6/7. Haemoglobin and Gas Transport

Question 1

What is the role of blood in gas transport?

Answer 1

Transports O2 from lungs to tissues to use in energy production and transports the waste product of this process CO2 from tissues to lungs for removal.

Question 2

How much O2 is dissolved per litre of plasma?

Answer 2

3ml

Question 3

How is the carrying capacity of blood increased to 200ml/L?

Answer 3

Haemoglobin in red blood cells

Question 4

How is CO2 carried?

Answer 4

In various forms, in solution in plasma

Question 5

What is arterial partial pressure of O2 determined by?

Answer 5

O2 solubility and the partial pressure of O2 in the gaseous phase that is driving O2 into solution

Question 6

What does arterial partial pressure of O2 refer to?

Answer 6

The O2 in solution

Question 7

What are the values assigned to the partial pressure of a gas in solution equal to?

Answer 7

The partial pressure in gaseous phase that is driving that gas into solution

Question 8

What is the solubility of O2 in water?

Answer 8

Low

0.03ml/L/mmHg

Question 9

What is PaO2 sometimes referred to as?

Answer 9

Oxygen tension

Question 10

What is the PO2 in solution equal to?

Answer 10

PO2 in the gaseous phase that results in that oxygen concentration in the liquid phase

Question 11

Why is it important that gases do not travel in the gaseous phase in plasma?

Answer 11

If they did there would be bubbles in the blood which would result in a fatal air embolism

Question 12

What is the oxygen demand of resting tissues?

Answer 12

250ml/min

Question 13

What percentage of arterial O2 is extracted by peripheral tissues at rest?

Answer 13

25%

Question 14

What is the O2 delivery to tissues?

Answer 14

15ml/min

Question 15

What is the O2 delivery to tissues using haemoglobin?

Answer 15

1000ml/min

Question 16

What does each litre of systemic arterial blood contain?

Answer 16

200ml of oxygen, of which more than 98% is bound to haemoglobin. The remaining oxygen is dissolved in plasma

Question 17

What reaction takes place when oxygen cooperatively binds to haemoglobin?

Answer 17

Oxygenation

Question 18

What volume of oxygen binds to each gram of haemoglobin?

Answer 18

1.34ml

Question 19

What is the most abundant form of haemoglobin in RBC?

Answer 19

HbA (92%)

Question 20

Apart from HbA what other forms of haemoglobin are found in RBC?

Answer 20

• HbA2 where the omega chains replace the beta
• HbF where gamma chains replace the beta
• Glycosylated Hb ( HbA1a, HbA1b, HbA1c)

Question 21

What is the major determinant of the degree to which haemoglobin is saturated with oxygen in arterial blood?

Answer 21

Partial pressure of oxygen

Question 22

How does Hb become saturated with oxygen?

Answer 22

Hb sequesters O2 from the plasma, maintaining a partial pressure gradient that continues to suck O2 out of the alveoli

Question 23

How long does it take for saturation to be complete on contact with the alveoli?

Answer 23

0.25s

Question 24

When is haemoglobin almost 100% saturated?

Answer 24

At the normal systemic arterial PO2 of 100mmHg

Question 25

At PO2 of 60mmHg, haemoglobin is 90% saturated. What does this permit?

Answer 25

This permits a relatively normal uptake of oxygen by the blood even when the alveolar PO2 is moderately reduced

Question 26

What is the reserve capacity at normal venous PO2?

Answer 26

75%

Question 27

What has a higher affinity for O2 than haemoglobin?

Answer 27

- Myoglobin | - Foetal haemoglobin

Question 28

Why does foetal haemoglobin have a higher affinity for oxygen than regular haemoglobin?

Answer 28

It is necessary for it extracting O2 from maternal/arterial blood

Question 29

Anaemia

Answer 29

Any condition where the oxygen carrying capacity of the blood is compromised

Question 30

Why does PaO2 remain normal in anaemia?

Answer 30

It has no effect on ventilation or diffusion

Question 31

What are 3 causes of anaemia?

Answer 31

- Iron deficiency - Haemorrhage - Vitamin B12 deficiency

Question 32

What does the affinity of haemoglobin for O2 change in response to?

Answer 32

Certain chemical factors

Question 33

What are 4 factors which can change the affinity of haemoglobin for O2?

Answer 33

- pH - PCO2 - Temperature - DPG

Question 34

What will shift the curve to the right?

Answer 34

- Lower pH - Higher PCO2 - Higher temperature - Additional DPG

Question 35

What will shift the curve to the left?

Answer 35

- Higher pH - Lower PCO2 - Lower temperature - No DPG

Question 36

When is there an increase in DPG?

Answer 36

In situations associated with inadequate oxygen supply such as heart/lung disease and living at altitude

Question 37

What happens when CO binds to haemoglobin?

Answer 37

It forms carboxyhaemoglobin which binds readily to O2 and dissociates very slowly

Question 38

How many times greater is the affinity of caarboxyhaemoglobin for oxygen than haemoglobin for oxygen?

Answer 38

250 time greater

Question 39

What is the minimum PCO required to cause progressive carboxyhaemglobin formation?

Answer 39

0.4mmHg

Question 40

What are the symptoms of CO poisoning?

Answer 40

- Hypoxia and anaemia - Nausea and headaches - Cherry red skin and mucous membranes

Question 41

What can Co poisoning result in?

Answer 41

Potential brain damage and death

Question 42

Why is the respiration rate unaffected with CO poisoning?

Answer 42

There is normal PCO2

Question 43

Hypoxia

Answer 43

Inadequate supply of oxygen to tissues

Question 44

What are the 5 main types of hypoxia?

Answer 44

- Hypoxic hypoxia - Anaemic hypoxia - Ischaemic hypoxia - Histotoxic hypoxia - Metabolic hypoxia

Question 45

Hypoxic Hypoxia

Answer 45

Reduction in O2 diffusion at lungs either due to decreased PO2atoms or tissue pathology

Question 46

Anaemic Hypoxia

Answer 46

Reduction in O2 carrying capacity of blood due to anaemia

Question 47

Ischaemic Hypoxia

Answer 47

Heart disease results in inefficient pumping of blood to lungs/around the body

Question 48

Histotoxic Hypoxia

Answer 48

Poisoning prevents cells utilising oxygen delivered to them

Question 49

Metabolic Hypoxia

Answer 49

Oxygen delivery to the tissues does not meet increased oxygen demand by cells

Question 50

What happens to CO2 molecules when they diffuse from the tissues into the blood?

Answer 50

- 7% remains dissolved in plasma and erythrocytes - 23% combines in the erythrocytes with deoxyhaemogolbin to form carbamino compounds - 70% combines in the erythrocytes with water to form carbonic acid which then dissociates to yield bicarbonate and H+ ions

Question 51

What happens to most of the bicarbonate?

Answer 51

It moves out of the erythrocytes into the plasma in exchange for Cl ions and the excess H+ ions bind to deoxyhaemoglobin.

Question 52

What happens in the pulmonary capillaries?

Answer 52

Co2 moves down its concentration gradient from blood to alveoli

Question 53

Why is pH normally stable?

Answer 53

All CO2 produced is eliminated in expired air

Question 54

What will alter plasma PCO2 and plasma [H+]?

Answer 54

Hypoventilation and hyperventiliation

Question 55

What does hypoventilation lead to?

Answer 55

It causes CO2 retention which leads to increased {H+} bringing about respiratory acidosis

Question 56

What does hyperventilation lead to?

Answer 56

Blowing off more CO2 leads to decreased [H+] bringing about respiratory alkalosis