The skin, the largest organ in the body, and its accessory structures constitute the integumentary system. 6.2 Skin and its tissues
Skin is a protective covering, helps regulate body temperature, houses sensory receptors, synthesizes chemicals, and excretes wastes. It is composed of an epidermis and a dermis separated by a basement membrane. A subcutaneous layer, not part of the skin, lies beneath the dermis. The subcutaneous layer is composed of areolar tissue and adipose tissue that helps conserve body heat. This layer contains blood vessels that supply the skin. * Epidermis
* The epidermis is stratified squamous epithelium that lacks blood vessels. * The deepest layer, called the stratum basale, contains cells that divide and grow. * Epidermal cells undergo keratinization as they are pushed toward the surface. * The outermost layer, called the stratum corneum, is composed of dead epidermal cells. * Production of epidermal cells balances the rate at which they are lost at the surface. * The epidermis protects underlying tissues against water loss, mechanical injury, and the effects of harmful chemicals. * Melanin, a pigment produced from the amino acid tyrosine, provides skin color and protects underlying cells from the effects of ultraviolet light. * Melanocytes transfer melanin to nearby epidermal cells. * All humans have about the same concentration of melanocytes. Skin color is largely due to the amount of melanin in the epidermis. * 1. Each person inherits genes for melanin production. * Dark skin is due to genes that cause large amounts of melanin to be produced; lighter skin is due to genes that cause lesser amount of melanin to form * Mutant genes may cause a lack of melanin in the skin. * 2. Enviornmental factors that influence skin color include sunlight, ultraviolet light, and X rays. These factors darken...