textbookchap2 - UNIT 13: Intergumentary Function ripples on...

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U NIT 13: Intergumentary Function ripples on the surface of the skin. On the fingertips these ripples are called fingerprints. They are perhaps a person's most individualistic characteristic and they almost never change. The dermis is a broad layer of connective tissue composed of collagen and elastic fibers, blood and lymph vessels, nerves, sweat and sebaceous glands, and hair roots. The dermis is often referred to as the "true skin." The subcutaneous tissue is primarily adipose tissue. It is here that the skin is anchored to the muscles and bones. Fat is deposited and distributed according to the person's sex and, in part, accounts for the difference in body shape between men and women. Overeating results in increased deposition of fat beneath the skin. The subcutaneous tissues and amount of fat deposited are important factors in body temperature regulation. Hair Hair is present over the entire body except for the palms of the hands and soles of the feet. The hair consists of a root formed in the dermis and a hair shaft that projects beyond the skin. It grows in a cavity called a hair follicle. The prolif- eration of cells in the bulb of the hair causes the hair to form (see Fig. 51-I). Hair follicles undergo cycles of growth and rest. The rate of growth varies; beard growth is the most rapid, followed by hair on the scalp, axillae, thighs, and eyebrows. The growing phase, anagen, may last 3 to 6 years for the scalp before ceasing. During telogen, or the resting phase, hair sheds from the body. The hair follicle will recycle into the growing phase spontaneously, or it can be induced by plucking out hairs. New hair growth and resting telogen hair can be found side by side on all parts of the body. About 80% of the hair follicles on a normal scalp are in the growing phase at any one time. Hairs in different parts of the body serve different functions. The hairs of the eyes (eyebrows and lashes), nose, and ears screen dust, bugs, and airborne debris. Hair of the skin serves as thermal insulation in lower animals. This function is enhanced during cold or fright by the piloerection (hairs "standing on end") caused by contraction of the tiny arrector muscles attached to the hair follicle. The piloerector response that occurs in humans is probably vestigial. The color of hair is due to the presence of varying amounts of melanin within the hair shaft. Gray or white hair is the result of loss of pigment. Growth of hair in certain locations on the body is under the control of sex hormones. The best examples are the hair on the face (beard and mustache) and the hair on the chest and back that are controlled by the presence of the male hormones (androgens). Hair quantity and distribution can be affected by
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This note was uploaded on 09/13/2011 for the course LEARNING L 110 taught by Professor Afrancis during the Spring '11 term at Community College of Philadelphia.

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textbookchap2 - UNIT 13: Intergumentary Function ripples on...

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