Britannica Sources used in this answer

What are the three sections of the small intestine?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram of the human digestive system viewed from the front, showing and labeling organs including the mouth, teeth, tongue, salivary glands, pharynx, esophagus, liver, stomach, gallbladder, pancreas, large intestine, small intestine, appendix, rectum, and anus. — digestion The human digestive system as seen from the front.

The small intestine is a long, coiled tube that serves as the primary site for the digestion and absorption of nutrients. It is anatomically and functionally divided into three successive regions:1

Duodenum: The first and shortest segment, which receives partially digested food from the stomach. It is approximately 23 to 28 cm (9 to 11 inches) long and is the site where digestive juices from the pancreas, liver, and gallbladder enter the tract to neutralize stomach acid and aid in chemical digestion.213
Jejunum: The middle section of the small intestine, comprising about two-fifths of the remaining tract. It is characterized by a deep red color due to an extensive blood supply and exhibits rapid, vigorous peristaltic movements.21
Ileum: The final and longest segment, accounting for about three-fifths of the small intestine. It is responsible for the absorption of vitamin B12 and the reabsorption of bile salts before the remaining contents pass into the large intestine.14