Thejejunumis the second part of thesmall intestineinhumansand mosthigher vertebrates,includingmammals,reptiles,andbirds.Its lining is specialized for the absorption byenterocytesof small nutrientmoleculeswhich have been previously digested byenzymesin theduodenum.
| Jejunum | |
|---|---|
 Small intestine | |
 Superior and inferior duodenal fossæ. | |
| Details | |
| Pronunciation | /dʒɪˈdʒuːnəm/jij-OO-nəm[2][3] |
| Precursor | Midgut |
| 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 | |
The jejunum lies between theduodenumand theileumand 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]
Structure
editThe 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 transportof sugarfructoseand theactive transportofamino acids,smallpeptides,vitamins,and mostglucose.The villi in the jejunum are much longer than in the duodenum or ileum.
ThepHin the jejunum is usually between 7 and 8 (neutral or slightlyalkaline).
The jejunum and the ileum are suspended bymesenterywhich gives the bowel great mobility within theabdomen.It also contains circular and longitudinalsmooth musclewhich helps to move food along by a process known asperistalsis.
Histology
editThe jejunum contains very fewBrunner's glands(found in the duodenum) orPeyer's patches(found in the ileum). However, there are a few jejunallymph nodessuspended in its mesentery. The jejunum has many largecircular foldsin itssubmucosacalledplicae circularesthat 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 subtlehistologicaldifferences:
- 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 containslymphoid tissue,only the ileum has abundantPeyer's patches,which are unencapsulatedlymphoid nodulesthat contain large numbers oflymphocytesand immune cells, likemicrofold cells.
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Transmission electron microscope(TEM) image of human jejunum -
TEM image of mouse jejunum (14,000-fold magnification) -
Dog jejunum (magnified 100-fold)
Function
editThe lining of the jejunum is specialized for the absorption byenterocytesof small nutrient particles which have been previously digested byenzymesin theduodenum.Once absorbed, nutrients (with the exception of fat, which goes to the lymph) pass from the enterocytes into theenterohepatic circulationand enter thelivervia the hepatic portal vein, where the blood is processed.[6]
Other animals
editInfish,the divisions of the small intestine are not as clear and the termsmiddle intestineormid-gutmay be used instead of jejunum.[7]
History
editEtymology
editJejunumis derived from theLatinwordjējūnus(iēiūnus),meaning "fasting."It was so called because this part of thesmall intestinewas frequently found to be void of food followingdeath,[8]due to its intensiveperistalticactivity relative to theduodenumandileum.
TheEarly Modern Englishadjectivejejuneis derived from the same root.[9]
References
edit- ^Nosek, Thomas M."Section 6/6ch2/s6ch2_30".Essentials of Human Physiology.Archived fromthe originalon 2016-03-24.
- ^OED2nd edition, 1989.
- ^Entry "jejunum"inMerriam-Webster Online Dictionary.
- ^abDrake, Richard L.; Vogl, Wayne; Tibbitts, Adam W. M. Mitchell; illustrations by Richard; Richardson, Paul (2005).Gray's anatomy for students.Philadelphia: Elsevier/Churchill Livingstone. pp.273–275.ISBN978-0-8089-2306-0.
- ^Deakin, Barbara Young; et al. (2006).Wheater's functional histology: a text and colour atlas(5th ed.). Churchill Livingstone/Elsevier. p. 263.ISBN978-0-443-068-508.
- ^CRANE, RK (Oct 1960). "Intestinal absorption of sugars".Physiological Reviews.40(4):789–825.doi:10.1152/physrev.1960.40.4.789.PMID13696269.
- ^ Guillaume, Jean; Praxis Publishing; Sadasivam Kaushik; Pierre Bergot; Robert Metailler (2001).Nutrition and Feeding of Fish and Crustaceans.Springer. p. 31.ISBN9781852332419.Retrieved2009-01-09.
- ^Harper, Douglas."jejunum".Etymology Online.Retrieved15 November2014.
- ^"Oxford English Dictionary: jejune, adj".
External links
edit- Gastrolab.net:The Jejunum
- Peyer's patchesArchived2016-03-04 at theWayback Machine
- Anatomy photo:37:11-0100at the SUNY Downstate Medical Center – "Abdominal Cavity: The Jejunum and the Ileum"
- Anatomy image:7856at the SUNY Downstate Medical Center
