1. The Function of Skin

2. The skin has four basic functions I. Protection A. Physical barrier to disease, dirt, and dehydration A. Physical barrier to disease, dirt, and dehydration 1. Bacteria and other invaders are prevented entry by the top dead layer of skin and the acidic, oily secretion from sebaceous glands (sebum). 1. Bacteria and other invaders are prevented entry by the top dead layer of skin and the acidic, oily secretion from sebaceous glands (sebum). 2. Keratinization of the dead skin outer layer also prevents water from entering or leaving the skin. 2. Keratinization of the dead skin outer layer also prevents water from entering or leaving the skin.

3. The progressive maturation of a keratinocyte is characterized by the accumulation of keratin, called keratinization. The cells of the stratum granulosum (SGR) accumulate dense basophilic keratohyalin granules (seen on the close-up view). The cells of the stratum granulosum (SGR) accumulate dense basophilic keratohyalin granules (seen on the close-up view). These granules contain lipids, which along with the desmosomal connections, help to form a waterproof barrier that functions to prevent fluid loss from the body. These granules contain lipids, which along with the desmosomal connections, help to form a waterproof barrier that functions to prevent fluid loss from the body.

4. B. The skin also protects the rest of your body from harmful ultraviolet radiation through the production of melanin in the melanocytes. Melanin absorbs the sun’s rays. MELANOCYTES

5. II. Vitamin D Synthesis A.The skin produces a precursor to Vitamin D. The sun’s rays convert this into Vitamin D. B.Vitamin D is converted in the liver and kidneys into the hormone calcitriol, which regulates bone growth.

6. III. Touch and Talk A.Special nerve receptors control pressure, pain, and temperature sensing. B. A great many of these receptors occur in the hands.

7. IV. Regulation of Body Temperature A. Only 40% of the energy from ATP is used. The rest is given off as heat from the muscles. B. The skin keeps the amount needed and releases the rest through sweat

8. C. Blood vessels control the temperature regulation by dilating or constricting. D. Bad things happen when a constant temp. is not kept 1. Hyperthermia—Higher body temp. than normal results in dehydration (from excess sweating) and heat stroke. 2. Hypothermia—Lower body temp. than normal interferes with the body’s normal functions and eventually ends in death.