| Jejunum | |
|---|---|
 Small intestine | |
 Superior and inferior duodenal fossæ. | |
| Details | |
| Pronunciation | /dʒɪˈdʒuːnəm/jij-OO-nəm[2][3] |
| Precursor | laude |
| Part of | Small intestine |
| System | Digestive system |
| Artery | Jejunal arteries |
| Vein | Jejunal veins |
| Nerve | Celiac ganglia,vagus[1] |
| Identifiers | |
| Latin | jejunum |
| MeSH | D007583 |
| TA98 | A05.6.03.001 |
| TA2 | 2958 |
| FMA | 7207 |
| Anatomical terminology | |
 |
| Major parts of the |
| Gastrointestinal tract |
|---|
Thejejunum is the second part of thesmall intestine inhumans and mosthigher vertebrates, includingmammals,reptiles, andbirds. Its lining is specialized for the absorption byenterocytes of small nutrientmolecules which have been previously digested byenzymes in theduodenum.
The jejunum lies between theduodenum and theileum and is considered to start at thesuspensory muscle of the duodenum, a location called theduodenojejunal flexure.[4] The division between the jejunum and ileum is not anatomically distinct.[5] In adulthumans, the small intestine is usually 6–7 m (20–23 ft) long (post mortem), about two-fifths of which (about 2.5 m (8.2 ft)) is the jejunum.[4]
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The interior surface of the jejunum—which is exposed to ingested food—is covered in finger–like projections of mucosa, calledvilli, which increase the surface area of tissue available to absorb nutrients from ingested foodstuffs. The epithelial cells which line these villi havemicrovilli. The transport of nutrients across epithelial cells through the jejunum and ileum includes thepassive transport of sugarfructose and theactive transport ofamino acids, smallpeptides,vitamins, and mostglucose. The villi in the jejunum are much longer than in the duodenum or ileum.
ThepH in the jejunum is usually between 7 and 8 (neutral or slightlyalkaline).
The jejunum and the ileum are suspended bymesentery which gives the bowel great mobility within theabdomen. It also contains circular and longitudinalsmooth muscle which helps to move food along by a process known asperistalsis.
The jejunum contains very fewBrunner's glands (found in the duodenum) orPeyer's patches (found in the ileum). However, there are a few jejunallymph nodes suspended in its mesentery. The jejunum has many largecircular folds in itssubmucosa calledplicae 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 subtlehistological differences:
The lining of the jejunum is specialized for the absorption byenterocytes of small nutrient particles which have been previously digested byenzymes in theduodenum. Once absorbed, nutrients (with the exception of fat, which goes to the lymph) pass from the enterocytes into theenterohepatic circulation and enter theliver via the hepatic portal vein, where the blood is processed.[6]
Infish, the divisions of the small intestine are not as clear and the termsmiddle intestine ormid-gut may be used instead of jejunum.[7]
Jejunum is derived from theLatin wordjējūnus (iēiūnus), meaning "fasting." It was so called because this part of thesmall intestine was frequently found to be void of food followingdeath,[8] due to its intensiveperistaltic activity relative to theduodenum andileum.
TheEarly Modern English adjectivejejune is derived from the same root.[9]
