Precapillary sphincters

A) serve as valves in veins.
B) are found in the tunica media.
C) carry blood under high pressure.
D) control the blood flow into capillary beds.
E) are voluntary structures.

Precapillary Sphincters

Circular muscular valves located at the entrance of capillaries, regulating blood flow into the capillary beds according to the body's needs.

Tunica Media

Middle, usually muscular, coat of an artery or another tubular structure.

Capillary Beds

Networks of capillaries, the smallest blood vessels, that facilitate the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between blood and tissues.