Page 324 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

280 SECTION III CARDIOvASCuLAR ``CARdIOvASCulAR—EMbRYOlOGY CARDIOvASCuLAR ``CARdIOvASCulAR—EMbRYOlOGY

` `CARdIOvASCulAR—EMbRYOlOGY

Heart morphogenesis First functional organ in vertebrate embryos; beats spontaneously by week 4 of development.
Cardiac looping Primary heart tube loops to establish left-right Defect in left-right Dynein (involved in L/R
polarity; begins in week 4 of development. asymmetry) can lead to Dextrocardia, as
seen in Kartagener syndrome (1° ciliary
Dyskinesia).
First aortic
arch Aortic roots Pericardium SVC Aortic arch
Bulbus Truncus Ascending aorta
cordis Primitive
arteriosus left atrium Pulmonary trunk
Sinus Left
horn atrium
Right
Cardinal Ventricle atrium
veins Atrium
Sinus
venosus
Left ventricle Ventricles
22 days 24 days 35 days 50 days
Septation of the chambers
Atria Septum primum grows toward endocardial 6. Septum primum closes against septum
cushions, narrowing foramen primum. secundum, sealing the foramen ovale soon
Foramen secundum forms in septum after birth because of  LA pressure and  RA
primum (foramen primum regresses). pressure.
Septum secundum develops on the right side 7. Septum secundum and septum primum fuse
of septum primum, as foramen secundum during infancy/early childhood, forming the
maintains right-to-left shunt. atrial septum.
Septum secundum expands and covers most
of foramen secundum. The residual foramen Patent foramen ovale—caused by failure of
is the foramen ovale. septum primum and septum secundum
Remaining portion of septum primum forms to fuse after birth; most are left untreated.
the one-way valve of the foramen ovale. Can lead to paradoxical emboli (venous
thromboemboli entering the systemic arterial
circulation) as can occur in ASD.

Septum Foramen Developing
primum secundum septum
secundum
Foramen
primum RA LA Dorsal Foramen
endocardial Septum secundum Septum
cushion primum primum
Foramen
primum
Septum Foramen Degenerating
secundum secundum septum primum
Foramen Septum Foramen
ovale primum ovale
Septum (closed)
secundum

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