The colon is a tube-like muscle. This tube has a very smooth lining. The lining is made up of millions of cells. The colon in an adult is about 1.2 – 1.8 m long. The rectum is the last 15cm of the colon. Colectomy is necessary when adenomatous polyps (growths that arise from the mucosa), diverticular disease (when pouches in the wall of the colon extend outward), inflammatory bowel disease, and cancer of the colon and rectum are happened.