Chapter 12 Digestion(new)消化.ppt

?Movement of colon Segmentation contraction, peristalsis, mass action contraction. Less movement. 12.6 Absorption Small intestine as main sites of absorption: The large absorptive surface area. Including valvulae connivent, villi and microvilli. Chyme stays in small intestine for longer time: 3-8h. Abundant capillaries and lymphatic capillaries. Food has been digested into small molecules. Absorption the process of transporting small molecules from the lumen of the gut into blood. Pathway of absorption: Blood circulation Lymphatic circulation, and then go entry blood circulation. Sites of absorption: Duodenum and jejunum: Most nutrients. Terminal ileum: Bile salts and vitamin B12. Pathways for absorption: Transcellular absorption: Paracellular absorption: Basic mechanisms of absorption: Simple diffusion Facilitating diffusion Active transportion The absorption of main substances Water: Most water in small intestine, less water in stomach and large intestine by simple diffusion for maintaining the osmotic pressure. Sodium absorption: Sites of absorption: jejunum ileum colon Active transportation combined with glucose, amino acids. 葡萄糖 葡萄糖 ○ 氨基酸转运系统 Na+ 蛋白酶 氨基肽酶 Iron absorption: Sites of absorption: duodenum and jejunum. The transferrin (Tf) was needed for iron absorption. Glucose and amino acid: Secondary facilitated transport: Na+, carrier. Fat absorption: In lumen: Form Mixed micelles. The end products of lipid (free fatty acid, glyceride, cholesterol) combine with bile salts. Hydrophilic. Contact with microvilli. At the surface of epithelial cells: Free fatty acid, cholesterol and glycerides? epithelial cells. Bile salts ? back to lumen. In the epithelial cells: Free fatty acid with shorter chains, part glycerol ? diffuse ? blood. Free fatty acid with longer chains, cholesterol and glycerides ? chylomicron ? Golgi complex ? lymphatic capillaries ? blood circulation. * * Gastrin (blue), produced by the lower part of the stomach, enters the bloodstream