Protein signalling in heart development

These cells can differentiate into endocardium which lines the heart chamber and valves and the myocardium which forms the musculature of the ventricles and the atria.

The notochord secretes BMP antagonists (Chordin and Noggin) to prevent formation of cardiac mesoderm in inappropriate places.

Other cardiogenic signals such as BMP and FGF activate the expression of cardiac specific transcription factors such as homeodomain protein Nkx2.5.

If this migration event is blocked, cardia bifida results where the two heart primordia remain separated.

The surrounding mesocardium degenerates to leave the primitive heart attached only by its arterial and venous ends, which are anatomically fixed to the pharyngeal arches and the septum transversum, respectively.

The direction of asymmetry is established much earlier during embryonic development, possibly by the clockwise rotation of cilia, and leads to sided expression of Pitx2.

From the roof of the primitive atrium descends the septum primum, which grows towards the endocardial cushions within the atrial canal.

The atrial canal is in turn divided into a right and left side by the atrioventricular septum, which originates from the union of the dorsal and ventral endocardial cushion.

The truncus arteriosus and the adjacent bulbus cordis partition by means of cells from the neural crest.