Crohn's disease. Cutaway illustration of the junction of the small and large intestines in a case of Crohn's disease (regional enteritis). Small intestine inflammation (enteritis) is shown by red and yellow patches (lower centre) in its final part, the terminal ileum. This connects to the large intestine via the ileocaecal valve, leading into the caecum (lower left), and the ascending colon (upper left). The appendix (lower left) and mesenteric arteries (upper right) are also shown. Crohn's disease causes inflammation, thickening, and ulceration of the intestinal tract. Its cause is unknown. Symptoms include abdominal pain, diarrhoea and weight loss.