The jejunum (plural: jejuna or jejunums) is the second part of the small intestine, following the duodenum and before the ileum.
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Summary
location: peritoneal cavity
function: absorption of carbohydrates, amino acids and fatty acids
blood supply and drainage: jejunal branches of the superior mesenteric artery and vein
Gross anatomy
The jejunum measures on average 2.5 m in length 1. It is differentiated from the duodenum by the duodenal-jejunal flexure, however there is no discrete anatomical landmark differentiating it from the ileum.
Relations
Together with the ileum, the jejunum lies in the free margin of the mesentery as a continuation of the duodenum.
Arterial supply
jejunal branches from the superior mesenteric artery
Venous drainage
corresponding veins which drain into the superior mesenteric vein
Lymphatic drainage
lymphatics drain into the superior mesenteric lymph nodes
Innervation
sympathetic: lateral horn cells of spinal segments T9 and T10
parasympathetic: vagus nerve via the superior mesenteric plexus augments the peristaltic activity
Radiographic features
CT/MRI
Distension of the small bowel with enteric contrast is commonly used to improve assessment. An anti-spasmodic drug may also be administered during the examination.
CT enteroclysis and MR enteroclysis involve the administration of enteric contrast through a nasojejunal tube, while CT enterography and MR enterography require the patient to drink oral contrast material.
Fluoroscopy
Small bowel follow-through examination (SBFT)
The jejunum has a delicate feathery appearance and is located in the left upper abdomen. It can be differentiated from ileum by having a greater calibre, thicker and more numerous folds (see: jejunum vs ileum).
Small bowel enteroclysis allows better demonstration of the mucosa, although it is not widely used due to its invasive nature.
Development
The jejunum arises from the midgut, and is formed by all three germinal layers (endoderm, ectoderm and mesoderm). During week 6-10 of gestation, herniation of the midgut occurs, causing it to lie outside the peritoneal cavity. Subsequently, it rotates 270 degrees before it is returned to its final anatomical position 3. Abnormalities of this process are associated with intestinal malrotation.
History and etymology
Jejunum means "empty" in Latin 4.
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