Alveolus

In the syllabus and the exam

The alveolus sits at the centre of the gaseous exchange content standard, where structure-function questions ask candidates to link its features, namely a wall one cell thick, a moist lining, a huge total surface area from millions of air sacs, and a surrounding capillary network, to an efficient rate of diffusion. A very common exam format gives a diagram of the alveolus and capillary and asks candidates to label structures, state the direction of oxygen and carbon dioxide movement, and explain how each named feature increases the efficiency of gaseous exchange, so answers must pair a feature with its functional reason rather than listing features alone. Candidates sometimes confuse the alveolus with the whole lung or with a bronchiole; the alveolus specifically refers to the individual air sac where actual exchange with blood happens, not the airways that merely conduct air towards it.

Example

Each alveolus is surrounded by a dense network of capillaries so that oxygen can diffuse into the blood as soon as it reaches the lungs.

Related terms

Gaseous exchangeTracheaDiaphragm

Source:SRC-DSKP-EN