Andersons pediatric cardiology 1288
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DevelopmentofthePharyngealArch
Arteries7–12
AsdescribedinChapter3,theintrapericardialcomponentsofthearterialtrunks
areformedwithinthedistalpartoftheoutflowtract.Theyareproducedbythe
ongoingmigrationofnonmyocardialcellsintothearterialpoleoftheheartfrom
thesecondheartfieldandtheneuralcrestduringtheninthandtenthdaysof
murinedevelopment.Theseriesofpairedarteriesthatconnectthe
extrapericardialaorticsactotheinitiallypaireddorsalaortasextendthrough
segmentsofpharyngealmesenchymeandencirclethetracheoesophageal
pedicle.Thesegmentsofpharyngealmesenchyme,alongwiththeircontained
arteries,developinsequenceandinacranial-to-caudaldirection.Each
protuberance,orarch,iscoveredbyendodermontheinsideandbyectodermon
theoutside.Thefirstfourarchesalsocontainamesodermalcorealongwith
additionalmesenchymederivedfromtheneuralcrest.Asfarasweknow,the
sequenceandmechanismofformationofthearchesandtheircontainedarteries
asseeninthemouseisparalleledinthedevelopinghumanheart.Sincethe
sequencehasbestbeeninvestigatedinthemouse,weusetheseimagesto
demonstratethechanges.Thearterialchannelsarefirstseenduringthelatter
halfofmurineembryonicday8andcontinuetoappearduringembryonicday
9.5(Fig.48.2).Bytheendofmurineembryonicday9.5,whichisequivalentto
Carnegiestage11inthedevelopinghuman,threepairsofarteriesoccupythe
firstthroughthirdpairsofpharyngealarches.Bythebeginningofembryonic
day10.5,bywhichtimethefourthpairofarterieshasbeguntoappear,the
arteriesinthefirstandsecondarcheshavealreadybeguntoregress.These
vesselsformacapillarynetworkwithinthedevelopingjawbutmakeno
significantcontributiontothefinalstructureofthebrachiocephalicbranchesof
theaorticarch.Formationofthesixthpairofarchestakesplaceduringthelatter
partofembryonicday10.5(Fig.48.3).Likethearteriesofthefirstfourarches,
thesixtharcharteriesalsooccupyadiscretesegmentofpharyngeal
mesenchyme.Unlikethefirstfourarches,however,thesixthpharyngealarches
donotcontainbony,muscular,orneuralelements.
FIG.48.2 Reconstructedepiscopicdatasetsfromdevelopingmice
sacrificedduringembryonicday9.5.Theupperpanelsarefromamouse
with19somites,whereasthemouseprovidingthematerialforthelower
panelshad27somites.Thearterialchannelsrunningfromtheaorticsacto
thedorsalaortashavebeenreconstructedinthepanelsatleft,whereas
thepanelsatrightshowtherelationshipofthearterialchannelstothe
pharyngealmesenchyme.
FIG.48.3 Reconstructedepiscopicdatasetsfromdevelopingmice
sacrificedduringembryonicday10.5showingtheongoingdevelopmentof
thearcharteriesconcomitantwithregressionofthearchesformedinthe
firstandsecondarches.Notethatthedorsalaortascontinuecraniallyas
thecarotidducts.Theimagesshownintheupperpanelsarefroman
embryowith32somites,whereastheembryofromwhichthelowerpanels
werepreparedhad40somites.
Bythebeginningofembryonicday11.5,thebilateralsymmetryofthearteries
isreadilyevident,althoughbythistimeonlythreesetsofarteriesare
recognizable.Thisisduetotheregressionofthearteriesofthefirstandsecond
arches(Fig.48.4).Itisduringembryonicday11.5thatcollateralchannelscanbe
foundinuptohalfofalltheembryos(seeFig.48.4,right),althoughthe
collateralchannelsarenotseenpriortotheformationofthesixthpairofarch
