消化.ppt

Absorption,Introduction . absorption sites: 1. mouth & esophagus-none 2. stomach - water , alcohol 3. ileum- water, saline 4. small intestine-important sites,12指肠,空肠,回肠,结肠,水、乙醇,水、盐,. Structure basis of absorption in small intestine,a. large surface area : villi, microvilli enhance area( 200m2 ) b. chyme stays in intestine for a long time : 3-8 h c. food have been digested to smaller , absorbent products,二Basic mechanisms of absorption,. Absorption form : active transport , simple diffusion , facilitate diffusion . Passway : transepithelial pathway (transcellular pathway ) paraepithelial pathway,Major Nutrients by small intestine absorption,Water Electrolytes Na+ ，K+，Cl-，HCO3-，Ca 2+，Fe 2+，Fe 3+，Mg2+，Cu2+，PO3- ，etc. Vitamins Nutrients Carbohydrate Protein Fat, Various nutrients absorption,1. Water: passive , osmotic diffusion 2. Salts : Na+ active transport, Na+-K+ pump,Fe 2+ active transport (acid ,Vt C increase absorption) Ca 2+ active transport (H+, Vt D, fat increase absorption Negative ions : cl- , HCO3- by Na+- pump,3. Carbohydrate or saccharide : secondary active transport the contransport carrier at the luminal border bind 2 Na+ and 1 glucose 4. Protein: secondary active transport ,(transportation of amino acid is same with glucose),5. Fat metabolism products: fatty acid , mono-glyceride , cholesterol long chain : * through formation of mixed micelles; * chylomicron ; * absorbed into lymphatic ; short chain: direct into blood . 6. Cholesterol: 1). only free cholesterol can be absorbed 2). mixed micelle chylomicron lympha 3). bile salt