Final answer:
Precapillary sphincters, when closed, prevent blood flow to tissues from arterioles by directing blood through a thoroughfare channel and bypassing the capillary bed.
Step-by-step explanation:
The closure of a precapillary sphincter prevents blood flow to tissues from arterioles. Precapillary sphincters are circular smooth muscle cells that regulate the flow of blood from the metarteriole to the capillaries they supply. When the surrounding tissues need oxygen and have excess waste products, the precapillary sphincters open, allowing blood to pass through. If all the precapillary sphincters in a capillary bed are closed, blood bypasses the capillaries through a thoroughfare channel directly into the venous circulation.