Orthokeratin is a type of keratin that lacks cell nuclei. This contrasts with parakeratin, which retains shrunken nuclei within its cells. Both are key components of keratinization, the process that forms the protective outer layer of skin and mucosa. Orthokeratin's defining characteristic is its lack of nuclei, resulting in a more dense and structured keratin layer. This difference in nuclear presence leads to variations in the appearance and properties of keratinized tissues. For example, the contents of an epidermal cyst are described as having “flaky” laminated orthokeratin, distinct from the denser keratin found in pilar cysts. The function of keratin, whether orthokeratin or parakeratin, remains consistent: providing a protective barrier.
The term "orthokeratin" is frequently encountered in the context of the microscopic examination of tissue samples, aiding in the diagnosis of various skin conditions. The presence or absence of nuclei in keratinized cells provides valuable diagnostic information for dermatologists and pathologists. Note that the term "orthokeratin" is also used in relation to orthokeratology, or "ortho-k", a vision correction method utilizing special contact lenses to reshape the cornea. This is a distinct but related usage. While orthokeratology involves the cornea, the term "orthokeratin" in this context does not refer directly to the specific corneal tissue composition.
- Orthokeratin: Non-nucleated keratin forming a protective barrier.
- Parakeratin: Keratin containing shrunken (pyknotic) nuclei.
- Diagnostic Use: The presence or absence of nuclei helps distinguish different types of keratinization in tissue samples.
The difference between orthokeratin and parakeratin reflects the varying levels of cellular maturation and keratinization occurring in different tissues and under varying conditions. The study of these variations aids in understanding the biology of skin and mucous membranes, and helps in diagnosing related diseases.
