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Respiratory > 6 Haemoglobin & Gas transport > Flashcards

6 Haemoglobin & Gas transport Flashcards

1
Q

How much Oxygen is dissolved in every litre of plasma?

A

3ml/L

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2
Q

What is the oxygen carrying capacity of the blood?

A

200 ml/L

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3
Q

What determines the arterial partial pressure of O2?

A

Oxygen dissolved in the blood
NOT the oxygen carried by haemoglobin

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4
Q

What 2 factors influence how much O2 is dissolved?

A
  • Its solubility
  • The partial pressure of gaseous oxygen driving O2 into solution (partial pressure in alveoli)
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5
Q

What is the partial pressure of the oxygen in solution?

A

100mmHg (oxygen tension)
Equal to PO2 driving it across

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6
Q

What is the oxygen demand of resting cells?

A

250ml/min

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7
Q

What is cardiac output?

A

Around 5L/min

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8
Q

How much haemoglobin is in the average person?

A

150g/L

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9
Q

How much oxygen is carried in every gram of haemoglobin?

A

1.34ml of O2 per gram of haemoglobin

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10
Q

How much oxygen is carried in the haemoglobin of a normal person?
[150g haemoglobin/L]
[5L/min cardiac output]
[1.34ml O2/g of haemoglobin]

A

5 litres every minute
-> 5L x 150g = 750g/min

1.34ml O2/g
-> 750 x 1.34 = 1000ml/min

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11
Q

How much of the arterial O2 is extracted by tissue at rest?

A

Only 25%
Resting tissues use 250ml/min and haemoglobin carries 1000ml/min

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12
Q

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

A

Haemoglobin takes up arterial oxygen so the gradient doesnt reach equilibrium

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13
Q

What is the most common form of Haemoglobin?

A

HbA
Makes up 92% of haemoglobin
Made of 2 alpha & 2 beta chains

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14
Q

What are some other types of haemoglobin?

A

HbA2
HbF (Foetal)
Glycosylated Hb
myoglobin

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15
Q

What makes up foetal haemoglobin?

A

2 Alpha chains
2 Gamma chains

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16
Q

What makes up HbA2?

A

2 Alpha chains
2 Delta chains

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17
Q

What are the types of glycosylated Hb?

A

HbA1a
HbA1b
HbA1c

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18
Q

Where is myoglobin found?

A

Oxidative muscle fibres

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19
Q

How does a foetus extract O2 from maternal blood?

A

HbF has higher affinity for O2 than HbA.

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20
Q

How do muscles extract O2 from the blood?

A

Myoglobin has higher O2 affinity than HbA

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21
Q

How long is haemoglobin in contact with the alveoli?

A

Around 0.75 seconds
Only takes 0.25s to become saturated

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22
Q

How far can PAO2 drop before haem saturation goes below 90%?

A

PAO2 can be 60mmHg without losing much arterial oxygen

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23
Q

What factors can affect the affinty of haemoglobin for Oxygen?

A
  • pH
  • PaCO2
  • Temperature
  • Diphosphoglycerate
24
Q

What kind of people produce more diphosphoglycerate?

A

People who live at high altitude
Those with heart or lung disease

25
Q

What is the main determinant of haemoglobin saturation?

A

The PaO2

26
Q

See graphs for how saturation is affected by various factors

A
27
Q

What decreases haemoglobin’s affinity for oxygen?

A
  • pH drop
  • PaCO2 increase
  • Temp rise
28
Q

What is the physiological benefit of decreasing haemoglobin’s affinity for oxygen?

A

Low pH, high PaCO2 & high temp exist in actively metabolising tissues and decrease haemoglobin’s affinity for oxygen.

This facilitates dissociation of oxygen from haemoglobin.

29
Q

What increases haemoglobin’s affinity for oxygen?

A
  • pH rise
  • PCO2 fall
  • Temp fall
30
Q

Whats the effect of increased haemoglobin affinity for oxygen?

A

Oxygen unloading is more difficult at tissues
Easier to collect oxygen in pulmonary circulation

31
Q

What does 2,3-DPG do?

A

Decreases haemoglobin’s affinity for oxygen

32
Q

What makes 2.3-DPG?

A

Erythrocytes

33
Q

Why is 2,3-DPG made in situations with inadequate oxygen?

A

Helps maintain oxygen release at tissues.

34
Q

Define anaemia?

A

Any condition where O2 carrying capacity of blood is compromised

35
Q

Give some examples of Anaemic conditions?

A
  • Fe deficiency, cant make enough haem
  • Haemorrhage, losing blood
  • Vit B12 deficiency
36
Q

Why is PaO2 normal in anaemia?

A

No problem with ventilation or gas exchange
No reduction in amount dissolved in blood

37
Q

How does anaemia affect the saturation of haemoglobin?

A

RBCs would still be fully saturated its just theres less of them

38
Q

What do CO & haemoglobin form?

A

Carboxyhaemoglobin

39
Q

Describe the affinity of CO for Haemoglobin?

A

CO has affinity 250x greater than O2 for haemoglobin, prevents transport of oxygen

40
Q

What partial pressure of CO causes carboxyhaemoglobin formation?

A

0.4mmHg PaCO needed to cause progressive carboxyhaemoglobin formation

41
Q

What are the symptoms of CO poisoning?

A
  • Hypoxia & Anaemia
  • Nausea & Headaches
  • Cherry red skin & Mucous membranes
  • Potential brain damage & death
42
Q

What is the main thing that drives ventilation?

A

Getting rid of CO2

43
Q

How many types of hypoxia are there?

A

5

44
Q

Define hypoxia?

A

An inadequate supply of oxygen to tissues

45
Q

What is the most common form of hypoxia?

A

Hypoxic Hypoxia
- Tissue pathology
- Decreased atmospheric PO2
- Reduced O2 diffusion at lungs

46
Q

What is the cause of anaemic hypoxia?

A

Anaemia leads to reduced O2 carrying capacity

47
Q

What is the cause of Ischaemic (stagnant) hypoxia?

A

Heart Pathology
-> Inefficient blood pumping

48
Q

How does histotoxic Hypoxia occur?

A

Tissue Poisoning (e.g. Hydrogen sulphide or cyanide)
-> Cells cant use oxygen thats delivered to them

49
Q

What causes metabolic hypoxia?

A

Tissue Oxygen demand increases
-> Oxygen delivery to tissues doesn’t meet new demands

50
Q

How is CO2 transported in the blood?

A
  • 70% as carbonate in solution
  • 7% in solution alone
  • 23% in RBCs as carbamino compounds (Formed with deoxyhaemoglobin)
51
Q

Whats the equation for how CO2 affects ECF pH?

A

CO2 + H2O ↔ H2CO3 ↔ HCO3 + H+

52
Q

What is carbonate/carbonic acid?

A

Carbonic acid = H2CO3
Carbonate = HCO3

53
Q

Why does plasma pH alter during hypo/hyperventilation?

A

They alter PaCO2, moving the equation and altering [H+]

54
Q

How does hypoventilation affect plasma pH?

A

Hypoventilation
-> CO2 retention
-> [H+] increases
-> Respiratory acidosis

55
Q

How does hyperventilation affect plasma pH?

A

Hyperventilation
-> Blowing off more CO2 than normal
-> [H+] decreases
-> Respiratory Alkalosis

Respiratory (30 decks)

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