Concept preview

What you will be able to do

1. 01Trace the path of food from the mouth through esophagus, stomach, small intestine, large intestine, and out the rectum and anus.
2. 02Explain peristalsis and how the muscular gut wall moves food along.
3. 03Distinguish ingestion, digestion, absorption, and egestion.
4. 04Describe the four layers of the gut wall and the overview role of each organ.

The digestive system, also called the alimentary canal or gut, is essentially one long, muscular tube that runs from your mouth all the way to your anus, coiled and folded to fit inside the trunk but measuring roughly nine metres end to end in an adult. Because the tube is open at both ends, the space inside it — the lumen — is continuous with the outside world, which leads to a genuinely surprising idea: food sitting in your stomach or intestine is, in a strict biological sense, still outside your body. Nothing has truly entered you until it has crossed the gut wall and passed into the blood. The task of the digestive tract, then, is to break large lumps of food into molecules small enough to slip across that wall, and to move everything steadily and in the right order from one specialised region to the next.