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In the skin we find three types of glands: the sweat glands, the apocrine glands and the sebaceous glands.
Each sweat gland sinks up to the hypodermis and includes a convoluted part, which represents the secreting unit, and a ductal portion, which opens onto the body surface by means of a pore (excretory duct).
In the convoluted part of the gland there is a primary secretion of sweat, which takes on a composition very similar to that of the plasma, except for the protein fraction (practically absent in the sweat). The rich vascularization of the gland serves precisely to guarantee the right supply of the substances necessary for the production of this liquid.
When the primary secretion passes through the excretory duct, most of the electrolytes are reabsorbed (in particular sodium and chlorine) and together with them a certain amount of water, which follows the flow due to osmotic questions. The extent of resorption depends on the rate of gland secretion. If the production of sweat is slow (poor sweating) the reabsorption is greater, on the contrary, when the flow is rapid reabsorption is less.
Each of us has about 3 million sweat glands and, unlike many other animals, these glands are distributed over the entire surface of the body, although with different density. Moreover, their activity is intermittent; each sweat gland alternates periods of quiescence with other periods of activity. We have seen that even in the phases of maximum sweating, at least half of these glands are inactive.
The ability of sweat secretion is surprising. In fact, each gland can produce significantly more sweat than its weight. Suffice it to say that when the temperature rises considerably, an acclimatized organism can expel up to 4-6 liters of sweat every 60 minutes.
The sweating power is greater in men, who generally have a more active metabolism and with it a greater need to disperse the heat produced. However, there are no significant variations between individuals belonging to different races.
Sweat consists of:
water (99%)
organic and inorganic substances (1%)
Among the organic components there are various nitrogen compounds (urea, creatinine, uric acid and ammonia). Lactate is also present.
Ammonia, in addition to being part of the composition of fresh sweat, is produced in large quantities by the bacteria that populate the skin surface. The abundance of this substance contributes to giving an unpleasant smell to the product of the sweat glands.
Sweat eliminates various substances (drugs and non), including those contained in particular types of food.
Sweat pH is slightly acid, usually between 4 and 6.5. The presence of lactate tends to acidify this liquid, while ammonia shifts the pH towards higher values.
There are three types of sweating: thermal, psychic and pharmacological.
Thermal perspiration is induced by an increase in body temperature and is different in the various areas of the body.
Psychic perspiration occurs in response to particular moods; it is, for example, induced by anxiety, stress and emotions. The response to these stimuli is subjective, but generally limited to very specific body areas. Unlike thermal perspiration, which is always accompanied by dilation of blood vessels, psychic sweating induces vasoconstriction. From here originates the term "cold sweat", because the skin, due to vasoconstriction, is pale and cold.
Pharmacological sweating can be induced by various chemical components, derived from catecholamines, antipyretics, antidepressants, but also from some foods and spices.
Finally, there are some special conditions, such as fever, infections and metabolic imbalances (diabetes, obesity, hyperthyroidism) that can amplify the production of sweat.
The main function of the sweat glands is linked to their considerable contribution to thermoregulation. Thanks to sweat and skin vasodilation, body temperature can remain relatively constant even in particularly hot environments.
It is very important to keep in mind that sweat alone is not enough to cool the body; in order to have heat dispersion it is necessary that this liquid evaporates. In fact sweat, passing from the liquid state to the vapor state, removes heat from the body. In particular, 0.58 kcal is removed from the body for one gram of water that evaporates from the body surface.
The environmental humidity hinders the evaporation of sweat and this explains the state of discomfort perceived when one is in hot humid environments.
Too much sweating in a short time leads to a risk of dehydration and excessive loss of salts (NaCl).
Problems related to sweating
The most serious is heat stroke, which can occur when the individual exposes himself to particularly high temperatures, associated with a high humidity. This situation hinders the skin's evaporation of sweat, considerably increasing the internal temperature. As a result, the body overheats and the hypothalamic center that regulates temodispersion goes haywire. The consequences can be very serious, so much so that, unless action is taken to immediately cool the body, perhaps with an ice bath, the risk of mortality is quite high. This risk increases during the practice of heavy physical activities, both work and sport. The subjects most at risk are children, the elderly and heart patients.
A second problem, less serious than the previous one, is heat collapse. It is caused, essentially, by an excess of sweating which, due to the consequent dehydration, decreases the mass of circulating blood. In turn, this condition, called hypovolemia, causes the appearance of symptoms such as weakness, dizziness, hypotension and, in extreme cases, shock and cardiovascular collapse.
Heat collapse can be overcome with the simple and gradual reintegration of lost liquids, possibly by placing the subject in a cool and shady place.
Other functions of the sweat glands
Sweat enters the composition of the hydrolipidic film, that thin liquid film that protects the epidermis.
In addition to repelling bacterial aggressions, thanks to its acid pH which opposes the skin colonization of numerous microorganisms, sweat contains antibodies (IgA, IgG, IgE), which increase its defensive action against external aggressions.
Finally, the sweat glands also perform an excretory function, which is however moderate, especially when compared with that of the main excretory organs of the organism (kidneys).
the apocrine glands »
