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How digestion works: the digestive system, how food moves, how it is broken down, and how the body controls it
For anyone who wants to understand their stomach and gut; anyone who was told something is wrong with their digestion and wants to follow what their care team says; anyone reading a report full of words like duodenum, ileum, cecum or peristalsis; and anyone looking after someone who is. It passes on, by name, what the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, part of the NIH) says: what the digestive system is, from the mouth to the anus, with the liver, pancreas and gallbladder; why digestion matters; how food moves, step by step; how chewing, stomach acid, bile and enzymes break it down, organ by organ; where the nutrients go; and how hormones and nerves, talking with the brain, control it all. It builds the words to say to your care team, so you do not have to find them, and prints a card.
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More help
- On this site: An upset stomach, heartburn or constipation: find the right page · Indigestion · Gas and bloating · Heartburn.
- Related: Constipation · Gallstones · Fatty liver disease · Celiac disease.
- Getting ready: Get ready for your appointment · Symptom diary · When you need a doctor and can’t pay.
- In a crisis: Help right now (988, 911). All our free tools.
An upset stomach, and not sure this is the right page? The pages on this site for throwing up, diarrhea, heartburn and constipation, on one list.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor or nurse has reviewed it. The facts were read on October 19, 2026 on NIDDK’s (NIH) page Your Digestive System & How It Works (last reviewed December 2017) and its Spanish page El aparato digestivo y su funcionamiento (last reviewed December 2018), which says the same. NIDDK gives no numbers on this page, and we add none. Ours: “if you believe it is an emergency, call 911” (NIDDK names no 911 on this page); 988; the plain-words list of the parts, which only gathers what NIDDK says each part is; that the page does not say what to eat, or anything about products sold for gut bacteria; the questions to ask; the links to our other pages; and the order of the steps. What we left out: the section on clinical trials, NIDDK’s video, and NIDDK’s links to other sites. Nothing you tick or type here is saved or sent.