How do the intestines work?

Between your stomach and the exit lies a folded tube 3 to 5 metres long, with an inner surface of about 30 square metres and 38 trillion bacteria living in it. Peristalsis squeezes behind the food and relaxes in front.

Read how it works: How do the intestines work? · The history of understanding the intestines · More boxes on Glassbox

Chapters in this interactive model

1. The intestines, unpacked: A long, folded tube: the small intestine does the absorbing, the large one saves water.
2. A huge surface in a small tube: Folds on folds on folds: how 3 metres of tube gets about 30 square metres of lining.
3. Squeeze, mix, sweep: Rings of muscle push food along, slosh it back and forth, and tidy up between meals.
4. Chemistry in the duodenum: Bile and pancreatic juice arrive, and big food molecules are cut into small ones.
5. Trillions of tiny helpers: The colon saves water and feeds a huge colony of bacteria, which feed you back.
6. Keeping it healthy, and what goes wrong: Fibre and water, diarrhoea and ORS, milk sugar, gluten and the appendix.