Ulcerative Colitis

Ulcerative colitis is defined by continuity, rectal origin and mucosal depth

Ulcerative colitis (UC) is a chronic immune-mediated inflammation confined to the colon and rectum, which (unlike Crohn's) is continuous rather than patchy, always begins in the rectum, and spreads a variable distance proximally without skipping segments. Critically, inflammation is limited to the mucosa and submucosa rather than extending through the full bowel wall. These three anatomical rules (colon-only, rectum-always-involved, continuous, mucosal) are the key that unlocks almost everything else about the disease: its symptoms, its complications and how it differs from Crohn's.