The large intestine consists of mainly 4 regions: cecum, colon, rectum, and anal canal. The colon, which forms the major part of large intestine, is further divided into 4 main portions: ascending colon, transverse colon, descending colon, and sigmoid colon. The next about 15 cm long continuation of the colon is termed as the rectum. The main functions of colon and rectum include final digestion and absorption of food with the help of bacteria commonly found in these parts and production of some vitamins. The wall of the large intestine (colon and rectum) mainly consists of 4 layers – Mucosa, Submucosa, Muscularis Propria, and Serosa.
Adenocarcinoma (affecting mucosal cells that lines the innermost lining of the large intestine) is the most commonly encountered (more than 95% of all cases) colorectal cancer.