Methods for thermoregulation of the human body. How is thermoregulation carried out in the body? Thermoregulation of the human body physical properties of heat therapy

The main parameters ensuring the process of heat exchange between a person and the environment, as shown above, are microclimate indicators. Under natural conditions on the Earth's surface (sea level), they vary within significant limits. Thus, the ambient temperature varies from -88 to + 60 °C; air mobility - from 0 to 60 m/s; relative humidity - from 10 to 100% and atmospheric pressure - from 680 to 810 mm Hg. Art.

Along with changes in microclimate parameters, a person’s thermal well-being also changes. Conditions that disrupt the thermal balance cause reactions in the body that contribute to its restoration. The processes of regulating heat release to maintain a constant human body temperature are called thermoregulation. It allows you to keep your body temperature constant. Thermoregulation is carried out mainly in three ways: biochemically; by changing the intensity of blood circulation and the intensity of sweating.

Thermoregulation by biochemical means, called chemical thermoregulation, consists of changing heat production in the body by regulating the rate of oxidative reactions. Changing the intensity of blood circulation and sweating changes the release of heat into the environment and is therefore called physical thermoregulation.

Thermoregulation of the body is carried out simultaneously by all means. Thus, when the air temperature decreases, an increase in heat transfer due to an increase in the temperature difference is prevented by such processes as a decrease in skin humidity, and therefore a decrease in heat transfer through evaporation, a decrease in the temperature of the skin due to a decrease in the intensity of blood transport from internal organs, and at the same time a decrease in the difference temperatures It has been experimentally established that optimal metabolism in the body and, accordingly, maximum activity performance occur if the components of the heat transfer process are within the following limits:

Q to? thirty %; Q p? 50 %; Q tm? 20 %.

This balance characterizes the absence of tension in the thermoregulation system.

Microclimate parameters have a direct impact on a person’s thermal well-being and performance. It has been established that at air temperatures above 25 °C, a person’s performance begins to decline. The maximum temperature of inhaled air at which a person is able to breathe for several minutes without special protective equipment is about 11°C.

A person's tolerance to temperature, as well as his sense of heat, largely depends on the humidity and speed of the surrounding air. The higher the relative humidity, the less sweat evaporates per unit time and the faster the body overheats. High humidity at t* gt has a particularly adverse effect on a person’s thermal well-being; 30 °C, since almost all the heat generated is released into the environment through the evaporation of sweat. When humidity increases, sweat does not evaporate, but flows down in drops from the surface of the skin. A so-called torrential flow of sweat occurs, exhausting the body and not providing the necessary heat transfer. Together with sweat, the body loses a significant amount of mineral salts, trace elements and water-soluble vitamins (C, B1, B2). Under unfavorable conditions, fluid loss can reach 8... 10 liters per shift and with it up to 40 g of table salt (in total there is about 140 g of NaCl in the body). Losses of more than 30 g of NaCl are extremely dangerous for the human body, as they lead to impaired gastric secretion, muscle spasms, and cramps. Compensation for water loss in the human body at high temperatures occurs due to the breakdown of carbohydrates, fats and proteins.

To restore the water-salt balance of workers in hot shops, replenishment points with salted (about 0.5% NaCl) carbonated drinking water are installed at the rate of 4...5 liters per person per shift. A number of factories use a protein-vitamin drink for these purposes. In hot climates, it is recommended to drink chilled drinking water or tea.

Prolonged exposure to high temperatures, especially in combination with high humidity, can lead to a significant accumulation of heat in the body and the development of overheating of the body above the permissible level - hyperthermia - a condition in which the body temperature rises to 38...39 ° C. With hyperthermia and, as a consequence, heat stroke, headache, dizziness, general weakness, distortion of color perception, dry mouth, nausea, vomiting, profuse sweating, increased pulse and breathing are observed. In this case, pallor, cyanosis are observed, the pupils are dilated, at times convulsions and loss of consciousness occur.

In hot shops of industrial enterprises, most technological processes take place at temperatures significantly higher than the ambient air temperature. Heated surfaces emit streams of radiant energy into space, which can lead to negative consequences. Infrared rays have a mainly thermal effect on the human body, which disrupts the activity of the cardiovascular and nervous systems. The rays can cause burns to the skin and eyes. The most common and severe eye damage caused by exposure to infrared rays is cataracts.

Production processes carried out at low temperatures, high air mobility and humidity can cause cooling and even hypothermia of the body - hypothermia. In the initial period of exposure to moderate cold, a decrease in respiratory rate and an increase in inhalation volume are observed. With prolonged exposure to cold, breathing becomes irregular, the frequency and volume of inhalation increase. The appearance of muscle tremors, in which external work is not performed and all energy is converted into heat, can delay the decrease in the temperature of the internal organs for some time. The result of low temperatures is cold injuries.

Human thermoregulation is a set of extremely important mechanisms that maintain the stability of the body’s temperature regime in different environmental conditions. But why does a person need a constant body temperature so much, and what happens if it starts to fluctuate? How do thermoregulatory processes occur and what to do if the natural mechanism fails? More about all this below.

Man, like most mammals, is a homeothermic creature. Homeothermy is the body’s ability to ensure a constant temperature level, mainly through physiological and biochemical reactions.

Thermoregulation of the human body is an evolutionarily formed set of mechanisms that operate due to humoral (through the liquid medium) and nervous regulation, metabolism (metabolism) and energy metabolism. Different mechanisms have different methods and conditions of operation, so their activation depends on the time of day, the gender of the person, the number of years lived, and even the position of the Earth in orbit.

Human heat map

Thermoregulation in the human body is carried out reflexively. Special systems whose action is aimed at controlling temperature regulate the intensity of heat release or absorption.

Human thermoregulation system

Maintaining the body temperature at a constant set level is carried out using two opposing mechanisms of thermoregulation of the human body - heat release and heat production.

Mechanism of heat production

The mechanism of heat production, or chemical thermoregulation of a person, is a process that contributes to an increase in body temperature. It occurs in all metabolisms, but mostly in muscle fibers, liver cells and brown fat cells. One way or another, all tissue structures participate in the production of heat. In every cell of the human body, oxidative processes occur that break down organic substances, during which some of the released energy is spent on heating the body, and the main amount is spent on the synthesis of adenosine triphosphate acid (ATP). This connection is a convenient form for storing, transporting and exploiting energy.

This is what an ATP molecule looks like

When the temperature drops, the rate of metabolic processes in the human body reflexively decreases, and vice versa. Chemical regulation is activated in cases where the physical component of heat exchange is not enough to maintain a normal temperature value.

The mechanism of heat production is activated when signals from cold receptors are received. This happens when the ambient temperature drops below the so-called “comfort zone,” which for a lightly dressed person lies in the temperature range from 17 to 21 degrees, and for a naked person is approximately 27-28 degrees. It is worth noting that for each individual the “comfort zone” is determined individually; it can vary depending on health status, body weight, place of residence, time of year, etc.

To increase heat production in the body, thermogenesis mechanisms are activated. Among them are the following.

1. Contractive.

This mechanism is activated by muscle work, during which the decomposition of adenositriphphosphate is accelerated. When it splits, secondary heat is released, effectively warming the body.

In this case, muscle contractions occur involuntarily - upon receipt of impulses emanating from the cerebral cortex. As a result, a significant (up to five times) increase in heat production can be observed in the human body.

This is how the skin reacts to cold

With a slight decrease in temperature, the thermoregulatory tone increases, which is clearly manifested in the appearance of “goosebumps” on the skin and the raising of hairs.

Uncontrolled muscle contractions during contractile thermogenesis are called cold shivering. It is possible to increase the body temperature with the help of muscle contractions consciously - by showing physical activity. Physical activity increases heat production up to 15 times.

2. Non-contractive.

This type of thermogenesis can increase heat production almost threefold. It is based on the catabolism (breakdown) of fatty acids. This mechanism is regulated by the sympathetic nervous system and hormones secreted by the thyroid gland and adrenal medulla.

Heat transfer mechanism

The heat transfer mechanism, or the physical component of thermoregulation, is the process of ridding the body of excess heat. A constant temperature is maintained by heat removal through the skin (by conduction and convection), radiation and moisture removal.

Part of the heat transfer occurs due to the thermal conductivity of the skin and the layer of fatty tissue. The process is regulated largely by blood circulation. In this case, heat from human skin is transferred to solid objects when touched (conduction) or to the surrounding air (convection). Convection makes up a significant part of heat transfer - 25-30% of human heat is transferred to the air.

Radiation or emission is the transfer of human energy into space or onto surrounding objects that have a lower temperature. Up to half of human heat is lost with radiation.

And finally, the evaporation of moisture from the surface of the skin or from the respiratory organs, which accounts for 23-29% of heat loss. The more the body temperature exceeds the norm, the more actively the body cools itself through evaporation - the surface of the body becomes covered with sweat.

In the case when the ambient temperature significantly exceeds the internal indicator of the body, evaporation remains the only effective cooling mechanism; all others stop working. If the high external temperature is also accompanied by high humidity, which makes sweating (i.e., water evaporation) difficult, then a person can overheat and get heatstroke.

Let us consider the mechanisms of physical regulation of body temperature in more detail:

Perspiration

The essence of this type of heat transfer is that energy is directed into the environment by evaporating moisture from the skin and mucous membranes lining the respiratory tract.

This type of heat transfer is one of the most important, since, as already noted, it can continue in an environment with high temperatures, provided that the percentage of air humidity is less than 100. This is explained by the fact that the higher the air humidity, the worse the water will evaporate.

An important condition for the effectiveness of perspiration is air circulation. Therefore, if a person wears clothes that are impermeable to air exchange, then after some time the sweat will lose the ability to evaporate, since the air humidity under the clothes will exceed 100%. This will cause overheating.

In the process of sweating, the human body's energy is spent breaking the molecular bonds of the liquid. Losing its molecular bonds, water takes on a gaseous state, and in the meantime, excess energy leaves the body.

The evaporation of water from the mucous membranes of the respiratory tract and evaporation through the surface tissue - the epithelium (even when the skin seems to be dry) is called imperceptible perspiration. The active work of the sweat glands, during which profuse sweating and heat transfer occurs, is called tangible perspiration.

Emission of electromagnetic waves

This heat transfer method works by emitting infrared electromagnetic waves. According to the laws of physics, any object whose temperature rises above the ambient temperature begins to give off heat through radiation.

Human infrared radiation

To prevent excessive heat loss in this way, mankind invented clothing. The fabric of clothing helps create a layer of air, the temperature of which takes on the value of body temperature. This reduces radiation.

The amount of heat dissipated by an object is proportional to the surface area of the radiation. This means that by changing your body position, you can regulate your heat output.

Conduction

Conduction or heat conduction occurs when a person touches any other object. But getting rid of excess heat can only occur if the object with which the person came into contact has a lower temperature.

It is important to remember that air with a low percentage of humidity and fat have a low thermal conductivity value, therefore they are heat insulators.

Convection

The essence of this method of heat transfer is the transfer of energy by air circulating around the body, provided that its temperature is lower than body temperature. Cool air at the moment of contact with the skin warms up and rushes upward, being replaced by a new dose of cold air located lower due to its high density.

Clothing plays an important role in preventing the body from losing too much heat during convection. It represents a barrier that slows down air circulation and thus convection.

Thermoregulation center

The center of human thermoregulation is located in the brain, namely in the hypothalamus. The hypothalamus is a part of the diencephalon, which includes many cells (about 30 nuclei). The functions of this formation are to maintain homeostasis (i.e., the body’s ability to self-regulate) and the activity of the neuroendocrine system.

One of the most important functions of the hypothalamus is to ensure and control actions aimed at thermoregulating the body.

When performing this function in the center of thermoregulation in a person, the following processes occur:

Peripheral and central thermoreceptors transmit information to the anterior hypothalamus.
Depending on whether our body needs heating or cooling, the heat production center or the heat transfer center is activated.

When impulses are transmitted from cold receptors, the heat production center begins to function. It is located at the back of the hypothalamus. From the nuclei, impulses move through the sympathetic nervous system, increasing the rate of metabolic processes, constricting blood vessels, and activating skeletal muscles.

If the body begins to overheat, the heat transfer center begins to actively work. It is located in the nuclei of the anterior hypothalamus. The impulses that arise there are antagonists of the heat production mechanism. Under their influence, a person’s blood vessels dilate, sweating increases, and the body cools down.

Other parts of the central unequal system also take part in human thermoregulation, namely the cerebral cortex, the limbic system and the reticular formation.

The main function of the temperature center in the brain is to maintain a constant temperature regime. It is determined by the total value of the body’s temperature, when both mechanisms (heat production and heat transfer) are least active.

The internal secretion organs also play an important role in the thermoregulation of the human body. At low temperatures, the thyroid gland increases the production of hormones that accelerate metabolic processes. The adrenal glands have the ability to control heat loss through hormones that regulate oxidation processes.

Disorders of thermoregulation of the body: causes, symptoms and treatment

Thermoregulation disorders are sudden changes in body temperature or deviations from the norm of 36.6 degrees Celsius.

Temperature fluctuations can be caused by both external and internal factors, such as diseases.

Experts distinguish the following thermoregulation disorders:

chills;
chills with hyperkinesis (involuntary muscle contractions);
hypothermia (hypothermia). Dedicated to hypothermia;
hyperthermia (overheating of the body).

There are many reasons for thermoregulation disorders, the most common of which are listed below:

Acquired or congenital defect of the hypothalamus (if this is the problem, then temperature changes may be accompanied by malfunctions in the gastrointestinal tract, respiratory system, and cardiovascular system).
Climate change (as an external factor).
Alcohol abuse.
A consequence of the aging process.
Mental disorders.
Vegetative-vascular dystonia (on our website you can read about temperature changes during VSD).

Depending on the cause, temperature changes can be accompanied by various symptoms, common of which are fever, headache, loss of consciousness, disruptions in the digestive system, and rapid breathing.

If there are disturbances in the body's temperature regulation, you should consult a neurologist. The basic principles of treating this problem are:

taking medications that affect the patient’s emotional state (if the cause is mental disorders);
taking medications that affect the activity of the central nervous system;
taking medications that promote increased heat transfer in the blood vessels of the skin;
general therapy, which includes: physical activity, hardening, healthy eating, taking vitamins.

Heat exchange between a person and the environment. A person is constantly in a state of exchange of heat with the environment. Human activity is accompanied by the continuous release of heat into the environment. Its amount depends on the degree of physical stress in certain climatic conditions and ranges from 85 J/s (at rest) to 500 J/s (during hard work). For the normal course of physiological processes in the human body, it is necessary that the heat generated by the body (Qt) be completely given to the environment (Qt), that is, there would be heat balance Q tv = Q then. An excess of heat release from the body over heat transfer to the environment (Qt > Qto) leads to heating of the body and an increase in body temperature. This thermal well-being is characterized by the concept hot. On the contrary, the excess of heat transfer over heat release (Q TV< Q то) приводит к охлаждению организма и снижению его температуры. Такое тепловое самочувствие характеризуется понятием Cold.

One of the important indicators of the body’s thermal state is the average body temperature (internal organs) of about 36.5 °C. Even minor deviations from this temperature in one direction or another lead to a deterioration in a person’s well-being. It depends on the degree of disturbance of the thermal balance and the level of energy consumption when performing physical work.

Heat exchange between the human body and the environment depends on microclimate parameters: ambient temperature, air speed, relative air humidity. To understand the influence of a particular indicator on heat transfer, it is necessary to consider the mechanisms by which heat is transferred from one object to another (in particular, from a person to the environment and vice versa).

The release of heat by the human body occurs through:

Thermal conductivity Q t;

Convection q k as a result of washing away the human body with air;

Radiation to surrounding surfaces Q from;

Evaporation of moisture from the surface of the skin Q is and during breathing Q c.

Heat can only be transferred from a body at a higher temperature to a body at a lower temperature. The intensity of heat transfer depends on the difference in body temperatures (in our case, this is the temperature of the human body and the temperature of the objects and air surrounding the person) and the heat-insulating properties of clothing. Since the human body temperature relative to the value of 36.5 ° C changes in a small range, the change in heat transfer from a person occurs mainly due to changes in the temperature of the human environment. If the temperature of the air or objects surrounding a person is higher than 36.5 ° C, there is no transfer of heat from the person, but, on the contrary, heating of the person.

Human clothing has heat-insulating properties: the warmer it is, the less heat transfers from a person to the environment. Thus, it is possible to regulate the heat exchange between a person and the environment due to the ambient temperature and the choice of clothing with different heat-insulating properties.

Air near a warm object heats up. Heated air has a lower density and, being lighter, rises, and its place is taken by colder air from the environment. The phenomenon of exchange of portions of air due to the difference in densities of warm and cold air is called natural convection.

If a warm object is blown with cold air, then the process of replacing the warmer layers of air in the object with colder ones accelerates. In this case, the heated object will have colder air, the temperature difference between the heated object and the surrounding air will be greater and the intensity of heat transfer from the object to the surrounding air will increase. This phenomenon is called forced convection. Thus, heat exchange between a person and the environment can be regulated by changing the speed of air movement, i.e. The lower the ambient temperature and the higher the air speed, the greater the transfer of heat by convection.

Thermal energy, transforming on the surface of a hot body into radiant (electromagnetic wave) - infrared radiation, is transferred to another (cold surface), where it again turns into heat. The greater the temperature difference between a person and surrounding objects, the higher the radiant flux. Moreover, the radiant flux can come from a person if the temperature of surrounding objects is less than the temperature of the person, and vice versa, if the surrounding objects are more heated, i.e. The lower the temperature of the surfaces surrounding a person, the greater the radiant flux during heat exchange by radiation.

The intensity of evaporation, and therefore the amount of heat transfer from the body to the environment, depends: firstly, on the ambient temperature: the higher the temperature, the higher the intensity of evaporation; secondly, on air humidity: the higher the humidity, the lower the intensity of evaporation; thirdly, on the speed of movement: the intensity of evaporation increases with increasing air speed; fourthly, on the intensity of work: the level of sweating increases in proportion to the severity of the work performed.

During the process of breathing, the ambient air entering the human lungs is heated and at the same time saturated with water vapor. Thus, heat is removed from the human body with exhaled air (Qв). The amount of heat released by a person with exhaled air depends on his physical activity, humidity and temperature of the surrounding (inhaled) air. The greater the physical activity and the lower the ambient temperature, the more heat is released with the exhaled air. As the temperature and humidity of the surrounding air increase, the amount of heat removed through respiration decreases.

Thus, the direction of heat flows Q t Q to Q from can be from a person to the air and objects surrounding him and vice versa, depending on what is greater - the temperature of the person’s body or the surrounding air and bodies surrounding him.

The heat release of the human body is determined primarily by the magnitude of the muscle load during human activity, and the heat transfer is determined by the temperature of the surrounding air and objects, the speed of movement and the relative humidity of the air.

Microclimate parameters in the natural environment and in industrial conditions can vary within wide limits. Along with changes in microclimate parameters, a person’s thermal well-being also changes. A disturbance in the thermal balance in one direction or another causes reactions in the human body that contribute to its restoration.

The processes of regulating heat generation to maintain a constant human body temperature are called thermoregulation. It allows you to keep the temperature of the internal organs constant (36.5 ° C) and does not contain specific organs. Resistance to cold or heat occurs under the control of the nervous system, which includes specific organs in a specific functional system that ensures maintaining a constant temperature in the most effective and economical way. The physiological system of thermoregulation includes the regulation of heat production and heat transfer.

Thermoregulation is carried out in the following ways: biochemically, by changing the intensity of blood circulation and the intensity of sweating.

Thermoregulation by biochemical means consists of changing the intensity of oxidative processes occurring in the human body. The external manifestation of biochemical regulatory processes is muscle tremors, which, as already mentioned, occurs when the body is hypothermic. Increases heat release to 125...200 J/s. As a result of complex chemical reactions during the digestion of food, heat is generated, which is spent on maintaining life processes: the work of the heart and respiratory organs.

Thermoregulation by changing the intensity of blood circulation lies in the body’s ability to regulate the volume of blood supplied, which in this case can be considered as a carrier of heat from internal organs to the surface of the human body by narrowing or expanding blood vessels.

At high ambient temperatures, the blood vessels of the skin dilate, and more blood flows to it from the internal organs and, therefore, more heat is transferred to the environment.

At low temperatures, the opposite phenomenon occurs: blood vessels narrow, the amount of blood, and, consequently, heat supplied to the skin, decreases, its temperature decreases and, as a consequence, a decrease in the transfer of heat from a person to the environment.

Thermoregulation by changing the intensity of sweating consists in changing the process of heat transfer due to evaporation. Cooling the body through evaporation is of great importance. Thus, at an ambient temperature of 36 °C, heat is transferred from a person to the environment almost exclusively through the evaporation of sweat. All methods are involved in regulating the heat exchange process simultaneously, but to a greater or lesser extent.

It has been experimentally established that optimal metabolism in the body and, accordingly, maximum labor productivity occur if the components of the heat transfer process are within the following limits:

Q to +Q t =30%; Q out of -45

Q is =20% Q in =5%

This balance characterizes the absence of tension in the thermoregulation system.

The parameters of the air microclimate that determine optimal metabolism in the body and in which there are no unpleasant sensations and tension in the thermoregulation system are called comfortable or optimal. The zone in which the environment completely removes the heat generated by the body and there is no tension in the thermoregulatory system is called comfort zone. Conditions under which the normal thermal state of a person is disrupted are called uncomfortable.

With slight tension in the thermoregulation system and slight discomfort, acceptable meteorological conditions are established. When the permissible values of meteorological parameters are exceeded, the thermoregulation system works under strain, a person experiences severe discomfort, the thermal balance is disturbed and the body begins to overheat or hypothermia, depending on which direction the thermal balance is disturbed.

Adaptation and acclimatization when working in heating and cooling climates. The body of those working under conditions of constant exposure to high or low temperatures is in a state of dynamic equilibrium with the external environment (dynamic stereotypy) - This is an equilibrium established due to the adaptation of the human body to certain meteorological conditions.

Adaptation to a heating or cooling microclimate is based on processes aimed at maintaining a certain level and interconnection of physiological systems, organs, control mechanisms that ensure high vital activity of the body.

At the initial stages, adaptation is carried out due to the activation of compensatory mechanisms - primary reflex reactions aimed at eliminating or weakening functional changes in the body caused by thermal stimuli. In the process of adaptation (adaptation), all the activities of the body, through neurohumoral mechanisms, are brought into increasingly precise and subtle balance with the environment.

As a result of the adaptation process, a stable state of the body's vital systems is established in changed microclimatic environmental conditions - acclimatization.

Acclimatization - adaptation to new climatic conditions is a special case of adaptation; it develops as a result of prolonged exposure to high and low temperatures. Characteristic features of adaptation and acclimatization are an improvement in general condition, easier tolerance of high and low temperatures, and a reduction in the period of restoration of physiological functions and performance.

Adaptation to high temperatures is expressed in increased muscle work and a significant decrease in basal metabolism. When working in high room temperatures, adaptation occurs due to a decrease in heat production, the formation of a stable redistribution of blood vessels, so that heat transfer from the body surface is facilitated. Sweating from excessive - in the emergency phase - turns into adequate to the high temperature. During the adaptation process, with severe sweating, a decrease in the concentration of chlorides in sweat is observed, which helps to reduce disturbances in water-salt metabolism. Blood pressure decreases, pulse and respiration rates decrease, and body temperature decreases slightly.

Adaptation to exposure to cold. Frequent and prolonged exposure to cold leads to increased metabolism and increased heat production. When working in cold shops or refrigerators during the first days, in response to low temperatures, heat production increases uneconomically, excessively, heat transfer is not yet sufficiently limited. After establishing a phase of stable adaptation, the processes of heat production become more intense, and heat loss decreases and is ultimately balanced in such a way as to most perfectly maintain a stable body temperature in new conditions.

In this case, active adaptation is joined by mechanisms that ensure adaptation of receptors to cold, that is, an increase in the threshold of stimulation of these receptors. The skin temperature is restored faster, there is less pronounced constriction of the skin vessels, greater blood supply, and the volume of circulating blood increases.

In progress adaptation to infrared radiation the excitability of the receptors decreases, there is a slight increase in heart rate and increase in body temperature, an increase in the intensity of sweating, an increase in the amount of fatty substances and a decrease in the concentration of chlorides in sweat.

Adaptation is observed provided that fluctuations in the parameters of the industrial microclimate do not go beyond the compensatory capabilities of the body. Sharp fluctuations in meteorological conditions make it difficult for the body to adapt to them. Heat stimuli that are excessive in intensity and duration can lead to disruption of adaptation. Failures of adaptation are associated with a decrease in the immunological reactivity of the body and entail a variety of adverse consequences, in particular, increased morbidity.

Violation of the body's thermoregulation or a disorder of the constancy of body temperature is provoked by dysfunction of the central nervous system. When thermoregulation processes are disrupted, two types of reactions are possible. If body temperature rises, peripheral vessels dilate and sweating begins. If the temperature, on the contrary, decreases, the blood vessels narrow, the muscles contract, the limbs become cold, and trembling appears.

Higher animals, which have the property of constant body temperature, have a system for maintaining temperature in balance. Thermoregulation balances heat production and heat release. There are two main types of thermoregulation: chemical (its main mechanism is increased heat generation during muscle contractions - muscle tremors) and physical (increased heat exchange due to the evaporation of fluid from the surface of the body during sweating). In addition, the intensity of metabolic processes and the narrowing or expansion of skin vessels have a certain significance for heat production and heat transfer.

The thermoregulation center is located in the brain stem. In addition, hormones of the endocrine glands play a certain role in thermoregulation, in particular. Violation of body thermoregulation associated with a decrease in temperature is called hypothermia. A disturbance in the thermoregulation of the body in humans associated with an increase in temperature is called hyperthermia.

Violation of thermoregulation processes: hyperthermia

Hyperthermia (overheating) occurs when the mechanisms of thermoregulation are disrupted, in which heat production prevails over heat transfer. Body temperature can reach 43 °C or more.

The most common causes of such a violation of human thermoregulation are an increase in ambient temperature and the appearance of factors that prevent adequate heat transfer (for example, excessively warm clothing, high air humidity, etc.).

When this type of thermoregulation disorder occurs, adaptation mechanisms are activated: behavioral reactions by which a person tries to avoid exposure to excess heat (for example, turning on a fan), strengthening heat transfer mechanisms, reducing heat production and stress response. In accordance with the results of the interaction of hyperthermia and adaptation processes, the stage of compensation and the stage of decompensation of hyperthermia are distinguished.

During the compensation stage, the arterial vessels of the skin expand and the associated increase in heat transfer occurs. With a further increase in temperature, heat transfer begins to occur mainly only due to sweating.

In the stage of decompensation, a violation of adaptation mechanisms is observed, sweating is significantly reduced, body temperature can rise to 41-43 ° C. There is a disruption of the functions and structures of cells due to the direct damaging effects of high temperature, which leads to severe dysfunction of systems and organs, primarily the central nervous system and the cardiovascular system.

Heatstroke- this is a variant of hyperthermia, in which adaptation mechanisms are quickly depleted. This can occur both at high intensity of the thermal factor, and as a result of low efficiency of the adaptation mechanisms of a particular organism. The symptoms of such a violation of thermoregulation are the same as in the stage of decompensation of hyperthermia in general, but more severe and growing much faster, and therefore heat stroke is accompanied by high mortality. The leading mechanisms of the pathogenesis of changes in the body correspond to those during hyperthermia in general. But with such a violation of the thermoregulation of the human body, particular importance is attached to intoxication, acute heart failure, respiratory arrest, swelling and hemorrhages in the brain.

Sunstroke- This is a form of hyperthermia. It occurs due to the direct effect of the heat of the sun's rays on the body. With such a pathology of thermoregulation, the above-described mechanisms of hyperthermia are activated, but the leading one is brain damage.

Pathology of body thermoregulation: fever

Fever should be distinguished from hyperthermia. Fever- this is the body’s reaction to irritants of an infectious and non-infectious nature, characterized by an increase in body temperature. With fever (unlike hyperthermia), a balance between heat production and heat loss is maintained, but at a higher than normal level.

The reason for this violation of thermoregulation is the appearance of pyrogenic substances (pyrogens) in the body. They are divided into exogenous (products of bacterial activity) and endogenous (products of the breakdown of damaged cells, altered blood serum proteins, etc.).

The following stages of this pathology of human thermoregulation are distinguished:

temperature rise stage;
the stage when the temperature is at a higher level than normal;
stage of temperature reduction.

Fever up to 38 °C is called subfebrile, up to 39 °C moderate, or febrile, up to 41 °C - high, or pyretic, above 41 °C - excessive, or hyperpyretic.

The types of temperature curves (graphs of daily temperature fluctuations) can have diagnostic value, as they often differ significantly for various diseases.

Persistent fever is characterized by daily temperature fluctuations of no more than 1 °C. With laxative fever, the difference between morning and evening temperatures is 1-2 °C, and with debilitating (hectic) fever - 3-5 °C. Intermittent fever is characterized by large variations in morning and evening temperatures with periodic normalization. Relapsing fever combines periods of several days during which the temperature is normal, and periods of elevated temperature, which alternate one after another. With perverted fever, the morning temperature exceeds the evening temperature, and atypical fever does not have any patterns at all.

With a sharp decrease in temperature, they speak of a critical decrease, or crisis (this may be accompanied by a pronounced decrease - collapse); its gradual decrease is called lytic, or lysis.

A number of changes occur in systems and organs during fever.

Thus, in the central nervous system during fever, a phenomenon of depression is observed. A concomitant symptom of such a violation of the body's thermoregulation is tachycardia, approximately 8-10 beats per minute for every degree of elevation (however, in some diseases, for example, with, there may be bradycardia, which is associated with the inhibitory effect of a bacterial toxin on the heart). At the height of the fever, breathing may become rapid.

Fever, however, also has a positive meaning. Thus, during fever, the reproduction of some viruses is inhibited, the vital processes and division of many bacteria are suppressed, the intensity of immune reactions increases, the growth of tumors is inhibited, and the body’s resistance to infections increases.

With similar symptoms, the causes of these disturbances in the body’s thermoregulation are different. Fever is caused by pyrogens, and hyperthermia is caused by high ambient temperatures.

With a pathology such as fever, the mechanisms of thermoregulation continue to operate (the balance between heat production and heat transfer occurs to a higher level); with hyperthermia, a breakdown of the thermoregulation mechanisms occurs.

Fever is the body's reaction to certain external and internal influences with certain positive qualities, hyperthermia is, of course, a pathological process harmful to the body.

Impaired body thermoregulation: hypothermia

Hypothermia is a condition characterized by a decrease in body temperature below normal.

The leading cause of such a violation of the body's thermoregulation is a decrease in ambient temperature. In addition, hypothermia against the background of a slight decrease in external temperature is caused by disturbances in heat generation mechanisms: extensive muscle paralysis, impaired heat production due to a decrease in metabolic rate with reduced production of adrenal hormones (including damage to the hypothalamic-pituitary region), as well as an extreme degree of exhaustion. The following factors can also contribute to hypothermia: increased air humidity, wet clothes, immersion in cold water, wind (which increases heat transfer); In addition, fasting, overwork, alcohol intoxication, injuries and illnesses lead to a decrease in the body's resistance to hypothermia. The consequences of impaired thermoregulation can be general hypothermia and local cold injury - frostbite.

According to the time of death, acute (within an hour), subacute (within 4 hours), and slow (over 4 hours) hypothermia are distinguished.

Just as with hyperthermia, the development of hypothermia is divided into a stage of compensation and a stage of decompensation.

The compensation stage is characterized by behavioral reactions (a person tries to warm up), a decrease in heat transfer (skin vessels narrow, sweating stops), an increase in heat production (BP and heart rate increase, blood flow in internal organs and the intensity of metabolic processes in organs and tissues increases, muscle tremors appear). Body temperature decreases slightly.

If the cold continues to act, and the adaptation mechanisms cannot cope with its pathogenic effects, then the stage of decompensation begins. The thermoregulation system is disrupted, the brain's regulatory centers are depressed, which leads to a drop in cardiac activity, a weakening of breathing intensity, hypoxia and acidosis, dysfunction of organs and tissues, as well as microcirculation. The consequence of this is a disturbance in the exchange of water and electrolytes and the appearance of cerebral edema. Death occurs due to cessation of blood circulation and respiration due to increasing inhibition of the regulatory centers of the central nervous system.

Frostbite usually affects areas of the body that are not protected or poorly protected by clothing (nose, ears, fingers and toes). In response to exposure to cold, signs of thermoregulation disorders occur, such as spasm of skin vessels, followed by their dilation and arterial hyperemia; with continued exposure to cold, secondary vasospasm may occur, which leads to tissue ischemia and damage, including necrosis of the skin and deeper tissues.

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Introduction

1. The hypothalamus is your thermostat

1.1 Conduction and convection

1.2 Radiation

1.3 Evaporation

2.1 Sweat glands

2.2 Smooth muscle surrounding arterioles

2.3 Skeletal muscle

2.4 Endocrine glands

3. Adaptation and thermoregulation

3.1 Adaptation to low temperatures

3.1.1 Physiological responses to exercise in low ambient temperatures

3.1.2 Metabolic reactions

3.2 Adaptation to high temperatures

3.3 Assessment of thermal irritations

4. Mechanisms of thermoregulation

Mechanisms that regulate body temperature are similar to a thermostat that regulates the ambient air temperature, although they have a more complex functioning and higher accuracy. Sensitive nerve endings - thermoreceptors - detect changes in body temperature and transmit this information to the body's thermostat - the hypothalamus. In response to changes in receptor impulses, the hypothalamus activates mechanisms that regulate the warming or cooling of the body. Like a thermostat, the hypothalamus has a baseline temperature level that it tries to maintain. This is normal body temperature. The slightest deviation from this level leads to a signal being sent to the thermoregulatory center located in the hypothalamus about the need for correction (Fig. 1).

Changes in body temperature are perceived by two types of thermoreceptors: central and peripheral. Central receptors are located in the hypothalamus and control the temperature of the blood flowing through the brain. They are very sensitive to the slightest (from 0.01°C) changes in blood temperature. Changing the temperature of the blood passing through the hypothalamus activates reflexes that, depending on need, either retain or release heat.

Peripheral receptors, localized over the entire surface of the skin, control the ambient temperature. They send information to the hypothalamus as well as the cerebral cortex, providing conscious perception of temperature so that you can voluntarily control whether you are in a cold or hot environment.

In order for a body to transfer heat to the environment, the heat it generates must “have access” to the external environment. Heat from deep in the body (core) is transported by the blood to the skin, from where it can be transferred to the environment through one of the following four mechanisms: conduction, convection, radiation and evaporation. (Fig. 2)

1.1 Conduction and convection

Heat conduction is the transfer of heat from one object to another due to direct molecular contact. For example, heat generated deep within the body can be transferred through adjacent tissues until it reaches the surface of the body. It can then be transferred to clothing or the surrounding air. If the air temperature is higher than the surface temperature of the skin, the heat of the air is transferred to the surface of the skin, increasing its temperature.

Convection is the transfer of heat through a moving stream of air or liquid. The air around us is in constant motion. Circulating around our body, touching the surface of the skin, the air carries away molecules that have received heat as a result of contact with the skin. The stronger the air movement, the higher the intensity of heat transfer due to convection. When combined with conduction, convection can also provide an increase in body temperature when in an environment with high air temperatures.

1.2 Radiation

At rest, radiation is the main process by which the body transfers excess heat. At normal room temperature, the body of a naked person transfers about 60% of its “excess” heat through radiation. Heat is transmitted in the form of infrared rays.

1.3 Evaporation

Evaporation is the primary heat dissipation process during exercise. During muscular activity, the body loses about 80% of heat due to evaporation, while at rest - no more than 20%. Some evaporation occurs without us noticing, but as the liquid evaporates, heat is also lost. These are the so-called imperceptible heat losses. They make up about 10%. It should be noted that insensible heat loss is relatively constant. As body temperature rises, the process of sweating intensifies. When sweat reaches the surface of the skin, the heat from the skin changes it from a liquid to a gaseous state. Thus, as body temperature rises, the role of sweating increases significantly.

The transfer of heat by the body to external harm is carried out by conduction, convection, radiation and evaporation. When performing physical activity, the main mechanism for heat transfer is evaporation, especially if the ambient temperature approaches body temperature.

2. Effectors that change body temperature

When body temperature fluctuates, the restoration of normal body temperature is usually carried out by the following four factors:

1) sweat glands;

2) smooth muscle surrounding the arterioles;

3) skeletal muscles;

4) a number of endocrine glands.

When the temperature of the skin or blood rises, the hypothalamus sends impulses to the sweat glands about the need for active secretion of sweat, which moisturizes the skin. The higher your body temperature, the more you sweat. Its evaporation removes heat from the surface of the skin.

When the temperature of the skin and blood increases, the hypothalamus sends signals to the smooth muscles of the arterioles that supply blood to the skin, causing them to dilate. As a result, blood supply to the skin increases. Blood carries heat from deep within the body to the surface of the skin, where it is dissipated into the external environment by conduction, convection, radiation and evaporation.

Skeletal muscle comes into action when there is a need to generate more heat. In conditions of low air temperature, skin thermoreceptors send signals to the hypothalamus. In the same way, when the blood temperature decreases, the change is recorded by the central receptors of the hypothalamus. In response to the information received, the hypothalamus activates brain centers that regulate muscle tone. These centers stimulate the tremor process, which is a rapid cycle of involuntary contraction and relaxation of skeletal muscles. As a result of this increased muscle activity, more heat is produced to maintain or increase body temperature.

Body cells increase their metabolic rate under the influence of a number of hormones. This affects heat balance as increased metabolism causes increased energy production. Cooling the body stimulates the release of thyroxine from the thyroid gland. Thyroxine can increase the metabolic rate in the body by more than 100%. In addition, adrenaline and norepinephrine increase the activity of the sympathetic nervous system. Consequently, they directly affect the metabolic rate of almost all cells of the body. What happens to the human body when temperature parameters change? In this case, it develops specific adaptation reactions in relation to each factor, that is, it adapts. Adaptation is the process of adapting to environmental conditions. How does adaptation to temperature changes occur?