skin [AS, scinn] , the tough, supple cutaneous membrane that covers the entire surface of the body. It is composed of a thick layer of connective tissue called the dermis and an epidermis made of five layers of cells. Skin color varies according to the amount of melanin in the epidermis. Genetic differences determine the amount of melanin. The ultraviolet rays of the sun stimulate the production of melanin, which absorbs the rays and simultaneously darkens the skin. Modified skin continues into various parts of the body, such as mucous membrane, as in the lining of the vagina, the bladder, the lungs, the intestines, the nose, and the mouth. Mucous membrane lacks the heavily keratinized layer of the outside skin. The skin helps to cool the body when the temperature rises by radiating the heat of increased blood flow in expanded blood vessels and by providing a surface for the evaporation of sweat. When the temperature drops, the blood vessels constrict and the production of sweat diminishes. Also called cutaneous membrane, integument. See also dermis.
