Jejunum

Jejunum
Small intestine
Superior and inferior duodenal fossæ.
Details
Precursor	midgut
Artery	jejunal arteries
Vein	jejunal veins
Nerve	celiac ganglia, vagus
Identifiers
Latin	Jejunum
MeSH	A03.556.124.684.500
Dorlands /Elsevier	Jejunum
TA	A05.6.03.001
FMA	7207
Anatomical terminology []

The jejunum (/dʒᵻˈdʒuːnəm/) is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds.

The jejunum lies between the duodenum and the ileum. The jejunum is considered to begin at the attachment of the suspensory muscle of the duodenum to the duodenum, a location called the duodenojejunal flexure. The division between the jejunum and ileum is not anatomically distinct. In adult humans, the small intestine is usually 6-7m long, about two-fifths of which (2.5 m) is the jejunum.

The interior surface of the jejunum—which is exposed to ingested food—is covered in finger-like projections of mucosa, called villi, which increase the surface area of tissue available to absorb nutrients from ingested foodstuffs. The epithelial cells which line these villi have microvilli. The transport of nutrients across epithelial cells through the jejunum and ileum includes the passive transport of sugar fructose and the active transport of amino acids, small peptides, vitamins, and most glucose. The villi in the jejunum are much longer than in the duodenum or ileum.

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

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.