Jejunum

Major parts of the
Gastrointestinal tract
Upper gastrointestinal tract Mouth Pharynx Esophagus Stomach Duodenum
Lower gastrointestinal tract Small intestine Jejunum Ileum Large intestine Cecum Appendix Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anus
See also Gastrointestinal wall Human digestive system Anatomical terminology Outline of anatomy
v t e

The jejunum is the second part of the

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

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.

Histology

The jejunum contains very few

There is no line of demarcation between the jejunum and the ileum. However, there are subtle

• The jejunum has less fat inside its mesentery than the ileum.
• The jejunum is typically of larger diameter than the ileum.
• The villi of the jejunum look like long, finger-like projections, and are a histologically identifiable structure.
• While the length of the entire intestinal tract contains
  lymphoid nodules that contain large numbers of lymphocytes and immune cells, like microfold cells
  .

• 
  Transmission electron microscope (TEM) image of human jejunum
• 
  TEM image of mouse jejunum (14,000-fold magnification)
• 
  Dog jejunum (magnified 100-fold)

Function

The lining of the jejunum is specialized for the absorption by

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.^[7]

History

Etymology

Jejunum is derived from the Latin word jējūnus (iēiūnus), meaning "fasting." 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.

The Early Modern English adjective jejune is derived from the same root.^[9]

References