parakeratinized

Parakeratinized describes a type of stratified squamous epithelium in which keratinization occurs, but the superficial layer of keratinocytes retains pyknotic nuclei. This differs from orthokeratinized epithelium, in which the stratum corneum is anuclear, and from non-keratinized epithelium, where keratinization is minimal or absent at the surface. In parakeratinized tissue, the surface cells are keratinized but still show retained nuclei, reflecting a distinct pattern of epidermal differentiation.

Histologically, parakeratinized epithelium has a granular cell layer and a superficially keratinized layer where the cells preserve pyknotic or partially condensed nuclei. The presence of nuclei in the stratum corneum distinguishes parakeratosis from orthokeratosis. The exact extent of nuclear retention can vary with location and condition, yielding a continuum between fully non-keratinized and fully orthokeratinized patterns.

In humans, parakeratinization is a normal feature of certain mucosal surfaces, particularly in parts of the oral cavity such as the gingiva and hard palate, where the epithelium is thick and subject to mechanical stress. Other areas of the mucosa may be non-keratinized or orthokeratinized, reflecting functional demands. The degree of parakeratosis can also be influenced by age, mechanical factors, and hormonal or inflammatory states.

Clinically, parakeratinization is a descriptive histologic finding rather than a specific diagnosis. In pathology, parakeratosis can accompany various inflammatory or hyperplastic processes and must be interpreted in the context of the tissue and accompanying features. It is important to distinguish parakeratinized from orthokeratinized and non-keratinized patterns when assessing mucosal health and disease.