Myogenic autoregulation maintains relatively constant blood flow to the kidney and brain despite mean arterial pressure changes from 70–180 mmHg. What is the cellular mechanism underlying the myogenic response?
- A Increased flow velocity activates endothelial nitric oxide synthase, causing vasodilation proportional to pressure rise
- B Increased transmural pressure stretches vascular smooth muscle, opening mechanosensitive cation channels and depolarizing the cell, activating voltage-gated Ca²⁺ channels and causing vasoconstriction ✓
- C Tubuloglomerular feedback signals smooth muscle to contract via angiotensin II release from the macula densa
- D Metabolic vasodilators (adenosine, CO₂) accumulate when pressure drops, causing vasodilation that maintains flow
Correct answer: B. Increased transmural pressure stretches vascular smooth muscle, opening mechanosensitive cation channels and depolarizing the cell, activating voltage-gated Ca²⁺ channels and causing vasoconstriction
Explanation
The myogenic response is an intrinsic property of vascular smooth muscle: increased intraluminal pressure distends the vessel wall, mechanosensitive stretch-activated cation channels (TRPC/Piezo) allow Na⁺ and Ca²⁺ entry, depolarizing the cell. Depolarization opens L-type voltage-gated Ca²⁺ channels, raising intracellular Ca²⁺ and triggering smooth muscle contraction (vasoconstriction)—increasing vascular resistance proportionally to the pressure rise and limiting the increase in flow.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.