Intestinal absorption in health and disease--sugars.
Carbohydrates are mostly digested to glucose, fructose and galactose before absorption by the small intestine. Absorption across the brush border and basolateral membranes of enterocytes is mediated by sodium-dependent and -independent membrane proteins. Glucose and galactose transport across the brush border occurs by a Na(+)/glucose (galactose) co-transporter (SGLT1), whereas passive fructose transport is mediated by a uniporter (GLUT5). The passive exit of all three sugars out of the cell across the basolateral membrane occurs through two uniporters (GLUT2 and GLUT5). Mutations in SGLT1 cause a major defect in glucose and galactose absorption (glucose-galactose Malabsorption), but mutations in GLUT2 do not appear to disrupt glucose and galactose absorption. Studies on GLUT1 null mice and Fanconi-Bickel patients suggest that there is another exit pathway for glucose and galactose that may involve exocytosis. There are no known defects of fructose absorption.
Wright
Ernest M
EM
Departments of Physiology and Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-1751, USA. ewright@mednet.ucla.edu
Martín
Martín G
MG
Turk
Eric
E
D000818:Animals; D050260:Carbohydrate Metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D051273:Glucose Transporter Type 2; D051296:Glucose Transporter Type 5; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000378:metabolism; D007408:Intestinal Absorption / Q000502:physiology; D008286:Malabsorption Syndromes / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000172:deficiency; D009154:Mutation
D004040:Dietary Carbohydrates; D051273:Glucose Transporter Type 2; D051296:Glucose Transporter Type 5; D009004:Monosaccharide Transport Proteins; D005632:Fructose; D005947:Glucose; D005690:Galactose