Large Intestine

The large intestine is the final major segment of the digestive tract, about 1.5 meters (roughly 5 feet) long. It is shorter than the small intestine but has a much wider lumen, hence "large." Its main jobs are to absorb water and electrolytes from undigested material and to compact, store, and eliminate the resulting stool.

Structure and Location

It begins at the cecum, a pouch in the lower right abdomen where the small intestine joins, with the worm-like appendix attached. From there it forms a frame around the abdominal cavity as the colon: the ascending colon rises on the right, the transverse colon crosses to the left, the descending colon drops on the left, and the S-shaped sigmoid colon leads to the rectum and finally the anal canal.

The colon has three signature features that distinguish it from the small intestine: teniae coli (three longitudinal bands of muscle running its length), haustra (the pouches created when those bands contract, giving a segmented look), and epiploic appendages (small fat-filled tags on the surface). Blood comes from the superior mesenteric artery (right colon) and inferior mesenteric artery (left colon), which connect through the marginal artery.

Function

By the time material reaches the colon, most nutrients are gone. The lining reabsorbs water and electrolytes such as sodium, converting liquid waste into solid stool, and secretes mucus to ease its passage. The large intestine also hosts the gut microbiome, trillions of bacteria that ferment leftover fiber, produce certain vitamins (including vitamin K), and support gut health. Slow, coordinated muscle contractions move stool toward the rectum for elimination.

Clinical Relevance

The large intestine is a frequent site of disease. Colorectal cancer is among the most common cancers and is screened for with colonoscopy. Diverticulosis (small wall pouches) and diverticulitis, inflammatory bowel disease (ulcerative colitis and Crohn disease), and appendicitis also arise here. This page is educational, not medical advice.