What is the gastrointestinal tract?

The gastrointestinal (GI) tract is the soft tissue tube in the human body that begins at the mouth and ends at the anus, through which all nutrition passes, is processed, and is eliminated. Digestion is the primary function of the tract, and is accomplished through muscle movement and the release of enzymes and hormones. The entire gastrointestinal tract of an adult human averages 20 to 25 feet (approximately 6.1 to 7.6 m) in length and is made up of the upper and lower gastrointestinal tracts. Another term used for the gastrointestinal tract is the alimentary canal.

Each part of the gastrointestinal tract above the duodenum is considered part of the upper gastrointestinal tract. The upper gastrointestinal tract includes the mouth, pharynx, esophagus, and stomach; the lower gastrointestinal tract includes the small intestine, large intestine or colon, rectum, and anus. Although the liver, gallbladder, and pancreas assist the body in its digestive processing functions, they are not considered part of the actual gastrointestinal tract.

The small intestine is usually about 20 feet (about 6 m) long and is made up of the duodenum, jejunum, and ileum, which leads to the large intestine. It is in the duodenum that the main chemical digestion of food takes place. At Trietz's ligament, the duodenum ends and the jejunum begins. The purpose of the jejunum is to extract and absorb nutrients through active and passive transport mechanisms. When nutrition reaches the ileum, it has far fewer nutrients to extract and passes through the lower GI tract at a faster rate.

The large intestine works by taking in undigested food and removing water so that the food forms solid waste that can be excreted as fecal matter. A large intestine is usually about 5 feet (about 1.5 m) long and includes the cecum, colon, rectum, and anus. There are more than 700 species of bacteria in the large intestine. The main purposes of the large intestine are to produce vitamins for blood absorption, neutralize acidity caused by the formation of fatty acids, produce antibodies, strengthen the autoimmune system, and remove waste from the rectum through the anus.

Some common problems of the gastrointestinal tract, such as simple indigestion, gastritis, constipation or diarrhea, can often be controlled and cured through a healthy diet rich in fiber and low in sugars. Other long-term gastrointestinal problems such as Crohn's disease, appendicitis, gastroesophageal reflux disease (GERD), duodenal ulcers, viral infections, and irritable bowel syndrome (IBS) should not be ignored, as they usually require care and medical attention. Gastroenterologists and gastrointestinal specialists are doctors who should generally be consulted about disorders of the gastrointestinal tract.

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