Myoendothelial Relationships in Cerebral Arteries of the Human Fetus

Regional close cellular appositions between elements of tunica media and intima (myoendothelial appositions) in cerebral arteries of the human fetus were studied through an electron microscope. Plasmalemmal appositions were observed between endothelial cells and smooth muscle cells in cerebral arteries. The form of these myoendothelial appositions varied from simple flat appositions of plasmalemma and cytoplasmic processes to extensive finger-shaped indentations of endothelial cells onto medial smooth cells. Simple membranous appositions predominated among these cellular appositions of cerebral arteries in the human fetus. The finger-shaped myoendothelial appositions were also observed in the arteries of the surface of the brain. Some of these myoendothelial contacts seem to contain myoendothelial tight junctions (zonula occludens). The myoendothelial appositions may help in the detection and propagation of mechanical (autoregulation) and humoral signals, and may serve as a mechanical support of the fragile cerebral arteries of the human fetus.