生理学 消化和吸收(英语)

DigestionandAbsorptionFunctionsofGastrointestinalSystemAbsorptionofnutrients,provideenergy,waterandelectrolytesExcretionofwasteproductsEndocrinefunctionsImmunefunctions2DigestionTheprocessesthatthefoodandlargemoleculesaredegradedtoproducesmallmoleculesthatcanbeabsorbedbythewallofgastrointestinaltract.BreaksdownCarbohydrates(starchandsugar)→singlesugarmoleculesProteins→aminoacidsFats→fattyacids,glycerol3chemicaldigestionmechanicaldigestion(motility)Themovementthatmixandcirculatethegastrointestinalcontentsandpropelthemalongthetract.

Absorption

istheprocessoftransportingsmallmoleculesfromthelumenofthegutintobloodstreamorlymphaticvessel.DigestionandAbsorption41.Characteristicsofgastrointestinalsmoothmuscles*

Generalcharacteristics

①Lowerelectricalexcitabilityandslowcontraction;②largeextensibility;③tonicity;④autorhythmicity(slowandunsteady);⑤insensitivityofelectrostimulationandsensitivityofstretch,temperature,chemicalstimulus,etc.

Electricalproperties

①Restingpotential②Slowwavepotential③Actionpotential5(1)CharacteristicsofrestingpotentialValueofRPinGItractsmoothmuscleissmallerthanthatofskeletalmuscles(-50～-60mv);RPisunstableandfluctuanttogeneratespontaneousdepolarizationcontinuously;RPmainlyresultsfromK+equilibriumpotential,andNa+,Cl-,Ca2+,etc.alsoinvolveinRPforming.6(2)SlowwavepotentialSlowwavesorbasicelectricalrhythm(BER)isakindofslow,spontaneousandrecurringdepolarizationwave.Slowwavesarenotactionpotential,butshowundulatingchangesintherestingmembranepotential.7Basicelectricalrhythm(BER)Thebasicelectricalrhythm(BER)isaslowspontaneousdepolarizedwaveintheGI.BERofsmoothmusclecellsformthebasis(actionpotential)ofstomachcontractions.TheabilityofBERtoinducesmoothmusclecontractionisalteredbytheactivityofextrinsicnervesandhormones,broughtintoplaybystomachandintestinereceptors.8Dr.Alzoghaibi99ElectricalActivityinGISmoothMuscleBERBERMakingGIsmoothmusclecontraction10

(3)Actionpotential(AP)Whendepolarizingslowwaveexceedsthresholdpotential,itcaninduceactionpotentialwhichisshortduration,10-20ms,alsonamedfastwave.APdifferencesbetweenskeletalmuscleandsmoothmuscle：spikepotentialsrisingisslow,durationislongerandamplitudeislower;Ca2+isinvolvedindepolarization(slowchannel:Ca2+-Na+channel);K+isinvolvedinrepolarization,andK+outwardcurrentcombineswithCa2+inwardcurrent;Basedonslowwave,APformationtriggersmoothmusclecontraction.112.Secretionofthedigestiveglands12SecretionofthedigestiveglandsDigestiveglands：salivarygland,pancreatic,liver,gastricglandsandintestinalgland,etc.Secretoryvolume:6~8L/dayFunctionsofthedigestivejuice*Dilutingfood(foodosmoticpressureissimilartoblood);ChangingpHvalue(itissuitableforenzymedigestion);Amylase(淀粉酶),proteinase(蛋白酶),lipidase(脂肪酶)hydrolyzefood;Mucus,antibody,agreatquantityofliquid(protectiveeffect).13NeuralinnervationEntericnervoussystem(ENS)Intrinsicsetofnerves-“brainofgut”Neuronsextendingfromesophagustoanus2plexusesMyentericplexus–GItractmotilitySubmucosalplexus–controllingsecretionsAutonomicnervoussystemExtrinsicsetofnervesParasympatheticstimulationincreasessecretionandactivitybystimulatingENSSympatheticstimulationdecreasessecretionsandactivitybyinhibitingENS14Parasympathetic:Thedorsalmotornucleusofthevagussuppliesefferentvagusnervefibersto:Loweresophagus,Stomach,SmallintestineandProximalcolonThesacraloutflowarisesfromneuronesinthesacralspinalcode(S2-S4)→pelvicnerve→innervationofthedistalcolon,rectumandanalcanal.Pre-ganglionicfiberssynapsewithganglioniccellslocatedintheentericnervoussystem.ThepreganglionicneurotransmitterismainlyAcetylcholine.Increaseofparasympatheticnerveactivity→Stimulatoryeffects,e.g.↑gastric,pancreaticandsmallintestinalsecretion,↑bloodflowandmusclecontraction.1515ExtrinsicGITInnervationsSympathetic:Arisesfromthoracicandupperlumberspinalcord(T5-L2).Pre-ganglionicfiberssynapseoutsideGItractinpre-vertebralgangliaPost-ganglionicadrenergicfibersinnervatethecellsofthemyentericandsubmucosalplexusElementsfromthetwoplexusesinnervatethesmoothmuscle,secretoryandendocrinecells.ThepostganglionicneurotransmitterismainlyEpinephrine(adrenaline).Increaseofsympatheticnerveactivity→inhibitoryeffects,e.g.↓secretion,↓motilityand↓bloodflow.

1616EntericNervoussystemTheintrinsicnervesmakeupaverydensenetworkembeddedinthewallsoftheesophagus,stomach,smallintestine,andcolon.1717Organizationoftheentericnervoussystem18Sympatheticandparasympatheticnervessynapsewithnervecellbodiesoftheentericnervoussystemingut.Sympatheticnervesexerttheireffectthroughthereleaseoftheneuraltransmitternorepinephrine,whichisgenerallyinhibitory,whiletheparasympatheticnervesexerttheireffectthroughthereleaseofacetylcholine,whichisgenerallyexcitatory.Entericnervoussystemreleasesavarietyofneurotransmitters:acetylcholine,nitricoxide(NO),vasoactiveintestinalpeptide(VIP),enkephalins,serotonin,andsubstanceP.Theexactroleandinteractionofeachofthesechemicalmediatorsisstillbeingresolved.

Neuralcontrolofthegastrointestinaltract19Guthormones

Gastrointestinalhormone（胃肠激素）Thehormonesproducedbyendocrinecellsinthegastrointestinalmucosaandareinvolvedinthecontrolofgastrointestinalmotilityadsecretion.Gastrointestinalendocrinecell(胃肠内分泌细胞)opentypecell,开放型细胞closedtypecell,闭合型细胞20

Gastrin(fromantrum):increaseacidsecretionCholesystokinin(CCK,Duodenum):causesgallbalddercontractionandpancreaticsecretionSecretin:inhibitsacidsecretionandstimulatespancreaticHCO3-secretionGIP(GastricInhibitoryPeptide):reducesgastricmotilityandstimulatesinsulinsecretionMotilin:increasesGImotility&stimulatetheproductionofpepsinInsulinGlucagonsomatostatinGITHormones21Functionsofgastrointestinalhormones**ToregulatedigestiveglandsecretionanddigestivetractmovementTrophicaction(营养作用)TomodulateotherhormonessecretionBrain-gutpeptide*（脑-肠肽）

22DigestioninthemouthMechanicaldigestioninthemouthChewingormasticationFoodmanipulatedbytongue,groundbyteeth,andmixedwithsalivaFormsbolusChemicaldigestioninthemouthSalivaryamylasesecretedbysalivaryglandsactsonstarchesOnlymonosaccharidescanbeabsorbedContinuestoactuntilinactivatedbystomachacidLinguallipasesecretedbylingualglandsoftongueactsontriglyceridesBecomesactivatedinacidicenvironmentofstomach23SalivaSalivaryglandsproduceabout1.5litersofsalivadailySalivaryamylase(ptyalin)beginstobreakdownstarch(inactivatedinthestomach)Salivarylipase:beginsfatdigestion,buthasminimaleffectMucustolubricatethefoodforeasierswallowingLysozymetokillbacteria24MotilityinthemouthMastication:chewingChewingisimportantbecause-Thefoodislubricatedbybeingmixedwithsaliva-Thefoodisexposedtosalivaryamylaseenzyme,whichbeginsdigestionofstarch-Itbreaksthefoodintosmallpieces.Swallowingisunderthecontrolofextrinsicnervesandtheswallowingcenter(brainstem).25DeglutitionActofswallowingFacilitatedbysecretionsofsalivaandmucusInvolvesmouth,pharynx,andesophagus3stagesVoluntary–boluspassedtooropharynxPharyngeal–involuntarypassagethroughpharynxintoesophagusEsophageal–involuntarypassagethroughesophagustostomachPeristalsispushesbolusforward26Deglutition(swallowing)27TheEsophagusLongtubeConnectspharynxtothestomachPeristalsis,musclecontractionLoweresophagealsphincterHeartburn/media/grossovw.gif28PeristalsisMuscularcontractionsthatmovefoodalongthroughoutGItract29Anatomyofstomach30Figure23.11b31TABLE.AREASOFTHESTOMACH,CELLTYPESINEACH,ANDTHEIRSECRETIONS

STOMACHREGIONSCELLTYPESECRETIONSCardiacglandareaMucuscellsMucusOxynticglandareaParietal(oxyntic)cellsAcid,instrinsicfactorChief(peptic)cellsPepsinogen,gastriclipaseNeckmucouscellsMucusPyloricglandareaMucuscellsMucus,Pepsinogen(antrum)GcellsGastrin

δ

cellsSomatostatinECLcellshistamine

GastricSecretion*32Gastricjuice

Storagecapacityof1~2L.Secretoryvolume:1~2.5L/dCharacter:achromic,acidic（pH0.9-1.5）Component:waterinorganicsalt:(HCl、HCO3-、

Na+、

K+,etc.)organics:(pepsinogen,mucoprotein,intrinsicfactor)33Mechanismofgastricacidsecretionandafter-mealalkalinetideChannelCarrierPumpATPNa+K+CA:CarbonicAnhydraseHClOH-:hydroxyl;HCO3-:Bicarbonate34Functionofhydrochloricacid**①Activatingpepsinogen(胃蛋白酶原);②Supplyingacidenvironmentforpepsindecomposingprotein；③Foodproteindenaturationandeasydecomposition；④Killbacteriainfoodintothestomach；⑤Promotingpancreatic,smallintestinalandbilesecretion；⑥HelpingFe2+、Ca2+secretion.35Pepsinogenchiefcellsregulatedprimarilybyvagalnerve(Ach)stimulationduringboththecephalicandgastricphases.Acidisimportantnotonlyforpepsinformationbutalsoforenhancingitssecretion.Acidtriggerstheentericnervestostimulatepepsinogenreleasebyrealeasingacetylcholine.Acidintheduodenumstimulatesthereleaseofsecretin,whichstimulatespepsinogenreleasefromchiefcells.Becauseacidenhancespepsinogenrelease,thereleaseismaximumonlywhenthereissufficientacidpresenttoactivatetheenzyme.36

PepsinogenPepsinproteinpeptonepH2-3.5HClFunctionofpepsinogen（胃蛋白酶原)37intrinsicfactorsecretionIntrinsicfactorsecretedbyparietalcellsisessentialfortheabsorptionofvitaminB12bytheileum(wherehavethespecificreceptors).ItbindsvitaminB12presentiningestedfood,andtheformationofthiscomplexiscrucialforabsorptionofthevitaminbytheileum.Withoutintrinsicfactor,thevitamincannotbeabsorbed.Littleisknownabouttheregulationofintrinsicfactorsecretion.38FunctionofIntrinsicFactorVitaminB12VitaminB12VitaminB12VitaminB12VitaminB12VitaminB12VitaminB12VitaminB12IntrinsicFactorFormationoftheIntrinsicFactor-VitaminB12complexIntestinalLumenBloodIleumAbsorption39MucusandHCO3-

Solubleandinsolublemucusaresecretedbycellsofthestomach.Solublemucusmixeswiththecontentsofthestomachandhelpstolubricatechyme.Insolublemucusformsaprotectivebarrieragainstthehighacidityofthestomachcontent.Secretionofbothformsofmucusincreaseinassociationwithameal.Vagalnervestimulationincreasesthesecretionofsolublemucuswhilechemicalsandphysicalirritationstimulatesthesecretionofinsolublemucus.40GastricmucusModeofGastricMucus--HCO3-BarriermucuslayerGastricCavityGastricMucosaEpithelialCells41Gastricmucus-HCO3-barrier—protectionofgastricmucosaagainstthecausticeffectsoftheHClGastricCavity42UlcersGastricUlcersMucosalbarrierisdefectiveallowingH+andpepsintodigestportionofmucosaHelicobacterpyloriproducesNH4+fromureaNH4+breaksdownmucosalbarriertoH+

DuodenalUlcersMorecommonH+secretoryratesarehigherthannormalExcessH+damagesduodenalmucosa43PhasesofdigestionCephalicphase(30%)Smell,sight,thoughtorinitialtasteoffoodactivatesneuralcenters–preparesmouthandstomachforfoodtobeeatenGastricphase(60%)NeuralandhormonalmechanismspromotegastricsecretionandmotilityIntestinalphase(10%)BeginswhenfoodentersmallintestineSlowsexitofchymefromstomachStimulatesflowofbileandpancreaticjuice44AcidsecretionofthecephalicphaseTaste,smellandsightoffood,VagusnerveimpulsesGastricsecretionofthecephalicphaseisthebestforfooddigestion45StudyongastricacidsecretionofthecephalicphaseShamfeedingexperiment1.Foodflowoutfromthecutofesophagus;2.Stomach;3.Collectinggastricliquidfromstomachfistula.IvanPetrovichPavlov’sconditionalreflex46Thegastricphaseincludesstimulithatdependuponthepresenceoffoodinthestomach.Foodreducestheacidityofthestomachcontents,whichreducessomatostatinreleaseandremovesitsinhibitoryeffect.Also,distentionofthestomachthroughmechanoreceptorsandtheentericnervoussystemdirectlyactivateparietalcellsaswellasstimulategastrinrelease.Finally,digestedproteinstimulatesgastrinrelease.Thegastricphaseisresponsibleforstimulatingthemajority(60%)ofacidsecretion.Gastricacidsecretionofthegastricphase

47Gastricacidsecretionofthegastricphase

ProteinFood48Whenproteinmetabolitesreachtheduodemum,theyproduceanadditionalstimulationofacidsecretionknownastheintestinalphase.Thisstimulationistheresultofdistentionprobablymediatedthroughtheactionofanintestinalhormone,enterooxyntin,onparietalcellsandthepresenceofabsorbedaminoacidsstimulatingparietalcells.Asfoodmovefromthestomachintothesmallintestine,reflexesareinitiatedthatinhibitgastricacidsecretion.Theremovaloffoodfromthestomachallowstheacidityofthestomachfluidtoincrease,whichinitiatestheinhibitoryeffectsofsomatostatin.Inaddition,theacidity,osmolarity,andfatcontentofthefoodintheduodenuminitiatereflexesthatreducegastricacidsecretion.Themediatorsandpathwaysofthesehavenotbeendetermined.Theneteffectisthatacidsecretionslowlyreturnstothatduringtheinterdigestiveperiod.Gastricacidsecretionoftheintestinalphase

49RegulationofHClSecretionAChReleasedfromvagusnerveBindstoreceptorsonparietalcellsProducesH+secretionbyparietalcellsAtropineblocksmuscarinicreceptorsonparietalcellsHistamineReleasedfrommastlikecellsingastricmucosaBindstoH2receptorsonparietalcellsProducesH+secretionbyparietalcellsCimetidineblocksH2receptorsGastrinReleasedintocirculationbyGcellsofstomachantrumBindstoreceptorsonparietalcellsStimulatesH+secretion50histamineCellgastrinCellgastrinParasympatheticpostganglionicneuronCellEffectsofacetylcholine,histamineandgastrinonparietalcellandinterrelationshipRegulationofacidsecretion51RegulationofacidsecretionParietalcellmembraneIP3M3ReceptorH2ReceptorAcetylcholineHistamineGastrininthebloodACIP3BlockNonblockEffectsofacetylcholine,histamineandgastrinonparietalcellandinterrelationship.A:atropin;CM:cimetidineMReceptor

InitiateacascadeofcellulareventsStimulateSecretionParasympatheticpostganglionicneuronECLcellsGcellsInhibitedbysomatostatin52InhibitionofAcidSecretionHydrochloricacid(HCl)Solutionscontainingaminoacids,andfattyacidsHypertonicsolutionInhibitoryhormones(Enterogastrones):Somatostatin(D-cells)inantrumSecretin(S-cells)induodenumGlucose-dependentinsulinotropicpeptide(GIP)induodenum53Motilityofstomach1ToniccontractionTomaintainacontinuouscompressionToaccommodatethereceivedfoodwithoutsignificantgastricwalldistentionorpressure542Receptiverelaxation -triggeredbyswallowingreflexAdaptiverelaxation -triggeredbystretchreceptors(vago-vagalreflex) -lostinvagotomy

thresholdoffullnessandpainFeedbackrelaxation -triggeredbychymeinsmallintestine55Motilityofstomach3GastricperistalsisArrowshowingpartialliquidchymepushedintoduodenumviapylorusandmorechymepushedforthandbackinstomachcavitybeingsmallpieces5657StomachEmptyingStomachemptyingisaprocessofchymecomingfromstomachtoduodenum.Largestomachvolumesemptyfasterthansmallvolumes.Liquidsemptyfasterthansolids,andsolidsmustbereducedtoparticleslessthan2mm3toemptyrapidly.Gastricemptyingisdeterminedreflexlybyneuralandhumonalinputtothesmoothmuscle.Theinitationofthesereflexesisinfluencedbythecontentsofboththestomachandsmallintestines58ControloriginatedfromstomachDistensionofthestomach,gastrinincreasetheforceofantralcontractionsthroughlongandshortreflexs.ControloriginatedfromduodenumGastricemptyingisinhibitedbydistentionoftheduodenum,orthepresenceoffat,highacidityorhypertonicsolutionsinthelumenoftheduodenum.

Otherhormoneslikegastrininhibitorypeptide(GIP)andsecretinhavebeenshowntoinhibitstomachemptying

59Intheinterdigestiveperiodwhenthestomachisempty,every90minutesastrongcontraction,MMC,passesthoughthecaudadstomachandintotheintestine.TheMMCsweepsanyremainingparticlesfromthestomachintotheduodenumandisthoughttohavea“housecleaning”function.TheMMCisinitiatedbythecyclicalreleaseofthehormonemotilinfromthesmallintestineandisinhibitedbyfoodinthestomach.Itisnotknownhowthecyclicalreleaseofmotilinisproduced.4migratingmotorcomplex(MMC)

60Differentpressurephasicchangesinmigratingmotorcomplex(MMC)fromgastricantrumtoduodenumduringdigestiveperiods.DifferentpressurephasicchangesinMMCfromgastricantrumtoduodenumduringdigestiveperiods.III:PhasicwaveshiftsfromProximalgastricantrumtodistalgastricantrum,andtoduodenum;II:Phasicwaveistransientandtransitionalphase;I:restingphase.DistalgastricantrumProximalgastricantrumProximalduodenumDistalduodenum61VomitingTheexpulsionofgastriccontentsthroughthemouth,causedbyforcefulandsustainedcontractionoftheabdominalmusclesanddiaphragm62Pancreas

FunctionsofthePancreasEndocrinecellsofthepancreaticislets:SecreteinsulinandglucagonintobloodstreamExocrinecells:Acinarcellsandepithelialcellsofductsystemsecretepancreaticjuice63PancreasPancreaticEnzymesPancreaticalpha-amylaseAcarbohydraseBreaksdownstarchesSimilartosalivaryamylasePancreaticlipaseBreaksdowncomplexlipidsReleasesproducts(e.g.,fattyacids)thatareeasilyabsorbedPancreaticEnzymesNucleasesBreakdownnucleicacidsProteolyticenzymesBreakcertainproteinsapartProteasesbreaklargeproteincomplexesPeptidasesbreaksmallpeptidesintoaminoacids70%ofallpancreaticenzymeproductionSecretedasinactiveproenzymesActivatedafterreachingsmallintestine64PancreaticSecretionfor

ProteolyticEnzymes

65BicarbonateIonProductioninPancreas1-CO2diffusestotheinterioroftheductulecellsfrombloodandcombineswithH2ObycarbonicanhydrasetoformH2CO3whichwilldissociateintoHCO3-

andH+.TheHCO3-isactivelytransportedintothelumen.2-TheH+formedfromthedissociatedH2CO3isexchangedforNa+ionsbyactivetransportthroughblood,whichwilldiffuseoractivelybetransportedtothelumentoneutralizethe–vechargesofHCO3-.3-ThemovementofHCO3-andNa+ionstothelumencausesanosmoticgradientcauseswatertomovefrombloodtoductulecellsofthepancreasproducingeventuallytheHCO3-solution.66BicarbonateIonProductioninPancreas67HCO3-Cl-Cl-CarbonicAnhydraseSiteofSecretinactionH2O+CO2

CO2

CAH2CO3H+

Na+

K+

Na+

MechanismofPancreaticDuctuleCellsSecretionHormones,likesecretin,stimulateHCO3-secretionPancreaticDuctuleCellsPumpCarrierCarrierChannelCapillaryInterstitialfluidBasolateralmembraneLuminalmembranePancreaticjuice68RegulationofthepancreaticsecretionThereisnopancreaticsecretionduringdigestiveintervalperiod.Pancretaicjuicebeginstosecretsaccompanyingtheintakeoffood.Thepancreaticsecretionisregulatedbythenervousandhumoralfactor69(6)RegulationofthepancreaticsecretionCephalic(smell,taste)andgastricphases(fooddistention)stimulatetheenzymecomponentofsecretionthroughtheactiononacinarcellsofacetylcholinereleasedfromvagalnerves.Intestinalphaseisinitiatedbyacid,protein,andfatinduodenalcontents.Acidreleasessecretin(byScell),whichistheprimarystimulusofaqueouscomponent;fatandproteinreleasecholecystokinin(CCK),whichstimulatesenzymaticcomponent;allthreesubstancesstimulatevagalnervereleaseofacetylcholinecausingsecretionofenzymaticcomponent.CCKandAchincreasethefunctionofsecretin.70RegulationofPancreaticSecretionpancreasACh71BileJuice

Bileisabitter-tasting,darkgreentoyellowishbrownfluid,producedbytheliver,itisstoredinthegallbladderanduponeatingisdischargedintotheduodenum..Theprincipalfunctionofthegallbladderistoserveasastoragereservoirforbile.Themaincomponentsofbilearewater,bilesalts,bilepigments,andcholesterolBilesaltshasnoenzymeandactsasemulsifyingagentsinthedigestionandabsorptionoffats.Cholesterolandbilepigmentsfromthebreakdownofhemoglobinareexcretedfromthebodyinthebile.72PhysicalpropertiesHepaticbile:pH7.4,colourisgoldenyellow,Bladderbile:pH6.8,colorisgreendarktoyellow(darker)Volumeofbileproducedreachestooneliterofbileperday(dependingonbodysize).73BileJuiceBileComposition;Water(85%),bilesalts(10%),(Cholic,chenodeoxycholic,deoxycholic,andlithocholicacid)mucuspigments(3%),bilepigmentse.gbilirubinglucuronidefats(1%),suchasPhospholipids(lecithin),cholesterol.0.7%inorganicsalts.74Functionofbilejuice1-Itisimportantinthedigestionandabsorptionoflipids;

Bileactsasasurfactant,helpingtoemulsifythefatsinthefood.Bilesaltanionshaveahydrophilicsideandahydrophobicside,andthereforetendtoaggregatearounddropletsoffat(triglyceridesandphosphiolipids)toformmicelles,withthehydrophobicsidestowardsthefatandhydrophilictowardstheoutside.Thehydrophilicsidesarepositivelychargedduetothelecithinandotherphospholipidsthatcomposebile,andthischargepreventsfatdropletscoatedwithbilefromre-aggregatingintolargerfatparticles.75FunctionofbilejuiceThedispersionoffoodfatintomicellesthusprovidealargelyincreasedsurfaceareafortheactionoftheenzymepancreaticlipasethusaidinginthedigestionoflipids.2-Bileservesastherouteofexcretionforbilirubin.3-Thealkalinebilehasthefunctionofneutralizinganyexcessstomachacidbeforeitenterstheileum.4-.Bilesaltsalsoactasbactericides,destroyingmanyofthemicrobesthatmaybepresentinthefood.76(3)Bilesaltemulsifiesfatstoformmicellesoflipidmetabolitesandcomplexessubstances*Bileacidsandphospholipidsareamphipathicmolecules,whichmeansthattheyhavebothwater-solubleandwater-insolubleportions.Thisenablesthemtodissolvefatsinthewaterymixtureofthesmallintestineandtoformaggregatesoflipidscalledmicelles.Bothfunctionsgreatlyfacilitatethedigestionandabsorptionoffats.77AbnormalitiesassociatedwithbileGallstone;Themajorityofgallstonesaremadeupofcholesterol,(cholesteroltendstoaccreteintolumpsinthegallbladder)Causesofgallstones;-Toomuchabsorbtionofwaterfromthebile.-Toomuchcholesterolinbile.-Inflammationoftheepithelium.78Bilesecretionstimulation1-Underneuralcontrolmediatedbyacetylcholine.2-Underhormonalcontrol;Whenfoodisreleasedbythestomachintotheduodenumintheformofchyme,theduodenumreleasescholecystokinin,whichisthemainstimulantcausingthegallbladdertoreleasetheconcentratedbiletocompletedigestion.-Gastrinandsecretinalsostimulatebilesecretion.Lackofbilesaltsintheenterohepaticcirculationstimulatesbilesynthesisandsecretion.79EnterohepaticCirculation

About95%ofthesaltssecretedinbilearereabsorbedactivelyintheterminalileumandre-used.Bloodfromtheileumflowsdirectlytothehepaticportalveinandreturnstotheliverwherethehepatocytesreabsorbthesaltsandreturnthemtothebileductstobere-used,sometimestwotothreetimeswitheachmeal.80TheGallbladderStoresbileConcentratesitReleasestosmallintestinewhenneeded81Compositionandpropertiesofintestinejuicemucine,variousenzyme(enterokinase肠激酶),immunoglobulins;ions;leukocytes;epitheliocytes(200gperday).pHofintestinejuiceis7,5-8,0;productionperday–near1,8-2,5L.

Functions:endinghydrolysesofallnutritivesubstances;protectiveofmucuswall;supportofchymeinfluidcondition;formedofbasereactionofintestinecontents.Increasesecretion:parasympatheticnerves,secretine,andglucagons82Toniccontraction:thebaseoftheothercontractions2.Segmentationcontractions(1)def.Whenaportionofthesmallintestinebecomesdistendedwithchyme,thestretchoftheintestinalwallelicitsarhythmicalcontractionandrelaxationoflocalizedcircularmusclesspacedatintervalsalongtheintestine,(2)function:mixthechymewiththedigestivejuiceincreaseitsexposuretothemucosalsurfaceTypesofsmallintestinalmovement83MotilitiesofsmallintestineSegmentationContractionCircularmusclecontractssendingchymeinbothoradandcaudaddirectionsIntestinethenrelaxesallowingchymetomergebacktogether

Pe