Hair

Hair, outgrowth of the skin in mammals, sometimes thickening to form wool or fur. Each hair consists of a shaft, most of which extends above the surface of the skin, and a root located in a tubular follicle below the skin surface. The lower end of the root is enlarged to form the bulb, the lower part of which surrounds a cone-shaped projection of connective tissue, the papilla. The blood supply to the hair follicle comes through capillary networks that enter the papilla. The root of the hair forms a matrix of growing and dividing cells. As new cells are formed, the older cells are pushed upward and the hair “grows.” The hairshaft in the upper part of the follicle and the exposed part of the shaft above the skin consists of dead, cornified cells. Cutting the exposed part of the shaft has no effect on the growth of the hair. Associated with the hair follicles are the sebaceous glands, which secrete an oily substance that lubricates the shaft of the hair.