<Tr> <Td_colspan="2"> Illustration of a capillary system with precapillary sphincters </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> A precapillary sphincter is a band of smooth muscle that adjusts blood flow into capillaries mainly in the mesenteric microcirculation . At the point where each of the capillaries originates from an arteriole, a smooth muscle fiber encircles 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 . The entire capillary bed may be bypassed by blood flow through arteriovenous anastomoses or through preferential flow through metarterioles . If the sphincter is damaged or cannot contract, blood can flow into the capillary bed at high pressures . When capillary pressures are high (as per gravity, etc .), fluid passes out of the capillaries into the interstitial space, and edema or fluid swelling is the result . </P> <P> Precapillary sphincters and metarterioles were discovered in the mesenteric circulation in the 1950s . Medical and physiological textbooks, such as Guyton, Boron and Fulton, etc. were quick to claim the existence of said sphincters and metarterioles all over the body, despite lack of evidence . At least since 1976 there has been considerable debate about the existence of precapillary sphincters and metarterioles . As of 2013 it is held that they are unique to the mesenteric circulation and some researchers have suggested the term precapillary resistance instead . </P>

Which of the following would cause relaxation of precapillary sphincters