Keratinocyte
Definition
Keratinocytes are the predominant cell type in the epidermis, making up approximately 90% of epidermal cells. They are produced in the basal layer (stratum basale) of the epidermis through cell division and gradually migrate upward over about 28 days in a process called keratinization. During this journey, they progressively fill with the protein keratin, flatten, lose their nucleus, and eventually die, forming the tough, protective corneocytes of the stratum corneum. Keratinocytes play a vital role beyond structural protection — they produce antimicrobial peptides, secrete cytokines that regulate immune responses, and synthesize lipids that contribute to the skin barrier. They also produce melanosomes transferred from melanocytes, distributing pigment throughout the epidermis for UV protection. Disruptions in normal keratinocyte behavior contribute to conditions like psoriasis, eczema, and skin cancer.
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