Physiology of human thermoregulation
For the normal functioning of the human body, the temperature of its internal organs and blood is required of about 37 ° C, and temperature fluctuations should not exceed 1.5 ° C. The work of the thermoregulation system depends largely on the operation of thermistors - nervous formations specifically sensitive to changes in ambient temperature.
Thermoreceptor in humans are locatedmain in the skin cover of the body, the mucous membranes of the mouth, the upper respiratory tract. They are also available in the walls of the subcutaneous veins and on the mucous domestic organs. Most of the thermistors in the skin of the face, less on the torso and even less on the legs. Allocate "thermal" and "cold" thermistors.
Consider the work of the "thermal" thermostretors. If the ambient temperature is compatible with the life of the body, then a constant impulse is incorporated from thermoreceptors by conductive paths to the central nervous system, which affects thermoregulation. With an increase in ambient temperature, the direct action of heat radiation or an increase in the body's heat product (muscular work), thermoregulation is carried out using reactions change heat transfer. Its most important part is vascular regulation, consisting in changing the blood flow of the skin and the speed of volumetric blood flow through the skin by changing the tone of its vessels. In humans, the maximum expansion of the vessels of the skin on the state of the maximum narrowing reduces the total magnitude of the thermal insulation of the skin on average 6 times. Different areas of leather are involved in thermoregulation. For example, up to 60% of the main exchange of the main exchange can be assigned to the hands of hands, although the area of \u200b\u200bthe brushes is only about 6% of the entire surface of the skin. With an increase in muscle work, the skin sections over the working muscles are of particular importance. Part of the blood from them rushes directly in the veins of the corresponding areas of the skin, which greatly facilitates the return of heat from the muscles through the Convention.
In addition to the vascular component, sweating plays a large role in the thermoregulation system. The process of leakage of water through the epithelium and subsequent evaporation is called impregnimate Puspirationand absorbs approximately 20% of the heat transfer of the main exchange. Immount to duspiration is not regulated and only depends on the ambient temperature. Pope allocate sweat glands located in the skin. In the threat of the organism overheating, the sympathetic nervous system stimulates the work of sweat glands, isolated at intensive operation to 1.5 liters of sweat per hour or more.
Managing all the reactions of maintaining the constant body temperature in different conditions It is carried out by special nervous centers localized in the brain. These centers receive information on conductive paths from heat-sensitive neurons located in different parts of the central nervous system, and from peripheral thermistors.
It is assumed that the thermoregulation system responds to a change in the amount of temperature of central and peripheral points of the body and the main object of its regulation is the average temperature, which is maintained with high accuracy. In humans in the temperature of the temperature comfort (28-30 ° C for the naked person), the vascular thermostat reaction develops with a change in the average body temperature of only 0.1 ° C or less. Moreover, any conditions that impede heat transfer (high humidity and immobility of air) or the heat-proof (physical stress, enhanced nutrition) are factors that contribute to overheating.
Overheating of the body (hyperthermia) is a condition characterized by a violation of the heat balance, an increase in the thermal content of the body. The main path of heat transfer in human hyperthermia is evaporation of moisture from the body surface and through the respiratory tract. It should be noted that overheating is not associated with the primary violation of the thermoregulation function.
The overheating of the human body is observed in production with high ambient temperature or under conditions that impede heat transfer from the body surface, as well as in areas with a hot climate. At high ambient temperatures, the heating of the body contributes to the growth of heat-producing, which occurs with muscle work, especially in impermeable clothing, high humidity and air immobility. In the conditions of difficult heat transfer, children of early age are easily overheated, which have no thermoregulation system, as well as adults with a violation of the function function.
Conducted studies of high temperatures on the human body in the nature of changes in thermal exchange, cardiovascular and respiratory systems allowed allocated four degrees of organism overheating (by A.N. Azhaev):
I degree (Sustainable fixture)- The ambient temperature is about 40 ° C. The heat transfer is carried out by evaporation of moisture from the body surface and from the respiratory tract. The heat transfer is equal to the thermal load and the body temperature does not increase. The overall condition is satisfactory, complaints are reduced to the feeling of heat, often lethargy and drowsiness, reluctance to work and move.
II degree (partial fixture)- The ambient temperature is about 50 ° C. The heat load is not compensated by the evaporation of moisture, and heat accumulates in the body. Temperature of the body can reach 38.5 ° C. Systolic pressure rises by 5-15 mm Hg. Art., and the diastolic is reduced by 10-20 mm Hg. Art. The minute and systolic volume of the heart increase, the pulmonary ventilation, the amount of absorbed oxygen and dedicated carbon dioxide. The pulse is rapidly 40-60 beats per minute. There is a sharp hyperemia of the skin, profuse sweating. Characterized by the feeling of heat.
III degree (breaking fixtures) - When exposed to a temperature of 60 ° C and higher. Temperature of the body can reach 39.5-40 ° C. Systolic pressure rises at 20-30 mm Hg. Art., A diastolic is reduced by 30-40 mm Hg. Art., It may be brought to the effect of "infinite tone" (zero diastolic pressure). The number of heart abbreviations increases to 160 beats per minute, but the systolic volume of the heart decreases. Due to the amplification of pulmonary ventilation, the amount of absorbed oxygen and dedicated carbon dioxide increases. The skin is sharply hyperemic. Sweat flows drops. Patients complain about deterioration of well-being, the feeling of strong heat, heartbeat, pressure in whiskeys and headache. Correction may occur, motor anxiety.
IV degree (lack of adaptation) - This is, in fact, there is a heat blow when a gross violation of the activities of the cardiovascular system and the central nervous system occurs.
It should be noted that the severity of the organism overheating depends not only on the size of the ambient temperature, but also on the duration of its exposure to the human body.
At high ambient temperatures, four clinical syndrome develop:
1) thermal cramps
2) thermal exhaustion
3) thermal injury at voltage
4) heat blow
Each of these states can be retrained on the basis of various clinical manifestations, but there are many common and these states between them can be considered as a variety of syndromes of the same origin.
The symptom complex of thermal lesion is developing at high temperatures (more than 32 ° C) and with high relative humidity of air (more than 60%).
Most vulnerable:
Elderly people
Persons suffering from mental illness
alcoholic persons
Antipsychotic faces, diuretic, anticholinergic drugs
Persons in places with poor ventilation
Especially many thermal syndromes develop in the first days of heat, before the acclimatization comes.
Acclimatization
Usually acclimatization lasts 4-7 days.
1.Cclimatization does not increase the threshold pottingwhich is the most effective natural way of fighting heat loads and can occur with minor changes, and sometimes in the absence of changes in the temperature of the median departments of the body. As long as the sweating continues, a person can withstand a significant increase in temperature, providing a rise in water and sodium chloride, the most important physiological components of sweat. The main mechanism of salt delay in hot weather is the ability to secure sweat with a very low content of sodium chloride.
2. Russian way to adapt the body to high temperatures is expansion of peripheral blood vesselsWhat promotes heat dissipation.
Other changes include:
Reduced total circulating blood
Reducing renal blood flow
Raising the level of antidiuretic hormone (ADG) and Aldosterone
Sodium decrease in urine
Increase the respiratory frequency and heart rate
Hyperldosteronismit leads to the loss of potassium, which can increase during the compensation of sodium loss without the appropriate ignition of potassium. Initially, an increase in cardiac output is noted, but since the thermal load remains, the venous return is reduced, which can lead to the development of heart failure. If the ambient temperature for a long time exceeds the body temperature, then the heat is maintained and the hyperpyrassia develops.
Heat cramps
The convulsions arising from the tension of muscles in overheating conditions, the so-called ferrous cramps or a fire cramps include the most benign thermal lesions.
Causes are characterized by painful spasms in arbitrarily reduced muscles, usually arising from hard work. As a rule, this syndrome is developing only in trained people.
Temperature external environment it may not exceed the body temperature, as well as there is no need for a long stay in the sun. Body temperaturedoes not rise. Muscle cramps usually arise after a profuse sweating and can develop in non-human people in dense clothing with increased physical exertion even in low ambient temperatures. In physical work, the main load falls on the muscles of the limbs, so they are more susceptible to the development of convulsion. In the interdictuous period Physical inspection does not reveal any changes.
In blood testsit is usually noted to increase the concentration of uniform elements and a decrease in the content of sodium chloride. A characteristic feature is Reducing sodium excretion with urine.
Treatmentconduct sodium chloride. Almost instantaneous cessation of seizures with the introduction of sodium chloride and water made it possible to assume that the cause of convulsion is to reduce the content of these main electrolytes in the body.
Sometimes the muscles of the abdominal wall are involved in convulsions, which can resemble a picture of an acute abdomen. This patient may mistakenly perform operational intervention, which often leads to extremely unfavorable results. In such cases, a preliminary administration of a physiological solution can be prevented by an unnecessary operation.
Heat exhaustion
Thermal exhaustion (heat shock, exhaust) is a condition arising from long (for hours) exposure to high ambient temperature.
Heat exhaustion Refers to the most frequent thermal syndromes. Thermal shock to the same degree develops Both with exercise, and alone. Start usually sudden duration Shock short.
It arises due to the insufficiency of the response of the heart vessels on an extremely high temperature and is particularly often developing in the elderly people taking diuretic drugs.
Also, an excessive loss of fluid may result in thermal exhaustion as a result of a strong sweating, which in turn leads to fatigue, reduced blood pressure and sometimes to the collapse. The effects of high temperature can cause a loss of too much fluid from then, especially in the process of heavy physical work or exercise. The salts (electrolytes) are also lost with liquids, and this aggravates the circulatory disorder and brain functions. As a result, thermal exhaustion can develop. At the same time, the condition of a person inspires concerns, but rarely leads to difficult consequences.
Symptoms and diagnostics
Thermal exhaustion (exhaustion) due to dehydration occurs when the body loses a lot of fluid (from then, exhaled air, etc.) without adequate replenishment.
Water deficiency exceeding 2.5% body weight causes initial disorders
With a shortage of water in 5.5-6.5%, pronounced disorders develop
Water deficiency in 7-14% leads to a difficult state
Water deficiency in 15-25% leads to death
Precede the shock can:
weakness
dizziness
headache
anorexia
nausea, vomiting
Cooking for defecation
fainting
With thermal depletion, due to dehydration, the victim arises a feeling of thirst; The face of pale gray, the lips of the impaired, the eyes of the smeared, the skin and mucous membranes are dry, the skin loses elasticity and is sometimes covered by projected rash. The body temperature is moderately increased (up to 37.5-38 ° C). The separation of urine is reduced or stopped at all. The salivation is absent, the articulation of speech is broken, swallowing is disturbed. Blood pressure is reduced. In severe cases, severe violations of the brain function are observed - headache, ringing in ears, coordination disorders, convulsions of individual muscle groups, paresthesia (loss of sensitivity), anxiety, hallucination, loss of consciousness. Thermal exhaustion (exhaustion) due to the loss of salts (sodium, potassium, calcium, etc.) develops with abundant sweating, vomiting, and also if unsuccessful water is used for thickening. Manifestations grow gradually. There are fatigue, weakness, drowsiness, headaches, dizziness. Thirst is not expressed. The skin is pale, wet, without loss of elasticity, mucous membranes are also wet. The separation of urine is not violated or slightly reduced. It is often nauseous, less often - vomiting; Poor tolerated drinking water. The body temperature is normal or somewhat increased. Characterized by frequent pulse, decrease in blood pressure and sharply pronounced orthostatic disorders: when moving to a vertical position, the lift of the head is often developing fainting or collapse. In severe cases, convulsions and loss of consciousness are possible.
Thermal exhaustion is easy to diagnose on the basis of the specified symptoms.
During acutepatient skin stage acquires ash-gray, becomes cold and wet to the touch, pupils are expanded. Blood pressure can be low with elevated pulse pressure. Since extreme weakness is developing very quickly, the body temperature remains normal or even somewhat decreases. The duration of the thermal load and the volume of the resulting fluid is determined by the severity of the hemoconcentration.
Treatment
The patient is transferred to the cool room and arrange in the lying position. Usually the spontaneous restoration of consciousness occurs.
Treatment comes down mainly to replenishing the loss of fluid and salts. With heat wear, due to the loss of fluid, moderate cooling of the victim is carried out (cold rings on the head, wrapping of a wet sheet, move to the air-conditioned room, etc.). Those who are able to drink, assign abundant drink - 1-2 l for 15 minutes, then sips. For an hour, the amount of liquid (water, cold tea, fruit juices) can reach 3-5 liters per day - 6-8 liters. If the victim cannot drink independently, then the liquid (5% glucose solution) is administered intravenously, subcutaneously or in the enema (1-1.5 l). After restoring the ability to drink a free water mode, and the forced injection of the fluid must be stopped, as this may lead to water poisoning (disgust to water, abdominal pain, difficulty breathing, etc.).
The injured with thermal waste due to the loss of salts should be put so that the legs are in a high-rise position. If a person is able to drink and it does not occur vomiting, it is given inside the salted water or, preferably, the solution of the following composition: 1.17 g of sodium chloride (sodium sodium), 0.84 g sodium bicarbonate (drinking soda) and 0.3 Mr. potassium chloride per 1 liter of water. If drinking is impossible, saline solutions type Ringer, Butler, Lactasol, etc. are introduced.
With the fall of blood pressure with all forms of thermal exhaustion, along with the replenishment of fluid loss, preparations are introduced, stimulating vascular tone, for example sulfocamphocaine, Mesoth, et al. To eliminate seizures, preparations of type Sibaz, relaignium, etc. Patients with heavy forms of thermal exhaustion are used after assistance hospitalization.
Thermal injury at voltage
This syndrome occurs with significant physical voltage under conditions of high ambient temperature (about 26.7 ° C) with elevated relative humidity. Most often, this syndrome develops in runners involved in competitions without appropriate acclimatization, in inadequate conditions or with improper hydration before and during the race.
The predisposing factors are:
obesity
age
The presence of thermal impacts in history
In contrast to the classic heat impact during thermal injury from the voltage, there is plenty of sweating and lower body temperature (39-40 ° C compared to 41.4 ° C and higher with thermal impact).
Clinically manifestedheadache, piloeline ("goose skin") in the region chest and the upper shoulder belt, the chills, the study of breathing, nausea, vomiting, convulsions in muscles, ataxia, gait, incoherence to speech, in some cases the loss of consciousness is possible.
In case of inspectionreveal tachycardia, hypotension, decrease in peripheral resistance.
Laboratory dataspecify the hemokoncentration, hypernatremia, changes in hepatic and muscle enzymes, hypocalcemia, hypophosphatemia, and, in some cases, hypoglycemia. Sometimes thrombocytopenia arise, hemolysis, disseminated intravascular coagulation, rhabdomyolysis, myoglobinuria and acute tubular necrosis.
Extensive damage to the endothelium of blood vessels, any of the internal organs, can lead to its insufficiency. These serious complications can be avoided by appointing a praid treatment, consisting in wrapping a patient with wet cool sheets to reduce the temperature of the median body of the body up to 38 ° C, massage limbs to improve blood outflow from the center to the periphery, as well as the introduction of liquids containing a glucose hypotonic solution. Both salts. Patients should be hospitalized and observed within 36 hours.
Thermal injury at voltage can be prevented in the following ways:
run in the morning clock (up to 8 hours) when the temperature and humidity of the air are not high
Provide adequate hydration of an athlete before starting the race, for which 300 ml of water should be drinking 10 minutes before the start and 250 ml each 3-4 km (the reception of salted or sweet liquid should be avoided)
Organize first aid points every 5 km highway
warn runners so that they do not increase the ramp of the run after most of the track go
Avoid drinking alcohol shortly before the race
Heatstroke
Heat hyperpyracy, heat shock or sunstroke Most often occurs in the elderly with chronic diseases, such as atherosclerosis and stagnant heart failure, especially in patients receiving diuretics.
Other predisposing factors are diabetes mellitus, alcoholism, the use of anticholinergic drugs, skin lesions that impede heat transfer, such as ectodermal dysplasia, congenital absence of sweat glands, expressed sclerodermia.
The thermal blow is often developing from warriors and recruits during the first workouts, sometimes runners for long distances.
Development mechanismthe heat strike is not known. Most patients have a sweating, but some remains. The narrowing of the vessels arising from thermal impact prevents the cooling of the median departments of the body, but it is not clear whether it is the cause or result. Staying in the sun is not a prerequisite for the development of thermal impact.
Profit periodcan manifest itself a few symptoms. Sometimes the first sign is the loss of consciousness. In addition, there are headache, dizziness, fainting, gastrointestinal disorders, confusion of consciousness, breathing. In the most severe cases, a delicious state may develop.
In case of inspectionhyperemia and pronounced general weakness attracts attention. The rectal temperature usually exceeds 41.1 ° C, and the internal temperature of the organism is 44.4 ° C. The skin is hot and dry to the touch, the calculation in most cases is absent. The number of heart abbreviations is inexped, breathing rapid, superficial, blood pressure is usually low. Muscles Drying, tendon reflexes can be reduced. Depending on the severity of the state, drowsiness, stupor or to whom. Fully outcome preceded shock.
Various changes are detected in blood and urine examination:
As a rule, it is hemoconcentration, leukocytosis, proteinuria, cylindruria, an increase in blood urea nitrogen.
A respiratory alkalosis is noted with subsequent metabolic acidosis, and acidosis.
The content of potassium in blood plasma is usually within normal limits or somewhat lowered, and hypocalcemia and hypophosphatems are also noted.
May also arisethrombocytopenia, increasing prothrombin time, coagulation time and bleeding, Afibrinogenemia and fibrinolysis, disseminated intravascular coagulation.
All of these factors can lead to diffuse bleeding. The liver is often amazed. This usually occurs within 24-36 hours and manifests the jaundice, as well as changes in hepatic enzymes. Frequent complication of thermal impact is renal failure.
With electrocardiographyreveal tachycardia, sinus arrhythmia, flattening and subsequent inversion of teeth T, depression of ST segment. The literature describes diffuse myocardial necrosis with signs of myocardial infarction on the ECG.
Death with thermal impact, the reason for which is renal failure and other complications, may occur within a few hours. In most cases, however, patients die in a few weeks after a thermal impact due to myocardial infarction, heart failure, renal failure, bronchopneumonia, bacteremia.
With autopsy findextensive damage to the parenchyma of various internal organs or in the result of hyperpirection as such, or due to pheteching hemorrhages in the brain, heart, kidney or liver.
The thermal blow requires immediate intensive treatment. Time is of great importance.
The patient should be put in a cool, well-ventilated room
Remove most of the clothes.
Since the sweating stops, the external methods of heat dissipation should be used.
The patient should be placed in a bath with ice water - this is the most effective environment.
Ice water does not contribute to the development of shock or pronounced narrowing of the vessels of the skin.
This procedure should be done as in more early deadlines.
The patient must constantly be under the supervision of the doctor, it is necessary to monitor the rectal temperature.
The aqueous procedures are stopped with a decrease in temperature to 38.3 ° C, however, repeated during the resumption of febrilite.
Other treatments are less effectiveHowever, if there is no possibility to provide a bath, then you should wrap the patient in a cold wet sheet and arrange good ventilation of the room.
After the patient's bath, you should be added to the cool, well-ventilated room. Simultaneously with cooling, it is necessary to carry out skin massage, as it stimulates blood outflow from the body surface to overheated internal organs and the brain and contributes to the acceleration of heat transfer.
The hydrogenation is shown by hypotonic crystaloid solutions. To relieve chills, you can apply phenothiazine. Stimulating substances such as epinephrine and drugs are contraindicated. You should put the urinary catheter and follow the separation of urine.
Fast cooling in ice water, limb massages and powerful hydration, ensuring proper ventilation, preventing aspiration, coma treatment and seizures, warning arrhythmia - all these manipulations lead to the fact that most patients, especially young and healthy, survive.
Unfortunately, in weakened patients and elderly people who have a heat blow diagnosed, as a rule, after several hours of hypertension, the outcome is less favorable.
The dehydration and development of heart failure should be feared. In cases of bleeding, it is necessary to overflow fresh blood, and if there is a disseminated intravascular coagulation - to introduce heparin (7500 units). Print Oliguria is an indication for the early start of dialysis.
Prevention of thermal strike
Determined in each individual case with a specific environment. For example, long transitions to the hot period are recommended to be carried out in a cooler clock of the day in light porous clothes, more often to arrange the valves in shady ventilated places. It is necessary to respect the drinking mode rule, due to which you can escape the water-salt exchange in the body. Instead of water, you can use cold acidified or sweetened tea, rice or cherry decoction, bread kvass. Wider use of carbohydrates, dairy products with restriction of products containing acidic radicals (porridge, etc.) are recommended.
High ambient temperature forces to carry the main meal for evening hours with a breakfast consumption - 35, for lunch - 25, for dinner - 40% daily diet.
In hot workshops, air cooling devices are installed by spraying water, water procedures (souls, poultry, etc.) are widely used, set breaks in operation, limit the techniques of protein and oily food.
Important in the prevention of thermal impact is pre-training, with which it is possible to achieve an increase in adaptation to the action of thermal factors.
With any fire allocated thermal energy. The amount of heat released depends on the conditions of the air exchange in the fire center, the thermophysical properties of the surrounding materials (including construction), the fire hazard properties of combustible substances and materials included in the fire load.
The concept of "increased ambient temperature", in my opinion, is not entirely accurate. In my opinion, under this concept, it is still necessary to mean the "increased temperature of combustion products", since the environment when evaluating fire hazard is almost always considered as surrounding (unnecessary) air with an initial temperature.
When considering elevated ambient temperatures as a dangerous fire factor, it should be noted that the dangerous impact of heated combustion products on the human body is determined primarily by air humidity. The greater the humidity of the air, the more likely the burns are higher. The maximum allowable value at elevated ambient temperature in our country is 70 ° C.
Increased temperature of combustion products is a danger not only for a person, but may cause fire spread.
Smoke. Loss of visibility in smoke.
Smoke is a mixture of combustion products, in which small particles of liquid and solids are weighted.
Due to the presence in the composition of solid and liquid particles, when light passes through it, the intensity of the latter decreases, which ultimately leads to a decrease and loss of visibility in smoke.
Directly, a decrease in visibility in the smoke does not represent the threats to the life and health of people as a dangerous factor of fire. However, I want to note the following. If a person runs into a smoke corridor, then with some critical visibility, because of fear, he may return back. Moreover, the percentage of people returned back increases with a decrease in visibility. This is confirmed by research conducted in England and the United States.
As the practice of calculating hazardous fire factors shows, the blocking of evacuation paths is most often about loss of visibility in smoke.
The limit value for loss of visibility in smoke in our country is the value of 20 m.
Flame and sparks. Heat flow.
As they say in the famous saying: "There is no smoke without fire." A significant part of fires flows in fiery burning mode. Despite the fact that fires can begin with raids, mostly all of them then go into fiery burning.
The flame, or open fire presents a significant threat to the life and health of people, and also contributes to the spread of a fire on the object. The spread of the fire can be carried out on tens of meters due to the thermal radiation of the flame. The criterion for evaluating flames, as a dangerous fire factor, is a heat flux or heat density.
As a rule, in buildings (residential and public), the flame does not represent a significant danger, because Until the moment when the fire develops significantly, people manage to evacuate. But, unfortunately, it does not always happen.
The flame, the heat flux, created by them, is at production facilities, especially where combustible gases are treated, flammable and combustible fluids. The accidents at such facilities can be spontaneous, and the thermal stream created during fires represents the threat of life and health of people at considerable distances from the fire focus.
The limit value of the heat flux, adopted in our country, is 1.4 kW / m 2, in foreign practice, this value is 2.5 kW / m 2.
Toxic combustion products.
Toxic combustion products are, in my opinion, the most dangerous of dangerous fire factors (sorry for tautology), especially in residential and public buildings. In our country to toxic products Burning includes carbon dioxide ( carbon dioxide), carbon monoxide (carbon monoxide) and chloride.
In our country, the maximum permissible values \u200b\u200bof hazardous fire factors for each of the toxic gaseous gorgeous products are adopted as follows:
Carbon dioxide CO2 - 0.11 kg / m 3;
Carbon monoxide CO - 1.16 · 10 -3 kg / m 3;
HCL-2.3 · 10 -5 kg \u200b\u200b/ m 3.
In foreign practice to toxic combustion products include carbon black gas and cyanorod (HCN), carbon dioxide is attributed to the category of suffocating gases, the chloride is attributed to irritant gases. Also, abroad, in particular in the United States, the so-called "Fractional Effective Dose" (FED) concept is adopted, which takes into account the amplification of toxic effects in the action of several toxic components simultaneously. This phenomenon is called "synergism".
The temperature is an important and frequently limiting environmental factor. The spread of various types and the number of populations is significantly dependent on temperature. What is it connected and what are the reasons for such a dependence?
The temperature range that is registered in the universe is a thousand degrees, but the habitat limits of living beings on Earth is significantly already: most often from - 200 ° C to + 100 ° C. Most of the organisms have a much narrower range of temperatures, and the largest range has the lowest organized beings of microorganisms, in particular, bacteria. Bacteria have the ability to live in conditions where other organisms die. Thus, they are found in hot springs at a temperature of about 90 ° C and even 250 ° C, while the most stable insects die if the ambient temperature exceeds 50 ° C. The existence of bacteria in a wide range of temperatures is provided by their ability to move into such forms as disputes having durable cell walls that carry out adverse environmental conditions.
The range of tolerance in terrestrial animals is generally more than that of aquatic (not counting microorganisms). Temperature variability, temporary and spatial, is powerful environmental factor medium. Living organisms adapt to various temperature conditions; Some can live with constant or relatively constant temperatures, others are better adapted to temperature fluctuations.
The impact of the temperature factor on the organisms is reduced to its effect on the metabolic rate. If we proceed from the Rut-Gooff rule for chemical reactionsIt should be concluded that an increase in temperature will cause a proportional increase in the rate of biochemical metabolic processes. However, in living organisms, the reaction rate depends on the activity of enzymes that have its own temperature optimis. The speed of enzymatic reactions depends on the temperature is nonlinear. Given all the variety of enzymatic reactions in living beings, it should be concluded that the situation in living systems differs significantly from relatively simple chemical reactions (flowing in non-residential systems).
When analyzing the relationship between organisms and ambient temperature, all organisms are divided into two types: homoothermal and pallotermann. Such a separation refers to the animal world; sometimes animals are divided into warm-blooded and cold-blooded.
Homeothermal organisms have a constant temperature and maintain it, despite the change in the temperature in the environment. On the contrary, the causting organisms do not spend energy to maintain a constant body temperature, and it varies depending on the ambient temperature.
Such a separation is of a somewhat conditional nature, since many organisms are not absolutely caught or homoothermal. Many reptiles, fish and insects (bees, butterflies, dragonflies) can regulate the body temperature for a certain time, and mammals at unusually low temperatures weaken or suspend endothermic telepositional body temperature. So, even in such "classic" homoothermal animals, like mammals, during winter hibernation, the body temperature drops.
Despite the well-known conventionality of dividing all organisms living on Earth for these two large groups, it shows that there are two strategic options for adaptation to the conditions of the medium temperature. They have developed in the course of evolution and differ significantly in a number of fundamental properties: in terms of the level and stability of the body temperature, according to thermal energy sources, according to thermoregulation mechanisms.
Poikilotermic animals are ectotherm, they have a relatively low level of metabolism. Temperature of the body, the speed of physiological biochemical processes and the total activity directly depend on the temperature of the medium. Adaptation (compensation) in pykilotermic organisms occur at the level of exchange processes: the optimum of enzyme activity corresponds to the temperature mode.
Poikilotermia strategy is that the organisms do not spend energy on active thermoregulation and provides stability in the range of average temperatures that remain sufficiently long time. When the temperature parameters exit for certain limits, organisms are terminated. Adaptations to changing temperatures in these animals are private.
In homoothermic organisms there is a range of devices to changing conditions for the temperature of the medium. Temperature adaption associated with maintaining the constant level of body temperature and. reduced to get energy to ensure high level Metabolism. The intensity of the latter they have 1 to 2 orders of magnitude higher than that of Pykiloterm. Physiological biochemical processes in them proceed in optimal temperature conditions. The heat balance is based on the use of its own heat product, therefore they are related to endothermal organisms. A regulatory role in maintaining a constant body temperature plays a nervous system.
The homeothermia strategy is associated with high energy costs to maintain a constant body temperature. Homoothermia is characteristic of higher organisms. These include two classes of higher vertebrates: birds and mammals. The evolution of these groups was aimed at weakening dependence on external factors Environments by increasing the role of central regulatory mechanisms, in particular, the nervous system. Most of the types of living organisms are caught. They are widely burned on Earth and occupy a variety of environmental niches.
The reaction of a specific point of temperature is not constant and may vary depending on the time of exposure to ambient temperature and a number of other conditions. In other words, the body can adapt to change temperature mode. If the device is recorded in laboratory conditions, the process is usually called acclimationif in natural - acclimatization. However, the difference between these terms lies not at the place of registration of the reaction, but in its essence: in the first case, we are talking about the so-called phenotypic, and in the second genotypic adaptation, i.e. adaptation at the genetic level. In the event that the body cannot adapt to changing the temperature regime, it dies. The cause of the death of the body at high temperatures is the violation of homeostasis and the intensity of metabolism, denaturation of proteins and inactivation of enzymes, dehydration. The irreversible disorders of the structure of proteins occur at a temperature of about 60 ° C. That is the threshold of "thermal death" in a number of simplest and some lower multicellular organisms. Adaptation to changes in temperatures is expressed in them in the formation of such forms of existence, like cysts, disputes, seeds. In animals, "thermal death" occurs earlier than the denaturation of proteins occurs, due to violations of the nervous system and other regulatory mechanisms.
At low temperatures, the exchange slows down or even suspended, the formation of ice crystals inside the cells, which leads to their destruction, an increase in the intracellular concentration of salts, disorders of the osmotic equilibrium and denaturation of proteins. The frost-resistant plants withstand a complete winter friction due to ultrastructural rearrangements aimed at dehydration of cells. Seeds withstand temperatures close to absolute zero.
Almost 75% of the heat of the body is spent on radiation in the environment and is carried out by moving air. About 22% goes to evaporation and is lost with the discharge. And only about 2-3% is spent on the heating of food and air consumed.
At low temperature medium, the body increases heat product and reduces heat transfer. This happens at the expense of the following mechanisms. After irritation of the skin receptors at the central nervous system signal, the vessels of the skin, subcutaneous fiber and mucous membranes occur. Remember how the person crushes in the cold looks. His lips have missed, the face of pale, on the body "goose skin" - a sign of involuntary reduction of its muscles. But it is worth heating how the cheeks are republishing, lips - the expansion of capillaries occurs.
Due to the contraction of the capillaries in the cold blood flow in surface tissues, the body slows down and the body decreases in the amount. This leads to a decrease in radiation - the most important article of the heat consumption. Only by regulating the blood flow of the blood vessels and mucous membranes can be reduced (or increase) by 70% of the heat loss of the body.
In patients and uncrowered people, thermal adjusting systems may not cope with their tasks. Therefore, weakened and untrained people (especially children) even a small cooling causes worsening of well-being, colds and chronic diseases. Yes, and in healthy people, sharp cooling, especially with high humidity and air movement (draft), often ends with a cold or even more serious diseases (or their complications).
With the heat, the skin vessels are expanding reflexively, breathing, pulse, often drops blood pressure. The skin temperature rises, which leads to a larger heat loss due to radiation. But the main mechanism of regulation in the case of overheating is sweating. The cooling intensity depends on the volume and velocity of the sweat from the body surface. It is believed that the inhabitants of the roast belt and sweat glands of the skin are more developed than those living in the north. Allocated fat substances also contribute to more rapid evaporation of sweat.
At high ambient temperatures, human well-being deteriorated sharply. Particularly unfavorable combination of high temperature and high humidity. For example, at a temperature of 40 ° C and relative humidity, 30% well-being can be approximately the same as at 30 ° C and a humidity of 80%. With elevated values \u200b\u200bof these elements, the well-being of people, as a rule, suffers greatly.
Human moisture content on a hot day with the physical work of the average difficulty in the open air range from 2 to 4-6 liters. Let's say if you dig a garden on the sun, then lose about 2-4 liters of moisture, and tourists on a hot day can "reset" due to moisture content up to 6 kg. With large physical exertion and in hot weather, the drinking mode should be especially observed and take care of thermal impact.
Even in the usual, not very sunny weather on the beach anywhere from a Rublevsky or Klyazmin reservoir or on the edge of the forest moisture content can be up to 100-200 per hour. At moderate air temperature - about 15 ° C - and in a state of rest, a person highlights on average 1 g of sweat in 1 minute.
With an increase in temperature up to 30 ° C, the sweating increases 4-5 times. The same effect is observed when a person starts to work or begins to move. So, already when walking through the open highway, the selection of sweat increases by 2-3 times, and when running - 4-6 times compared with a quiet state.
Energy and moisture content costs should be taken into account when organizing physical work, tourist hiking, dosing load at sports games, as well as in everyday life. This is especially true of patients and older people.
IN middle lane The European part of our country, in particular in the suburbs, the flow of heat to the body is less than its consumption. Therefore, to maintain the constancy of the inner medium, we wear one or another clothing and support a certain temperature of your home. The thermostatic properties of clothing are estimated in special units - "CLO" (from English. Clothes - clothing).
So, the shape and degree of temperature of the temperature per person are different in different seasons, with different household and production atmosphere.
This effect depends on the magnitude and sign of deviations of the actual observed metatheological values, from some optimal combination, which is customary to be called "comfortable". The fact is that there is not only the arrival of heat, but also humidity and the intensity of air movement affect the heat supply. Therefore, the comfort zone, that is, such parameters of the external environment, in which a person feels in the best possible way (without experiencing heat, stuffiness, cold, dampness, etc.), is determined by a number of conditions - not only weather, but also other concomitant factors of human vital activity.
The feeling of the cold or heat, among other things, depends on the nature of the nervous system, the size and weight of the body, the general state of health and, of course, managing a person. How to surprise us sometimes easily dressed in frosty weather. And they feel at all worse than we, wrapped in fur coats and scarves, respectively, the thermometer testimony. Much is due to both the lifestyle, household traditions of people. For example, the great artist I.E. Repin slept all-round with open windows, the famous polar travelers (Nansen, Amundsen, Peeli) adhered to even more stringent rules.
Comfortable for Moscow conditions is the air temperature of about 23 ° C, for polar regions - 17 ° C, and for the south of the country-25 ° C. The temperature estimate depends not only on the place, but also on the observation time. So, in the suburbs, the temperature plus 4-6 ° C in March is regarded as warm, but already in mid-May we will consider it cold.
On holiday beaches you can find shields where the integrated assessment of man's heat dissipation is given while simultaneously actions of several factors - air temperature and humidity, atmospheric pressure and wind, as well as solar radiation. This is equivalent to efficient temperature (EET) or radiation-equivalent effective temperature (raete). The latter, except for the cumulative action of temperature and humidity, also characterizes the effect of solar radiation.
Depending on the values \u200b\u200bof meteo elements, each of them can weaken or strengthen the effect of another on a living organism. Thus, high humidity enhances the effect on the body of both high and low temperatures. Strong wind in combination with high or low temperatures contributes to overheating, and in others - the supercooling of the body. Moderate wind in hot weather is a favorable factor in the fight against overheating. The most favorable is the temperature of the external environment in the range of 18-20 ° C with a relative humidity of 40-60% and weak wind.
Each organism lives, develops and effectively multiplies in a certain ambient temperature range. On the temperature scale, thus, you can specify two points that determine the zone of life of this species, called the temperature tolerance zone, and the zone of lethal temperatures outside the tolerance zone. Points that limit the zone of temperature tolerance are called critical. They are determined on the basis of mortality data on the border of the tolerance zone. In the boundaries of the temperature tolerance zone and abroad, there are a number of characteristic manifestations or reactions of the body. The center of the tolerance zone is thermal optimum, in the boundaries of which all processes of vital activity proceed most economically. In the high temperature band, the temperature of the temperature cobster occurs. Further increase in temperature leads to overheating of the body and his death. At temperatures below, the optimal body enters the unfavorable zone where it takes place from the cold. A further decrease in temperature, in particular the transition through 00, causes the supercooling of body fluids from the beginning, after which, depending on the degree of salt concentration in these liquids, the body reaches the point of critical temperature. At this point, the freezing of body fluids begins, and the temperature of the body from the beginning rise briefly, after which the slow freezing of body fluids occurs, and the body goes into an anabea state. The complete freezing of body fluids leads to death. The death of low temperatures depends on the development stage of the body.
In humans, normal life is possible in the range of just a few degrees: a decrease in body temperature below 360s and the increase above 40-410C is dangerous and may have severe consequences for the body (freezing, thermal blow).
The sensation of ambient temperature depends on the temperature of the skin, which, at the temperature of the environment, 32-350c does not feel neither supercooling or overheating. The perception of temperature conditions of the medium is associated with the daily rhythm of human metabolism and related conditions. Temperature comfort area for man is 17-270c. The subjective feeling of climatic comfort is associated with the level of human activity, radiation temperature, clothing, temperature and relative humidity Air, as well as wind speed. In apartments where the air movement does not have great importance, the conditions of heat exchange and human well-being are determined temperature conditions and humidity. High humidity compensates for lower temperature.
The ambient temperature, affecting the body through the body surface receptors, changes the focus of many physiological mechanisms of the body. The decrease in temperature is accompanied by an increase in the excitability of the nervous system, as well as to strengthen the secretion of adrenal hormones. The level of main exchange is increasing. The total and local hypothermia causes the churring and mucous membranes, inflammation of the walls of vessels and nerve trunks. Cooling during pathess, sharp temperature differences and deep cooling of the internal organs lead to colds.
The effect of low temperatures per person is intensified under the action of wind. The joint action of wind and cold is especially subject to arms and legs, which are often open even in conditions of harsh winter. Of three parts of the face: forehead, cheeks and nose - the most sensitive is the forehead, which in normal conditions - One of the warmest body surface areas.
Facility to cold in humans is provided in various ways. Critical temperature for Europeans without clothes enclosed within 270 to 290c. With a decrease in temperature below the critical European reacts to an increase in metabolism. However, the indigenous inhabitants of Australia, especially in its central and southern parts, sleep at night, not shelting the body. With night supercooling, insulating hypothermia occurs in sleeping aborigines. It consists in cooling the surface of the body by several degrees without metabolic reactions, which leads to a decrease in heat loss. Such adaptation, however, is absent from Eskimos living in the coldest Arctic areas. They are inherent in European-type metabolic adaptations. This is due to the nature of clothing, which perfectly protects their body from the ambient temperature reaching - 500c.
Thus, in a person when adapting to cold is rebuilt different kinds The metabolism is preserved by hypertrophied adrenal glands. A superficial layer of open areas of leather is compacted, the fat layer increases, brown fat is deposited in the cooled places. In the reaction of adaptation to cold, all physiological systems of the body are involved. The overall metabolism increases, the function of the thyroid gland, the blood circulation of the brain, heart muscle, liver, increases the number of catecholamines. This increase in metabolic reactions creates a reserve of the body's existence at low temperatures.
With increasing temperature, the main exchange in humans is reduced. The first respiratory react and cardiovascular system. A significant increase in temperature causes the expansion of peripheral blood vessels, the increase in pulse and respiration, an increase in the minute volume of blood and decrease in blood pressure. Bloodstock in the muscles and internal organs is reduced. Also falls the excitability of the nervous system.
Human resistance to heat is significantly higher than the exposure to cold, which is due to the release of sweat. This process can remove energy from the human body, 14 times the magnitude of its production in metabolism is at rest. Thus, the effectiveness of thermoregulation by means of sweat is huge.
In case of a sudden increase in the temperature of the environment, the human body responds to relaxation and the impossibility of performing tasks normally carried out at a slightly lower temperatures. There is a desire to get rid of clothes, strong sweating and increased irritability. The device to elevated temperatures lasts, as a rule, several days and consists in increasing the body temperature, slowing the rhythm of cardiac activity and the increase in sweating.
If the temperature of the external environment reaches 27-380s (blood temperature), the heat transfer is carried out mainly due to the sweating. In the case of its difficulty with high humidity of the environment, the organism overheating occurs. This is accompanied by an increase in body temperature, impaired input and salt metabolism and vitamin equilibrium. The formation of non-oprified metabolic products occurs. Blood thickening begins. When overheating, blood circulation and respiration can occur. Initially there is an increase, and then drop blood pressure. With repeated high temperatures, there is an increase in tolerance to thermal factors. The change in the ambient temperature aside from the temperature of the temperature comfort when disrupting adaptation is accompanied by a violation of the processes of self-regulation and the occurrence of pathological reactions.
The main form of protection of the body from overheating is cool clothing - light, well ventilated, long, with folds. It reduces the absorption of radiation energy by half, and water loss - up to 2/3.