Ultrastructure of aging human umbilical artery and vein.

Qualitative and quantitative changes in the human umbilical artery and vein were observed in 15 human specimens at different stages of development. Features such as intimal thickening and cellular lipid accumulation were found in umbilical vasculature. Cellular origin and quantification of lipid-containing cells were determined by electron microscopy. Within 1 month after birth, lipid-containing cells originating from macrophages were observed in the umbilical artery, while those originating from smooth muscle cells were observed in both the umbilical artery and vein. Lipid droplet formation appeared to be independent and different in macrophages and smooth muscle cells; the former cells were stimulated to produce lipid droplets primarily by plasma insudation and the latter cells primarily by hypoxia. These findings indicate that ultrastructural changes observed in closing umbilical vasculature may closely parallel and serve as a model for atherosclerotic changes which occur in mature vessels.