The skin is an organ made up of all four of the primary tissue types: epithelium, connective tissue, muscle, and nerve. These tissues are organized into a variety of structures , such as hairs, glands and ducts, blood vessels, and sensory receptors. These structures are themselves organized to form the functional organ, and they enable the skin perform its functions which include: 1) acting as a covering for the body that prevents disease-related organisms and harmful substances form entering the body as well as excess amounts of water from leaving the body, 2) acting as a mechanism for the excretion of nitrogenous wastes through the production of sweat, 3) acting as a storage place for certain nutrients, 4) acting as a mechanism in the body's ability to thermoregulate itself, and 5) acting as an instrument of sensory reception, receiving stimuli from the outside environment.
The skin is composed of several tissue layers. In the skin's outer layer or epidermis, which is composed of stratified squamous cells, active cell division constantly occurs. The new cells push from deep within the layer toward the outside. The new cells continually replenish the epidermis's outermost layer, the stratum corneum, which consists of hardened, dead cells that are continually being sloughed off the body. The skin's inner layer or dermis consists of connective tissue surrounding several types of specialized structures. Hair follicles are formed from invaginations of the epidermis. While the hair roots are embedded deep within
the dermis, the hair shafts, extending at a slant, project beyond both the dermis
