Scanning electron microscopic observation of the vascular wall cells in human dental pulp

The following six vascular segment types were identified in human dental pulp based on morphological differences in the periendothelial cells: (a) muscular arterioles with at least two compact layers of smooth muscle (SM) cells; (b) terminal arterioles with at least one compact muscle layer; (c) precapillary arterioles with an incomplete muscle layer; (d) capillaries with scattered pericytes; (e) postcapillary venules with clustered pericytes; and (f) muscular venules with at least one layer of flattened SM cells. In almost all muscular and terminal arterioles, the surface of SM cells showed marked to slight irregularities indicating vasoconstriction apparently caused by local administration of anesthetic containing epinephrine. Flattened SM cells in muscular venules also showed surface irregularities. SM cells in precapillary arterioles and pericytes in capillaries and most postcapillary venules, however, showed no distinct features of constriction.