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Keratinocyte
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Your epidermis is made almost entirely of a single kind of cell: the keratinocyte. It is called that because it makes and stores keratin, a fibrous protein that stays inside the cell and is what gives skin, hair and nails their toughness, and what makes water bead off instead of soaking in.
These cells do not stay put. They are all born at the bottom, in the basal layer, from cells that divide nonstop. Each new cell pushes the ones above it a little higher, and so the keratinocyte travels up toward the surface. By the time it reaches the stratum corneum it is already dead and it flakes off, that is, falls away, and another one coming up from below takes its place. What you touch when you touch your skin is, literally, dead keratinocytes full of keratin.
In brief
The keratinocyte is the cell that makes and stores keratin, and it forms every layer of the epidermis except the basal layer.
Keratin is a fibrous protein inside the cell that gives hair, nails and skin their toughness and their resistance to water.
All keratinocytes come from the basal cells, which divide nonstop; new ones push the old ones toward the surface, and in the stratum corneum they are already dead and flake off.
Sources (1)
- OpenStax, Rice UniversityAnatomy and Physiology 2e, 5.1 Layers of the SkinPublished
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