keratinization

Definition

Target type: biologicalprocess

The process in which the cytoplasm of the outermost cells of the vertebrate epidermis is replaced by keratin. Keratinization occurs in the stratum corneum, feathers, hair, claws, nails, hooves, and horns. [GOC:dph, GOC:ebc, GOC:sdb_2009, GOC:tb]

Keratinization is a complex biological process involving the differentiation of epithelial cells, primarily in the epidermis, to form a tough, protective layer of keratin. This process is essential for maintaining the integrity of the skin and protecting the underlying tissues from damage.

**The process of keratinization can be divided into several stages:**

1. **Proliferation:** The basal layer of the epidermis, known as the stratum basale, contains rapidly dividing keratinocytes. These cells continuously divide and move upwards, replacing older cells.
2. **Differentiation:** As keratinocytes migrate upwards, they undergo a series of structural and biochemical changes. This includes:
* **Increased production of keratin filaments:** Keratin is a fibrous protein that forms the primary structural component of keratinized cells.
* **Formation of desmosomes:** These are specialized cell junctions that tightly connect adjacent keratinocytes, providing structural integrity and stability to the epidermis.
* **Production of keratohyalin granules:** These granules contain proteins that are involved in the cross-linking of keratin filaments.
* **Accumulation of lamellar granules:** These granules contain lipids that form a waterproof barrier, preventing water loss from the skin.
3. **Maturation:** In the upper layers of the epidermis, keratinocytes undergo further changes:
* **Keratohyalin granules coalesce:** The keratohyalin granules fuse with keratin filaments, forming a dense, fibrous matrix.
* **Cells flatten and lose their nuclei:** As keratinocytes mature, they lose their organelles, including their nucleus, becoming essentially dead cells filled with keratin.
* **Lamellar granules release lipids:** The lipids from lamellar granules form a multi-layered structure called the "cornified cell envelope," which provides the skin with its waterproof barrier.

**The final stage of keratinization results in the formation of the stratum corneum, the outermost layer of the epidermis.** This layer is composed of flattened, dead cells tightly packed with keratin. The stratum corneum provides a strong, protective barrier against abrasion, dehydration, and microbial invasion.

**In summary, keratinization is a highly regulated process involving:**

* **Cell proliferation and differentiation.**
* **Production and assembly of keratin filaments.**
* **Formation of desmosomes and other cell junctions.**
* **Accumulation of keratohyalin and lamellar granules.**
* **Cell flattening and nuclear degradation.**
* **Formation of the cornified cell envelope.**

This complex process ultimately results in the formation of a tough, protective layer of keratinized cells that is essential for maintaining skin integrity and protecting the body from environmental damage.'
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Proteins (2)

Compounds (3)