| Skin Forms a remarkable protective barrier against | | | | underlying "prickle" cells, which move upward to |
| the outside world, helping to regulate temperature | | | | replace them as they are shed (around 90 percent of |
| and fluid balance, keeping out harmful germs and | | | | household dust is dead skin cells). The epidermis also |
| chemicals, and offering natural protection against | | | | contains melanocytes, cells that secrete melanin, the |
| sunlight. It grows hair, sweats, produces oil for | | | | pigment responsible for varying skin color. Melanin |
| self-lubrication, and gives an accurate perception of | | | | production is stimulated by sunlight: in white races this |
| touch, heat, cold, and pain, as well as the more | | | | creates a tan, which offers some protection against |
| complex sensations such as tickle, itch, and pressure. | | | | further exposure to the sun's ultraviolet rays. |
| Skin caliber varies in different body sites, from the | | | | Under the epidermis is the middle layer, or dermis, a |
| thin, delicate tissue of the eyelid, to the thick, hard | | | | bulky fibrous and protein layer containing hair follicles, |
| padding of the heel. Some sites have particular | | | | sweat, and sebaceous (oil-producing) glands, and |
| characteristics - luxuriant hair growth on the scalp, | | | | specialized sensory receptors for conveying |
| sweating in the armpits, highly-tuned touch | | | | information about touch, temperature, and pain. Mast |
| discrimination in the fingertips - yet the basic | | | | cells in the dermis respond to physical or chemical |
| structure of the skin is the same everywhere, | | | | damage by releasing histamine, a substance leading to |
| although its actual thickness varies between different | | | | allergic responses. |
| physical types. Redheads, for example, have | | | | Finally there is a layer of subcutaneous fatty tissue |
| considerably thinner skin than brunettes, and, | | | | that gives the skin its feeling of softness and |
| consequently, their skin often reacts with more | | | | plumpness and acts as insulation against the cold. The |
| sensitivity. | | | | blood vessels supplying nourishment to the outer skin |
| The outer of the three skin layers, the epidermis, | | | | layers are carried in this layer. |
| comprises the skin surface of dead "horny" cells, and | | | | |