Introduction

The Gastrointestinal Tract

The gastrointestinal (GI) tract (the digestive system) is a tube that extends from the mouth to the anus. It is a complex organ system that first carries food from the mouth down the esophagus to the stomach and then through the small and large intestine to be excreted out through the rectum and anus.

Esophagus

The esophagus, commonly called the food pipe, is a narrow muscular tube, about nine and a half inches long that begins below the tongue and ends at the stomach.

Stomach

In the stomach, acids and stomach motion break food down into particles small enough so that nutrients can be absorbed by the small intestine.

Small Intestine

The small intestine, despite its name, is the longest part of the gastrointestinal tract and is about 20 feet long. Food that passes from the stomach into the small intestine first passes through three parts:

• First it enters the duodenum
• Then the jejunum, and
• Finally the ileum.

Most of the digestive process occurs in the small intestine.

Large Intestine

Undigested material, such as plant fiber, is passed to the large intestine, mostly in liquid form. The large intestine is approximately 6 feet long and is the final portion of the digestive tract. It follows the small intestine and includes the cecum, the appendix, the colon, and the rectum, which extends to the anus.

Cecum and Appendix. The cecum and the appendix are located in the lower-right quadrant of the abdomen.

Colon. The colon absorbs excess water and salts into the blood. The remaining waste matter is converted to feces through bacterial action. The colon is divided into four major sections:

• The first section, the ascending colon, extends upward from the cecum on the right side of the abdomen.
• The second section, the transverse colon, crosses the upper abdomen to the left side.
• The third section extends downward on the left side of the abdomen toward the pelvis and is called the descending colon.
• The final section is the sigmoid colon.

Rectum and Anus. Feces are stored in the descending and sigmoid colon until they pass through the rectum and anus. The rectum extends through the pelvis from the end of the sigmoid colon to the anus.