Precapillary sphincter

    The precapillary sphincter is a band of smooth muscle that adjusts the blood flow into each capillary. At the point where each true capillary originates from a metarteriole, a smooth muscle fiber usually encircles the capillary. This is called the precapillary sphincter. This sphincter can open and close the entrance to the capillary. Blood flow in a capillary changes as vasomotion occurs. The entire capillary bed may be bypassed by blood flow through arteriovenous anastomoses.

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