Perspiration Totally Explained

Everything about Perspiration totally explained

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's 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 . 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.

Mechanism

Sweat glands are innervated by the sympathetic nervous system; however, because the primary neurotransmitter involved with the innervation of sweat receptors is acetylcholine, and many of the glands are under the control of the hippocampus via nerve pathways typically thought of as parasympathetic. The nerve terminal releases acetylcholine, which binds to M₃ receptors on the sweat gland and causes the secretion of sweat. Acetylcholine is partially degraded by Cholinesterase enzyme (AchE); thus anything which interferes with AchE activity causes too much sweating.
There are two kinds of sweat glands, and they differ greatly in both the composition of the sweat and its purpose:

Eccrine sweat glands are distributed over the entire body surface, but are particularly abundant on the palms of hands, soles of feet, and on the forehead. These produce sweat that's composed chiefly of water with various salts. These glands are used for body temperature regulation.
Apocrine sweat glands produce sweat that contains fatty materials. These glands are mainly present in the armpits and around the genital area and their activity is the main cause of sweat odor, due to the bacteria that break down the organic compounds in the sweat from these glands. Apocrine glands produce the "oily" portion of sweat, while the more numerous eccrine glands produce the "watery" component of sweat.

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. 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). . 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 .

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