Gas transport

Question 1

Describe the structure of haemoglobin

Answer 1

• 4 haem units and their associated globin molecule.
• haem is a pigment containing iron to which oxygen can bind to
• Globin is a polypeptide which cradles the haem and prevents irreversible binding of the O2

Question 2

How does cooperative binding of oxygen to haemoglobin work?

Answer 2

One haemoglobin molecule can bind 4 molecules of O2. Binding of one O2 molecule increases the affinity of the other units for O2
- gives a sigmoid shape

Question 3

How does partial pressure of oxygen affect haemoglobin saturation?

Answer 3

An increase in PO2 will give an increase in O2 saturation of Hb

Question 4

Which 4 factors affect the oxyhaemoglobin dissociation curve?

Answer 4

Temperature
pH
PCO2
Concentration of 2,3-diphosphoglycerate (2,3-DPG) in red blood cells - by product of glycolysis

Question 5

Reduction in pH, increase in temperature and increase in PCO2, all of which occur in skeletal muscle during exercise, shift the curve to the … ? Give an explanation

Answer 5

Right
- This means that for a given PO2, the Hb saturation is lower, hence unloading of O2 under these conditions is more efficient

Question 6

What are the 3 ways CO2 is transported in blood?

Answer 6

• Dissolved in plasma (5%)
• As carbamino compounds (30%)
• As bicarbonate (HCO3-) ions (65%)

Question 7

What is a carbamino compound?

Answer 7

CO2 that combines with a protein e.g. Hb

Question 8

What is formed when CO2 combines with water?

Answer 8

Carbonic acid - under the influence of carbonic anhydrase

Question 9

What is the chloride shift?

Answer 9

HCO3- produced is transported out into the plasma in exchange for chloride ions (Cl-) to maintain the electrochemical neutrality of the erythrocyte

Question 10

How are excess hydrogen ions buffered in the RBC?

Answer 10

H+ combines with deoxyHb within the erythrocyte

Question 11

Which vessels in the pulmonary circulation contribute to half of the vascular resistance?

Answer 11

Capillaries

Question 12

What enables small pulmonary arteries to constrict and dilate? in which species is this layer very thick

Answer 12

Smooth muscle

- pigs and cattle

Question 13

What is usually the net effect of sympathetic stimulation on the vessels, and by which receptors?

Answer 13

Vasoconstriction

alpha receptors

Question 14

The action of what substances affects the vasodilation through parasympathetic stimulation?

Answer 14

Nitric oxide

Question 15

What effect does alveolar hypoxia have on vessels?

Answer 15

Vasoconstrictor
- A low PAO2 occurs where the ventilation of alveoli is reduced and, to ensure the VA:Q ratio remains optimal, this alveolar hypoxia causes vasoconstriction of the small arteries supplying that portion of lung

Question 16

What effect can alveolar hypoxia have on the heart?

Answer 16

• can have generalised vasoconstriction of pulmonary circulation
• increased afterload on right side of the heart
• can lead to right sided congestive heart failure