Enterocyte Information
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.
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Functions
Apical membrane and Basolateral membraneThe 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
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 is created by an insufficient amount of lactase (a disaccharidase) enzyme, which is used to break down the sugar. As a result of this deficiency, undigested lactose cannot be absorbed and is instead passed on to the colonic bacteria, which metabolize the lactose. The bacteria release gas and metabolic products that enhance colonic motility. Although rare, if one is to completely eliminate lactose products from the diet, within a month, the subject will develop lactose intolerance.
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
- ^ 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"]. Indian Journal of Medical Research 133: p. 158. icmr.nic.in/ijmr/2011/february/0204.pdf.
External links
- Histology at BU 11706loa - "Digestive System: Alimentary Canal — jejunum, goblet cells and enterocytes"
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Etymology
This entry lacks etymological information. If you are familiar with the origin of this word, please add it to the page as described here. Noun enterocyte (plural enterocytes)- A cell found in the lining of the intestines and colon, participating in absorption of nutrients and secretion of digestive enzymes.
- 2009, January 9, “Michael Buszczak et al.”, Drosophila Stem Cells Share a Common Requirement for the Histone H2B Ubiquitin Protease Scrawny, volume 323, number 5911:
- ISCs signal to their daughters by Delta-Notch signaling to specify enterocyte versus enteroendocrine cell fate, but the pathway must remain inactive in the ISCs themselves to avoid differentiation.
- 2009, January 9, “Michael Buszczak et al.”, Drosophila Stem Cells Share a Common Requirement for the Histone H2B Ubiquitin Protease Scrawny, volume 323, number 5911: