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Epidermis

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Updated February 03, 2014

Definition: The epidermis is the outer layer of skin. The thickness of the epidermis varies in different types of skin. It is thinnest on the eyelids at .05 mm and thickest on the palms and soles at 1.5 mm.

The epidermis contains 5 layers. From bottom to top the layers are named stratum basale, stratum spinosum, stratum granulosum, stratum licidum, and stratum corneum. The bottom layer, the stratum basale, has cells that are shaped like columns. In this layer the cells divide and push already formed cells into higher layers. As the cells move into the higher layers, they flatten and eventually die. The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks.

There are three types of specialized cells in the epidermis. The melanocyte produces pigment (melanin), the Langerhans' cell is the frontline defense of the immune system in the skin, and the Merkel's cell's function is not clearly known.

Pronunciation: ep-i-DIR-miss (noun)
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