生理学英文版

Chapter6DIGESTION&ABSORPTION§1.Introduction

Conceptof

digestion

&

absorption

*

Mechanical&chemicaldigestion

Characteristicsofdigestivesmoothmuscles

*

Generalcharacteristics

*

Electrophysiologicalcharacteristics

Restingpotential(RP)Slowwaveorbasicelectricalrhythm(BER)Actionpotential(AP)Electricalactivities&contractionofdigestivesmoothmuscles

Secretionof

digestiveglands

*

Mainfunctionsofdigestivefluids

Gastrointestinalinnervation

*

Intrinsic(orenteric)nervoussystem

Submucosal

&myentericplexus

*

Extrinsicnervoussystem

Parasympathetic&sympatheticnerves

Gastrointestinalhormones

*

Generalfunctions

*

Brain-gutpeptidesIntrinsic(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)pouchIntestinalphase

Mechanisms:

Mainlyhumoralregulation

Chemical&MechanicalstimulationinitiatingreleasesofGastrin,Entero-oxyntin&Otherhumoralfactors

Experiment:Pavlovpouch

Characteristics:

Smallquantity(10%)

Loweracidity&digestivepowerCephalic,gastric,&intestinalphaseofgastricjuicesecretionSummaryofcephalic,gastric,&intestinalphaseofgastricjuicesecretionInhibitoryregulation

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)§4.Digestionintheintestine

Pancreaticjuice

&itssecretion

*

Nature,Compositions&functions

pH7.8~8.4,colorless&odourless,1~2L/day

Bicarbonate(HCO3)NeutralizeHCl&provideaweakbasicmediumfavoringdigestiveenzymeactionPancreaticenzymes:amylase,lipase,colipase,trypsinogen&chymtrypsinogen,etc.

Turntrypsinogenintotrypsinbyentero-kinase,turnchymtrypsinogenintochym-trypsinbytrypsin

Trypsininhibitor:apolypeptide*

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

Secretion

of

thesmallintestine

*Intestinalglands

Brunner’sgland(basicmucus)

LieberkuhnCrypt(mainpart)

*

Nature,Compositions&functions

pH7.6,iso-osmoticsolution,1~3L/day

Enterokinase,theonlyonesecreted

Oligopeptidase,

oligosaccharidasethosecontainedintheepithelialcells

*RegulationofsecretionofsmallintestineMainlythroughplexusreflexinitiatedbyinflationoftheintestine

Movementsof

thesmallintestine

*Movementinthedigestiveinterphase

MMCsimilartothatinthestomach

*Mainmovementformsindigestivephase

Toniccontraction:thesameasinstomach

Segmentation:peculiartothesmallintestine

Peristalsis:0.5~2.0cm/s

Peristalticrush:2~25cm/s

*RegulationofsmallintestinalmovementSegmentationofthesmallintestine

*RegulationofsmallintestinalmovementIntrinsicplexus:receive

mechanical&chemicalstimuliandthencauseperistalsisExtrinsicplexus:parasympatheticnerveintestinalactivities;sympatheticnever

intestinalactivitiesHumoralfactors:gastrin,CCK,Enk,5-HT,etc.

Functionsof

theileocecalsphincter

*Permitsomeofchymetosquirtintothececumeachtimewhenaperistalsiswavereachesit

*Preventrefluxofcoloniccontentsintotheileum§5.Digestioninthecolon

Mainfunction

ofthecolonAbsorbwater

AbsorbVitB&Ksynthesizedbybacteria

Formation&temporarilystoragefeces

Secretion

ofthecolonpH8.3~8.4,Mucus&HCO3

Protectmucosaagainstinjuries&lubricatefeces

Movements

ofthecolon

Haustraltoandfromovement,Segmentationor

Polyhaustralpushingmovement,Peristalsis,

Massperistalsis

Feces&

Defecation

*

Feces:

containinorganicmaterial,undigestedplantfibers,bacteria,water,etc.

*

Defecation:

areflexinitiatedbydistensionoftherectumwithfeces

Reflexprocess,Primary&highercenters

Actionofcolonicbacteria

*

Benefit:

synthesisVit.Bco&K

*

Harm:

producesomepoisonoussubstances

Actionofdietaryfibersontheintestinalfunction

Reduceabsorptionofwater;Enhancecolonicmovement;Increasethevolumeoffeces;Lowthecaloricratioofthefood§6.Absorptioninthesmallintestine

SitesofabsorptionOralcavity&Stomach:little

Duodenum&Upperjejunum:mostnutrients

Il