Flashcards in Septation Deck (14):
What four events occur during internal remodeling of the heart tube? Wks 5-7
1. Atrial septation
2. Formation of endocardial cushions and septation of atrioventricular canal
3. Ventricular septation
4. Septation of the conus and truncus arteriosus
Describe action of the septum primum
Septum prium grows down towards endocardial cushions to divide atria
What does the foramen secundum do?
Foramen secundum perforates through septum primum
What is the foramen primum?
Inferior to septum primum, closed by fusion with endocardial cuchions (2nd ½ of wk 6)
What is the oval foramen/foramen ovale?
opening between the ridge of septudm secundum and the flap valve of septum primum
What are the steps involved in the process of the atrioventricular (AV) canal?
At the end of the 4th week, two mesenchymal (endocardial) cushions appear at the
anterior and posterior borders of the AV canal. Asymmetric growth enlarges the AV canal
to the right, aligning the common AV canal over both ventricles. Endocardial cushions fuse
in the 7th week dividing the heart into R and L AV canals. The fused endocardial cushions
also serve as an anchoring point for atrial and ventricular septa and AV valves.
How are AV valves formed?
A portion of inlet myocardium is covered by endocardial cushion tissue (C)
• The myocardium covered by cushion tissue is undermined
• Sulcus invaginates into the atrioventricular groove with chamber growth
• Myocardium retracts and is replaced by dense connective tissue
• Myocardium remaining nearer the apex forms the papillary muscle
Describe what happens to the great arteries around the 5th week.
Mesenchymal cushions appear along the walls of the conus and truncus. These grow
toward the aortic sac and conus and spiral around each other. Fusion of the endocardial
ridges creates the aortico-pulmonary (spiral AP) septum. AP septum divides the conus and
truncus into an aortic and pulmonary channel.
Where do the neural crest cells migrate through with respect to the heart and what do
they contribute to?
Migrate through pharyngeal arches 3, 4, 5, & 6 to the outflow region of the heart.
Contribute to endocardial cushion formation in both the truncus arteriosus and conus cordis
Explain the process to make the complete ventricular septum?
Complex process involving, inlet (endocardial cushions), trabecular (muscular), and
outlet (conotruncal cushions).
• Three components fuse
• Muscular and conotruncal components meet at the outlet septum.
• Junction of three components closed by the membranous septum (inferior endocardial
What do the semilunar valves develop from? How do they develop?
Develop from mesenchymal endocardial cushions that septate the conus cordis; also
contributions from neural crest cells. Valves grow by cellular proliferation in a stagnant
zone at the boundary layer created by blood flow.
What is the pro-epicardium?
Transient structure located below the developing A/V canal of the early heart. Group of
multipotent cells that contribute to all vascular cells of heart. Undergo transformation to
invest the surface of the heart and form epicardium
What are the coronary artery cells derived from?
Epicardial derived cells subsequently diversity into subepicardial mesenchymal cells.
Give rise to fibroblasts, pericytes, and endothelial and smooth muscle cells that comprise
the coronary vasculature