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The epidermis is largely made of four cells. The keratinocytes, melanocytes, Merkel cells, and Langerhans cells. All four types are found in the deepest epidermal layer, the basal layer. The most abundant are the keratinocytes, which form a strong barrier tht prevents the passage of pathogens and molecules through the epidermis.

Keratinocytes-1

makes up most of the epidermis. They are made by the "stem cells" in the "basal layer", which is the deepest layer of the epidermis. As they move towards the surface of the epidermis, keratinocytes undergo changes to become the tough, dead cells of the most superficial (apical) epidermal layer.

Keratinocytes-2

As they mature, keratinocytes undergo "keratinization."

Keratinocytes-keratinization

Which is the process of making and accumulating excessive amounts of the fibrous protein "keratin."

Keratinocytes-keratin

Keratin is an insoluble, very long-lived protein. As they form, the cells become linked tightly together by proteinaceous "desomosomes."

Keratinocytes-desomosomes

(tight junctions) to form a water-tight barrier. They also produce glue like "keratohyaline" granules and release vesicles filled with a waterproofing "glycolipid" outside the cell. By the end they are a layer of dead, tightly bound cells covered with water-proofing.This makes skin fairly resistant to pathogens and water tight. These cells make up "dandruff."

Merkel cells

these combine with sensory neurons to form the sensory receptors for touch. (merkel discs) located where the epidermis meets the dermis.

Langerhans cells

macrophages that migrate into the epidermis from the bone marrow.

Melanocytes

is the "basal layer" (fewer than stem cells and keratinocytes) produce the brownish pigment "melanin."

Stem cells

divide to produce new keratinocytes

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