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fluid secreted by the sweat glands of mammalian skin and containing water, salts, and waste products of body metabolism such as urea. The dissolved solid content of sweat is only one eighth that of an equal volume of urine, the body's main
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sweating, the formation of sweat and its excretion by the sweat glands onto the surface of the skin.
Perspiration is well manifested in man, higher and lower apes, and ungulates (mainly perissodactyls). In rodents, insectivores, bats, terrestrial predators, and lower mammals (duck-billed platypus and echidna) it is almost nonexistent. In man perspiration is continuous. It is performed principally by reflex action—reflex receptors are located in the skin, mucosa, and muscles. Adequate stimuli for the perspiration reflex are high air temperature, ingestion of hot or pungent food or large quantities of fluids, physical exertion, fever, and emotional states. Perspiration centers are located in the cerebral cortex, hypothalamus, medulla oblongta, and spinal cord. Perspiration may be increased or decreased by means of medicinal preparations. It depends on blood circulation in the skin: when the blood vessels are dilated it increases; when they are constricted it decreases. It is an adaptation of the body to temperatures over 33°C. Perspiration is involved in thermoregulation and in maintenance of the water and salt balances of the body. Perspiration is important as an excretory function, especially with diseases of the kidneys.
Perspiration disorders may be quantitative (general or local) or qualitative. Quantitative disorders are more frequent and are expressed as increase (hyperhidrosis), decrease (hypohidrosis), or absence (anhidrosis) of perspiration. General hyperhidrosis occurs with various infections, intoxications, functional disturbances of the endocrine glands (hyperthyroidism), and other diseases. Increased perspiration may also be produced by the severe emotional excitement of fear or pain, in which case on pale, cold skin a “cold sweat” appears. Local perspiration disorders arise with many skin diseases, such as eczema, psoriasis, and shingles. Hypohidroses and anhidroses are observed in the region of scars after burns and wounds, as well as in leprosy and certain vascular diseases. Disorders of perspiration arise most often when there is disease of various sections of the nervous system, such as expressed hyperhidrosis of the hands and feet, which occurs in neuroses.
Qualitative perspiration disorders are manifested by changes in composition and color of excreted sweat. Thus, the sweat may sometimes be fatty because of admixture with the secretions of the sebaceous glands in seborrhea. With diabetes mellitus it may contain increased sugar. With uremia, increased amounts of urea and uric acid are noted. Treatment is directed toward the basic disease. Local symptomatic agents are also used.