Electricalactivities&contractionofdigestivesmoothmusclesIntrinsic(orenteric)nervoussystemExtrinsicnervoussystem§2.Digestioninthemouth&esophagus

Saliva&itsfunction

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Nature&Compositionofsaliva

pH6.6~7.1,99%water

Salivaryamylase,lysozyme,salt,etc.

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Functions

ofsaliva

Moistenthecavity&solvefood;keepthemouthclean;anti-bacteria;digeststarch

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RegulationofsalivarysecretionPureneuroregulationConditioned&unconditionedreflex

Masticationorchewing&itseffects

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Definition

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Effects

Breakuplargefoodparticles;mixesthefoodwithsaliva;aidswallowing

Deglutitionorswallowing

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Definition

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Process

1st,2nd&3rdphasePeristalsis&loweresophagealsphincterPeristalsisoftheesophagus§3.Digestioninthestomach

Gastricjuice&itssecretion

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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

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Gastricemptying&itscontrol

Definition&somerulesCarbohydrate>proteins>lipids,Mix4~6h

Discontinuousemptying

Adaptingfordigestion&absorption

Controlofemptying

Promotioninstomach:vagovagal&plexusreflex,gastrinrelease

Inhibitioninduodenum:entero-gastricreflex&enterogastrone

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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

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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

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Water