Thermoregulation mechanisms. Human thermoregulation: what is it? The mechanism of chemical thermoregulation is food substances
Regulation of temperature consists in coordinating heat-processes (chemical thermoregulation) and heat transfer (physical thermoregulation).
Heat Production processes. In all organs due to the process of metabolism, heat product flow occurs. Therefore, blood that reaches the organs, as a rule, has a higher temperature than that flowing. But the role of various organs in the heat-product is different. In a state of rest on the liver accounts for about 20% of the total heat product, on other internal organs - 56%, by - 20%, during physical exertion on skeletal muscles - up to 90%, on internal organs - only 8%.
Thus, the powerful backup source of heat products is the muscle in their reduction. The change in the activity of their metabolism under locomotions is the main mechanism of heat product. Among various locomotions, several stages of muscle participation in heat-product can be distinguished.
1. Thermoregulation tone. At the same time, the muscles are not reduced. Only their tone and metabolism increase. This tone arises in general in the muscles of the neck, body and limbs. As a result, heat product increases by 50-100%.
2. The shiver arises unconsciously and lies in the periodic activity of high-voltage motor units on the background of thermoregulation tone. When trembling, all the energy is directed only to an increase in heat generation, while in conventional locomotions, part of the energy is consumed to move the corresponding limb, and the part is the thermogenesis. When trembling, heat products rises by 2-3 times. A shiver begins often with the muscles of the neck, faces. This is due to the fact that first of all the blood temperature should increase, which flows to the brain.
3. Arbitrary reductions are to consciously increase muscle contraction. This is observed in low external temperature conditions, when the first two stages are not enough. With arbitrary abbreviations, heat products may increase by 10-20 times.
The regulation of heat-product in the muscles of Cutyazan with the influence of A-motor meters on the function and metabolism / muscles, in other tissues - the sympathetic nervous system and catecholamines (increase the intensity of metabolism by 50%) and the action of hormones, especially thyroxine, which increases the heat product almost twice.
A significant role in the thermogenesis of lipids, which is distinguished by hydrolysis significantly more energy (9.3 kcal / g) than carbohydrates (4.1 kcal / g). Of particular importance, in particular in children, has brown fat.
Processes of heat transfer It happens in the following ways - radiation, convection, evaporation and thermal conductivity.
Radiation occurs with the help of infrared long-wave radiation. This requires a temperature gradient between warm skin and cold walls and other environmental objects. Thus, the magnitude of radiation depends on the temperature and surface of the skin.
The thermal conductivity is carried out with direct contact of the body with objects (stool, bed, etc.). At the same time, the rate of heat transfer from a heated body to a less heated object is determined by the temperature gradient and their thermal industry. The return of heat by this way significantly (14 times) increases when a person is in the water. Partly by carrying out heat transferred from the internal organs to the body surface. But this process is inhibited due to the low thermal conductivity of fat.
Convection path. The air in contact with the body surface, in the presence of temperatures, heats up. At the same time it becomes easier and, rising from the body, frees the place for new air portions. Thus, it takes part of the heat. The intensity of natural convection can be increased due to an additional air movement, a decrease in obstacles when it is admitted to the body (appropriate clothing).
Evaporation sweat. At room temperature in a man, about 20% of heat is given due to evaporation.
Thermal conductivity, Convection and radiation are the passive pathways of heat transfer based on the laws of physics. They are effective only while maintaining a positive temperature gradient. The less the temperature difference between the body and the environment, the less heat is given. With the same indicators or at high ambient temperatures, the mentioned paths are not only not effective, but the body is heating. Under these conditions, only one heat recovery mechanism is triggered in the body associated with the processes of sweating and Potoviparovoyvane. Here are used both physical patterns (energy costs per evaporation process) and biological (sweating). Cooling the skin contributes to the fact that 0.58 kcal is consumed for evaporation of 1 ml. If not happens
swift evaporation, the effectiveness of heat transfer decreases sharply. M.
The rate of evaporation is a hundred depends on the temperature gradient and the saturation of the surrounding air water ferry. The higher the humidity, the less effective it becomes the heat transfer. The effectiveness of heat transfer decreases dramatically when in water or in dense clothing. At the same time, the body is forced to compensate for the absence of sweatparovane due to an increase in sweating.
Evaporation has two mechanisms: a) Pospiration - without the participation of sweat glands b) evaporation - with the active participation of sweat glands.
Puspiration - evaporation of water from the surface of the lungs, mucous membranes, leather, which is always wet. This evaporation is not regulated, it depends on the temperature gradient and the humidity of the ambient air, its value is about 600 ml / day. The higher the humidity, the less effective this type of heat transfer.
The mechanism of secretion of sweat. Potted iron consists of two parts: the gland itself, which is located in the subthermal layer, and output ducts opening on the surface of the skin. The primary secret is formed in the gland, and in the ducts, due to reabsorption, a secondary secret is formed - sweat.
Primary secret like blood plasma. The difference lies in the fact that in this secret there are no proteins and glucose, less Na +. So, in the initial sweat, sodium concentration is about 144 nmol / l, chlorine - 104 nmol / l. These ions are actively absorbed when the sweat passes through output ducts, providing water absorption. The absorption process largely depends on the rate of formation and the promotion of sweat that these processes are active, the greater Na + and Sl-remains. With a strong sweating in the sweat, up to half of the concentration of these ions can remain. The strong intake is accompanied by an increase in the concentration of urea (up to 4 times higher than in plasma) and potassium (up to 1.2 times more than in plasma). The total high concentration of ions, forming a high level of osmotic pressure, provides a decrease in reabsorption and isolation from then a large amount of water.
With a strong sweating, a lot of NaCl can be spent (up to 15-30 g / day). However, there are mechanisms in the body that ensure the preservation of these important ions with a large sweating. They are involved in adaptation processes, in particular, aldosterone enhances Na + reabsorption.
The functions of the sweat glands are adjusted by special mechanisms. The sympathetic nervous system is influenced by their activity, but the mediator is acetylcholine. Secretory cells, except m-cholinoreceptors, also have adrenoreceptors that react to the catecholas of blood. The activation of the functions of the sweat glands is accompanied by an increase in its blood supply.
The amount of sweat allocated can reach 1.5 l / h, and in adapted people - up to 3 l / h.
At room temperature in a man, about 60% of heat is given due to radiation, about 12-15% - air convection, about 20% - evaporation, 2-5% of thermal conductivity. But this ratio depends on a number of conditions, in particular on the temperature of the external environment.
The main role in the regulation of heat transfer processes is played by the blood supply to the skin. The narrowing of the vessels of the skin, the discovery of arteriovenous anastomoses contributes to a smaller influx of heat from the kernel to the shell and maintain it in the body. On the contrary, when the leather vessels expansion, its temperature can increase by 7-8 ° C. It also increases the heat transfer.
Conditionally, the skin can be called a radiator system of the body. Bloodstock in the skin can vary from 0 to 30% mock. The tone of the skin vessels is controlled by a sympathetic nervous system.
Thus, the body temperature is a balance between heat-product and heat transfer processes. When heat-producing prevails over the heat transfer, the body temperature increases and, on the contrary, if the heat transfer is higher than the heat product, the body temperature is reduced.
A. Human life can only leak in a narrow temperature range.
The temperature has a significant impact on the flow of vital processes in the human body and on its physiological activity. Life processes are limited to a narrow temperature range of the internal environment in which basic enzyme reactions may occur. For a person, a decrease in body temperature below 25 ° C and its increase above 43 ° C is usually mortally. Especially sensitive to changes in temperature nerve cells.
Heat It causes intensive sweating, which leads to dehydration of the body, loss of mineral salts and water-soluble vitamins. The consequence of these processes is blood thickening, a violation of salt metabolism, gastric secretion, the development of a vitamin deficit. The permissible reduction in weight during evaporation is 2-3%. When weight loss from evaporation is 6%, mental activity is violated, and with 15-20% weight loss, death comes. The systematic action of high temperature causes changes in the cardiovascular system: the increase in the pulse, the change in blood pressure, weakening the functional ability of the heart. The long-term exposure to the high temperature leads to the accumulation of heat in the body, while the body temperature can increase to 38-41 ° C and a thermal blow may occur with the loss of consciousness.
Low temperatures There may be causes of cooling and supercooling the organism. When cooling in the body, the heat transfer is reflexively decreased and heat-product increases. Reducing heat transfer occurs due to spasms (narrowing) of vessels, increasing the thermal resistance of the body tissues. The long-term exposure to the low temperature leads to a resistant vascular spa, tissue disorders. The growth of heat-product during cooling is achieved by an increase in oxidative metabolic processes in the body (a decrease in body temperature at 1 ° C is accompanied by an increase in metabolic processes at 10 ° C). The impact of low temperatures is accompanied by an increase in blood pressure, the inhalation volume and a decrease in respiratory frequency. Cooling the body changes carbohydrate exchange. Big cooling is accompanied by a decrease in body temperature, oppression of organs and body systems.
B. The core and the outer shell of the body.
From the point of view of thermoregulation, the human body can be represented consisting of two components - external shell and internal nuclei.
Core- this is part of the body, which has a constant temperature (internal organs), and shell- Part of the body in which there is a temperature gradient (these are tissues of the surface layer of the body with a thickness of 2.5 cm). Through the shell there is heat exchange between the core and the environment, that is, changes in the thermal conductivity of the shell determine the constancy of the kernel temperature. The thermal conductivity varies due to changes in the blood supply and blood flow of the shell tissue.
The temperature of different sections of the kernel is different. For example, in the liver: 37.8-38.0 ° C, in the brain: 36.9-37.8 ° C. In general, the temperature of the core of the human body is 37.0 ° C. This is achieved using the processes of endogenous thermoregulation, the result of which is a stable equilibrium between the amount of heat produced in the body ( heat Production) and the amount of heat dissipated by the body for the same time in the environment ( heat Press).
The human skin temperature in different areas ranges from 24.4 ° C to 34.4 ° C. The lowest temperature is observed on the fingers of the legs, the highest - in the armpit. It is based on the temperature measurement in the armpit, the body is usually judged at the moment of time.
According to averaged data, the average temperature of the nude person in a comfortable air temperature is 33-34 ° C. There are daily fluctuations in body temperature. The amplitude of oscillations can reach 1 ° C. Temperature of the body is minimal in the preliminary clock (3-4 hours) and the maximum in the daytime (16-18 hours).
Also known is the phenomenon of asymmetry of temperature. It is observed about 54% of cases, and the temperature in the left axillary depression is slightly higher than in the right. Asymmetry and other areas of the skin are possible, and the severity of asymmetry is more than 0.5 ° C testifies to pathology.
V. Heat exchange. The balance of heat generation and heat transfer in the human body.
The human life processes are accompanied by continuous heat generation in its body and the impact of the formed heat into the environment. The exchange of thermal energy between the organism and the environment is called heat exchange. The heat product and heat transfer is due to the activities of the central nervous system, regulating the metabolism, blood circulation, sweating and activity of skeletal muscles.
The human body is a self-regulatory system with an internal source of heat, in which, under normal conditions, heat-product (amount of formed heat) is equal to the amount of heat given to the external environment (heat transfer). The constancy of the body temperature is called isothermia. It ensures the independence of metabolic processes in tissues and organs from ambient temperature fluctuations.
The internal temperature of the human body is constant (36.5-37 ° C) due to the control of the intensity of heat-product and heat transfer, depending on the temperature of the external environment. And the temperature of the human skin when exposed to external conditions can be changed in relatively wide limits.
In the body of a person for 1 hour, so much heat is formed as needed to boil 1 liter of icy water. And if the body was impenetrable to heat the case, then an hour later, the body temperature would have risen about 1.5 ° C, while the clock would reach the boiling point of water. During severe physical work, heat formation increases several times. Still, the temperature of our body does not change. Why? It is precisely in the balancing of the processes of education and heat of heat in the body.
The leading factor determining the level of thermal balance is environmental temperature. With its deviation from a comfortable zone in the body, a new level of thermal balance is established, providing isothermia in the new environment environments. Such a constancy of body temperature is ensured by the mechanism thermoregulationcomprising heat generation process and heat generation process that is regulated by neuro-endocrine through.
The concept of the thermoregulation of the body.
Temoregulation - This is a combination of physiological processes aimed at maintaining the relative constancy temperature of the organism nucleus under conditions of changes in the temperature of the medium using the regulation of heat-product and heat transfer. The thermoregulation is aimed at preventing disorders of the thermal balance of the body or on its restoration, if such violations have already occurred, and is carried out by neuro-humoral through.
It is believed that the thermoregulation is characterized only by homoothermal animals (they include mammals (including a person), birds), the body of which has the ability to maintain the temperature of the internal areas of the body at a relatively constant and fairly high level (about 37-38 ° C in mammals and 40-42 ° C in birds) regardless of changes in ambient temperature.
The thermoregulation mechanism can be represented as a cybernotetic self-governing system with feedback. The ambient temperature fluctuations act on special receptor education ( thermoreceptor), sensitive to temperature change. The thermoreceptors are transmitted to the thermoregulation centers information about the thermal state of the organ, in turn, the thermoregulation centers through the nerve fibers, hormones and other biologically active substances change the level of heat transfer and heat production or body sections (local thermoregulation), or the body as a whole. When the thermoregulation centers are turned off with special chemicals, the body loses the ability to maintain the constancy of temperature. This feature in recent years is used in medicine for artificial cooling of the body during complex surgical operations on the heart.
Skin thermoreceptors.
It is estimated that a person has about 150.000 cold and 16,000 thermal receptors that react to changes in the temperature of the internal organs. Thermoreceptors are located in the skin, in the internal organs, respiratory tract, skeletal muscles and the central nervous system.
Thermoreceptor leather is quickly adapting and react not so much at the temperature itself as its changes. The maximum number of receptors is in the area of \u200b\u200bthe head and neck, the minimum on the limbs.
Cold receptors are less sensitive and their sensitivity threshold is 0.012 ° C (when cooled). The threshold of the sensitivity of thermal receptors is higher and is 0.007 ° C. This is probably due to the greater hazard for the body of overheating.
D. Types of thermoregulation.
Thermoregulation can be divided into two main types.:
1. Physical thermoregulation:
Evaporation (sweating);
Radiation (radiation);
Convection.
2. Chemical thermoregulation.
Contractile thermogenesis;
Non-culture thermogenesis.
Physical thermoregulation (The process that removes heat from the body) - ensures the preservation of the constancy of the body temperature due to the change in the heat of heat by the organism by conducting through the skin (conduction and convection), radiaysuscript (radiation) and evaporation of water. The return of the heat generated in the body is regulated by changing the thermal conductivity of the skin, subcutaneous fat layer and epidermis. The heat transfer is largely regulated by the dynamics of blood circulation in thermal conducting and heat-insulating tissues. With an increase in the ambient temperature in the heat transfer begins to dominate evaporation.
Conduction, convection and radiation are the passive pathways of heat transfer based on the laws of physics. They are effective only while maintaining a positive temperature gradient. The less the temperature difference between the body and the environment, the less heat is given. With the same indicators or at high ambient temperatures, the mentioned paths are not only not effective, but the body is also occurring. Under these conditions, only one heat recovery mechanism is triggered in the body - sweating.
At low ambient temperature (15 ° C and below), about 90% of the daily heat transfer occurs due to heat control and heat emission. Under these conditions, there is no visible sweating. At air temperature of 18-22 ° C, heat transfer due to thermal conductivity and heat emission decreases, but the heat loss increases by the organism by evaporation of moisture from the surface of the skin. With increasing ambient temperature up to 35 ° C, heat transfer with radiation and convection becomes impossible, and the body temperature is maintained at a constant level solely by evaporation of water from the surface of the skin and alveoli lungs. With high humidity, when the evaporation of water is difficult, body overheating may occur and develop a heat blow.
In a person at rest at air temperature of about 20 ° C and a total heat transfer equative to 419 kJ (100 kcal) per hour, 66% is lost using radiation, water evaporation - 19%, convection - 15% of the total heat loss by the body.
Chemical thermoregulation(The process that ensures the formation of heat in the body) is implemented through the metabolism and through the heat products of such tissues as muscles, as well as the liver, brown fat, that is, changes in the level of heat generation - due to the gain or weakening the intensity of metabolism in the cells of the body. When oxidizing organic substances, energy is released. Part of the energy goes to the synthesis of ATP (adenosine trifosphate is a nucleotide, which plays an extremely important role in the exchange of energy and substances in the body). This potential energy can be used by the body in its future activities. The source of heat in the body is all tissues. Blood, flowing through the fabric, heats up. An increase in ambient temperature causes a reflex reduction in metabolism, as a result of this, heat generation decreases in the body. With a decrease in the ambient temperature, the intensity of metabolic processes increases reflectically and heat generation is enhanced.
The inclusion of chemical thermoregulation occurs when physical thermoregulation turns out to be insufficient to maintain the constancy of the body temperature.
Consider these types of thermoregulation.
Physical thermoregulation:
Under physical thermoregulation Understand the combination of physiological processes leading to changes in the level of heat transfer. There are the following ways to recover the heat by the organism in the environment:
Evaporation (sweating);
Radiation (radiation);
Heat transfer (conduction);
Convection.
Consider them in more detail:
1. Evaporation (sweating):
Evaporation (sweating)- This is a recovery of thermal energy into the environment due to the evaporation of sweat or moisture from the surface of the skin and mucous membranes of the respiratory tract. A person is constantly released by sweat by sweat glands of the skin ("tangible", or fervor, water loss), the mucous membranes of the respiratory tract ("irrevomable" water loss) are moistened. At the same time, the "tangible" water loss by the body has a more significant impact on the total amount of heat than the heat of heat than "irrelevant".
At the outer medium temperature, about 20 ° C, the evaporation of moisture is about 36 g / h. Since the evaporation of 1 g of water in humans spent 0.58 kcal of thermal energy, it is not difficult to calculate that by evaporation by the organism of an adult, it gives about 20% of the entire heat dissipation in these conditions. Increased external temperature, physical work, long-term stay in thermal insulation clothing reinforce the sweating and it may increase to 500-2,000 g / h.
A person does not tolerate the relatively low ambient temperature (32 ° C) during wet air. In absolutely dry air, a person may be without noticeable overheating for 2-3 hours at a temperature of 50-55 ° C. It is also poorly transferred by air-impenetrable clothing (rubber, dense, etc.), which prevents the evaporation of sweat: a layer of air between clothing and the body is quickly saturated with pairs and further evaporation of sweat stops.
In the process of heat transfer using evaporation, although it is only one of the methods of thermoregulation, there is one exceptional dignity - if the external temperature exceeds the average temperature of the skin, then the body can not give heat to the external medium with other methods of thermoregulation (radiation, convection and conduction), Which we will look below. The body under these conditions begins to absorb heat from the outside, and the only way of heat scattering becomes an increase in the evaporation of moisture from the body surface. Such evaporation is possible until the environmental humidity remains less than 100%. With intensive sweating, high humidity and low air movement, when sweat drops, not soying to evaporate, merge and flow from the body surface, heat transfer by evaporation becomes less effective.
When evaporating sweat, our body gives its energy. Actually, due to the energy of our body, the fluid molecule (i.e. sweat) tear the molecular bonds and move from the liquid to the gaseous state. Energy is spent on the break of connections, and, as a result, the body temperature drops. The refrigerator works on the same principle. It manages to maintain the temperature inside the chamber, much lower than the ambient temperature. It does this due to electricity consumed. And we do it using the energy obtained from the splitting of food products.
Reduce heat from evaporation can help control over the selection of clothing. Clothes need to be selected on the basis of weather conditions and current activity. Do not be lazy to remove excessive clothes when the loads are growing. You will sweat less. And do not be lazy to wear it again when the loads stop. Remove moisture and windpower if there is no rain with the wind, otherwise the clothes will mock from the inside, from your sweat. And, in contact with wet clothing, we lose heat and thermal conductivity. Water 25 times better than air carries out heat. So, in wet clothing we lose heat 25 times faster. That is why it is important to support dry clothes.
Evaporation is divided into 2 types:
but) Unprecedable permission (without the participation of sweat glands) is the evaporation of water from the surface of light, mucous membranes of the respiratory tract and water, leaking through the epithelium of the skin (evaporation from the surface of the skin, even if the skin is dry).
During the day through the respiratory tract, 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 by thermal shortness of breathing. Through the epidermis, on average, about 240 ml of water seeps per day. Consequently, this way the body loses up to 139 kcal per day. This value, as a rule, does not depend on the regulation processes and various environmental factors.
b) felt permissions(with the active participation of sweat glands) - This is the return of heat by evaporation of sweat. On average, 400-500 ml of sweat is distinguished during a comfortable temperature of the medium, therefore, up to 300 kcal of energy are given. The evaporation of 1 liters of Pot in a person with a body weight of 75 kg can lower the body temperature at 10 ° C. However, if necessary, the volume of sweating may increase to 12 l per day, i.e. By sweating, you can lose up to 7.000 kcal per day.
Evaporation efficiency largely depends on the medium: the higher the temperature and lower humidity, the higher the efficiency of sweating as a heat recoil mechanism. With 100% humidity, evaporation is impossible. With high humidity of atmospheric air, high temperatures are heavier than at low humidity. In saturated water vapor air (for example, in the bath) sweat is highlighted in large quantities, but does not evaporate and flows from the skin. Such sweating does not contribute to heat recovery: only the part of the sweat, which evaporates from the surface of the skin, is important for heat transfer (this part of the sweat is an effective sweating).
2. Radiation (radiation):
Radiation (radiation)- This is a way of recoil heat into the environment of the human body surface in the form of electromagnetic waves of the infrared range (A \u003d 5-20 μM). Due to the radiation, all objects give energy, the temperature of which is above absolute zero. Electromagnetic radiation freely pass through the vacuum, the atmospheric air for it can also be considered "transparent".
As is known, any object that is heated above the ambient temperature radiates heat. Everyone felt it sitting by the fire. The fire radiates heat and heats the items around. At the same time, the fire loses its warmth.
The human body begins to emit heat as soon as the ambient temperature drops lower than the skin surface temperature. To prevent the heat loss by radiation, you need to protect the open areas of the body. This is done with clothes. Thus, we create a layer of air in clothing between the skin and the environment. The temperature of this layer will be equal to the body temperature and heat loss by radiation decrease. Why does heat loss not stop at all? Because now the heated clothing will emit heat, losing it. And, even putting on another layer of clothing, you do not stop radiation.
The amount of heat dissipated by the organism into the environment by radiation is proportional to the area of \u200b\u200bthe radiation surface (body surface area, not covered with clothing) and the difference in the average values \u200b\u200bof skin temperature and the environment. At ambient temperature of 20 ° C and relative humidity of 40-60%, the body of an adult dispels about 40-50% of the total heat. If the ambient temperature exceeds the average skin temperature, the human body, absorbing infrared rays emitted by the surrounding objects is warmed.
The heat transfer by radiation increases when the ambient temperature decreases and decreases when it is increased. Under conditions of constant ambient temperature, radiation from the surface of the body increases with increasing skin temperature and decreases when it is reduced. If the average surface temperatures of the skin and the environment are aligned (the temperature difference becomes equal to zero), then the return of heat by radiation becomes impossible.
Reduced the heat transfer of the body by radiation by reducing the area of \u200b\u200bthe radiation surface - by changing body position. For example, when a dog or a cat is cold, they turn into a tangle, thereby reducing the surface of heat transfer; When it is hot, animals, on the contrary, take the position at which the heat transfer surface increases as much as possible. This method of physical thermoregulation is not deprived of both a person, "turning around in the ball" during the sleep in the cold room.
3. Heat consideration (conduction):
Heat Conduction (Condition) - This is a way of returning heat, which takes place when contacting the body contact with other physical bodies. The amount of heat given to the organism into the environment in this method is proportional to the difference in the average temperature of the contacting bodies, the area of \u200b\u200bcontacting surfaces, the heat of thermal contact and the thermal conductivity of the inactive body.
Heat loss with thermal conductivity occurs when direct contact with a cold object occurs. At this point, our body gives its warmth. The speed of heat loss strongly depends on the thermal conductivity of the item with which we are in contact. For example, the thermal conductivity of the stone is 10 times higher than wood. Therefore, sitting on the stone, we will lose heat much faster. You probably noticed that sitting on the stone is somehow colder than on a log.
Decision? Isolate your body from cold items with bad heat conductors. Simply put, for example, if you are traveling in the mountains, it is arranged for the halt, sit on a tourist rug or clothing crust. For the night, be sure to put the touring rug for the sleeping bag, corresponding to weather conditions. Or, as a last resort, the thick layer of dry grass or needles. The Earth spends well (and therefore "selects") heat and is very cooled at night. In winter, do not take metal items with bare hands. Use gloves. In severe frosts from metal objects, you can get local frostbite.
Dry air, adipose tissue is characterized by low thermal conductivity and are thermal insulators (bad heat conductors). Clothing reduces heat transfer. The heat loss prevents the layer of motionless air, which is located between clothing and skin. The thermal insulation properties of clothing is higher than the smallest of its structure containing air. This explains the good thermal insulating properties of wool and fur clothing, which makes it possible to reduce heat scattering by heat conduction. The air temperature under clothing reaches 30 ° C. And, on the contrary, the naked body loses heat, since the air on its surface is replaced all the time. Therefore, the temperature of the skin of the nude body parts is much lower than dressed.
Wet, saturated with water vapor air is characterized by high thermal conductivity. Therefore, the residence of a person in a high humidity medium at low temperatures is accompanied by an increase in the body's heat loss. Wet clothing also loses its heat insulating properties.
4. Convection:
Convection- This is the method of heat transfer of the body, carried out by transferring heat by moving air particles (water). For heat scattering, convection requires strengthening the surface of the body with a lower temperature with a lower temperature than the skin temperature. At the same time, the air layer intensive with the skin is heated, reduces its density, rises and is replaced by colder and more dense air. Under conditions, when the air temperature is 20 ° C, and the relative humidity is 40-60%, the body of an adult dispels into the environment by heat resifying and convection about 25-30% of heat (basic convection). With increasing speed of air flow (wind, ventilation), the intensity of heat transfer (forced convection) is significantly increasing.
The essence of the convection process lies in the following - our body heats the air near the skin; The heated air becomes easier cold and climbs up, and it replaces cold air, which is heated again, it becomes easier and displaced by the next portion of the cold. If the heated air does not capture with clothes, then this process will be infinite. In fact, we are not warm clothes, but the air that she is delayed.
When the wind blows, the situation worsens. The wind bears huge portions of unheated air. Even when we wear a warm sweater, the wind is worthwhile to drive out of it warm air. The same thing happens when we are moving. Our body is "crashed" into the air, and it flows around us, acting as the wind. This also multiplies heat loss.
What's the solution? Wear a windproof layer: windbreaker and unproduced pants. Do not forget about the protection of the neck and head. Because of the active blood circulation of the brain, the neck and head are the most heated parts of the body, so heat losses are very large from them. Also, in cold weather you need to avoid blown places both while driving and when choosing a place for overnight.
Chemical thermoregulation:
Chemical thermoregulationthe heat generation is carried out due to changes in the level of metabolism (oxidative processes) caused by microvibration of muscles (oscillations), which leads to a change in the formation of heat in the body.
The heat source in the body is exothermic reactions of oxidation of proteins, fats, carbohydrates, as well as hydrolysis ATP (adenosine trifhosphate is a nucleotide, which plays an extremely important role in the exchange of energy and substances in the body; First of all, this compound is known as a universal energy source for all biochemical processes occurring in live systems). When nutrient cleavage, some of the released energy is accumulated in ATP, part is dissipated as heat (primary heat - 65-70% energy). When using macro-ergic bonds of ATP molecules, part of the energy goes to the performance of useful work, and part dissipates (secondary heat). Thus, two heat fluxes - primary and secondary - are heat-product.
Chemical thermoregulation is important for maintaining the constancy of body temperature both under normal conditions and when the ambient temperature changes. In humans, the gain of heat generation due to an increase in the intensity of metabolism is noted, in particular, when the ambient temperature becomes below the optimal temperature, or the comfort zone. For a person in ordinary light clothing, this zone is within 18-20 ° C, and for naked is 28 ° C.
The optimal temperature during staying in water is higher than in air. This is due to the fact that water with high heat capacity and thermal conductivity cools the body 14 times stronger than air, therefore, in the cool bath, the metabolism increases much more than during the air stay at the same temperature.
The most intensive heat generation in the body occurs in muscles. Even if a person lies motionless, but with a tense muscles, the intensity of oxidative processes, and at the same time heat generation, increase by 10%. A small motor activity leads to an increase in heat generation by 50-80%, and heavy muscle work - by 400-500%.
In chemical thermoregulation, liver and kidneys play a significant role. The blood temperature of the liver veins is above the blood temperature of the liver artery, which indicates intensive heat generation in this organ. When the body is cooled, heat products in the liver increases.
If necessary, increase the heat product, in addition to the possibility of obtaining heat from the outside, mechanisms are used in the body that increase the production of thermal energy. These mechanisms include contractileand non-worn thermogenesis.
1. Contracting thermogenesis.
This type of thermoregulation works if it is cold and you need to raise the body temperature. This method is in Reduced muscle. When cutting muscles, hydrolysis of ATP increases, therefore the flow of secondary warmth rising to warming the body increases.
The arbitrary activity of the muscular apparatus, mainly occurs under the influence of the bark of large hemispheres. At the same time, the increase in heat-product is possible by 3-5 times compared with the magnitude of the main exchange.
Usually, with a decrease in the temperature of the medium and blood temperature, the first reaction is increase the thermoregulation tone (The hair on the body "stand end", "goosebumps" appear). From the point of view of cutting mechanics, this tone is microvibration and allows you to increase heat for 25-40% of the initial level. Usually, the muscles of the neck, head, torso and limbs take part in the creation of tone.
With a more significant overcooling, the thermoregulation tone passes into a special type of muscle contractions - muscular cold tremor, in which the muscles do not make useful work and their reduction is directed exclusively to heat production. Hod shiver is an involuntary rhythmic activity of superficially arranged muscles, as a result of which the metabolic processes of the body are significantly enhanced, the consumption of oxygen and carbohydrates with muscle tissue increases, which attracts itself Increase heat generation. A shiver begins often with the muscles of the neck, faces. This is explained by the fact that, first of all, the blood temperature should increase, which flows to the brain. It is believed that heat-producing with cold tremors is 2-3 times higher than with arbitrary muscle activity.
The described mechanism works on the reflex level, without the participation of our consciousness. But it is possible to raise the body temperature conscious motor activity. When performing physical exertion of different power, heat products increases 5-15 times compared with the level of rest. The kernel temperature during the first 15-30 minutes of long-term work is fairly rapid up to a relatively stationary level, and then stored at this level or continues to slowly increase.
2. Incomliant thermogenesis:
This type of thermoregulation can lead both the increase and lower the body temperature. It is carried out by accelerating or slowing the catabolic metabolic processes (oxidation of fatty acids). And this, in turn, will lead to a decrease in or increasing heat product. Due to this type of thermogenesis, the level of heat-product in humans can grow 3 times compared with the level of the main exchange.
The regulation of non-conscientatory thermogenesis processes is carried out by activating the sympathetic nervous system, the production of hormones of the thyroid and brain layer of the adrenal glands.
E. The thermoregulation management.
Hypothalamus.
The thermoregulation system consists of a number of elements with interrelated functions. Information about the temperature comes from thermistors and with the help of the nervous system enters the brain.
The main role in thermoregulation plays hypothalamus. It contains the main centers of thermoregulation, which coordinate numerous and complex processes that ensure the preservation of body temperature at a constant level.
Hypothalamus - This is a small area in the intermediate brain, which includes a large number of cell groups (over 30 nuclei), which regulate the neuroendocrine activity of the brain and homeostasis (the ability to maintain the constancy of its internal state) of the body. The hypothalamus is connected by nervous ways with almost all departments of the central nervous system, including the bark, hippocampus, almond, cerebellum, brain barrel and spinal cord. Together with the hypophysome, the hypothalamus forms a hypothalamic-pituitary system in which the hypothalamus controls the release of pituitary hormones and is a central link between the nervous and endocrine system. It highlights hormones and neuropeptides, and regulates such functions as a feeling of hunger and thirst, thermoregulation of the body, sexual behavior, sleep and wakefulness (circadian rhythms). Research recent years show that hypothalamus plays an important role in the regulation of higher functions, such as memory and emotional state, and thereby participates in the formation of various aspects of behavior.
The destruction of the centers of the hypothalamus or violation of nervous bonds leads to the loss of the ability to adjust the body temperature.
In the front hypotalamus there are neurons that control the heat transfer processes(They provide physical thermoregulation - the narrowing of the vessels, sweating). In the destruction of the neurons of the front hypothalamus, the body poorly tolerates high temperatures, but physiological activity in cold conditions is preserved.
Rear hypothalamus neurons control heat generation processes(They provide chemical thermoregulation - strengthening heat generation, muscular trembling). If their damage is disturbed by the ability to strengthen the energy exchange, so the body does not tolerate the cold.
The heat-sensitive nerve cells of the precortic area of \u200b\u200bthe hypothalamus directly "measure" the temperature of the arterial blood flowing through the brain, and have high sensitivity to temperature changes (capable of distinguishing the difference in blood temperature in 0.011 ° C). The ratio of cold and heat-sensitive neurons in the hypothalamus is 1: 6, so central thermistors are preferably activated by increasing the temperature of the "core" of the human body.
Based on the analysis and integration of information on the value of blood temperature and peripheral tissues, in the precortic region of the hypothalamus is continuously determined by the mean (integral) body temperature. These data are transmitted through inserting neurons into the group of neurons of the front section of the hypothalamus, defined in the body a certain level of body temperature - "installation point" of thermoregulation. Based on the analysis and comparisons of the values \u200b\u200bof the average body temperature and the specified temperature value to be regulated, the mechanisms of the "installation point" through the effector neurons of the rear hypothalamus affect the processes of heat transfer or heat products in order to comply with the actual and predetermined temperature.
Thus, due to the function of the thermal control center, the equilibrium between heat-product and heat transfer is established, which allows to maintain the body temperature in the optimal organism for the life of the body.
Endocrine system.
The hypothalamus manages heat-product and heat transfer processes, sending nerve impulses to the glands of internal secretion, mainly thyroid, and adrenal glands.
Participation thyroid gland The thermoregulation is due to the fact that the effect of reduced temperature leads to enhanced allocation of its hormones (thyroxine, triiodothyronine), accelerating the metabolism and, therefore, heat generation.
Role adrenal glandsit is associated with the release of Catecholamines (adrenaline, norepinerenaline, dopamine), which, reinforcing or reducing oxidative processes in tissues (for example, muscular), increase or decrease the heat vessels and narrow or increase the skin vessels by changing the level of heat transfer.
1) Introduction ............................................................................33
2) Poikilotermia, heterothermia, homoothermia ........................... ... 4
3) principles of body temperature regulation, thermal balance ............ ... 5
4) Physiology temorotheptors ................................................... 6
5) the centers of thermoregulation ...................................................... ... 8
a) Centers of heat transfer ...................................................... ... 9
b) heat-product centers ................................................. ..10
6) Heat Production Mechanisms ................................................. ..10
a) contracting thermogenesis ............................................. 11
b) non-worn thermogenesis .......................................... 12
7) heat transfer mechanisms ...................................................... .12
a) heat transfer ......................................................... ... 13
b) heat emission ............................................................ .13
c) convection .............................................................................. ..14
d) evaporation .................................................................. ..14
8) metabolism .................................................................. .16
9) Food ..........................................................................................17
10) Conclusion ................................................................................... ... 20
11) List of literature used .......................................... ..23
Introduction
No matter how diverse forms of manifestation of life, they are always inextricably linked with the conversion of energy. Energy exchange is a feature inherent in each living cell. Rich with energy nutrients are absorbed and chemically converted, and the final methods of metabolism with lower energy content are separated from the cell. According to the first law of thermodynamics, the energy does not disappear and does not occur again. Organisms should receive energy in an environment available to them and return the corresponding amount of energy in the form less suitable for further use.
Around the century ago, the French physiologist Claude Bernard found that a living organism and the medium form a single system, the gap both between them occurs continuous metabolism and energy. The normal life activity of the body is maintained by the regulation of internal components requiring energy costs. The use of chemical energy in the body is called energy exchange: it is it that serves as an indicator of the overall condition and physiological activity of the body.
Exchange (or metabolic) processes, during which the specific elements of the body are synthesized from the absorbed foods, called anabolism; Accordingly, those metabolic processes, during which the structural elements of the body or absorbed food products are disintegrated, called catabolism.
Live organism produces heat that goes to heating the body. The specific heat capacity of the human body (the amount of heat required to heat the tissue is 1 ° C) equal to an average of 0.83 kcal / kg per 1 degree (for water - 1 kcal / kg per degree). To increase the body temperature of a person weighing 70 kg per 1 °, 58.1 kcal should be spent (0.83 70). On average, the person weighing 70 kg in peace distinguishes about 72 kcal / hour. Therefore, if there were no second process - heat transfer, then the human tissue would be heated at 1.24 ° (72: 58,1). However, this does not occur, since in normal conditions, the speed of heat products is equal to the speed of its loss. This is the name of the heat balance, which is based on the processes of regulation of heat-product and heat transfer. All together it is called thermoregulation.
Poikilotermia, heterothermia, homoothermia
In the evolution of the thermoregulation system, there is a lower level on which the body temperature of the animal depends mainly on the temperature of the medium: when it decreases, the body temperature also falls on the contrary. This state of the body temperature received the name of the cacototermia, and animals are caught. A typical Poikiloterman representative is a frog. In winter, the body temperature of the frog approaches zero. In this state, it is still capable of performing long-term jumps, but not more than 12-15 cm. In summer, the body temperature reaches it 20-25 ° C, and it can jump much further - to 1 m. Usually in low temperatures, caototermic animals flow To the anabiosis state. There are microorganisms for which the optimum temperature of the medium varies from 0 ° C to minus 60 ° C, for example, microbes living in the layer of ice, or, on the contrary, microorganisms that carry out the temperature of the medium from + 70 ° C to + 120 ° C, for example, Microbes hot springs.
Heat Production and heat transfer mechanisms.
A - The role of organs in heat
B - the role of organs in the heat transfer
A number of animals, such as a bat, rodents, some species of birds, for example, hummingbird belongs to the group of heterothermal organisms: at some conditions they are caught by the organisms, with other - homoothermal.
Mammals belong to homoothermal organisms (warm-blood), which have isothermia, or the constancy of the body temperature. However, isothermia has a relative nature: the temperature of the tissues located is not deeper than 3 cm from the body surface (leather, subcutaneous fiber, surface muscles), or shell, - largely depends on the external temperature, while the core of the body, i.e. the cent , internal organs, skeletal muscles, located deeper 3 cm, have a relatively constant temperature, regardless of ambient temperature. Thus, warm-blooded have a caustic casing and homoothermal "core", or "core".
Heat Production Organs and Heat Development Management.
To - Bark, KZh - Leather, TsGT - Centers of the Hypothalamus, CDC - Vasomotor Center, PM - Clean Brain, CM - Spinal Cam, GF - Guipophysia, TG - Tireotropic Hormon, GWS - Breasts of Internal Secretion, GM - Hormones, M - Muscle , IF - liver, PTP - digestive tract, a, b - flow of a differential impulse.
Accounting The average temperature of the brain, blood, internal organs is approaching 37 ° C. The physiological limit of oscillations of this temperature is 1.5 °. The change in blood and internal organ temperature in humans by 2-2.5 ° C on the middle level is accompanied by a violation of physiological functions, and the body temperature is above 43 ° C is almost incompatible with human life.
Principles of body temperature regulation,
Thermal Balance
The temperature of the nucleus (body) is determined by two streams - heat generation (heat product) and heat transfer (heat generation). With a thermal-neutral, or comfortable zone (at 27-32 ° C), there is a balance between heat-product and heat transfer. For example, in the conditions of physiological peace in the body, about 1.18 kcal / minute (or about 70 kcal per hour) is produced (or about 70 kcal per hour) and the same amount of heat is given to the environment. At low temperature medium, despite the protection mechanism, the weight loss increases by the body. Under these conditions, the body should be equivalent to the heat of body temperature to conserve body temperature. Thus, there is a new level of thermal balance. For example, at a temperature of air 10 ° C, the heat transfer reaches 120 kcal / hour (under comfort - 70 kcal / hour), therefore, to maintain the body temperature at a constant level, heat product flow should also increase to 120 kcal / hour.
At high ambient temperature, for example, at 40 ° C, heat recovery significantly decreases, for example, up to 40 kcal / hour (instead of 70 kcal / hour in a comfortable environment). To maintain the constancy of the body temperature, the heat products should also decrease approximately 40 kcal / hour. A new level of thermal balance is established, which provides maintenance of body temperature.
Thus, the leading factor determining the level of thermal balance is the ambient temperature.
Considering that heat products varies depending on the type of human physical activity, and the magnitude of heat transfer depends largely on the ambient temperature, the mechanisms of regulation of heat-product and heat transfer are needed. They are carried out with the participation of specialized brain structures combined into the center of thermoregulation. The principle of regulation is that the control device (thermoregulation center) receives information from thermistors. Based on this information, it produces such teams due to which the activity of control facilities (working structures that determine the intensity of heat-product and heat transfer) changes in such a way that there is a new level of thermal balance, as a result of which the body temperature remains at a constant level. The thermoregulation system can operate in tracking mode or on the principle of mismatch - the blood temperature has changed, the operation of control objects changes. However, in the thermoregulation system, a softer method of maintaining the constancy of the body temperature is also provided, which is based on the principle of regulation by perturbation: the change in the temperature of the medium is captured, and not waiting for it when it is reflected in the blood temperature, the system arises commands that change the operation of control objects in this way, That the blood temperature is saved constant. In addition, the thermoregulation system can function in the prediction control mode, i.e. early control (these are conditional reflexes): a person is just going to reach the winter street, and he has already increasing the products of heat required to compensate for heat loss that will occur A man on the street in low temperatures. In all cases, information about body temperature (kernel and shell) is required to optimally regulate the intensity of heat-product and heat transfer. It is transmitted to the CNS from thermistors.
Physiology of thermistors
The thermistors are located on different areas of the skin, in the internal organs (in the stomach, intestines, the urine, urinary bubble), in the respiratory tract, mucous, cornea of \u200b\u200bthe eye, skeletal muscles, blood vessels, including in the arteries, aortal and carotid zones, in many large veins, as well as in the crust of large hemispheres, spinal cord, reticular formation, middle brain, hypothalamus.
Thermoreceptors of the CNS are most likely neurons that simultaneously perform the role of receptors and the role of afferent neuron.
The most fully studied the thermistors of the skin. Most of the thermistors on the skin of the head (face) and neck. On average, 1 mm 2 of the surface of the skin accounts for 1 thermoreceptor. Skin thermistors are divided into cold and thermal. In turn, the cold is divided into actually cold (specific), responding only to temperature change, and tactful-cold, or non-specific, which can also be responsible for change in temperature and pressure.
Cold receptors are located at a depth of 0.17 mm from the skin surface. There are about 250 thousand of all. React to a change in temperature with a short latent period. In this case, the frequency of the potential of the action linearly depends on the temperature in the range from 41 ° to 10 ° C: the lower the temperature, the higher the pulsation frequency. Optimal sensitivity in the range from 15 ° to 30 ° C, and according to some data - up to 34 ° C.
Thermal receptors are deeper - at a distance of 0.3 mm from the skin surface. There are about 30 thousand them. React to a change in temperature linearly in the range from 20 ° to 50 ° C: the higher the temperature, the higher the frequency of generation of the action potential. Optimum sensitivity in the range of 34-43 ° C.
Among the cold and thermal receptors there are various receptor population sensitivity: some react to a change in temperature, equal to 0.1 ° C (highly sensitive receptors), others - to change the temperature equal to 1 ° C (medium sensitivity receptors), the third - to change 10 ° С (high-speed, or low sensitivity receptors).
Information from the skin receptors is in the central nervous system on the afferent fibers of the A-Delta group and the fibers of the group C, in the CNS it comes to different speeds. Most likely that pulses from cold receptors are on the fibers of A-Delta.
The impulsation from the skin receptors enters the spinal cord, where the second neurons are located, giving rise to the spinatelamic path, which ends in the values \u200b\u200bof the Talamus ventricular nuclei, from where the part of the information enters the sensor engine zone of the large hemispheres, and the part is to the hypothalamic centers of thermoregulation.
The highest sections of the CNS (bark and limbic system) provide the formation of heat supply (heat, cold, temperature comfort, temperature discomfort). The feeling of comfort is based on the flow of impulsation from the thermoreceptors of the shell (mainly leather). Therefore, the body can be "fooling" - if in high temperature conditions cool the body with cool water, as it happens with a summer bathing in a heat, then a feeling of temperature comfort is created.
Centers thermoregulation
The thermoregulation is mainly carried out with the participation of the CNS, although some processes of thermoregulation without CNS are also possible. So, it is known that blood vessels of the skin can react by themselves to the cold: due to the heat sensitivity of smooth muscle cells to cold, the smooth muscles relaxation occurs, so in the cold at the beginning there is a reflex spasm, which is accompanied by a painful feeling, and then the vessel is expanding due to the direct impact of the cold for smooth muscle cells. Thus, the combination of two regulation mechanisms makes it possible, on the one hand, to maintain heat, and on the other - do not allow tissues to test oxygen starvation.
The thermoregulation centers are in a broad sense a set of neurons participating in thermoregulation. They found in various fields of the central nervous system, including in the crust of large hemispheres, the limbic system (amygdalar complex, hippocampus), thalamus, hypothalamus, average, oblong and spinal cord. Each brain department fulfills its tasks. In particular, the bark, the limbic system and Talamus provide control over the activities of hypothalamic centers and spinal structures, forming adequate human behavior in various temperature conditions of the medium (working posture, clothing, arbitrary motor activity) and sensations of heat, cold or comfort. With the help of large hemispheres, advance (early) thermoregulation is carried out - conventional reflexes are formed. For example, a man who gathered to enter the street in the winter increases in advance the heat product.
Sympathetic and somatic nervous systems participate in thermoregulation. The sympathetic system regulates the processes of heat product (glycogenolysis, lipolysis), heat transfer processes (sweating, heat transfer by heat emission, heat management and convection - by changing the tone of the skin vessels). The somatic system regulates the tonic stress, an arbitrary and involuntary phase activity of skeletal muscles, i.e. the processes of contractile thermogenesis.
The main role in thermoregulation plays hypothalamus. It distinguishes the accumulations of neurons regulating heat transfer (heat transfer center) and heat product.
For the first time, the existence of such centers in the hypothalamus found K. Bernard. It produced a "heat injection" (mechanically irritated hypothalamus animal), after which the body temperature rises.
Animals with destroyed nuclei of the prevention area of \u200b\u200bthe hypothalamus poorly carry high ambient temperatures. The irritation of the electric shock of these structures leads to the expansion of the skin vessels, sweating, the appearance of thermal shortness. This is a cluster of nuclei (mainly paraventricular, suprasoptic, suprahiamatic) and got the name of the "Center for Heat Products".
In the destruction of the neurons of the rear departments of the hypothalamus, the animal does not tolerate the cold. Electrostimulation of this region causes an increase in body temperature, muscle tremor, an increase in lipolysis, glycogenolysis. These neurons believe that these neurons are mainly concentrated in the field of centromedical and domdomal nuclei of the hypothalamus. The accumulation of these cores received the name of the "Center for Heat Production".
The destruction of thermoregulation centers turns a homoothermal organism in the pallotermic.
According to K. P. Ivanov (1983, 1984), in the centers of heat product and heat transfer, there are sensory, integrating and efferent neurons. Sensory neurons perceive information from thermistors located on the periphery, as well as directly from blood, washing neurons. K. P. Ivanov divides sensory neurons into two types: 1) perceive information from peripheral thermistors and 2) perceiving blood temperature. Information from sensory neurons enters the integrating neurons, where the sum of all information about the state of the kernel temperature and body shell occurs, i.e., these neurons "calculate" the average body temperature. Then information enters command neurons, in which the current value of the average body temperature is pulled at the specified level. The question of neurons that set this level remains open. But probably there are such neurons, and they can be arranged in a crust, a limbic system or, more likely in the hypothalamus. So, if, as a result of comparison, the deviation from the specified level is detected, the effectant neurons are excited: in the center of heat transfer - these are neurons regulating the sweating, the tone of the skin vessels, the volume of circulating blood, and in the center of the heat-product - these are neurons that regulate the process of heat formation. It remains not yet clear, every center (heat transfer and heat products) is engaged in "calculations" and independently makes decisions, or there is another separate center where this process is performed.
Centers of heat transfer. When the efforts of the efferent neurons of the heat transfer center may decrease the skin of the skin vessels. This is carried out due to the impact of the efferent neurons of the heat transfer center ("skin vessels") on the Vasomotor Center, which, in turn, affects the activity of spinal sympathetic neurons, sending the flow of pulses to the smooth muscles of the skin vessels. As a result, when the hypothalamic neurons of the "Skin vessels" decreases the tone of the skin vessels, the skin blood flow increases and the return of heat increases due to heat emission, heat management and convection. The amplification of skin blood flow contributes to the increase in sweating (heat recovery by evaporation). If the change in the skin blood flow is not enough to return heat, then neurons are excited, which lead to the ejection of blood from blood depot and, thus, to an increase in heat transfer volume. If this mechanism does not contribute to the normalization of the temperature, the effectant neurons of the heat transfer center are excited, which excite the sympathetic neurons that activate sweat glands, these neurons of the hypothalamus can be conditionally called "stretching neurons", or neurons regulating sweating. Sympathetic neurons that activate the sweating are located in the side pillars of the spinal cord (TH 2 -L 2), and postganglyonic neurons are localized in sympathetic ganglia. Postgangngling fibers that go to sweat glands are cholinergic, their mediator is acetylcholine, which increases the activity of the sweat gland due to the interaction with its M-cholinoreceptors (Blocator - Atropin).
Centers of heat product. Efferterent neurons of the heat-product center can also be divided into several types, each of which includes the appropriate heat-product mechanism.
a) Some neurons at their excitation activate the sympathetic system, as a result of which the intensity of the processes generating energy (lipolysis, glycogenolysis, glycoliz, oxidative phosphorylation increases). In particular, the sympathetic nerves due to the interaction of their mediator (norepinenaline) with beta-adrenoreceptors activate the processes of glycogenolysis and glycolysis in the liver, the processes of lipolysis in the oil brown.
At the same time, when the sympathetic nervous system is excited, the secretion of the brain layer hormones is increments - adrenaline and norepinenaline, which increase the production of heat in the liver, skeletal muscles, a birch brown, activating glycogenolysis, glycoliz and lipolysis.
b) In the hypothalamus there are efferent neurons that affect the pituitary gland, and through it - on the thyroid gland: the products of iodine-containing hormones (T 3 and T 4) increase, which may increase the process of oxidative phosphorylation, increase the flow of primary heat, so on. e. Under their influence, the accumulation of energy in ATP is reduced, and most of the energy dissipates in the form of heat.
c) In the hypothalamic center of heat-product, there is also a population of efferent neurons, the excitation of which leads to the appearance of the thermoregulation tone (the tone increases in skeletal muscles, due to which heat generation increases by about 40-60%) or phase-like cuts of individual muscle occur
The fibers that were called "shivering". In all these cases, the team from the efferent neurons of the hypothalamus is transmitted, ultimately, on alpha-motoneurons. The central trembling path is an efferent path that comes from the hypothalamus to alpha-motnelones through intermediate formations, in particular, through the medium brain tire (textospinal journey) and through the red core (Rubrostinal tract). The details of this path are still not clear.
Heat Production Mechanisms
The source of heat in the body is exothermic reactions of oxidation of proteins, fats, carbohydrates, as well as hydrolysis of ATP. In the hydrolysis of nutrients, some of the released energy is accumulated into ATP, and the part is dissipated as heat (primary heat). When using the energy accumulated in AGF, part of the energy goes to perform useful work, the part is dissipated as heat (secondary heat). Thus, two heat fluxes - primary and secondary - are heat-product. With a high temperature of the medium or contact of a person with a hot body, part of the heat can be obtained from the outside (exogenous heat).
If necessary, to increase the heat product (for example, under conditions of low medium temperature), in addition to the possibility of heat obtaining from outside, there are mechanisms in the body that increase heat products.
Classification of heat-product mechanisms:
1. Creative thermogenesis - heat products as a result of reducing skeletal muscles:
a) arbitrary activity of the locomotor unit;
b) thermoregulation tone;
c) Cold muscle tremor, or involuntary rhythmic activity of skeletal muscles.
2. Socratic thermogenesis, or unrehable thermogenesis (heat production as a result of activation of glycolysis, glycogenolysis and lipolysis):
a) in skeletal muscles (due to disunity of oxidative phosphorylation);
b) in the liver;
c) in the beam;
d) due to the specific dynamic action of food.
Contracting thermogenesis
When cutting muscles, the hydrolysis of ATP increases, and therefore the flow of secondary heat is increasing, which goes to warming the body. Arbitrary muscular activity, mainly, occurs under the influence of the bark of large hemispheres. Man's experience shows that in low conditions of the medium it is necessary to move. Therefore, conditional reflex acts are being implemented, arbitrary motor activity increases. What it is higher, the higher the heat product. It is possible to increase it in 3-5 times compared with the magnitude of the main exchange. Usually, with a decrease in the temperature of the medium and blood temperature, the first reaction is an increase in the thermoregulation tone. For the first time, he was revealed in 1937 in animals, and in 1952 - in humans. With the help of the method of electromyography, it was shown that with increasing the tone of the muscles caused by the supercooling, the electrical activity of the muscles increases. From the point of view of cutting mechanics, the germormost tone is microvibration. On average, when it appears, heat-product increases by 20-45% of the initial level. With a more significant supercooling, the thermoregulation tone passes into the muscular cold trembling. The thermoregulation tone is economical than muscular trembling. Usually, the muscles of the head and neck are involved in its creation.
Shivering, or cold muscle tremor, is an involuntary rhythmic activity of superficial muscles, as a result of which heat-producing increases compared to the initial level 2-3 times. Usually, you first arise a trembling in the muscles of the head and neck, then the torso and, finally, the limbs. It is believed that the effectiveness of heat-product with trembling is 2.5 times higher than during arbitrary activities.
The signals from the neurons of the hypothalamus go through the "central shit" (tectum and the red core) to the alpha-motnelones of the spinal cord, from where the signals go to the appropriate muscles, causing their activity. The strip-like substances (muscle relaxants) due to the blockade of n-cholinoreceptors block the development of the thermoregulation tone and cold tremors. It is used to create artificial hypothermia, and also takes into account when conducting operational interventions under which Miorosanta applies.
Non-worn thermogenesis
It is carried out by increasing the processes of oxidation and reduce the efficiency of conjugation of oxidative phosphorylation. The main place of heat products are skeletal muscles, liver, brown fat. Due to this type of thermogenesis, heat products may increase 3 times.
In skeletal muscles, an increase in non-conscious thermogenesis is associated with a decrease in the efficiency of oxidative phosphorylation due to disagreement of oxidation and phosphorylation, in the liver - mainly by activating glycogenolysis and the subsequent glucose oxidation. Brown fat increases heat product due to lipolysis (under the influence of sympathetic effects and adrenaline). Brown fat is located in the occipital region, between the blades, in the medilion in the course of large vessels, in the axillary depressures. In peace of rest, about 10% of the heat is formed in the beam. When cooled, the role of brown fat rises sharply. When cold adaptation (residents of the Arctic zones) increases the mass of the brown fat and its contribution to the general heat product.
The regulation of non-conscientatory thermogenesis processes is carried out by activating the sympathetic system and production of thyroid hormones (they dismiss oxidative phosphorylation) and the brain layer of the adrenal glands.
Heat transfer mechanisms
The bulk of the heat is formed in the internal organs. Therefore, the inner stream of heat for removal from the body must come to the skin. The transfer of heat from the internal organs is carried out due to heat transfer (in such a way less than 50% of heat) and convection, i.e., heat-passenger. Blood due to its high heat capacity is a warm conductor of heat.
The second heat flow is a stream directed from the skin on Wednesday. It is called an outdoor stream. Considering heat transfer mechanisms, they usually mean this one stream.
The impact of heat on Wednesday is carried out with the help of 4 main mechanisms:
1) evaporation;
2) heat controlling;
3) heat emission;
4) convection.
Heat transfer mechanisms and heat release management.
To - Bark, KZh - Leather, TsGT - Centers of the Hypothalamus, SDC - Vasomotor Center, PM - The oblongable brain, cm - spinal cord, GF - pituitary gland, TG - thyrotropic hormone, ZVS - glands of internal secretion, GM - hormones, PTR - digestive The tract, KS - blood vessels, l - light, and, b - the flow of afferent impulsation.
The contribution of each mechanism to heat transfer is determined by the condition of the medium and the speed of heat production in the body. In temperature comfort, the bulk of heat is given due to heat transfer, heat emission and convection and only 19-20% - by evaporation. At high medium temperature, up to 75-90% of heat is given due to evaporation.
Heat Conduction - This is a way to recover the heat body, which directly contacts the human body. The lower the temperature of this body, the higher the temperature gradient, the higher the heat loss rate due to this mechanism. Usually this method of heat recovery is limited by clothing and air layers, which are good heat insulators, as well as subcutaneous fat layers. The thicker this layer, the less likelihood of heat transfer to the cold body.
Heavyweight - The return of heat from the skin sites, not covered with clothing. It occurs through long-wave infrared radiation, so this type of heat transfer is also called radiation heat transfer. Under the conditions of temperature comfort, up to 60% of heat are given at the expense of this mechanism. The efficiency of heat emission depends on the temperature gradient (the higher it is higher, the more heat is given), from the area with which radiation occurs, from the number of objects in the medium that absorb infrared rays.
Convection. The air in contact with the skin heats up and rises, its place occupies a "cold" portion of air, etc. In this way, due to the heat andarenenos, it is given under the conditions of temperature comfort to 15% heat.
In all listed mechanisms, skin blood flow plays a large role: when its intensity increases by reducing the tone of smooth muscle cells of arterioles and the closure of arteriovenous shunts - the return of heat increases significantly. This also contributes to an increase in the volume of circulating blood: the greater its value, the higher the possibility of heat transfer to Wednesday. The opposite processes occur in the cold - the skin blood flow decreases, including due to the direct transfer of arterial blood from the arteries in veins, bypassing the capillaries, the volume of circulating blood decreases, the behavioral response: a person or an animal instinctively occupies a "Kalachik" pose, since In this case, the heat recoil area decreases by 35%, the animals add and the reaction is added to this - the "goose leather" is added - the skin of the skin (piloserection), which increases the cells of the cutting cover and reduces the possibility of heat recoil.
The share of hands has a small part of the body surface - only 6%, but their skin is given to 60% of the heat using the dry heat transfer mechanism (heat emissions, convection).
Evaporation. The impact of heat occurs due to waste of energy (0.58 kcal per 1 ml of water) to evaporate water. There are two types of evaporation, or permissions: imperceptible and sensible perp.
a) imperceptible recreation is evaporation of water from mucous respiratory tract and water that seeps through the skin epithelium (tissue fluid). During the day through the respiratory tract, up to 400 ml of water evaporates, i.e. 400x0,58 kkal \u003d 232kkal / day. If necessary, this value can be increased due to the so-called heat shortness, which is due to the influence of the neurons of the heat transfer center on the respiratory neurons of the brain stem.
On average, about 240 ml of water seeps through the epidermis. Therefore, due to this, 240 0.58kkal \u003d 139 kkal / day is given. This value does not depend on the regulation processes and various environmental factors.
Both types of imperceptible per day allow you to give (400 + 240) 0.58 \u003d 371 kcal.
b) Fight permissions (heat recovery by evaporation of sweat). In the average per day at a comfortable temperature of the medium, 400-500 ml of sweat is distinguished, therefore, up to 300 kcal. However, if necessary, the volume of sweating may increase to 12 l / day, i.e., by sweating, you can give almost 7,000 kcal per day. For an hour, sweat glands can produce up to 1.5 liters, and by some sources - up to 3 liters.
Evaporation efficiency largely depends on the medium: the higher the temperature and below the humidity (air saturation of water vapor), the higher the effectiveness of the sweating as a heat recovery mechanism. With 100% air saturation in pairs of water, evaporation is impossible.
Sweet drain from the end part, or body, and sweat duct, which opens out the sweat sometimes. By the nature of secretion, swelling glands are divided into eccrine (murcinous) and apocryne. Apokric glands are localized mainly in the axillary depression, in the pubic area, as well as in the field of germ lips, perineum, the near-block circle of the breast. Apokric glands secrete a bold rich in organic compounds. The question of their innervation is discussed - some argue that it is adrenergic sympathetic, others believe that it is generally absent and the products of the secret depends on the hormones of the adrenal brainstabs (adrenaline and norepinenaline).
Current apocryne glands are the cereal glands located in the eyelids at eyelashes, as well as glands producing ear sulfur in the outer hearing aisle, and the nose glands (finally glands). In evaporation, however, apokrin glands are not involved. Eccrine, or frozen, sweat glands are located in the skin of almost all areas of the body. There are only more than 2 million them (although there are people who have almost completely absent). Most of all sweat glands on the palms and soles (over 400 per 1 cm 2) and in the skin of the pubis (about 300 per 1 cm 2). Speeding rate, as well as the inclusion in the activity of sweat glands, in different parts of the body varies very widely.
By chemical composition, sweat is a hypotonic solution: it contains 0.3% sodium chloride (in blood - almost 0.9%), urea, glucose, amino acids, ammonium, small amounts of lactic acid. PNT pH varies from 4.2 to 7, on average pH \u003d 6. Specific weight - 1,001-1.006. Since the sweat is a hypotonic medium, then with abundant sweating, water is more lost than salts, and an increase in osmotic pressure may occur in the blood. Thus, abundant sweating is fraught with a change in water-salt metabolism.
Sweet glands are innervated by sympathetic cholinergic fibers - acetylcholine is released in their endings, which interacts with M-cholinoreceptors, increasing sweat products. Preggangionary neurons are located in the side pillars of the spinal cord at the level of TH 2 -L 2, and postgangle neurons - in the sympathetic trunk.
If it is necessary to increase the heat transfer by dilapidation, the neurons of the cortex, the limbic system and, mainly hypothalamus occurs. From hypothalamic neurons, signals go to the neurons of the spinal cord and gradually involve different areas of the skin in the process of sweating: first the face, forehead, neck, then the body and limb.
There are various ways of active impact on the process of sweating. For example, many antipyretic drugs, or anti-pyrethics: aspirin and other salicylates - increase the swelling and, thus, reduce the body temperature (reinforced heat transfer by evaporation). The inflorescence of limes, raspberry berries, and and-stepmother leaves are also possessed.
METABOLISM
The exchange of substances is the process of metabolism of substances enrolled in the body, as a result of which more complex or, conversely, more simple substances can be formed from these substances.
The human body, as well as the organisms of other representatives of the animal and plant world, is an open thermodynamic system. It constantly flows the flow of free energy. At the same time, it gives energy to the environment, mainly implanted (associated). Thanks to these two streams, the entropy of a living organism (degree of disorder, chaos, degradation) remains on a constant (minimum) level. When for some reason, the flow of free energy (nonentropy) decreases (or the formation of related energy increases), then the total entropy of the organism increases, which can lead to its thermodynamic death.
According to thermodynamics of living systems, life is the fight against entropy, the struggle of the ordering system with degradation. According to the well-known fittings equation, the minimum entropy increase occurs if the speed of the negentropic flux is equal to the speed of the entropy flow on Wednesday.
Free energy for the body can only come with food. It is accumulated in complex chemical bonds of proteins, fats and carbohydrates. In order to free this energy, the nutrients are first subjected to hydrolysis, and then oxidation in anaerobic or aerobic conditions.
In the process of hydrolysis, which is carried out in the gastrointestinal tract, is released a slight piece of free energy (less than 0.5%). It cannot be used for the needs of bioenergy, since it is not accumulated by Macroerangs of the ATP type. It turns only in thermal energy (primary heat), which is used by the body to maintain temperature homeostasis.
The 2nd stage of energy release is an anaerobic oxidation process. In particular, in this way about 5% of all free energy from glucose during oxidation to lactic acid is released. This energy, however, is accumulated by the Macroeerg ATP and is used to perform useful work, for example, for muscle contraction, for the work of the sodium-potassium pump, but, ultimately, it also turns into warmth, which is called secondary heat.
The 3rd stage is the main stage of energy release - up to 94.5% of all energy, which is capable of freeing up in the body of the body. This process is carried out in the Krebs cycle: it occurs in it the oxidation of pyrovinoic acid (the product of glucose oxidation) and acetylcoenzyme A (amino acid oxidation product and fatty acids). In the process of aerobic oxidation, the free energy is released as a result of the separation of hydrogen and the transfer of its electrons and protons along the circuit of the respiratory enzymes per oxygen. At the same time, the release of energy is not simultaneously, but gradually, therefore most of this free energy (approximately 52-55%) can be accumulated into the Macroeherga Energy (ATP). The rest as a result of the "imperfection" of biological oxidation is lost in the form of primary heat. After using free energy stored in ATP, it turns into secondary warmth.
Thus, all free energy, which is released during the oxidation of nutrients, ultimately turns into thermal energy. Therefore, the amount of thermal energy, which the body allocates is distinguished by the method of determining the body's energy motor.
As a result of oxidation of glucose, amino acids and fatty acids in the body are converted into carbon dioxide and water.
The energy exchange of an animal organism (gross exchange) is made up of the main exchange and a working boost to the main exchange. The initial value of the level of metabolic processes is the main exchange. These standard conditions for determining the main exchange are characterized by the factors that may affect the intensity of the metabolic processes in humans. For example, the intensity of metabolism is susceptible to daily fluctuations, which increases in the morning and decreases at night. The intensity of the exchange is also increasing in physical and mental work. Significant influence on the level of exchange is the consumption of nutrients and their further digestion is especially in the event that the nutrients have a protein nature. This phenomenon is called specific dynamic methods. Eating the intensity of metabolism after adopting protein food can continue for 12-18 hours. And finally, if the ambient temperature becomes below the comfort temperature, the intensity of the exchange processes increases. Shifts in the direction of cooling lead to greater amplification of metabolism than the corresponding shifts towards increasing the temperature.
Even with the full and strict compliance with the standard conditions, the magnitude of the main exchange in healthy people can vary. This variability is explained by differences in age, field, growth, body weight. As a rule, the value of 4.2 kJ / kg h is taken as the approximate value of the standard (main) intensity of metabolism. For a person weighing 70 kg, the corresponding primary exchange rate is approximately 7100 kJ / day (1700 kcal / day).
FOOD
Power is a process of assimilating the organism of substances necessary to build and update its body tissues, as well as to cover energy costs.
In general, the evolution of the nutritional needs of animal organisms included the process of limiting its own synthesis of a number of compounds with simultaneous expansion of the consumption of organic compounds of certain types. This led to the allocation of a whole group of substances, irreplaceable for higher animals and a person, that is, necessary for metabolism, but not synthesized themselves.
The use of foods consisting mainly of complex compounds of plant or animal origin, for the energy or plastic needs of the body is possible only after the hydrolysis of these agents and the transformation into relatively simple compounds devoid of species specificity. The nutritional needs of different types of animals are different depending on what food substances the body is able to synthesize and what should be coming from the outside. And yet, mostly differences in nutritional needs are due to digestion (hydrolysis) foods. This is due to the fact that at the highest animal organisms intermediate metabolic processes proceed in a similar way.
In the exchange of substances (metabolism) and energy distinguish between two processes: anabolism and catabolism. Under anabolism understand the combination of processes aimed at building the structures of the body mainly through the synthesis of complex organic substances; By catabolism - a set of processes of decay of complex organic compounds and the use of relatively simple substances formed during the energy exchange processes. The basis of anabolism and catabolism is based on the processes of assimilation and dissimulation, which in the body are interrelated and in the normal organism is balanced.
In general, the needs of animals are quite homogeneous: they need similar nutrients for energy exchange; in substances of the type of amino acids, purines and some lipids to construct complex protein molecules and cellular structures; in special metabolic catalysts and cell membrane stabilizers; In inorganic ions and compounds of physicochemical processes in the body and, finally, in a universal biological solvent - water to create a cellular metabolic medium.
Ultimately, the composition of the food of highly organized organisms includes organic substances, the overwhelming part of which belongs to proteins, lipids and carbohydrates. The products of their hydrolysis - amino acids, fatty acids, glycerin and monosahara are spent on the energy supply of the body. In the energy exchange processes of amino acids, fatty acids and monosahara are interconnected by the common paths of their transformation. Therefore, as energy carriers, food substances can be interchanged in accordance with the energy value (the rule of isolation).
Energy (caloric) value of food is evaluated by the amount of thermal energy released during combustion of 1 g of the foodstuff (physiological heat of the combustion), which is traditionally expressed in kilocalories or on Si - in Joules (1 kcal \u003d 4,187 kJ). Calculations have shown that the energy value of fats (38.9 kJ / g; 9.3 kcal / g) is two times higher than protein of carbohydrates (17.2 kJ / g; 4.1 kcal / g). Proteins and carbohydrates have the same energy value and can be replaced with 1: 1 in the weight ratio.
To maintain the stationary state of the body, the total energy costs should be covered by the flow of dietary substances that are equivalent to equivalent energy supply in their chemical bonds. If the amount of incoming food for the coating is not enough, the energyrators are compensated for by the internal reserves, mainly fat. If the mass of incoming energy in energy exceeds energy consumption, then the process of fat stocking is underway regardless of food composition.
However, it should always be remembered that these three sources of energy are both the plastic material of the animal organism. Therefore, a long exception of one of the three nutrients from the edible diet and replacing the energy equivalent amount of another substance is unacceptable.
Conclusion
Life is conjugate with continuous energy consumption, which is necessary for the functioning of the body. From the point of view of thermodynamics, living organisms relate to open systems, since for their existence they continuously exchange with the outer medium substances and energy. The source of energy of living organisms is the chemical transformation of organic substances coming from the environment. The conversion of these substances from complex into simple and leads to the release of energy concluded in chemical bonds. Extraction of energy from chemical bonds is carried out mainly with the cost of molecular oxygen (aerobic exchange); Oxidation in a number of chains is preceded by oxless splitting (anaerobic exchange).
The main battery of energy for using it in cell processes is adenosine trifhosphate (ATP). Using the ATP energy, the synthesis of protein, cell division, maintaining their osmotic gradient, muscular abbreviation, etc. According to the first law of thermodynamics, the Chemical ATP energy, passing through intermediate stages, ultimately turns into a thermal, which is lost by the body. Therefore, the intensity of the body's energy exchange is the amount of energy motor to the function of cellular systems, accumulated energy and its loss in the form of heat.
The life of the body depends on the flow of chemical reactions with the transformation of all types of energy into thermal. The rate of chemical reactions, and therefore, the energy exchange depends on the temperature of the tissues. Heat as a finite energy conversion is able to move from a higher temperature in the region lower. The tissue temperature is determined by the ratio of the speed of metabolic heat product flow of their cellular structures and the rate of dispersion of the generated heat into the environment. Consequently, heat exchange between the organism and the external environment is an integral condition for the existence of animal organisms. To maintain the normal (optimal) body temperature in animal organisms there is a heat exchange system with a medium.
Animal organisms are divided into capeillem and homoothermal. Poikilotermic (standing at lower steps of the phylogenetic staircase) have imperfect, but still quite effective thermoregulation mechanisms. These mechanisms include a chemical temperature compensation system that allows you to hold steady energy exchange with significant body temperature drops, thermoregulation behavior (the choice of optimal medium temperature) and temperature hysteresis (the ability to capture heat from the external environment faster than to lose it).
Homoothermia is a later acquisition of the evolution of the animal world. True homoothermal animals include birds and mammals, since these animals are able to maintain a permanent range of 2 ° C of the body temperature of the MINA relatively wide fluctuations in the external temperature.
At the heart of homoothermia is higher than that of porcottermall animals, the level of energy exchange by strengthening the role of thyroid hormones, stimulating the operation of the cellular sodium pump. High energy exchange led to the formation of perfect mechanisms for the regulation of thermal energy in the body.
A number of animals belong to the group of heterothermal organisms: at some conditions they are caught by the organisms, with other - homoothermal.
To maintain a constant body temperature, homoothermal animals have chemical and physical thermoregulation. Physical thermoregulation is carried out by changing the thermal conductivity of coating tissues of the body (changing the blood flow of the skin, the pilooare, evaporation of moisture from the body surface or the oral cavity).
Chemical thermoregulation is carried out by increasing heat generation in the body. Two main sources of chemical thermoregulation (adjustable heat generation) are isolated: contractile thermogenesis due to the arbitrary activity of the locomotor device, thermoregulation tone and muscle tremors and non-consistent thermogenesis due to the buoy fat tissue, a specific dynamic effect of food, etc.
The control of heat exchange is carried out by the activity of dark-storyptors, the information from which enters the center of thermoregulation of the hypothalamus, controlling the reactions of chemical and physical thermoregulation.
A long stay in high or low ambient temperatures leads to significant changes in the properties of the body that increase its resistance to the action of appropriate temperature factors.
Building and updating body tissues, as well as the coating of the body's energy cells should be provided with adequate nutrition. In the exchange of substances and energy distinguish two processes: anabolism and catabolism. Under anabolism, the combination of processes aimed at building structures of the body mainly through the synthesis of complex organic substances. Catabolism is a combination of the decay processes of complex organic substances in order to release energy. The basis of anabolism and catabolism is based on the processes of assimilation and dissimulation, which are interrelated and balanced.
The food needs of animals are quite homogeneous: Required substances for energy exchange (proteins, fats, carbohydrates), substances for constructing complex protein molecules and cellular structures (amino acids, purines, lipids, carbohydrates), special exchange catalysts (vitamins) and cell membrane stabilizers (antioxidants) , inorganic ions and universal biological solvent - water.
The energy value of food is determined by the amount of thermal energy released during the combustion of the 1G edible substance (physiological heat of combustion).
Under rational nutrition, food is sufficient in quantitative and full in qualitative terms. The basis of rational nutrition is balanced, i.e. the optimal ratio of food consumed. Balanced nutrition should include proteins, fats and carbohydrates in the mass proportion, approximately 1: 1: 4. For food qualitatively, food must be full, i.e. contain proteins (including indispensable amino acids), essential fatty acids (the so-called vitamin F), vitamins, most of the catalyzing systems, and a large group of vitamin-like substances, inorganic elements and water .
BIBLIOGRAPHY
1) Mac-Murray V. The metabolism of a person. M., 1980.
2) Norton A., Edholm O. man in cold conditions. M., 1957.
3) General course of human and animal physiology / near Ed A. D. Nosdrachev. M., 1991. KN. 2.
4) Fundamentals of physiology / Ed. P. Konter. M., 1984.
5) Slonim A. D. Evolution of thermoregulation. L., 1986.
6) Physiology of thermoregulation: physiology manual / editor P. Ivanova. L., 1984.
7) human physiology / ed. N.A.Agadzhanyan, V.I. Cyrkina. St. Petersburg., 1998.
8) human physiology / ed. R. Schmidt, Tevs. M., 1986. T. 4.
Mechanisms of heat transfer of the body in conditions of cold and heat "\u003e
The mechanisms of heat transfer of the body in conditions of cold and heat: a) the redistribution of blood between the vessels of the internal organs and the leather surface vessels; b) Redistribution of blood in leather vessels.
Physical thermoregulation appeared at the later stages of evolution. Its mechanisms do not affect cellular exchange processes. The mechanisms of physical thermoregulation are turned on reflexively and have as any reflector mechanism three main components. First, these are receptors that perceive the change in temperature inside the body or the environment. The second link is the center of thermoregulation. The third links are effectors that change heat transfer processes while maintaining the body temperature at a constant level. In the body, except for sweating gland, there are no own effectors of the reflex mechanism of physical thermoregulation.
The value of physical thermoregulation
Physical thermoregulation is the regulation of heat transfer. Its mechanisms provide maintenance of body temperature at a constant level as under conditions when the body threatens overheating and when cooled.
Physical thermoregulation is carried out by changes in the heat of heat by the body. It takes particular importance in maintaining the constancy of the body temperature during the body's stay under an elevated ambient temperature.
The heat transfer is carried out by heat emission (radiation heat transfer), convection, i.e. movement and stirring of the heated air, heat control, i.e. Rotate heat with a substance in contact with the surface of the body. The nature of heat recoil body varies depending on the intensity of metabolism.
The loss of heat prevents the layer of still air, which is located between clothing and skin, as the air is a bad heat conductor. Significantly prevents the heat transfer layer of subcutaneous fatty fiber due to the low thermal conductivity of fat.
Regulation of temperature
The skin temperature, and, consequently, the intensity of heat emission and heat-leveling may vary in cold or hot conditions of the external environment as a result of the redistribution of blood in vessels and when changing the circulating blood volume.
In the cold, blood vessels of the skin, mainly arterioles, narrow; A greater amount of blood enters into the vessels of the abdominal cavity and thereby limited to the heat transfer. Surface layers of skin, getting less warm blood, emit less heat, so the heat transfer is reduced. In addition, with strong cooling of the skin, arteriovenous anastomoses occurs, which reduces the amount of blood coming into the capillaries, and thereby prevents the heat transfer.
The redistribution of the blood occurring in the cold is to reduce the amount of blood circulating through the surface vessels, and an increase in the amount of blood passing through the vessels of the internal organs, contributes to the preservation of heat in the internal organs, the temperature of which is supported at a constant level.
With an increase in the ambient temperature, the leather vessels expands, the amount of blood circulating in them increases. The volume of circulating blood in the whole body is also increasing due to the transition of water from tissues in the vessels, and also because the spleen and other bloodstream are thrown into the overall blood flow. An increase in the amount of blood circulating through the body surface vessels contributes to the heat transfer by radiation and convection. To preserve the constancy of the body temperature at high ambient temperatures, the sweating occurring due to heat transfer during the evaporation of water is important.
The thermoregulation is associated with the mechanisms for regulating the heat-product level (chemical regulation) and heat transfer (physical regulation). The balance of heat-product and heat transfer is controlled by a hypothalamus integrating sensory, vegetative, emotional and motor components of adaptive behavior.
The perception of temperature is carried out by receptor formations of the body surface (skin receptors) and deep temperature receptors in the respiratory tract, vessels, internal organs, in intermuschny nerve plexuses of the gastrointestinal tract. According to afferent nerves, the impulses from these receptors come to the center of thermoregulation in the hypothalamus. It activates various mechanisms providing or heat product, or heat transfer. The feedback mechanism involving the nervous system and blood flow changes the sensitivity of temperature receptors (Fig. 15.4, 15.5). Memo-sensitive formations are also located in different areas of the central nervous system - in the motor cortex, in the hypothalamus, in the brain barrel area (reticular formation, the oblong brain) and the spinal cord.
In the hypothalamus, which is sometimes called the "body thermostat", there is not only a center that integrates various sensory impulses associated with information about the thermal
Fig. 15.4.
the balance of the body, but also the regulatory center of motor reactions that control the temperature modes. After disrupting the functions of the hypothalamus, the ability to regulate the body temperature is lost.
The control of heat transfer control is connected with the front hypothalamus to prevent overheating - its neurons are sensitive to the temperature of the flowing blood. If the work of this center is violated, control of the body temperature in a cold medium is maintained, but in the heat it is missing and the body temperature rises significantly.
Another thermoregulation center, located in the rear hypothalamus, controls the size of the heat
Fig. 15.5. The participation of the nervous system in thermoregulation and thereby prevents excessive cooling. Violation of this center reduces the ability to strengthen energy exchange in a cold environment, and the body temperature drops.
Heat transmission from the inner areas of the body to limbs as a result of changes in the volume of blood flow is an important means of regulating heat transfer through vasomotor reactions. The limbs withstand a much larger temperature range than the inner areas of the body, and form excellent temperature "outstands", i.e. Places that can ensure the loss of large or smaller heat depending on the inflow of heat from the inner areas of the body through the bloodstream.
The thermoregulation is associated with the sympathetic nervous system (see Fig. 15.5). It is adjusted by the tone of vessels; As a result, the influx of blood to the skin is changed (see ch. 4). The expansion of subcutaneous vessels is accompanied by a slowdown in them and the heating of heat transfer (Fig. 15.6). With a strong heat, the influx of blood to the skin of the limbs increases sharply, and excess heat dissipates. The proximity of the veins to the skin surface increases blood cooling, which returns to the internal areas of the body.
When cooled, the vessels are narrowed, the inflow of blood on the periphery is reduced. In humans, as the blood passes through a large vessels of hands and yoga, its temperature drops. Chilled venous blood, returning inside the body by vessels located near the arteries, captures a large
Fig. 15.6. Reaction of surface vessels of the skin on the cold - narrowing (but) and heat - expansion (b)
the proportion of heat given by arterial blood flow. Such a system is called countercurrent heat exchange. It contributes to the return of a large amount of heat to the inner areas of the body after blood through the limbs. The total effect of such a system is a decrease in heat transfer. At air temperature close to zero, such a system is not beneficial, since as a result of intensive heat exchange between arterial and venous blood, the temperature of the fingers on the hands and on the legs can significantly decrease, which can cause frostbite.
The main source of heat-product is associated with muscle contractions that are under arbitrary control. Another type of reinforcement in the body can be a muscular tremor - a reaction to the cold. A small movement of muscles with trembling increases the efficiency of heat-product. When trembling rhythmically and at the same time with a high frequency, flexors and extensors of limbs and chewing muscles are reduced. Frequency and reduction strength can vary. The tremor is generated only if the indicated muscles are not involved in another type of activity. It can be overcome by arbitrary muscle work. Arbitrary movements, such as walking, are associated with muscle contraction, which overcomes trembling. And shiver, and walking is accompanied by the formation of heat. Rear hypothalamus neurons affect the frequency and strength of muscle contractions when trembling. The center comes from the center of thermoregulation in the front hypothalamus and from muscle receptors. The pulses from the brain comes to all levels of the spinal cord, where rhythmic signals arise, causing trembling in the muscles.
In addition, thermal energy is formed when the fats, stored in adipose tissue. The most effective in this sense is brown fat, located in newborn children between the blades and the sternum. Within a few days after the birth of the heat product, which is provided by the cells of the brown fat - the main reaction to the cold. Later in children, a shiver becomes such a reaction. Brown fat in large quantities occurs in animals that have a winter hibernation. Fat cleavage of white adipose tissue is less efficient. White fat contributes not to education, but to maintain heat.
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