Myogenic autoregulation of blood flow in the kidney involves which sequence of events when arterial pressure suddenly increases?
- A Increased wall tension → stretch-activated TRP cation channels open → afferent arteriole depolarisation → L-type Ca2+ channel activation → vasoconstriction → maintained RBF/GFR ✓
- B Increased flow → shear stress → endothelial NO release → cGMP-mediated smooth muscle relaxation → vasodilation
- C Increased pressure → macula densa senses increased NaCl → TGF signal → afferent arteriole constriction (tubuloglomerular feedback)
- D Increased pressure → baroreceptor reflex → sympathetic vasoconstriction → normalised RBF
Explanation
Renal myogenic autoregulation is intrinsic to vascular smooth muscle and operates independently of neural or hormonal input. When transmural pressure increases, the afferent arteriolar wall is stretched. Stretch-activated cation channels (notably TRP channels, especially TRPC6 and TRPM4) depolarise the membrane. This opens voltage-gated L-type Ca2+ channels, increasing cytoplasmic Ca2+ and triggering actomyosin-mediated vasoconstriction. The vasoconstriction normalises wall tension and maintains relatively constant RBF and GFR despite MAP changes between 80-180 mmHg. Tubuloglomerular feedback (option C) is a distinct, macula-densa-mediated mechanism that works in conjunction with myogenic autoregulation.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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