Andersons pediatric cardiology 1079
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FIG.41.3 Arrangementofthearterialtrunksatthetimeofbirth.Theduct
isthedirectcontinuationofthepulmonarytrunkandislargerthantheright
andleftpulmonaryarteries.Theductjoinswiththeisthmusoftheaortic
arch,withbothpathwayscontinuingasthedescendingaorta.The
extrapericardialcomponentoftheascendingaortagivesrisetothe
brachiocephalicartery,continuingasthearch,whichgivesrisetotheleft
commoncarotid,andleftsubclavianarteries.
Priortobirth,theductisverymuchthedirectcontinuationofthepulmonary
trunk,withtheleftandrightpulmonaryarteriestakingoriginassmaller
branchesfromthetrunk.Posteriorly,theductisrelatedposteriorlytotheleft
mainbronchus,whileanteriorlyitiscrossedbythevagusnerve.Thisgivesoff
theleftrecurrentlaryngealnerve,whichencirclestheductbeforeascending
behindtheaorticarchintotheneck(Fig.41.4).
FIG.41.4 Viewthroughaleftthoracotomyshowstherelationshipofthe
leftrecurrentlaryngealnervetothepersistentlypatentarterialduct(doubleheadedarrow).(CourtesyBensonWilcox,UniversityofNorthCarolina.)
Thepulmonaryarterialendofthevesseliscoveredbyareflectionofthe
pericardium.
Intermsofitsmicroscopicstructure,theductisamusculararteryendowed
withanintima,media,andadventitia,differingmarkedlyfromtheadjacent
pulmonarytrunkandaorta(Fig.41.5).
FIG.41.5 (A)Microscopictrichrome-stainedsectionshowingthe
markedlydifferentaspectofthemuscularwallsofthearterialduct
comparedwiththefibroelasticwallsoftheaortaandpulmonarytrunk.(B)
Notetheintimalmoundswithintheductallumen(left),whichcanbe
appreciatedintheopenedclosingduct(right).
Themediaoftheaortaiscomposedmainlyofcircumferentiallyarranged
elasticfibers,whereasthemediaoftheductconsistslargelyofspirallyarranged
smoothmusclecells,somewithcircularandotherswithlongitudinal
orientation,28withanincreasedcontentofhyaluronicacid.Theintimallayers
arethickerthanthoseoftheadjoiningvesselsandcontainincreasedamountsof
mucoidsubstance.29Inthenewborn,thetissuesareratherlooselyarranged,with
awell-definedinternalelasticlaminathatmaybesingleorfocallyduplicated,
withsmallinterruptionsencounteredregularly.Nocollagenisseeninthemedia
bylightmicroscopy,butabundantmaterialthatstrainspositivelyforacid
mucopolysaccharidesisobservedbetweenthemuscleandtheelasticlaminas.
Electronmicroscopyrevealsfinecollagenfibrilslyingbetweenadjacent
lamellasofsmoothmusclecellsandelastin.Duringthesecondhalfofgestation,
thesmoothmusclecellsshowdecreasingevidenceofsecretoryactivity,and
increasingmaturationoftheircontractileelements.
Itisknownthatvesselscannotclosebyisolatedcontractionofcircularly
arrangedmuscle,30socoincidentshorteningofthelessabundantlongitudinally
arrangedmusclefibersiscriticaltoeffectiveclosure.Theductisinnervated
mostlybyadrenergicfibers,supplyinglargelytheadventitiaandoutermedia,
withcholinergicfibersbeingextremelysparseortotallyabsent.31Vesselsare
alsofoundinitswallsthatmayhavearoleinfuelingcontractionatbirth.28
