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The epidermis is the outer layer of the three layers that make up the skin, the inner layers being the dermis and hypodermis.[1] The epidermis layer provides a barrier to infection from environmental pathogens[2] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.[3] The outermost part of the epidermis is composed of multiple layers of flattened cells,[4] that overlies a base layer (stratum basale) composed of columnar cells arranged perpendicularly.

The rows of cells develop from the stem cells in the basal layer. ENaCs are found to be expressed in all layers of the epidermis.[5]

Epidermis comes from Ancient Greek epi, meaning '"over" or "upon"'.

The epidermis has no blood supply and is nourished almost exclusively by diffused oxygen from the surrounding air.[6] It is 90% keratinocytes[4] (proliferating basal and differentiated suprabasal) but also contains melanocytes, Langerhans cells, Merkel cells,[7] and inflammatory cells. Rete ridges (or rete pegs) are epidermal thickenings that extend downward between dermal papillae.[8] Blood capillaries are found beneath the epidermis, and are linked to an arteriole and a venule.

In the epidermis, the cells are tightly interconnected to serve as a tight barrier. The junctions between the epidermal cells is adherens junction type. These junctions are formed by transmembrane proteins called cadherins. Inside the cell, the cadherins are linked to actin filaments. In immunofluorescence microscopy, the actin filament network appears as a thick border surrounding the cells.[5] Yet, as noted, the actin filaments are located inside the cell and run parallel to the cell membrane. Because of the proximity of the neighboring cells and tightness of the junctions, the actin immunofluorescence appears as a border between cells.[5]

The epidermis is composed of 4 or 5 layers depending on the region of skin being considered.[9] Those layers in descending order are:[2]

The Malpighian layer (stratum malpighi) is both the stratum basale and stratum spinosum.[4]

The epidermis is separated from the dermis, its underlying tissue, by a basement membrane.

This page was last edited on 13 July 2018, at 08:09 (UTC).
Reference: https://en.wikipedia.org/wiki/Epidermis under CC BY-SA license.

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