The intestine is part of the digestive system. It is the portion of the digestive tract that connects the stomach to the anus. The intestine is divided into 2 parts, the small intestine and the large intestine, and its role is to complete digestion. The small intestine is subdivided into 3 parts: the duodenum, the jejunum and the ileum. The large intestine is composed of the cecum, the colon and the rectum. The thin membrane of the small intestine is covered with folds and villi in order to increase the exchange surface with the bloodstream. Most proteins are thus assimilated in the small intestine, as well as carbohydrates and lipids. The large intestine is home to bacteria living in symbiosis with their host, which can break down molecules that the human body is unable to assimilate. This intestinal flora (or intestinal microbiota) is essential to the proper functioning of the digestive process. Colon and rectum are sometimes the seat of abnormal, uncontrolled proliferation of the cells of their mucous membrane. This causes a polyp-like lump (adenoma), which can degenerate into invasive colon cancer.