Superior mesenteric artery and inferior mesenteric artery are the two major blood vessels that supply lower gastrointestinal tract. Disruption of  blood vessel junction, formed by these two vessels, by any of the disease process results in bleeding. Diverticulosis is the most common etiology of lower GI bleeding accounting for 30% of all cases, followed by ano-rectal disease, ischemia of bowel, inflammatory bowel disease (IBD), neoplasia, and arteriovenous (AV) malformations. The characteristic gross and microscopic findings of lower gastrointestinal tracts depends upon the underlying pathology.
Lower gastrointestinal bleeding pathophysiology
Upper gastrointestinal bleeding pathophysiology
Lower gastrointestinal bleeding risk factors
Gastrointestinal varices pathophysiology
Upper gastrointestinal bleeding risk factors
Diverticulosis risk factors
Portal vein thrombosis pathophysiology
Nausea and vomiting pathophysiology