The development of the conduction system in the mouse embryo heart: II. Histogenesis of the atrioventricular node and bundle

摘要

Thehistogenesisoftheatrioventricular(A-V)nodeandbundlewasstudiedin11-and12-day-oldmouseembryos.Inyoungerembryos(9and10dayspostcoitum),theinnercelllayerofthedorsalwalloftheA-Vcanalformsaspecializedinterconnectingtissuebetweentheatrialandventricularmuscles.TheA-VnodeoriginatesfromthecellsatthedistalendofthisspecializedtissueandproliferatesintotheloosemesenchymeofthedorsalA-Vcushion.Theproliferationtakesplaceproximaltothedevelopinginterventricular(IV)septumwithwhichthespecializedinnerlayeroftheA-Vcanalisinterconnected.AtthesametimeaPAS-positivecellgroupdifferentiatesalongtheridgeofthedevelopingIVseptumandextendsfromtheprimitivenodetothemiddleportionoftherimoftheIVforamen,whereitdividesintoleftandrightbranches.In11-and12-dayembryos,theA-VnodeandHisbundleprimordiainterconnectwiththeventriculartrabeculaeandareincontactwiththemyocardiumoftheIVseptum.Inthe12-dayembryos,bloodcapillariesandconnectivetissuecellsbegintoisolatetheprimordiumoftheconductingsystemfromtheforceproducingmyocardium.IncompleteisolationoftheconductingandcontractingmusclecellsmayresultinthepersistenceofaberrantA-Vconnectingfibers.