Thermoregulation is a mechanism that allows living organisms to maintain a constant internal environment. Most processes in the human body depend on temperature: metabolism, protein and hormone synthesis, digestion, cognitive functions. In addition, overheating or hypothermia can lead to serious illness and even death.
Temperature range
Thermoregulation is extremely important for normal human life. The body temperature of healthy people is in a narrow range from 36.0 to 37.0 Celsius. A sharp decrease or increase in these values usually leads to death.
In the heat, a person sweats intensely. Losing fluid in this way leads to dehydration, sometimes quite serious. Together with sweat, vitamins and minerals leave the body. Due to dehydration, the blood becomes thicker, metabolism is disturbed. Normal water loss during sweating is up to three percent of the total body weight. If this value has exceeded the six percent barrier, cognitive function suffers. Twenty percent is enough for death. In addition, there is another danger. During a prolonged exposure to the sun, the body accumulates more heat than it releases into the environment, and according to the law of thermodynamic equilibrium, the human body gradually heats up to air temperature, that is, to 39-41 degrees Celsius. This entails heat stroke and loss of consciousness. The cardiovascular system also works for wear and tear: the pulse rises, the pressure rises, the blood hardly passes through the vessels.
Subcooling is no less dangerous for humans. In the cold, the blood vessels of the body narrow, which causes tissue ischemia. And if the exposure to cold temperature is long, it is possible to die off areas of the skin or muscles. Low temperatures also affect the metabolism, which takes place several times faster, because the body needs energy to heat.
Kernel and Shell
Conventionally, the entire human body can be divided into two levels: the core and the shell. The nucleus (for the most part these are internal organs) has a constant temperature of about thirty-seven degrees. This is achieved by the balance between heat production and heat transfer. The shell is a barrier between the environment and the core 2.5 cm thick. Thermoregulation is the ability of the shell to maintain a constant core temperature.
The skin of a healthy person in different areas can be heated from 24 to 36.6 degrees. The coldest are the tips of the fingers, and the warmest place is the armpit. Fluctuations in body temperature during the day reach one degree: the lowest - early in the morning, and the highest - at six in the evening.
Heat generation and heat transfer
What is thermoregulation and how is it maintained in the human body? This question is not as easy to answer as it seems at first glance. In our body, heat is continuously generated, which for the most part is spent on heating the external environment. This process is called heat transfer. It is regulated by the nervous system, its metabolism, heart activity, muscle contraction, etc. depend on its results.
Normally, heat production is equal to heat transfer, that is, isotherm is observed. The reasons for thermoregulation are simple - it helps to maintain the core temperature intact and provide a certain independence of the body from external conditions. For an hour, a person generates enough heat to boil a liter of water. And if not for the heat transfer, then within three days after birth, we all would literally be welded from the inside. Therefore, processes that help people get rid of excess heat are extremely important.
Hardening
Thermoregulation and hardening go hand in hand. The body adapts to the effects of ever lower or higher temperatures, new mechanisms are formed to maintain a constant core temperature.
At home, several of the most common hardening methods are known. For example, rubbing with cool water. The first time the water should be 30 degrees, then 28, 26 and so on, until it reaches 15 degrees Celsius. When the body gets used to the cold, you can switch to a shower or shower from rubdowns. Effective also recognized air and sun baths. Initially, the duration of the sessions should not exceed 15 minutes, but over time you can bring the time to 60. However, it is worth remembering that prolonged insolation can lead to skin problems and cancer.
Thermoreceptors
Skin plays a key role in the body's thermoregulation. As the largest organ of the human body, it performs many functions, including containing thermoreceptors (cold and thermal). It is known that there are about ten times more cold ones, therefore we are much more sensitive to low temperatures. The largest accumulation of receptors is on the face, neck, and least of all - at the fingertips. However, their sensitivity is inversely proportional to quantity. Despite the fact that there are more thermal receptors, they are almost two times more sensitive than cold ones.
Types of thermoregulation
Thermoregulation is a conglomeration of processes aimed at maintaining a constant body temperature through heat transfer. The mechanism of operation of this system can be described using the principle of "feedback". That is, first the ambient temperature changes, the skin receptors react to this and transmit a signal to the brain. And from there, regulation of heat production and its output comes from.
All processes of thermoregulation can be divided into two types:
- physical;
- chemical.
Physical thermoregulation, in turn, is divided into evaporation, radiation, heat conduction and convection. Among chemical processes , contractile and non-contractile thermogenesis are distinguished.
Physical thermoregulation
Physical thermoregulation is a set of processes that ensure the removal of heat from the body. For this, nature provides for several ways:
- conduction;
- convection;
- radiation;
- evaporation.
In addition, the body can regulate the intensity of blood circulation and the degree of expansion of blood vessels of the skin, which also affects the loss of heat. Another mechanism of heat transfer is sweating. It is most effective in the event of a hot climate or an artificial increase in ambient temperature.
At rest, at a comfortable temperature of 20 degrees Celsius, a person loses about sixty percent of the heat by radiation, evaporates only twenty, and the rest is conduction and convection. In just an hour, we lose about one hundred kilocalories or four hundred nineteen joules.
Evaporation and radiation
Evaporation is the release of energy into the environment due to the loss of moisture through the skin or mucous membranes. Otherwise, this process is called sweating. Being in a comfortable temperature (about twenty degrees Celsius), a person loses about 36 grams of fluid every hour. With increasing temperature or intense work, this figure sometimes increases to two liters per hour.
If the air is dry, then the temperature is tolerated by a person relatively well, as there is the possibility of evaporation of sweat. However, in humid climates, even thirty degrees of heat can be fatal.
Radiation is a way of heat transfer using electromagnetic radiation. A person radiates heat from the moment the ambient temperature drops below body temperature, that is, almost always. To prevent heat loss during the cold running time, you need to leave a minimum amount of exposed skin. Clothing can suspend radiation and reduce the amount of heat generated, but cannot completely stop it.
Even the position of the body is involved in thermoregulation. When the animal or person is cold, he tries to group (curl up) so that as little as possible the surface of the body is in contact with the external environment. Conversely, if it is warm, then both people and animals try to open up to increase the area of the skin for radiation.
Conduction and convection
Conduct is manifested when a person comes into contact with other bodies. It depends on the contact time, the area of the subject and the thermal conductivity of the material.
In order not to get frostbite or not get sick, you must adhere to elementary rules:
- do not sit on cold stones;
- In winter, do not grab bare metal objects with your bare hands;
- in nature, do not sit on bare ground, but always plant something (sleeping bag, rug, clothes);
- Do not walk in wet clothes in the winter.
Convection is a dynamic method of heat loss, which is carried out by moving particles of water or air, for example, such flows are created by wind or a fan. If simply, the body, generating heat, heats the air near the skin. It becomes lighter than cold, and rises higher, and a new portion takes its place. When we find ourselves in the wind or move quickly, the air around us also moves faster, therefore, the heat does not stay near the skin for a long time.
Chemical thermoregulation
Thermoregulation and metabolism are closely related concepts. The chemical method is based on a change in the intensity of the oxidation process and muscle vibration. Energy for heating the body is obtained by hydrolysis of ATP (adenosine triphosphate). It is necessary to turn complex compounds into simpler ones. The heat that is released is dissipated in the surrounding area. This is irreducible thermogenesis.
Depending on the ambient temperature, the metabolism may accelerate or slow down to maintain the constancy of the nucleus. The most comfortable person feels at 18-20 degrees Celsius. But this is for air. Water conducts heat more strongly, so the temperature should be higher. Muscles produce the most heat during aerobic glycolysis. Therefore, when we are cold, the body begins to tremble in order to increase heat production. This condition is called contractile thermogenesis.
Thermoregulation control
Thermoregulation of the brain goes the same way as the rest of the body, with the difference that it is here that the center is located, which controls the whole process. In the hypothalamus there is a center of thermoregulation, coordinating the speed of metabolic processes, muscle contraction, and tone of skin vessels.
Sensitive nerve cells of this part of the brain can distinguish between oscillations of hundredths and thousandths of a degree. They analyze the incoming information and, based on the feedback principle, regulate the internal temperature, setting it depending on external circumstances.
The thyroid gland and adrenal glands are subordinate to the hypothalamus. The first affects the metabolic rate, and the second - on vascular tone and oxidative processes in the muscles. Using neurotransmitters and hormones, the hypothalamus corrects the condition of the body in accordance with the circumstances.