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Respiratory > Pulmonary blood flow and gas exchange > Flashcards

Pulmonary blood flow and gas exchange Flashcards

1
Q

Describe the blood supply to the lungs

A

Pulmonary circulation:

  • Left and right pulmonary arteries from right ventricle of heart
  • Branches into capillaries which are involved in gas exchange

Bronchial circulation:

  • Bronchial circulation supplies the smooth muscle, nerves and lung tissue
  • Part of the systemic circulation
  • These are not involved with gas exchange
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2
Q

How does the pressure inside the pulmonary circulation compare to that of the systemic circulation?

A

Low pressure

High flow

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3
Q

In a perfect scenario, the pO2 and pCO2 in arterial blood should be equal to…

A

Alveolar pO2 and pCO2

O2 and CO2 diffuse down PP gradients, until the pp is the same on both sides

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4
Q

In a perfect scenario, the pO2 and pCO2 in venous blood should be equal to….

A

The pO2 and pCO2 in the tissues

same reason as the other question

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5
Q

What is the normal value for alveolar pO2

A

100 mmHg

13.3 kPa

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6
Q

What is the normal value for arterial pCO2?

A

40 mmHg

5.3 kPa

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7
Q

What is a normal value for venous pCO2?

A

46 mmHg

6.2 kPa

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8
Q

What 4 factors determine the rate of diffusion across a membrane?

A

Partial pressure gradient - proportional

Gas solubility - proportional

Surface area - proportional

Thickness of membrane - inversely proportional

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9
Q

Why is CO2 much better at diffusing across membranes than O2?

A

CO2 is much more soluble

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10
Q

Describe a pathology which affects surface area, for exchange, in the lungs

A

Emphysema

Type of COPD which causes destruction of alveoli

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11
Q

Describe 2 pathologies which affect the thickness of the membranes over which gas is exchanged

A

Fibrotic lung disease (fibrosis) - thickening of alveolar membranes due to scarring

Pulmonary oedema - fluid build up in interstitial space

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12
Q

Pulmonary oedema often has a larger effect on oxygen exchange than carbon dioxide exchange

Why is this?

A

Fluid build up largely consists of water

CO2 relatively soluble in water so can still diffuse(ish) whereas O2 can not

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13
Q

Explain where blood flow highest in the lungs

A

At the base

  • Arterial pressure exceeds alveolar pressure. This compresses the alveoli
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14
Q

Where is ventilation highest in the lungs?

A

At the base

however blood flow is greater

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15
Q

Explain why there is an imbalance in blood flow - ventilation at the apex of the lungs

A

Arterial pressure is greater than alveolar pressure

Alveoli are therefore compressed

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16
Q

At what rib number is ventilation and perfusion matched?

A

3

(although when youre upright, gravity and shit means about 75% of your lung has pretty much matched ventilation - perfusion)

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17
Q

What is shunt?

A

The dilution of oxygenated blood from better ventilated areas, with poorly oxygenated blood from poorly ventilated areas

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18
Q

How does the body react to shunt?

A

Decreased tissue pO2 around under-ventilated alveoli causes vasoconstriction

Blood is redirected to better ventilated areas

19
Q

How is the bodies reaction to shunt, different from other hypoxia induced responses?

A

In the systemic circulation, hypoxia causes vasodilation

In pulmonary circulation, hypoxia (shunt) causes constriction

20
Q

What is ‘alveolar dead space’?

A

When blood flow is too low

ventilation > blood flow

21
Q

How does the pulmonary circulation respond to alveolar dead space?

A

Increased alveolar pO2 causes vasodilation to increase blood flow

Decreased alveolar pCO2 causes mild bronchial constriction

22
Q

What 2 components make up physiological dead space?

A

Anatomical dead space

+

Alveolar dead space

23
Q

Describe how oxygen and carbon dioxide are transported in the blood

A

Oxygen:

  • Haemoglobin
  • Small amount dissolved in plasma

Carbon dioxide:

  • dissolved in plasma
  • carbonic acid (in RBCs)
  • carbamino compounds
24
Q

What is the carrying capacity of Haemoglobin for oxygen?

A

200 ml/L

25
Q

What is the carrying capacity of PLASMA for oxygen?

A

3 ml/L

26
Q

At rest, what is the max amount of oxygen that can be pumped around the body per minute?

A

Cardiac output = 5 L/min

Max capacity = 200 ml/L

5 x 200 = 1000 ml/min

27
Q

What is the normal demand for O2, of resting tissues?

A

250 ml/min

28
Q

Describe the different types of haemoglobin found in red blood cells

A

HbA - 92% abundant

HbA2

HbF

Glycosylated Hb

29
Q

Haemoglobin binds to oxygen that has diffused into the pulmonary circulation

This maintains a high rate of diffusion across the membrane, how?

A

Haemoglobin takes up the oxygen, so the partial pressure gradient remains high

High PP gradient means rate of diffusion remains high

30
Q

Aside from the effect created by haemoglobin binding to oxygen, what else maintains a high partial pressure gradient between the alveoli and blood?

A

High blood flow

Oxygenated blood is quickly replaced with new de-oxygenated blood

31
Q

How saturated is haemoglobin at normal venous partial pressures of oxygen?

How is this helpful for reducing hypoxia?

A

At pO2 of 40 mmHg, Haemoglobin is still 75% saturated

75% reserves of oxygen can be unloaded to tissues if needed - stops hypoxia

32
Q

Explain why foetal haemoglobin (HbF) differs from HbA?

A

They have a higher affinity for O2 than HbA

This is necessary so a foetus can extract oxygen from maternal blood at the placenta

33
Q

What is anaemia?

A

any condition where the oxygen carrying capacity of the blood is compromised

34
Q

Aside from the partial pressure of oxygen, other factors affect the affinity of Haemoglobin for oxygen

What would cause a decrease in affinity?

A

Decrease in pH

Increase in pCO2 (this would cause a decrease in pH)

Increase in temperature

2,3-disphosphoglycerate production

35
Q

What is the purpose of 2,3-diphosphoglycerate?

A

2,3-DPG is synthesised by erythrocytes

If inadequate supply of O2 (hypoxia)

By decreasing affinity, stimulates unloading of O2 to hypoxic tissues

36
Q

Why is Carbon monoxide shit for you

A

CO binds to haemoglobin to form carboxyhaemoglobin

Higher affinity than O2

Causes a bunch of problems

37
Q

What is hypoxia?

A

Inadequate supply of oxygen to tissues

38
Q

What are the 5 causes of hypoxia?

A

Hypoxaemic hypoxia

Anaemic hypoxia

Stagnant hypoxia

Histotoxic hypoxia

Metabolic hypoxia

39
Q

What is hypoxaemic hypoxia?

A

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

40
Q

What is anaemic hypoxia?

A

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

41
Q

What is stagnant hypoxia?

A

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

42
Q

What is histotoxic hypoxia?

A

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

43
Q

What is metabollic hypoxia?

A

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

44
Q

How would hypoventilation affect the pH of the blood?

CO2

A

Hypoventilation = CO2 retention

CO2 forms carbonic acid

Carbonic acid = higher [H+]

Decrease in pH = respiratory acidosis

Respiratory (32 decks)

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