cornification

Definition

Target type: biologicalprocess

A type of programmed cell death that occurs in the epidermis, morphologically and biochemically distinct from apoptosis. It leads to the formation of corneocytes, i.e. dead keratinocytes containing an amalgam of specific proteins (e.g., keratin, loricrin, SPR and involucrin) and lipids (e.g., fatty acids and ceramides), which are necessary for the function of the cornified skin layer (mechanical resistance, elasticity, water repellence and structural stability). [GOC:krc, PMID:18846107]

Cornification, also known as keratinization, is a complex biological process that involves the transformation of living cells into a tough, protective, and water-resistant layer of keratin. This process is crucial for the formation of skin, hair, and nails, as well as for the protection of internal organs.

The process of cornification begins with the proliferation and differentiation of keratinocytes, which are the main cell type in the epidermis, the outermost layer of skin. As these cells migrate upwards through the epidermis, they undergo a series of morphological and biochemical changes.

1. **Cell Proliferation and Differentiation:** Keratinocytes in the basal layer of the epidermis constantly divide and differentiate. As they move upwards, they synthesize and accumulate keratin proteins, primarily keratin filaments.

2. **Granule Formation:** Within the stratum granulosum (the granular layer), keratinocytes develop distinct membrane-bound granules called keratohyaline granules and lamellar granules. Keratohyaline granules contain proteins that will bind to keratin filaments, while lamellar granules release lipids that form a water-resistant barrier.

3. **Cell Dehydration and Apoptosis:** As the keratinocytes reach the stratum corneum (the outermost layer), they undergo programmed cell death (apoptosis) and lose their nucleus and organelles. This dehydration process is accompanied by the formation of tight junctions between cells, further contributing to the barrier function.

4. **Cross-linking and Maturation:** Keratin filaments aggregate and cross-link into a dense, organized network, forming a tough, protective layer. This network is embedded in a matrix of lipids and proteins, further reinforcing the barrier.

5. **Desquamation:** The outermost layer of the stratum corneum eventually sheds off in a process called desquamation, allowing for continuous renewal of the skin.

During cornification, the cells progressively lose their nuclei and other organelles, becoming flattened and tightly packed. The keratin proteins within the cells form a dense, organized network, creating a tough, protective barrier. This barrier helps protect the body from environmental factors such as pathogens, chemicals, and physical damage. It also prevents dehydration and helps maintain the body's water balance.

In summary, cornification is a complex and essential biological process that transforms living cells into a tough, protective, and water-resistant layer of keratin, crucial for maintaining the integrity and function of the skin, hair, and nails.'
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Proteins (4)

Compounds (8)