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Merck Manual

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Quick Facts

Small Intestine


The Manual's Editorial Staff

Last full review/revision Sep 2019| Content last modified Sep 2019
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Your digestive system breaks food down into separate nutrients that fuel your body.

Your digestive tract (also called the gastrointestinal or GI tract) is the hollow tube that food goes through when you swallow it, digest it, and then pass the waste products as stool.

What is the small intestine?

Your small intestine, also called the small bowel, is part of your digestive tract. It connects your stomach and large intestine. Most nutrients are absorbed through your small intestine.

Your small intestine has three parts:

  • Duodenum

  • Jejunum

  • Ileum

The duodenum is the first part of your small intestine. It comes off of your stomach. Food and liquid leave your stomach and go into your duodenum to continue being digested. Digestive juices from your pancreas and bile (a green fluid that helps digest fat) from your gallbladder come into your duodenum through small tubes called ducts. These juices help break down food and also neutralize stomach acid. The walls of the small intestine make chemicals called enzymes that also help digest food.

The jejunum and ileum are the 2nd and 3rd parts of the small intestine. They absorb nutrients.

The walls of the small intestine are lined with muscles that contract to push food along.

Locating the Small Intestine

Locating the Small Intestine
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