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Respiratory: Physiology > Gas transport in the blood > Flashcards

Gas transport in the blood Flashcards

1
Q

Where must O2 picked up by the blood be transported?

A

Must be transported via blood to tissues for cellular use

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2
Q

Where must CO2 produced in tissues be transported?

A

Must be transported via blood to lungs for removal from the body

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3
Q

What is the partial pressure of oxygen in the atmosphere?

A

21 kPa (160 mm Hg)

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4
Q

What I the partial pressure of O2 in alveolar air?

A

13.3 kPa (100 mm Hg)

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5
Q

What is Henry’s Law?

A

The amount of a given gas dissolved in a given type and volume of liquid
(e.g. blood) at a constant
temperature is: proportional to the partial pressure
of the gas in equilibrium with the liquid

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6
Q

What is the effect of partial pressure on gas solubility according to Henry’s Law?

A

If the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionally

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7
Q

What is the partial pressure of a gas in solution?

A

Its partial pressure in the gas mixture (gas phase) with which it is in equilibrium

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8
Q

Describe relationship between partial pressure and amount of oxygen dissolved in the blood with regard to Henry’s Law

A

The O2 amount dissolved in blood is proportional to the partial pressure

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9
Q

How much oxygen is dissolved in the blood at a Po2 of 13.3 kPa?

A

3ml O2 per litre of blood

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10
Q

How much O2 is delivered to tissues as dissolved O2 under resting conditions?

A

15ml/min (cardiac output is 5 L/min)

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11
Q

How much O2 is delivered to tissues as dissolved O2 during strenuous exercise?

A

90ml/min (cardiac output is 30 L/min)

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12
Q

What is resting consumption of O2 of body cells?

A

250ml/min

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13
Q

How much does O2 consumption increase with exercise?

A

25 folds

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14
Q

How is 250ml/min of O2 delivered to cells when only 15ml/min of dissolved O2 is carried in blood?

A

Most O2 in the blood is transported bound to haemoglobin in the red blood cells

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15
Q

What is normal O2 concentration in arterial blood (at a normal arterial Po2 of 13.3 kPa)?

A

200 ml/L

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16
Q

What is the normal concentration of haemoglobin in the blood?

A

150 g/L

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17
Q

What is the percentage of O2 bound to haemoglobin?

A

98.5%

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18
Q

What is the percentage of O2 carried in the dissolved form in blood?

A

1.5%

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19
Q

What are the 2 forms of oxygen present in the blood?

A
  • Bound to haemoglobin

* Physically dissolved (very little O2)

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20
Q

Why is oxygen binding to haemoglobin reversible?

A

To allow release of O2 into tissues

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21
Q

How many haem groups does a haemoglobin molecule have?

A

4

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22
Q

How many O2 molecules does each haem group reversibly bind with?

A

1 each

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23
Q

When is haemoglobin considered fully saturated?

A

When all the Hb present is carrying its maximum O2 load

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24
Q

What is the primary factor that determines the percent saturation of haemoglobin with O2?
i.e. binding of oxygen to haemoglobin

A

The partial oxygen pressure (Po2)

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25
Q

What is the effect of increasing Po2 on haemoglobin saturation?

A

Increases haemoglobin saturation

26
Q

What is the saturation of of haemoglobin at a Po2 of 13.3 kPa in the blood?

A

Almost 100% saturation

27
Q

What is the relationship between haemoglobin concentration and Hb saturation?

A

Hb concentration has no effect on Hb saturation - Po2 is the determining factor

200 g/L will carry more oxygen than 100 g/L but haemoglobin saturation will remain the same

28
Q

What is the Oxygen Delivery Index used to measure?

A

Oxygen delivery to the tissues

29
Q

What is the equation for Oxygen Delivery Index (DO2I)?

A

DO2I = CaO2 x CI

CaO2 = Oxygen content of arterial blood (ml/L)
CI = Cardiac index (L/min/metre^*2)
30
Q

What is Cardiac Index?

A

Relates the cardiac output to the body surface area (i.e. size of the individual)

31
Q

What is the normal range for Cardiac Index?

A

2.4 - 4.2 L/min/metre^*2

32
Q

What are the units for Oxygen Delivery Index?

A

ml/min/metre^*2

33
Q

What 2 factors does oxygen delivery to tissues (Oxygen Delivery Index) depend on?

A
  • Oxygen content of arterial blood (CaO2)

* The cardiac output (Cardiac Index)

34
Q

What 2 factors is O2 content of arterial blood determined by?

A
  • Haemoglobin concentration [Hb]

* Saturation of Hb with O2

35
Q

What is the equation for O2 content of arterial blood (CaO2)?

A

CaO2 = 1.34 x [Hb] x SaO2

[Hb] = haemoglobin concentration (gram/L)
SaO2 = %Hb saturated with O2 (determined by Po2)
1.34 = 1 gram of Hb carries 1.34 ml of O2 when fully saturated
36
Q

What are the 3 factors oxygen delivery to tissues (DO2I) can be impaired by?

A
  • Respiratory disease
  • Heart failure
  • Anaemia
37
Q

How does respiratory disease impair oxygen delivery to tissues?

A

Decreases arterial PO2 and thus, decreases Hb saturation with O2 and O2 content of the blood

38
Q

How does anaemia impair oxygen delivery to tissues?

A

Decreases Hb concentration and thus decreases O2 content of the blood

39
Q

How does heart failure impair oxygen delivery to tissues?

A

Decreases the cardiac output (Cardiac Index)

40
Q

What does partial pressure of inspired oxygen (PO2) depend on?

A
  • Total pressure (e.g. atmospheric pressure)

* Proportion of oxygen in gas mixture (21% in atmosphere)

41
Q

What is normal atmospheric pressure at sea level?

A

760 mm Hg (101 kPa)

42
Q

Does myoglobin show co-operativity?

A

No, but haemoglobin does

43
Q

What does binding of O2 to one haemoglobin subunit mean for the remaining subunits?

A

It increases the affinity of the remaining subunits for O2

44
Q

What curve is produced by oxygen binding to haemoglobin?

A

Sigmoid curve

45
Q

What happens to the curve once binding sites are occupied?

A

It flattens

46
Q

What do flat upper portions of the sigmoid curve mean?

A

Moderate fall in alveolar Po2 will not affect oxygen loading

Until Po2 falls to 8.0 kPa (which will not happen unless serious respiratory disease), Hb will almost be fully saturated

47
Q

What does the steep lower part of the sigmoid curve mean?

A

Peripheral tissues get a lot of oxygen for a small drop in capillary Po2

48
Q

What is the Bohr Effect?

A

Increased release of O2 by conditions at the tissues

49
Q

What causes release of O2 into tissues with regard to Bohr Effect?

A
  • Increased PCO2
  • Increased [H+]
  • Increased temperature
  • Increased 2,3-Biphosphoglycerate

All released from metabolically active cells (cells that require more oxygen)

50
Q

How does the Bohr Effect facilitate the release of oxygen to tissues?

A

Shifting oxygen dissociation curve to the right - more O2 released by curve when PO2 drops in tissue conditions than in arterial conditions (curve not shifted to right)

51
Q

How does foetal haemoglobin differ from adult haemoglobin?

A

Structure: -

  • HbF has 2 alpha and and 2 gamma subunits
  • Adult Hb has 2 alpha and 2 beta subunits
52
Q

Why does HbF have a higher affinity for O2 than Hb?

A

It interacts less with 2,3-Biphosphoglycerate in red blood cells

53
Q

What does the O2-Hb dissociation curve look like for HbF?

A

It has shifted to the left compared to adult Hb

54
Q

Why is higher oxygen affinity advantageous for the foetus?

A

It allows O2 to transfer from mother to foetus even if the PO2 is low

(More affinity for oxygen than mother’s haemoglobin)

55
Q

Where is myoglobin found?

A

Present in skeletal and cardiac muscles

56
Q

How many haem groups does myoglobin have?

A

1 haem group per molecule

57
Q

What does the dissociation curve for myoglobin look like?

A

Hyperbolic curve - not sigmoid

58
Q

Why is myoglobin not the primary means of transport for oxygen to tissues?

A

It only releases O2 at a very low PO2

59
Q

What is the function of myoglobin?

A

It provides a short-term storage of O2 in anaerobic conditions (e.g. exercise)

60
Q

What does presence of myoglobin in the blood indicate?

A

Indicates muscle damage

Respiratory: Physiology (6 decks)

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