Changes in the endothelial morphology of the developing semilunar heart valves. A TEM and SEM study in the chick.

In view of recent evidence showing that shape and orientation of endothelial cells is determined by blood flow, the endothelium of the semilunar valves was studied in the developing chick heart using transmission and scanning electron microscopy. The results reveal significant developmental modifications of endothelial morphology and structure. These modifications can be linked to modifications of local blood flow and can also explain several aspects of valvular morphogenesis. The results substantially support the hypothesis of an involvement of hemodynamics in the development of the semilunar valves.