Jejunum

At a glance

English

Jejunum

Latin (TA2)

Jejunum

System

Digestive

Region

Abdomen

Side

Single, on the midline

About the jejunum

The jejunum begins at the duodenojejunal flexure, just to the left of the second lumbar vertebra, and continues without any sharp boundary into the ileum. By convention it makes up roughly the first two-fifths of the small bowel beyond the duodenum, the ileum taking the remaining three-fifths. Its coils lie chiefly in the umbilical region and the upper left part of the abdomen, below the transverse colon and largely covered by the greater omentum.

Unlike the duodenum, it is wholly wrapped in peritoneum and hangs from the posterior abdominal wall by the mesentery. The root of the mesentery is short and runs obliquely from the flexure down to the right iliac fossa, but it fans out to a very long border attached to the bowel, which lets the loops move freely.

Several features help tell the jejunum from the ileum. It has a wider, thicker wall and a deeper red colour because it is better supplied with blood. Inside, the circular folds of the lining are tall and closely packed, giving a feathery look on contrast X-rays. The vessels in its mesentery form only one or two rows of arcades with long straight arteries, the vasa recta, running to the wall, and its mesentery holds less fat, so clear windows can be seen between vessels. Lymphoid patches are fewer than in the ileum.

Its lining, with circular folds, finger-like villi and microvilli on each cell, gives a huge surface area for absorbing the products of digestion: sugars, amino acids, fats, vitamins and minerals, along with much water. Coeliac disease, an immune reaction to gluten, typically flattens the villi of the upper small bowel, impairing absorption. Surgeons use loops of jejunum to rebuild the gut after removal of the stomach or pancreas, and feeding tubes can be placed directly into it.

Function and supply

Function

Absorbs most digested nutrients and much water from the gut contents, moving them on to the ileum by peristalsis.

Nerve supply

Vagal parasympathetic fibres and sympathetic fibres from the superior mesenteric plexus; pain from it is felt around the umbilicus.

Blood supply

Jejunal branches of the superior mesenteric artery through arcades and long vasa recta; veins drain to the superior mesenteric vein.