Jejunum

The jejunum (/dʒiːˈdʒuːnəm/) is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum.

The jejunum lies between the duodenum and the ileum. The change from the duodenum to the jejunum is usually defined as the Duodenojejunal flexure and is attached, and thus "hung up", to the ventricle (see stomach) by the ligament of Treitz. In adult humans, the small intestine is usually between 5.5 and 6m long, 2.5m of which is the jejunum.

The pH in the jejunum is usually between 7 and 9 (neutral or slightly alkaline).

If the jejunum is impacted by blunt force the emesis reflex will be initiated.

The jejunum and the ileum are suspended by mesentery which gives the bowel great mobility within the abdomen. It also contains circular and longitudinal smooth muscle which helps to move food along by a process known as peristalsis.