The final section of the digestive system, extending from the caecum, where it joins the small intestine, to the rectum. About 1.5 metres long and wider than the small intestine, it absorbs water, sodium, and potassium from liquid digestive residues, converting them into formed stool. Its resident microbiota, numbering in the trillions, ferment dietary fibre and other unabsorbed material, producing short-chain fatty acids that nourish the colon lining and synthesising some vitamins. The large intestine comprises the appendix, colon in its four segments, and rectum. Maintaining its health depends on adequate fibre, hydration, physical activity, and screening for colorectal cancer from middle age.