Differentiation of the epithelium of the human hard palate

The normal epithelium of the human hard palate is a keratinizing integument. There is considerable, mostly stereological, evidence that the differentiation and the type of keratinization in this epithelium differ from those of the epidermis. The objective of the present study was to correlate a systematic light- and electron microscopic description of this epithelium with stereological data, placing particular emphasis on differentiation phenomena. Twenty punch biopsies of 9 to 16 year-old females were studied. The observations show that (1) spinous cells are elongated or approximately isodiametrical in ridge regions and, above the level of the connective tissue papillae become disc-shaped in the upper stratum spinosum; (2) a prominent electron-lucent zone poor in organelles occurs at the cell periphery of basal and spinous cells; (3) the structure of desmosomes changes in the upper stratum granulosum with the distance between the intradesmosomal cytophasmic membranes gradually increasing from the basal to the granular layer; (4) single and composite keratohyalin granules display a different shape (i.e., spherical or irregular, patch-like) varying to a higher degree among individual cells than within a single cell of the stratum granulosum; (5) transitional cells can be observed; (6) the predominantly anuclear cells of the stratum corneum vary in their homogeneity and density, most cornefied cells revealing a find-granular keratin pattern lacking the filament profiles common in the epidermis. Consequently, while the type of keratinization appears to be independent from the type of keratohyalin granules produced, the differentiation process and the type of the terminally differentiated cells of the hard-palate epithelium differ from those of the epidermis.