Chapter6DIGESTION&ABSORPTION§1.Introduction

Conceptof

digestion

&

absorption

*

Mechanical&chemicaldigestion

Characteristicsofdigestivesmoothmuscles

*

Generalcharacteristics

*

Electrophysiologicalcharacteristics

Restingpotential(RP)Slowwaveorbasicelectricalrhythm(BER)Actionpotential(AP)生理學(xué)英文版第1頁(yè)Electricalactivities&contractionofdigestivesmoothmuscles生理學(xué)英文版第2頁(yè)

Secretionof

digestiveglands

*

Mainfunctionsofdigestivefluids

Gastrointestinalinnervation

*

Intrinsic(orenteric)nervoussystem

Submucosal

&myentericplexus

*

Extrinsicnervoussystem

Parasympathetic&sympatheticnerves

Gastrointestinalhormones

*

Generalfunctions

*

Brain-gutpeptides生理學(xué)英文版第3頁(yè)Intrinsic(orenteric)nervoussystem生理學(xué)英文版第4頁(yè)Extrinsicnervoussystem生理學(xué)英文版第5頁(yè)§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生理學(xué)英文版第6頁(yè)

Masticationorchewing&itseffects

*

Definition

*

Effects

Breakuplargefoodparticles;mixesthefoodwithsaliva;aidswallowing

Deglutitionorswallowing

*

Definition

*

Process

1st,2nd&3rdphasePeristalsis&loweresophagealsphincter生理學(xué)英文版第7頁(yè)P(yáng)eristalsisoftheesophagus生理學(xué)英文版第8頁(yè)§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:seenextpage生理學(xué)英文版第9頁(yè)RelationshipbetweenmaxvolumeofHClsecretion&thenumberofparietalcells生理學(xué)英文版第10頁(yè)

FunctionsofHCl:

Turnpepsinogenintopepsin&provideamediumoflowpHfavoringpepsinaction;

Killmanyswallowedvirulentorganisms;

Promotethesecretionofpacreas&bile;

Promotetheabsorptionofcalcium&ferrumPepsinogen

Secretedby

chiefcells&activatebyHClFunction:digestproteinsintoproteoses,peptones,polypeptides,withlittlefreeaminoacids生理學(xué)英文版第11頁(yè)Mucus

Secretedbyneck&surfacemucouscells,cardiac&pyloricglandsFunction:formmucus-bicarbonatebarrier

IntrinsicfactorSecretedbyparietalcells

Function:

PromotetheabsorptionofVitB12*

Regulationofgastricsecretion

EndogenousreleasingsubstancesAcetylcholine(ACh),gastrin&histamineSomatostatin(SST)(release-inhibiting)生理學(xué)英文版第12頁(yè)Mucus-bicarbonatebarrier生理學(xué)英文版第13頁(yè)Actionofacetylcholine,gastrin&histamineontheperietalcells生理學(xué)英文版第14頁(yè)Gastricsecretioninthedigestivephase

Cephalicphase

Mechanisms:

Conditioned&Unconditionedreflex

Vagalefferent&withGastrinsecretion

throughgastrin-releasingpeptide(GRP)

Experiment:ShamfeedingbyPavlov

Characteristics:

Largequantity(30%)

Highacidity&digestivepower生理學(xué)英文版第15頁(yè)ExperimentofShamfeedingbyPavlov生理學(xué)英文版第16頁(yè)Gastricphase

Mechanisms:

Distension

ofgastricfundus&bodyinitiatingvagovagal&localplexusreflexes

Distensionofpylorusinitiatingareleaseofgastrinthroughintrinsicplexus

ChemicalstimulationofGcellsinitiayingareleaseofgastrin

Experiment:

Pavlovpouch

Characteristics:

Largequantity(60%)

Highacidity&digestivepower生理學(xué)英文版第17頁(yè)Heidenhain(R)&Pavlov(L)pouch生理學(xué)英文版第18頁(yè)Intestinalphase

Mechanisms:

Mainlyhumoralregulation

Chemical&MechanicalstimulationinitiatingreleasesofGastrin,Entero-oxyntin&Otherhumoralfactors

Experiment:Pavlovpouch

Characteristics:

Smallquantity(10%)

Loweracidity&digestivepower生理學(xué)英文版第19頁(yè)Cephalic,gastric,&intestinalphaseofgastricjuicesecretion生理學(xué)英文版第20頁(yè)Summaryofcephalic,gastric,&intestinalphaseofgastricjuicesecretion生理學(xué)英文版第21頁(yè)Inhibitoryregulation

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

Hypertonicsolution:

Entero-gastricreflex生理學(xué)英文版第22頁(yè)

Gastricmotility&emptying

*Maintypesofgastricmotility

ToniccontractionMaintainingtheshape&placeofstomach,aswellastheintragastricpressure

ReceptiverelaxationDefinition&itsinnervationPeptideorNO–ergicvagalfibers

GastricperistalsisInitiatefrommiddlestomach,3times/minMix&grindfoodintochyme&helpempty生理學(xué)英文版第23頁(yè)

*

Gastricemptying&itscontrol

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

Discontinuousemptying

Adaptingfordigestion&absorption

Controlofemptying

Promotioninstomach:vagovagal&plexusreflex,gastrinrelease

Inhibitioninduodenum:entero-gastricreflex&enterogastrone生理學(xué)英文版第24頁(yè)

*

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&harm生理學(xué)英文版第25頁(yè)Migratingmotorcomplex(MMC)生理學(xué)英文版第26頁(yè)§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生理學(xué)英文版第27頁(yè)*

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生理學(xué)英文版第28頁(yè)

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生理學(xué)英文版第29頁(yè)*

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:enterohepaticcirculationofbilesalt生理學(xué)英文版第30頁(yè)Enterohepaticcirculationofbilesalt生理學(xué)英文版第31頁(yè)

Secretion

of

thesmallintestine

*Intestinalglands

Brunner’sgland(basicmucus)

LieberkuhnCrypt(mainpart)

*

Nature,Compositions&functions

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

Enterokinase,theonlyonesecreted

Oligopeptidase,

oligosaccharidasethosecontainedintheepithelialcells

*RegulationofsecretionofsmallintestineMainlythroughplexusreflexinitiatedbyinflationoftheintestine生理學(xué)英文版第32頁(yè)

Movementsof

thesmallintestine

*Movementinthedigestiveinterphase

MMCsimilartothatinthestomach

*Mainmovementformsindigestivephase

Toniccontraction:thesameasinstomach

Segmentation:peculiartothesmallintestine

Peristalsis:0.5~2.0cm/s

Peristalticrush:2~25cm/s

*Regulationofsmallintestinalmovement生理學(xué)英文版第33頁(yè)Segmentationofthesmallintestine生理學(xué)英文版第34頁(yè)

*RegulationofsmallintestinalmovementIntrinsicplexus:receive

mechanical&chemicalstimuliandthencauseperistalsisExtrinsicplexus:parasympatheticnerveintestinalactivities;sympatheticnever

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

Functionsof

theileocecalsphincter

*Permitsomeofchymetosquirtintothececumeachtimewhenaperistalsiswavereachesit

*Preventrefluxofcoloniccontentsintotheileum生理學(xué)英文版第35頁(yè)§5.Digestioninthecolon

Mainfunction

ofthecolonAbsorbwater

AbsorbVitB&Ksynthesizedbybacteria

Formation&temporarilystoragefeces

Secretion

ofthecolonpH8.3~8.4,Mucus&HCO3

Protectmucosaagainstinjuries&lubricatefeces

Movements

ofthecolon

Haustraltoandfromovement,Segmentationor

Polyhaustralpushingmovement,Peristalsis,

Massperistalsis生理學(xué)英文版第36頁(yè)

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生理學(xué)英文版第37頁(yè)§6.Absorptioninthesmallintestine

SitesofabsorptionOralcavity&Stomach:little

Duodenum&Upperjejunum:mostnutrients

Ileum:bilesalts&Vit