Most often, upper GI bleeding is caused by one of the following. This bleeding originates in the portions of the GI tract farther down the digestive system the segment of the small intestine farther from the stomach, large intestine, rectum, and anus. Diverticular disease, angiodysplasia, polyps, hemorrhoids, and anal fissures most commonly cause the bleeding. Blood in the stool can result from cancers, inflammatory bowel disease, and infectious diarrhea. The many causes of GI bleeding also are classified into upper or lower, depending on their location in the GI tract.
Ulcers usually occur in the stomach or duodenum.
Breakdown of the walls results in damage to blood vessels, causing bleeding. When the mucous membranes break down, they are unable to counteract the harsh effects of stomach acid. Helicobacter pylori are a type of bacteria that also promote formation of ulcers. General inflammation of the stomach wall, which can result in bleeding. Gastritis also results from an inability of the gastric lining to protect itself from the acid it produces.