Epidermis

The innermost or the inner skin layer of cells of the epidermis, called basal cells, have fibers fixed to intracellular structures, called desmosomes, that link the cells together. The basal cells divide rapidly, forcing daughter cells toward the skin surface. Basal cells also synthesize keratin, a protein found in hair and nails; synthesis continues in the daughter cells, so that keratin fills the cells near the surface. As dead surface cells are shed, they are replaced from below.

Although outer epidermal cells absorb water readily the deeper cells are watertight. The treelike melanocyte cells the deeper epidermis produce a dark brown pigment called melanin. The pigment is introduced into nearby cells through the “branch tips” of the melanocyte cells, units called melanosomes. A third type of epithelial cell, the Langerhans cell, functions in immune responses of the skin. The epidermis lacks blood vessel and obtains its nutrition from capillaries in the dermis. It is well supplied by nerve endings that branch between the epidermal cells.