The anatomy of the digestive system is designed to move food through the body, processing it for energy and absorbing important vitamins and minerals along the way. The pathway that food takes is called the digestive tract. A body begins to digest food in the mouth, then moves it through the esophagus, stomach, small intestine, and large intestine, and finally expels the waste through the anus. The liver, pancreas, gallbladder, and parts of the nervous system and the circulatory system also play more minor roles in digestion, but are thus considered parts of the anatomy of the digestive system as well.
Food that enters the mouth immediately begins to break down due to saliva, a secretion of the salivary glands. Teeth break the food down into digestible parts, and the saliva contains enzymes which begin to break down carbohydrates. The tongue helps move the food around the mouth and eventually pushes it to the back of the throat to be swallowed.
Once a person swallows, an involuntary process of movement through the digestive tract begins, and the process is facilitated by a muscle structure built into parts of the anatomy of the digestive system. From the mouth, food enters the esophagus, which is the pipeline from the mouth to the stomach. Its walls have muscles which can expand and contract to some degree to allow larger and smaller pieces of food through it. At the end of the esophagus is the esophageal sphincter, which is the gateway to the stomach.
The stomach is where most of the digestive action takes place, and it is vital to the anatomy of the digestive system. Stomach acid in the form of enzymes and hydrochloric acid break down the food further, churning it into a liquid called chyme. Muscles in the stomach wall keep the food moving, pouring it slowly into the small intestine.
The small intestine is the longest part of the anatomy of the digestive system. It is approximately 24 feet (7.3 m) long, and it connects the stomach to the large intestine, or colon. Muscles in the small intestine walls keep food moving through a process called peristalsis. While inside the small intestine, food is broken down further and energy and nutrients are absorbed through the intestinal wall and into the blood stream. Juices from other organs, such as the pancreas and liver, also migrate through the intestinal wall to facilitate digestion.
The large intestine is about a fifth of the length of the small intestine, but it is larger in diameter. The walls of the colon continue to absorb nutrients, but leave the rest in the form of byproducts of the digestive process. This waste, called feces, can then be expelled from the body through a bowel movement.