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Respiratory Physiology > Haemoglobin and gas transport > Flashcards

Haemoglobin and gas transport Flashcards

1
Q

How much oxygen is dissolved per litre of plasma?

A

3ml

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2
Q

Haemoglobin in red blood cells increases the oxygen carrying capacity to what?

A

200 ml/L

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3
Q

How is the bulk of CO2 transported?

A

In solution in plasma

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4
Q

Arterial partial pressure of oxygen is determined by what?

A

The oxygen dissolved in the blood (not haemoglobin)

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5
Q

What 2 factors influence how much O2 is dissolved, thus determining arterial partial pressure?

A

O2 solubility

The partial pressure of oxygen in the gaseous phase driving the O2 into solution (partial pressure in the alveoli)

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6
Q

What is the partial pressure of the oxygen in solution?

A

100mmHg, called the oxygen tension

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7
Q

Partial pressure of a gas in solution is equal to…

A

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

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8
Q

Gases travel in solution in the plasma rather than in a gaseous phase, why?

A

Gas in blood means bubbles in blood leading to a fatal air embolism

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9
Q

Oxygen delivery to the tissues can be calculated using what equation?

A

Arterial O2 content (ml/L) x Cardiac output (L/min)

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10
Q

O2 demand of resting tissues is…

A

250ml/min

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11
Q

What is the cardiac output?

A

5 L/min

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12
Q

How much haemoglobin is in the body?

A

150g/L

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13
Q

How much oxygen is carried in a gram of haemoglobin?

A

1.34ml O2 per g

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14
Q

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

A

Only 25%

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15
Q

How is the PO2 gradient maintained between the blood and alveoli?

A

Haemoglobin takes up arterial oxygen so the gradient doesnt reach equilibrium

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16
Q

What percentage of haemoglobin is in the form HbA?

A

92%

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17
Q

What percentage of haemoglobin is in the form HbA2?

A

8%

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18
Q

What is the difference between HbA and HbA2?

A

Delta chains replace the beta chains

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19
Q

Haemoglobin in the form HbF (foetal) is formed when beta chains are replaced by what chains?

A

Gamma chains

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20
Q

What is HbA made of?

A

2 alpha and 2 beta chains

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21
Q

What makes up foetal haemoglobin?

A

2 Alpha chains 2 Gamma chains

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22
Q

What makes up HbA2?

A

2 Alpha chains 2 Delta chains

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23
Q

What are the types of glycosylated Hb?

A

HbA1a HbA1b HbA1c

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24
Q

Where is myoglobin found?

A

Oxidative muscle fibres

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25
Q

How does a foetus extract O2 from maternal blood?

A

HbF has a much higher affinity for O2 than HbA.

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26
Q

How do muscles extract O2 from the blood?

A

BY having a higher O2 afinity than HbA

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27
Q

Oxygen is moved out of the alveoli down a partial pressure gradient until what?

A

The haemoglobin becomes saturated with oxygen

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28
Q

How long is haemoglobin in contact with the alveoli?

A

0.75s

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29
Q

Within how many seconds of contact with the alveoli is saturation complete?

A

Only 0.25s out of the 0.75

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30
Q

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

A

Partial pressure of oxygen in arterial blood

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31
Q

Oxygen is moved out of the alveoli down a partial pressure gradient until what?

A

The haemoglobin becomes saturated with oxygen

32
Q

What is the normal systemic arterial PO2 and what level of saturation is heamoglobin at during this level?

A

100mmHg - Haemoglobin is almost 100% saturated at this level

33
Q

What is the haemoglobin saturation when PO2 is 60mmHg? What does this allow for?

A

Still a high 90% which allows for a relatively normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced

34
Q

At normal venous PO2, what is the reserve capacity?

A

75%

35
Q

What do the higher affinities of myoglobin and foetal haemoglobin (compared to HbA) allow them to do?

A

Extract more oxygen from skeletal muscle for myoglobin

Foetal Haemoglobin - extract more oxygen from from the maternal blood

36
Q

Define anaemia

A

Anaemia is defined as any condition where the oxygen carrying capacity of the blood is compromised

37
Q

Can red blood cells to be fully saturated with oxygen in anaemia?

A

Yes

38
Q

Why is it possible for red blood cells to be fully saturated with oxygen in anaemia?

A

As PaO2 is normal - there is no problem with ventilation or diffusion so alveolar volume and diffusion should be normal (exception is iron deficiency anaemia)

39
Q

Is it possible to have low PaO2, and normal total blood O2 content?

A

No

40
Q

Why is there a low oxygen content in anaemia?

A

Due to a low haemoglobin content as red blood cells are missing/not being synthesised properly due to anaemia

41
Q

Why is iron deficiency anemia different?

A

As the number of O2 binding sites will be reduced BUT but those present will still be saturated if PaO2 is normal

42
Q

What decreases the affinity of haemoglobin for oxygen

A

Decreased pH
Increased PCO2
Increased temperature Increased binding of DPG

43
Q

In what state do these conditions have to be?

A

They have to exist locally in actively metabolising tissues

44
Q

What is a positive and negative aspect to increased haemoglobin affinity for O2?

A

It aids the collection of oxygen in the pulmonary circulation but makes O2 offloading more difficult

45
Q

What is DPG

A

2,3-diphosphoglycerate

46
Q

What is DPG synthesized by?

A

The erythrocytes (red blood cells)

47
Q

When would DPG levels be increased and how does it help?

A

In situations associated with inadequate oxygen supply (heart or lung disease, living at high altitude) and helps maintain oxygen release in the tissues.

48
Q

How is carbon monoxide formed?

A

Incomplete combustion of carbon

49
Q

Carbon monoxide binds to haemoglobin to form what?

A

Carboxyhaemoglobin

50
Q

How much greater an affinity does haemoglobin have for CO over O2?

A

250x

51
Q

Why is haemoglobins affinity for CO being so high a problem?

A

Because it will bind readily and dissociate very slowly making it hard to remove

Also only a small amount of CO - PCO of only 0.4mmHg causes progressive carboxyhaemoglobin formation

52
Q

Typical PHYSICAL symptoms of carbon monoxide poisoning?

A

Cherry red skin, mucous membranes and nail beds

Headaches

53
Q

Other sympotms of CO poisoning?

A

Aneamia and hypoxia

54
Q

Why is repiration rate unchanged during CO poisoning?

A

As the arterial PCO2 levels remain unchanged and the main thing that drives ventilation is removing CO2

55
Q

Eventual outcomes of CO poisoning?

A

Brain damage

Death

56
Q

The treatment for CO poisoning is administering 100% oxygen, why is this treatment difficult?

A

Haemoglobin is already 98% saturated with oxygen, so providing pure oxygen can only increase this by 2%

57
Q

5 main types of hypoxia?

A 
Hypoxic 
Anaemic 
Ischaemic 
Histoxic 
Metabolic
58
Q

What is the most common hypoxia?

A

Hypoxic

59
Q

Describe Hypoxic hypoxia

A

Reduction in O2 diffusion at lungs either due to decreased PO2atmos or tissue pathology

60
Q

What is anaemic hypoxia?

A

Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency).

61
Q

What is ischaemic (stagnant) hypoxia?

A

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

62
Q

What is histotoxic hypoxia?

A

Poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide

63
Q

What is metabolic hypoxia?

A

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

64
Q

What is hypoxia then?

A

A deficiency/inadequacy in the volume of oxygen reaching the tissues

65
Q

When CO2 molecules diffuse from tissue to the blood, what percentage remains dissolved in plasma and erythrocytes?

A

7%

66
Q

What does 23% of the CO2 do when diffusing from tissue to blood?

A

Combines in the erythrocytes with deoxyhemoglobin to form carbamino compounds

67
Q

What does the remaining 70% do?

A

Combines in the erythrocytes with water to form carbonic acid

68
Q

What does the carbonic acid go on to form?

A

Bicarbonate and H+ ions

69
Q

What does this bicarbonate and H+ ions go on to do?

A

Bicarbonate moves out of the erythrocytes into the plasma in exchange for Cl- ions (chloride shift)

Excess H+ ions bind to deoxyhemoglobin

70
Q

What equation shows why CO2 can change the ECF’s pH?

A

CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+

71
Q

Why is pH normally stable?

A

Because the all CO2 produced is eliminated in expired air

72
Q

CO2 retention leading to increased [H]+ will cause what?

A

Respiratory acidosis

73
Q

Blowing off more CO2 leading to decreased [H]+ will cause what?

A

Respiratory alkalosis

74
Q

Is respiratory alkalosis found in hypo or hyper-ventilation?

A

Hyperventilation

75
Q

Is respiratory acidosis found in hypo or hyper-ventilation?

A

Hypoventilaton

Respiratory Physiology (13 decks)

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