What Structure Within a Capillary Bed Controls Shunting of Blood

Question

What structure within a capillary bed controls shunting of blood from the arteriole to the venule?
A) precapillary valve
B) endothelium
C) precapillary sphincter
D) pericardium
E) shunt valve

Accepted Answer

The precapillary sphincter is a ring of smooth muscle fibers located at the origin of each true capillary. It can contract or relax in response to local chemical conditions, such as low oxygen or high carbon dioxide. When it contracts, it narrows or closes the entrance to the capillary, forcing blood to flow through a nearby metarteriole or arteriovenous anastomosis, shunting the blood away from the capillary bed. When the sphincter relaxes, blood flows into the capillary bed, allowing for exchange between the blood and tissues.