Matthew Landry HUEC 3115 Human Nutrition and Metabolism Nutrient Amino Acids Glucose Fructose SCFA LCFA Vitamin C Thiamin Riboflavin Choline Niacin Pantothenic Acid Folate Vitamin B12 Mechanism of Absorption Duodenum primary Jejunum primary and Ileum Requires carriers for absorption however paracellular absorption can occur in occasional situations Depending on the amino acid a different amino acid transporter may be required and some require sodium for activation Duodenum Jejunum and Ileum by active transport Requires energy as ATP and the involvement of a specific receptor The glucose galactose receptor has been designed sodium glucose transporter 1 SGLT1 It simultaneously transports Na and glucose in the same direction symport At high glucose concentrations glucose is absorbed by facilitated transporter type 2 GLUT2 Duodenum Jejunum and Ileum by a specific facilitative transporter GLUT5 Is also independent of the active NA ATPase dependent transport by SGLT1 Duodenum Jejunum and Ileum Are able to passively diffuse through the cell membrane Other short chains are incorporated into micelles Duodenum Jejunum and Ileum incorporated into micelles for transport across the brush border The mechanism for transporting fatty acids across the apical membrane is not fully understood Two suggested mechanism are a protein independent diffusion model and a protein dependent model which uses fatty acid transport proteins FATP Duodenum Jejunum and Ileum Ascorbic acid by sodium dependent vitamin C transporters SVCT 1 and 2 Dehydroascorbic acid by glucose transporters GLUT 1 and 3 Duodenum Jejunum primary and Ileum primary Absorption is both passive and active high concentrations favors passive Mediated by two thiamin transporters ThTr1 and ThTr2 Active sodium dependent and sodium independent carrier mediated thiamin transport has also been suggested Duodenum by a saturable energy dependent sodium independent carrier riboflavin transporter 2 RFT2 When large amounts are consumed absorption may occur my diffusion Duodenum Jejunum and Ileum by transport proteins in the enterocyte Stomach Duodenum Jejunum and Ileum Readily absorbed in the small intestines by sodium dependent carrier mediated facilitated diffusion At high concentrations absorbed almost completely by passive diffusion Jejunum by passive diffusion when present in high concentrations and by a sodium dependent multivitamin transporter SMVT when present in low concentrations Duodenum and Jejunum by proton coupled folate transporter PCFT Ileum the vitamin B12 IF complex interacts with a protein Matthew Landry HUEC 3115 Human Nutrition and Metabolism Biotin Vitamin B6 Vitamin A Vitamin D Vitamin E Vitamin K Calcium Phosphorus Magnesium Sodium receptor called cubilin and amnionless which facilitates attachment to the ileal cell s plasma membrane Binding of the complex to the receptor triggers active endocytotic internalization Duodenum primary and colon occurs by passive diffusion with consumption of pharmacological doses With physiological intakes absorption by high affinity carrier mediated and sodium dependent multivitamin transporter SMVT2 Jejunum PL PN and PM are absorbed by passive diffusion At physiological doses the vitamin is absorbed rapidly in its free form Duodenum and Jejunum incorporated into micelles and are absorbed by passive diffusion across the border Additionally carotenoids also may be absorbed by a carotenoid transporter called scavenger receptor class B type 1 SR B1 1 2 Duodenum Jejunum and Ileum primary Absorbed from a micelle in association with fat and with aid of bile salts by passive diffusion Jejunum by passive diffusion as part of a micelle Bile salts are required for emulsification solubilization and micelle formation Little is known about tocotrienol absorption however the involvement of Niemann Pick C1 like 1 NPC1L1 transporter in tocotrienol absorption has been suggested Duodenum Jejunum Ileum and Colon Phylloquinone is absorbed primarily in the jejunum as part of micelles Some may be absorbed by active trans port from the proximal small intestines Menaquinones are absorbed by passive diffusion from the ileum and colon Duodenum Jejunum and Ileum by a saturable carrier mediated active transport and diffusion The main transport operates in the duodenum and proximal jejunum requires energy and is regulated by calcitriol uses a vitamin D dependent membrane channel protein called transient receptor potential TRP vanilloid V 6 a vitamin D dependent cytosolic binding protein called calbindin D9k that shuttles the calcium acorss the cell cytosol and a vitamin D dependent calcium ATPase pump on the luminal side The second route is paracellular diffusion a passive nonsaturable nonregualted process in the jejunum and ileum Duodenum primary Jejunum primary and Ileum by a saturable carrier mediated active transport and diffusion Duodenum Jejunum primary Ileum primary and colon mostly when a disease has interfered with small intestines absorption by a saturable carrier mediated active transport and diffusion The transient receptor potential TRP melastatin divalent cation permeable channel protein TRMP6 Duodenum Jejunum Ileum and Colon absorption by the Na Glucose cotransport system throughout the small intestines the Na and Cl cotransport system in the small intestines and proximal colon and an electrogenic sodium absorption Matthew Landry HUEC 3115 Human Nutrition and Metabolism Potassium Chloride Iron Iodine Selenium Zinc Cooper Chromium Manganese Molybdenum Fluoride mechanism primarily in the colon Duodenum Jejunum and Ileum Exact location unknown By passive diffusion or by a K H ATPase pump Duodenum Jejunum and Ileum Na Glucose cotransport system throughout the small intestines as Cl follows the actively absorbed Na through a paracellular pathway Na creates an electrical gradient that provides the drive for the diffusion of Cl Additionally the Na and Cl cotransport system in the small intestines Duodenum primary Jejunum and Ileum heme iron is absorbed intact across the brush border by heme carrier protein 1 hep1 A proton coupled folate transporter PCFT has also been identified Nonheme is absorbed by the divalent cation DCT or DMT It may be coupled with H transport symport A membrane protein integrin may facilitate ferric iron absorption Stomach primary and duodenum diffusion Jejunum by active sodium dependent transport Duodenum primary and jejunum upper portion carrier mediated transport and diffusion Zrt and Irt