With a length of approximately 6.4 m (the distance between the net and the service line of a tennis court), the small intestine plays an important role in the absorption of nutrients from the food you eat. The food particles here are blended with 3 digestive juices, originating from the liver, pancreas and the intestine itself. The duodenum which is connected to the stomach is the reaction site for the bile (from the liver) and pancreatic juice (from the pancreas). The long ileum secretes juices with chemicals that breaks down the food; its inner wall is covered with microscopic finger-like projections, villi, which increase the absorption surface of the intestinal wall. The broken down food mixture is further absorbed as it passes through the large intestinal wall into the bloodstream.

About 95% of the water in the alimentary canal is reabsorbed into the cells of the large intestine When the large intestine fails to reabsorb the water, the person will have fluid bowel. This symptom is called diarrhea, which can result in serious water and ion loss from the body.

After the absorption, the undigested food, together with the dead and living bacteria, as well as the lining cells on the wall of the large intestine join to form feces which are brown and semi-solid. The feces are stored in the rectum. At a certain point, they will be pushed out of the auus at the end of the alimentary canal. This action is call the bowel movement.