Perspiration

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"Sweat" redirects here. For other uses, see Sweat (disambiguation).

Perspiration (also called sweating or sometimes transpiration) is the production and evaporation of a fluid, consisting primarily of water as well as a smaller amount of sodium chloride (the main constituent of "table salt"), that is excreted by the sweat glands in the skin of mammals. Sweat also contains the chemicals or odorants 2-methylphenol (o-cresol) and 4-methylphenol (p-cresol).

In humans, sweating is primarily a means of thermoregulation, although it has been proposed that components of male sweat can act as pheromonal cues [1]. Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water. Hence, in hot weather, or when the individual's muscles heat up due to exertion, more sweat is produced. Sweating is increased by nervousness and nausea and decreased by cold. Animals with few sweat glands, such as dogs, accomplish similar temperature regulation results by panting, which evaporates water from the moist lining of the oral cavity and pharynx. Primates and horses have armpits that sweat similarly to those of humans.

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[edit] Mechanism

Sweating is controlled from a center in the preoptic & anterior regions of the hypothalamus where thermosensitive neurones are located. The heat regulatory function of the hypothalamus is also affected by inputs from temperature receptors in the skin. High skin temperature reduces the hypothalamic set point for sweating and increases the gain of the hypothalamic feedback system in response to variations in core temperature. Overall though, the sweating response to a rise in hypothalamic temperature (‘core temp’) is much larger than the response to the same increase in average skin temperature.

Sweat is not pure water; it always contains a small amount (0.2 - 1%) of solute . When a person moves from a cold climate to a hot climate, adaptive changes occur in their sweating mechanism. These are referred to as acclimatisation: the maximum rate of sweating increases and its solute composition decreases. The daily water loss in sweat is very variable: from 100 to 8,000 mls/day. The solute loss can be as much as 350 mmols/day (or 90 mmols/day acclimatised) of sodium under the most extreme conditions. In a cool climate & in the absence of exercise, sodium loss can be very low (less than 5 mmols/day). [Na+] in sweat is 30-65 mmol/l depending on degree of acclimatisation.

[edit] Composition

Sweat contains mainly water. It also contains minerals, as well as lactate and urea. Mineral composition will vary with the individual, the acclimatisation to heat, exercise and sweating, the particular stress source (exercise, sauna, etc.), the duration of sweating, and the composition of minerals in the body. An indication of the minerals content is is: sodium 0.9 gram/liter, potassium 0.2 gram/liter, calcium 0.015 gram/liter, magnesium 0.0013 gram/liter[2]. Also many other trace elements are excreted in sweat, again an indication of their concentration is (although measurements can vary fifteenfold): zinc (0.4 mg/l), copper (0.3 - 0.8 mg/l), iron (1 mg/l), chromium (0.1 mg/l), nickel (0.05 mg/l), lead (0.05 mg/l). [3] [4]. Probably many other less abundant trace minerals will leave the body through sweating with correspondingly lower concentrations. In humans sweat is hyposmotic relatively to the plasma [5].

[edit] See also

[edit] References

  1. ^ Smelling a single component of male sweat alters levels of cortisol in women", C. Wyart et al., Journal of Neuroscience, February 7, 2006
  2. ^ Sweat mineral-element responses during 7 h of exer...[Int J Sport Nutr Exerc Metab. 2007] - PubMed Result
  3. ^ Cohn JR, Emmett EA, The excretion of trace metals in human sweat., Ann Clin Lab Sci. 1978 Jul-Aug;8(4):270-5., http://www.ncbi.nlm.nih.gov/pubmed/686643
  4. ^ Saraymen et al., Sweat Copper, Zinc, Iron, Magnesium and Chomium levels in national westler. 1973
  5. ^ BRS Physiology 4th edition, Linda S. Constanzo, page155

[edit] External links

[edit] Further reading

  • Ferner S, Koszmagk R, Lehmann A, Heilmann W., Z Erkr Atmungsorgane. 1990;175(2):70-5. 'Reference values of Na(+) and Cl(-) concentrations in adult sweat'
  • E. R. Nadel, R. W. Bullard, and J. A. Stolwijk, "Importance of skin temperature in the regulation of sweating", Journal of Applied Physiology, Vol. 31, Issue 1, 80-87, July 1, 1971
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