EsophagusfullWord文件下载.docx

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（WewouldliketoacknowledgeandthankDr.I.T.Beckforhiscontributionofseveralofthefiguresforthechapterandvaluableeditorialadvice.）

Theesophagusisahollowmuscularorganwhoseprimaryfunctionistopropelintothestomachthefoodorfluidbolusthatitreceivesfromthepharynx.Symptomsofesophagealdiseaseareamongthemostcommonlyencounteredingastroenterology.Fortunately,mostsymptomsareduetobenigndiseasethatcanbeeasilyremedied.Thephysicianmustbeonthelookout,however,forthemoreseriousdisorders,whichcanpresentwithasimilarspectrumofsymptoms.Thischapterwillfocusonthepathophysiology,diagnosisandmanagementofthemorecommonesophagealdisorders.Rarediseasesinvolvingtheesophaguswillbedealtwithonlybriefly. 

2.Anatomy

2.1MuscularAnatomy

Theesophagusisahollowmusculartubeclosedproximallybytheupperesophagealsphincter（UES）anddistallybytheloweresophagealsphincter（LES）.TheUESconsistspredominantlyofthecricopharyngeusandthecaudalfibersoftheinferiorpharyngealconstrictormuscles.TheUESformsatransverseslitattheC5-C6vertebrallevelduetosurroundingbonystructuresandcartilage.Intheproximalone-quartertoone-thirdoftheesophagus,themuscleisstriated.Thereisthenatransitionzoneofvariablelengthwherethereisamixtureofbothsmoothandstriatedmuscle.Thedistalone-halftoone-thirdoftheesophagealbodyandLESarecomposedofsmoothmuscle.TheLESislocatedatthejunctionbetweentheesophagusandstomach,usuallylocalizedatorjustbelowthediaphragmatichiatus.Despiteitsdistinctphysiologicalfunction,itisnoteasilydistinguishedanatomically.

2.2Innervation

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Themotorinnervationoftheesophagusisviathevagusnerves.ThecellbodiesofthevagalefferentfibersinnervatingtheUESandtheproximalstriated-muscleesophagusariseinthenucleusambiguus,whereasfibersdestinedforthedistalsmooth-musclesegmentandtheLESoriginateinthedorsalmotornucleus.TheesophagusandLESalsoreceivesympatheticnervesupply（bothmotorandsensory）arisingfromspinalsegmentsT1-T10.Sensoryinnervationisalsocarriedviathevagusandconsistsofbipolarnervesthathavetheircellbodiesinthenodoseganglionandprojectfromtheretothebrainstem.

2.3BloodSupply

ArterialbloodsupplytotheUESandcervicalesophagusisviabranchesoftheinferiorthyroidartery.Mostofthethoracicesophagusissuppliedbypairedaorticesophagealarteriesorterminalbranchesofbronchialarteries.TheLESandthemostdistalsegmentoftheesophagusaresuppliedbytheleftgastricarteryandbyabranchoftheleftphrenicartery.Venousdrainageisviaanextensivesubmucosalplexusthatdrainsintothesuperiorvenacavafromtheproximalesophagusandintotheazygoussystemfromthemid-esophagus.Inthedistalesophagus,collateralsfromtheleftgastricvein（abranchoftheportalvein）andtheazygosinterconnectinthesubmucosa.Thisconnectionbetweentheportalandsystemicvenoussystemsisclinicallyimportant;

whenthereishypertension,varicealdilationcanoccurinthisarea.Thesesubmucosalesophagealvaricescanbethesourceofmajorgastrointestinalhemorrhage.

2.4LymphaticDrainage

Intheproximalthirdoftheesophagus,lymphaticsdrainintothedeepcervicallymphnodes,whereasinthemiddlethird,drainageisintothesuperiorandposteriormediastinalnodes.Thedistal-thirdlymphaticsfollowtheleftgastricarterytothegastricandceliaclymphnodes.Thereisconsiderableinterconnectionamongthesethreedrainageregions.

2.5Histology

Thewalloftheesophagusconsistsofmucosa,submucosaandmuscularispropria.Unlikeotherareasofthegut,itdoesnothaveadistinctserosalcovering,butiscoveredbyathinlayeroflooseconnectivetissue.ThemucosaconsistsofstratifiedsquamousepitheliuminallregionsoftheesophagusexcepttheLES,wherebothsquamousandcolumnarepitheliummaycoexist.Beneaththeepitheliumarethelaminapropriaandthelongitudinallyorientedmuscularismucosa.Thesubmucosacontainsconnectivetissueaswellaslymphocytes,plasmacellsandnervecells（Meissner'

splexus）.Themuscularispropriaconsistsofaninnercircularandanouterlongitudinalmusclelayer.Thecircularmusclelayerprovidesthesequentialperistalticcontractionthatpropelsthefoodbolustowardthestomach.BetweenthecircularandlongitudinalmusclelayersliesanothernerveplexuscalledthemyentericorAuerbach'

splexus,whichmediatesmuchoftheintrinsicnervouscontrolofesophagealmotorfunction. 

3.Physiology

Themajorfunctionoftheesophagusistopropelswallowedfoodorfluidintothestomach.Thisiscarriedoutbysequentialor"

peristaltic"

contractionoftheesophagealbodyinconcertwithappropriatelytimedrelaxationoftheupperandloweresophagealsphincters.Theesophagusalsoclearsanyrefluxedgastriccontentsbackintothestomachandtakespartinsuchreflexactivitiesasvomitingandbelching.

3.1Deglutition:

PrimaryPeristalsis

Theactofdeglutitionisacomplexreflexactivity.Theinitialphaseisundervoluntarycontrol.Foodischewed,mixedwithsalivaandformedintoanappropriatelysizedbolusbeforebeingthrusttotheposteriorpharynxbythetongue.Oncethebolusreachestheposteriorpharynx,receptorsareactivatedthatinitiatetheinvoluntaryphaseofdeglutition.Thisinvolvesthecarefullysequencedcontractionofmyriadheadandneckmuscles.Thefoodbolusisrapidlyengulfedandpushedtowardtheesophagusbythepharyngealconstrictormuscles.Simultaneouslythereisactivationofmusclesthatliftthepalateandcloseoffandelevatethelarynxinordertopreventmisdirectionofthebolus.Almostimmediatelyuponactivationofthisreflex,theUESopensjustlongenoughtoallowthefoodbolustopassthrough;

itthenrapidlyshutstopreventretrogradepassageofthebolus.Theoropharyngealphaseisthuscompletedandtheesophagealphasetakesover.Thisinvolvestwomajorphenomena:

（1）thesequentialcontractionofthecircularmuscleoftheesophagealbody,whichresultsinacontractilewavethatmigratestowardthestomach;

and

（2）therelaxationandopeningoftheLES,whichallowsthebolustopass.TheperistalticsequenceandassociatedUESandLESrelaxationinducedbyswallowingaretermedprimaryperistalsis.Thesecanbeassessedmanometricallyusinganintraluminaltubetomeasurepressures.ThetypicalsequenceseenduringprimaryperistalsisisdepictedinFigure1.Secondaryperistalsisreferstoaperistalticsequencethatoccursinresponsetodistentionoftheesophagus.Thisisalocalizedperistalticwavethatusuallybeginsjustabovetheareaofdistention.ItisassociatedwithLESrelaxation,butnotwithUESrelaxationordeglutition.

3.2UpperEsophagealSphincterFunction

TheUESservesasapressurebarriertopreventretrogradeflowofesophagealcontentsandtheentryofairintotheesophagusduringinspiration.Thishigh-pressurezoneiscreatedbytoniccontractionoftheUESmuscles,whichisproducedbytonicneuronaldischargeofvagallowermotorneurons.WithdeglutitionthisneuronaldischargeceasestemporarilyandpermitsrelaxationoftheUES.UESopeningwillnotoccurwithrelaxationofthemusclesalone;

itrequireselevationandanteriordisplacementofthelarynx,whichismediatedbycontractionofthesuprahyoidmuscles.Relaxationlastsforonlyonesecondandisfollowedbyapostrelaxationcontraction（Figure1）.

3.3EsophagealBodyPeristalsis

Thereisafundamentaldifferenceinthecontrolmechanismsofperistalsisbetweentheupper（striated-muscle）esophagusandthelower（smooth-muscle）esophagus.Inthestriated-musclesegment,peristalsisisproducedbysequentialfiringofvagallowermotorneuronssothatuppersegmentscontractfirstandmoreaboralsegmentssubsequently.Inthesmooth-musclesegment,thevagalpreganglionicefferentfibershavesomeroleintheaboralsequencingofcontraction,butintrinsicneuronsarealsocapableofevokingperistalsisindependentlyoftheextrinsicnervoussystem.Transectionofvagalmotorfiberstotheesophagusinexperimentalanimalswillabolishprimaryperistalsisthroughouttheesophagus;

however,inthissetting,distention-inducedorsecondaryperistalsiswillbemaintainedinthesmooth-musclebutnotinthestriated-musclesegment.Furthermore,ifvagalefferentfibersarestimulatedelectrically（Figure2）,asimultaneouscontractionwillbeproducedinthestriated-muscleesophagusthatbeginswiththeonsetoftheelectricalstimulus,laststhroughoutthestimulus,andendsabruptlywhenthestimulusisterminated.Inthesmooth-muscleesophagus,however,theresponsetovagalefferentnervestimulationisquitedifferent,inthattheonsetofcontractionsisdelayedrelativetotheonsetofthestimulus.Thelatencytoonsetofthecontractionincreasesinthemoredistalsegmentsoftheesophagus（i.e.,theevokedcontractionsareperistaltic）.

Thisexperimentalobservationindicatesthatintrinsicneuromuscularmechanismsexistandcanmediateperistalsisontheirown.Furtherevidenceforthismechanismisfoundinstudieswherestripsofesophagealcircularsmoothmusclearestimulatedelectricallyinvitro.Thelatencytocontractionafterstimulationisshortestinthestripstakenfromtheproximalsmooth-musclesegmentandincreasesprogressivelyinthemoredistalstrips.

Thislatencygradientofcontractionisclearlyimportantintheproductionofesophagealperistalsis.Althoughtheexactmechanismsareunclear,initialordeglutitiveinhibitionisim