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Small Intestine

The organ where most digestion occurs. It measures about 20 feet and includes the duodenum, jejunum, and ileum.

PubMed Health Glossary
(Source: NIH - National Institute of Diabetes and Digestive and Kidney Diseases)

Drawing of the small intestine showing the duodenum, jejunum, and ileum. Also shown are the stomach, appendix, colon, and rectum. Click to enlarge

The small intestine and nearby organs National Institutes of Health

About the Intestine

The intestine is a winding muscular tube extending from the stomach to the anus. Its main purpose is to digest food. But the intestine is not only there for digestion: it also produces various substances that carry messages to other parts of the body, and plays an important role in fighting germs and regulating the body's water balance. For some people, the intestine reflects how they are feeling: for instance, they might get a stomach ache, diarrhoea or constipation when they are stressed or upset about something.

The small intestine, which is directly connected to the stomach, is 3 to 5 m long and is made up of the duodenum, jejunum and ileum. The inside wall of the small intestine is folded like the body of an accordion. This makes the surface area very big and the food can make contact with a large number of intestinal cells.

In the small intestine, substances produced by the body (enzymes)... Read more about the Small Intestine

Terms to know

Appendix
A 4-inch pouch attached to the cecum, the first part of the large intestine. The appendix's function, if any, is unknown.
Colon (Bowel)
The longest part of the large intestine, which is a tube-like organ connected to the small intestine at one end and the anus at the other. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum and leaves the body through the anus.
Duodenum
The first part of the small intestine that connects to the stomach.
Ileum
The lower end of the small intestine.
Jejunum
The middle section of the small intestine between the duodenum and ileum.
Rectum
The last several inches of the large intestine closest to the anus.
Stomach
An organ that is part of the digestive system. The stomach helps digest food by mixing it with digestive juices and churning it into a thin liquid.

Terms to know

Appendix
A 4-inch pouch attached to the cecum, the first part of the large intestine. The appendix's function, if any,...
Colon (Bowel)
The longest part of the large intestine, which is a tube-like organ connected to the small intestine at one e...
Duodenum
The first part of the small intestine that connects to the stomach....
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