massive
quantities of antibody, when
exposed to the same antigen
again. This type of immunity is
most effective and generally
persists for a long time - sometimes
even for life.

When a bacterial infection occurs and an antigen is presented for the first time, time is taken
for the B and T cells to proliferate. Once the B cells have differentiated into plasma cells,
specific antibodies can be secreted. This primary response lasts several days or weeks
and then the concentration of antibody decreases as the plasma cells stops secreting them.
Once the infection is eradicated, plasma cells die, but B memory cells are left in the body.
If another infection of the same pathogen occurs, then the same antigen is reintroduced.
There is a more rapid response, called the secondary response. This is much faster
because there are many more memory B-cells that can produce many plasma cells and the
appropriate antibody. These destroy the pathogen before it has the chance to cause any
symptoms to occur.
Memory cells are the basis for immunological memory – they last for many years, often a
lifetime. It is possible for suffer repeated infections from a single pathogen because
pathogens occur in different form, each having minor changes in the shape of the antigen,
due to a possible mutation, and therefore requiring a primary response.
Acquired active immunity - This is achieved by injecting small amounts of antigen - the
vaccine - into the body of an individual. The whole process is called vaccination or
immunisation. The small dose of antigen is usually safe because the pathogen is either
killed or attenuated (= crippled). This ensures that the individual does not contract the

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disease itself, but is stimulated to manufacture antibodies against the antigen. Often a
second, booster, injection is given and this stimulates a much quicker production of antibody
which is long lasting and which protects the individual from the disease for a considerable
time. Several types of vaccine are currently in use.
Monoclonal Antibodies
Monoclonal antibodies (mAb or moAb) are antibodies that are identical because they were
produced by one type of immune cell and are all clones of a single parent cell. Given
(almost) any substance, it is possible to create monoclonal antibodies that specifically bind to
that substance; they can then serve to detect or purify that substance. This has become an
important tool in biochemistry, molecular biology and medicine.

The production of monoclonal antibodies, using the hybridoma method

Monoclonal antibodies are obtained from clones of single B cells. Unfortunately, B cells will
not grow in culture and this problem has to be got round by fusing them with malignant B
myeloma cells i.e. cancerous B cells. Myeloma cells will continue to grow and divide
indefinitely, though they do not produce antibodies. The fused cells produced from myeloma
cells with B cells are known as hybridomas. The hybridoma cells will also continue to grow
and divide (given suitable and adequate nutrients) and they do secrete antibodies. The
antibodies that they secrete are the specific antibodies that were produced by the original
clone of B cells. The production of monoclonal antibodies involves the following stages:
• A mouse is injected with antigen for which the antibodies are required
• An immune response takes place and the mouse plasma cells start to make the antibody
• Plasma cells are extracted from the mouse
• The plasma cells are fused with B cell myeloma cells
• The resulting hybridoma cells are separated individually and allowed to grow, divide and
produce antibodies
• Some antibodies are removed and tested with the relevant antigen, to make sure they are
the correct monclonals
• Those hybridoma cells which are producing the required antibodies are cultured in a large
fermenter
• The monoclonal antibodies are harvested and purified

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The use of monoclonal antibodies in the diagnosis and treatment of disease and
pregnancy testing

Diagnosis – because the monoclonal antibodies produced from a clone of B cells are all
identical, they can be used to identify macromolecules with a very high degree of specificity.
For example, they are now routinely used for the following:
• Blood typing before transfusions
• Tissue typing before transplants
• Identification of pathogens – using monoclonals, it is now possible to distinguish between
different strains of certain pathogens, which would, otherwise, be every difficult
• Identification and location of tumours
• Detection of HIV
• Distinguishing between different types of leukaemia Treatment – principally, there are
two ways in which monoclonal antibodies are used in the treatment of disease:
• Production of passive vaccines – monoclonal antibodies can be injected directly into the
blood to attack a particular pathogen
• ‘Magic bullets’ – monoclonal antibodies can be produced which will combine specifically
with cancer cells. It is now possible to bond cancer drugs to such antibodies. In this way,
the drugs can be delivered directly to the tumour, thereby reducing the risk of damaging
healthy cells.

Pregnancy testing – soon after becoming pregnant, women produce a hormone, called
human chorionic gonadotrophin (HGC). This hormone is produced by the placenta, so can
only be present during pregnancy. Monoclonal antibodies are now used to detect the
presence of this hormone in the urine – such a pregnancy test can be done very quickly and
easily. This type of pregnancy testing kits work as follows:
• The kit consists of a ‘sampler’, which is a type of dipstick with an absorbent pad
• On the surface of the pad are monoclonal antibodies, specific to HGC and to which
coloured latex particles are attached – when the pad is moistened, the molecules of the
antibody begin to move
• The sampler is dipped into urine – if HGC is present, it will bind to the monoclonal
antibodies and will be drawn up the pad
• Further up the pad is an area at which there is a line of immobilised HCG antibodies
• Any HCG molecules drawn up the pad will bind with these antibodies and the latex
particles will create a coloured line. This is a positive result.
• Further along the pad is a second line of immobilised antibodies, to which will bind any
HCG antibodies without HCG. A coloured line in this second area (but no coloured line in

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 the first area) will confirm that the HCG antibodies have moved up the pad, but that the
result is negative.

Rituximab belongs to a group of cancer drugs known as monoclonal antibodies. It is used to

treat several types of non-Hodgkin lymphoma. Rituximab locks onto a protein called CD20
which is found on the surface of one of the main types of normal white blood cells (B-cell
lymphocytes). It is also present on the surface of most of the abnormal B-cell lymphocytes
which occur in most types of non-Hodgkin lymphoma. Rituximab attacks both abnormal
(malignant) and normal B-cell lymphocytes. However, the body quickly replaces any normal
white blood cells which are damaged, so the risk of side effects from this is very small.

Practice questions

Quesdtion 1

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2. Antigens are typically present on
a. viruses. b. bacteria. c. fungi. d. tumor cells. e. all of these

3. Compared to adaptive immunity, innate immunity has a(n) ____ response time, is
triggered by ____, and has ____ memory.
a. slow; pathogens; long-term b. immediate; tissue damage; no
c. slow; tissue damage; long-term d. slow; pathogens; no
e. immediate; pathogens; long term

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4. The first response in active immunity is
a. the production of white blood cells. b. the production of complement.
c. the production of interferon. d. inflammation. e. wound healing.

5. Memory cell production is associated with

a. the body's first line of defense. b. the body's second line of defense.
c. the body's third line of defense. d. complement production.
e. acute inflammation.

6. White blood cells seen engulfing large numbers of bacterial cells are most likely
a. neutrophils. b. macrophages. c. mast cells. d. eosinophils.
e. lymphocytes.

7. Antibodies are
a. proteins. b. steroids. c. polysaccharides. d. lipoproteins. e. any of these

7. The antigen binds to the ____ of an antibody.

a. constant region b. neutral region c. variable region d. active site
e. charged region

8. The cell-mediated response

a. involves helper T cells.
b. involves the action of antibodies to destroy invaders.
c. acts only on extracellular pathogens.
d. results in the production of clones of B cells. e. all of these

9. Passive immunity can be obtained by

a. having the disease. b. receiving a vaccination against the disease.
c. receiving antibodies by some means.
d. being exposed to a pathogen. e. all of these

10. The immune system's attack on the body's own cells

a. is an autoimmune response. b. results in anaphylactic shock.
c. is a type of acquired immune deficiency syndrome.
d. is due to the inactivation of helper T cells.
e. is due to an error in the production of MHC markers.

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11. Social and Preventative Medicine

Body mass index, or BMI, is a new term to most people. However, it is the measurement of
choice for many physicians and researchers studying obesity. BMI uses a mathematical
formula that takes into account both a person's height and weight. BMI equals a person's
weight in kilograms divided by height in meters squared. (BMI=kg/m2).

Risk of Associated Disease According to BMI and Waist Size

Waist less than or equal to 40 in. (men) or Over 40 in. (men) or 35 in.
BMI
35 in. (women) (women)
18.5 or Underweight -- N/A
less
18.5 - Normal -- N/A
24.9
25.0 - Overweight Increased High
29.9
30.0 - Obese High Very High
34.9
35.0 - Obese Very High Very High
39.9
40 or Extremely Extremely High Extremely High
greater Obese

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Balanced diet

Generally, a balanced diet is said to include:

1. Sufficient calories to maintain a

person's metabolic and activity needs,
but not so excessive as to result in fat
storage greater than roughly 30% of
body mass (see Body fat percentage);
2. Sufficient quantities of fat, including
monounsaturated fat, polyunsaturated
fat and saturated fat, with a balance of
omega-6 and long-chain omega-3
lipids;
3. Maintenance of a good ratio between
carbohydrates and lipids : four grams
of the first for one gram of the second.
4. Avoidance of saturated fat (although
the "evidence" for this claim is forever
in debate after the testimony of results
provided by the Framingham Heart
Study of 1948-1998)
5. Avoidance of trans fat.
6. Sufficient essential amino acids ("complete protein") to provide cellular replenishment
and transport proteins;
7. Essential micronutrients such as vitamins and certain minerals.
8. Avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene)
substances;
9. Avoiding foods contaminated by human pathogens (e.g. e. coli, tapeworm eggs);
10. Avoiding chronic high doses of certain foods that are benign or beneficial in small or
occasional doses, such as
o foods or substances with directly toxic properties at high chronic doses (e.g.
ethyl alcohol);
o foods that may interfere at high doses with other body processes (e.g. refined
table salt);
o foods that may burden or exhaust normal functions (e.g. refined
carbohydrates without adequate dietary fibre).

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 GUIDELINES TO A
UNDERLYING PRINCIPLE
HEALTHY DIET
Our diets contain more than enough fat to supply
- reduce total fat
the essential fatty acids/uses e.g. fuel for muscle
consumption
respiration once glucose and stores of glycogen
- shift the balance in fat
are used up. Excess fat is stored as fat reserves.
consumption from saturated
Fat A high intake of saturated fatty acids is associated
to unsaturated fatty acids
with high levels of blood cholesterol and increases
- monounsaturated fats are
the risk of atheroscelosis.
better than saturated or
Plant fats - usually unsaturated
polyunsaturated fats
Animal fats usually saturated
Modern diets tend to supply more than enough
salt - e.g. salt in prepared foods and other
- reduce salt intake packaged foods. NaC1 is important in maintaining
(more salt may be tendency of blood to take up water. Na+ & C1-
Salt necessary e.g. if doing have major roles in nerve impulse transmission.
strenuous exercise in hot Excess dietary salt can cause fluid retention
climate) (oedema) & may contribute to high blood pressure
(hypertension). Salt loss from excessive sweating
& inadequate intake can cause heat exhaustion
Allows bacteria to grow on teeth, producing acids
which dissolve the outer surface (enamel) causing
tooth decay. Glucose can be obtained by breaking
Sugar
- reduce sugar intake down carbohydrates. Glucose (the respiratory
-
substrate) is stored as glycogen in the liver.
Surplus glucose is converted to fat for long term
storage.

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 SOLUBLE FIBRE - binds CHOLESTEROL into a
complex that cannot be absorbed from the
intestine so it is passed out in stools. Important in
small intestine - slows digestion and absorption;
products are released over a longer time
(important to diabetics). INSOLUBLE FIBRE -
Fibre
- eat a high fibre diet important in colon. Absorbs water and swells;
-
stretches walls of intestine and stimulates
peristalsis. Speeds up passage of food through
colon and so reduces the time for possible
carcinogens to be in contact with intestinal wall.
Reduces the risk of constipation, piles and colon
cancer.
Atherosclerosis is a disease affecting arterial blood vessels. It is a chronic inflammatory
response in the walls of arteries, in large part due to the deposition of lipoproteins (plasma
proteins that carry cholesterol and triglycerides). It is commonly referred to as a "hardening"
or "furring" of the arteries. It is caused by the formation of multiple plaques within the
arteries.
Coronary heart disease (CHD), also called coronary artery disease (CAD), ischaemic heart
disease, atherosclerotic heart disease, is the end result of the accumulation of atheromatous
plaques within the walls of the arteries that supply the myocardium (the muscle of the heart)
with oxygen and nutrients. While the symptoms and signs of coronary heart disease are
noted in the advanced state of disease, most individuals with coronary heart disease show
no evidence of disease for decades as the disease progresses before the first onset of
symptoms, often a "sudden" heart attack, finally arise. After decades of progression, some of
these atheromatous plaques may rupture and (along with the activation of the blood clotting
system) start limiting blood flow to the heart muscle. The disease is the most common cause
of sudden death
Hypertension, commonly referred to as "high blood pressure" or HTN, is a medical
condition in which the blood pressure is chronically elevated. While it is formally called
arterial hypertension, the word "hypertension" without a qualifier usually refers to arterial
hypertension. Hypertension can be classified as either essential (primary) or secondary.
Essential hypertension indicates that no specific medical cause can be found to explain a
patient's condition. Secondary hypertension indicates that the high blood pressure is a result
of (i.e. secondary to) another condition, such as kidney disease or certain tumors (especially
of the adrenal gland). Persistent hypertension is one of the risk factors for strokes, heart

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attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure.
Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At
severely high pressures, mean arterial pressures 50% or more above average, a person can
expect to live no more than a few years unless appropriately treated.[2]
Hypertension is considered to be present when a person's systolic blood pressure is
consistently 140 mmHg or greater, and/or their diastolic blood pressure is consistently
90 mmHg or greater.
Stroke (or cerebrovascular accident (CVA)) is the clinical designation for a rapidly
developing loss of brain function due to an interruption in the blood supply to all or part of the
brain. This phenomenon can be caused by thrombosis, embolism, or hemorrhage (=
haemorrhage).[1] In medicine the process of being struck down by a stroke, fit or feint is
sometimes called an ictus, from the Latin icere (“to strike”), especially prior to the definitive
diagnosis being made.
Stroke is a medical emergency and can cause permanent neurological damage or even
death if not promptly diagnosed and treated. It is the third leading cause of death and the
leading cause of adult disability in the United States and industrialized European nations. It is
predicted that stroke will soon become the leading cause of death worldwide.[2]
The symptoms of stroke can be quite heterogeneous, and patients with the same cause of
stroke can have widely differing handicaps. Conversely, patients with the same clinical
handicap can in fact have different underlying causes.
The cause of stroke is an interruption in the blood supply, with a resulting depletion of
oxygen and glucose in the affected area. This immediately reduces or abolishes neuronal
function, and also initiates an ischemic cascade which causes neurons to die or be seriously
damaged, further impairing brain function.
Risk factors for stroke include advanced age, hypertension (high blood pressure), previous
stroke or TIA (transient ischaemic attack), diabetes mellitus, high cholesterol, cigarette
smoking, atrial fibrillation, migraine[3] with aura, and thrombophilia. In clinical practice, blood
pressure is the most important modifiable risk factor of stroke; however many other risk
factors, such as cigarette smoking cessation and treatment of atrial fibrillation with
anticoagulant drugs, are important.

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Benefits of Exercise

The effects of exercise on the incidence of certain diseases

Heart disease

• Regular exercise increases heart efficiency, and makes heart contraction more efficient
(i.e. more powerful).
• It increases blood HDL (high density lipoprotein) levels. HDLs carry cholesterol away
from the tissues back to the liver, where they are secreted into bile. So HDLs are
beneficial and reduce the risk of heart disease. LDLs carry most of the cholesterol in
the blood. They deliver cholesterol to the cells. LDLs increase the incidence of
atheroma. The ratio of plasma LDL cholesterol: plasma HDL cholesterol is important:
the lower the ratio, the lower the risk of atheroma.
• Artery wall elasticity is maintained improved/improved by regular exercise.
• Resting heart rate is lowered; this decreases the ‘loading’ (strain) on the heart.
• Resting blood pressure is lowered, meaning that less effort is needed for the heart to
pump.
• Exercise may lead to weight loss, which would decrease the loading on the heart.

Circulatory problems e.g. atheroma

• Exercise reduces stress.

• Regular exercise reduces the amount of adrenaline release (adrenaline promotes the
breakdown of glycogen for respiration).
• Exercise increases the metabolism of fats.
• Exercise increases HDL and lowers LDL.
• The points above contribute to reducing the chance of atheroma being deposited on
the inner lining of the arteries.

General benefits
1. Exercise improves your mood.
Need to blow off some steam after a stressful day? A workout at the gym or a brisk 30-
minute walk can help you calm down.

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Exercise stimulates various brain chemicals, which may leave you feeling happier and more
relaxed than you were before you worked out. You'll also look better and feel better when
you exercise regularly, which can boost your confidence and improve your self-esteem.
Exercise even reduces feelings of depression and anxiety.
2. Exercise combats chronic diseases.
Worried about heart disease? Hoping to prevent osteoporosis? Regular exercise might be
the ticket.
Regular exercise can help you prevent — or manage — high blood pressure. Your
cholesterol will benefit, too. Regular exercise boosts high-density lipoprotein (HDL), or
"good," cholesterol while decreasing low-density lipoprotein (LDL), or "bad," cholesterol. This
one-two punch keeps your blood flowing smoothly by lowering the buildup of plaques in your
arteries.
And there's more. Regular exercise can help you prevent type 2 diabetes, osteoporosis and
certain types of cancer.
3. Exercise helps you manage your weight.
Want to drop those excess pounds? Trade some couch time for walking or other physical
activities.
This one's a no-brainer. When you exercise, you burn calories. The more intensely you
exercise, the more calories you burn — and the easier it is to keep your weight under control.
You don't even need to set aside major chunks of time for working out. Take the stairs
instead of the elevator. Walk during your lunch break. Do jumping jacks during commercials.
Better yet, turn off the TV and take a brisk walk. Dedicated workouts are great, but activity
you accumulate throughout the day helps you burn calories, too.
4. Exercise strengthens your heart and lungs.
Winded by grocery shopping or household chores? Don't throw in the towel. Regular
exercise can leave you breathing easier.
Exercise delivers oxygen and nutrients to your tissues. In fact, regular exercise helps your
entire cardiovascular system — the circulation of blood through your heart and blood vessels
— work more efficiently. Big deal? You bet! When your heart and lungs work more efficiently,
you'll have more energy to do the things you enjoy.

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5. Exercise promotes better sleep.
Struggling to fall asleep? Or stay asleep? It might help to boost your physical activity during
the day.
A good night's sleep can improve your concentration, productivity and mood. And, you
guessed it, exercise is sometimes the key to better sleep. Regular exercise can help you fall
asleep faster and deepen your sleep. The timing is up to you — but if you're having trouble
sleeping, you might want to try late afternoon workouts. The natural dip in body temperature
five to six hours after you exercise might help you fall asleep.
Malnutrition
Marasmus is a form of severe protein-energy malnutrition characterized by energy
deficiency. Other PEMs include kwashiorkor and cachexia. Marasmus is caused by a severe
deficiency of nearly all nutrients, especially protein and calories.
A child with marasmus looks emaciated and body weight may be reduced to less than 80%
of the normal weight for that height. Marasmus occurrence increases prior to age 1 whereas
kwashiorkor occurrence increases after 18 months.
Symptoms
The malnutrition associated with marasmus leads to extensive tissue and muscle wasting, as
well as variable edema. Other common characteristics include dry skin, loose skin folds
hanging over the glutei, axillae, etc. There is also drastic loss of adipose tissue from normal
areas of fat deposits like buttocks and thighs. The afflicted are often fretful, irritable, and
voraciously hungry.
It is essential to treat not only the symptoms but also the complications of the disorder,
including infections, dehydration and circulation disorders, which are frequently lethal and
lead to high mortality if ignored.
Ultimately, marasmus progresses to the point of no return when the body's machinery for
protein synthesis, itself made of protein, has been degraded. At this point, attempts to correct
the disorder by giving food or protein will fail to prevent death.
Kwashiorkor is a type of malnutrition with controversial causes, but it is commonly believed
to be caused by insufficient protein intake. It usually affects children aged 1–4 years,
although it also occurs in older children and adults. Jamaican paediatrician Cicely D.
Williams introduced the name into international scientific circles in her 1935 Lancet article.
When a child is nursing, it receives certain amino acids vital to growth from its mother's milk.
When the child is weaned, if the diet that replaces the milk is high in starches and

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carbohydrates, and deficient in protein (as is common in parts of the world where the bulk of
the diet consists of starchy vegetables, or where famine has struck), the child may develop
kwashiorkor.
Symptoms
Symptoms of kwashiorkor include a swollen abdomen known as a pot belly, as well as
alternating bands of pale and dark hair (flag sign) and weight loss. Common skin symptoms
include dermatitis and depigmented skin.
Victims of kwashiorkor fail to produce antibodies following vaccination against diseases,
including diphtheria and typhoid. Generally, the disease can be treated by adding food
energy and protein to the diet; however, it can have a long-term impact on a child's physical
and mental development, and in severe cases may lead to death.
Dengue Fever
Dengue Fever and dengue haemorrhagic fever (a more severe form) are the most common
mosquito-borne viral diseases in the world. It is caused by members of the flavivirus family.
Dengue fever is an illness caused by infection with a virus transmitted by the Aedes
mosquito. There are four types of this virus (serotypes 1 to 4) which can infect you. If you get
a second dengue infection (from another mosquito bite), particularly with serotype 2, you can
get an even worse infection such as Dengue Haemorrhagic Fever and Dengue Shock
Syndrome which can be fatal. Dengue fever usually starts suddenly with a high fever, rash,
severe headache, pain behind the eyes, and muscle and joint pain. The severity of the joint
pain has given dengue the name "breakbone fever." Nausea, vomiting, and loss of appetite
are common. A rash usually appears 3 to 4 days after the start of the fever. The illness can
last up to 10 days, but complete recovery can take as long as a month. Older children and
adults are usually sicker than young children.
Most dengue infections result in relatively mild illness, but some can progress to dengue
hemorrhagic fever. With dengue hemorrhagic fever, the blood vessels start to leak and
cause bleeding from the nose, mouth, and gums. Bruising can be a sign of bleeding inside
the body. Without prompt treatment, the blood vessels can collapse, causing shock (dengue
shock syndrome). Dengue hemorrhagic fever is fatal in about 5 percent of cases, mostly
among children and young adults.

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How is Dengue Fever spread?
Dengue fever is spread through the bite of the Aedes mosquitoes. It is not spread from one
person to another.
The transmission cycle for dengue starts when:
Infected Aedes mosquito bites a healthy person.
4-7 days later, the infected person develops fever (after the virus multiplies i.e., incubation
period). The person usually then sees a doctor.
When fever starts, the person becomes infectious for about 5 days.
If an Aedes mosquito bites the person during this period when he is infectious, it will pick up
the dengue virus in his blood.
The virus takes 7-10 days to
multiply in the second
mosquito.
The mosquito then becomes
infective and the cycle starts
again when it bites another
person.
An infected person does not
spread the virus to another person
directly but he becomes a source
of dengue virus for the Aedes
mosquitoes. The treatment of
dengue fever is symptomatic and
supportive in nature. Bedrest and
mild analgesic-antipyretic therapy
are often helpful in relieving
lethargy, malaise, and fever
associated with the disease.
Where does the Aedes
Mosquito breed?
A puddle of water about the size
and depth of 20-cent coin is

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sufficient for an Aedes mosquito to breed in.
The Aedes mosquitoes are commonly found breeding in clear stagnant water in flower
vases, flower pot plates, roof gutters, earthen jars for water storage or decorative purposes,
watering cans, and bamboo pole holders. The Aedes mosquito can also breed in unusual
places such as water trapped in the hardened soil in potted plates, and the rim of unwanted
pails.
The flavivirus life cycle
Dengue (DF) and dengue hemorrhagic fever (DHF) are caused by one of four closely
related, but antigenically distinct, virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the
genus Flavivirus. Infection with one of these serotypes provides immunity to only that
serotype for life, so persons living in a dengue-endemic area can have more than one
dengue infection during their lifetime. DF and DHF are primarily diseases of tropical and sub
tropical areas, and the four different dengue serotypes are maintained in a cycle that
involves humans and the Aedes mosquito. However, Aedes aegypti, a domestic, day-biting
mosquito that prefers to feed on humans, is the most common Aedes species. Infections
produce a spectrum of clinical illness ranging from a nonspecific viral syndrome to severe
and fatal hemorrhagic disease. Important risk factors for DHF include the strain of the
infecting virus, as well as the age, and especially the prior dengue infection history of the
patient.

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Substance Abuse
Drug abuse has a wide range of definitions related to taking a psychoactive drug or
performance enhancing drug for a non-therapeutic or non-medical effect. Some of the most
commonly abused drugs include alcohol, amphetamines, barbiturates, benzodiazepines,
cocaine, methaqualone, and opium alkaloids. Use of these drugs may lead to criminal
penalty in addition to possible physical, social, and psychological harm, both strongly
depending on local jurisdiction
Medical definitions describe alcoholism as a disease which results in a persistent use of
alcohol despite negative consequences. Alcoholism may also refer to a preoccupation with
or compulsion toward the consumption of alcohol and/or an impaired ability to recognize the
negative effects of excessive alcohol consumption.
Drug addiction is a condition characterized by compulsive drug intake, craving and seeking,
despite what the majority of society may perceive as the negative consequences associated
with drug use
Drug Dependence
Physical dependence refers to a state resulting from habitual use of a drug, where negative
physical withdrawal symptoms result from abrupt discontinuation
Increased heart rate and/or blood pressure, sweating, and tremors are common signs of
withdrawal. More serious symptoms such as confusion, seizures, and visual hallucinations
indicate a serious emergency and the need for immediate medical care. Alcohol,
benzodiazepines, and barbiturates are the only commonly abused substances that can be
fatal in withdrawal. Though extremely unpleasant and potentially dramatic, withdrawal from
opiates does not pose a direct medical threat.
Psychological dependency is a dependency of the mind, and leads to psychological
withdrawal symptoms (such as cravings, irritability, insomnia, depression, anorexia etc).
Addiction can in theory be derived from any rewarding behavior, and is believed to be
strongly associated with the dopaminergic system of the brain's reward system (as in the
case of cocaine and amphetamines). Some claim that it is a habitual means to avoid
undesired activity, but typically it is only so to a clinical level in individuals who have
emotional, social, or psychological dysfunctions (psychological addiction is defined as such),
replacing normal positive stimuli not otherwise attained

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What are the effects of alcoholism?
Alcohol depresses your central nervous system by acting as a sedative. In some people, the
initial reaction may be stimulation, but as drinking continues, sedating or calming effects
occur. By depressing the control centers of your brain, alcohol relaxes you and reduces your
inhibitions. The more you drink, the more you're sedated. Initially, alcohol affects
thought, emotion and judgment. In sufficient amounts, alcohol impairs speech and muscle
coordination and produces sleep. Taken in large enough quantities, alcohol is a lethal poison
- it can cause life-threatening coma by severely depressing the vital centers of your brain.
Excessive use of alcohol can produce several harmful effects on your brain and
nervous system and cause fatigue, short-term memory loss, as well as weakness and
paralysis of your eye muscles. Short-term effects
A small amount of alcohol will relax you and make you feel less anxious. But alcohol is a
depressant of the central nervous system. In increasing amounts it suppresses the part of
your brain that controls judgement, resulting in a loss of inhibitions. It also affects your
physical co-ordination, causing blurred vision, slurred speech and loss of balance. Drinking a
very large amount at one time (binge drinking) can lead to unconsciousness, coma, and
even death. Vomiting while unconscious can lead to death by asphyxiation (suffocation).
Alcohol is involved in a large proportion of fatal road accidents, assaults and incidents of
domestic violence.
It can also have these other severe health effects:
Liver disorders. Drinking heavily can cause you to develop alcoholic hepatitis, an
inflammation of the liver. Signs and symptoms may include loss of appetite, nausea,
vomiting, abdominal pain and tenderness, fever, yellowing of the skin (jaundice) and
sometimes mental confusion. Over years of drinking, hepatitis may lead to cirrhosis, the
irreversible and progressive destruction of liver tissue. A healthy liver processes nutrients
into molecules your body can use, manufactures bile to help digest fats and regulates the
amounts of sugar, protein and fat that enter your bloodstream.
Gastrointestinal problems. Alcohol can result in inflammation of the lining of the stomach
(gastritis), which can lead to tears in the upper part of your stomach and lower part of your
esophagus. Alcohol can also interfere with the absorption of the B vitamins, particularly folic
acid and thiamin, and other nutrients. Heavy drinking can also damage your pancreas
(pancreatitis). The pancreas has two functions: (1) it produces the hormones insulin and
glucagon, which help regulate your metabolism, and (2) it produces pancreatic juices and
enzymes that help digest fats, proteins and carbohydrates.

155
 cardiovascular problems. Excessive drinking can lead to high blood pressure and damage
your heart muscle (cardiomyopathy). These conditions can put you at increased risk of heart
failure or stroke.
Diabetes complications. Alcohol prevents the release of glucose from your liver and can
increase the risk of your blood sugar falling too low (hypoglycemia). This is dangerous if you
have diabetes and are already taking insulin to lower your blood sugar level.
Sexual function and menstruation. Alcohol abuse can cause erectile dysfunction in men.
In women, it can interrupt menstruation.
Neurologic complications. Excessive drinking can affect your nervous system, causing
numbness of your hands and feet, disordered thinking and dementia.
Increased risk of cancer. Chronic alcohol abuse has been linked to a higher risk of cancer
of the esophagus, larynx, liver and colon.
Higher incidence of suicide and murder
Fetal alcohol syndrome (FAS) is a disorder of permanent birth defects that occurs in the
offspring of women who drink alcohol during pregnancy. It is unknown whether amount,
frequency or timing of alcohol consumption during pregnancy causes a difference in degree
of damage done to the fetus. Thus, the current recommendation is not to drink at all during
pregnancy. Alcohol crosses the placental barrier and can stunt fetal growth or weight, create
distinctive facial stigmata, damage neurons and brain structures, and cause other physical,
mental, or behavioral problems. The main effect of FAS is permanent central nervous system
damage, especially to the brain. Developing brain cells and structures are underdeveloped or
malformed by prenatal alcohol exposure, often creating an array of primary cognitive and
functional disabilities (including poor memory, attention deficits, impulsive behavior, and poor
cause-effect reasoning) as well as secondary disabilities (for example, mental health
problems, and drug addiction). The risk of brain damage exists during each trimester, since
the fetal brain develops throughout the entire pregnancy. Fetal alcohol exposure is the
leading known cause of mental retardation in the Western world.
Evidence of the dangers of smoking
Epidemiological evidence looks for patterns in the diseases, which smokers suffer from. It
only shows an association and not a causal link. Experimental evidence attempts to prove a
causal link.
Chronic obstructive pulmonary disease is very rare in non-smokers and 90% of deaths
from it can be attributed to smoking. 98% of people with emphysema smoke and 20% of

156
smokers suffer from it. Deaths from pneumonia and influenza are twice as high among
smokers.
Lung cancer is eighteen times more likely in smokers and one third of all cancer deaths can
be attributed to smoking. 25% of smokers die from lung cancer and the risks are higher if
they inhale, start young, smoke a large number of cigarettes a day and smoke over a long
period of time. The risks of developing lung cancer fall as soon as smoking stops but it takes
ten years for the risks to fall to that of a non-smoker. Experimental evidence includes the
development of tumours in animals exposed to smoke and the identification of carcinogens
in tar. Both lung cancer and chronic obstructive lung disease have been observed in dogs
and tar has caused cancerous growths in the skin of mice.
Cardiovascular diseases are degenerative diseases of the heart and circulatory system.
They are responsible for 50% of deaths in developed countries and are multifactorial -
smoking being one risk factor.
Atherosclerosis This is caused by a build-up of fatty material in artery walls, which reduces
the flow of blood and therefore oxygen to the tissues. An atheroma is a build up of
cholesterol, fibres, dead muscle cells and platelets and is more likely to develop upon
damage to the artery wall by high blood pressure, carbon monoxide or nicotine. Blood clots
(thrombosis) become more likely and if one develops in the coronary artery a heart attack
may be the result, while if it occurs in an artery supplying the brain, a stroke may result.
Coronary heart disease This is a disease of the coronary arteries, which branch from the
aorta, to supply the heart muscle. If atherosclerosis, of these vessels occurs, then the heart
has to work harder and blood pressure rises. This makes it difficult for the heart to receive
the extra nutrients and oxygen it requires during exercise.
Three forms exist:
•Angina is severe chest pains upon exercising caused by a shortage of blood to the heart
muscle but causes no death of heart tissue and stops upon resting.
•Heart attacks occur upon the blocking of a moderate branch of the coronary artery by a
blood clot and cause starvation and death of heart tissue.
•Heart failure is when the coronary artery starts to block up and results in a gradual
weakening of the heart.
Stroke These occur if an artery in the brain bursts and blood leaks into the brain tissue or
when an artery supplying the brain becomes blocked. The brain tissue becomes starved of

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oxygen and dies. Strokes can be fatal or very mild and may affect speech, memory and
control of the body.
Links between smoking and cardiovascular disease
Smoking increases the concentration of blood cholesterol, which is a risk factor, so smokers
increase the risk of having heart disease or a stroke. The risks of developing the disease
increases with age and men are more at risk than women. Being overweight increases the
risk as does eating a diet high in saturated fat and salt. Diets with more antioxidants
(vitamins) and soluble fibre decrease the risk as does taking regular exercise. Having
diabetes raises the risks and high alcohol intake is another contributory factor.

158