[A comparative ultrastructural and morphometric analysis of the smooth myocytes in the tunicae intima and media of the human fetal aorta].

Transmission electron microscopy was used for studying the thoracic part of the aorta of 9 human fetuses of 20-28 weeks of development. In the medial tunic of the human fetus aorta there are smooth myocytes (SM) of the contractile and synthetic phenotypes. The latter are localized mainly in the inner part of the media. In the inner tunic there are also SM of the synthetic phenotype. With the help of processes they make contacts with endotheliocytes and processes of SM of the media. In the gaps between the subendothelial SM and endothelium there are particles of elastin which form the structure resembling an additional elastic membrane. It is reasonable to think that the migration of SM into the intima is a stage of normal development of the vessel associated with the adaptation to local hemodynamic conditions rather than an initial manifestation of atherosclerosis.