Module 3 - Mass transport in animals

Question 1

3 marks

The oxygen dissociation curve for heamoglobin shifts right during vigorous exercise. Explain the advanatge of this shift

Answer 1

1. Low pH due to increased CO2/ increased respiration
2. Increased dissociation of haemoglobin
3. Oygen diffuses from r.b.c to tissues

Question 2

3 marks

How does exposure to CO affect loading and unloading of oxygen by haemologlobin

Answer 2

1. A low Po2 Hb exposed to CO has a higher affinity for oxygen than normal Hb
2. In respiring tissue its unloading less oxygen than it should
3. At high Po2 (lungs) it has a lower affinity for oxygen than normal Hb- only 50% saturation of the no CO Hb (less oxygen loaded at lungs)

Question 3

3 marks

Explain why the thickness of the aorta wall changes all the time during each cardiac cycle

Answer 3

1. Aorta wall stretches because ventricle contracts (pressure increases)
2. Aorta wall recoils because ventricle relaxes (pressure falls)
3. Maintain smooth flow / pressure

Question 4

What does atheroma lead to

Answer 4

Atheroma leads to blockage of coronary artery

Question 5

Name the type of blood vessel that controls blood flow to muscles and explain how these blood vessels change blood flow during exercise.

Answer 5

1. Arteriole;
2. (Circular/smooth) muscle relaxes;
3. Widens/dilates (lumen of) blood vessel so increases blood flow;

Question 6

2 marks

There is a small increase in pressure and in rate of blood flow in the aorta.
Explain how this happens and its importance.

Answer 6

1. Elastic recoil of the aorta wall
2. Smooths the blood flow

Question 7

What factor limits the minimum internal diameter of the lumen of a capillary

Answer 7

Diameter of red blood cell

Question 8

2 marks

How is the pressure in the ventricle related to the thickness of ventricle wall

Answer 8

• Thickness of wall increases because ventricle wall contracts
• Contraction caused by increase in pressure

Question 9

3 marks

Explain why high blood pressure leads to the accumulation of tissue fluid

Answer 9

• High blood pressure (as ventricle contracts)= high hydrostatic pressure
• Increase in outward pressure from arteriole end of capillary
• So more tissue fluid formed

Question 10

3 marks

Why does venule end of capillary have lower blood plasma water potential

Answer 10

1. Water has left capillary
2. Proteins in blood too large to leave
3. Higher concentration of blood plasma proteins

Question 11

Why does carbonmonoxide kill people. Use loading and unloading of O2.

Answer 11

At low pO2, Hb exposed to CO has higher affinity for O2 than normal Hb
In respiring tissues it is unloading less O2 than it should
At high PO2, it has lower affinity for O2 than normal Hb- less O2 loaded to lungs

Question 12

6 marks

Explain how tissue fluid is formed and how it may be returned to the circulartory system

Answer 12

1. High hydrostatic pressure at arterial end
2. Soluble molecules pass out
3. Proteins remain - too large
4. This lower water potential at venule end
5. Water moves back into venule end via osmosis
6. Lymphatic system collects any excess tissue fluid which returns to blood

Question 13

2 marks

High absorption of salt from the diet can result in a higher than normal
concentration of salt in the blood plasma entering capillaries. This can lead to a
build-up of tissue fluid.
Explain how.

Answer 13

1. Higher salt results in higher blood pressure–> higher hydrostatic pressure
2. So more fluid forced out of arteriole end of capillary
   OR
3. Higher salt results in lower water potential of tissue fluid
4. So less water returns to capillary by osmosis at venule end

Question 14

6 marks

Explain how the structures of the walls of arteries, veins and capillaries are related to their functions.

Answer 14

Artery
1. thickest wall, enabling it to carry blood at high pressure / withstand pressure surges
2. most elastic tissue, which evens out pressure
3. most muscle which maintains pressure
4. muscle in wall to control blood flow
Vein
5. thin wall does not have to withstand high pressure
Capillary
6. thin wall, allowing diffusion
7. only endothelium present, allowing short diffusion pathway
All vessels
8. have endothelium that reduces friction

Question 15

3 marks

Explain how oxygen in a RBC is made available for respiration in active tissues

Answer 15

• Low pH due to increased CO2 due to increased respiration;
• Increased dissociation of haemoglobin
• Oxygen diffuses from r.b.c. to tissues

Question 16

2 marks

A decrease in the pH of blood plasma reduces the affinity of haemoglobin for oxygen.
Explain how aerobic respiration in cells leads to a change in the pH of blood plasma.

Answer 16

1. CO2 is produced
2. Forms carbonic acid
3. Hydrogen ions released

Question 17

2 marks

What is the advantage to tissue cells of a reduction in the affinity of haemoglobin for oxygen when the plasma pH decreases?

Answer 17

1. Low pH due to high rates of respiration
2. Cells need more oxygen
3. More oxygen released

Question 18

4 marks

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.
Details of breathing are not required.

Answer 18

1. Trachea and bronchi and bronchioles
2. Down pressure gradient
3. Down diffusion gradient
4. Across alveolar epithelium
5. Across capillary endothelium