Watch a bite of food travel from your mouth to the end of the tract. At each stop you will see what happens to it and how long it really stays there.
Rotate the body and click any organ — or use the colored legend — to see its job. Food only travels through the tube (mouth to anus); the liver, gallbladder and pancreas never touch food but pour in the juices that digest it.
A sandwich is made of huge molecules — starch, proteins and fats — far too big to pass through the wall of your gut into your blood. Digestion is the process of breaking these big molecules into small ones your body can absorb and use: starch into glucose, proteins into amino acids, and fats into fatty acids and glycerol. The digestive system is basically one long tube from mouth to anus, several metres long, with helper organs attached.
Food is broken down in two ways. Mechanical digestion is physical: teeth chew and the stomach churns, making smaller pieces with more surface. Chemical digestion uses enzymes that cut molecules apart: amylase for starch (mouth and pancreas), pepsin and trypsin for proteins (stomach and pancreas), and lipase for fats (pancreas). The liver makes bile, which is not an enzyme but breaks fat into tiny droplets so lipase can reach it.
Most absorption happens in the small intestine. Its lining is folded, the folds are covered in finger-like villi, and each villus cell has even smaller microvilli. Together they give an absorbing surface of about $30\,\mathrm{m^2}$. Each villus has a network of blood capillaries (for sugars and amino acids) and a lacteal (for fats), so nutrients pass straight into the circulation and on to the liver. The large intestine then recovers most of the remaining water, and its bacteria ferment the fibre we cannot digest.
Press Follow a meal and watch the bite of food: it becomes a bolus in the mouth, soupy chyme in the stomach, shrinks as nutrients leave the small intestine (the green and red dots are nutrients entering the blood), then turns brown and solid in the large intestine. Click the liver, gallbladder and pancreas — food never passes through them, yet digestion would fail without them. Turn off the body outline and rotate to see how the large intestine frames the small one.
| Organ | What happens | Enzymes / juices | Typical time |
|---|---|---|---|
| Mouth | Chewing; bolus formed; starch digestion starts | Salivary amylase | ~1 minute |
| Esophagus | Peristalsis moves food down | Mucus only | ~5–10 s |
| Stomach | Churning; protein digestion starts; microbes killed | HCl, pepsin | 2–4 h |
| Small intestine | Digestion finished; nutrients absorbed by villi | Bile; pancreatic amylase, lipase, trypsin; brush-border enzymes | 3–5 h |
| Large intestine | Water and salts absorbed; bacteria ferment fibre | (bacteria) | ~1–2 days |
| Rectum & anus | Feces stored, then egested | — | varies |
| Liver | Makes bile; processes absorbed nutrients | Bile | (no food) |
| Gallbladder | Stores and concentrates bile | Bile | (no food) |
| Pancreas | Makes most digestive enzymes; neutralises acid | Amylase, lipase, proteases, bicarbonate | (no food) |
Carbohydrates start in the mouth (salivary amylase) and finish in the small intestine (pancreatic amylase, then maltase and other brush-border enzymes) — ending as glucose. Proteins start in the stomach (pepsin, which works best in acid) and finish in the small intestine (trypsin and peptidases) — ending as amino acids. Fats are digested almost entirely in the small intestine, after bile emulsifies them and lipase splits them into fatty acids and glycerol.
The stomach makes acid strong enough to kill most bacteria and an enzyme that digests protein — yet its own wall is protein. It survives because a thick layer of alkaline mucus coats the lining, pepsin is released in an inactive form (pepsinogen) that only switches on inside the stomach cavity, and the lining cells are replaced every few days. When the mucus barrier fails, for example because of Helicobacter pylori bacteria or some painkillers, a stomach ulcer can form.
The digestive system is the group of organs that breaks food down into small molecules your body can absorb, and gets rid of what is left. It is made of one long tube, the alimentary canal (mouth, esophagus, stomach, small intestine, large intestine, rectum and anus), plus accessory organs — the salivary glands, liver, gallbladder and pancreas — that add digestive juices.
Key takeaway: one tube from mouth to anus plus four helper organs that add juices.Food travels mouth → pharynx (throat) → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine (cecum, colon) → rectum → anus. The liver, gallbladder and pancreas are not on this path; they connect to the duodenum through ducts.
Key takeaway: mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.Mechanical digestion physically breaks food into smaller pieces — chewing by the teeth and churning by the stomach — without changing the molecules. Chemical digestion uses enzymes and acid to break the chemical bonds in big molecules, turning starch into glucose, proteins into amino acids and fats into fatty acids and glycerol. Mechanical digestion helps chemical digestion by giving enzymes more surface to work on.
Key takeaway: mechanical = smaller pieces; chemical = smaller molecules, made by enzymes.Almost all nutrients are absorbed in the small intestine, through millions of finger-like villi and their microvilli. Sugars and amino acids enter blood capillaries and go to the liver first; fats enter lymph vessels called lacteals. The large intestine mainly absorbs water and salts, and a few vitamins made by gut bacteria.
Key takeaway: nutrients are absorbed in the small intestine; water mostly in the large intestine.It varies a lot, but typically: a few seconds in the esophagus, about 2–4 hours in the stomach, 3–5 hours in the small intestine and about 1–2 days in the large intestine. The whole journey from eating to egestion usually takes about 1–3 days. Fibre, fluid, exercise and the type of meal all change the speed.
Key takeaway: usually 1–3 days in total, most of it in the large intestine.The liver makes bile, which emulsifies fats into tiny droplets. The gallbladder stores and concentrates that bile and squeezes it into the duodenum after a fatty meal. The pancreas makes pancreatic juice containing amylase, lipase and proteases, plus bicarbonate that neutralises stomach acid. Food never passes through these three organs.
Key takeaway: liver makes bile, gallbladder stores it, pancreas makes most of the enzymes.Absorption depends on surface area. Folds, villi and microvilli together give the small intestine an absorbing surface of about 30 m², and its length gives food several hours of contact with that surface. A thin wall (one cell thick over each villus) and a rich blood supply keep the distance short and the concentration gradient steep, so nutrients diffuse and are transported in quickly.
Key takeaway: huge surface + thin wall + good blood supply = fast absorption.