PhysiologyTier 1Medical Sciences concept

Renal blood flow autoregulation - mechanism and site

Core concept

  • RBF and GFR held near-constant across a MAP of ~80-180 mmHg - intrinsic to the kidney (persists in a denervated, isolated organ)
  • Two mechanisms, both acting on the AFFERENT arteriole
    • 1. Myogenic reflex - fast (1-2 s)
      • inc wall stretch -> vascular smooth muscle depolarisation -> Ca influx -> afferent constriction
      • Contributes ~50% of autoregulation
    • 2. Tubuloglomerular feedback (TGF) - slower (10-60 s)
      • inc GFR -> inc NaCl delivery to the macula densa -> uptake via NKCC2
      • -> ATP/adenosine release -> A1 receptor -> afferent CONSTRICTION -> dec GFR
      • Simultaneously dec renin release (and the converse when NaCl delivery falls)
    • A third, slower arm: RAAS-mediated efferent constriction preserves GFR when perfusion falls below the autoregulatory range
  • -> the afferent arteriole controls flow; the efferent arteriole controls filtration fraction

3 more sections, plus exam facts

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