动物生理学6消化与吸收.ppt
6.6 Absorption,吸收：消化管腔内经过消化后的营养物质、水和无机盐类等透过消化管粘膜上皮进入血液和淋巴的过程。6.6.1 吸收部位和途径 Absorption of nutrients,vitamins,electrolytes,and minerals occurs almost exclusively in the small intestine.The mucosa of small intestine is arranged in a series of annular fold that are lined by finger-like villi that increase the available absorptive surface to 300 times that of the equivalent flat surface area.In the small intestine,most absorption involves an active transport system through the brush border membrane.The exception are short chain fatty acids and other small liquid-soluble molecules that traverse the apical membrane by simple diffusion.,吸收的部位,主要吸收部位：小肠粘膜,为什么说小肠是吸收的主要部位？,可被吸收的小分子物质时间保证吸收面积通透性小肠运动和绒毛舒缩,吸收的机制,被动转运主动转运,营养物质和水可以两条途径进入血液或淋巴：跨细胞途径：通过绒毛柱状上皮细胞的腔面膜进入细 胞，再通过细胞底-侧面膜；旁细胞途径：物质或水通过细胞间的紧密连接，进入 细胞间隙。,6.6.2 Absorption of major nutrients in small intestine 小肠每日可吸收数百克糖，100克以上的脂肪，50100克氨基酸，50100克无机盐和68L水。需要时，上述吸收量可增加数倍。Water and electrolytes Approximately 8 litter of water daily are absorbed in the small intestine,about 1.3 litter in the colon.This water is absorbed mainly by osmosis.Electrolytes are absorbed more readily from duodenum and jejunum than from ileum.Monovalent ions like Na+,K+,Cl,HCO3 are absorbed more rapidly than polyvalent ones,such as Ca+and Mn+,水、无机盐和维生素的吸收,水的吸收,Na+的吸收,扩散入细胞，Na+泵出粘膜细胞，伴随水的转运。,Ca2+的吸收,主要在十二指肠吸收。主动吸收，但也有被动过程参与。酸性环境、维生素D促进钙吸收。脂肪酸、胆汁酸与钙结合形成水溶性复合物阻碍钙吸收。,Fe2+的吸收,方式：Fe2+机制：主动吸收 维生素C、胃酸促进铁吸收,转铁蛋白(transferrin,Tf)铁蛋白(ferritin,Ft),CarbohydratesComplex polysaccharides and some disccharides are ultimately broken down in the intestinal tract into simpler forms-the monosaccharides,which are readily aborbed.Glucose and other hexoses(6-carbon sugars)and pantoses(5-carbon sugars)are readily absorbed from the duodenal and ileal mucosas into the blood capillaries.Glucose and galactose,are transported across the mucosa by an active process called carrier mediated transport.吸收方式：单糖吸收速度：葡萄糖、半乳糖果糖甘露糖葡萄糖吸收机制：Na+的协同转运途径：血液,Protein,方式：氨基酸与小分子肽机制：载体介导（Na+依赖性）途径：血液,lipid,脂肪：甘油三酯（甘油、脂肪酸）类脂：胆固醇、胆固醇酯、磷脂、糖脂等,脂肪分解产物和胆固醇、磷脂及胆汁酸盐混合微团十二指肠和空肠上部依靠浓度梯度的简单扩散作用被吸收。短链的脂肪酸由血液经门静脉入肝。长链脂肪酸和甘油一酯、甘油二酯被吸收后，在粘膜上皮细胞的内质网上重新合成甘油三酯，再与磷脂、胆固醇、胆固醇酯和载脂蛋白构成乳糜微粒，通过淋巴管进入血液循环。,脂肪酸的吸收,主要吸收部位：十二指肠和近侧空肠中短链脂肪酸：血长链脂肪酸与甘油一酯：乳糜微粒，淋巴为主脂溶性维生素：随脂肪吸收,胆固醇cholesterol的吸收,空肠和回肠游离的胆固醇直接被吸收胆固醇酯则经胆汁酸盐乳化后，再经胆固醇酯酶水解生成胆固醇而被吸收进入肠粘膜细胞的胆固醇再酯化成胆固醇酯，大部分掺入乳糜微粒。,磷脂的吸收,在磷脂酶的作用下，水解为脂肪酸、甘油、磷酸、胆碱或胆胺，被吸收后在肠壁内重新合成完整的磷脂分子，参与组成乳糜微粒而进入血液循环。,vitamin,水溶性维生素：单纯扩散方式，小肠上部 维生素 B12:与内因子结合，回肠脂溶性维生素A、D、E、K：与脂肪相同方式被吸收,Upon entry into the stomach,vitamin B12 becomes bound to haptocorrin(R factor),a glycoprotein.The resulting complex enters the duodenum,where pancreatic enzymes digest haptocorrin.In the less acidic environment of the small intestine,B12 can then bind to intrinsic factor.This new complex travels to the ileum,where special epithelial cells endocytose them.Inside the cell,B12 dissociate once again and bind to another protein,transcobalamin II.The new complex can exit the epithelial cells to enter the liver.,附：高血脂、高脂蛋白血症,血浆中所含的脂类物质统称血脂。如果空腹时血脂水平升高，超出正常范围，称高血脂症。高脂蛋白血症发生的原因可能是由于载脂蛋白、脂蛋白受体或脂蛋白代谢的关键酶缺陷所引起的脂质代谢紊乱。包括脂类产生过多，降解和转运发生障碍，或两种情况兼而有之。,动脉粥样硬化,动脉粥样硬化发生的原因主要是血浆胆固醇增多，沉积在大、中动脉内膜上所致，其发病过程与血浆脂蛋白代谢密切相关。LDL和VLDL增多可促使动脉粥样硬化的发生，而HDL能与LDL争夺血管壁平滑肌细胞膜上的受体，抑制细胞摄取LDL的能力，从而防止了血管内皮细胞中LDL的蓄积。肥胖者和糖尿病患者的血浆HDL水平较低，故易发生冠心病。,
