CVS 3 Embryology- Development of the CVS Flashcards
What does septation create?
Interatrial septum, interventricular septum and sepation of ventricular outflow tract to give pulmonary trunk and aorta giving 4 chambers of heart and selective outflow
What are the endocardial cushions developed from?
neural crest cells that have migrated
Where do the endocardial cushions develop?
The atrioventricular region
In the first step of septation, the endocardial cushions divide the heart into what?
right and left channels
What are the two septa that divide the atria?
Septum primum- grows down towards fused endocardial cushions
Septum secundum-second cresent shaped septum
What are the three holes across the septa?
Ostium primum- hole present before septum primum fuses with the endocardial cushions
Ostium secundum- this appears in septum primum also, before the closure of ostium primum
Foramen ovale- hole in the septum secundum
By what process is the ostium secundum formed?
apoptosis
Which holes are involved in the right to left shunt in the atria of the fetus?
ostium secundum(L) and foramen ovale(R)
What feautures of the atria are derived from the primitive atrium?
auricles (muscular pouch area in each atrium)
What does the right atrium absorb?
sinus venosus
What does the left atrium sprout and absorb?
sprouts pulmonary vein then grows to absorb it and its first 4 branches
What is the fossa ovalis?
Depression in the right atrial septum that is the remnant of the shunt used in utero to bypass the lungs
What two components does the ventricular septum have?
muscular which forms most of septum and grows up towards the fused endocardial cushions and membranous
What is the foramen called when the muscular portion of the heart is starting to grow up towards the fused endocardial cushions?
the primary interventricular foramen
How is the primary interventricular foramen closed?
the gap is filled by by the membranous portion of the interventricular septum which is dervied from the endocardial cushions
What is the septation of the outflow tract called?
The conotruncal septum
How does the conotruncal septum form?
Endocardial cushions appear in the truncus arteriosus and grow towards each other in a spiral to form a spiral septum
Why does the fetal circulation bypass the liver?
Liver greedy as has a raft of functions so uses up oxygenated blood
Why does the fetal circulation bypass the lungs?
Because the lungs are high resistance and non functional
What changes occur as soon as a baby is born?
Left atrial pressure increases causing the atrial foramen to close and the ductus arteriosus contracts. Ductus venosus closes
What is the ductus venosus?
Shunt from umbilical vein to inferior vena cava that allows blood to bypass the liver in the fetus
How does the foramen ovale close?
The two septums are pushed together when the left atrial pressure increases above that of the right and so the holes in the septums no longer align so blood cannot be passed through
What is the fate of the foramen ovale?
becomes fossa ovalis
What is the fate of the ductus arteriosus?
becomes ligamentum arteriosum
What is the fate of the ductus venosus?
becomes ligamentum venosum
What is the fate of the umbilical vein?
becomes ligamentum teres (hepatis)
What causes transposition of the great vessels?
conotruncal septum not adopting spiral course
How common are congenital heart defects?
Very- 6-8/1000 births
What causes tetralogy of fallot?
unequal division of conus cordis
