The large intestine is the final part of the digestive tract, about 1.5 m long, running from the ileocaecal junction to the anus. It frames the small intestine and is made up of the caecum and appendix, colon, rectum and anal canal. Most of the colon is marked by three muscle bands (taeniae coli), pouches (haustra) and small fatty tags (omental appendices).
| Location | From the right iliac fossa up the right side, across the upper abdomen, down the left side and into the pelvis to the anus |
|---|---|
| Parts | |
| Nerve Supply | Vagus nerve (parasympathetic); Pelvic splanchnic nerves, S2-S4 (parasympathetic to distal colon and rectum); Superior and inferior mesenteric plexuses (sympathetic) |
| Blood Supply | Ileocolic artery; Right colic artery; Middle colic artery; Left colic artery; Sigmoid arteries; Marginal artery; Superior, middle and inferior rectal arteries |
| Venous drainage |
|
| Lymphatic drainage |
|
Absorbs water and electrolytes, hosts the gut microbiota that ferment fibre into short-chain fatty acids, and stores and expels faeces.
Its blood supply changes from the superior mesenteric artery to the inferior mesenteric artery near the left colic flexure, which is why that region is vulnerable to ischaemia. Colorectal cancer is one of the most common cancers, and screening by stool testing or colonoscopy reduces deaths. Changes in bowel habit, rectal bleeding and iron deficiency anaemia are key warning signs.
Adenocarcinoma usually arising from an adenomatous polyp; right-sided tumours often present with anaemia and left-sided ones with obstruction or bleeding.
Outpouchings of the colonic lining through weak points in the wall, most common in the sigmoid colon, that can bleed or become inflamed.
Chronic inflammatory disease of the colonic lining that starts in the rectum and extends continuously, causing bloody diarrhoea.
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