are formed in the mesoderm between buccopharyngeal membrane and cranial part of intraembryonic coelom (cardiogenic area). • Fusion between the endocardial tubes to form a single tube. • Mesoderm that surrounds the tube is called myo-epicardial mantle which forms myocardium of the heart. • After folding, heart tube with the mantle will lies ventral to pharynx in pericardial bulge. • The cranial (arterial) end is fixed with arteries of the fetus, while the caudal (venous) end is fixed to veins of the fetus. • Elongation of the tube leads to formation of U-shaped tube. Dr.Sherif Fahmy
the tube will form 4 chambers: Sinus venosus, Primitive atrium, Primitive ventricle and Bulbus cordis. -Elongation of the tube leads to formation of U-shaped tube. -More elongation of the tube leads to formation of S-shaped tube. -Sinus venosus comes caudal to primitive atrium which is dorsal to primitive ventricle. Bulbus cordis on the right of primitive ventricle. -Sinus venosus, pulmonary vein and primitive atrium will form the common atrium which is divided into right and left atria by interatrial septum. -Primitive ventricle with proximal and middle parts of bulbus cordis will form right and left ventricles, while distal part (truncus arteriosus) will form ascending aorta and pulmonary trunk.
tube that is formed of body and 2 horns; each horn receives 3 veins (vitelline, umbilical and common cardinal vein). • The body joins the back of right side of primitive atrium by sinu-atrial orifice which is guarded by right and left valves. While back of left side of primitive atrium is joined by pulmonary vein. • Left sinus horn becomes reduced in size due to degeneration of left vitelline and umbilical veins as well as shift of blood from left anterior cardinal to right anterior cardinal by an anastomosis (becomes left brachiocephalic vein. Left horn remains as coronary sinus. Dr.Sherif Fahmy
and right horn are absorbed by widening of sinu-atrial orifice to form sinus venarum of right atrium. -Cranial ends of 2 valves fuse together to form septum spurium that forms upper part of crista terminalis. Left valve will fuse with interatrial septum while right valve forms rest of crista as well as valves of inferior vena cava and coronary sinus. Absorption of pulmonary vein: -Pulmonary vein has 2 divisions and each has 2 more divisions. Absorption will form wall of left atrium and 4 pulmonary veins will open separately to the left atrium. It forms the smooth part of the wall of left atrium. Dr.Sherif Fahmy
of primitive atrium Absorbed pulmonary veins Sinus venarum (smooth posterior of right atrium) Smooth wall of left atrium S.V.C Septum intermedium Azygos vein Primitive ventricle Left brachio-cephalic vein Dr.Sherif Fahmy
Primitive atrium: forms rough anterior (musculi pectinati) wall and auricle of right atrium. • Sinus venosus: forms posterior smooth wall of right atrium (sinus venarum). • Right ½ of atrio-ventricular canal: forms right atrioventricular orifice, inside which 3 cusps are formed (tricuspid valve). • Rt & Lt sino-atrial valves remain as crista terminalis and valves of inferior vena cava and coronary sinus. Dr.Sherif Fahmy
1- Primitive atrium: forms rough part of left atrium in the left auricle (musculi pectinati). • 2- Pulmonary trunk: absorped to form the smooth wall of the left atrium. • 3- Left ½ of atrio-ventricular canal: forms the left atrio- ventricular orifice in which 2 cusps are developed. Dr.Sherif Fahmy
that downgrows from the roof of common chamber. • It is separated from atrio-ventricular canal by osteum primum. More downgrowth will close the osteum primum while the upper part degenerates to form osteum secundum. 2- Septum secundum: • Downward growth of crescentic septum secundum to the right side of septum primum to cover osteum secundum which becomes foramen ovale. 3- Septum intermedium: • It is formed by fusion between ventral and dorsal atrio-ventricular cushions to separates between right and left atrio-ventricular orifices. Dr.Sherif Fahmy
then becomes ventral to it. • Proximal part of bulbus cordis enlarges to form right ventricle. The mid-prtion will form outflow part of each ventricle. The distal part forms truncus arteriosus (ascending aorta and pulmonary trunk). • Conus cordis is divided by conus septum which is formed by fusion between right & left bulbar ridges. Dr.Sherif Fahmy
ventricle and inlet of right ventricle. 2- Bulbus cordis ➢Proximal portion of forms most of right ventricle. ➢Midportion (Conus Cordis) forms the outflow parts of both ventricles. Dr.Sherif Fahmy
right ventricle except inlet from primitive ventricle. 2- Mid-portion (Conus cordis): forms outflow parts of both ventricles. 3- Distal part (truncus arteriosus): forms orifices and main parts of ascending aorta and pulmonary trunk. Dr.Sherif Fahmy
proliferation of myoblasts. -Dilatation of both ventricles. 2- Membranous part: developed by migrated cells from: -Inferior atrio-ventricular cushions. -Lower part of bulbar ridges. Anomalies of interventricular septum: 1- Septal defect in muscular or membranous part. 2- Complete absence of the septum. Dr.Sherif Fahmy
of aortico- pulmonary septum. is manifested by pulmonary stenosis, overriding aorta, ventricular septal defect and hypertrophy of right ventricle. Persistant truncus arteriosus: due to failure of formation of bulbar cushions. It is usually accompanied with membranous ventricular septal defect. Transposition of great arteries (TGA): Aorta arise from right ventricle while pulmonary trunk arises from left ventricle due to loss of spiral shape of the septum. Dr.Sherif Fahmy
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