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Renal autoregulation under anaesthesia — FRCA Primary MCQ

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HardPhysiologyRenal autoregulation under anaesthesiaFRCA Primary

A 62-year-old patient with chronic hypertension bleeds during surgery. Mean arterial pressure falls from 105 to 58 mmHg and urine output drops. Which mechanism normally maintains glomerular filtration over moderate pressure changes?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — ADH-mediated water retention in collecting ducts

Renal autoregulation maintains renal blood flow and GFR through myogenic afferent arteriolar responses and tubuloglomerular feedback. ADH changes water handling but does not primarily maintain GFR over acute pressure changes. Severe hypotension or chronic hypertension can move the patient outside the autoregulatory range. The teaching point is that urine output is a late and imperfect marker of renal perfusion.

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