L2 Development of the heart (1) Flashcards
Beginning of formation of heart tube.
lateral embryonic folding > endodermal ends move medially to fuse (gut) > followed by splanchnic mesoderm.
Formation of 2 endocardial tubes.
thickening of splanchnic mesoderm in the cardiogenic area > 2 solid angioblastic cords > Both cords start canalizing to form 2 endocardial tubes.
Origin of endocardium.
formed by thin endocardial tube (the inner part of the tubes).
Origin of myocardium.
The splanchnic mesoderm surrounding the pericardial coelom (around the endocardium).
Origin of epicardium.
The mesothelial cells of the pericardial cavity (around myocardium, outer part of the tubes).
Formation of final single endocardial tube.
the 2 tubes move closer > myocardium release cardiac jelly (distention) > distinct regions > one tube.
End of formation of endocardial tube.
tube is attached to splanchnic mesoderm by ventral and dorsal mesocardium > ventral mesocardium disappears > dorsal mesocardium disappears (transverse sinus).
Origin of pericardial cavity.
intra-embryonic coelom around the heart.
Divisions of heart tube from top to down.
bulbus cordis, ventricle, atrium, sinus venosus (formed by cardiac jelly).
Divisions of bulbus cordis from top to down.
truncus arteriosus, conus arteriosus, conus cordis.
Bending of bulboventricular tube.
bulbus cordis , ventricle grow faster than rest > Bulbus cordis moves, downwards, forwards & right > The ventricle moves to the left.
Circulation through primordial heart.
sinus venosus > atrium > ventricle > bulbus cordis.
Dextocardia.
The heart tube is abnormally bent to the left instead of right (isolated anomaly or situs inversus totalis).
Formation of atrioventricular canal.
Anterior & posterior endocardial AV cushions project > the approach and fuse > AV septum > right and left AV canal.
Formation of septum primum.
grows from the roof of atrium towards AV cushion > space between septum primum and AV cushion (foramen primum) > foramen primum disappears > upper openeing appears (foramen secondum).
Formation of septum secondum.
thick muscular septum grows to the right of septum primum > It has an oval foramen lower down (foramen ovale).
Valve of foramen ovale.
formed by septum primum & secondum > It allows blood to move from Rt. to Lt. atrium & not in the opposite direction > After birth, the foramen ovale functionally closes & the 2 septae fuse > Then the lower part of septum primum will be called fossa ovalis & margins of foramen ovale will become limbus fossa ovalis.
Complete absence of inter-atrial septum (ASD).
Failure of development of both septa > Cyanosis, rapid breathing, heart failure.
Secondum defects (ASD).
The septum primum totally resorbed due to excessive formation of foramen secondum or Absence of septum secondum (no clinical significance unless large defect > heart failure).
Endocardial cushion defect (ASD).
cushions fail to fuse > Persistent single atrio -ventricular canal, defect in all septa, Abnormal valve leaflets > Heart failure, cyanosis, Associated anomalies (Down’s syndrome).
