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JGA Anatomy — FRCA Primary MCQ

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HardPhysiology - RenalJGA AnatomyFRCA Primary

Macula-densa cells sense persistently low NaCl delivery in the distal nephron of an otherwise intact kidney. Which immediate local response best supports restoration of glomerular filtration?

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Correct answer: A — Reduced adenosine signalling, afferent dilatation and increased renin release

The best answer is “Reduced adenosine signalling, afferent dilatation and increased renin release”. Low macula-densa NaCl reduces ATP/adenosine-mediated afferent constrictor tone, allowing relative afferent dilatation, and stimulates renin release from juxtaglomerular granular cells. The resulting renin–angiotensin response helps preserve filtration pressure. High distal NaCl produces the opposite adenosine-mediated afferent constriction. Macula densa does not directly secrete aldosterone or erythropoietin.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Renal physiology of glucose handling and therapeutic implications: https://pmc.ncbi.nlm.nih.gov/articles/PMC6993194/