The major part of the large intestine. The colon is a segmented tube, about 1.3 m long and 6.5 cm wide, that forms a large loop in the abdomen. It consists of 4 sections: the ascending, transverse, and descending colons, and the S-shaped sigmoid colon, which connects with the rectum. The main functions of the colon are to absorb water and mineral salts from the digested material passed on from the small intestine and to concentrate the waste material for expulsion as faeces. The colon consists of 4 layers: a tough outer membrane; a layer of muscles that contract and relax to move the contents along (see peristalsis); a submucous coat containing blood vessels that absorb water and salts; and finally an innermost layer that produces mucus to lubricate the passage of material. (See also digestive system; intestine, disorders of.)
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