The gastrointestinal tract is a long hollow tube which stretches from the head and moves downwards. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Also, the salivary glands, liver, gallbladder, and pancreas are important parts of this system.

The most important function of the GI tract is to break down carbohydrates, fats, and proteins into small molecules which can be absorbed by the cell membranes. In this way the cells get the energy required to maintain good health.

The first step of digestion begins in the mouth when food is chewed and starch is broken down by ptyalin. Ptyalin is an enzyme secreted in the saliva. Food then enters the stomach, it gets broken into tiny particles and further it is transformed by gastric juices. The solid portion remains in the stomach for one to six hours until it liquefies completely; liquid passes into the duodenum (small intestine), where numerous enzymes produced by the pancreas, along with bile from the liver, break it down further for absorption. When it finally arrives in the large intestine, all nutritional value has been spent. The only process remaining at this stage is the removal of water, just before the final elimination.

Different areas of the gastrointestinal tracts are prone to different disorders. Most of the disorders are common. However, some disorders may be fatal.