The digestive tract describes the path from mouth to anus in which energy and useful nutrients are removed from food, transferred to the body, and undigestible material is eventually expelled. Its components are:
The esophagus, a muscular tube which transfers food from the mouth to the stomach.
The stomach, which excretes a powerful acid (stronger than the hydrochloric acid typically found in laboratories) which denatures and partially dissolves the swallowed food. Water and simple sugars can be extracted at this point.
The duodenum and small intestine, where alkaline materials, enzymes and gut bacteria are added to the food to continue digestion. The cells of the small intestine can absorb the nutrients released at this point, as well as most of the rest of the water in the food.
The large intestine, where food is restored to a less alkaline state for passage, and any other available nutrients and water is absorbed.
As the digestive tract comprises the longest continuous system of the body, there are several diseases that can affect each part of it. Since the tract contains material that is harmful anywhere else in the body, any perforation or leak can cause serious complications in the patient. Too much or too little of any particular food, such as water or fat, can lead to an inability of food to pass through the tract, or can cause food to pass through without being digested properly. Some diseases, such as cholera, attack the digestive system directly.