Crohn’s disease is an inflammatory bowel disease characterized by sever, chronic inflammation of the intestinal wall or any portion of the gastrointestinal tract. The lower portion of the small intestine (ileum) and the rectum are most commonly affected by the disorder. symptoms may include watery diarrhea, abdominal pain, fever, and weight loss. Ulcerative colitis (UC) is a disease that affects your large intestine, or colon. It causes irritation and swelling called inflammation. Eventually that leads to sores called ulcers in the lining there.