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Second Year - Biomedical Sciences BS22001 > Lecture 23 - O2 And CO2 Transfer Between Alveolus, Blood And Tissue > Flashcards

Lecture 23 - O2 And CO2 Transfer Between Alveolus, Blood And Tissue Flashcards

1
Q

Where does gas exchange occur

A

Across the blood-gas barrier

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2
Q

Gas exchange across the alveolus occurs by

A

Diffusion

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3
Q

What is Ficks law of diffusion

A

Dt = (Kt)(S)(1/Tnt)

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4
Q

In what to forms is the oxygen transported in blood

A

Physically and chemically

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5
Q

How is oxygen physically transported

A

Plasma soluble oxygen (2%)

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6
Q

Why is there a partial pressure of oxygen in the alveolus

A

As plasma soluble oxygen is less soluble than carbon dioxide

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7
Q

How is oxygen transported chemically

A

By being bound to haemoglobin

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8
Q

What is the interaction between oxygen and Hb like

A

It is rapid and reversible

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9
Q

What does the reversibility of the oxygen-Hb bond allow

A

For oxygen to off-load onto tissues

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10
Q

How is oxygen content determined

A

By the amount of Hb and oygen in the blood

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11
Q

What is oxygen saturation

A

The proportion of oxygen-saturated Hb relative to the total Hb in the blood

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12
Q

What does the P50 value represent

A

The Poxygen required for half the maximal Hb saturation

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13
Q

What pressure does the venous blood enter the alveolus at

A

40mmHg

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14
Q

What doe sthe arterial plateau phase ensure

A

That maximal Hb-oxygen saturation even in alveolar Poxygen is below the normal oxygen level

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15
Q

What does normoxic mean

A

Normal levels of oxygen

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16
Q

What does the steep phase of the oxygen-haemoglobin dissociation curve favour

A

Off-loading of arterial oxygen to tissues

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17
Q

What happens to the Hb-oxygen dissociation for small changes in the tissue Poxygen

A

There is greater Hb-oxygen dissociation

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18
Q

What factors shift the oxyhaemoglobin dissociation curve to the left

A

Foetal Hb

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19
Q

What happens when the oxyhaemoglobin dissociation curve is shifted to the left

A

There is an increased Hb-oxygen affinity and a reduced carbon dioxide off-loading

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20
Q

What factors shift the oxyhaemoglobin dissociation curve to the right

A

Fever, hypoxic glycolysis and the Bohr effect

21
Q

What causes the Bohr effect

A

Acidosis and an increase in Pcarbon dioxide

22
Q

What happens when the oxyhaemoglobin dissociation curve is shifted to the right

A

There is a decreased Hb-oxygen affinity and an increased carbon dioxide off-loading

23
Q

What is Hb

A

A heterotetramer

24
Q

What is Hb composed of

A

2 alpha and 2 beta subunits

25
Q

What does Hb contain

A

4 iron-binding HEME domains

26
Q

Within Hb what is the oxygen bound to

A

The Fe3+ ions in the centre of the HEME ring

27
Q

What alters the affinity of oxygen to Hb

A

Carbon dioxide, pH and 2,3 BPG

28
Q

How do carbon dioxide, pH and 2,3 BPG cause a change in affinity of oxygen to Hb

A

By interacting with the charged amino groups between the alpha and beta subunits

29
Q

What does the amino terminus of the Hb-alpha subunit bind to

A

The carboxy-terminal histidine in the beta subunit

30
Q

The interaction between the Hb-alpha subunit and the carboxy-terminal histidine in the beta subunit is sensitive to what

A

pH and carbon dioxide

31
Q

What happens to interactions during acidosis

A

The decreased pH favours the alpha-beta interaction and reduces the binding of oxygen to the HEME

32
Q

WHat effect does carbon dioxide have

A

It lower blood pH and reduces Hb affinity for oxygen

33
Q

In what two ways does increased Pco2 release o2 from Hb

A

The production of carbonic acid in the red blood cells and the carbamate reaction at the N-terminal amno group of the Hb alpha-subunit

34
Q

What effect does carbon monoxide have on the oxyhaemoglobin curve and why

A

Its afiinity for Hb is 240 times greater than oxygen, it forms carboxyhaemoglobin and causes the curve to shift left which reduces oxygen off-loading

35
Q

What effect does anemia have on the oxyhaemoglobin curve

A

It causes it to shift right as the oxygencapacity is lowered

36
Q

How is carbon dioxide carried physically

A

By plasma soluble carbon dioxide

37
Q

What are the two forms of plasma soluble carbon dioxide

A

Soluble carbon dioxide gas (5%) or the bicarbonate ion (90%)

38
Q

How is carbon dioxide chemically transported

A

through carbamino haemoglobin (5%)

39
Q

What is the carbon dioxide dissociation curve altered by

A

Tissue oxygenation

40
Q

What improves the carriage of carbon dioxide

A

The deoxygenation of blood

41
Q

What effect is tissue oxygenation

A

The Haldane effect

42
Q

What do the Bohr and Haldane effects enable

A

Reciprocal oxygen and carbon dioxide gas exchange

43
Q

What defines the ventilation:perfusion relationship in the lung

A

Oxygen and carbon dioxide

44
Q

Where does the oxygen equilibriate from

A

The alveolus to the blood

45
Q

Where does the carbon dioxide equilibriate from

A

The blood to the alveolus

46
Q

What allows fine tuning of oxygen uptake and carbon dioxide clearing

A

Breathing and lung-perfusion

47
Q

in what situation is the fine tuning of oxygen uptake and carbon dioxide clearing needed

A

High altitude mountaineering, tolerance of G-force and external pressure (diving)

48
Q

Equation to calculate alveolar Poxygen

A

pAoxygen = F1oxygen(pATM-SVP)-pAcardon dioxide(F1oxygen + (1-F1oxygen)/RQ))

Second Year - Biomedical Sciences BS22001 (28 decks)

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