The lung’s own low-pressure circuit: why it carries the whole cardiac output at a tenth of the systemic resistance, why gravity makes the base of the lung wetter than the apex, and what happens when ventilation and perfusion stop matching. Long essays are rarely set from this chapter, but short notes and viva come from it constantly: special features of pulmonary circulation, factors affecting and regulating pulmonary blood flow, pulmonary edema, drowning, and above all the ventilation-perfusion ratio.
Topics, in the book’s order
- Pulmonary circulation · pp. 914–920 · asked once
- Pulmonary edema and drowning · p. 918
- Ventilation–perfusion ratio · pp. 918–920 · asked 3 times
When you’ve read them: Quiz 106 · Pulmonary Circulation and Ventilation-Perfusion Ratio, 15 questions.
After this chapter you should be able to
- describe how blood is arranged around the alveoli, and list what makes pulmonary circulation special
- list the factors that affect pulmonary blood flow
- explain why perfusion differs between Zone 1, Zone 2 and Zone 3 of the lung
- explain how fluid is filtered across pulmonary capillaries, and how pulmonary edema develops
- explain why the ventilation-perfusion ratio matters for lung function
- explain why the ratio differs between apex and base, and what that means physiologically and clinically
- describe the bronchial circulation and its physiological role
Viva checklist
- Functions of the pulmonary circulation, all four
- Special features of pulmonary circulation; mean pulmonary arterial pressure
- Physiological significance of a low pulmonary vascular resistance; capillary recruitment and distension
- Volume of blood in the pulmonary circuit, and its split between arteries, veins and capillaries
- Factors affecting pulmonary blood flow and pulmonary vascular resistance; why resistance is lowest at FRC
- Effect of gravity: the three zones, and the waterfall effect
- Active versus passive regulation of pulmonary blood flow
- Names of pulmonary vasoconstrictors and vasodilators
- Hypoxic pulmonary vasoconstriction, and how it differs from systemic hypoxia
- Forces governing filtration across pulmonary capillaries; the role of surface tension and of lymphatics
- Causes of pulmonary edema, its effects on the lung, and the basis of its treatment
- Fresh-water versus salt-water drowning: cause of death in each
- Normal ventilation-perfusion ratio, and its values at apex and base
- Anatomical shunt, physiological shunt and venous admixture