Keratinocytes are the largest population of epidermal cells in the skin. They acquire their name through their function as warehouses for keratin, the protein which provides a physical barrier in the most superficial dead cells of the stratum corneum.
The keratinocyte is first formed when a daughter cell produced in the stratum basale differentiates within the stratum spinosum. As more cells are produced in the stratum basale, cells above are forced upwards to the surface over a period of about 2 months. During transit, keratinocytes lose synthetic organelles e.g. rough endoplasmic reticulum and Golgi apparatus. There is increased production of intracellular tonofilament, cytoskeleton connecting cytoplasm and desmosomes, and keratohyaline. Tonofilament and keratohyaline combine to form matrix and keratin respectively at the level of the stratum corneum.
Keratinocytes in the stratum spinosum contain lamellar bodies which store complex carbohydrates, lipids and hydrolytic enzymes. The constituents are discharged into the intercellular space in the stratum corneum. They provide a complex glycoprotein adhesive between cells. Acid phosphatase enzymes shed in the stratum corneum dissolve this attachment and permit shedding of the most superficial dead cells.
Disorders of keratinocytes may present in several ways:
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