Anatomy & Physiology

Anatomy & Physiology Study Guide highest numbers. The functions of merocrine sweat gland activity include cooling the surface of the skin to reduce body temperature, excreting water and electrolytes, and providing protection from environmental hazards. Other Integumentary Glands The skin contains a variety of specialized glands that are restricted to specific locations. The mammary glands of the breasts are anatomically related to apocrine sweat glands. A complex interaction between sex hormones and pituitary hormones controls their development and secretion. Ceruminous glands are modified sweat glands in the passageway of the external ear. Their secretions combine with those of nearby sebaceous glands, forming a mixture called cerumen, or earwax. Hair Hair is composed of keratinized dead cells that have been pushed to the surface. Hair, hair follicles, sebaceous and sweat glands, and nails are accessory structures of the integument. These structures are derived from the epidermis during embryological development and are known as epidermal derivatives. Although located in the dermis, they project through the epidermis to the surface of the skin. Hairs project above the surface of the skin almost everywhere, except over the lips and portions of the hands, feet, and external genital. About 2.5 million hairs cover the human body, and 75 percent of them are on the general body surface, not on the head. Hairs are nonliving structures produced in organs called hair follicles. The hairs and hair follicles on the body have important functions, which include the hairs on the head, protecting the scalp from ultraviolet radiation, providing cushion for light impacts to the head, and insulating the skull. The hair at the openings to the nostrils and external ear canals help prevent the entry of foreign particles and insects. The eyebrows keep sweat out of the eyes. Hairs are also important as sensory receptors. Hair extends on to the epidermis through a hair follicle. Each hair follicle opens onto the surface of the epidermis and extends into the dermis, some as far as the hypodermis. Deep to the epidermis, each follicle is wrapped in a dense connective tissue sheath. The base of each hair follicle is surrounded by a root hair plexus with sensory nerves. As a result, the movement of the shaft of a single hair can be felt. This sensitivity provides an early-warning system that may help prevent injury. Each hair is a long, cylindrical structure that extends outward, past the epidermal called the hair root. The hair root—the portion that anchors the hair into the skin—begins at the base of the hair, at the hair bulb, and extends distally to the point at which the internal organization of the hair is complete, about halfway to the skin surface. The hair shaft, part of which we see on the surface, extends from this halfway point to the exposed tip of the hair. Hair Production Hair production begins at the base of a hair follicle. A mass of epithelial cells forms a cap, called the hair bulb, which surrounds a small hair papilla. The superficial cells of the hair bulb are responsible for producing the hair; they form a layer called the hair matrix.

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