Epidermis is the top, or outermost, layer of skin. Its thickness varies from 0.07 to 0.12 mm over most of the body, to 0.8 mm on the palms and 1.4 mm on the soles. Its surface layer, consisting of dead cells, contains keratin, a tough protein that protects the skin’s integrity. This layer forms the waterproof, protective cover over the body's surface and is made up of stratified, or layered, squamous epithelium. A squamous cell is a flat, scale-like cell and epithelium is the tissue composed of cells that line the cavities and surfaces of structures throughout the body. These cells are arranged in 4 to 5 separate layers, depending on the area of the body, over a basement membrane. Only one layer is actually in direct contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Not all of the epidermal cells are flat. Epithelial cells are named according to the type of cell at the surface, which are squamous cells. Epidermal cells in the deeper layers may be shaped more like columns or cubes. This type of epithelium is well suited to areas in the body subject to constant abrasion, as it is thicker than the squamous cell, and layers can be sloughed off and replaced before the basement membrane is exposed. As the cells move through the layers toward the surface, they incorporate more keratin and become more flattened. There are no blood vessels in the epidermis. Cells in the deepest layers are nourished by diffusion from capillaries in the upper layers of the dermis, the skin layer that lies beneath the epidermis. In normal skin, the rate of production equals the rate of loss, taking about two weeks for a cell to journey from the basal cell layer to the top of the granular cell layer, and an additional four weeks to cross the stratum corneum. The entire epidermis is replaced by new cell growth over a period of about 48 days.
Q: [Abrasion] - A wound caused by superficial damage to the skin, no deeper than the epidermis. It is less severe than a laceration, and bleeding, if present, is minimal [Image]
Q: [Epithelium] - A tissue composed of cells that line the cavities and surfaces of structures throughout the body
Q: [Diffusion] - An intermingling of molecules, ions, etc., resulting from random thermal agitation, as in the dispersion of a vapor in air.