消化与吸收.ppt

第六章消化和吸收,Digestiveorgansincludeoralcavity,pharynx,esophagus,stomach,smallservestobind2)Multiplemechanismsareinvolved,六、储存和排泄,IncludestemporarystorageenclosedbygastroesophagealAlcohol1.52.5L/dayMucus（粘液/黏液）:surfaceandneckmucouscellsIntrinsicfactor（内因子）:parietalcells（壁细胞）HCl:parietalcellsPepsinogen:chiefcells（主细胞）.,1.盐酸（胃酸）的分泌,HClisproducedbyparietalcellswhichactivelytransportH+intolumenviaaproton(H+)pump（质子泵）Cl-issecretedbyfacilitateddiffusionH+comesfromdissociationofH2CO3Cl-comesfrombloodsideofcellinexchangeforHC03-,HCl分泌量：基础排酸量：空腹时，正常人05mmol/h。最大排酸量：2025mmol/h（组胺试验）。最大排酸量主要取决于壁细胞的数量，也与壁细胞的功能状态有关。HCl作用：激活胃蛋白酶原，提供胃蛋白酶适宜环境；使蛋白质变性，利于蛋白质的水解；促进胰液、胆汁和小肠液的分泌；有助于小肠对铁和钙的吸收；抑制和杀死细菌。,影响胃酸分泌的因素,PhysiologicalagonistsofHClsecretion:gastrin;acetylcholine,histamine;2)PhysiologicalbrakeonHClsecretion:somatostatinprostaglandins,来源：主细胞分泌作用：胃蛋白酶原特点：,胃酸,胃蛋白酶水解蛋白,胃蛋白酶原没有活性，需在胃酸的作用下转化为有活性的胃蛋白酶（pepsin)；最适pH2.0，pH.0则失活；对蛋白消化并非必需（蛋白质消化小肠内为主）；安静时：少量、恒定的速率分泌；刺激时：大量、迅速分泌。,2.胃蛋白酶原(Pepsinogen),来源:粘液由表面上皮细胞、贲门腺和幽门腺细胞、泌酸腺颈部细胞分泌；HCO3-主要由非泌酸细胞分泌，少量由组织间液渗入胃内。成分:粘液主要成分为糖蛋白，具有较高的粘滞性和形成凝胶的特性。PH值为中性。作用:形成胃粘液-HCO3-屏障，保护胃粘膜。,润滑：防止食物的机械损伤；中和胃酸：HCO3-+H+H2CO3防止高H+和胃蛋白酶对自身的侵蚀。,3.粘液(mucus)和HCO3-,4.内因子(intrinsicfactor)来源：壁细胞分泌成分：糖蛋白（有2个亚单位）亚单位A与Vit12复合物:防Vit12被水解酶破坏；亚单位B与回肠末端上皮的特异受体结合从而吸收12作用：促进回肠末端维生素12的吸收。临床：当壁细胞受损或减少时，可发生巨幼红细胞性贫血。特点:分泌能力和刺激因素与胃酸相当。,巴氏小胃(左)和海氏小胃(右),假饲实验示意图,IngestiontriggerssecretionofgastricjuiceNeuralandhormonalmechanismsregulatethereleaseofgastricjuiceStimulatory&inhibitoryeventsoccurinthreephasesCephalic(reflex)phase:priortofoodentryGastricphase:oncefoodentersthestomachIntestinalphase:aspartiallydigestedfoodenterstheduodenum,（二）胃液分泌的调节,CephalicPhase,Taste,smell,tactilesensationsoffoodinthemouth,oreventhoughtsoffoodstimulatethemedullaoblongata.Parasympathetic(vagal)efferentimpulsetothestomach.Preganglionicparasympatheticfibersstimulatepostganglionicneuronsintheentericplexusofthestomach.Postganglionicneuronsstimulatesecretionbyparietalandchiefcells(HClandpepsin)andstimulatereleaseofgastrin.GastriniscarriedthroughthecirculationbacktothestomachwhereitstimulatesfurthersecretionofHClandpepsin.,GastricPhase,Distentionofthestomachactivatesaparasympatheticreflex.Actionpotentialsarecarriedbythevagusnervestothemedullaoblongata.Medullaoblongatastimulatesfurthersecretionsofthestomach.Distentionalsostimulateslocalreflexesthatamplifystomachsecretions.,IntestinalPhase,ChymeintheduodenumwithapHlessthan2orcontaininglipidsinhibitsgastricsecretionsbythreemechanismsa)Sensoryinputtothemedullafromtheduodenuminhibitsthemotorinputfromthemedullatothestomach&stopssecretionofpepsin&HCl.b)Localreflexesinhibitgastricsecretionc)Secretin,gastricinhibitorypolypeptide&cholecystokininproducedbytheduodenuminhibitgastricsecretionsinthestomach.,影响胃液分泌的因素促进抑制食物蛋白质糖盐酸脂肪高渗溶液-激素胃泌素糖皮质激素胰泌素胰高血糖素ACTH胰岛素生长抑素抑胃肽PG缩胆囊素肠泌酸素肠抑胃素缩胆囊素-药物ACh组胺阿托品甲氰咪呱咖啡因乙醇奥美拉唑Ca2+毛果云香碱-神经迷走N壁内N丛反射交感N肠-胃反射迷走-迷走反射情绪应激状态恶劣情绪,胃液分泌的调节,二、胃的运动（一）胃运动的形式及调节紧张性收缩(toniccontraction):胃壁平滑肌缓慢而持续的收缩。作用：增强胃内压，有助于胃液渗入食物和促进胃排空；保持胃的正常形状和位置，不致出现胃下垂。容受性舒张(Receptiverelaxation):进食时反射性胃壁平滑肌的舒张。作用：增加胃容量（50ml1.5L）和贮存食物，防食糜过早排入十二指肠。蠕动(Peristalsis):蠕动波起自胃体中部，逐步向幽门部推进。迷走神经、胃泌素、胃动素使其频率和强度增加；交感神经、胰泌素、抑胃肽作用则相反。作用：使食糜与胃液充分混合和研磨。,（二）胃的排空（gastricemptying）概念：食糜由胃排入十二指肠的过程。速度：因食物而异（流体、粒小、等渗的快）水糖蛋白脂肪10min2h23h56h（一餐混合食物由胃完全排空约需4-6小时）动力:直接动力胃与十二指肠的压力差。原动力胃的运动。影响因素：胃内促进排空的因素：壁内N丛的局部反射和迷走-迷走反射；胃泌素。十二指肠内抑制排空的因素：肠-胃反射；肠抑胃素（胰泌素、抑胃肽等）。,胃内食物,机械扩张,蛋白质分解产物,迷走-迷走反射,壁内N丛局部反射,胃蠕动紧张性,胃内压,胃排空,胃窦G细胞,胃泌素,十二指肠食糜,高渗溶液,盐酸、脂肪,胃蠕动紧张性,胃内压,胃排空暂停,肠-胃反射,肠抑胃素,胃内压,再次胃排空,胃蠕动紧张性,食糜在肠内吸收,抑制因素解除,影响胃排空的因素,Protectivemechanismsinclude:Impermeabilityofparietal&chiefcellstoHClAlayerofalkalinemucuscontainingHC03-TightjunctionsbetweenadjacentepithelialcellsRapidrateofcelldivision(entireepitheliumreplacedin3days)Prostaglandins(PGs)inhibitgastricsecretionsWhichiswhyPGblockerssuchasNSAIDscancauseulcers,ProtectiveMechanismsofStomachandStomachPathophysiology,GastricandDuodenalUlcers,Peptic-hydrochloricacid/pepsinpresentStress-inducedulcers(reducedBicarbonate)80%ofgastric,90%ofduodenalulcersareduetoH.pyloriinfection(40%ofgeneralpopulation)weakensmucusbarriercausesacidproduction(decreasedBicarb)NSAIDscanalsocontribute(COX-1inhibitors)GastrinCarcinomas(Zollinger-Ellisonsyndrome)-secretegastrincauseexcessiveacidsecretionTreatmenttripletherapy(2antibiotics,oneantacidorbismuth)vagotomy,DumpingSyndromeUncontrolledgastricemptyingduetolackoffeedbackinhibitionbyduodenumpost-surgicalneurologi