[Fine structural study of keratinization of the filiform papillae in the tongue in humans]

The fine structure of the keratinization of the papilla filiformis of the human tongue was described for the first time; Two biopsies of normal tongue tissue were fixed in 2,5% phosphate-buffered glutaraldehyde, postfixed in 1% osmiumtetroxyde, embedded in Durcopan und contrasted ultrathin sections were examined by electron microscopes JEM 7A and 100B. The findings show a highly configurated epithel-connective tissue border with basal lamina and irregular hemidesmosomes. The epithelial structure of the interpapillary area is identical with the fine structure of the human buccal mucosa, which was classified as non-keratinized or incompletely keratinized. Accordingly, a stratum granulosum is missing. After loss of nucleus and organelles, surface cells become flattened, parallel to the surface of the tongue and have a fine fibrillar cytoplasm. The papilla filiformis is formed by cell growth along the secondary connective tissue papillae and consequently tube-like epithelial structures appear. In the papillary area basal and stratum spinosum cells show epidermal structural features. A difference from epidermal and other oral epithelial cells becomes apparent for the first time in the stratum granulosum by the appearance of a great number of round, small, electron-dense KHG, surrounded by ribosomes. The KHG are not associated with tonofilaments. In the area of the walls of the tubes 1...3 mum large, electron-dense structures are formed by fusion of several KHG. With further differentiation these large KHG disintegrate into bulky or granular masses, filling the cell cytoplasm and thus mask the tonofilaments. The cells at the borders of the tubes show a great structural variability. After the disintegration of nucleus and organelles, the cytoplasm is formed by randomly oriented filaments of different packing or by fiber-bundles. Yet the interfibrilla embedding substance, typical of orthokeratinization is mostly lackingmin some cells of the tubeborders, masses of disintegrated KHG substance are masking the fibrillar cell cytoplasm. In other areas, where the KHG do not increase by fusion, intense fibrillar packing and abrupt keratinization becomes apparent. At the rim of the tube fully keratinized epithelial threads are regularly found. These are lacking at the bottom of the tubes. All surface areas show a strong tendency towards desquamation. Thus a more or less wide surface plaque is formed on the tongue, consisting of desquamated and disintegrated surface cells and of bacterial. Groups of little differentiated basal cells, which can be considered as the initial material for an accelerated regeneration, can be evaluated as a truly remarkable finding. This accelerated regeneration might be due to an increased wear of the inclompletely keratinized cells of the bulk of the papilla filiformis of the human tongue. Based on the findings of this study, an attempt was made, to explain the pathological reactions of human tongue epithelium in various systemic diseases.