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Baroreceptor reflex haemorrhage — FRCA Primary MCQ

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HardPhysiologyBaroreceptor reflex haemorrhageFRCA Primary

A patient loses 900 mL of blood during laparotomy. Before vasopressors are given, heart rate rises and peripheral vasoconstriction is evident. Which reflex pathway is most responsible?

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Correct answer: E — Reduced carotid sinus firing increases sympathetic outflow

Acute blood loss reduces arterial stretch, decreasing carotid sinus and aortic baroreceptor firing, which increases sympathetic outflow and reduces vagal tone. Increased baroreceptor firing would occur with hypertension and would slow the heart. Atrial stretch is reduced in haemorrhage, favouring rather than suppressing vasopressin. The baroreflex is rapid but may be overwhelmed by continuing bleeding and anaesthetic vasodilatation.

Reference: Ganong Review of Medical Physiology