Ultrastructural features in the structure of blood capillaries of the Haversian canal.

Electron microscopy was used to study osteon capillaries of the compact tissue of human growing long bones. The capillaries were found to be of the continuous type. On the lumenal surface of endothelial cells of the arterial capillaries there were a great number of micropinocytotic vesicles as well as a lot of branching cytoplasmic processes forming a characteristic spongioid layer. Vesicles and filopodia were considerably fewer on the basal surface of the cells. The endothelial cells of the venous capillaries had a small number of micropinocytotic vesicles and single cytoplasmic projections on their lumenal and basal surfaces. The capillary wall contained a great amount of pericytes. There were a lot of micropinocytotic vesicles in the cytoplasm.