sweat

sweat

sweat or perspiration, 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 vehicle of salt excretion; however, excessive sweating may produce severe salt loss (see heat exhaustion). Human sweat glands are of two types, eccrine and apocrine. The eccrine glands, found everywhere on the body surface, are vital to the regulation of body temperature. Evaporation of the sweat secreted by the eccrines cools the body, dissipating the heat generated by metabolic processes. The release of such sweat is usually imperceptible; yet even in cool weather an individual will lose from 1 pt to 3 qt of fluid per day. Only when environmental conditions are especially hot or humid, or during periods of exercise or emotional stress, does the output of sweat exceed the rate of evaporation, so that noticeable beads of moisture appear on the skin. When such conditions are extreme, the body may lose up to 20 qt of fluid per day. Production of sweat is controlled by the temperature-regulating center of the hypothalamus. The apocrine glands, which occur only in the armpits and about the ears, nipples, navel, and anogenital region, are scent glands. They function in response to stress or sexual stimulation, playing no part in temperature regulation. The apocrines exude a sticky fluid quite different from the watery sweat of the eccrines. Apocrine fluid is rich in organic substances that are odorless when fresh but are quickly degraded by bacteria on the skin to produce characteristic odors. Copious sweating in the armpits comes not from the apocrines but from the eccrines interspersed among them.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Sweat

 

a colorless, slightly opalescent fluid secreted by the sweat glands.

Human sweat contains 98 to 99 percent water, about 0.1 percent urea, uric acid, creatinine, serine, fats, volatile fatty acids, cholesterol, and alkaline metal salts, including chlorides (NaCl predominates— about 0.3 percent), phosphates, and sulfates, as well as sulfuric acid esters and aromatic oxygen acids. The secretion of the sebaceous glands is always mixed with the sweat that gathers on the skin surface. The composition of sweat depends on the condition of the body, the intensity of sweat excretion, and the presence of various substances in the blood. Sweat may be acid, with a pH of 3.8–6.2, or alkaline, when there is decomposition of urea and production of ammonia. In man from 0.5 to 10 liters of sweat or more per day are excreted, depending on intensity of muscle work, temperature of the external environment, and the quantity of water imbibed. Thus, with heavy muscle work, sweat contains a significant quantity of lactic acid and nitrogenous substances. In pathological states, sweat may contain glucose (sugar diabetes), bile pigments, cystine (cystinuria), and sometimes erythrocytes (bloody sweat).

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

sweat

[swet]

(chemistry)

Exudation of nitroglycerin from dynamite due to separation of nitroglycerin from its adsorbent.

(metallurgy)

Exudate of low-melting-point constituents from a metal on solidification.

(physiology)

The secretion of the sweat glands. Also known as perspiration.

(science and technology)

Formation of moisture beads on a surface as a result of concentration.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

sweat

1. the secretion from the sweat glands, esp when profuse and visible, as during strenuous activity, from excessive heat, etc.; commonly also called perspiration

2. Chiefly US an exercise gallop given to a horse, esp on the day of a race

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005