orthokeratinized

Orthokeratinized refers to a type of keratinized stratified squamous epithelium in which the superficial cells become fully cornified and lose their nuclei and most organelles as they reach the surface. This results in an anucleate stratum corneum composed of densely packed keratin filaments. The underlying layers typically include a basal cell layer, a prickle (spinous) layer, and a granular layer in which keratohyalin granules accumulate. The keratinization process ends with a thick, protective outer layer that lacks nuclei.

In terms of distribution, orthokeratinized epithelium is characteristic of the epidermis of the skin, especially in areas subject to mechanical stress such as the palms and soles. It can also be found in keratinized mucosa of the oral cavity, including the hard palate and gingiva, where a fully cornified surface provides robust protection.

Orthokeratinized versus parakeratinized: the key distinction lies in the outermost layer. Parakeratinized epithelium retains nuclei in the superficial keratinocytes, and its stratum corneum is not completely anucleate. In orthokeratinization, the surface lacks nuclei entirely, reflecting complete keratinization.

Clinical and histological relevance: identifying orthokeratinized epithelium helps characterize normal versus keratinized tissue in various sites and can aid in distinguishing maturation states or disease processes in epithelial tissue.