Segment that makes up most of the large intestine .
Though the two terms are often used interchangeably, the colon technically excludes the cecum (a pouch at the beginning of the large intestine), rectum , and anal canal . It runs up the right side of the abdomen (ascending colon), across it (transverse colon), and down the left side (descending colon); its last section (sigmoid colon) joins the rectum. It has no digestive function but lubricates waste products, absorbs remaining fluids and salts, and stores waste products until excretion . Problems involving the colon include ulcerative colitis , constipation and diarrhea , gas discomfort, megacolon (enlarged colon), and cancer.