Ulcerative colitis vs. Crohn’s disease

Let’s discuss how they differ:
1) The affected site
Crohn’s disease affects any part of the gastrointestinal tract, especially the ileocecal regions, and it usually doesn’t affect the rectum. The lesion extends in a discontinuous pattern (Skip lesions) and affects all three layers of the intestinal wall (transmural lesion).
Ulcerative colitis always affects the rectum and extends proximally to involve the colon. It affects the terminal part of the ileum only in 5% of the cases. The lesion extends in a continuous pattern and affects only the first two layers of the intestinal wall (mucosa and submucosa).