Regulation of Body Temperature and Fever

Generality

The fever consists in the increase of the body temperature, due to an alteration of the normal "set point" value (about 37 ° C) regulated by the deputed nerve centers, which - housed in the hypothalamus - regulate the production of heat in the organism and its dispersion.

Very often, fever is a response to bacterial or viral infections that stimulate some blood cells (white blood cells) to proliferate and secrete different chemical substances. Some of these substances act on cerebral thermoregulatory centers by raising the set point value; they therefore behave as pyrogens (inducers of fever).

Since the increase in temperature induced by endogenous pyrogens (IL-1 and TNF-α) stimulates an increase in the speed of many immune responses against invading microorganisms, within certain limits fever is considered beneficial, since it improves the organism's capacity to defend yourself .

Body temperature is one of the vital parameters useful for monitoring a patient's condition: measuring body temperature can be useful to check if a person is sick or if the therapeutic treatment is working. There are several ways to measure fever.

Body temperature regulation

Body temperature is regulated by the balance between thermogenesis and thermodispersion, that is between the production and the consequent cession of heat by the body. Our body continuously produces heat ( thermogenesis ) as a by-product of chemical transformations (metabolism) that occur continuously in all cells (second principle of thermodynamics).

If the heat produced is not eliminated, during muscular rest and in normal environmental conditions, the average temperature of the human body would increase by about 1.5 ° C every hour. The organism is able to maintain a dynamic balance between entry (thermogenesis and absorption) and heat output ( thermodispersion ) from the system, mainly through the evaporation of water from the mucous membranes (favored by breathing) and through sweating (about 30 ml of sweat / h in perspiratio insensibilis ). For this reason, the body temperature remains constantly around 37 ° C, as the body eliminates as much heat as it absorbs and / or produces.

The body temperature regulator center is located hypothalamically. This physiological "thermostat" is not only able to receive signals from peripheral receptors (hot - cold), but is also directly sensitive to the temperature of the blood that irrigates it. The hypothalamus, in turn, generates efferent signals that influence the production and dispersion of heat, through the sympathetic and somatomotor system.

The normal temperature of an adult is in a range of 36.4 to 37.2 ° C. This parameter is different in the various parts of the human body and depends, within certain limits, on the temperature of the environment, on physical activity and on a series of other factors:

The body temperature varies over time: during the day it undergoes variations ranging from 0.5 to 1 ° C, touching the minimum at dawn, between 4 and 6 in the morning and the maximum in the late afternoon, between 17 and 20 ( circadian rhythm ).
In women there is a rhythm correlated with the menstrual cycle : the temperature increases by about 0.6 ° C to ovulation and remains so until menstruation.
Body temperature increases slightly after meals .
Pregnancy, some hormonal alterations (especially of the thyroid) and age can change body temperature.
Finally, the central temperature can also increase by 1 ° C or more in the case of intense physical work or sports activities .

Normal results

Body temperature is in a range of 36.4 to 37.2 ° C.

Body temperature can spontaneously vary in relation to:

Individual characteristics (sex, hormonal alterations, etc.);
Age (in children over 6 months, the daily temperature can vary from 1 to 2 degrees; in the elderly it is on average lower);
Time of day (often higher in the evening);
Seat of the body in which the temperature was measured ;
Physical activity;
Ambient temperature and humidity;
Nutrition status;
Strong emotions;
Menstrual cycle (in women);
Taking some medications;
Vaccinations (children may have a slight increase in temperature in the following days);
Teething (in a child);
Wear heavy clothing.

What is fever?

Fever consists in raising the body temperature above normal values. This alteration is caused by a shift to pathological values of the hypothalamic temperature regulation system, which undergoes the influence of endogenous chemical mediators: the pyrogenic cytokines. These endogenous pyrogens are released in response to the action of infectious agents and their products (exogenous pyrogens) or in response to non-infectious inflammatory and necrotic foci. Fever is an acute phase response to various causes, capable of inducing infection and / or disease, so it is a common clinical sign in many medical conditions.

If the increase in body temperature reaches :

is defined

38 ° C

38.5 ° C

39 ° C

39.5 ° C

41 °

> 41 ° C

grade fever

Mild fever

Moderate fever

High fever