A precapillary sphincter is a band of contractile mural cells either classified as smooth muscle or pericytes that adjusts blood flow into capillaries.

The precapillary sphincter has now also been found in the brain, where it regulates blood flow to the capillary bed.

[2] If the sphincter is damaged or cannot contract, blood can flow into the capillary bed at high pressures.

[citation needed] Precapillary sphincters and metarterioles were discovered in the mesenteric circulation in the 1950s.

[5] In 2020, precapillary sphincters were identified as a mechanism for controlling cerebral blood flow.