Surface ultrastructure of human skin.

The normal human skin surface was studied with a combination of scanning electron microscope, surface replication method, and transmission electron microscope. All specimens were prepared with the critical point drying (CPD) method. Horny cells were found to stack up in columnar fashion with their peripheries overlapping. The surface of a non-nucleated horny cell, therefore, showed a dome-shaped elevation in the center, transmitting the nuclear bulge of the underlying granular cells; parallel double lines at the periphery representing its true cell border and depressed, step-like imprint of the cell border of the cell which once overlapped; and on high magnification the true surface of the separated desmosomes. The surfaces of the horny cells showed many bizarre marks but were relatively smooth. The underside of the surface horny cells, however, bore villi except in areas overlapping the periphery of the underlying cell. Tissue cultured keratinocytes also stacked up when the keratinized and the cell periphery also overlapped. However, the overlapped cell border did not leave the imprint on the underlying cell, probably because of the lack of pressure from above.