Electron microscopy of the epithelial lining of the human oral mucosa

Abstract

Electron microscopic observations have been made on the squamous epithelium lining of human oral mucosa with a view to exploring the ultrastructural changes associated with the partial keratinization and the total desquamation processes characteristic of this tissue. The keratohyaline granules appear to possess an inherent electron density demonstrable not only in osmium-fixed material but also in formalin-fixed material. These granules are widely scattered through the cytoplasm of normal epithelial cells from the intermediary and superficial layers of human oral epithelium. This is true even though the epithelium may not be classified as keratinized from a convenitonal optical microscopic point of view, under which the dimensions of these granules tend to be too small to be readily detectable. The keratohyaline granules appear to arise in association with (1) certain foldings of the nuclear membrane, (2) nucleolar fragmentations and formation of nucleolar satellites migrating to the nucleolar surface, and (3) the formation of cytoplasmic complexes in near proximity to the nuclei containing granules of various dimensions and mitochondrial fragments besides the high-density keratohyaline granules. The possible nucleolar contribution to the origin and to the organic nature of the keratohyaline granules has been discussed. The possible additional existence of some electron-dense mineral components in these granules has also been considered. In addition to these changes in the internal machinery of the keratinizing epithelium, certain ultrastructural changes in the peripheral cell membranes have been described. These were characterized by a great increase in total cell surface and by the development of deep foldings of the cell membrane interdigitating with grooves in adjacent cells. Finally, it was noted that, while the deeper cells appeared to be held together by a relatively dense cementing substance, the superficial cells separated more readily and had little or no intercellular cementing substance between them.