Editing Jejunum (section)

==Structure==
{{uncited section|date=December 2024}}

{{See also|Small intestine}}

The interior surface of the jejunum—which is exposed to ingested food—is covered in finger–like projections of mucosa, called [[Intestinal villus|villi]], which increase the surface area of tissue available to absorb nutrients from ingested foodstuffs. The epithelial cells which line these villi have [[Microvillus|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 acid]]s, small [[peptide]]s, [[vitamin]]s, 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 8 (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]].

===Histology===

The jejunum contains very few [[Brunner's glands]] (found in the duodenum) or [[Peyer's patches]] (found in the ileum). However, there are a few jejunal [[lymph node]]s suspended in its mesentery. The jejunum has many large [[circular folds]] in its [[submucosa]] called [[plicae circulares]] that increase the surface area for nutrient absorption. The plicae circulares are best developed in the jejunum.

There is no line of demarcation between the jejunum and the ileum. However, there are subtle [[histological]] differences:
* 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 tissue]], only the ileum has abundant [[Peyer's patches]], which are unencapsulated [[lymphoid nodule]]s that contain large numbers of [[lymphocyte]]s and immune cells, like [[microfold cell]]s.

<gallery mode="packed">
 Image:Microvilli.jpg|[[Transmission electron microscopy|Transmission electron microscope]] (TEM) image of human jejunum
 Image:Nudemousejejunum EM.jpg|TEM image of mouse jejunum (14,000-fold magnification)
 Image:Dogjejunum100x.jpg|Dog jejunum (magnified 100-fold)
</gallery>