Humans, as is known, belong to homeothermic, or warm-blooded, organisms. Does this mean that his body temperature is constant, i.e. does the body not respond to changes in ambient temperature? Reacts, and even very sensitively. The constancy of body temperature is, in fact, the result of continuously occurring reactions in the body that maintain its thermal balance unchanged.

From the point of view of metabolic processes, heat production is a side effect of chemical reactions of biological oxidation, during which nutrients entering the body - fats, proteins, carbohydrates - undergo transformations resulting in the formation of water and carbon dioxide. The same reactions with the release of thermal energy occur in the organisms of poikilothermic, or cold-blooded, animals, but due to their significantly lower intensity, the body temperature of poikilothermic animals only slightly exceeds the ambient temperature and changes in accordance with the latter.

All chemical reactions occurring in a living organism depend on temperature. And in poikilothermic animals, the intensity of energy conversion processes, according to Van’t Hoff’s rule*, increases in proportion to the external temperature. In homeothermic animals, this dependence is masked by other effects. If a homeothermic organism is cooled below a comfortable ambient temperature, the intensity of metabolic processes and, consequently, its heat production increases, preventing a decrease in body temperature. If thermoregulation in these animals is blocked (for example, due to anesthesia or damage to certain areas of the central nervous system), the curve of heat production versus temperature will be the same as for poikilothermic organisms. But even in this case, significant quantitative differences remain between metabolic processes in poikilothermic and homeothermic animals: at a given body temperature, the intensity of energy metabolism per unit of body mass in homeothermic organisms is at least 3 times higher than the metabolic intensity in poikilothermic organisms.

Many non-mammalian and non-avian animals are able to change their body temperature to some extent through “behavioral thermoregulation” (for example, fish can swim into warmer water, lizards and snakes can take “sunbathing”). Truly homeothermic organisms are capable of using both behavioral and autonomous methods of thermoregulation; in particular, they can, if necessary, produce additional heat due to the activation of metabolism, while other organisms are forced to rely on external sources of heat.

The temperature of most warm-blooded mammals ranges from 36 to 40 °C, despite significant differences in body size. At the same time, the metabolic rate (M) depends on body weight (m) as its exponential function: M = k x m 0.75, i.e. the value of M/m 0.75 is the same for a mouse and an elephant, although in a mouse the metabolic rate per 1 kg of body weight is significantly higher than in an elephant. This so-called law of decrease in metabolic rate depending on body weight reflects the fact that heat production corresponds to the intensity of heat transfer into the surrounding space. For a given temperature difference between the internal environment of the body and the environment, heat loss per unit of body mass turns out to be greater, the greater the ratio between the surface and volume of the body, and the latter ratio decreases with increasing body size.

Body temperature and heat balance

When additional heat is required to maintain a constant body temperature, it can be generated by:

1) voluntary motor activity;
2) involuntary rhythmic muscle activity (shivering caused by cold);
3) acceleration of metabolic processes not associated with muscle contraction.

In adults, shivering is the most important involuntary mechanism of thermogenesis. “Non-shivering thermogenesis” occurs in newborn animals and children, as well as in small, cold-adapted animals and in hibernating animals. The main source of “non-shivering thermogenesis” is the so-called brown fat, a tissue characterized by an excess of mitochondria and a “multilacular” distribution of fat (numerous small droplets of fat surrounded by mitochondria). This tissue is found between the shoulder blades, in the armpits and in some other places.

In order for body temperature not to change, heat production must equal heat transfer. According to Newton's law of cooling, the heat given off by a body (less losses due to evaporation) is proportional to the temperature difference between the inside of the body and the surrounding space. In humans, heat transfer is zero at an ambient temperature of 37 °C, and as the temperature decreases, it increases. Heat transfer also depends on heat conduction within the body and peripheral blood flow.

Thermogenesis associated with metabolism under resting conditions (Fig. 1) is balanced by heat transfer processes in the ambient temperature zone T 2 -T 3 , if skin blood flow gradually decreases as the temperature decreases from T 3 to T 2 . At temperatures below T 2 constancy of body temperature can only be maintained by increasing thermogenesis in proportion to heat loss. The greatest heat production provided by these mechanisms in humans corresponds to a metabolic level that is 3–5 times higher than the intensity of the basal metabolic rate, and characterizes the lower limit of the range of thermoregulation T 1 . If this limit is exceeded, hypothermia develops, which can lead to death from hypothermia.

At ambient temperatures above T 3 temperature equilibrium could be maintained by weakening the intensity of metabolic processes. In fact, the temperature balance is established due to an additional heat transfer mechanism - the evaporation of sweat. Temperature T 4 corresponds to the upper limit of the thermoregulation range, which is determined by the maximum intensity of sweat production. At ambient temperatures above T 4 hyperthermia occurs, which can lead to death from overheating. Temperature range T 2 -T 3 , within which the body temperature can be maintained at a constant level without the participation of additional mechanisms of heat production or sweating is called thermoneutral zone. In this range, metabolic rate and heat production are, by definition, minimal.

Human body temperature

The heat generated by the body normally (i.e., under equilibrium conditions) is given off to the surrounding space by the surface of the body, therefore the temperature of the parts of the body near its surface should be lower than the temperature of its central parts. Due to the irregularity of the geometric shapes of the body, the temperature distribution in it is described by a complex function. For example, when a lightly dressed adult is in a room with an air temperature of 20 ° C, the temperature of the deep muscle part of the thigh is 35 ° C, the deep layers of the calf muscle is 33 ° C, the temperature in the center of the foot is only 27–28 ° C, and the rectal temperature is equal to approximately 37 °C. Fluctuations in body temperature caused by changes in external temperature are most pronounced near the surface of the body and at the ends of the limbs (Fig. 2).

Rice. 2. Temperature of various areas of the human body in cold (A) and warm (B) conditions

Core body temperature itself is not constant, either spatially or temporally. Under thermoneutral conditions, temperature differences in the internal regions of the body are 0.2–1.2 °C; even in the brain, the temperature difference between the central and external parts reaches more than 1 ° C. The highest temperature is observed in the rectum, and not in the liver, as previously thought. In practice, changes in temperature over time are usually of interest, so it is measured in one specific area.

For clinical purposes, it is preferable to measure rectal temperature (the thermometer is inserted through the anus into the rectum to a standard depth of 10–15 cm). Oral, or rather sublingual, temperature is usually 0.2–0.5 °C lower than rectal. It is affected by the temperature of inhaled air, food and drink.

In sports medicine studies, esophageal temperature (above the opening of the stomach) is often measured, which is recorded using flexible temperature sensors. Such measurements reflect changes in body temperature more quickly than recording rectal temperature.

Axillary temperature can also serve as an indicator of core body temperature because when the arm is pressed tightly against the chest, temperature gradients shift so that the boundary of the core reaches the armpit. However, this takes some time. Especially after being in the cold, when the surface tissues were cooled and vasoconstriction occurred in them (this especially often happens with a cold). In this case, about half an hour should pass to establish thermal equilibrium in these tissues.

In some cases, core temperature is measured in the outer ear canal. This is done using a flexible sensor, which is placed near the eardrum and protected from external temperature influences using a cotton swab.

Typically, skin temperature is measured to determine the temperature of the surface layer of the body. In this case, measuring at one point gives an inadequate result. Therefore, in practice, the average skin temperature is usually measured in the forehead, chest, abdomen, shoulder, forearm, back of the hand, thigh, lower leg and dorsal surface of the foot. When calculating, the area of ​​the corresponding body surface is taken into account. The “average skin temperature” found in this way at a comfortable ambient temperature is approximately 33–34 °C.

Human body temperature fluctuates throughout the day: it is minimum in the pre-dawn hours and maximum (often with two peaks) in the daytime (Fig. 3). The amplitude of daily fluctuations is approximately 1 °C. In animals that are active at night, the temperature maximum is observed at night. The easiest way to explain these facts would be that the increase in temperature occurs as a result of increased physical activity, but this explanation turns out to be incorrect.

Temperature fluctuations are one of many daily rhythms. Even if we exclude all orienting external signals (light, temperature changes, eating hours), body temperature

continues to oscillate rhythmically, but the period of oscillation in this case is from 24 to 25 hours. Thus, daily fluctuations in body temperature are based on an endogenous rhythm (“biological clock”), usually synchronized with external signals, in particular with the rotation of the Earth. During travel associated with crossing the earth's meridians, it usually takes 1–2 weeks for the temperature rhythm to come into line with the lifestyle determined by the local time new to the body.

The rhythm of daily temperature changes is superimposed by rhythms with longer periods, for example, a temperature rhythm synchronized with the menstrual cycle.

During walking, for example, heat production is 3–4 times higher, and during strenuous physical work, even 7–10 times higher than at rest. It also increases in the first hours after eating (by about 10–20%). Rectal temperatures during marathon running can reach 39–40 °C, and in some cases - almost 41 °C. But the average skin temperature decreases due to exercise-induced sweating and evaporation. During submaximal work, while sweating occurs, the increase in core temperature is almost independent of the ambient temperature in the range of 15–35 °C. Dehydration of the body leads to a rise in core temperature and significantly reduces performance.

Heat dissipation

How does the heat that has arisen in the depths of the body leave it? Partially with secretions and exhaled air, but the role of the main cooler is played by blood. Due to its high heat capacity, blood is very well suited for this purpose. It takes heat from the cells of the tissues and organs it bathes and carries it through the blood vessels to the skin and mucous membranes. This is where heat transfer mainly occurs. Therefore, the blood flowing out of the skin is approximately 3 °C colder than the blood flowing in. If the body is deprived of the ability to remove heat, then in just 2 hours its temperature rises by 4 ° C, and a rise in temperature to 43–44 ° C is, as a rule, incompatible with life.

Heat transfer in the extremities is determined to some extent by the fact that blood flow here occurs according to the countercurrent principle. The deep large vessels of the extremities are located in parallel, due to which the blood flowing through the arteries to the periphery gives off its heat to nearby veins. Thus, the capillaries located at the ends of the limbs receive pre-cooled blood, which is why the fingers and toes are most sensitive to low temperatures.

The components of heat transfer are: heat conduction H P, convection H To, radiation H izl and evaporation H isp. The total heat flow is determined by the sum of these components:

N nar= N P+ N To+ N izl+ N isp .

Heat transfer by conduction occurs when the body comes into contact (standing, sitting or lying down) with a dense substrate. The amount of heat flow is determined by the temperature and thermal conductivity of the adjacent substrate.

If the skin is warmer than the surrounding air, the layer of air adjacent to it heats up, rises and is replaced by colder, denser air. The driving force behind this convective flow is the difference between the temperatures of the body and the surrounding environment near it. The more movement occurs in the outside air, the thinner the boundary layer becomes (maximum thickness 8 mm).

For the range of biological temperatures, heat transfer due to H radiation can be described with sufficient accuracy using the equation:

N izl= h izl x(T skin- T izl) x A,

where T skin– average skin temperature, T izl– average radiation temperature (temperature of surrounding surfaces, for example the walls of a room),
A is the effective surface area of ​​the body and
h izl– coefficient of heat transfer due to radiation.
Coefficient h izl takes into account the emissivity of the skin, which for long-wave infrared radiation is approximately 1, regardless of pigmentation, i.e. the skin emits almost as much energy as a completely black body.

About 20% of the heat transfer from the human body under neutral temperature conditions occurs due to the evaporation of water from the surface of the skin or from the mucous membranes of the respiratory tract. Heat transfer by evaporation occurs even at 100% relative humidity of the surrounding air. This occurs as long as the skin temperature is higher than the ambient temperature and the skin is fully hydrated due to sufficient sweat production.

When the ambient temperature exceeds body temperature, heat transfer can only occur through evaporation. The cooling efficiency due to sweating is very high: with the evaporation of 1 liter of water, the human body can give up a third of all the heat generated under resting conditions for the whole day.

Influence of clothing

The effectiveness of clothing as a heat insulator is due to the smallest volumes of air in the structure of the woven fabric or in the pile, in which no noticeable convective currents arise. In this case, heat is transferred only by conduction, and air is a poor conductor of heat.

Environmental factors and thermal comfort

The influence of the environment on the thermal regime of the human body is determined by at least four physical factors: air temperature, humidity, radiation temperature and air (wind) speed. These factors determine whether the subject feels “thermal comfort”, whether he is hot or cold. The condition for comfort is that the body does not need the functioning of thermoregulation mechanisms, i.e. it would not require shivering or sweating, and the blood flow in the peripheral organs could maintain an intermediate rate. This condition corresponds to the thermoneutral zone mentioned above.

These four physical factors are to some extent interchangeable with regard to the sensation of comfort and the need for thermoregulation. In other words, the feeling of cold caused by low air temperature can be weakened by a corresponding increase in radiation temperature. If the atmosphere seems stuffy, the feeling can be alleviated by lowering the humidity or temperature. If the radiation temperature is low (cold walls), increasing the air temperature is required to achieve comfort.

According to recent studies, the value of a comfortable temperature for a lightly dressed (shirt, shorts, long cotton trousers) seated subject is approximately 25–26 ° C with an air humidity of 50% and equal air and wall temperatures. The corresponding value for a naked subject is 28 °C. The average skin temperature is approximately 34 °C. During physical work, as the subject expends more and more physical effort, the comfortable temperature decreases. For example, for light office work, the preferred air temperature is approximately 22 °C. Oddly enough, during heavy physical work, the room temperature, at which sweating does not occur, feels too cold.

Diagram in Fig. Figure 4 shows how the values ​​of comfortable temperature, humidity and ambient air temperature correlate during light physical work. Each degree of discomfort can be associated with one temperature value - the effective temperature (ET). The numerical value of ET is found by projecting onto the X-axis the point at which the discomfort line intersects the curve corresponding to 50% relative humidity. For example, all combinations of temperature and humidity values ​​in the dark gray area (30 °C at 100% relative humidity or 45 °C at 20% relative humidity, etc.) correspond to an effective temperature of 37 °C, which in turn corresponds to a certain degree of discomfort. In the range of lower temperatures, the influence of humidity is less (the slope of the discomfort lines is steeper), since in this case the contribution of evaporation to the total heat transfer is insignificant. Discomfort increases with average skin temperature and humidity. When the parameters defining the maximum skin humidity (100%) are exceeded, the thermal balance can no longer be maintained. Thus, a person is able to withstand conditions beyond this limit only for a short time; sweat flows in streams because more of it is released than can evaporate. The lines of discomfort, of course, shift depending on the thermal insulation provided by clothing, wind speed and the nature of physical activity.

Comfortable water temperature values

Water has significantly greater thermal conductivity and heat capacity compared to air. When water is in motion, the resulting turbulent flow near the surface of the body removes heat so quickly that at a water temperature of 10 ° C, even strong physical stress does not allow maintaining thermal equilibrium, and hypothermia occurs. If the body is at complete rest, to achieve thermal comfort, the water temperature should be 35–36 °C. Depending on the thickness of the insulating adipose tissue, the lower limit of comfortable temperature in water ranges from 31 to 36 °C.

To be continued

* According to Van't Hoff's rule, when the temperature changes by 10 °C (ranging from 20 to 40 °C), oxygen consumption by tissues changes in the same direction by 2-3 times.

About the author of books and articles: doctor, leading acupuncturist of Belarus, candidate of medical sciences, Molostov Valery Dmitrievich, published 23 books in Moscow and Minsk (on neurology, acupuncture, massage, manual therapy and on the aging of society as an organism), home phone: Minsk, (8---107 -375-17) 240–70–75, E-mail: [email protected]. My page on the Internet: www.molostov-valery.ru, where books are posted (previously published in Moscow and Minsk) with a detailed justification for the real existence of the idea described here.

Which organ of the human body produces heat?

Every person knows well that our body temperature is 36.6 degrees Celsius. But for a long time medicine has not resolved the question of which organ produces heat in animals, including humans. Finally, Russian physiologists have found the answer to this question. (For example, read the research of Dr. Molostov). It turns out that heat is produced by only one organ - the skin. And heat is produced by acupuncture points into which acupuncturists love to insert needles. A very unexpected discovery for the entire world of science was research on the physiological role of acupuncture points. Not a single scientist in the world in other countries (even in the USA, Germany and France) has engaged in such research.

Picture 1.

This article is dedicated to acupuncture points, about which I can tell you a lot of interesting things, since I am a professional acupuncturist by profession. See Figure 1. There are 3,478 acupuncture points found on human skin. By the way, the number of acupuncture points in a cat, cow, elephant, ram, dog, chicken, elephant, bison is exactly the same - 3478 acupuncture points. And acupuncture points in animals are located anatomically exactly where they are in humans. It can be assumed that all warm-blooded animals on Earth have some common ancestor, for example, some kind of marine ichthyosaur. It is interesting to note that all “warm-blooded” animals have acupuncture points, and all cold-blooded animals (worms, frogs, fish, snakes) do not have acupuncture points on the surface of their skin. See Figure 2 and 3.

Figure 2. Warm-blooded.

Figure 3. Cold-blooded.

What is the mechanism of heat generation (production) in warm-blooded animals? It turns out that the energy “substance” for generating heat inside acupuncture points is the electricity that is generated in the body of the animal itself and the person. Physiology claims that many animal and human organs play the role of small power plants. The largest generators of electricity are the heart (produces 60% of the electricity) and the brain (generates 30% of the electricity). The five senses also produce electricity: vision, hearing, touch, smell, and taste. They also work like microscopic power plants, but they transform light, sound and chemical energies into electrical potentials of a specific wavelength. How does the eye generate electricity? Light enters the retina of the eye, where it is transformed into a continuous stream of electrical impulses entering through the optic nerve into the visual centers of the cerebral cortex. The same transformers (not generators) of electrical energy are other sense organs: ears, tactile glomeruli of the skin, olfactory bulbs in the nasal mucosa, taste nerve networks in the mucous membrane of the tongue.

What is the fate of the electrons produced by the heart, brain and five senses? It turns out that there is a very strange pattern: only 5% of the electrical energy they produce is absorbed by all electricity generators. The remaining 95% of the electrical energy from these organs travels through the intercellular space to the skin and acupuncture points. Static electricity covers the entire surface of the skin. On the surface of the skin, electricity “spreads”, just as the waters of the ocean spread over the surface of the Earth. Next, acupuncture points absorb static currents, which cover the skin with a “thin layer”, burning them in their “furnaces” " See Figure 4. The “burning of electrons” produces heat for the human body in the amount of 36.6 degrees Celsius.

Figure 4. Electrons are absorbed by an acupuncture point.

Figure 5. Acupuncture.

This is the mechanism for producing heat by the body of our body and the body of an animal. True, the question remains unanswered: why does a person have a normal body temperature, which is exactly plus 36.6º Celsius? Medical science cannot answer the question “Why does inserting needles into acupuncture points have a healing effect on a person?” See Figure 5. This problem has not yet been studied either. Let's hope that in the next decade scientists will find the answer to these questions. By the way, stopping the activity of electricity generators in the human body is the only cause of natural death of an absolutely healthy, but very old person. It turns out that in old people, the production of electrical energy in the brain and heart first decreases and then stops. See Figure 6. The death of the old organism occurs at the moment when the “power plants” in the heart (Ashof-Tavarovsky node) and in the brain (reticuloendothelial formation) stop generating electricity.

Figure 6. Old man.

Then breathing and heartbeat immediately stop, and death occurs. It is for this reason that absolutely healthy, but very old people, over 100 years old, die. Knowing this information, you can easily extend the life of old people: you need to insert small electrical generators into the heart and brain - and the person will live forever. After all, as long as the heartbeat and breathing continue, the body will live. A healthy brain, liver, kidneys, stomach, intestines and other organs can function for a millennium.

Heat value
Heat sources
Heat production and heat supply
Use of heat
New heat supply technologies

Heat value

Heat is one of the sources of life on Earth. Thanks to fire, the origin and development of human society became possible. From ancient times to this day, heat sources have served us faithfully. Despite the unprecedented level of technological development, man, like many thousands of years ago, still needs warmth. As the world's population grows, the need for heat increases.

Heat is one of the most important resources of the human environment. A person needs it to maintain his own life. Heat is also required for technologies, without which modern man cannot imagine his existence.

Heat sources

The most ancient source of heat is the Sun. Later, fire was at man's disposal. On its basis, man created a technology for producing heat from organic fuel.

Relatively recently, nuclear technologies began to be used to produce heat. However, burning fossil fuels still remains the main method of heat production.

Heat production and heat supply

By developing technology, man has learned to produce heat in large volumes and transfer it over fairly long distances. Heat for large cities is produced at large thermal power plants. On the other hand, there are still many consumers who are supplied with heat by small and medium-sized boiler houses. In rural areas, households are heated by domestic boilers and stoves.

Heat production technologies make a significant contribution to environmental pollution. When burning fuel, a person emits a large amount of harmful substances into the surrounding air.

Use of heat

In general, a person produces much more heat than he uses for his own benefit. We simply dissipate a lot of heat into the surrounding air.

Heat is lost
due to imperfect heat production technologies,
when transporting heat through heat pipes,
due to imperfect heating systems,
due to the imperfection of housing,
due to imperfect ventilation of buildings,
when removing “excess” heat in various technological processes,
when burning production waste,
with exhaust gases from vehicles powered by internal combustion engines.

To describe the state of affairs in the production and consumption of heat by humans, the word wastefulness is well suited. An example, I would say, of blatant wastefulness is the flaring of associated gas in oil fields.

New heat supply technologies

Human society spends a lot of effort and money to obtain heat:
extracts fuel deep underground;
transports fuel from fields to enterprises and homes;
builds installations for heat generation;
builds heating networks for heat distribution.

Probably, we should think: is everything reasonable here, is everything justified?

The so-called technical and economic advantages of modern heat supply systems are essentially momentary. They are associated with significant environmental pollution and unreasonable use of resources.

There is heat that does not need to be extracted. This is the heat of the Sun. It needs to be used.

One of the ultimate goals of heating technology is the production and delivery of hot water. Have you ever used an outdoor shower? A container with a tap installed in an open place under the rays of the Sun. A very simple and affordable way to supply warm (even hot) water. What's stopping you from using it?

With the help of heat pumps, people use the heat of the Earth. A heat pump does not require fuel, nor does it require a long heating pipeline with its heat losses. The amount of electricity required to operate a heat pump is relatively small.

The benefits of the most modern and advanced technology will be negated if its fruits are used stupidly. Why produce heat away from consumers, transport it, then distribute it among homes, heating the Earth and the surrounding air along the way?

It is necessary to develop distributed heat production as close as possible to the places of consumption, or even combined with them. A method of heat production called cogeneration has long been known. Cogeneration plants produce electricity, heat and cold. For the fruitful use of this technology, it is necessary to develop the human environment as a unified system of resources and technologies.

It seems that in order to create new heat supply technologies it is necessary
review existing technologies,
try to get away from their shortcomings,
gather on a single basis to interact and complement each other,
take full advantage of their advantages.
This implies understanding

Heat generation, or heat production, is determined by the intensity of metabolism. Regulation of heat production by increasing or decreasing metabolism is referred to as chemical thermoregulation.

The heat generated by the body is constantly released into the external environment surrounding it. If heat transfer did not exist, the body would die from overheating. Heat transfer can increase and decrease. Regulation of heat transfer by changing the physiological functions that carry it out is referred to as physical thermoregulation.

The amount of heat generated in the body depends on the level of metabolism in the organs, which is determined by the trophic function of the nervous system. The greatest amount of heat is generated in organs with intense metabolism - in skeletal muscles and glands, mainly in the liver and kidneys. The smallest amount of heat is released in bones, cartilage and connective tissue.

When the ambient temperature increases, heat generation decreases, and when it decreases, it increases. Consequently, there is an inversely proportional relationship between the ambient temperature and heat generation. In summer, heat generation decreases, and in winter it increases.

The relationship between heat generation and heat transfer depends on the ambient temperature. At an environment of 15-25°C, heat generation at rest in clothing is at the same level and is balanced by heat transfer (zone of indifference). When the ambient temperature is below 15°C, then under the same conditions, heat production increases at 0°C and gradually decreases to 15°C (lower zone of increased metabolism). If the ambient temperature is 25-35°C, the metabolism decreases slightly (low metabolism zone) and thermoregulation is maintained. When the ambient temperature rises above 35°C, thermoregulation is disrupted, metabolism and body temperature increase (upper zone of increased metabolism, overheating zone). Consequently, increasing the temperature of the external environment or warming the body reduces heat production only to a certain level at a certain temperature of the external environment. This temperature is called critical, since its further increase leads not to a decrease, but to an increase in heat generation and an increase in body temperature. In the same way, during cooling, there is a critical temperature of the external environment, below which heat production begins to decrease.

With muscle rest, the increase in heat generation when the body cools is insignificant.

A particularly significant increase in heat generation at low ambient temperatures is observed during trembling and muscle work. Incorrect, small muscle contractions - trembling and increased movements that a person makes in the cold in order to warm up and get rid of chills or trembling, increase trophic functions, significantly increase metabolism and heat production. Heat production also increases slightly with goose bumps - contraction of the muscles of the hair follicles.

It is necessary to take into account that walking increases heat production by almost 2 times, and fast running - by 4-5 times; body temperature can increase by several tenths of a degree, and an increase in temperature during work accelerates oxidative processes and thereby contributes to the oxidation of protein breakdown products. However, with prolonged intensive work at an ambient temperature above 25°C, body temperature can increase by 1-1.5°C, which already causes changes and disruptions in vital functions. When, during muscular work in a high ambient temperature, the body temperature rises to more than 39 ° C, heat stroke may occur. Muscles account for 65-75% of heat generation, and during intensive work even 90%.

The rest of the heat is generated in the glandular organs, mainly in the liver.

The body at rest continuously loses heat: 1) by heat radiation, or heat transfer from the skin to the surrounding air; 2) heat conduction, or direct heat transfer to those objects that come into contact with the skin; 3) evaporation from the surface of the skin and lungs.

Under resting conditions, 70-80% of the heat is released into the environment by the skin by heat radiation and heat conduction, and about 20% by evaporation of water in the skin (sweating) and in the lungs. Heat transfer by heating exhaled air, urine and feces is negligible, it accounts for 1.5-3% of the total heat transfer.

During muscular work, the release of heat by evaporation increases sharply (in humans, mainly by sweating), reaching 90% of the total daily heat generation.

Heat transfer by heat radiation and heat conduction depends on the temperature difference between the skin and the environment. The higher the skin temperature, the greater the heat transfer through these pathways. The temperature of the skin depends on the flow of blood to it. When the ambient temperature increases, the arterioles and capillaries of the skin. But since the difference in skin temperature decreases, the absolute value of heat transfer at high ambient temperatures is less than at low ones.

When the skin temperature is compared with the ambient temperature, heat transfer stops. With a further increase in ambient temperature, the skin not only does not lose heat, but itself heats up. In this case, heat transfer by heat radiation and heat transfer is absent and only heat transfer by evaporation is retained.

On the contrary, in the cold, the arterioles and capillaries of the skin narrow, the skin becomes pale, the amount of blood flowing through the dog decreases, the skin temperature drops, the temperature difference between the skin and the environment is smoothed out, and heat transfer decreases.

A person reduces heat transfer with artificial coverings (underwear, clothing, etc.). The more air there is in these covers, the easier it is to retain heat.

Regulation of heat transfer by water evaporation plays an important role, especially during muscular work and a significant increase in ambient temperature. When 1 dm 3 of water evaporates from the surface of the skin or mucous membranes, 2428.4 kJ is lost by the body.

Loss of water from the skin occurs due to the penetration of water from deep tissues to the surface of the skin and mainly due to the functioning of the sweat glands. At average ambient temperature, an adult loses 1674.8-2093.5 kJ daily by evaporation from the skin.

Due to the sharp increase in sweating with increasing ambient temperature and during muscular work, heat transfer also increases significantly, although not all sweat evaporates.

Large losses of sweat are accompanied by losses of large amounts of mineral salts, since the content of table salt alone in sweat is 0.3-0.6%. With a loss of 5-10 dm3 of sweat, 25-30 grams of table salt are lost. Therefore, if the thirst that arises from profuse sweating is satisfied with water, then severe disorders occur due to the loss of significant amounts of salts (convulsions, etc.). Already with the loss of 2 dm 3 of sweat, a deficiency of salts in the body results. These losses are replenished by drinking water containing 0.5-0.6% table salt, which is recommended to drink during profuse, prolonged sweating.

Water evaporation constantly occurs from the surface of the lungs. The exhaled air is saturated with water vapor by 95-98% and therefore the drier the inhaled air, the more heat is given off by evaporation from the lungs. Under normal conditions, the lungs evaporate 300-400 cm 3 of water every day, which corresponds to 732.7-962.9 kJ. At high temperatures, breathing becomes more frequent, and in the cold it becomes rare. Evaporation of water from the surface of the skin and lungs becomes the only way of heat transfer when the air temperature reaches body temperature. Under these conditions, more than 100 cm 3 of sweat per hour evaporates at rest, which allows you to release about 251.2 kJ per hour.

The evaporation of water from the surface of the skin and lungs depends on the relative humidity of the air. It stops in air saturated with water vapor. Therefore, being in humid hot air, such as a bathhouse, is difficult to tolerate. A person feels unwell in damp air, even at a relatively low ambient temperature - at 30°C. Leather and rubber clothing is poorly tolerated, as it is impermeable to and makes it impossible for sweat to evaporate, so sweat accumulates under such clothing. With high air temperatures and muscle work in leather and rubber clothing, a person’s body temperature rises.

Overheating a person in a room saturated with water vapor is especially dangerous, as it makes it impossible to get rid of excess heat in the most effective way - evaporation.

On the contrary, in dry air a person can relatively easily tolerate a much higher temperature than in humid air.

Air movement is of great importance for increasing heat transfer by heat radiation, heat conduction and evaporation. Increasing the speed of air movement increases heat transfer. In a draft and wind, heat loss increases sharply. But if the surrounding air has a high temperature and is saturated with water vapor, then air movement does not cool. Consequently, physical thermoregulation is provided by: 1) the cardiovascular system, which determines the inflow and outflow of blood in the blood vessels of the skin, and, consequently, the amount of heat given off by the skin to the environment; 2) the respiratory system, i.e. changes in pulmonary ventilation; 3) changes in the function of the sweat glands.

Heat transfer is regulated by the nervous system and through hormones. Conditioned reflexes to environments in which the body has been repeatedly heated or cooled are essential.

Changes in the functions of the cardiovascular system, respiration and sweat glands are reflexively regulated by irritation of external sensory organs and especially irritation of skin receptors with changes in external temperature, as well as irritation of the nerve endings of internal organs with fluctuations in temperature inside the body. Physiological mechanisms of physical thermoregulation are carried out by the cerebral hemispheres, intermediate, medulla oblongata and spinal cord.

Heat transfer changes when hormones enter, changing the functions of organs involved in physical thermoregulation.

Taking medications that cause an increase in body temperature.

Body temperature is most often measured with a medical mercury thermometer. In 1714, the Polish-German physicist Daniel Gabriel Fahrenheit made a mercury thermometer, and in 1742, the Swedish scientist Andres Celsius proposed a scale for a mercury thermometer graduated from 34 to 42 °C with divisions of 0.1 °C.

Medical devices for measuring body temperature.

▪ A mercury thermometer is a glass flask with a capillary that contains mercury (2 grams). It is designed so that the mercury column, when the tank is heated, shows a figure corresponding to body temperature.

▪ Ear infrared thermometer. The time for changing the temperature with an ear infrared thermometer is one to four seconds.

▪ Digital thermometer. The time for measuring body temperature is approximately one to three seconds. This thermometer is the safest.

▪ Electric thermometer. Using an electric thermometer, you can measure the temperature in body cavities: esophagus, stomach, intestines, etc.

▪ The radio capsule is equipped with a sensor that transmits signals.

▪ Thermal imaging and thermography make it possible to determine the increase in the intensity of thermal radiation, which occurs when blood circulation and metabolic processes change in individual organs and tissues due to their pathology.

Body temperature is measured 2 times a day: in the morning on an empty stomach (from 6 a.m. to 7 a.m.) and in the evening before the last meal (from 5 p.m. to 6 p.m.) for 10 minutes.

Measuring body temperature every 3 hours - called the temperature profile.

The thermometer readings are entered into a temperature sheet, where dots indicate morning and evening temperatures. Based on the marks over several days, a temperature curve is drawn up.

Physiological thermoregulation system (from the Greek “thermo” - heat, “regulation” - control) is a set of physiological mechanisms that regulate body temperature.

Thermoregulation can be carried out in two ways:

Ø by changing the rate of heat production (heat generation)

Ø by changing the rate of heat transfer (heat transfer)

The processes of heat formation and release are carried out under the control of the nervous system and endocrine glands.

Heat formation in the body.

The exchange of thermal energy between the body and the environment is called heat exchange.

Energy is required for vital processes to occur in the body. It is formed as a result of the breakdown of chemicals (mainly carbohydrates and fats) that we consume in food. The energy that was previously hidden in them is released, consumed and, ultimately, given off by the body in the form of heat. Most of the heat is generated in the muscles.

On the periphery (skin, internal organs) they have cold and thermal receptors that perceive temperature fluctuations in the external environment. So, when the ambient temperature drops, the skin receptors are irritated, and excitement arises in them, which goes to the central nervous system and from there to the muscles, causing them to contract. Thus, the trembling and chills that we experience during the cold season or in a cold room are reflex acts that contribute to increased metabolism, and therefore increased heat production. This process occurs even when a person is at complete rest; the temperature of muscle tissue at rest and work can fluctuate within 7 ° C. During muscle work, heat generation increases 4-5 times. The temperature of internal organs: brain, heart, endocrine glands, stomach, intestines, liver, kidneys and other organs depends on the intensity of metabolic processes. The “hottest” organ of the body is the liver: the temperature in the liver tissue is 38-38.5 ° C. The temperature in the rectum is 37-37.7 ° C. However, it can fluctuate depending on the presence of feces in it, its blood supply mucous and other reasons. The lowest skin temperature is observed on the hands and feet, 24-28° C. A relatively uniform distribution of heat in the body is ensured by the blood. Passing through the brain, heart, liver, and other “warm” organs, the blood heats up while simultaneously cooling them. And, passing through the superficial muscles, skin and other “cold” organs, the blood cools while simultaneously warming them. However, the surface temperature of the body remains slightly lower than the temperature inside the body. The formation of heat in the body is accompanied by its release. The body loses as much heat as it generates, otherwise the person would die within a few hours. If there were no heat transfer mechanisms, the body temperature of an adult at rest would increase by 1.24° C every hour.

Constancy of body temperature is called isothermal. To maintain a constant body temperature of 36.6°C, a person needs to spend 200 kcal per day. A decrease in body temperature even by 0.1° leads to a decrease in immunity.

Chemical thermoregulation - process of heat formation in the body , caused by an increase in the intensity of metabolic processes in tissues, it is controlled by the posterior parts of the hypothalamus.

Physical thermoregulation controlled by the anterior parts of the hypothalamus, and are the center of heat transfer from the body to the external environment through convection (heat conduction), radiation (heat radiation) and water evaporation.

Convection- provides heat transfer to air or liquid adjacent to the body. The greater the temperature difference between the surface of the body and the surrounding air, the more intense the heat transfer.

Heat transfer increases with air movement, such as wind. The intensity of heat transfer largely depends on the thermal conductivity of the environment. Heat transfer occurs faster in water than in air. Clothing reduces or even stops heat conduction.

Radiation - Heat is released from the body by infrared radiation from the surface of the body. Due to this, the body loses the bulk of heat. The intensity of heat conduction and heat radiation is largely determined by skin temperature. Heat transfer is regulated by a reflex change in the lumen of the skin vessels. As the ambient temperature rises, the arterioles and capillaries expand, and the skin becomes warm and red. This increases the processes of heat conduction and heat radiation. When the air temperature drops, the arterioles and capillaries of the skin narrow. The skin becomes pale, the amount of blood flowing through its vessels decreases. This leads to a decrease in its temperature, heat transfer decreases, and the body retains heat.

Evaporation of water from the surface of the body (2/3 moisture), and during breathing (1/3 moisture). Evaporation of water from the surface of the body occurs when sweat is secreted. Even in the complete absence of visible sweating, up to 0.5 liters of water evaporates through the skin per day - invisible sweating. On average, a person loses about 0.8 liters of sweat per day, and with it 500 kcal of heat. In hot countries, in hot workshops, a person loses a large amount of fluid through sweat. At temperatures up to 50°C, a person loses up to 12 liters of sweat per day. At the same time, a feeling of thirst appears, which is not quenched by drinking water. This is due to the fact that a large amount of mineral salts is lost through sweat. For this purpose, 0.5% table salt is added to drinking water. It quenches thirst and improves well-being.

Subcutaneous fat prevents heat transfer. The thicker the layer of fat, the worse it is performed. Therefore, people with a thick layer of fat in the subcutaneous tissue tolerate cold more easily than thin people. The evaporation of 1 liter of sweat in a person weighing 75 kg can lower body temperature by 10° C.

In a state of relative rest, an adult person releases 15% of heat into the external environment through heat conduction, about 66% through heat radiation, and 19% through water evaporation.

Fever (febris), or fever- a general reaction of the body to any irritation, characterized by an increase in body temperature above 37°C, due to a violation of thermoregulation. During fever, heat generation prevails over heat transfer. One of the causes of fever is infection. Bacteria or their toxins, circulating in the blood, cause disruption of thermoregulation.

Types of fevers

Depending on the degree of temperature increase, the following types of fevers are distinguished:

§ subfebrile temperature - 37-38 °C:

a) low-grade fever - 37-37.5 °C;

b) low-grade fever - 37.5-38 °C;

§ moderate fever - 38-39 ° C;

§ high fever - 39-40 °C;

§ excessively high fever - over 40 ° C;

§ hyperpyretic - 41-42 °C, it is accompanied by severe nervous phenomena and is itself life-threatening.

Types of fevers

Based on the nature of body temperature fluctuations during the day, the following types of fevers are distinguished:

persistent fever- long-term, high, usually not less than 39°, temperature with daily fluctuations of no more than 1°; characteristic of typhus, typhoid fever and lobar pneumonia (Fig. 1).

Fig.1. Persistent fever

laxative(remitting) fever, high temperature, daily temperature fluctuations exceed 1-2 °C, with a morning minimum above 37 °C; characteristic of tuberculosis, purulent diseases, focal pneumonia, in stage III of typhoid fever (Fig. 2).

Rice. 2. Laxative fever

intermittent(intermittent) fever (febris intermittens) - the temperature rises to 39 ° C - 40 ° C and above, followed by a rapid drop to normal or slightly below normal. Fluctuations are repeated every 1-2 or 3 days, observed in malaria (Fig. 3).

Rice. 3. Intermittent fever

wavy(undulating) fever (febris undulans) - it is characterized by periodic increases in temperature, and then a decrease in the level to normal numbers. Such “waves” follow one another for a long time; characteristic of brucellosis, lymphogranulomatosis (Fig. 4).

Rice. 4. Undulating fever

relapsing fever(febris recurrens) - the correct alternation of increasing and decreasing temperature over several days. Characteristic of relapsing fever (Fig. 5).

Rice. 5. Relapsing fever

wrong(atypical or irregular) fever(febris irregularis) irregular daily temperature fluctuations of varying magnitude and duration, often observed in rheumatism, endocarditis, sepsis, tuberculosis, influenza, diphtheria, dysentery, pleurisy (Fig. 6).

Rice. 6. Incorrect fever

exhausting(hectic) fever (febris hectica) is characterized by large (2-4 °C) daily temperature fluctuations, which alternate with its drop to normal or below. A rise in temperature is accompanied by chills, and a fall by profuse sweating, typical of severe pulmonary tuberculosis, suppuration, and sepsis (Fig. 7).

reverse ( perverted) fever(febris inversus) - morning temperature is higher than evening temperature; sometimes observed in sepsis, tuberculosis, brucellosis (Fig. 7).

Rice. 7. a - hectic fever