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Respiratory block > Gas transport in blood > Flashcards

Gas transport in blood Flashcards

1
Q

How does O2 travel ?

A

In solution in plasma

Bound to haemoglobin protein in RBCs

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2
Q

How much oxygen dissolves in plasma per litre ?

A

3ml

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3
Q

What is oxygen carrying capacity in the blood with the help of haemoglobin ?

A

200ml O2 per whole blood, 197ml of which is bound to haemoglobin in RBCs

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4
Q

What % of CO2 is transported in solution in plasma ?

A

77%

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5
Q

What % of CO2 is stored within haemoglobin ?

A

23%

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6
Q

What does each molecule of haemoglobin contain ?

A

4 haem groups, each of which contains one Fe2+ which binds one O2 molecule, so each haemoglobin binds 4 molecules of O2

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7
Q

Partial pressure of O2 in

A
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8
Q

Partial pressure of O2 in alveoli is determined by what ?

A

Alveolar ventilation

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9
Q

what is the amount of O2 that is in solution in plasma determined by ?

A

Partial pressure of O2 in alveoli

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10
Q

What is the amount of O2 carried in haemoglobin determined by ?

A

the amount of O2 that is in plasma- determined by partial pressure of O2 in plasma

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11
Q

What is the relationship between haemoglobin and plasma O2 ?

A

Hb effectively sequesters O2 from the plasma Partial pressure gradient is maintained - continues to suck O2 out of the alveoli until haemoglobin becomes saturated with O2

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12
Q

How long does it take for haemoglobin to become saturated?

A

0.25 seconds

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13
Q

What is total contact time with alveoli ?

A

0.75 seconds

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14
Q

Is there a small or large drop in haemoglobin saturation when alveolar PO2 is reduced ?

A

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

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15
Q

What happens to haemoglobin at normal systemic PaO2 of 100mmHg ?

A

Almost 100% saturated

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16
Q

What happens to haemoglobin at PaO2 of 60mmHg ?

A

Still 90% saturated with O2

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17
Q

What factors affect the affinity of haemoglobin to oxygen ?

A

pH- decrease in pH, makes ECF more acidic, curve shifts to right

PCO2- increase, curve shifts to the right

Temperature- increase, curve shifts to right

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18
Q

What is the Bohr effect ?

A

Shift of haemoglobin binding curve to the right

Higher PO2 needed for the same saturation

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19
Q

What other factors affect the curve ?

A

The affinity of haemoglobin for oxygen is decreased by a decrease in pH, or and increase in PCO2, or temperature. These conditions exist locally in actively metabolising tissues and facilitate the dissociation of oxygen from haemoglobin.

Conversely a rise in pH or a fall in PCO2, or temperature increases the affinity of haemoglobin for oxygen. These conditions make oxygen unloading more difficult but aid collection of oxygen in the pulmonary circulation.

The affinity of haemoglobin for oxygen is decreased by binding 2,3-diphosphoglycerate (2,3-DPG)

20
Q

What synthesises DPG ?

A

Erythrocytes

21
Q

When does production of 2,3 - DPG increase ?

A

When there is inadequate oxygen supply (heart or lung disease) and helps maintain oxygen release in the tissues. (Increasing affinity therefore decreases affinity for oxygen, making release more likely)

22
Q

What is the purpose of the factors that alter the saturation of haemoglobin ?

A

Reflect conditions found in actively metabolising tissues and act to facilitate the dissociation of oxygen from haemoglobin. OR Can act to aid the collection of oxygen in the pulmonary circulation

23
Q

How is carboxyhaemoglobin made ?

A

CO binds to haemoglobin

24
Q

Which has higher affinity O2 or CO ?

A

CO - 250 times greater

25
Q

What are the symptoms of carboxyhaemoglobin ?

A

Hypoxia and anaemia, nausea and headaches Cherry red skin and mucous membranes, potential brain damage and death

26
Q

Why does breathing rate stay normal even when there is carboxyhaemoglobin ?

A

Normal arterial PCO2

27
Q

What is the fate of the carbon dioxide that diffuses from tissue to blood ?

A

7% remains dissolved in the plasma and erythrocytes, 23% combines with deoxyhaemoglobin to form carbamino compounds 70% combines in erythrocytes with water to form carbonic acid

28
Q

What is the fate of carbonic acid formed by carbon dioxide and water ?

A

Dissociates to yield bicarbonate and H+ ions Most of the bicarbonate then moves out of the erythrocytes into the plasma in exchange for Cl- ions (chloride shift) & the excess H+ ions bind to deoxyhaemoglobin. The reverse occurs in the pulmonary capillaries and CO2 moves down its concentration gradient from blood to alveoli

29
Q

Is arterial partial pressure of O2 the same as arterial 02 content ?

A

No, Arterial partial pressure refers to the O2 in solution and is determined by the O2 solubility and the partial pressure of the O2 in the gaseous phase that is driving O2 into solution

30
Q

What is the partial pressure of a gas in solution equal to ?

A

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

31
Q

What is O2 solubility in water ?

A

LOW 0.03ml/L/mmHg

32
Q

PO2 in solution is said to be ?

A

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

33
Q

How does fatal air embolism occur ?

A

Bubbles in the blood Gases travelling in the gaseous phase in the plasma

34
Q

What is average cardiac output ?

A

5L/min

35
Q

What is 02 demand of resting tissues ?

A

250ml/min

36
Q

How much oxygen can a gram of haemoglobin carry ?

A

1.34ml

37
Q

What is the concentration of haemoglobin in the blood ?

A

150g/L

38
Q

How much arterial O2 is extracted by peripheral tissues at rest ?

A

25%, 1000 ml/min O2 transport far greater than the 250 ml/min demand

39
Q

What form does 92% of haemoglobin take?

A

HbA

40
Q

Describe the types of haemoglobin that comprise 8% of total haemoglobin ?

A

HbA2 (δ chains replace β), HbF (γ chains replace β), and glycosylated Hb (HbA1a, HbA1b, HbA1c)

41
Q

What stores oxygen in muscle cells ?

A

Myoglobin - high content in oxidative muscle fibres

42
Q

What is the function of foetal haemoglobin ?

A

Pulls oxygen from adult haemoglobin and delivers it to the foetus

43
Q

What is hypoxemic hypoxia ?

A

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

44
Q

What is anaemic hypoxia ?

A

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

45
Q

What is Ischaemic (stagnant) hypoxia ?

A

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

46
Q

What is histotoxic hypoxia ?

A

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

47
Q

What is metabolic hypoxia ?

A

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

Respiratory block (38 decks)

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