生理學(xué)教學(xué)課件：第六章 消化和吸收15中英班

第六章消化和吸收

DigestionandAbsorption1GastrointestinalSystem2DigestionandAbsorptionDigestion:breakdownoffoodintomolecularcomponentssmallenoughtocrosstheplasmamembrane

MechanicaldigestionChemicaldigestionAbsorption:passageofthemoleculesintothebody'sinteriorandtheirpassagethroughoutthebody

3GeneralpropertiesofgastrointestinalsmoothmuscleLowexcitabilityHighdistensibilityToniccontractionAutorhythmicityHighsensitivitytotemperature,stretchandchemicalstimulation4

ElectrophysiologicalcharacteristicsRestingmembranepotential-50~-60mVIonicbasisEm(selectivemembranepermeabilitytoK+,Na+,Cl-andCa2+)ElectrogenicNa+-K+pump5

ElectrophysiologicalcharacteristicsSlowwave(basicelectricalrhythm)Thespontaneousrhythmic,subthreshold

depolarizationsofthecellmembrane(slowwave)ofthegastrointestinaltractthatcharacterizestheunderlyingelectricalactivityofthebowelInitiatedintheinterstitialcellsofCajal(ICC)(pacemakercell)Intensity:10~15mV67NormalBERfrequenciesinthegastrointestinalsystemSpikepotential(Actionpotential)Duration:10~20msIonicmechanism:Depolarization:Ca2+influxRepolarization:K+efflux9Secretionofdigestiveglands

Mainfunctionsofdigestivefluids1112NeuralcontrolofgastrointestinalfunctionEntericnervoussystem(intrinsic)Autonomicnervoussystem(extrinsic)13141517SympatheticnerveNEInhibitory(-)AutonomicnervoussystemParasympatheticnerveMainlyAChStimulatory(+)GastrointestinalhormonesAPUD（amineprecursoruptakeanddecarboxylation）ThehormonessynthesizedbyalargenumberofendocrinecellswithinthegastrointestinaltractPhysiologicalfunctionsControlofthedigestivefunctionControlofthereleaseofotherhormonesTrophicaction

19GastrointestinalhormonesmaintypesGastrinissecretedbythe“G”cellsoftheantrumofthestomach.Secretinwasthefirstgastrointestinalhormonediscoveredandissecretedbythe“S”cellsinthemucosaoftheduodenum.Cholecystokininissecretedby“I”cellsinthemucosaoftheduodenumandjejunum.Gastricinhibitorypeptideissecretedbythemucosaoftheuppersmallintestine.Motilinissecretedbytheupperduodenumduringfasting.202122Themajorfunctionofthegastrointestinalsystemistoprocessfood,bysodoing,providenutrientstothecellsofthebody.Processesotherthanabsorptionthathelpfulfillthisfunctionaremotilityandsecretion.Themusculatureofthedigestivetractismainlysmoothmuscle.Slowwaveandactionpotentialsarethemainformsofelectricalactivityinthegutmusculature.Thedigestivetractisinnervatedbythesympathetic,parasympathetic,andentericdivisionsoftheautonomicnervoussystem.BothmotilityandsecretionareregulatedbyneuralandhormonalmechanismsSummary

23DigestionintheMouth

Nature&Compositionofsaliva

pH6.6~7.1,99%waterSalivaryamylase,lysozyme,salt,etc.24Functionsofsaliva

Moistenthecavity&solvefood;keepthemouthclean;anti-bacteria;digeststarch

Regulationofsalivarysecretion

PureneuroregulationConditioned&unconditionedreflex25Breakuplargefoodparticles;mixesthefoodwithsaliva;aidswallowingChewing261.oralphase2.pharyngealphaseEsophagealphaseSwallowing2728Peristalsis-PropulsiveMovements29SummaryLongreflexsecretionofsalivalubricatesthemouthandprovidessalivaryamylase,anenzymethatinitiatesthedigestionofstarch,themajordietarycarbohydrate.ChewingreducesthesizeoffoodparticlesandmixesthemwithsalivaSwallowing,amusculareventthatiscoordinatedbylongreflexes,propelsfoodrapidlyfromthemouththroughtheesophagusintothestomachbyperistalsis(themovingwaveofcontraction).30√Digestioninthestomach313233GastricjuicePropertiespH0.9~1.51~2.5L/dayMajorcomponentsHydrochloricacidPepsinogenMucusIntrinsicfactor34HydrochloricacidSecretedbytheparietalcellsOutputBasal:0~5mmol/hMaximal:20~25mmol/h35MechanismofHClsecretionActivetransportHugeH+gradient(3million)373839RoleofHClAcidsterilizationActivationofpepsinogenPromotionofsecretinsecretionAssistedeffectofironandcalciumabsorption40PepsinogenMW:42,500SecretedbythechiefcellsasaninactiveprecursorofpepsinActivatedinthestomach,initiallybyH+ionsandthenbyactivepepsin,autocatalyticactivationActivepepsin(MW:35,000)4142

EffectofpepsinPepsinisanendopeptidase,whichattackspeptidebondsintheinterioroflargeproteinmoleculesProteinsProteosesPeptonesPolypeptidesPepsin43MucusSecretedbytheepithelialcellsalloverthemucosaandbytheneckmucuscellsintheupperportionofthegastricglandsandpyloricglandsRoleLubricationofthemucosalsurfaceProtectionofthetissuefrommechanicaldamagebyfoodparticles4445Mucus-HCO3-barrier47IntrinsicfactorAhighmolecularweightglycoprotein,synthesizedandsecretedbytheparietalcellsTheintrinsicfactorbindstoVitB12andfacilitatesitsabsorption4849SecretionofotherenzymesGastriclipaseGastricamylaseGelatinase51RegulationofgastricsecretionBasicfactorsthatstimulategastricsecretionAcetylcholine(+allsecretorycells)Gastrin(+parietalcells)Histamine(+parietalcells)52RegulationofgastricsecretionNervousregulation‘Short’reflexpathways‘Short’excitatoryreflexes:mediatedbycholinergicneuronsintheplexuses‘Short’inhibitoryreflexes:mediatedbynon-adrenergicnon-cholinergic(NANC)neurons53RegulationofgastricsecretionNervousregulation‘Long’autonomicpathways‘Long’excitatoryreflexes:parasympathetic‘Long’inhibitorypathways:sympathetic54RegulationofgastricsecretionHumoralregulationExcitatory

ACh Histamine

Gastrin

Inhibitory

Somatostatin

Secretin 5-hydroxytryptamine(5-HT) Prostaglandin55PhasesofgastricsecretionCephalicphaseGastricphaseIntestinalphase56

Cephalicphase頭期

Mechanisms:Conditioned&Unconditionedreflex

Vagalefferent&withGastrinsecretionthroughgastrin-releasingpeptide(GRP)Experiment:ShamfeedingbyPavlov

Characteristics:Largequantity(30%)

Highacidity&digestivepower57ExperimentofShamfeedingbyPavlov

58Gastricphase

Mechanisms:Distensionofgastricfundus&bodyinitiating

vagovagal&localplexusreflexesDistensionofpylorusinitiatingareleaseof

gastrinthroughintrinsicplexusChemicalstimulationofGcellsinitiayingareleaseofgastrinExperiment:PavlovpouchCharacteristics:Largequantity(60%)

Highacidity&digestivepower59Intestinalphase

Mechanisms:Mainlyhumoralregulation

Chemical&MechanicalstimulationinitiatingreleasesofGastrin,Entero-

oxyntin&OtherhumoralfactorsExperiment:PavlovpouchCharacteristics:

Smallquantity(10%)

Loweracidity&digestivepower606163InhibitoryregulationHydrochloricacid(HCl)

AtypicalexampleofnegativefeedbackConditions&Mechanisms:pH≤1.2~1.5inthegastricantrumInhibitionofGcells,ReleaseofSSTpH≤2.5intheduodenumReleaseofsecretin,bulbogastroneFat:Initiatingreleaseofenterogastrone

Hypertonicsolution:Entero-gastricreflex64MotorfunctionofthestomachProximalstomach

cardia

fundus

corpus(body)Distalstomach

antrum

pylorus pyloricsphincter

65MotorfunctionofthestomachToniccontractionMaintainingtheshape&placeofstomach,aswellastheintragastricpressure66MotorfunctionofthestomachReceptiverelaxationStoragefunction(1.0~1.5L)Vago-vagalreflexPeristalsisBERinthestomach

Initiatefrommiddlestomach,3times/minMix&grindfoodintochyme&helpempty676869ContractionsintheemptystomachMigratingMotorComplex(MMC)Periodicwavesofcontraction,whichmovealongthegastrointestinaltractfromstomachtocolonPurposeofthisactivity:to‘sweep’debrisoutofthedigestivetractduringtheinterdigestiveperiodMMCscanleadtohungercontractions,whichareassociatedwithdiscomfort,referredtoas‘hungerpains’70Migratingmotorcomplex(MMC)71EmptyingrateFluid>viscousSmallparticle>largeparticleIsosmotic>hyper-&hypo-osmoticCarbohydrates>Protein>FatRegularmeal4～6hrsEmptyingofthestomach7273Regulationofstomachemptying(Gastricfactorsthatpromoteemptying)

Gastricfoodvolume：

Gastrin

：74(Duodenalfactorsthatinhibitstomachemptying)

EnterogastricnervousreflexesFatCholecystokinin75VomitingSummary

Thegastricchiefcellsecretespepsinogen,which,whenactivatedtotheenzymepepsin,initiatesthedigestionofproteinParietalcellssecreteHClandintrinsicfactor,andchiefcellssecretepepsinogen.Thegastricmucosacontainssurfacemucouscellsthatsecretemucusandbicarbonateions,whichprotectthestomachfromtheacidinthestomachcavity.Gastricsecretionisunderneuralandhormonalcontrolandconsistsofthreephases:cephalic,gastricandintestinal.Themigratingmotorcomplexisthegastrointestinalmotilitypatternoftheinterdigestivestate78Digestioninsmallintestine798081PancreaticjuicepH7.8~8.4~1500ml/dayIsosmotic

Components:Pancreaticdigestiveenzymes:secretedbypancreaticaciniSodianbicarbonate:secretedbysmallductulesandlargerducts82SecretionofpancreaticdigestiveenzymesCarbohydratesPancreaticamylaseFatPancreaticlipas

Proteinstrypsin,chymotrypsin

83StarchesMaltoseand3to9glucosepolymersPancreaticamylase848586Acutepancreatitis87Acutepancreatitis88Controleofpancreticsecretion

Pancreaticsecretionisunderneuralandhumoral

controle,mainlythelater.NervouscontroleStimulationofvagusnervecausessmallamountofpancreaticjuice,richinenzymes

89RegulationofpancreaticsecretionBasicstimulithatcausepancreaticsecretionCholecystokinin:SecretedbyIcellsStimulatestheacinarcellstosecretelargeamountsofenzymesSecretin:ReleasedbyScellsActsprimarilyontheductcellstostimulatethesecretionofalargevolumeofsolutionwithahighHCO3-concentration9091Secretionofbilebytheliver9293CompositionofbileHCO3-

BilesaltsPhospholipidsCholesterolBilepigments…94FunctionsofbileEmulsifyingordetergentfunctionofbilesaltsBilesaltshelpintheabsorptionof:FattyacidMonoglyceridesCholesterolOtherlipids95Emulsifyinglargefatparticlestofacilitateitsdigestion9697Bilesaltsinteractwithcholesteroltoformmicellestofacilitatetheabsorptionofinsolublefatproducts98Increasingbilesynthesis&secretion99RegulationofbilesecretionSubstancesincreasingbileproductionBilesalts(Enterohepaticcirculationofthebile)Secretin:stimulatingH2OandHCO3-secretionfromtheductcellsSubstanceinhibitingbileproductionSomatostatin100101neuralcontrolofbilesecretion

humoralcontrolofbilesecretion

AChCCKGastrin

secretin

ControlofBileSecretionandEduction

102103SmallintestinaljuicesSecretedby:BrunnersglandsCryptsofLieberkuhn1~3L/daypH7.6Isosmotic104SmallintestinaljuicesComponentsH2OElectrolytes(Na+,K+,Ca2+,Cl-)MucusIgAEnterokinase105SpecifictypesofintestinalcontractileactivityMigratingMotorComplex(MMC)LocalareasofperistalticcontractionPresentintheinterdigestiveperiodanddisappearwhenfeedingbeginsSweepingmaterial(undigestedfoodresidues,deadmucosalcells,bacteria)intothecolonandkeepingthesmallintestinecleanRegulatedbyautonomicnervesandbythereleaseofmotilin

Movementofsmallintestine

ToniccontractionmaintainingabasalstateofintestinalsmoothmusclecontractionThemostcommontypeofactivityintheintestineduringdigestion&absorptionConsistingofthealternatecontraction&relaxationofadjacentbandsofcircularsmoothmuscleMixingfood&digestivesecretions&facilitatesbothdigestion&absorptionofdigestiveproductsbythemucosalepitheliumRegulatedbyexcitatory&inhibitoryneuronsintheplexusesSegmentaion Peristalsis&peristalsisrushAutoregulation:RegulatedbyBER

NeuralReflexes:mainlyby‘short’reflexesintheintrinsicplexuseswhichareresponsibleforperistalsisandsegmentationalsobyextrinsicnerves(sympathetic&vagalnerves)whichmediate‘long’reflexesHormonalcontrols:Gastrin,CCK,motilin,5-HT(+);secretin,VIP,glucagon(-)Regulationofintestinalmotility110Ileocecalsphincter111SummaryTheintercalatedductcellsofthepancreassecretealargevolumeofawater-electrolytesecretionwithahighconcentrationofbicarbonate,anionthatislargelyresponsiblefortheneutralizationofacidingastriccontents.Thepancreaticacinarcellssecreteawidevarietyofdigestiveenzymes,whosecombinedactionsalmostcompletethedigestionoffood.Betweenmeals,bileisstoredandconcentratedinthegallbladder.Whenfoodiseaten,thisorgancontractsinresponsetothereleaseofcholecystokininandpropelsbileintotheduodenum.Bilesaltsaresynth