A quantitative electron microscopic analysis of the keratinizing epithelium of normal human hard palate

Summary The epithelium of normal human hard palate was subjected to stereologic analysis. Ten biopsies were selected from a total of twenty specimens collected from 9 to 16 year old females, and processed for light- and electron microscopy. At two levels of magnification, electron micrographs were sampled from three strata (basale, spinosum, granulosum) in two locations (epithelial ridges and portions over connective tissue papillae). Stereologic point counting procedures were employed to analyse a total 1560 electron micrographs. In general, the thickness of the palate epithelium was 0.12 mm (over papillae) and 0.31 mm (in ridges), the epithelium is distinctly stratified, and homogeneously ortho-keratinized. From basal to granular layers, the composition of strata revealed decreasing densities of nuclei, mitochondria, membrane-bound organelles and aggregates of free ribosomes. Keratohyalin bodies and membrane coating granules increased, and cytoplasmic filaments with a constant diameter of about 85 Å increased from 14 to 30% of cytoplasmic unit volume. The cytoplasmic ground substance occupied a stable 50% of the epithelial cytoplasm in all strata. The composition of basal layers in ridges differed from that over connective tissue papillae. The data are discussed in relation to the observations that (1) an increasing gradient of filament density is not the most characteristic feature of ortho-keratinizing oral epithelium and (2) differences in the degree of differentiation in cells of the stratum basale coincided with the comparable frequency distribution pattern of dividing cells.The authors are thankful to Miss K. Rossinsky for excellent technical assistance, to Mrs. M. Graf-de Beer for competent data computation and to Mrs. S. Münzel-Pedrazzoli for help in morphometric analysis. This study was in part supported by Grants Nos. 51 and 106 of the Hartmann Müller Foundation and by a Grant from the Foundation of Scientific Research at the University of Zürich.