Ulcerative colitis – Definition – Ulcerative colitis is a chronic disease characterized by inflammation and sores, or ulcers, within the large intestine; it is one of the two major irritable bowel diseases (IBD), along with Crohn’s disease. Relevance – Although the cause of ulcerative colitis is unknown, people with this condition tend to have abnormal immune responses and symptoms include anemia, nausea, fever, weight loss, fatigue, rectal bleeding, and more.