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

Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been previously digested by enzymes in the duodenum.

However, there are subtle histological differences: The lining of the jejunum is specialized for the absorption by enterocytes of small nutrient particles which have been previously digested by enzymes in the duodenum.

Once absorbed, nutrients (with the exception of fat, which goes to the lymph) pass from the enterocytes into the enterohepatic circulation and enter the liver via the hepatic portal vein, where the blood is processed.

It was so called because this part of the small intestine was frequently found to be void of food following death,[8] due to its intensive peristaltic activity relative to the duodenum and ileum.