by Scott Christmas

Created on: February 16, 2007   Last Updated: April 26, 2007

The Digestive System

The digestive system consists of the gastrointestinal (GI) tract, which is the area where food is ingested, digested, and excreted, as well as a series of accessory organs that aid in the work of the GI tract.

The GI tract includes the following organs:

Mouth
Pharynx (throat)
Esophagus
Stomach
Small Instestine
Large Intestine
Rectum
Anus

About 30 feet long in the average adult, the GI tract is a single, continuous tube, open at both ends, and made up of four layers, with a mucus membrane lining the surface. Using a method called peristalsis, food is moved through the GI tract with a series of muscle contractions that literally squeeze the food along, much as you might squeeze a lump of orange pulp from one end of a straw to the other.

Beginning at the mouth, the GI tract runs into the pharynx (otherwise known as the throat), which connects directly throught the esophagus. The esophagus, which is situated in front of the trachea (the windpipe), pushes through the diaphragm muscle at the bottom of the lungs and enters the stomach through the cardiac orifice. This orifice has a muscle at the end called the cardiac sphincter, which allows food to pass into the stomach.

The stomach is made up of three parts - the fundus, the body, and the pylorus - in that order. The surface of the stomach is covered by folds called rugae. These rugae flatten out when the stomach is full, and they are what allow you to know that it is time to stop eating.

Like at the entrance, food in the stomach exits through a muscle called the pyloric sphincter. This muscle allows food to pass into the duodenum, which is the upper portion of the small intestine.

22 feet in length, the small intestine is made up of a long, narrow tube that folds around upon itself. From the duodenum, food passes through the mid-portion of the small intestine, known as the jejunum, on into the lower portion of the small intestine, which is called illeum. From the illeum, the food passes through the illeocecal valve into the cecum of the large intestine.

The large intestine is about 5 feet long, and curves up, around, and over the small instestine. Projecting down from the cecum is the appendix. The cecum leads upward into the ascending colon. At the liver, the ascending colon makes a right turn across the front of the belly. This portion of the colon is called the transverse colon. At the spleen, it makes another turn downward, becoming the descending colon. The descending colon empties into the sigmoid

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