Abstract
The ultrastructure of human diabetic placental capillaries diagnosed as a White's Class A, were investigated. The capillaries have a continuous endothelium rich in micropinocytotic vesicles, osmiophilic granules, and microfilaments, as well as increased number of cellular organellae. Many endothelial cells are enlarged with a subsequent reduction in the size of the lumen. Luminal endothelial extensions frequently show projections like apocrine flaps and marginal folds, although these cells are connected by zonulae occludentes characterized by 2 to 4 focal regions of membrane contact. The endothelial cells are provided with pseudopodial extensions which may be responsible for the exchange of materials between the vessels, vinous stroma, and vessel lumen, as well as for intermittent constriction. The basal laminae were found to be both unilaminar and multilamellar. Numerous osmiophilic granules are seen in the endothelial cells and pericytes as well in vinous epithelial- and stromal cellular components. These may be concerned with diplacental transport at the level of the fetal capillary, which is controlled by both the cytoplasm of the endothelial cells and by other cellular elements. The significance of the morphological changes between the endothelial cells and pericytes is discussed.
