Formation of the atrioventricular valves
- During 5th-8th weeks, endocardial cushion tissues in superior (dorsal) and inferior (ventral) regions fuse in the midline, dividing the common atrioventricular canal into right and left atrioventricular orifices.
- Atrioventricular valve formation occurs due to growth of atria and apical inlet portion of ventricles and lagging of atrioventricular canal region.
- Then the sulcus tissue invaginates into the ventricular cavity: the ECT at the tip of this tissue contains a layer of atrial, ventricular, and sulcus tissue.
- Inlet portion of ventricles forms tethering cords (chordae tendinae), which hold the valve leaflets. Note that the sulcus tissue comes in contact with ECT at tip of valve, interrupting muscular continuity between atria and ventricle.