Hematochezia occurs when fresh blood passes through the rectum. This form of bloody stool should not be confused with melena, where feces is dark and tarry due to bleeding in the upper intestines. Hematochezia usually comes from the lower intestines, but can also derive from spontaneous bleeding anywhere in the GI tract. Though hematochezia can be frightening, in many cases the cause is benign and the issue will resolve itself.
Mesenteric arteries supply blood to most of the gastrointestinal tract, specifically the small bowel and colon. During intense exercise, athletes may experience hypohydration or uncompensated body water loss. This interrupts mesenteric blood flow, leading to rectal bleeding. This cause is more prevalent among distance runners, and though people should seek medical attention if it occurs, athletes can also train their stomachs by altering their carbohydrate and fluid intake before and during races.
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