5) There is no doubt that the hypodermis, sebaceous and sweat glands, nails and hair play an important role in maintaining normal physiological condition of the skin. Raven, Evert & Eichhorn emphasized that hypodermis protects the body from excessive cooling, protects it against external irritants or trauma; it is the depot, in which fat stores are deposited, expended in the event of sickness, hunger, and pregnancy. Human skin performs excretory function with the sweat glands, while sebaceous glands secrete a secret, called sebum, which softens the skin, giving it elasticity. Nails protect the tissue of nail bed from various environmental stimuli, while hair protects the head from overheating and from hypothermia. For instance, vellus hair is involved in touch, eyelashes protect the eyes, hair in nose and ears retain dust. Lastly, hair and nails are mostly made of keratin (a type of protein), which forms also the outer layer of human skin.
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