(End 3rd wk WIUL) Angiogenic cells appear from splanchnic mesoderm and gives rise to 2 primitive endocardial tubes (cephalic end), 2 dorsal aortae (caudal). Lateral flexion allows the 2 tubes to fuse in the midline (d17-22). 1 - Initially, Heart consists of a simple tube, ancored at one end by the differentiating arterial trunks and at the other by extensive venous channels which drain into the atrium. 2 - Being fixed at both ends, cardiac tubes grows rapidly in length (simultaneous growth in the primitive ventricle & bulbus cordis) and the embroynic ventricle is bent into a C-shaped loop to the right of the midline. Primitive Ventricle (anterior&lateral growth) Right & Left Ventricle Primitive Atrium (Posteriorly) Right & Left Atrium The primitive ventricle displaces the bulbous cordis superiorly. DEVELOPMENT OF THE HEART 3 - As Development continues, the ventricular region swings back to midline and expands&grows in length, covering the atrium and great veins Extensive sacculations will eventually become the R Atrium & L Atrium. The future left ventricle lies left to the interventricular groove and the embryonic right ventricular region communicates with the truncus arteriosus. A 4 chambered heart is formed from this convoluted tube by the formation of septa. 4 - Septation (mid 4th wk - end 5th wk): Within the heart, the atriaventricular groove appears as a deep invagination, constricting the atriaventricular canal. The canal becomes divided along its longitudinal axis by the growth of endocardial cushions, separating atria from ventricles. 5 - A proliferating muscular septum advances across the common ventricle toward the base of the heart, this is called the interventricular septum. 6 - Simultaneously the interatrial septum rapidly grows toward the endocardial cushions, constricting the foramen between the atrial chambers ‘foramen primum’. 7 - A new opening appears before foramen primum disappears, The ‘foramen secundum’ provides uninterrupeted shunting of blood from right atrium to left atrium 8 - Another interatrial septum ‘septum secundum’ develops to the right of septum primum, overlapping the foreman secundum (5-6 wks), this incomplete partition forms the foramen ovale. TISSUES GIVING RISE TO HEART & PERICARDIUM: Somatic mesoderm: Fibrous pericardium Splanchnic mesoderm: Cardia Jelly, Endocardium, myocardium, epicardium 1 2 3 4 5 6 7 8