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Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells found in the small intestines and colon. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase surface area for the digestion and transport of molecules from the intestinal lumen. The cells also have a secretory role.

Functions [edit]

Apical membrane and Basolateral membrane

The major functions of enterocytes include:^[1]

Ion uptake, including sodium, calcium, magnesium, and iron. This typically occurs through active transport.
Water uptake. This follows the osmotic gradient established by Na+/K+ ATPase on the basolateral surface. This can occur transcellularly or paracellularly.
Sugar uptake. Polysaccharidases and disaccharidases 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 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 and the Cori Cycles and can be synthesized with lipase.
Lipid uptake. Lipids are broken down by pancreatic lipase and bile, and then diffuse into the enterocytes. Smaller lipids are transported into intestinal capillaries, while larger lipids are processed by the Golgi and smooth endoplasmic reticulum into lipoprotein chylomicra and exocytozed into lacteals.
Vitamin B12 uptake. Receptors bind to the vitamin B₁₂-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. IgA 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.

Pathology [edit]

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 (a disaccharidase) 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.

Toxins such as cholera toxin may increase the secretion or decrease the intake of water and electrolytes, leading to possibly severe dehydration and electrolyte imbalance.^[2]

References [edit]

^ Ross, M.H. & Pawlina, W. 2003. Histology: A Text and Atlas, 4th Edition. Lippincott Williams & Wilkins, Philadelphia.
^ Joaquín Sánchez, Jan Holmgren (February 2011). [icmr.nic.in/ijmr/2011/february/0204.pdf "Cholera toxin – A foe & a friend"] Check |url= scheme (help). Indian Journal of Medical Research 133. p. 158.

External links [edit]

BU Histology Learning System: 11706loa - "Digestive System: Alimentary Canal — jejunum, goblet cells and enterocytes"

UpToDate Contents

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English Journal

Enzymes involved in l-carnitine biosynthesis are expressed by small intestinal enterocytes in mice: Implications for gut health.

Shekhawat PS, Sonne S, Carter AL, Matern D, Ganapathy V.SourceDepartment of Pediatrics, Medical College of Georgia, Georgia Health Sciences University, Augusta, GA 30912, United States; Department of Biochemistry and Molecular Biology, Medical College of Georgia, Georgia Health Sciences University, Augusta, GA 30912, United States. Electronic address: shekhawatp@ecu.edu.
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BACKGROUND: Carnitine is essential for mitochondrial β-oxidation of long-chain fatty acids. Deficiency of carnitine leads to severe gut atrophy, ulceration and inflammation in animal models of carnitine deficiency. Genetic studies in large populations have linked mutations in the carnitine transpor
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c-di-GMP signaling regulates E. coli O157:H7 adhesion to colonic epithelium.

Hu J, Wang B, Fang X, Means WJ, McCormick RJ, Gomelsky M, Zhu MJ.SourceDepartment of Animal Science, University of Wyoming, Laramie, WY 82071, USA.
Veterinary microbiology.Vet Microbiol.2013 Jun 28;164(3-4):344-51. doi: 10.1016/j.vetmic.2013.02.023. Epub 2013 Mar 4.
Escherichia coli O157:H7 is an important foodborne pathogen that causes serious illness in humans at low infectious doses. The main source of infections is beef or greens contaminated with E. coli O157:H7 shed by cattle. Here we investigated the role of c-di-GMP-dependent signal transduction in catt
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Influence of MDR1 C1236T polymorphism on lopinavir plasma concentration and virological response in HIV-1-infected children.

Bellusci CP, Rocco C, Aulicino P, Mecikovsky D, Curras V, Hegoburu S, Bramuglia GF, Bologna R, Sen L, Mangano A.SourceLaboratorio de Biología Celular y Retrovirus - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Hospital de Pediatría "Juan P. Garrahan", Buenos Aires, Argentina.
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BACKGROUND: Variability in MDR1 and PXR has been associated with differences in drug plasma levels and response to antiretroviral therapy. We investigated whether polymorphisms in MDR1 (T-129C, C1236T and C3435T) and PXR (C63396T) affect lopinavir plasma concentration and the virological or immunolo
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Japanese Journal

溶血性尿毒症症候群患児から単離した腸管出血性大腸菌O165 : HNMの病原性遺伝子解析

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日本小児科学会雑誌 115(1), 56-61, 2011-01-01
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Plasma citrulline measurement using UPLC tandem mass-spectrometry to determine small intestinal enterocyte pathology

DEMACKER Pierre N. M.,BEIJERS Antonius M.,VAN DAAL Henny,DONNELLY J. Peter,BLIJLEVENS Nicole M. A.,VAN DEN OUWELAND Johannes M. W.
Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 877(4), 387-392, 2009-02-01
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腸管出血性大腸菌における病原性遺伝子の協調的発現制御機構

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