Inflamed colon. Endoscope view of colitis (inflammation of the colon) due to ischaemia (reduced blood supply). The colon is the largest part of the large intestine. Large areas of ulceration (white) are seen here, surrounded by red areas of inflammation. The ulcers have also become infected. Ischaemia is an uncommon cause of colitis and is caused by narrowing of the arteries supplying the intestines by atherosclerosis.