. . . "Beltina.org The Gastrointestinal System Jejunum - function and definitionJejunum - function and definitionJejunum is the middle segment of the SMALL INTESTINE, between the ILEUM and the DUODENUM. The jejunum is six to eight feet long and handles absorption of carbohydrates and proteins, as well as vitamins such as VITAMIN K and minerals such as iron." .