Explain the detection and response to hypoxaemia.
A logical approach to answering this question included a definition of hypoxaemia and then a discussion of the sensors, integrators and effectors involved. It was expected that candidates would cover the peripheral chemoreceptor response (including the respiratory, cardiovascular and autonomic effects), time course of the ventilatory response, hypoxia-inducible factors, vascular effects (hypoxic vasoconstriction in the pulmonary circulation and vasodilatation in the systemic circulation) and metabolic changes (switch to anaerobic metabolism). No marks were awarded for discussing the causes of hypoxaemia. Many candidates incorrectly stated that hypoxaemia is detected by the central chemoreceptors.