Editing Enterocyte

{{Short description|Type of intestinal cell}}
{{Infobox cell
| Name        = Enterocyte
| Latin       = enterocytus
| Image       = File:Cell enterocyte.png
| Caption     = Schematic drawing of an enterocyte: the [[intestinal lumen]] is above the brush border.
| Image2      =
| Caption2    =
| Precursor   =
| System      =
| Location = [[Small intestine]]
| Shape = [[Simple columnar]]
| Function = [[Epithelial cells]]
}}
'''Enterocytes''', or '''intestinal absorptive cells''', are [[simple columnar]] [[epithelial cells]] which line the inner surface of the [[Small intestine|small]] and [[Large intestine|large intestines]]. A [[glycocalyx]] surface coat contains [[digestive enzyme]]s. [[Microvilli]] on the apical surface increase its surface area. This facilitates transport of numerous small molecules into the enterocyte from the intestinal [[Lumen (anatomy)|lumen]]. These include broken down [[protein]]s, [[fat]]s, and [[sugar]]s, as well as water, [[electrolyte]]s, [[vitamin]]s, and [[bile salt]]s. Enterocytes also have an [[endocrine]] role, secreting hormones such as [[leptin]].

==Function==
The major functions of enterocytes include:<ref>{{cite book |last=Ross |first=M.H. |last2=Pawlina |first2=W. |date=2003 |title=Histology: A Text and Atlas |edition=4th |publisher=Lippincott Williams & Wilkins |isbn=978-0-683-30242-4 |oclc=50334073}}</ref>
*'''Ion uptake''', including [[sodium]], [[calcium]], [[magnesium]], [[iron]], [[zinc]], and [[copper]]. This typically occurs through [[active transport]].
*'''Water uptake'''. This follows the osmotic gradient established by [[NaKATPase|Na+/K+ ATPase]] on the basolateral surface. This can occur [[diffusion|transcellularly]] or [[paracellular transport|paracellularly]].
*'''Sugar uptake'''. Polysaccharidases and [[disaccharidase]]s in the [[glycocalyx]] break down large sugar molecules, which are then absorbed. [[Glucose]] crosses the [[apical membrane]] of the enterocyte using the [[sodium-glucose cotransporter]].  It moves through the [[cytosol]] (cytoplasm) and exits the enterocyte via the [[basolateral membrane]] (into the [[blood capillary]]) using [[GLUT2]]. [[Galactose]] uses the same transport system. [[Fructose]], on the other hand, crosses the apical membrane of the enterocyte, using [[GLUT5]]. It is thought to cross into the blood capillary using one of the other [[glucose transporter|GLUT transporters]].
*'''Peptide and amino acid uptake'''. Peptidases in the glycocalyx cleave proteins to amino acids or small peptides. [[Enteropeptidase]] (also known as enterokinase) is responsible for activating [[pancreatic]] [[trypsinogen]] into [[trypsin]], which activates other pancreatic [[zymogens]]. They are involved in the [[Krebs cycle|Krebs]] and the [[Cori Cycle]]s and can be synthesized with [[lipase]].
*'''Lipid uptake'''. Lipids are broken down by [[Human pancreatic lipase|pancreatic lipase]] aided by [[bile]], and then diffuse into the enterocytes. Smaller lipids are transported into intestinal capillaries, while larger lipids are processed by the [[Golgi apparatus|Golgi]] and [[smooth endoplasmic reticulum]] into lipoprotein [[chylomicra]] and [[exocytosis|exocytozed]] into [[lacteals]].
*'''Vitamin B12 uptake'''. Receptors bind to the [[vitamin B12]]-[[intrinsic factor|gastric intrinsic factor]] complex and are taken into the cell.
*'''Resorption of unconjugated bile salts'''. Bile that was released and not used in emulsification of lipids are reabsorbed in the [[ileum]]. Also known as the [[enterohepatic circulation]].
*'''Secretion of immunoglobulins'''. [[Immunoglobulin A]] from [[plasma cells]] in the [[mucosa]] are absorbed through receptor-mediated [[endocytosis]] on the basolateral surface and released as a receptor-IgA complex into the intestinal lumen. The receptor component confers additional stability to the molecule.

==Clinical significance==
*[[Fructose malabsorption|Dietary fructose intolerance]] occurs when there is a deficiency in the amount of [[fructose carrier]].
*[[Lactose intolerance]] is the most common problem of carbohydrate digestion and occurs when the human body doesn't produce a sufficient amount of [[lactase]] enzyme to break down the sugar lactose found in dairy. As a result of this deficiency, undigested lactose is not absorbed and is instead passed on to the colon. There bacteria metabolize the lactose and in doing so release gas and metabolic products that enhance colonic motility. This causes gas and other uncomfortable symptoms.
*[[Cholera toxin]] may increase the secretion or decrease the intake of water and electrolytes, leading to possibly severe [[dehydration]] and [[electrolyte imbalance]].<ref>{{cite journal |url=http://icmr.nic.in/ijmr/2011/february/0204.pdf |title=Cholera toxin – A foe & a friend |author=Joaquín Sánchez, Jan Holmgren |journal=Indian Journal of Medical Research |volume=133 |page=158 | date=February 2011 }}</ref>
*[[Rotavirus]] selectively invades and kills mature enterocytes in the small intestine.<ref>Robbins and Cotran Pathologic Basis of Disease, Chapter 17, 749-819</ref>

==Stem cell aging==
[[Adult stem cell|Intestinal stem cell]] aging has been studied in ''[[Drosophila]]'' as a model for understanding the biology of stem cell/niche aging.<ref name = Park2018>{{cite journal |vauthors=Park JS, Jeon HJ, Pyo JH, Kim YS, Yoo MA |title=Deficiency in DNA damage response of enterocytes accelerates intestinal stem cell aging in Drosophila |journal=Aging (Albany NY) |volume=10 |issue=3 |pages=322–338 |date=March 2018 |pmid=29514136 |pmc=5892683 |doi=10.18632/aging.101390 }}</ref>  Using knockdown mutants defective in various genes that function in the [[DNA damage (naturally occurring)|DNA damage]] response in enterocytes, it was shown that deficiency in the DNA damage response accelerates intestinal stem cell aging, thus providing a better understanding of the molecular mechanisms of this aging process.<ref name = Park2018/>

== See also ==
*[[List of human cell types derived from the germ layers]]

== References ==
{{Reflist}}

==External links==
* {{BUHistology|11706loa}} — "Digestive System: Alimentary Canal&nbsp;— jejunum, goblet cells and enterocytes"

{{Gastrointestinal physiology}}
{{Authority control}}

[[Category:Epithelial cells]]
[[Category:Digestive system]]