The organization of the elastic tissues of the human and rabbit aorta was studied by scanning and transmission electron microscopy of tissues treated with 88% formic acid at 45℃. When the tissues were treated with formic acid until they became semitransparent, fixed tissues showed the same organization of the elastic tissues as unfixed tissues. When tissues were treated with formic acid for a short time, the intimal elastic lamina was observed as a plate with numerous small pores or fenestrae, whereas long treatment revealed that the lamina consisted of a network of elastic fibers. The tunica media consisted of concentrically arranged elastic lamellae. There were 50-60 elastic lamellae in humans and about 30 in the rabbit. The elastic fibers, that consisted of elastic microfibrils, ran longitudinally, repeatedly branching and anastomosing, and formed the network of the elastic lamella. Between the adjacent elastic lamellae stretched interlamellar elastic fibers. Thus, the elastic tissues in the aorta formed an integral network, which seems to be highly associated with the aortic function of distributing the pressure applied to the vascular wall. Disruptions of the integrity of the elastic tissue architecture may be responsible for the increased incidence of hypertension with age.
scanning electron microscopy