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Electricalactivities&contractionofdigestivesmoothmusclesIntrinsic(orenteric)nervoussystemExtrinsicnervoussystem§2.Digestioninthemouth&esophagus
Saliva&itsfunction
*
Nature&Compositionofsaliva
pH6.6~7.1,99%water
Salivaryamylase,lysozyme,salt,etc.
*
Functions
ofsaliva
Moistenthecavity&solvefood;keepthemouthclean;anti-bacteria;digeststarch
*
RegulationofsalivarysecretionPureneuroregulationConditioned&unconditionedreflex
Masticationorchewing&itseffects
*
Definition
*
Effects
Breakuplargefoodparticles;mixesthefoodwithsaliva;aidswallowing
Deglutitionorswallowing
*
Definition
*
Process
1st,2nd&3rdphasePeristalsis&loweresophagealsphincterPeristalsisoftheesophagus§3.Digestioninthestomach
Gastricjuice&itssecretion
*
Nature,Compositions&functions
pH0.9~1.5,colorless,1.5~2.5L/day
Hydrochloricacid
(HCl)SecretedbyparietalcellsBasicsecretion:0~5mmol/hMaxsecretion:20~25mmol/hMechanismofHClsecretionFunctions:seenextpageRelationshipbetweenmaxvolumeofHClsecretion&thenumberofparietalcells
FunctionsofHCl:
Turnpepsinogenintopepsin&provideamediumoflowpHfavoringpepsinaction;
Killmanyswallowedvirulentorganisms;
Promotethesecretionofpacreas&bile;
Promotetheabsorptionofcalcium&ferrumPepsinogen
Secretedby
chiefcells&activatebyHClFunction:digestproteinsintoproteoses,peptones,polypeptides,withlittlefreeaminoacidsMucus
Secretedbyneck&surfacemucouscells,cardiac&pyloricglandsFunction:formmucus-bicarbonatebarrier
IntrinsicfactorSecretedbyparietalcells
Function:
PromotetheabsorptionofVitB12*
Regulationofgastricsecretion
EndogenousreleasingsubstancesAcetylcholine(ACh),gastrin&histamineSomatostatin(SST)(release-inhibiting)Mucus-bicarbonatebarrierActionofacetylcholine,gastrin&histamineontheperietalcellsGastricsecretioninthedigestivephase
Cephalicphase
Mechanisms:
Conditioned&Unconditionedreflex
Vagalefferent&withGastrinsecretion
throughgastrin-releasingpeptide(GRP)
Experiment:ShamfeedingbyPavlov
Characteristics:
Largequantity(30%)
Highacidity&digestivepowerExperimentofShamfeedingbyPavlovGastricphase
Mechanisms:
Distension
ofgastricfundus&bodyinitiatingvagovagal&localplexusreflexes
Distensionofpylorusinitiatingareleaseofgastrinthroughintrinsicplexus
ChemicalstimulationofGcellsinitiayingareleaseofgastrin
Experiment:
Pavlovpouch
Characteristics:
Largequantity(60%)
Highacidity&digestivepowerHeidenhain(R)&Pavlov(L)pouchInhibitoryregulation
Hydrochloricacid(HCl)AtypicalexampleofnegativefeedbackConditions&Mechanisms:pH≤1.2~1.5inthegastricantrumInhibitionofGcells,ReleaseofSSTpH≤2.5intheduodenumReleaseofsecretin,bulbogastroneFat:Initiatingreleaseofenterogastrone
Hypertonicsolution:
Entero-gastricreflex
Gastricmotility&emptying
*Maintypesofgastricmotility
ToniccontractionMaintainingtheshape&placeofstomach,aswellastheintragastricpressure
ReceptiverelaxationDefinition&itsinnervationPeptideorNO–ergicvagalfibers
GastricperistalsisInitiatefrommiddlestomach,3times/minMix&grindfoodintochyme&helpempty
*
Gastricemptying&itscontrol
Definition&somerulesCarbohydrate>proteins>lipids,Mix4~6h
Discontinuousemptying
Adaptingfordigestion&absorption
Controlofemptying
Promotioninstomach:vagovagal&plexusreflex,gastrinrelease
Inhibitioninduodenum:entero-gastricreflex&enterogastrone
*
Gastricmotilityinthedigestiveinterphase
Migratingmotorcomplex(MMC)
PhaseI:restingphase,90~120min
PhaseII:irregularspike&sporadicperistalsis,30~45min
PhaseIII:largeamountofspikes®ularstrongcontraction,5~10min
PhaseIV:transitionperiod,about5min
Significance:actasastreetcleanerVomiting
Definition:areflex,benefit&harmMigratingmotorcomplex(MMC)*
Regulationofpancreaticsecretion
Nervousregulation
Vagusnerve:ACh,gastrinCharacteristics:H2O&HCO3
,enzymesSympatheticnerve:ACh,NA
Characteristics:weakeffect
Humoralreulation
Secretin:H2O&HCO3
,enzymes
Cholecystokinin(CCK):
Characteristics:H2O&HCO3
,enzymes
Feedback:
CCK-releasingpeptide
Bile
secretion
&
gallbladderemptying
*
Nature,Compositions&functions
Hepaticbile:pH7.4,goldenyellow
Bladderbile:pH6.8,colorbecomedarker
Compositions:H2O,ions,bileacid,bilepigment,fattyacid,cholesterol,lecithin,
mucoprotein,etc.,butnoenzymeFunctionsofbile(mainlybybilesalt):
Fatemulsification;lipidabsorption;Promotetheabsorptionoffat-solubleVits*
Controlofbilesecretion&gallbladderemptying
Nervousregulation
Vagusnerve:ACh,gastrinHepaticbilesecretion(smallamounts)Gallbladdercontraction(slightly)
Humoralreulation
Gastrin:
directtohepaticcells&gallbladder;indirecttostomachHClsecretin
Secretin:acttobileduct¬tohepaticcells,so:H2O&HCO3
,bilesalt()
Cholecystokinin(CCK):gallbladdercontraction&Oddi’ssphincterdialation
Bilesalt:enterohepaticcirculationofbilesaltEnterohepaticcirculationofbilesalt§5.Digestioninthecolon
Mainfunction
ofthecolonAbsorbwater
AbsorbVitB&Ksynthesizedbybacteria
Formation&temporarilystoragefeces
Secretion
ofthecolonpH8.3~8.4,Mucus&HCO3
Protectmucosaagainstinjuries&lubricatefeces
Movements
ofthecolon
Haustraltoandfromovement,Segmentationor
Polyhaustralpushingmovement,Peristalsis,
MassperistalsisSitesofabsorption
Absorptionofmainnutrients
*
Water
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