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Further atrial development

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

As septation of the primitive atrium is occurring, there are a number of developments within the forming right and left atria:

  • right atrium:
    • incorporates the remains of the primitive sinus venosus posteriorly:
      • this region forms the smooth-walled part of the mature right atrium, termed the sinus venarum
      • the junction between the sinus venosum and the original atrium is visible as the crista terminalis
    • at the entrance to the right atrium from the sinus venosum, there are two folds, the right and left venous valves:
    • superiorly, both folds fuse to form an elevation termed the septum spurium; eventually, the septum spurium contributes to the septum secundum
      • the right valve has several fates:
        • superiorly it degenerates
        • inferiorly it forms the valve of the inferior vena cava and the valve of the coronary sinus
      • the left valve contributes to the development of the septum secundum

the left atrium:

þþ a single primitive vein originates from the dorsosuperior wall of the chamber

  • it grows posteriorly to merge with the veins developing from the lung buds
  • expansion of the chamber consumes the single vein as part of the posterior wall; eventually, the connection that this vein made to the veins from the lung buds also becomes incorporated into the wall of the left atrium; finally, expansion results in individual veins opening by separate orifices into the chamber
  • the region of fusion with the veins forms the majority of the surface of mature left atrium; it is smooth walled
  • the only remnant of the original left atrium in the mature heart is the auricle

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