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In humans, the average body temperature is generally fixed, by convention, at 37 ° C. However, this is an approximate value, since the temperature can vary considerably from individual to individual, but also in the same subject.
Man is a homeothermic animal and as such has the ability to keep his body temperature relatively constant, despite the climatic variations of the outside world (obviously within certain limits). This balance is maintained thanks to the fine balancing of the processes of production, absorption and elimination of thermal energy. Among the main causes of thermogenesis (heat production) we remember the basal metabolism, the specific dynamic action of food, muscle activity, the release of pyrogenic substances and emotional stress. The dispersion of heat occurs. by convention, conduction and irradiation, that is through sweating, breathing, perspiratio insensibilis and conditioning of the environment.
Regardless of where it is determined, body temperature should be measured after about half an hour of absolute rest.
The temperature of the superficial layers of the skin is strongly influenced by environmental conditions and clothing, especially at the extremities (hands and feet). To give an idea, if the ambient temperature is 20 ° C and the clothing is light, only the deep skin layers of the head, neck, thorax and abdomen maintain thermal homeostasis. On the other hand, a deep temperature of 34 ° C is recorded at the level of the thigh, which drops to 32 ° C at the level of the arms and 31 ° C at the level of the calf. On the outermost skin layers the temperature fluctuates from 28 ° C (fingertips) to 36.5 ° C (axillary temperature).
In order for spermatogenesis (the testicular synthesis of new spermatozoa) to take place, it is essential that the temperature of the scrotum is 2-4 ° C lower than that of the body.
. The most practical and accurate method of measuring the temperature of a newborn or very young child is the rectal one. . This phenomenon, called food thermogenesis, is mediated by the activation of the brown adipose tissue, which in this case burns the lipids for the sole purpose of getting rid of the caloric surplus. It is therefore a real intrinsic anti-obesity mechanism, a condition that this would also pose a problem to the organism itself (it would slow down, for example, the flight from lions ...) The digestive processes, of course, also consume chemical energy and as such produce heat, particularly when the meal is rich in proteins.
The brown adipose tissue is activated massively even during exposure to cold temperatures; in this case the fats are burned (rather than deposited in the white adipose tissue) for the sole purpose of maintaining homeothermy.
The ingestion of hot or cold foods can slightly vary the body temperature, but they are above all the so-called nerve foods (green tea, black tea, coffee, cocoa and chocolate, cola-based drinks and supplements such as guarana, caffeine, theobromine, mate , synephrine and the like) to significantly elevate thermogenesis.
Alcohol deserves a separate discussion, as it causes vasodilation and increased skin blood flow, effectively increasing heat dissipation. Drinking alcohol to warm up in cold weather therefore does not make much sense, as it contrasts with one of the main thermoconservative mechanisms, which is precisely the vasoconstriction.
, remaining that way until the beginning of the menstrual flow.. The lowest values (basal temperature) are recorded in the early morning hours, while the highest values are reached in the late afternoon. In the case of night work or intercontinental travel, the circadian rhythms undergo important variations.
: elevation of body temperature above normal maximum values, caused by the alteration of the hypothalamic center of thermoregulation. In its most classic presentation, fever is sustained by the release of particular substances (pyrogenic cytokines) by the immune cells involved in the fight against invading microorganisms (bacteria, viruses, fungi). In turn, fever favors the elimination of pathogens.
HYPERTHERMIA: abnormal elevation of body temperature, due to an excessive accumulation of heat for production and / or absorption higher than the thermo-dispersive capacity. Hyperthermia is typical of hyperthyroidism, exposure to high temperatures and heat stroke.
HYPOTHERMIA: lowering of body temperature below 35 ° C detected at the rectal level. Possible causative agents include prolonged exposure to very low ambient temperatures (frostbite), acute alcoholism (due to the aforementioned vasodilatory mechanism of ethanol), hypoglycemia, cachexia, myxedema and hypoxemia (both of pulmonary and cardiac origin).
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