skin

skin Tough, elastic outer covering of invertebrates. In mammals, it is the largest organ of the body and serves many functions. It protects the body from injury and from the entry of some microorganisms and prevents dehydration. Nerve endings in the skin provide the sensations of touch, warmth, cold, and pain. It helps to regulate body temperature through sweating, regulates moisture loss, and keeps itself smooth and pliable with an oily secretion from the sebaceous glands. Structurally the skin consists of two main layers: an outer layer (epidermis) and an inner layer (dermis). The top layer of epidermis is made of closely packed dead cells constantly shed as microscopic scales. Below this is a layer of living cells that contain pigment and nerve fibres, and that divide to replace outer layers. The dermis contains dense networks of connective tissue, blood vessels, nerves, glands, and hair follicles.