Thermoregulation of the body. hardening

In the processes of homeostasis in all warm-blooded animals and humans great importance has thermoregulation - the ability to maintain body temperature at a constant level, regardless of fluctuations in ambient temperature ( isotherm ). Unlike animals, whose body temperature is directly dependent on the ambient temperature (amphibians, reptiles, fish), the level of body temperature of warm-blooded organisms allows them to maintain their activity in different conditions habitats, thus increasing their adaptive capacity.

The constancy of body temperature is due to the processes of heat generation and heat transfer. These processes are regulated by complex reflex acts, which arise in response to temperature irritation of the receptors of the skin, skin and subcutaneous vessels, as well as the central nervous system. Thermoreceptors that perceive cold or heat are located in the anterior part of the hypothalamus, in the reticular formation of the midbrain, and also in the spinal cord (see Fig. Nervous system). The hypothalamus contains the main thermoregulatory centers that coordinate complex processes providing isotherm. The centers of some thermoregulatory reflexes are located in the spinal cord, a certain part in the processes of thermoregulation is taken by the cerebral cortex, glands internal secretion(primarily thyroid and adrenals). When cooled, the thyroid gland more actively secretes a hormone that activates metabolism and, as a result, increases heat production. The adrenal glands increase the secretion of adrenaline, which narrows the skin vessels, reducing heat transfer, and increases heat generation due to increased oxidation processes in the tissues.

Since different organs have different metabolic activity, their temperature may vary. The liver has the highest temperature (37.8–38°C), as it is located deep inside the body and has the most high level metabolic processes. The temperature of the skin is more dependent on the ambient temperature and, due to the high heat transfer, is the lowest (30–34 ° C), while it can vary significantly: the highest on the trunk and head, the lowest on the extremities.

Body temperature has a circadian (circadian) regime and ranges from 0.5–0.7°C: the maximum is observed during muscular work and at 16–18 pm, the minimum is at rest and at 3–4 am. Measure body temperature in armpit(36.5–36.9°C), at infants often in the rectum, where it is higher and is 37.2-37.5 ° C.

The constancy of body temperature in humans is maintained only when the processes of heat generation and heat transfer of the body are in equilibrium (Fig. 1.25). This is achieved through physical and chemical mechanisms of thermoregulation.

Chemical thermoregulation occurs through the activation of metabolic processes in the tissues of the body, leading to increased heat generation. In humans, an increase in heat generation is noted when the ambient temperature drops below the optimum (the so-called thermal comfort zone). In clothes, the comfort temperature is 18-20°C, without it - 28°C. The most intense heat generation is observed in the muscles, liver and kidneys.

Physical thermoregulation occurs through a decrease or increase in heat transfer due to a change in heat radiation (radiative heat transfer), convection (mixing of air heated by the body) and evaporation of water from the surface of the skin and lungs. At rest at a temperature of 20 ° C in humans, radiation is 66%, evaporation - 19%, convection - 15% total loss body heat. The layer of subcutaneous fatty tissue prevents heat transfer, since its adipose tissue has low thermal conductivity, and clothing that creates a layer of still air around the body.

Rice. 1.25.

Heat transfer by radiation and convection is possible only at ambient temperatures up to 35 ° C, at higher air temperatures the body temperature is maintained only by evaporation of sweat; heat transfer by evaporation and with intense muscle load becomes the leading one. The efficiency of this type of heat transfer depends on the humidity of the air and the breathability of the clothing. Breathing is also involved in maintaining body temperature: during exhalation, the lungs release water in the form of water vapor, this type of heat transfer is regulated by a change in the respiratory rate.

An important mechanism of thermoregulation is the redistribution of blood in the vessels and the volume of circulating blood. At low temperatures, the arterioles of the skin narrow, large quantity blood enters the vessels abdominal cavity, as a result of which heat transfer is limited, and the internal organs are additionally warmed. With even stronger cooling, the vessels that ensure the discharge of blood from the arteries into the veins (arteriovenous anastomoses) open, and the flow of blood into the capillaries further decreases. With an increase in body temperature, the skin vessels expand, the volume of blood flowing through the skin vessels increases, which leads to cooling of the blood in the skin vessels due to heat transfer from the body surface (Fig. 1.26).

Rice. 1.26. The mechanism of heat transfer in the cold (A) and in heat(B)

Additional means of thermoregulation can serve as a change in body position, goosebumps, chills. So, when a person is cold, he curls up into a "ball", reducing the heat transfer surface. " Goose pimples"- a rudimentary reaction that has been preserved in humans in the process of evolution from animal ancestors covered with wool - allows you to raise the wool, thus increasing the layer of warm still air around the body and close excretory ducts sweat glands, reducing the evaporation of water from the surface of the body. Chills that occur when hypothermia leads to additional education heat as a result muscle work (small shiver), which goes to warm the body.

Changes in thermoregulation in ontogeny. In the process of ontogenesis, the ability to maintain a constant body temperature develops gradually. A newborn baby is characterized by unstable thermoregulation: it easily occurs cooling or overheating of the body when the ambient temperature changes, even a small muscle load (prolonged crying) can lead to an increase in body temperature. The ability to thermoregulate in premature babies is very low, so they need special conditions to maintain body temperature.

The main thermoregulatory reactions of the body are formed in infancy. In the first months of life, protection against heat loss by the body is carried out mainly by subcutaneous fatty tissue. Such a static mechanism does not allow sufficient regulation of heat transfer in accordance with the current situation, so children infancy easily exposed to hypothermia and overheating. The child's body is adapted to reduce heat transfer from a relatively large surface of the body, mainly due to thermal insulation by subcutaneous fatty tissue. In addition, at this age, brown adipose tissue functions in the child's body. It is saturated with mitochondria involved in intracellular energy processes, and "warms" the large vessels located along the spine. Vasomotor reactions, which determine the tone of superficially located vessels and regulate heat transfer, are actively formed during the first year of life. Since they are still imperfect, hypothermia or overheating of the body easily occurs, therefore, when caring for babies and raising them, the thermal regime must be observed quite strictly. After a year, muscles begin to connect to the production of heat, and brown adipose tissue gradually ceases to function. However, heat transfer mechanisms are still imperfect and the comfort temperature remains high - about 30°C. At the age of 3 to 7 years, a significant place is occupied by the mechanisms of chemical (metabolic) thermoregulation. From the age of 6, a rapid improvement in the vasomotor reactions of peripheral vessels begins, and by the age of 10, physical thermoregulation approaches the level of an adult in its effectiveness. AT adolescence blood flow increases, which leads to an increase in skin temperature. In addition, instability vascular tone, characteristic of this age, reduces the possibilities of physical thermoregulation, and in order to maintain a constant body temperature, it again becomes necessary to increase heat production due to the activation of metabolic processes. Therefore, in puberty the possibilities of thermoregulation are reduced, reducing in a certain way the adaptive resources of the body. AT adolescence temperature homeostasis becomes more stable, thermoregulatory reactions are more economical. In the elderly and old age slow down metabolic processes, the possibilities of adaptive regulation of vascular tone and the muscle component of physical thermoregulation are reduced, which leads to a decrease in body temperature, an easy occurrence of hypothermia, inflammatory and colds.

For normal flow physiological processes in the human body, it is necessary that the heat released by the body be completely removed to the environment, since the functioning of the body requires the flow of chemical and biochemical processes in it in sufficient strict temperature limits (36.5 - 37.0 ° C).

Conditions that violate the heat balance cause responses in the body that contribute to its recovery due to the adaptive and compensatory capabilities of the body.

Heat management processes to maintain constant temperature human body within 36 - 37 ° C are called thermoregulation.

Thermoregulation is a physiological process controlled by the central nervous system..

The processes of heat release regulation are carried out mainly in three ways: biochemical; by changing the intensity of blood circulation and the intensity of perspiration.

Thermoregulation by biochemical means It consists in changing the intensity of metabolism (oxidative processes) when the body is overheated or cooled.

Thermoregulation by changing the intensity of blood circulation is the ability of the body to regulate the supply of blood (coolant) from internal organs to the surface of the body, as a result of narrowing or expansion blood vessels depending on the ambient temperature. The blood supply at high temperatures can be 20 to 30 times greater than at low temperatures. In the fingers, the blood supply can change 600 times.

Thermoregulation by changing the intensity of excretion sweat is carried out by changing the process of heat transfer and as a result of evaporation of the released sweat.

Thermoregulation of the body is carried out simultaneously by all means, which eliminates hypothermia and overheating of the body, as it ensures a balance between the amount of heat continuously generated in the body (chemical thermoregulation) and the excess heat continuously given off to the environment (physical thermoregulation), i.e., heat balance is maintained organism.

Thermoregulation ( Q) can be represented as follows:

Q = M ± R ± C – E(1)

Maintaining a constant body temperature is determined by the body's heat production M, that is, the processes of metabolism in cells (digestion of food, burning of sugar and fat stores), produced as a result of physical activity(performing work, the energy consumption of which determines the category of work, involuntary muscle trembling).

Heat dissipation or heat gain R at the expense infrared radiation the body into the surrounding space or irradiation with an infrared stream of the surface of the human body from this space;

heat transfer or heat gain C by convection, that is, through heating or cooling of the body by air washed over the surface of the body;

heat dissipation E, due to the evaporation of moisture from the surface of the skin, mucous membranes of the upper respiratory tract, lungs.

A change in microclimate parameters causes a change percentage quantities that determine the heat balance of the human body.

AT normal conditions with a weak movement of air, a person at rest loses about 45% of all the thermal energy produced by the body as a result of thermal radiation; convection up to 30% and evaporation up to 25%.

At the same time: over 80% of the heat is given off through the skin, about 1-3% through the respiratory organs, about 7% of the heat is spent on warming the food, water and inhaled air.

With an increase in the temperature of the outside air and the same values ​​of relative humidity, the evaporation of the skin increases as a result of sweating from the surface of the human body. sweating plays important role in maintaining human comfort. So, under normal atmospheric conditions, the body releases from 0.4 to 0.6 liters of sweat per day, and 0.6 kcal is expended per hour of perspiration. When working in conditions elevated temperature and humidity, the heat transfer of the body is difficult.

Biology and genetics

There are several mechanisms of heat transfer to the environment. Radiation is the release of heat in the form of electromagnetic waves in the infrared range. The amount of heat dissipated by the body into the environment by radiation is proportional to the surface area of ​​the radiation, the surface area of ​​the body not covered by clothing and the temperature gradient. At an ambient temperature of 20°C and a relative humidity of 4060, the body of an adult person dissipates by radiation about 4050 of the total heat given off.

Thermoregulation, types of thermoregulation.

thermoregulation this is a set of physiological processes whose activity is aimed at maintaining the relative constancy of the core temperature in conditions of changing environmental temperature by regulating heat production and heat transfer. Thermoregulation is aimed at preventing violations of the thermal balance of the body or at its restoration, if such violations have already occurred, and is carried out by the neuro-humoral way.

Thermoregulation can be divided into two main types: chemical and physical thermoregulation.

They, in turn, are also divided into several types:

1. Chemical thermoregulation

Contractile thermogenesis

non-shivering thermogenesis.

1. Physical thermoregulation

Radiation.

Heat conduction (conduction)

Convection

Evaporation

Consider these types of thermoregulation in more detail.

Chemical thermoregulation

Contractile thermogenesis

This type of thermoregulation works when we are cold and need to raise our body temperature. This method consists in muscle contraction.

With muscle contraction, ATP hydrolysis increases, therefore, the flow of secondary heat, which goes to warm the body, increases.

Voluntary activity of the muscular apparatus, mainly occurs under the influence of the cortex hemispheres. At the same time, an increase in heat production is possible by a factor of 35 compared to the value of the main exchange.

Usually, with a decrease in the temperature of the environment and blood temperature, the first reaction is an increase in thermoregulatory tone.(hair on the body "stands on end", "goosebumps" appear). From the point of view of the mechanics of contraction, this tone is a microvibration and allows you to increase heat production by 25-40% of the initial level. Usually, the muscles of the head and neck take part in creating the tone.

With more significant hypothermia, the thermoregulatory tone turns intomuscle cold shiver. Cold shivering is an involuntary rhythmic activity of superficially located muscles, as a result of which heat production increases. It is believed that heat production during cold shivering is 2.5 times higher than during voluntary muscle activity.

The described mechanism works on reflex level without the participation of our consciousness. But it is possible to raise the body temperature with the help of conscious physical activity.

While doing physical activity of different power, heat production increases by 515 times compared with the rest level. During the first 1530 minutes of continuous operation, the core temperature rises rather quickly to a relatively stationary level, and then remains at this level or continues to rise slowly.

Non-shivering thermogenesis

This type of thermoregulation can lead to both an increase and a decrease in body temperature.

It is carried out by accelerating or slowing down catabolic metabolic processes. And this, in turn, will lead to a decrease or increase in heat production. Due to this type of thermogenesis, heat production can increase by 3 times.

The regulation of the processes of non-shivering thermogenesis is carried out by activating the sympathetic nervous system, the production of thyroid hormones and the adrenal medulla.

Physical thermoregulation

Physical thermoregulation is understood as a set of physiological processes leading to a change in the level of heat transfer. There are several mechanisms of heat transfer to the environment.

1. Radiation Heat transfer in the form of infrared electromagnetic waves. Radiation gives energy to all objects whose temperature is higher absolute zero. Electromagnetic radiation travels freely through a vacuum, atmospheric air for it, too, can be considered "transparent". The amount of heat dissipated by the body into the environment by radiation is proportional to the surface area of ​​the radiation (surface area of ​​the body not covered by clothing) and the temperature gradient. At an ambient temperature of 20°C and a relative air humidity of 4060%, the body of an adult person dissipates by radiation about 4050% of all heat given off.
2. Heat conduction (conduction)a method of heat transfer during direct contact of the body with other physical objects. The amount of heat given off to the environment in this way is proportional to the difference in the average temperatures of the contacting bodies, the area of ​​the contacting surfaces, the time of thermal contact and thermal conductivity.
3. Convection heat transfer, carried out by the transfer of heat by moving particles of air (water). The air in contact with the skin heats up and rises, its place is taken by a “cold” portion of air, etc. Under conditions of thermal comfort, the body loses up to 15% of all heat given off in this way.
4. Evaporation transfer of thermal energy to the environment due to the evaporation of sweat or moisture from the surface of the skin and mucous membranes of the respiratory tract. Due to evaporation, the body at a comfortable temperature gives off about 20% of all dissipated heat. Evaporation is divided into 2 types.

Imperceptible perspirationevaporation of water from the mucous membranes of the respiratory tract(through breath) and water seeping through the epithelium of the skin (Evaporation from the surface of the skin.It goes even if the skin is dry.).

In a day through Airways up to 400 ml of water evaporates, i.e. the body loses up to 232 kcal per day. If necessary, this value can be increased due to thermal shortness of breath.

About 240 ml of water seeps through the epidermis on average per day. Therefore, in this way the body loses up to 139 kcal per day. This value, as a rule, does not depend on the processes of regulation and various environmental factors.

Perceived perspirationHeat dissipation through evaporation of sweat . On average, 400500 ml of sweat is released per day at a comfortable temperature of the environment, therefore, up to 300 kcal of energy is given off. However, if necessary, the volume of sweating can increase up to 12　 l per day, i.e. By sweating, you can lose up to 7000 kcal per day.

The efficiency of evaporation largely depends on the environment: the higher the temperature and the lower the humidity, the higher the efficiency of perspiration as a heat transfer mechanism. At 100% humidity, evaporation is impossible.

Thermoregulation called the ability of the human body to regulate heat exchange with the environment and maintain body temperature within certain limits (36.1 - 37.2 ° C).

Thermoregulation is provided by changing two components of the heat exchange process: heat production and heat transfer.

Of the two ways to maintain thermal equilibrium, the regulation of heat transfer is of primary importance, since. this path is more variable and manageable in the body, while the regulation of heat production plays a positive role mainly when low temperatures air, at high temperatures, the possibility of regulating heat transfer by reducing heat production is limited.

Normal thermal well-being takes place when the thermal balance is maintained

Qt.r.= Qt.v.

Here Qt.o.- the amount of heat generated by a person, and Qt.v.- the amount of heat received by a person from the environment. This correspondence characterizes the environment as comfortable. In conditions of comfort, a person does not experience thermal sensations of cold or overheating that disturb him.

The heat balance equation (“man - environment”) has the form

Qt.o. \u003d q to + q t + q and + q use + q d,

where q to is the convection index;

q t- an indicator of thermal conductivity through clothing;

q and is the radiation index;

q Spanish - skin evaporation rate;

q d - rate of evaporation of moisture during breathing.

Heat exchange between a person and the environment is carried out: convection as a result of washing the body with air ( q to), thermal conductivity through clothing ( q t), radiation to the surrounding surfaces ( q and), evaporation of moisture from the surface of the skin ( q Spanish), evaporation of moisture during breathing ( q d).

The amount of heat generated by the human body depends on the degree physical tension in certain climatic conditions and ranges from 85 (at rest) to 500 J / s (hard work). At rest at an ambient temperature of +18 °C, the proportion q to and q t is about 30%, q and– 45%, q Spanish - 20%, q d - 5% of all heat removed.

The processes of heat emission regulation are carried out mainly in three ways: biochemically; by changing the intensity of blood circulation and the intensity of perspiration.

Thermoregulation by biochemical means is to change the intensity of oxidative processes occurring in the body. For example, muscle tremors that occur when the body is strongly cooled increase the release of heat up to 125...200 J/s.

Thermoregulation by changing the intensity of blood circulation is the ability of the body to regulate the flow of blood (which is in this case a coolant) from the internal organs to the surface of the body by narrowing or expanding blood vessels. The transfer of heat with the blood flow is of great importance due to the low coefficients of thermal conductivity of tissues. human body- 0.314..1.45 W/(m °C). At high temperatures environment, the blood vessels of the skin expand and blood flows to it from the internal organs a large number of blood and, consequently, more heat is given off environment. At low temperatures, the opposite phenomenon occurs: narrowing of the blood vessels of the skin, a decrease in blood flow to skin and therefore less heat is given off external environment. In the fingers, the blood supply can change even 600 times.

Thermoregulation by changing the intensity of perspiration is to change the process of heat transfer due to evaporation. Evaporative cooling of the human body is of great importance. So, at 1L = 18°C,<р = 60 %, и» = 0 количество теплоты, отдаваемой человеком в окружающую среду при испарении влаги, составляет около 18 % общей теплоотдачи. При увеличении температуры окружающей среды до + 27°С доля (?„ возрастает до 30 % и при 36,6° С достигает 100 %.

Thermoregulation of the body is carried out simultaneously in all ways. So, with a decrease in air temperature, an increase in heat transfer due to an increase in temperature difference is prevented by such processes as a decrease in skin moisture and, consequently, a decrease in heat transfer by evaporation, a decrease in the temperature of the skin by reducing the intensity of blood transport from internal organs and, at the same time, a decrease in temperature difference .

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: e * 5% This balance characterizes the absence of tension in the thermoregulation system.

The parameters of the microclimate of the air environment, which determine the 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 thermoregulation system, is called the comfort zone. Conditions under which the normal thermal state of a person is violated are called uncomfortable. With a slight tension in the thermoregulation system and slight discomfort, acceptable meteorological conditions are established.

Body temperature

Body temperature- This is an indicator of heat transfer in the body, which is a biological constant.

- Poikilothermia- non-constant body temperature, depending on the ambient temperature (cold-blooded animals).

- Homeothermia- constant body temperature, independent of the environment (warm-blooded animals).

- Isothermia- constant body temperature.

During the day, there is an increase and decrease in body temperature. The minimum t of the body is at 2 - 4 o'clock in the morning, the maximum t at 16 - 19 o'clock. The temperature is different in different parts of the body and in different organs. The hottest organ is the liver, its temperature is 38-40 °C. In the rectum t is 37.2 - 37.5 ° C, in the armpit 36.6 - 36.8 ° C,

Types of thermoregulation

Constancy of body temperature it is possible only if the amount of heat generated in the body is equal to the amount of heat given off by it to the environment, i.e. it is determined by the equality of heat generation and heat transfer.

Thermoregulation includes

Chemical thermoregulation- the process of generating heat in the body (heat production).