test 2 part 2 Flashcards
Heart Folding – Day 24
Diverticula (trabeculae) appear in two sharply defined areas
Along front of endocardial tube
Just proximally and distal to the primary interventricular foramen.
Early embryonic Ventricle - Primitive LV
Proximal 1/3 of bulbus cordis - Primitive RV
What does the diverticula do on the folding of the heart
These diverticula expand the capacity of the heart
Give them the densely trabeculated appearance
The trabeculae inside the heart leads to valves, chordeae tendinae, papillary muscles, and atrioventricular valves.
Heart Folding results in
Aortic arches – truncus arteriosus – conus cordis – bulbus cordis
As the primitive atria grow, the truncus arteriosus is positioned in a depression between the roof of the right and left primitive atria.
Now everything is ready for… SEPTATION!!
Cardiac Septation
Starts at Day 27
Lasts 10 days (Day 27-37)
During which the embryo grows from 5mm to 16-17mm
The formation of the cardiac septa occur simultaneously
During this time, no major changes in external appearance
Cardiac Septation
Day 27
primitive right and left ventricles are local widenings of the original heart tube
Connected to each other via narrow channel
Interventricular Foramen
Blood reaches primitive LV via small opening from the primitive atria
AV Canal
During ventricular development, 2 important processes occur simultaneously, that result in the “chamberization” of the ventricles
- Division of the AV Canal into a Right and Left AV orifice via the endocardial cushions
- Ventricular Septation
Endocardial Cushions
Develop in the Atrioventricular and Conotruncal regions
Assist in the formation of the atrial and ventricular (membranous) septa, AV Canals, Valves, Aortic and Pulmonary Channels.
At the end of week 4 with endocardial cushions
Atrioventricular endocardial cushions appear at the AV Canal.
2 lateral AV cushions appear on the right and left side of the canal
Anterior and posterior cushions push into the lumen and fuse
Results in the complete division of the canal into right and left AV orifices.
Final and the end of week 5.
The role of the endocardial cushions is to:
Form a barrier between the atria and ventricles
Right –left division of the canal
- The resulting canals are eventually occupied by the mitral and tricuspid valves.
Ventricular Septation
End of week 4
The ventricular septum is formed by the outgrowth of the muscular ridge at the interventricular foramen.
2 primative ventricles
expand
Medial walls become apposed and merge
The ventricular septum grows upward from the apex of the heart to the base of the heart.
Interventricular foramen is the space above the membranous septum
Shrinks when the conus septum is complete and by the creation of the outflow tracts
Outgrowth of tissue from the endocardial cushion along the top of the muscular interventricular septum closes the foramen
Fuses with the abutting part of the conus septum.
Atrial Septation
At day 27-28, the paired atria fuse together for form a common atrium.
Atrial septation occurs simultaneously and in cooperation with ventricular septation
Atrial septation also lasts approximately 10 days.
How Atrial Septation works
Sickle-shaped crest grows from the roof of the common atrium
First portion of the Septum Primum
Extends toward the endocardial cushions in the AV Canal.
Does not connect to endocardial cushions. Leaves a space called the Ostium Primum
Formed by the opening between the lower rim of the septum primum and the endocaridal cushions.
Extensions of the endocardial cushions grow along the edge of the septum primum, closing the Ostium Primum
Before closure, Apoptosis (cell death) makes perforations in the upper part of the septum primum
Forms the Ostium Secundum
Allows for blood flow to shunt from the right to the left
simplified version of atrial septation
- Septum primum grows downward from the roof of the common atrium.
- Apoptosis of a small superior portion of septum primum occurs during continued downward growth, resulting in a foramen secundum.
- After fusing with the endocardial cushion, if there is a small residual opening at the ECC it is called ostium primum ASD
- The septum secundum then grows downward, covering the foramen secundum.
- The septum secundum then grows further downward and creates a foramen ovale at the ECC.
- The two septa together now act as a valve to allow blood to enter the left atrium via the foramen ovale, then the septum secundum.
Outflow Tract Septation in the trucus
By the 5th week opposing ridges appear in the truncus
These cushions lie on the right superior wall
Will grow distally and to the left.
And on the left inferior wall
Will grow distally and to the right
Both cushions grow toward the aortic sac
Twist around each other and eventually fuse
Form the aorticopulmonary septum
Divides the truncus into aortic and pulmonary channels.
Outflow Tract Septation in the conus cordis
Similar cushions appear along the right dorsal and left ventral walls of the conus cordis
Grow toward each other and distally
Unite with the truncus septum
Divides the conus into anterolateral portion (RV outflow) and posteromedial portion (LV outflow)
