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Area Postrema No BBB — FRCA Primary MCQ

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HardPhysiology - NeurophysiologyArea Postrema No BBBFRCA Primary

A hydrophilic emetogenic drug poorly penetrates an intact blood–brain barrier yet causes vomiting. Which structure can detect circulating emetogenic signals because it lies outside the typical barrier?

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Correct answer: E — Area postrema at the caudal fourth-ventricle floor

The best answer is “Area postrema at the caudal fourth-ventricle floor”. The area postrema is a circumventricular structure at the caudal fourth-ventricle floor with permeable capillaries, enabling detection of circulating toxins and emetogenic drugs. It contributes to the chemoreceptor-trigger zone. The cortex, hippocampus, internal capsule and superior colliculus are protected by the usual blood–brain barrier and do not have this specialised humoral-sensing role.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Mechanisms of Nausea and Vomiting: https://pmc.ncbi.nlm.nih.gov/articles/PMC8198651/