the major part of the large intestine. The colon is a muscular tube about 5 feet long. It is divided into 4 sections, starting with the ascending, transverse, descending, and ending with the sigmoid colon. It continues the process of absorbing water and mineral nutrients from food that was started in the small intestine. The cecum and the rectum mark the beginning and end of the colon, though they are not actually part of it. See also cecum, rectum.