Determinants of pulmonary blood flow

Question 1

What is a major factor determining pulmonary blood flow?

Answer 1

posture

Question 2

How does posture affect pulmonary blood flow?

Answer 2

Upper regions of the lung:

• decreased hydrostatic pressure
• the vessels partially collapse
• this increases resistance
• this decreases blood flow

Lower regions of the lung:

• increased hydrostatic pressure
• the vessels distend
• this decreases resistance
• this increases blood flow

Question 3

How does hypoxia regulate pulmonary blood flow?

Answer 3

If there is hypoxia in the lungs then the blood will be diverted away from these poorly ventilated alveoli. This means that hypoxia causes vasoconstriction

Question 4

What are 5 things that control pulmonary blood flow?

Answer 4

• posture
• hypoxia
• endothelin1
• NO
• SNS regulation

Question 5

What is the effect of NO on pulmonary circulation? Is this an intrinsic or extrinsic control?

Answer 5

intrinsic control
No is released from the endothelium and this relaxes smooth muscle, causing vasodilation so there is decreased resistance and increased blood flow

Question 6

What is the effect of endothelin-1 on pulmonary blood flow? Is this an intrinsic or extrinsic control?

Answer 6

Intrinsic control
Endothelin-1 is released from the endothelium. This causes a contraction of the smooth muscle cells and so there is vasoconstriction. This increases the resistance and there is decreased blood flow

Question 7

What is the effect of SNS control of pulmonary blood flow?

Answer 7

Adrenaline is released from the sympathetic nerve fibres and it can bind to the α1-adrenoreceptors which causes vasoconstriction (eg. is the right and left pulmonary artery). This increases resistance and increases pulmonary pressure.
It can also bind to β2 adrenoreceptors which causes vasodilation. This decreases the resistance and decreases the pulmonary pressure. This normally happens in the smaller resistance vessels

Question 8

Give an example of when activation of β2 adrenoreceptors would be needed

Answer 8

If you go up a mountain, there is generalised hypoxia which causes activation of the SNS and there is activation of the β2-adrenoreceptors and this causes vasodilation (to overcome the hypoxic vasoconstriction)