A precapillary sphincter encircles each capillary branch at the point where it branches from the arteriole. Contraction of the precapillary sphincter can close the branches off to blood flow. If the sphincter is damaged or can not contract, blood can flow into the capillary bed at high pressures. This can be seen in people who have to stand all day. Their feet and ankles often swell from the excess fluid accumulating there.
Capillaries are fragile and can be damaged easily.
It is often ruptured capillaries in the skin that cause bruises when one falls or sustains a blow. Find great deals on quality laboratory equipment. Inc. All rights reserved.