A patient receiving cisplatin develops severe nausea and vomiting despite having an intact gastrointestinal tract. The chemoreceptor trigger zone responsible for this response lies in the area postrema, which is unusual among CNS regions because:

• A It lies outside the dura mater within the subarachnoid space
• B It receives its blood supply from the vertebral arteries rather than the carotid circulation
• C Its neurons are myelinated by oligodendrocytes rather than Schwann cells
• D Its capillary endothelium is fenestrated and lacks a functional blood-brain barrier ✓

Explanation

The circumventricular organs, including the area postrema, organum vasculosum of the lamina terminalis and median eminence, have fenestrated capillaries that lack tight junctions, so circulating chemicals can act on their neurons. This is why systemic emetogenic drugs trigger vomiting from the chemoreceptor trigger zone. Option B is wrong because all these structures share the standard vertebrobasilar supply territory of the medulla and hypothalamus; the defining feature is barrier absence, not arterial source.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.