At the point where each of the capillaries originates from an arteriole, contractile mural cells encircle the capillary. This is called the precapillary sphincter. ... The sphincter can open and close the entrance to the capillary, by which contraction causes blood flow in a capillary to change as vasomotion occurs.

What happens when precapillary sphincters close?

If the precapillary sphincters are open, the blood will flow into the associated branches of the capillary bed. If all of the sphincters are closed, then the blood will flow directly from the arteriole to the venule through the thoroughfare channel.

What causes precapillary sphincters to open and close?

high oxygen, low carbon dioxide and high pH cause smooth muscle cells in arterioles and precapillary sphincters to contract, decreasing local blood flow.