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Systems: Respiratory AB > 6/7. Haemoglobin and Gas Transport > Flashcards

6/7. Haemoglobin and Gas Transport Flashcards

1
Q

What is the role of blood in gas transport?

A

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.

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2
Q

How much O2 is dissolved per litre of plasma?

A

3ml

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3
Q

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

A

Haemoglobin in red blood cells

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4
Q

How is CO2 carried?

A

In various forms, in solution in plasma

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5
Q

What is arterial partial pressure of O2 determined by?

A

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

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6
Q

What does arterial partial pressure of O2 refer to?

A

The O2 in solution

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7
Q

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

A

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

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8
Q

What is the solubility of O2 in water?

A

Low

0.03ml/L/mmHg

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9
Q

What is PaO2 sometimes referred to as?

A

Oxygen tension

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10
Q

What is the PO2 in solution equal to?

A

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

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11
Q

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

A

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

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12
Q

What is the oxygen demand of resting tissues?

A

250ml/min

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13
Q

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

A

25%

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14
Q

What is the O2 delivery to tissues?

A

15ml/min

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15
Q

What is the O2 delivery to tissues using haemoglobin?

A

1000ml/min

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16
Q

What does each litre of systemic arterial blood contain?

A

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

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17
Q

What reaction takes place when oxygen cooperatively binds to haemoglobin?

A

Oxygenation

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18
Q

What volume of oxygen binds to each gram of haemoglobin?

A

1.34ml

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19
Q

What is the most abundant form of haemoglobin in RBC?

A

HbA (92%)

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20
Q

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

A
  • HbA2 where the omega chains replace the beta
  • HbF where gamma chains replace the beta
  • Glycosylated Hb ( HbA1a, HbA1b, HbA1c)
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21
Q

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

A

Partial pressure of oxygen

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22
Q

How does Hb become saturated with oxygen?

A

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

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23
Q

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

A

0.25s

24
Q

When is haemoglobin almost 100% saturated?

A

At the normal systemic arterial PO2 of 100mmHg

25
Q

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

A

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

26
Q

What is the reserve capacity at normal venous PO2?

A

75%

27
Q

What has a higher affinity for O2 than haemoglobin?

A
  • Myoglobin

- Foetal haemoglobin

28
Q

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

A

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

29
Q

Anaemia

A

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

30
Q

Why does PaO2 remain normal in anaemia?

A

It has no effect on ventilation or diffusion

31
Q

What are 3 causes of anaemia?

A
  • Iron deficiency
  • Haemorrhage
  • Vitamin B12 deficiency
32
Q

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

A

Certain chemical factors

33
Q

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

A
  • pH
  • PCO2
  • Temperature
  • DPG
34
Q

What will shift the curve to the right?

A
  • Lower pH
  • Higher PCO2
  • Higher temperature
  • Additional DPG
35
Q

What will shift the curve to the left?

A
  • Higher pH
  • Lower PCO2
  • Lower temperature
  • No DPG
36
Q

When is there an increase in DPG?

A

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

37
Q

What happens when CO binds to haemoglobin?

A

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

38
Q

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

A

250 time greater

39
Q

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

A

0.4mmHg

40
Q

What are the symptoms of CO poisoning?

A
  • Hypoxia and anaemia
  • Nausea and headaches
  • Cherry red skin and mucous membranes
41
Q

What can Co poisoning result in?

A

Potential brain damage and death

42
Q

Why is the respiration rate unaffected with CO poisoning?

A

There is normal PCO2

43
Q

Hypoxia

A

Inadequate supply of oxygen to tissues

44
Q

What are the 5 main types of hypoxia?

A
  • Hypoxic hypoxia
  • Anaemic hypoxia
  • Ischaemic hypoxia
  • Histotoxic hypoxia
  • Metabolic hypoxia
45
Q

Hypoxic Hypoxia

A

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

46
Q

Anaemic Hypoxia

A

Reduction in O2 carrying capacity of blood due to anaemia

47
Q

Ischaemic Hypoxia

A

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

48
Q

Histotoxic Hypoxia

A

Poisoning prevents cells utilising oxygen delivered to them

49
Q

Metabolic Hypoxia

A

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

50
Q

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

A
  • 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
51
Q

What happens to most of the bicarbonate?

A

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

52
Q

What happens in the pulmonary capillaries?

A

Co2 moves down its concentration gradient from blood to alveoli

53
Q

Why is pH normally stable?

A

All CO2 produced is eliminated in expired air

54
Q

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

A

Hypoventilation and hyperventiliation

55
Q

What does hypoventilation lead to?

A

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

56
Q

What does hyperventilation lead to?

A

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

Systems: Respiratory AB (39 decks)

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