Respiratory and circulatory systems. Blood
The origin of the brain Saveliev Sergey Vyacheslavovich
§ 6. Consumption of oxygen by the brain
It is completely wrong to link the intensity of brain metabolism with the total oxygen consumption of the body (Schmidt-Nielsen, 1982). Indeed, in a shrew, oxygen consumption per 1 kg of body weight is 7.4 l / h, and in an elephant - 0.07 l / h. However, this is the total oxygen consumption, which differs by orders of magnitude in different parts the bodies of both the elephant and the shrew. Moreover, in animals with different biology, the amount of oxygen consumption by the same organs of the body also varies significantly. The notion of a change in brain oxygen consumption proportional to body size remains a strange misconception. If in any mammal the oxygen consumption of the brain becomes less than 12.6 l / (kg-h), death occurs. At this level of oxygen, the brain can only remain active for 10–15 seconds. After 30-120 seconds, the reflex activity fades, and after 5-6 minutes, the death of neurons begins. In other words, the nervous tissue has practically no own resources. Neither the shrew, nor even the elephant, would have had any chance of surviving if the oxygen consumption of the brain was not provided special mechanisms. The brain receives oxygen, water with electrolyte solutions and nutrients according to laws that have nothing to do with the intensity of the metabolism of other organs. The values of consumption of all “expendable” components are relatively stable and cannot be below a certain level, which ensures the functional activity of the brain.
It should be noted that the brain often renders decisive influence on the metabolism of the whole animal. The energy consumption of the brain cannot be below a certain value. Ensuring this level is achieved in different systematic groups by changing the rate of blood circulation in the vessels of the nervous system. The reason for these differences are changes in the number of capillaries in 1 mm of brain tissue. Of course, in different departments brain, the length of capillaries can vary significantly. Depending on the physiological load, the lumen of the capillaries can also change dynamically. Nevertheless, this very average indicator illuminates the reasons for the increase in heart rate in small mammals. The smaller the capillary network of the brain, the greater must be the speed of blood flow in order to provide the necessary supply of oxygen and nutrients. You can increase metabolism due to heart rate, breathing and the speed of food intake. This is what happens in small mammals. Information about the density of capillaries in the brain of animals is very sketchy. However, there is a general trend showing the evolutionary development of the capillary network of the brain. In a pond frog, the capillary length of 1 mm 3 of brain tissue is about 160 mm; in a whole-headed cartilaginous fish, 500; in a shark, 100; mice 700, rats - 900, rabbits - 600, cats - 900, dogs - 900, and primates and humans - 12001400 mm. It should be taken into account that when the length of capillaries is shortened, the area of their contact surface with nervous tissue decreases exponentially. This indicates that in order to maintain a minimum level of oxygen supply to the brain in shrews, the heart must contract several times more frequently than in primates and humans. Indeed, for a person this value is 60–90 per minute, and for a shrew it is 130–450. The mass of the shrew's heart should be proportionately larger. It is about 4% in humans, 8% in capuchin, and 14% in shrews of the total body weight. Therefore, one of the key organs that determine the metabolism of animals is the brain.
Let's try to estimate the real share of energy consumed by the body of animals with different brain and body weights. The large relative mass of the nervous system of small mammals makes high demands on the level of metabolism of the brain itself. The cost of maintaining it is comparable to the cost of maintaining the human brain, which is well researched. The basic consumption of nutrients and oxygen by the human brain is approximately 8-10% of the entire body. When the organism is inactive, this value is more or less constant, although it can fluctuate significantly in large and small representatives of this species. However, even this value is disproportionately large. The human brain is 1/50 of body weight, and consumes 1/10 of all energy - 5 times more than any other organ. These are somewhat underestimated figures, since oxygen consumption alone is 18%. Let us add the cost of maintaining the spinal cord and peripheral system and get about 1/7. Consequently, in an inactive state, the human nervous system consumes about 15% of the energy of the whole organism. Now consider the situation with the actively working brain and peripheral nervous system. According to the most conservative estimates, the energy costs of one brain more than double. Considering the generalized increase in the activity of the entire nervous system, it can be confidently assumed that about 25-30% of all body expenses are accounted for by its maintenance (Fig. I-8).
The nervous system of mammals turns out to be an extremely “expensive” organ, so the less time the brain works in intensive mode, the cheaper its maintenance is. The problem is solved in different ways. One of the methods is associated with minimizing the time of the intensive mode of the nervous system. This is achieved by a large set of innate, instinctive behavior programs that are stored in the brain as a set of instructions. Instructions for various forms behaviors need only minor adjustments for specific conditions. The brain is almost never used to make individual decisions based on the animal's personal experience. Survival becomes statistical process application of ready-made forms of behavior to specific environmental conditions. Energy costs for the maintenance of the brain become a limiter of intellectual activity for small animals.
For example, suppose an American scallopus mole decides to use its brain like primates or humans do. Consider the initial conditions. A mole weighing 40 g has a brain weighing 1.2 g and a spinal cord, together with a peripheral nervous system, weighing approximately 0.9 g. Having nervous system, which is more than 5% of body weight, the mole spends about 30% of all energy resources organism. If he thinks about solving a chess problem, then the cost of his body to maintain the brain will double, and the mole will instantly die of hunger. Even if the mole pushes into the intestines of the infinite earthworm from black caviar he will still die anyway. The brain will need so much energy that there will be insoluble problems with the rate of oxygen production and the delivery of initial metabolic components from gastrointestinal tract. Similar difficulties will arise with the excretion of metabolic products of the nervous system and its elementary cooling. Thus, small insectivores and rodents are doomed not to become chess players. Their brain is instinctive, and the energy problems of its content pose insurmountable barriers to the development of individual behavior. At the individual level, only variability in the application of innate behavioral programs can arise.
Rice. I-8. metabolic processes in the primate brain.
In the metabolism of the nervous system, three main dynamic processes can be distinguished: the exchange of oxygen and carbon dioxide, consumption organic matter and excretion of catabolism products, exchange of water and electrolyte solutions. The proportion of consumption of these substances by the human brain is indicated at the bottom. The exchange of water and electrolyte solutions is calculated as the time it takes for all body water to pass through the brain. The top line is the passive state, the bottom line is hard work nervous system.
However, it is enough to slightly increase the size of the body, and a qualitatively different situation arises. gray rat (Rattus rattus) has a nervous system weighing approximately 1/60 of body weight. This is already enough to reach noticeable decrease relative brain metabolism. It makes no sense to retell the results of intellectual experiments and observations of rats, and the degree of individualization of behavior is not comparable to that of moles and shrews. Obvious advantage increase in body weight is to reduce the cost of maintaining the brain. Permanently working peripheral departments are not as costly as the brain, so an increase in body weight leads to a relative "cheapening" of the brain.
Therefore, to create an individualized brain, an animal with a sufficiently large body mass is needed. In other words, there is a kind of barrier that, through the size of the body and the mass of the brain, limits the ability of animals to learn and individualize behavior. A small animal with a large brain and high maintenance costs will not be able to provide energy costs for increasing its activity. Thus, solutions to complex problems or deep individualization of adaptive behavior cannot be expected. If the animal is large, and the size of the brain is relatively small, then significant fluctuations in the energy costs for its maintenance are permissible. In this situation, both individualization of behavior and complex processes learning. However, even in a large animal with good developed brain there are energy problems. The nervous system is too expensive for intensive exploitation. A small and intensively working nervous system consumes a huge proportion of the body's resources. This situation is unfavorable. An energetically justified solution can only be a short-term use of the brain to solve specific problems. This is observed in large mammals. Brief activity is quickly replaced by prolonged rest.
Thus, a small and a large nervous system has its own advantages. To implement instinctive behavior, you can have a small brain, but its adaptability is reduced to modifications of the instinct. big brain costs its owner quite expensive, but high energy costs are fully justified. A big brain allows you to deal with challenging tasks who do not have ready-made instinctive solutions. The cost of implementing such mechanisms of adaptive behavior is very high, so both animals and humans try to use the brain as little as possible.
Privilege of the nervous system
The nervous system of many animals (and especially in mammals) has one property that puts it in an exceptional position. This property is associated with its isolation from the rest of the organism. As the main mechanism for integrating work internal organs and the basis of behavior, it is " foreign body» for your own body. The immune system views the nervous system as something like a thorn in the side. If the immune system “gets” to the brain, then severe autoimmune processes begin that are incompatible with life.
A paradoxical situation arises. The nervous system consumes a huge part of the oxygen and nutrients of the whole body, which it receives through the blood. At the same time, it must be carefully isolated from circulatory system, because it is considered by the cells of the immune system as a foreign object.
From the point of view of biological expediency, there is a clear contradiction. The main integrating organ should not be foreign to the immune system. Nevertheless, this is a fact that is quite easy to find a clear explanation. There are too many specialized organic components in the brain that are not used anywhere else in the body. Create in immune system the mechanism of their recognition as "their" cells is extremely difficult and unjustified. It is much "cheaper" to simply separate the nervous system from the rest of the body. This principle of isolation is implemented in the testes, ovaries and nervous system. In its most general form, the isolation of the nervous system is maintained by the blood-brain barrier, which consists of several types of specialized cells. To deal with the isolation of the nervous system from the rest of the organism, it is necessary to consider the elementary principles of its structure.
From the book The Newest Book of Facts. Volume 1 [Astronomy and astrophysics. Geography and other earth sciences. Biology and Medicine] author From the book Eye of the Mind author Hofstadter Douglas Robert From the book Brain and Soul [How nervous activity shapes our inner world] by Frith Chris26 Douglas Hofstadter A Conversation with Einstein's Brain Achilles and the Tortoise accidentally collide on the banks of an octagonal pond in the Luxembourg Gardens in Paris. This pond has always served as a favorite place for boat trips of young couples; these days their boats are often
From the book The Newest Book of Facts. Volume 1. Astronomy and astrophysics. Geography and other earth sciences. Biology and medicine author Kondrashov Anatoly PavlovichWe perceive not the world, but its model created by the brain What we perceive is not those raw and ambiguous signals coming from the outside world to our eyes, ears and fingers. Our perception is much richer - it combines all these raw
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From book Current state biosphere and environmental policy author Kolesnik Yu. A.Chapter 4 Obstacles to Oxygen In a normal atmosphere, hemoglobin binds only oxygen. This means that oxygen binding is not affected by other air components such as nitrogen, carbon dioxide, water vapor or argon. Hemoglobin collects
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To the question How much oxygen does the brain take? given by the author Miscalculation the best answer is Although in an adult the weight of the brain is only about 2% of the weight of the body, the brain consumes approximately 25% of the total oxygen absorbed by the body ...
The brain consumes about the same amount of oxygen as an active muscle.
(“resting” brain consumes 9% of all energy and 20% oxygen, “thinking” - consumes about 25% of nutrients entering the body and about 33% necessary for the body oxygen)
Answer from Marksman[guru]
Why is it so hard on the brain...
Answer from Neurosis[guru]
miser
Answer from throw[active]
All nutrients and oxygen, and in general everything that is needed, is delivered to the organs through the blood, and as you know, the composition of the blood is observed by the body very strictly ... the slightest deviation leads to various pathologies. From this point of view, the concentration of oxygen in the blood is constant and delivered to the organs according to their mass ratio, and not 10-30, and even more so, not 90% of carbohydrates, as noted above. Well, as it was rightly said, it depends on the current to what extent certain tissues are loaded with work, where redox processes go faster there and blood transfer is more intense, and therefore the absorption of oxygen .. there can be no talk of any average statistical percentages. And the greatest consumption of oxygen is still in the muscles ... and not in the brain :))))
Answer from Lady Galina cskdf[guru]
If the brain is tense, i.e. works, it takes exactly as much as it needs, because it is the BRAIN! Well, if he is lazy, then why does he need oxygen? He will die without the desire to work. Is it true?
Answer from Christina is me[active]
I don't have one....
Answer from Georgy Yurievich[guru]
And if the brains are chicken
Answer from Belkina Ekaterina[guru]
It depends on the brain and thought process.
Answer from Ivanov Ivan[guru]
According to various estimates, 10-30%.
But this is not more important, but that other organs can do without oxygen for a very long time,
then the brain in a few minutes perishes in parts (stroke) or completely.
The blood flow through which hemoglobin carries oxygen to the brain is blocked - and that's it.
And with a lack of O2 in the air, there is also no mechanism for it to mobilize all of it on the brain, so here it is the first to suffer
Answer from success[guru]
As much as you need for the full functioning of the body!
Answer from Irka-durka[expert]
a 4e tebya takou vopros zainteresoval=)
Answer from Fuzzy genie[guru]
15 percent oxygen.
Answer from Alexander Solid[guru]
The supply of oxygen to the brain depends on the color in which the hair is dyed. If a woman has blond, straw or gray hair, then more oxygen enters the brain through each hair. And if dark, chestnut or black, then the structure of the hair becomes clogged with paint and makes it difficult for oxygen to enter.
The smallest supply of oxygen to the brain is seen in those women who dye their hair in different colors simultaneously. (red - purple - green)
In women with long blonde hair(I call them blondes) the highest percentage of oxygen in the brain! Scientists believe that it is the amount of oxygen flowing inside the hair that affects oxidative, mental and other biological processes. It is for this reason that in blondes, dizziness, an inadequate assessment of the world around her occurs more often.
Answer from B-boy haseky[guru]
1% brain
Answer from Olga Senik[guru]
As a percentage, it is difficult to estimate the amount of oxygen consumed. this is a rather individual and mobile indicator, in conditions of hypoxia (lack of oxygen) other tissues can temporarily switch to anaerobic metabolic pathways, and the brain works only on oxygen (and glucose, by the way), therefore, in these conditions of oxygen deficiency, the PERCENTAGE oxygen consumption by the brain increases accordingly .
Answer from User deleted[guru]
brains get from 3 to 8% oxygen
Answer from Svetlana[guru]
ha ha ha ha ha
Answer from Oleg Agafonov[guru]
Hello.
Takes 0%, because. he (oxygen) cannot get there (into the brain) in any way ...))
Bye.
Answer from Alexandra[guru]
The human body, when it is in a calm, relaxed state, absorbs about three hundred cubic centimeters of oxygen per minute. The brain takes on a sixth part - that's fifty cubic centimeters, regardless of whether a person is sleeping or awake. And out of five hundred grams of carbohydrates that the human body absorbs, the brain takes on ninety.
Answer from Aqua Irina[guru]
..it all depends on the amount of brain...
The brain greedily absorbs oxygen. This can be easily verified by determining the concentration of oxygen in the arterial and venous blood. During rest, the brain consumes 20 times more oxygen by mail than muscle tissue. With intense mental work, oxygen consumption by the brain clearly increases.
Such figures also testify to the insatiable need of the brain for oxygen. The weight of the brain of an adult is usually 2-2.5 percent of body weight. At the same time, the brain consumes 1/5 or even 1/4 of the total oxygen consumed by the human body.
We don't think well in a stuffy room. It seems to have been experienced by everyone. Some people are especially difficult to tolerate the lack of oxygen. What about our children? They tolerate oxygen deficiency even worse. And this is no coincidence. In a child under the age of four, about half of the oxygen consumed by the body is consumed by the brain.
Brain tissue is the most sensitive to drugs and ethyl alcohol. Even small concentrations of alcohol depress her breathing...
The researchers calculated that the reserves of oxygen dissolved in the blood, in the blood vessels of the brain and in the tissue itself, are very limited. Just for 10 seconds, he has enough of his own resources. If oxygen is not supplied with the blood stream, then a biochemical catastrophe can occur very soon.
In fact, why does brain tissue need a lot of oxygen?
Probably, in order for the work to be done, the brain could live. And here we meet with a phenomenon that is characteristic only of the brain.
To do work, you need to burn some kind of fuel. This is almost the only fuel for the brain is glucose. Oxygen is mainly used for the oxidation of this substance. The end products of glucose conversion are carbon dioxide and water. However, in this case, another universal source of energy is formed - the ATP molecule. It provides almost all the energy costs of the brain.
The brain is, in a certain sense, unmercenary. He does not have any kind of solid reserves of glucose and lives, as they say, today.
You can verify this by simple experience. With an ordinary safety razor, we cut the thinnest slices of the internal organs of laboratory mice: liver, kidneys, muscles. Sections of the cerebral cortex are more difficult to make, but possible.
Place the sections of each organ separately in saline, poured into small vessels with a volume of several cubic centimeters each. We will attach glass pressure gauges with divisions to the vessels. Pour into the pressure gauge a large number of specially prepared and colored liquid. Now we will lower our entire structure into a bath with warm water, but so that the manometer is outside the bath, and the vessel is inside it. The temperature of the water in the bath is 37 degrees, that is, close to the body temperature of a laboratory animal.
Sections of organs breathe and consume oxygen. The volume of gas in the vessel decreases, and this is reflected in the readings of the manometer. A column of liquid creeps up. Of course, slowly, but quite noticeably. Thus, it is possible to calculate how many cubic millimeters of oxygen have been absorbed by a sample of 100 milligrams of tissue in one minute.
And here we are faced with an unusual phenomenon. Sections of tissues of the liver, kidneys, muscles consume oxygen at a constant rate for quite a long time. In any case, this process can be observed for five and ten minutes. Another thing is brain tissue. Her breathing quickly slows down, but as soon as a drop of glucose solution is added, she comes to life and breathes again at the same rate.
The experience we have made is very clear. It testifies that the nerve cells of the cerebral cortex cover their energy needs almost exclusively at the expense of glucose, which is transported with the blood stream.
And now a legitimate question arises: how does the oxidation of glucose form another universal source of energy - molecules of adenosine triphosphoric acid?
Hippocrates - the great doctor Ancient Greece- in one of his writings he wrote: "There is in a person both bitter, and salty, and sweet, and sour, and hard, and soft, and much more in an infinite number, variety in properties, quantity, strength." Using the example of oxidative transformations of glucose in the human brain and the formation of another universal source of energy - adenosine triphosphoric acid, one can trace the system of amazing transformations of "sweet", glucose, into ATP, "sour", according to Hippocrates.
If you simply burn glucose molecules in a stream of oxygen, water and carbon dioxide are formed. At the same time, it will stand out significant amount energy. Of course, this way of generating energy is unacceptable for a living cell. The energy in the cell is consumed in small portions. It should be formed gradually and accumulate "in reserve". Having a reserve of "canned energy", a living cell is able to respond extremely quickly to changes. external environment. Moreover, the process of energy production the cell can then slow down, then sharply speed up.
Each of us has seen this countless times. For example, you were sitting quietly in a chair. Energy consumption in muscle tissue was relatively small. You quickly got up and rushed to run fast; the biochemical power plant is running at full capacity.
A long chain of biochemical transformations of glucose began. It includes dozens of chemical transformations of a gradually splitting molecule of the original compound. But in this case we are interested final result. With the complete oxidation of one molecule of glucose, thirty-eight molecules of adenosine triphosphoric acid are synthesized.
Now it becomes clear why energy is generated in the brain mainly by oxidizing glucose, by breathing. With this method, it is formed especially a lot. The process of thinking is accompanied by a significant expenditure of energy in the truest sense of the word.
Consumption of O 2 at rest.The amount of oxygen consumed by the tissue depends on functional state its constituent cells. In table. 23.1 shows data on the consumption of oxygen by various organs and their parts when the body is at rest at normal temperature. The rate of oxygen consumption by one or another organ () is usually
expressed in ml O 2 per 1 G or 100 g of mass in 1 min (this takes into account the mass of the organ in vivo). In accordance with Fick principle determined based on blood flow() through one or another organ and differences in concentrations About 2 incoming to the body arterial blood and venous blood flowing from it ():
(1)
When the body is at rest, oxygen is relatively intensively absorbed by the myocardium, the gray matter of the brain(particularly bark), liver And cortex of the kidneys. In the same time skeletal muscles, the spleen and white matter of the brain consume less oxygen (Table 23.1).
Differences in oxygen consumption different sections one And the same organ. Can be measured in many organs blood flow through limited areas of tissue by determining the clearance of inert gases(for example, 85 Kg, 133 Xe and H 2). Thus, if it is possible to take a blood sample from a vein that drains from a given area, then this method allows you to determine the oxygen consumption in it. In addition, a few years ago, a method of positron emission tomography (PET) was developed, which makes it possible to directly measure blood flow and O 2 consumption in certain parts of organs. This method has been successfully used to study the human brain. Before the introduction of the PET method, as can be seen from Table. 23.1, measure regional consumption About 2 was possible only in a few organs.
When studying oxygen consumption by brain tissues of various mammals, it was shown that the cortex hemispheres consumes from 8 10 −2 to 0.1 ml O 2 g −1 min −1 . Based on the consumption of O 2 by the whole brain and cortex, it is possible to calculate the average consumption of O 2 white matter of the brain. This value is about 1 10 −2 mL g −1 min −1 . Direct measurement absorption of O 2 by brain regions in healthy subjects by positron emission tomography gave the following values: for gray matter(V different areas) - from about 4 to 6-10 -2 ml g -1 -min -1, for white matter-2-10 −2 mlg −1 min −1 . It can be assumed that oxygen consumption varies not only depending on the site, but also in different cells one area. Indeed, when measuring (using platinum microelectrodes) the regional consumption of O 2 by the superficial cell layers of the cerebral cortex, it was shown that under conditions of mild anesthesia, this consumption within small areas varies from approximately 4-10-2 to 0.12 ml. g −1 -min −1 . The results of autograph
CHAPTER 23
| Table 23.1. The average values of blood flow velocity (), arteriovenous difference in O 2 () and consumption of 0 2 () in various bodies human at 37 °C | ||||
| Organ |  |  |  | Data source |
| Blood |  |  |  |  |
| Skeletal muscles: at rest with severe physical activity |  |  |  |  |
| Spleen | ||||
| Brain: cortex white matter |  |  |  |  |
| Liver |  |  |  |  |
| Kidney: cortex outer layer of the medulla inner layer of the medulla |  |  |  |  |
| Heart: at rest with heavy exertion |  |  |  |  |
Physical studies of regional blood flow (using iodine-14 C-antipyrine) and regional glucose consumption (using 14 C-2 deoxyglucose) in the cerebral cortex suggest that these parameters also differ significantly in neighboring areas. In people older than 30 years, regional blood flow and O 2 consumption in the gray matter of the brain gradually decrease with age. Approximately the same differences in oxygen consumption were found between individual parts of the kidneys. IN cortex kidneys, the average consumption of O 2 is several times higher than in inland areas And papillae of the medulla. Since the needs of the kidneys for oxygen depend mainly on the intensity of active reabsorption of Na + from the lumen of the tubules in the tissue, it is believed that such pronounced differences in the regional consumption of O 2 are mainly due to the difference between the values of this reabsorption in the cortical and medulla .
O 2 consumption under conditions increased activity organ. IN In the event that the activity of any organ increases for one reason or another, the rate of energy metabolism in it increases, and, consequently, the need for cells in oxygen. During exercise consumption
About 2 myocardial tissues can increase by 3-4 times, and working skeletal muscles- more than 20-50 times compared to the level of rest. Consumption About 2 tissues kidney increases with an increase in the rate of Na + reabsorption.
In most organs the rate of absorption of O 2 does not depend on the speed of blood flow in them (provided that the tension of O 2 in the tissues is large enough). The kidneys are an exception. There is a critical perfusion rate, exceeding which causes the formation of an ultrafiltrate; at this level of filtration increased blood flow accompanied increased consumption About 2 kidney tissue. This feature is due to the fact that the intensity glomerular filtration(and hence Na + reabsorption) is proportional to the blood flow velocity.
Dependence of O 2 consumption on temperature. O2 consumption by tissues is extremely sensitive to changes in temperature. With a decrease in body temperature, energy metabolism slows down, and the need for most organs in oxygen decreases. With normal thermoregulation, the activity of the organons involved in maintaining the heat balance increases, and their oxygen consumption increases. Such organs include, in particular, skeletal muscles; their thermoregulatory function is carried out by increasing muscle tone and trembling (p. 667). Increase in body temperature
63β PART VI. BREATH
accompanied by an increase in the demand of most organs for oxygen. According to the van't Hoff rule, when the temperature changes by 10 o C in the range from 20 to 40 o C, oxygen consumption by tissues changes in the same direction by 2 3 times (Q 10 = 2-3). For some surgical operations it may be necessary to temporarily stop blood circulation (and, consequently, the supply of organs with O 2 and nutrients). At the same time, in order to reduce the oxygen demand of organs, hypothermia (decrease in body temperature) is often used: the patient is given such deep anesthesia, in which thermoregulatory mechanisms are suppressed.
The circulatory system consists of the heart and blood vessels. Rhythmic contractions of the heart muscle ensure the continuous movement of blood into closed system vessels. Blood, performing a trophic function, transfers nutrients from the small intestine to the cells of the whole organism, it also ensures the transport of oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs, performing the respiratory function.
At the same time, a large number of biologically active substances circulate in the blood. active substances, which regulate and combine the functional activity of body cells. Blood provides temperature equalization various parts body. Respiratory system includes nasal cavity, larynx, trachea, bronchi and lungs. In the process of breathing from atmospheric air through the alveoli of the lungs, oxygen constantly enters the body, and carbon dioxide is released from the body.
Breathing process is a whole complex physiological processes, in the implementation of which not only Breathe-helping machine but also the circulatory system. The trachea in its lower part is divided into two bronchi, each of which, entering the lungs, branches out in a tree-like manner. The final smallest branches of the bronchi (bronchioles) pass into closed alveolar passages, in the walls of which there are a large number of spherical formations - pulmonary vesicles (alveoli). Each alveolus is surrounded by a dense network blood capillaries. The total surface of all pulmonary vesicles is very large, it is 50 times greater than the surface of human skin and is more than 100 m2. The lungs are located in a hermetically sealed cavity chest. They are covered with a thin smooth shell - the pleura, the same shell lines the inside of the chest cavity. The space formed between these two sheets of pleura is called the pleural cavity.
Pressure in pleural cavity always below atmospheric when exhaling by 3-4 mm Hg. Art., when inhaling, by 7-9 mm. The breathing mechanism is carried out reflexively (automatically). At rest, the exchange of air in the lungs occurs as a result of respiratory rhythmic movements of the chest. When lowered into chest cavity pressure into the lungs (quite passively due to the pressure difference), a portion of air is sucked in - an inhalation occurs. Then the chest cavity decreases and the air is pushed out of the lungs - exhalation occurs. The expansion of the chest cavity is carried out as a result of the activity of the respiratory muscles. At rest, when inhaling, the chest cavity expands with a special respiratory muscle, which was discussed earlier - the diaphragm, as well as the external intercostal muscles; with intensive physical work other (skeletal) muscles are included. Exhalation at rest is pronounced passively, with relaxation of the muscles that carried out the inhalation, the chest under the influence of gravity and atmospheric pressure decreases.
With intensive physical work, the abdominal muscles, internal intercostal and other skeletal muscles participate in exhalation. Systematic classes exercise and sports strengthen the respiratory muscles and contribute to an increase in the volume and mobility (excursions) of the chest. The stage of respiration in which oxygen from atmospheric air passes into the blood, and carbon dioxide from the blood into atmospheric air, is called external respiration; the transfer of gases by the blood is the next stage, and, finally, tissue (or internal) respiration is the consumption of oxygen by cells and the release of carbon dioxide by them as a result biochemical reactions associated with the formation of energy to ensure the vital processes of the body.
External (lung) breathing carried out in the alveoli of the lungs. Here, through the semi-permeable walls of the alveoli and capillaries, oxygen passes from the alveolar air that fills the cavities of the alveoli. Molecules of oxygen and carbon dioxide carry out this transition in hundredths of a second. After the transfer of oxygen by the blood to the tissues, tissue (intracellular) respiration takes place. Oxygen passes from the blood into the interstitial fluid and from there to tissue cells, where it is used to ensure metabolic processes. Carbon dioxide, intensively formed in the cells, passes into the interstitial fluid and then into the blood. With the help of blood, it is transported to the lungs, from which it is excreted from the body.
The passage of oxygen and carbon dioxide through the semi-permeable walls of the alveoli, capillaries and erythrocyte membranes. white matter, surrounding gray, consists of processes that connect the nerve cells of the spinal cord; ascending sensitive (efferent), connecting all organs and tissues human body(except for the head) with the brain, descending motor (afferent) pathways from the brain to the motor cells of the spinal cord.
Thus, it is not difficult to imagine that the spinal cord performs reflex and conductor functions for nerve impulses. IN various departments The spinal cord contains motor neurons (motor nerve cells) that innervate the muscles of the upper limbs, back, chest, abdomen, and lower limbs.
IN sacral region located centers of defecation, urination and sexual activity. An important function of motor neurons is to constantly provide the necessary muscle tone, due to which all reflex motor acts are carried out gently and smoothly. The tone of the centers of the spinal cord is regulated by the higher parts of the central nervous system. Spinal cord injury results in various violations associated with failure conductive function. All kinds of injuries and diseases of the spinal cord can lead to a disorder of pain, temperature sensitivity, disruption of the structure of complex arbitrary movements, muscle tone, etc. The brain is a cluster huge amount nerve cells. It consists of the anterior, intermediate, middle and posterior sections.
The structure of the brain incomparably more complex than the structure of any organ of the human body. Let's name some features and vital functions. So, for example, such a formation of the hindbrain as medulla, is the location of the most important reflex centers(respiratory, food, regulating blood circulation, sweating). Therefore, the defeat of this part of the brain causes instant death. We will not talk in detail about the specifics of the structure and functions of the cerebral cortex, however, it should be noted that the cerebral cortex is the youngest part of the brain in phylogenetic terms (phylogenesis is the process of development of plant and animal organisms during the existence of life on Earth).
In the process of evolution, the cerebral cortex acquires significant structural and functional features and becomes the highest department of the central nervous system, which forms the activity of the organism as a whole in its relationship with the environment. Apparently, it will be useful to characterize some more anatomical and physiological features of the human brain.
The human brain weighs an average of 1400 g. The relationship between brain weight and human body weight, according to various authors, is relatively small. Numerous studies have established that the normal activity of the brain is associated with blood supply. As is known, the main source of energy necessary for the functioning of nerve elements is the process of glucose oxidation. However, the brain has no reserves of carbohydrates, much less oxygen, and therefore normal exchange substances in it entirely depends on the constant delivery of energy resources with the blood.
The brain is active not only during wakefulness, but also during sleep. The brain tissue consumes 5 times more oxygen than the heart, and 20 times more than the muscles. Constituting only about 2% of the human body weight, the brain absorbs 18-25% of the oxygen consumed by the entire body. The brain significantly surpasses other organs in the consumption of glucose. They use 60-70% of the glucose formed by the liver, which is 115 g per day, and this despite the fact that the brain is in one of the last places in terms of the amount of blood it contains.
The deterioration of the blood supply to the brain may be associated with hypodynamia ( in a sedentary manner life). With physical inactivity, the most common complaints are headaches of various localization, intensity and duration, dizziness, weakness, decreased mental performance, memory impairment, irritability. The autonomic nervous system is a specialized department of the unified nervous system of the brain, which is regulated, in particular, by the cerebral cortex.
Unlike the somatic nervous system, which innervates the voluntary (skeletal) muscles and provides general sensitivity of the body and other sensory organs, the autonomic nervous system regulates the activity of internal organs - respiration, circulation, excretion, reproduction, glands. internal secretion etc. The autonomic nervous system is divided into sympathetic and parasympathetic systems.
The activity of the heart, blood vessels, digestive organs, excretion, genital, etc.; regulation of metabolism, thermogenesis, participation in the formation of emotional reactions (fear, anger, joy) - all this is under the control of the sympathetic and parasympathetic nervous systems and all under the same control from the higher part of the central nervous system. It has been experimentally shown that their influence, although antagonistic, is coordinated in regulation. essential functions organism. Receptors and analyzers. The main condition for the normal existence of an organism is its ability to quickly adapt to changes. environment. This ability is realized through the presence special education- receptors.
Receptors, having strict specificity, transform external stimuli(sound, temperature, light, pressure, etc.) in nerve impulses, which nerve fibers transmitted to the central nervous system. Human receptors are divided into two main groups: extero (external) and intero (internal) receptors. Each of these receptors is integral part analyzing system, which receives impulses and which is called the analyzer.
The analyzer consists of three sections - the receptor, the conductive part and the central formation in the brain. The highest department of the analyzer is cortical. Without going into details, we list only the names of analyzers, the role of which in the life of any person is known to many. This is a skin analyzer (tactile, pain, thermal, cold sensitivity), motor (receptors in muscles, joints, tendons and ligaments are excited under the influence of pressure and stretching), vestibular (perceives the position of the body in space), visual (light and color), auditory (sound), olfactory (smell), gustatory (taste), visceral (state of a number of internal organs).
