The endocardial cushions contribute to the formation of which cardiac structure?

The endocardial cushions play a crucial role in the development of the heart, particularly in the formation of the septum that divides the heart's chambers. Specifically, these cushions are areas of tissue in the heart that contribute to the formation of the inter-atrial and inter-ventricular septa, as well as the valves between the atria and ventricles.

In the context of the septum primum, it is the initial septal structure that forms between the atria during early cardiac development. The endocardial cushions help to fuse with the septum primum and aid in the closure of the foramen ovale, a significant function in transitioning from fetal to postnatal circulation. This fusion is vital for normal heart function and ensures that blood flows properly through the correct pathways post-birth.

While the other structures listed, such as the aortic valve and pulmonary valve, are important components of the heart, they do not directly arise from the endocardial cushions. Instead, the valves are more so developed from different structures within the heart, which highlights why the septum primum is the correct answer in relation to the contribution of the endocardial cushions.