Inflammatory bowel disease inflammatory changes. Crohn's can affect any part of the gastrointestinal tract, from mouth to anus ("skip lesions"), although a majority of the cases start in the terminal ileum. Ulcerative colitis, in contrast, is restricted to the colon and the rectum. Microscopically, ulcerative colitis is restricted to the mucosa (epithelial lining of the gut), while Crohn's disease affects the full thickness of the bowel wall ("transmural lesions"). Lastly, Crohn's disease and ulcerative colitis present with extra-intestinal manifestations (such as liver problems, arthritis, skin manifestations and eye problems) in different proportions. In 10–15% of cases, a definitive diagnosis neither of Crohn's disease
Crohn's disease Crohn's disease may develop anemia due to vitamin B, folate, iron deficiency, or due to anemia of chronic disease. The most common is iron deficiency anemia from chronic blood loss, reduced dietary intake, and persistent inflammation leading to increased hepcidin levels, restricting iron absorption in the duodenum. As Crohn's disease most commonly affects the terminal ileum where the vitamin B12/intrinsic factor complex is absorbed, B12 deficiency may be seen. This is particularly common after surgery to remove the ileum. Involvement of the duodenum and jejunum can impair the absorption of many other nutrients including folate. If Crohn's disease affects the