+ Site Statistics
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Translate
+ Recently Requested

On the coupling of membrane digestion with intestinal absorption of sugars and amino acids

On the coupling of membrane digestion with intestinal absorption of sugars and amino acids

American Journal of Physiology 265(3 Pt 1): G409-G417

An hypothesis is advanced to account for the large paracellular component of absorption of nutrients by the small intestine. High concentrations of hexoses and amino acids in the immediate vicinity of transporters and cell junctions are generated by membrane-bound saccharases and peptidases. After saturation of membrane carriers, the concentrations of monomers in the microenvironment increase until paracellular plus transcellular absorption equals rates of formation. During hydrolysis of maltose, the concentration of glucose at which rates of absorption and formation are equal is 200-300 mM, and at these concentrations paracellular transport accounts for 60-80% of total absorption. Transcellular concentrative transport provides the force for osmotic flow and at the game time triggers contraction of perijunctional actomyosin, thereby increasing transjunctional coefficients of osmotic flow and solvent drag. Paracellular absorption requires no oxidative energy other than that required to maintain the transjunctional concentration gradient and to energize contraction of cytoskeletal elements controlling junctional permeability and functional surface of lateral membranes. Almost all glucose generated by membrane hydrolysis is absorbed, but some may diffuse from high concentration in the microenvironment to the lumen thus accounting for the small amounts of free glucose found in macrosamples of chyme. Unstirred layers adjacent to the brush border retard back diffusion to lumen, thus maintaining high concentrations for passive paracellular absorption. Coupling of membrane digestion with paracellular transport provides almost perfect matching of absorption to digestive loads because transport by solvent drag is proportional to concentration at cell junctions and this in turn is proportional to rate of hydrolysis. Adaptive changes of membrane-bound hydrolases and transporters induced by dietary changes, lactation, or development can be interpreted in terms of coupling between membrane digestion, paracellular and transcellular mechanisms rather than transcellular transport alone.

(PDF emailed within 0-6 h: $19.90)

Accession: 002448002

Download citation: RISBibTeXText

PMID: 8214061

DOI: 10.1152/ajpgi.1993.265.3.G409

Related references

Digestion and intestinal absorption of sugars, amino acids, water and electrolytes in total fasting and semistarvation. Verhandlungen der Deutschen Gesellschaft für Innere Medizin 83: 448-452, 1977

Intestinal absorption of sugars and amino acids. American Journal of Clinical Nutrition 8: 137-146, 1960

Significance of the unstirred layer for the digestion and absorption of sugars and amino acids from di peptides and di saccharides. Gastroenterologie Clinique et Biologique 2(3): 327, 1978

Mechanism of the intestinal absorption of sugars and amino acids. Friedman, M H F (Ed ) Functions Of The Stomach And Intestine Proceedings Of The J Earl Thomas Memorial Symposium Philadelphia, Pa , U S A , Nov 19-20, 1973 Xv+462p Illus University Park Press: Baltimore, Md , U S A ; London, England ISBN 0-8391-0715-3: 273-283, 1975

Intestinal absorption of sugars and amino acids in the earthworm. Revista Espanola de Fisiologia 33(3): 227-232, 1977

Intestinal absorption in vivo and drugs. II. Action of some drugs on intestinal absorption of 2 amino acids and 2 sugars in rats. Bollettino Della Societa Italiana di Biologia Sperimentale 43(16): 953-956, 1967

Interaction between sugars and amino acids in intestinal absorption by rat, in vivo. Experientia 31(10): 1171-1173, 1975

Absorption kinetics of amino acids and reducing sugars during digestion of barley or wheat meals in the pig: preliminary data. Annales de Biologie Animale, Biochimie, Biophysique 19(3B): 739-747, 1979

Intestinal absorption of amino acids and sugars during postnatal development of mink. FASEB Journal 12(4): A369, March 17, 1998

Inhibition of intestinal absorption of sugars and amino acids by prenylamine (Segontin). Deutsche Medizinische Wochenschrift 97(10): 394-396, 1972

Studies on the competitive intestinal absorption of amino acids, and sugars in two teleost fishes. Revista Espanola de Fisiologia 35(1): 111-114, 1979

Renal excretion of amino acids and sugars in young children with impaired intestinal absorption. Rossiiskii Vestnik Perinatologii i Pediatrii 40(2): 54, 1995

In vivo intestinal absorption and drugs part 2 action of certain drugs on the absorption of 2 amino acids and 2 sugars in the rats. Bollettino Societa Italiana Biologia Sperimentale 43(16): 953-956, 1967

Absorption of amino acids in different parts of the small intestine in growing pigs 4. effect of sugars on absorption of amino acids and water. Acta Physiologica Polonica 32(5): 585-594, 1981

Intestinal transport of amino acids and sugars: advances using membrane vesicles. Annual Review of Physiology 46: 417-433, 1984