Development of the Heart

Development of the Heart Begins to form angiogenic cell clusters formed in the splanchnic mesoderm. Involves fusion of two endocardial tubes into a single primitive heart tube. Primitive heart tube It is formed by fusion of two endocardial heart tubes of mesodermal origin in the cardiogenic region. It develops into the endocardium, and the splanchnic mesoderm surrounding the tube develops into the myocardium and epicardium. It forms five dilations including the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium,and sinus venosus. It undergoes a folding into a U-shape, bringing the arterial and venous ends of the heart together and moving the ventricle caudally and the atrium cranially. Fate of five dilations of the primitive heart tube Truncus arteriosus (ventral aorta) forms aorta and pulmonary trunk by formation of the aorticopulmonary (AP) septum. Bulbus cordis forms conus arteriosus (smooth part of right ventricle) and aortic vestibule (left ventricle). Primitive ventricle forms trabeculated part of right and left ventricles. Primitive atrium forms trabeculated part of right and left atrium. Sinus venosus forms sinus venarum (smooth part of right atrium), coronary sinus, and oblique vein of left atrium. Division of the heart into four chambers Heart divides into its four chambers by formation of its septum and valves. Four main septa involved in dividing the heart include the AP septum, the atrial septum, the AV septum, and the IV septum. Partition of the truncus arteriosus and bulbus cordis The truncal ridges and the bulbar ridges derived from neural crest mesenchyme grow in a spiral fashion and fuse to form the AP septum. The AP septum divides the truncus arteriosus into the aorta and pulmonary trunk. Partition of the primitive atrium Septum primum grows toward the AV endocardial cushions from the roof of the primitive atrium. Septum secundum forms to the right of the septum primum and fuses with the septum primum to form the atrial septum , which separates the right and left atria. Foramen primum forms between the free edge of the septum primum and the AV septum , allowing a passage between the right and left atria. The foramen is closed by growth of the septum primum. Foramen secundum forms in the center of the septum primum. Foramen ovale an oval opening in the septum secundum that provides a communication between the atria. Partition of the AV canal The dorsal and ventral AV endocardial cushions fuse to form the AV septum. The AV septum partitions the AV canal into the right and left AV canals. Partition of the primitive ventricle Muscular IV septum develops as outgrowth of muscular wall in the floor of the primitive ventricle and grows toward the AV septum but stops to create the IV foramen, leaving the septum incomplete. Membranous IV septum forms by fusion of the bulbar ridges with the endocardial cushion, the AP septum, and the muscular part of the IV septum. The membranous IV septum closes the IV foramen,completing partition of the ventricles. ◄.....Go back to the Gross Anatomy homepage