According to myogenic hypothesis of renal autoregulation, the afferent arterioles contract in response to stretch induced by

Stretch on smooth muscle (afferent  arterioles) opens Ca+ channel, which causes contraction of afferent arterioles.the medullary interstitium. REGULATION OF GFR Regulation is done by: Blood pressure: Autoregulation Resistance of afferent and efferent anterioles - Autoregulation: Constant maintenance of renal blood flow or, GFR over the span of renal perfusion pressure (pressure in renal artery minus pressure in renal vein ) from 80 to about 170mm Hg - Mechanism of autoregulation: i) Myogenic mechanism- contraction or relaxation of anteriolar smooth muscle in response to changes in vascular pressures; mediated by Ca++ ii) Tubule glomerular feedback (TGF) mechanism-mediated by macula densa cells (described later)