Chronic ulcerative colitis, gross specimen. Ulcerative colitis is inflammation of the bowel, typically arising in the rectum (as is seen here) and often extending to involve part of or most of the large intestine. This form of colitis is characterized by deep ulcers, which are usually superficial but may perforate the bowel wall in some cases. The affected bowel lining becomes haemorrhagic, contributing to diarrhoea and the passing of blood and mucus. Risk of developing colorectal cancer is significantly increased in someone who has had extensive ulcerative colitis for over ten years.