Histological and ultrastructural observations on the keratinizing epithelia of the palate of the rat

Abstract

The epithelia of the hard and soft palate of the rat show two different types of keratinization and the soft palate shows a higher cell renewal rate. The two epithelia presented ultrastructural differences in all their layers. In the soft palate, the cells were larger with bulky cytoplasm and often appeared to be binucleate. They had fewer tonofilaments and the keratohyalin granules often consisted of two components. Lamellated membrane-coating granules occurred in the stratum granulosum and many similar lamellae were found intercellularly at the boundary with the stratum corneum. In the hard palate, the cells were smaller, flatter and had wide bundles of electron-dense tonofilaments. Keratohyalin granules also consisted of two components but they differed from those in the soft palate. Lamellated membrane-coating granules were numerous but intercellular lamellae were rarely seen at any level. Unlike parts of the rat tongue, the hard palate did not undergo “hard” keratinization. Intercellular lamellae have been found to be more obvious in epithelia of rapid cell turnover in other sites.