The beginning of a true capillary is surrounded by a precapillary sphincter. The opening and closing of precapillary sphincters is controlled by .

Local Chemical condition

Explanation:

Precapillary sphincter is a small smooth muscles that regulates the flow of blood into the capillaries.

Blood flows to the surrounding branches of the capillary due to the fact that surrounding capillaries require oxygen when the sphincters are open and the blood flows directly from the arteriole( which is a small artery) to the venule( which is a small vein) when the sphincters are closed

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