Esoph motility Physiology.docx
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Esoph motility Physiology.docx
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EsophmotilityPhysiology
Physiologyofesophagealmotility
HiroshiMashimo,M.D.,Ph.D.and RajK.Goyal,M.D.
EsophagealAnatomy
Theesophagusisatubularmuscularstructurethatspansfromthedistalpharynxinthenecktothegastroesophagealjunctionbelowthediaphragm.Thedistalendofthetubularesophagusisnormallyintheabdomenandflaresintothegastricfundus.Functionally,theesophagusextendsfromthelowerborderoftheupperesophagealsphincter(UES)tothelowerborderoftheloweresophagealsphincter(LES).Thus,althoughtheUESisnotapartoftheesophagus,theLESisanintegralpartofit(Figure1).
Notethatthecervicalesophagusandthesmallpartofthethoracicesophagusthatincludestheupperesophagealsphincterarecomposedofstriatedmuscle.Thelowertwothirdsoftheesophagus,includingthethoracicandabdominalpartscontainingtheloweresophagealsphincter,arecomposedofsmoothmuscles.Thediseasesofthestriatedmuscleincludepolymyositisandmyastheniagravis,whereassclerodermaandachalasiaarediseasesthatinvolvethesmoothmuscleportionoftheesophagus.(Source:
AGAGastroenterologyTeachingProject,2001,2ndEd.Unit9,EsophagealDisorders,Slide12,usedwithpermission.Copyright©AmericanGastroenterologicalAssociation,Bethesda,MD)
UpperEndoftheEsophagusandUpperEsophagealSphincter
TheupperendoftheesophagusiswelldefinedbythelowerborderofthecricoidcartilageandthelowerextentoftheUES.TheanatomiccorrelateoftheUESisthecricoidcartilageanteriorlyandtheC-shapedfibersofcricopharyngeusonthesidesandposteriorly.ThecricopharyngeusispresentinthelowerpartoftheUESandobliquefibersoftheinferiorconstrictorintheupperpart.Anatomically,theUESispartofthepharynxandisappropriatelytermedtheinferiorpharyngealsphincter.Thus,anatomically,thelowerborderofthecricoidcartilageand,functionally,thelowerborderoftheUESdefinetheupperendoftheesophagus.
LowerEndoftheEsophagusandLowerEsophagealSphincter
Thelowerendoftheesophagusisdefinedanatomicallybythejunctionoftheesophaguswiththestomachand,functionally,bythejunctionoftheinferiorborderofthehigh-pressurezoneoftheLEScomparedtothelowerpressureinthestomach.
Althoughthenormalesophagogastricjunction(EGJ)canbeeasilydefinedmanometrically,itsanatomic,radiologic,andendoscopicidentificationsaredifficultandhavebeencontroversial.
Onbariumswallowstudies,theEGJisdifficulttoidentifyinnormalsubjectsbecausetheswallowofcontrastisassociatedwithrelaxationoftheLES,whichobliteratestheEGJ.However,inpatientswithachalasia,theEGJismarkedbythelowerendofabeak-likepersistentnarrowingoftheLESandflareofthegastricfundus.Thisjunctionisoftenseenbelowthediaphragm.Rarely,acontractedLESmaybeidentifiedinoneofthemanytimedexposuresduringanormalbariumswallow.Duringswallowing,innormalsubjects,theLESisrepresentedradiographicallyasthe"ampulla"(correspondingtothevestibuledescribedbyanatomists)andthelowerextentoftheampullamarkstheEGJ.TheampullarysegmentisnotseenwhentheEGJisnormallylocatedbelowthediaphragmbecauseitisnotpossibletofullydistendthissegmentwithbariumbecauseofthediaphragmandtheintraabdominallocation.However,whenthereisahiatalhernia,theesophagealampullamaybeidentifiedjustabovethehernia.Inpatientswithamucosalloweresophagealring(Schatzki'sring),theEGJismarkedbythisnarrowing(Figure2).
Figure2-Anatomicradiographiclandmarksoftheloweresophagealsphincter(LES).
Normally,inbetweenswallows,theLESremainsclosed.WithabariumswallowtheLESopensanditsidentityislostunlesssomeconstrictionlesionsarepresent.Forexample,theanatomicinferioresophagealsphinctermaybeidentifiedasamuscularring(alsoknownascontractileringorAring)ormucosalring(alsocalledSchatzki'sringorBring)locatedatthesquamocolumnarjunction.UsuallythesquamocolumnarjunctionformsazigzaglinewithoutaconstrictioninwhichcasethelowermostpartoftheLEScannotbeidentified.NotethatarelaxedLEScanopenwiderthantheesophagealbodyitselfandhasbeencalledavestibulebytheanatomistsandanampullabytheradiologists.ESO,esophagus.(Source:
GoyalRK.Theloweresophagealsphincter.ViewpointsonDigestiveDiseases.AmGastroenterolAssoc1976;8(3),withpermission.)
Onendoscopy,themuscularEGJishardtoidentify,andthereforerelianceisplacedonthesquamocolumnarmucosaljunctionorthejunctionoftheflatesophagealmucosalliningwiththeupperextentofthegastricmucosalfolds.However,thesquamocolumnarmucosaljunctionisoftenvisualizedasazigzagline(Z-line).Therefore,theEGJishardtoidentifyexceptwhenastraight-linesquamocolumnarjunctionandamucosalloweresophagealring(Schatzki'sring)arepresent.Moreover,patientswithshort-segmentBarrettesophagushavethelowermostpartoftheesophagus(i.e.,theLES)linedbycolumnarmucosa,makingendoscopicdeterminationofthesquamocolumnarjunctionanunreliablemarkerforEGJ.Insuchcases,theupperextentofthegastricfoldsmayserveasamarkerfortheEGJ.
Basedonthemuscularanatomy,theEGJismarkedbyapointwherethetubularesophagusflaresintothegastricfundus.However,thispointisoftendifficulttoidentify.OthersurrogatemarkersfortheanatomicEGJhavebeensuggested,butnoneofthemarefullysatisfactory.PainstakinganatomicdissectionofthemusclesattheEGJsuggeststhatEGJmaybemarkedbytheesophagealcircularfibersontherightsideoftheesophagusthatinsertintotheuppermostfibersofthegastricslingfibersontheleftside.
Theesophagusmaybedividedintothreesegments,namelythecervical,thoracic,andabdominalsegments,basedontheirlocation.Theesophagusissituatedintheposteriormediastinum,behindthetracheaandleftmainstembronchus,anditcurvesleftwardtocoursebehindtheheartandinfrontoftheaorta.Itpassesthroughanopeningofthediaphragmcalledtheesophagealhiatusthatislocatedanteriortotheopeningforthedescendingaorta.Normally,theLESstraddlestheesophagealhiatussothatitsupperhalfispresentinthechest,whereasitslowerhalfislocatedbelowthediaphragmintheabdominalcavity
LengthoftheEsophagus
ExclusiveoftheUESandtheLES,theadultesophagusmeasuresapproximately20cminlength(rangeof18to22cm).Measuredfromtheincisors,theesophagealbodybeginsapproximatelyat18to20cm,whichmarksthelowerborderoftheUESandendsatapproximately40cm(rangeof26to50cm).Theesophagusisaveragelyshorterinwomenandendsataround37cmfromtheincisors(rangeof22to41cm).Theterminal2-to4-cmregionoftheesophagusgenerallyconstitutestheLES.
EsophagealWall
Thewalloftheesophagus,asinotherpartsofthegut,ismadeofthemucosa,submucosa,andmuscularispropria(Figure3).However,unliketherestofthegut,theesophagushasnotrueserosalouterlayer,butiscoveredbyathinandpoorlydefinedlayerofconnectivetissue.Normally,themucosaoftheesophagusismadeofstratifiedsquamousepithelium,exceptattheLES,wherethesquamousepitheliumjoinsthegastriccolumnarepithelium.Comparedtotherestofthegut,therearefewglands,anditssecretoryfunctionislimited.Themuscularispropriaismadeoftheinnercircularandouterlongitudinalmusclelayers.Thereisalsoalessprominentlayerofmuscleorientedlongitudinallyandfoundbetweenthemucosaandthemuscularispropriacalledthemuscularismucosa.
Figure3-Esophagealwall.
(Source:
NettermedicalillustrationusedwithpermissionofElsevier.Allrightsreserved.)
∙
CervicalEsophagus(StriatedMusclePartoftheEsophagus)
Themuscularispropriaispredominantlymadeofentirelyskeletalmuscleintheupper(cervical)partoftheesophagus(approximately2to6cmoftheproximalesophagus),andsmoothmuscleinthelower(thoracic)partoftheesophagus.Avariablelengthofmixedinterdigitatingmuscletypeisfoundinthemidtransitioningportionoftheesophagus,generallyatthelevelofthecarina(approximatelystarting4to8cmfromtheupperend,andextendingapproximately10to13cmfromthelowerborderofthecricoidcartilage.Rarely,theentireesophagusmayhavestriatedmuscleinitswall.
Thelongitudinalskeletalmusclefibersofthecervicalesophagusoriginatefromthesuperioraspectofthemedianridgeonthedorsalsurfaceofthecricoidcartilage,andthesefibersarejoinedbyfibersfromthecricopharyngeusandposterolateralcricoidcartilagelaterally.Thelongitudinalfiberstraveldorsallyandcaudallytomeetapproximately3cmbelowthecricoidcartilage,leavingatriangularareadevoidoflongitudinalmuscle,calledtheLaimer'striangle.
Ithadbeensuggestedthatesophagealstriatedmusclesdevelopfromthesmoothmusclesbyaprocessofcellulartransdifferentiation.Morerecentstudies,however,donotsupportthisview.Thestriatedmusclesconstitutetheupper2to6cmoftheproximalportionoftheesophagealbody.
Theesophagusisinnervatedbybothparasympatheticandsympatheticnerves.Theparasympatheticscontrolperistalsisviathevagusnerve.Themedullaryvagalpostganglionicefferentsarisefromthelowermotorneuronsinthenucleusretrofacialisandthecompactformationofthenucleusambiguus.Thesenervesaremyelinated,containcholineacetyltransferaseandcalcitoningene-relatedpeptide(CGRP),andmakedirectcontactontoindividualstriatedmusclefibersviathemotorendplates.Themainexcitatoryneurotransmitteratthemotorendplat
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