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Vasovagal syncope receptor physiology — FRCA Primary MCQ

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EasyPhysiologyVasovagal syncope receptor physiologyFRCA Primary

A fit trainee faints while watching central venous cannulation. Before losing consciousness, he is pale, sweaty and bradycardic with blood pressure 72/38 mmHg. Which receptor mechanism best explains the final cardiovascular response?

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Correct answer: E — Alpha-1 receptor activation in peripheral arterioles

Vasovagal syncope involves increased vagal efferent activity, causing bradycardia through muscarinic receptors in the sinoatrial and atrioventricular nodes. Alpha-1 activation would increase vascular tone rather than produce the collapse described. Beta-1 activation would increase heart rate and contractility. The key point is that the cardioinhibitory component is parasympathetic and muscarinic.

Reference: RCoA Primary FRCA Syllabus 2026; Ganong's Review of Medical Physiology; West's Respiratory Physiology