Lecture 12: Perfusion of the lung Flashcards
Where is perfusion greatest in the lung?
Perfusion is greatest at the base of the lung
What is the average pulmonary pressure?
14mmHg
- Pressure drops across the pulm. art to an arou nd 5mmHg in pulm. cap
What are some notes about lung circulation?
2 systems
- High pressure bronchial -> drains into left heart (never 100% oxygenated when ejected then)
- Pulmonary circuit
Describe capillaries of pulmonary circuit?
Not in tubes, they are wall structures giving a sheet like structure for cap. exchange.
Pillars support these walls.
Keeps walls thin and maximises exchange
How is pulmonary circulation controlled?
1) Physical factors affecting blood flow
2) Chemical control of pulmonary blood vessels
3) Autonomic control of pulmonary arterioles
What are the physical factors affecting blood flow?
Lungs can hold a lot of blood because of distension and recruitment of additional pulm. vessels (prevents oedema)
BUT
Conversely resistance decreases as pressure increases
Why is alveolar blood flow resistance U-shaped?
Total pulmonary vascular resistance is u shaped. It is produced by the total of alveolar and extra-alveolar resistance.
Low inflated lungs have high extra alveolar resistance provided by vessel resistance and alveolar contribution is low.
As lung volume increases, alveolar resistance increases but extra-alveolar resistance decreases (the inflated alveoli must crush vessels and drive vasodilation?).
U-Shaped because of this (total resistance)
Describe the chemical control of pulmonary blood vessels:
- Broncho agitation
= Decreased PO2 = Hypoxia
This results in a regional vasoconstriction to redirect blood to better oxygenated alveoli.
i.e If alveoli cant oxygenate blood then redirect blood flow.
(Opposite to systemic where hypoxia dilates)
What drives pulmonary vasoconstriction:
Vasoconstriction
1) Hypercapnia
2) Decreased pH
3) ANG 2
4) Adenosine
What drives pulmonary vasodilation
1) Bradykinin
2) Histamine
3) Vasopressin
All endothelium dependent and mediated by NO
What drives pulmonary hypertension?
Endothelial dysfunction and lack of NO
Describe the autonomic control of pulmonary arterioles;
1) Symp innervation
- Vasocon
- Reduce pulm. blood flow by 30%
2) Muscarinic
- Vasodilation
- M3 receptor, depend on endothelium
Wheres the highest blood flow in the lung?
At the base
What drives the un-even blood flow?
Alveoli at the top of the lung are large and have less capillary density
Alveoli are smaller at the base and have a higher cap. density therefore higher blood flow
THIS IS THANKS TO GRAVITY (also pressure gradient)
What is good about the un-even blood flow?
Built in capacity so that the apex of the lung can increase perfusion during exercise.
