CH.YBW.CTS.C08.Final.q 6/21/03 1:11 PM Page 110
110 CELLS, TISSUES, AND SKIN
eardrums, nail beds, and portions of the external genitalia. Sweat is mostly composed of water. It also contains some salts, lactic acid, vitamin C, and metabolic wastes, such as urea and ammonia. The principal function of sweat is to help regulate body temperature through the evaporation of water on the skin surface. In fact, on a hot day one can easily lose several liters of body water in this way. In addition, the slightly acidic pH of sweat inhibits growth of bacteria. Apocrine glands are a type of sweat gland, mainly located in the armpits and pubic region. They are usually larger than eccrine glands, and empty their contents into hair follicles. Although their secretion contains all the substances present in eccrine sweat, they also contain additional fatty acids and proteins. These substances make the secretion more viscous (thick), and also gives it a whitish-yellowish color. Apocrine secretion is typically odorless. However, bacterial action on the skin surface converts its proteins and fats into compounds that release an unpleasant odor. In fact, antiperspirants are designed to inhibit such secretions, whereas deodorants mask their odor. Apocrine glands do not function until puberty, at which time they are stimulated by a rise in sex hormones (testosterone and estrogen). Although their exact function is not known, they generally become most active when a person is emotionally upset or excited, such as when frightened, in pain, or sexually aroused. Apocrine glands also enlarge and shrink with the phases of a woman’s menstrual cycle. It is therefore unlikely these glands play a significant role in temperature regulation. Instead, it is generally assumed that apocrine glands are analogous to the sexual scent glands of other animals, and they also may play a scent role during a fight or flight response. It has been suggested that pubic and axillary (under arm) hair help disperse the odor of apocrine secretions; that is, a way of enhancing the spread of one’s scent. Ceruminous glands are modified apocrine glands found in the lining of the external ear canal. They secrete a thick, sticky