Ulcerative colitis. Light micrograph of a section through the colon (part of the large intestine) showing colonic glands (round structures). Colonic glands contain water-absorbing cells and mucus-secreting goblet cells, which dehydrate the feces and lubricate the colon surface for fecal passage. Ulcerative colitis is an inflammation of the colon characterised by loss of goblet cells and 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.