Why gastrointestinal bleeding?

Many. Varices, ulcers, vascular abnormalities, cancers, polyps, diverticulosis, ibd or hemorrhoids to name a few.
GI Bleeding. Gi bleeding can come from upper GI tract or lower. Upper gibleed comes from bleeding in the stomach, due to bleeding ulcer or as a result of Aspirin like drugs causing abrasions, and due to cancer, or esophageal varices dut ti cirrhosis liver. Lower GI bleeding comes from large bowel or rectum, it can be due to polyp, ibd, hemorroids and cancer to list a few causes.