The large intestine comprises of the second part of the alimentary canal. The large intestine consists of the cecum and colon. It begins at the right iliac region of the pelvis (the region just at or below the right waist) where is continues from the small intestine and continues up the abdomen. Thereafter it traverses across the width of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus.
Major function of the large intestine
The major function of the large intestine is to absorb water from the remaining indigestible food matter and transmit the useless waste material from the body.
Structure of the large intestine
The large intestine is made up of the colon and the rectum.
The colon is a tubular structure that is around 1.5 m, about one quarter of the length of the small bowel. Its largest diameter is at the cecum (7.5 cm) and narrowest in the sigmoid (2.5 cm). The colon is continuous with the small intestine from the ileocecal valve and ends finally at the anal verge. The parts of the colon include the ascending, transverse and descending colon.
The rectum is 10 cm in length in the adult. It starts at the peritoneal reflexion and follows the curve of the sacrum ending at the anal canal. The anal canal is 5 cm in length in the adult, has discrete upper and lower demarcations.
Over the surface of the large intestine are longitudinal muscle fibers called taeniae coli, each about 5 mm wide. There are three bands and they start at the base of the appendix and extend from the cecum to the rectum. There are sacculations called haustra that are characteristic features of the large intestine, and distinguish it from the rest of the intestines.