第六章-消化和吸收Digestion-and-absorption-学习要求-1

YUYanqin,PhDZhejiangUniversity,SchoolofMedicineDigestivesystemDigestion:Alimentarytract(消化道)Mechanicaldigestion

Digestivegland(消化腺)ChemicaldigestionAbsorption:ThefourprocessescarriedoutbytheGItract:digestion,secretion,absorption,andmotility.Functionsofthedigestivesystem ComponentsofthedigestivesystemStructureofthealimentarycanal（肠系膜）LowexcitabilityHighdistensibility（扩张性）ToniccontractionAutorhythmicityHighsensitivitytotemperature,stretchandchemicalstimulationRestingmembranepotential-40~-80mVIonicbasisEm(selectivemembranepermeabilitytoK+,Na+,Cl-andCa2+)ElectrogenicNa+-K+pumpSlowwave(basicelectricalrhythm，基本电节律)SantiagoRamonYCajalHeandCamilloGolgireceivedtheNobelPrizein1906forintroductionofthesilver-chromate（铬酸银）stainSlowwave(basicelectricalrhythm,BER)Intensity:10~15mVFrequency:3~12cpmIonicmechanism?spontaneousrhythmicchangesinNa+-K+pumpactivityJejunum：空肠Ileum：回肠Spikepotential(Actionpotential)Duration:10~20msIonicmechanism:Depolarization:Ca2+influxRepolarization:K+effluxEntericnervoussystem(intrinsic)Autonomicnervoussystem(extrinsic)Enteric(Intrinsic)nervoussystemMyentericplexus(Auerbach’splexus)Submucosalplexus(Meissner’splexus)RolesofentericnervoussystemSympatheticnerveNEInhibitory(-)AutonomicnervoussystemParasympatheticnerveMainlyAChStimulatory(+)FourmaintypesGastrin促胃液素Secretin促胰液素Cholecystokinin(CCK)胆囊收缩素Gastricinhibitorypeptide(GIP)抑胃肽Brain-gutpeptide（脑-肠肽）Definition:thepeptidewhichisfoundinthebrainandthegutalso.Classification:Gastrin促胃液素CCKPsubstanceDigestioninthestomachGastricjuice（胃液）PropertiespH0.9~1.51.5~2.5L/dayMajorcomponentsHydrochloricacid盐酸Pepsinogen胃蛋白酶原Mucus粘液Intrinsicfactor内因子GastricjuiceSecretedbyparietalcells壁细胞Chiefcells主细胞Mucousneckcells粘液颈细胞HydrochloricacidSecretedbytheparietalcellsOutputBasal:0~5mmol/hMaximal:20~25mmol/hMechanismofHClsecretionActivetransportH+pump(protonpump)Cl--HCO3-exchangeFOODAcidproductionbytheparietalcellsinthestomachdependsonthegenerationofcarbonicacid;subsequentmovementofhydrogenionsintothegastriclumenresultsfromprimaryactivetransport.Acidsterilization杀菌ActivationofpepsinogenPromotionofsecretin促胰液素secretionAssistedeffectofironandcalciumabsorptionRoleofHClOneinhibitoryandthreestimulatory

signalsthatalteracidsecretionbyparietalcellsinthestomach.ProtonpumpinhibitorsandhistamineblockersPepsinogenMW:42,500SecretedbythechiefcellsasaninactiveprecursorofpepsinActivatedinthestomach,initiallybyH+ionsandthenbyactivepepsin,autocatalyticactivationActivepepsin

(MW:35,000)EffectofpepsinPepsinisanendopeptidase,whichattackspeptidebondsintheinterioroflargeproteinmoleculesProteinsProteoses月示Peptones胨PolypeptidesPepsinMucusgastricpit:胃小凹Mucus-HCO3-barrierIntrinsicfactorAhighmolecularweightglycoprotein,synthesizedandsecretedbytheparietalcellsTheintrinsicfactorbindstoVitB12

andfacilitatesitsabsorptionVitB12RegulationofgastricsecretionBasicfactorsthatstimulategastricsecretionAcetylcholine(+allsecretorycells)Gastrin(+parietalcells)Histamine(+parietalcells)RegulationofgastricsecretionNervousregulation‘Short’reflexpathways‘Short’excitatoryreflexes:mediatedbycholinergicneuronsintheplexuses‘Short’inhibitoryreflexes:mediatedbynon-adrenergicnon-cholinergic(NANC)neuronsRegulationofgastricsecretionNervousregulation‘Long’autonomicpathways‘Long’excitatoryreflexes:parasympathetic‘Long’inhibitorypathways:sympatheticRegulationofgastricsecretionHumoralregulationExcitatory ACh Histamine Gastrin

Inhibitory Somatostatin Secretin 5-hydroxytryptamine(5-HT) Prostaglandin前列腺素PhasesofgastricsecretionInhibitionofgastricsecretionInhibitionofgastricsecretionMotorfunctionofthestomachProximalstomach cardia贲门

fundus胃底

corpus(body)胃体Distalstomach antrum胃窦

pylorus幽门

pyloricsphincter

幽门括约肌MotorfunctionofthestomachReceptiverelaxation容受性舒张Storagefunction(1.0~1.5L)Vago-vagalreflexPeristalsis蠕动BERinthestomachRhythmicwavesofsmoothmusclecontractioninthegutaretheresultofwavesofactionpotentialsmovingalongviagapjunctions.Emptyingofthestomach排空EmptyingofthestomachEmptyingrateSmallparticle>largeparticleIsosmotic>hyper-&hypo-osmoticCarbohydrates>Protei