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. It is 90% keratinocytes (proliferating basal and differentiated suprabasal) but also contains melanocytes, Langerhans cells, Merkel cells, and inflammatory cells. Rete ridges (or rete pegs) are epidermal thickenings that extend downward between dermal papillae. 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. 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.