Chapter 8: transport in mammals

Question 1

Define the term “closed circulatory system”

Answer 1

A circulatory system in which the blood pumped
by the heart is contained within blood vessels.
The blood does not come into direct contact with
the cells. Closed circulatory systems are found in
animals, e.g. vertebrates.

Question 2

Describe the journey of blood through the human
circulatory system with reference to the 4 major blood
vessels of the heart.

Answer 2

heart (r) → pulmonary artery → lungs →
pulmonary vein → heart (l) → aorta →
body → vena cava → heart (r)

Question 3

Define the term “double circulatory system”.

Answer 3

A circulatory system in which the blood flows through the
heart twice in two circuits. Blood is pumped from the
heart to the lungs before returning to the heart. It is then
pumped around the body, after which it returns to the
heart again. Double circulatory systems are found in
mammals.

Question 4

What are the advantages of a closed system?

Answer 4

● Lower blood volume required to keep
system moving

● Blood pressure can be controlled and
maintained

Question 5

What are the advantages of a double circulatory

system?

Answer 5

● Maintains blood pressure around the whole body
● Uptake of oxygen is more efficient
● Delivery of oxygen and nutrients more efficient
● BP can differ in pulmonary and systemic systems

Question 6

Relate the structure of arteries to their function.

Answer 6

● Thick, muscular walls to withstand high pressure
● Elastic tissue allows them to stretch and recoil to prevent
pressure surges
● Narrow lumen to maintain pressure
● Smooth muscle which enables them to vary blood flow
● Lined with smooth endothelium to reduce friction and ease
flow of blood

Question 7

Relate the structure of veins to their function.

Answer 7

● Wide lumen eases blood flow
● Thin walls eases compression by skeletal muscles
● Require valves to prevent backflow of blood
● Less muscular and elastic tissue as they don’t have
to control blood flow

Question 8

Relate the structure of capillaries to their function.

Answer 8

● Walls only one cell thick giving a short diffusion pathway

● Narrow lumen, red blood cells squeeze through,
decreasing the diffusion distance

● Numerous and highly branched, providing a large
surface area

Question 9

Relate the structure of arterioles and venules to their

function.

Answer 9

● Branch off arteries and veins in order to feed blood into
and take blood away from the capillaries

● Smaller than arteries and veins so that the change in
pressure is more gradual as blood passes through
increasingly small vessels

Question 10

Draw and describe the structure of an erythrocyte.

Answer 10

● Diameter- 6.2-8.2μm
● Thickness- 2-2.25μm
● Large surface area to volume ratio
● Form biconcave discs
● No nucleus and no large organelles to maximise O2 carrying ability 

1. Cell surface membrane
2. Cytoplasm - appear dark at edges, becoming lighter in the centre (pink gradient stain under light microscope)

Question 11

Draw and describe the structure of neutrophils.

Answer 11

● Lobed nucleus for flexibility
within blood vessels

● Granulocyte

1. Cell surface membrane
2. Cytoplasm (appears granular) stains light blue
3. Lobed nucleus- varies from 3-5 lobes- stains deep blue

Question 12

Draw & describe the structure of lymphocytes.

Answer 12

● Very large nucleus
● Small amount of cytoplasm
● Agranulocyte

1. Cell surface membrane
2. Cytoplasm- stains pale purple
3. Circular nucleus- stains dark purple

Question 13

What is tissue fluid?

Answer 13

A fluid surrounding cells and tissues that
contains glucose, amino acids, oxygen and
other nutrients. It supplies these to the cells,
while also removing any waste materials.

Question 14

Outline the different pressures involved in the

formation of tissue fluid.

Answer 14

● Hydrostatic pressure - higher at arterial end of capillary
than venous end
● Oncotic pressure - changing water potential of the
capillaries as water moves out, induced by proteins in the
plasma

Question 15

How is tissue fluid formed?

Answer 15

As blood is pumped through increasingly 
smaller vessels, hydrostatic pressure is 
greater than oncotic pressure, so fluid 
moves out of the capillaries. It then 
exchanges substances with the cells.

Question 16

Why does blood pressure fall along the capillary?

Answer 16

● Friction

● Lower volume of blood

Question 17

What happens at the venous end of the capillary?

Answer 17

● Oncotic pressure is greater than
hydrostatic pressure

● Fluid moves down its water potential gradient
back into the capillaries

Question 18

How is tissue fluid removed?

Answer 18

● Tissue fluid drains into the lymphatic
system where it is referred to as ‘lymph’

● The lymph returns to the blood via the
subclavian veins

Question 19

Give some examples of intracellular and extracellular

body fluids in which water is the primary component.

Answer 19

Water is a component of:
●  Blood plasma (for the transport of substances)
●  Cytoplasm
●  Tissue fluid (bathes cells)
●  Lymph
●  Urine for excretion
●  Serum

Question 20

*Why is water important in body fluids?

Answer 20

● Water acts as a solvent in order to transport material in
biofluids

● Water has a high specific heat capacity - a large amount of
energy is required to change its temperature - facilitating the
maintenance of homeostatic conditions

Question 21

Describe the role of haemoglobin.

Answer 21

Present in red blood cells. Oxygen molecules
bind to the haem groups and are transported
around the body. They are released where
oxygen is needed in respiring tissues.

Question 22

How does partial pressure of oxygen affect

oxygen-haemoglobin binding?

Answer 22

Haemoglobin has variable affinity for oxygen depending on the

partial pressure of oxygen, p(O2):

● At high p(O2), oxygen associates to form oxyhaemoglobin

● At low p(O2), oxygen dissociates to form deoxyhaemoglobin

Question 23

How is carbon dioxide carried from respiring cells to

the lungs?

Answer 23

● Transported in aqueous solution in the plasma
● As hydrogen carbonate ions in the plasma
● Carried as carbaminohaemoglobin in the blood

Question 24

What is the chloride shift?

Answer 24

● Process by which chloride ions move into the
erythrocytes in exchange for hydrogen carbonate
ions which diffuse out of the erythrocytes

● One-to-one exchange

Question 25

Why is the chloride shift important?

Answer 25

It maintains the electrochemical

equilibrium of the cell.

Question 26

What is the function of carbonic anhydrase?

Answer 26

Catalyses the reversible reaction
between water and carbon dioxide to
produce carbonic acid.

Question 27

Write equations to show the formation of hydrogen

carbonate ions in the plasma.

Answer 27

Carbonic anhydrase enzyme catalyses:

CO2 + H2O ⇌ H2CO3 (carbonic acid)

Carbonic acid dissociates:

H2CO3 ⇌ HCO3 - (hydrogen carbonate ions) + H+

Question 28

State the Bohr effect.

Answer 28

The loss of affinity of haemoglobin for
oxygen as the partial pressure of carbon
dioxide increases.

Question 29

Explain the role of carbonic anhydrase in the Bohr

effect.

Answer 29

● Carbonic anhydrase is present in red blood cells

● Catalyses the reaction of carbon dioxide and water to form
carbonic acid, which dissociates to produce H+ ions

● H+ ions combine with the haemoglobin to form haemoglobinic acid

● Encourages oxygen to dissociate from haemoglobin

Question 30

Why is a higher concentration of erythrocytes important

for human populations living at high altitudes?

Answer 30

● High altitude, low p(O2), oxygen saturation in
erythrocytes will decrease

● To carry an equal volume of O2 in blood, a
higher concentration of erythrocytes is required

Question 31

What is plasma?

Answer 31

● Main component of the blood (yellow liquid) that
carries red blood cells

● Contains proteins, nutrients, mineral ions,
hormones, dissolved gases and waste. Also
distributes heat

Question 32

Describe and explain the shape of a dissociation

curve for adult haemoglobin.

Answer 32

Sigmoidal curve (S-shaped):

● When first O2 molecule binds, it changes the tertiary structure of
haemoglobin so that it is easier for the second and third molecules to
bind

● Third molecule changes the tertiary structure of haemoglobin so that
it is more difficult for the fourth molecule to bind

Question 33

Draw a diagram of the human heart,
including the names of chambers,
vessels, and valves.

Answer 33

see pmt memorize this

Question 34

Describe what happens during cardiac diastole.

Answer 34

The heart is relaxed. Blood enters the atria,
increasing the pressure and opening the
atrioventricular valves. This allows blood to flow into
the ventricles. Pressure in the ventricles is lower
than in the arteries, so semilunar valves remain
closed.

Question 35

Describe what happens during atrial systole.

Answer 35

The atria contract, forcing the
atrioventricular valves open. Blood flows
into the ventricles.

Question 36

Describe what happens during ventricular systole.

Answer 36

The ventricles contract. The pressure 
increases, closing the atrioventricular valves 
to prevent backflow, and opening the 
semilunar valves. Blood flows into the 
arteries.

Question 37

Explain how the heart contracts

Answer 37

● SAN initiates and spreads impulse across the atria, so they contract.
Thick fibrous walls prevent impulse spreading directly to ventricles
● AVN receives, delays, and then conveys the impulse down the bundle
of His
● Impulse travels into the Purkinje fibres which branch across the
ventricles, so they contract from the bottom up.

Question 38

The walls of the chambers of the heart vary in

thickness - explain this.

Answer 38

● Walls of both atria relatively thin, only have to cap blood in
ventricles as ventricles fill mostly passively

● Left ventricle wall significantly thicker than right, left must
provide pressure for systemic flow, right only has to supply
pulmonary system. Both are thicker than the atria