Yagel - Cardiovascular Development

Cardiovascular Development Yegal01

Cardiovascular Development (Yagel01)

Consider fetal heart as:

-Venous sinus- gets Q from R and L vein systemically and from common pulmonary vein

-Sinoatrial Transition Zone (Lose the valve on left, see valve on right asRA invaginates…--> Eustachian valve at IVC and Thebesian Valve at CS)

-Eustachian valve continues into the terminal crest, coursing along post atrial wall, surrounds SVC entrance

-Atrium

-Atrioventricular Transition Zone (AV Canal)

-Ventricular Inlet Segment

-Primary Interventricular Transition Zone (The Primary Fold)

-Corresponds to the Primary Groove externally

-Will form the muscular IVS

-It establishes the boundary bn the arterial and AV regions of the ventricle (the ventriculoinfundibular fold)

-Initially, only the outlet segment is to the right of the primary fold, then the right AV bloodstream (heading into the inlet ventricle) "excavates" the posterior part of the fold to split off a separate inlet septum to it's left side (so now there's a separation bn the right and left AV blood streams as the enter the inlet ventricle). The R AV bld stream thus goes thru the canal at the right side of this new inlet septum and crosses the primary fold to get to the right outlet ventricle. However, the right side enlarges and forms the inlet part of the RV. As the RV inlet grows, it separates the right part of the primary fold from the inlet septum. The primary fold in this region becomes the septomarginal trabeculation of the mature heart. (SO--> the primary fold becomes the inlet septum and septomarginal trabeculation)

-Ventricular Outlet Segment (connects to the arterial trunk aka aortic sac)

-right side of the ventricular part of the heart loop (aka primitive RV but this is poor nomenclature)

-2 parts:

-Proximal Outlet segment- looks like the ventric inlet segment, w a thin, compact myocardial wall, w many trabeculations.

-Distal Outlet segment- smooth myocardial wall, w thick endocardial ridges that contribute to the septal structures of the GAs

Embryonic Tissue Layers

-Myocardium <-- splanchnic mesoderm forms a horseshoe shape in the front of the buccopharyngeal membrane, with the limbs of the horseshoe contributing to the venous poles of the heart, and the center yielding the ventricles

-Endocardium <--splanchnic mesoderm yields a singleendothelial plexus. Initially the space bn the end and myocardiumm is a jelly, that later gets invaded by mesenchymal cells from the endocardium causing local masses of endocardial cushion tissue to form at the AVC and distal outlet segments

-the Endocardial Tube is a continuous structure bn the heart, veins, and arteries, so cells can invade the jelly region from extracardiac sources (e.g. neural crest, epicardium)

-Epicardium: coelomic epithelium forms the myocardium and pericardium, which are continuous at the venous and arterial poles…; the epicardium starts at the transverse septum and starts to protrude into the pericardial cavity and sends out vesicles that gradually cover the myocardium and give rise to epicardial lining and subepicardial mesenchyme- including the vasculature

Septation & Valve Formation

…

In at the atrium, the wall invaginates to form Septum Primum, which connects to the inf AV endocardial cushion

--To the left of the L venous valve, bn it and the atrial septum premium, the atrial wall invaginates somewhat to form the Septum Secundum- it never becomes a full septum, but instead becomes a semicircular rim that fuses w the left venous valve. At birth, it forms the flap of the atrial septum premium, and is pressed to close the FO…

Outflow septation

-takes place in immediate continuity w the septation of the aortic sac (the GAs)

-extracardiac mesenchyme (descends from the region bn the 4th and 6th pharyngeal arch arteries) forms the ao-pulm septum bn the Asc Ao the the Pulm Trunk, AND sends two extensions two the myocardial wall of the distal outlet segment. These extensions are covered by the endocardial outlet ridges…