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What Is a Digestive Tract?

A system of organs make up the digestive system, and those that form the digestive tract (also called the alimentary tract or GI tract) are a series of hollow, roughly tubular organs through which a meal passes in the process of digestion, nutrient absorption and elimination of indigestible wastes. In all parts of the digestive tract, the interior hollow of the tube is called the lumen.

The esophagus (or food tube) lies in the chest, and it connects the throat to the stomach. The stomach lies in the abdomen (below the diaphragm, which separates the chest from the belly), and it is large enough to hold an entire meal. Specialized cells in the stomach lining (mucosa) secrete highly concentrated acid which, combined with the churning action of the stomach, helps break up the food and begin the process of digestion.

The small intestine is quite long (about 6 feet), and it is here that a meal is digested and that nutrients and water are absorbed into the system. The first section of the small intestine is the duodenum, it is roughly C-shaped and is about 10 inches in length. A short segment of the duodenum just beyond the stomach is bulb-shaped, and it is here that the garden variety duodenal ulcer occurs. It is in the duodenum that digestive juices from the pancreas and bile from the liver are added to the meal to digest protein, starches and fat. The second section of the small intestine, the jejunum, is about two feet in length. The third section, the ileum, is about 3 feet long. The end of the ileum (the terminal ileum) joins the large intestine at the ileocecal valve.

The large intestine includes the cecum (with its appendix), the colon and the rectum. The cecum is the roughly U-shaped portion lying below the ileocecal valve, and its appendix is the thin, worm-shaped organ well known for becoming inflamed (appendicitis). The colon is about 3 feet long, and it is here that excess water is removed from the stream of feces. Its serpentine shape and partially fixed position allow descriptive divisions of the colon into the ascending colon, the right colic (hepatic) flexure, the transverse colon, the left colic (splenic) flexure, the descending colon and the sigmoid colon. The S-shaped sigmoid colon functions with the rectum to control defecation. The anus is the outlet of the rectum.

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