Peripheral Chemoreceptors — FRCA Primary MCQ
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Correct answer: C — Carotid bodies lie near the carotid bifurcations and are the dominant peripheral sensors of reduced PaO2.
Explanation lettering: B = shown as A · D = shown as B · A = shown as C · C = shown as D
A is correct. The carotid bodies, situated near the bifurcations of the common carotid arteries, provide the dominant peripheral chemoreceptor response to a reduction in arterial PO2. They also respond to increased PaCO2 and reduced arterial pH. They sense PO2 rather than arterial oxygen content, so anaemia may markedly reduce oxygen content without directly stimulating them if PaO2 remains normal. Carotid-body afferents pass through the carotid sinus nerve of Hering and then the glossopharyngeal nerve (CN IX). Aortic-body afferents instead travel through the vagus nerve (CN X). In humans, bilateral carotid chemoreceptor denervation abolishes the normal normocapnic ventilatory response to acute hypoxia rather than leaving it intact.
Reference: Iturriaga R, Alcayaga J, Chapleau MW, Somers VK. Carotid body chemoreceptors: physiology, pathology, and implications for health and disease. Physiological Reviews. 2021;101:1177–1235. https://pubmed.ncbi.nlm.nih.gov/33570461/