Mesenteric artery ischemia and infarction occurs when there is a narrowing or blockage of one or more branches of the major arteries that supply the small and large intestines, called the mesenteric arteries. Narrowing of the arteries occurs when fat, cholesterol, and other substances build up in the walls of arteries (atherosclerosis). This narrowing reduces the blood flow and oxygen supply to a segment of the intestine, causing damage (ischemia). A complete blockage may also occur when a blood clot obstructs all blood flow through the artery, causing tissue death of that segment of intestine (infarction).