Electron microscopy of endothelial microvilli of large arteries.

Scanning electron microscopic investigations by others have revealed "hair-like" projections from the endothelial surface of the rabbit aorta. We have confirmed by transmission electron microscopy that endothelial microvilli are found, in a limited number of areas in the aortic arch, particularly at the presumed site of fetal origin of the ductus arterious and near the origin of the subclavian artery. The microvilli are almost uniform in diameter (about 0.1 mum) and are as long as 3 mum in length. The outer leaflet of the limiting membrane shows a fuzzy appearance, and thin filaments are recognized in their interiors. A profuse array of endothelial microvilli was also found over the entire surface of the large arteries of human fetuses. The possible hemodynamic significance of these processes is discussed.