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How does the myogenic response answer a sharp rise in flow through an arteriole?
ASmooth muscle relaxes, so the vessel dilates further
BSmooth muscle contracts, so the vessel constricts
CEndothelium releases nitric oxide and flow rises
DPrecapillary sphincters open and perfusion climbs
Answer & Solution
Correct answer: B. Smooth muscle contracts, so the vessel constricts
1. The myogenic response is a local reaction of arteriolar smooth muscle to being stretched.
2. It needs no nerve supply and no hormone, so it counts as autoregulation.
3. High flow stretches the wall more, and the stretched smooth muscle contracts.
4. That contraction narrows the vessel and brings flow back down, protecting the fragile capillaries downstream.
5. Low flow does the reverse: minimal stretch lets the muscle relax and the vessel dilate.
6. Relaxation in the face of high flow would worsen the overshoot and damage the small vessels.
7. Nitric oxide release and sphincter opening are chemical controls, not the stretch driven myogenic mechanism.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 20 "The Cardiovascular System: Blood Vessels and Circulation", section 20.4 Homeostatic Regulation of the Vascular System_
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