nonkeratinized

Nonkeratinized refers to a type of stratified squamous epithelium that lacks a surface layer of keratin. In this tissue, the surface cells remain alive and nucleated, rather than becoming flattened, anucleate, and filled with keratin as in keratinized epithelia. The epithelium is multilayered, with basal cells that proliferate and progressively differentiate toward the surface, where cells may flatten but retain cytoplasm and nuclei.

Nonkeratinized epithelium lines moist, exposed surfaces where protection must be maintained while allowing flexibility and permeability. The superficial cells are generally more viable and the tissue remains moist because it is kept by underlying secretions and mucus. The arrangement provides a protective barrier against abrasion and chemical exposure while supporting frictional movement and secretion.

Locations include the lining mucosa of the oral cavity (such as the lips, cheeks, floor of the mouth, and underside of the tongue), portions of the pharynx and esophagus, the vagina and cervix, the anal canal, and parts of the ocular surface such as the conjunctiva and corneal epithelium. By contrast, keratinized epithelia form the protective, water-resistant surface of the skin and certain regions of the oral cavity (such as the gingiva and hard palate).

Clinically, nonkeratinized epithelia are more susceptible to dehydration and certain chemical irritants due to the absence of a keratinized outer layer, but they offer greater flexibility and moisture retention in moist internal surfaces.