Enterocytes, or intestinal absorptive cells, are
simple columnar epithelial cellsfound in the small intestinesand colon. A glycocalyxsurface coat contains digestive enzymes. Microvillion the apical surface increase surface area for the digestion and transport of molecules from the intestinal lumen. The cells also have a secretory role.
The major functions of enterocytes include [ Ross, M.H. & Pawlina, W. 2003. "Histology: A Text and Atlas, 4th Edition." Lippincott Williams & Wilkins, Philadelphia.] :
*Ion uptake, including sodium, calcium, magnesium, and iron. This typically occurs through
*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.
Glucosecrosses the apical membraneof the enterocyte using the Na+ dependent glucose transporter. It moves through the cytosol(cytoplasm) and exits the enterocyte via the basolateral membrane(into the blood capillary) using GLUT-2 (Gene|SLC2A2). Galactoseuses the same transport system. Fructose, on the other hand, crosses the apical membrane of the enterocyte, using GLUT-5 (Gene|SLC2A5). 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.
Enteropeptidaseis responsible for activating pancreatic trypsinogeninto trypsin, which activates other pancreatic zymogens.
*Lipid uptake. Lipids are broken down by
pancreatic lipaseand bile, and then diffuse into the enterocytes. Smaller lipids are transported into intestinal capillaries, while larger lipids are processed by the Golgiand smooth endoplasmic reticuluminto lipoprotein chylomicraand exocytozed into lacteals.
*Vitamin uptake. Receptors bind to the vitamin Bssub|12-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 cellsin the mucosaare absorbed through receptor mediated endocytosison the basolateral surface and released as a receptor-IgA complex into the intestinal lumen. The receptor component confers additional stability to the molecule.
Dietary fructose intolerance occurs when there is a deficiency in the amount of
fructose carrier. Lactose intoleranceis 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.
Problems with the gastric intrinsic factor or its receptor can result in
* - "Digestive System: Alimentary Canal - jejunum, goblet cells and enterocytes"
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