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The act of breathing consists of rhythmically repeated inhalation and exhalation.
Inhalation is carried out as follows. Under the influence of nerve impulses, the muscles involved in the act of inhalation contract: the diaphragm, external intercostal muscles, etc. The diaphragm descends (flattens) during its contraction, which leads to an increase in the vertical size chest cavity. With the contraction of the external intercostal and some other muscles, the ribs rise, while the anteroposterior and transverse dimensions chest cavity. Thus, as a result of muscle contraction, the volume increases chest. Due to the fact that there is no air in the pleural cavity and the pressure in it is negative, simultaneously with an increase in the volume of the chest, the lungs also expand. With the expansion of the lungs, the air pressure inside them decreases (it becomes lower than atmospheric pressure) and atmospheric air rushes along respiratory tract into the lungs. Consequently, when inhaling, the following sequentially occurs: muscle contraction - an increase in the volume of the chest - the expansion of the lungs and a decrease in pressure inside the lungs - the flow of air through airways into the lungs.
Exhalation follows inhalation. The muscles involved in the act of inhalation relax (the diaphragm rises at the same time), the ribs, as a result of contraction of the internal intercostal and other muscles, and due to their heaviness, fall. The volume of the chest decreases, the lungs contract, the pressure in them rises (becomes higher than atmospheric pressure), and air rushes out through the airways.
The percentage composition of exhaled air is different. Oxygen in it remains only about 16%, and the amount of carbon dioxide increases to 4%. The content of water vapor also increases. Only nitrogen and inert gases in the exhaled air remain in the same amount as in the inhaled air.
Gas exchange in the lungs. Saturation of blood with oxygen and release of carbon dioxide by it occur in the pulmonary vesicles. Venous blood flows through their capillaries. It is separated from the air that fills the lungs by the thinnest, gas-permeable walls of capillaries and pulmonary vesicles.
The concentration of carbon dioxide in the venous blood is much higher than in the air entering the bubbles. Due to diffusion, this gas penetrates from the blood into the lung air. Thus the blood always gives carbon dioxide into the air, constantly changing in the lungs.
Oxygen enters the blood also by diffusion. In the inhaled air, its concentration is much higher than in venous blood moving through the capillaries of the lungs. Therefore, oxygen always penetrates into it. But then he enters into a chemical compound with hemoglobin, as a result of which the content of free oxygen in the blood decreases. Then a new portion of oxygen immediately penetrates into the blood, which is also bound by hemoglobin. This process continues for as long as the blood slowly flows through the capillaries of the lungs. Having absorbed a lot of oxygen, it becomes arterial. After passing through the heart, such blood enters the systemic circulation.
Gas exchange in tissues. Moving through the capillaries of the systemic circulation, the blood gives oxygen to tissue cells and is saturated with carbon dioxide.
Free oxygen entering the cells is used for oxidation organic compounds. Therefore, it is much less in the cells than in the arterial blood washing them. The fragile bond between oxygen and hemoglobin is broken. Oxygen diffuses into cells and is immediately used for oxidative processes occurring in them. Slowly flowing through the capillaries penetrating the tissues, the blood, due to diffusion, gives oxygen to the cells. This is how arterial blood is converted into venous blood (Fig. 84).
Oxidation of organic compounds in cells produces carbon dioxide. It diffuses into the blood. A small amount of carbon dioxide enters into an unstable combination with hemoglobin. But most of it combines with some salts dissolved in the blood. Carbon dioxide is carried away by the blood to the right side of the heart, and from there to the lungs.
By alternately inhaling and exhaling, a person ventilates the lungs, maintaining a relatively constant gas composition in the pulmonary vesicles (alveoli). A person breathes atmospheric air with a high oxygen content (20.9%) and low content carbon dioxide (0.03%), and exhales air, in which oxygen is 16.3%, and carbon dioxide is 4% (Table 13).
The composition of alveolar air is significantly different from the composition of atmospheric, inhaled air. It has less oxygen (14.2%).
And, which are part of the air, do not take part in respiration, and their content in the inhaled, exhaled and alveolar air is almost the same.
Table 13
Composition of inhaled, exhaled and alveolar air
Why is there more oxygen in exhaled air than in alveolar air? This is explained by the fact that during exhalation, the air that is in the respiratory organs, in the airways, is mixed with the alveolar air.
Partial pressure and gas pressure
AT lung from alveolarfresh air goes into and carbon dioxide from the blood enters the lungs. The transition of gases from air to liquid and from liquid to air occurs due to the difference in the partial pressure of these gases in air and liquid.
Partialpressure call part total pressure, which accounts for the fraction of this gas in the gas mixture. The higher the percentage of gas in the mixture, the correspondingly higher its partial pressure. Atmospheric air, as you know, is a mixture of gases. This mixture of oxygen gases contains 20.94%, carbon dioxide - 0.03% and nitrogen - 79.03%. Atmospheric air pressure 760 mm Hg. Art. The partial pressure of oxygen in atmospheric air is 20.94% of 760 mm, i.e. 159 mm, nitrogen - 79.03% of 760 mm, i.e. about 600 mm, carbon dioxide in atmospheric air is low - 0.03 % of 760 mm-0.2 mmHg Art.
For gases dissolved in a liquid, the term "voltage" is used, which corresponds to the term "partial pressure" used for free gases. Gas tension is expressed in the same units as pressure (in mmHg). If the partial pressure of the gas in environment higher than the voltage of that gas in the liquid, the gas dissolves in the liquid.
The partial pressure of oxygen in the alveolar air is 100-105 mm Hg. Art., and in the blood flowing to the lungs, the oxygen tension is on average 40 mm Hg. Art., therefore, in the lungs from the alveolar air passes into.
The movement of gases occurs according to the laws of diffusion, according to which a gas propagates from an environment with a high partial pressure to an environment with a lower pressure.
Gas exchange in the lungs
The transition in the lungs of oxygen from the alveolar air to and the entry of carbon dioxide from the blood into the lungs obey the laws described above.
Thanks to the work of I. M. Sechenov, it became possible to study the gas composition of the blood and the conditions of gas exchange in the lungs and tissues.
Gas exchange in the lungs takes place between the alveolar air and blood by diffusion. The alveoli of the lungs are surrounded by a dense network of capillaries. The walls of the alveoli and the walls of the capillariesthin, which contributes to the penetration of gases from the lungs into the blood and vice versa. Gas exchange depends on the surface through which the diffusion of gases is carried out, and the difference in the partial pressure (voltage) of the diffusing gases. Such conditions exist in the lungs. At deep breath alveoli stretch and their surface reaches 100-150 m 2 . The surface of the capillaries in the lungs is also large. There is also a sufficient difference in the partial pressure of the gases of the alveolar air and the tension of these gases in the venous blood (Table 14).
Table 14
The partial pressure of oxygen and carbon dioxide in the inhaled and alveolar air and their tension in the blood (in mm Hg)
From table 14 it follows that the difference between the tension of gases in the venous blood and their partial pressure in the alveolar air is 110-40 = 70 mm Hg for oxygen. Art., and for carbon dioxide 47-40=7 mm Hg. Art.
Empirically, it was possible to establish that with a difference in oxygen tension of 1 mm Hg. Art. in an adult at rest, 25-60 cm 3 of oxygen per minute can enter the bloodstream. Therefore, the oxygen pressure difference of 70 mm Hg. Art. enough to supply the body with oxygen different conditions its activities: physical work, sports exercises, etc.
The rate of diffusion of carbon dioxide from the blood is 25 times greater than that of oxygen, therefore, due to a difference of 7 mm Hg. Art. carbon dioxide is released from the blood.
Carrying gases in the blood
Blood carries oxygen and carbon dioxide. In the blood, as in any liquid, gases can be in two states: physically dissolved and chemically bound. Both oxygen and carbon dioxide dissolve in blood plasma in very small amounts. Most of oxygen and carbon dioxide is transported in a chemically bound form.
The main carrier of oxygen is blood. Each gram of hemoglobin binds 1.34 cm3 of oxygen. has the ability to combine with oxygen, forming oxyhemoglobin. The higher the partial pressure of oxygen, the more oxyhemoglobin is formed. in the alveolar airpartial pressure of oxygen 100-110 mm Hg. Art. Under these conditions, 97% of blood hemoglobin binds to oxygen. In the form of oxyhemoglobin, oxygen is carried by the blood to the tissues. Herethe partial pressure of oxygen is low and oxyhemoglobin - a fragile compound - releases oxygen, which is used by tissues. The binding of oxygen by hemoglobin is also affected by the tension of carbon dioxide. Carbon dioxide reduces the ability of hemoglobin to bind oxygen and promotes the dissociation of oxyhemoglobin. An increase in temperature also reduces the ability of hemoglobin to bind oxygen. It is known that the temperature in the tissues is higher than in the lungs. All these conditions help the dissociation of oxyhemoglobin, as a result of which the blood releases the oxygen released from the chemical compound into the tissue fluid.
The property of hemoglobin to bind oxygen is vitality for the body. Sometimes people die from a lack of oxygen in the body, surrounded by the cleanest air. This can happen to a person who finds himself in conditions reduced pressure(at high altitudes), where the rarefied atmosphere has a very low partial pressure of oxygen. April 15, 1875 Balloon"Zenith", on board of which there were three aeronauts, reached a height of 8000 m. When the balloon landed, only one person survived. The cause of death was a sharp decline partial pressure of oxygen at high altitude. At high altitudes (7-8 km), arterial blood in its gas composition approaches venous blood; all body tissues begin to experience an acute lack of oxygen, which leads to grave consequences. Climbing above 5000 m usually requires the use of special oxygen devices.
With special training, the body can adapt to the reduced oxygen content in the atmospheric air. A trained person deepens
Topic:Respiratory system
Lesson: The structure of the lungs. Gas exchange in the lungs and tissues
The human lungs are a paired cone-shaped organ (see Fig. 1). Outside, they are covered with a pulmonary pleura, the chest cavity is covered with a parietal pleura. Between the 2 layers of the pleura is pleural fluid, which reduces the force of friction during inhalation and exhalation.
Rice. one.
In 1 minute, the lungs pump 100 liters of air.
The bronchi branch, forming bronchioles, at the ends of which there are thin-walled pulmonary vesicles - alveoli (see Fig. 2).
Rice. 2.
The walls of the alveoli and capillaries are single-layer, which facilitates gas exchange. They are made up of epithelium. They secrete surfactant, which prevents the alveoli from sticking together, and substances that kill microorganisms. Waste biologically active substances are digested by phagocytes or excreted in the form of sputum.
Rice. 3.
Oxygen from the air of the alveoli passes into the blood, and carbon dioxide from the blood passes into the alveolar air (see Fig. 3).
This is due to partial pressure, since each gas dissolves in a liquid precisely due to its partial pressure.
If the partial pressure of a gas in the environment is higher than its pressure in the liquid, then the gas will dissolve in the liquid until equilibrium is formed.
The partial pressure of oxygen is 159 mm. rt. Art. in the atmosphere, and in venous blood - 44 mm. rt. Art. This allows oxygen from the atmosphere to pass into the blood.
Blood enters the lungs through the pulmonary arteries and spreads through the capillaries of the alveoli in a thin layer, which promotes gas exchange (see Fig. 4). Oxygen, passing from the alveolar air into the blood, interacts with hemoglobin to form oxyhemoglobin. In this form, oxygen is carried by the blood from the lungs to the tissues. There, the partial pressure is low, and oxyhemoglobin dissociates, releasing oxygen.
Rice. four.
The mechanisms of carbon dioxide release are similar to the mechanisms of oxygen intake. Carbon dioxide forms an unstable compound with hemoglobin - carbohemoglobin, which dissociates in the lungs.
Rice. 5.
Carbon monoxide forms a stable compound with hemoglobin, which does not dissociate. And such hemoglobin can no longer perform its function - to carry oxygen throughout the body. As a result, a person can die from suffocation even with normal operation lungs. Therefore, it is dangerous to be in a closed, unventilated room in which a car is running or a stove is heated.
Additional Information
A lot of people breathe frequently (more than 16 times per minute), while making shallow respiratory movements. As a result of such breathing, air enters only the upper parts of the lungs, and air stagnation occurs in the lower parts. In such an environment, intensive reproduction of bacteria and viruses occurs.
To independently check the correctness of breathing, you will need a stopwatch. It will be necessary to determine how much respiratory movements man does in a minute. In this case, it is necessary to monitor the process of inhalation and inhalation.
If muscles tense when breathing abdominals, this is an abdominal type of breathing. If the volume of the chest changes, it chest type breathing. If both of these mechanisms are used, then the person mixed type breathing.
If a person takes up to 14 breaths per minute, this is excellent result. If a person makes 15 - 18 movements - this is a good result. And if more than 18 movements - this is a bad result.
Bibliography
1. Kolesov D.V., Mash R.D., Belyaev I.N. Biology. 8. - M.: Bustard.
2. Pasechnik V.V., Kamensky A.A., Shvetsov G.G. / Ed. Pasechnik V.V. Biology. 8. - M.: Bustard.
3. Dragomilov A.G., Mash R.D. Biology. 8. - M.: Ventana-Count.
Homework
1. Kolesov D.V., Mash R.D., Belyaev I.N. Biology. 8. - M.: Bustard. - S. 141, assignments and question 1, 3, 4.
2. What role does partial pressure play in gas exchange?
3. What is the structure of the lungs?
4. Prepare a short message in which explain why nitrogen, carbon dioxide and other air components do not enter the blood during inhalation.
The blood that flows to the lungs from the heart (venous) contains little oxygen and a lot of carbon dioxide; the air in the alveoli, on the contrary, contains a lot of oxygen and less carbon dioxide. As a result, two-way diffusion occurs through the walls of the alveoli and capillaries. oxygen passes into the blood, and carbon dioxide moves from the blood to the alveoli. In the blood, oxygen enters the red blood cells and combines with hemoglobin. Oxygenated blood becomes arterial and enters the left atrium through the pulmonary veins.
In humans, the exchange of gases is completed in a few seconds, while the blood passes through the alveoli of the lungs. This is possible due to the huge surface of the lungs, communicating with external environment. General surface alveoli is over 90 m 3.
The exchange of gases in tissues is carried out in capillaries. Through their thin walls, oxygen enters from the blood into the tissue fluid and then into the cells, and carbon dioxide from the tissues passes into the blood. The concentration of oxygen in the blood is greater than in the cells, so it easily diffuses into them.
The concentration of carbon dioxide in the tissues where it is collected is higher than in the blood. Therefore, it passes into the blood, where it binds chemical compounds plasma and partly with hemoglobin, is transported by the blood to the lungs and released into the atmosphere.
To provide cells, tissues and organs with oxygen in the human body, there is respiratory system. It consists of the following organs: nasal cavity, nasopharynx, larynx, trachea, bronchi and lungs. In this article we will study their structure. And also consider gas exchange in tissues and lungs. Let's define the features external respiration, occurring between the organism and the atmosphere, and internal, flowing directly at the cellular level.
What are we breathing for?
Most people will answer without hesitation: to get oxygen. But they don't know why we need it. Many answer simply: oxygen is needed to breathe. It turns out some vicious circle. Biochemistry, which studies cellular metabolism, will help us break it.
The bright minds of mankind, studying this science, have long come to the conclusion that oxygen entering tissues and organs oxidizes carbohydrates, fats and proteins. In this case, energy-poor compounds are formed: water, ammonia. But the main thing is that as a result of these reactions, ATP is synthesized - a universal energy substance used by the cell for its life. It can be said that gas exchange in the tissues and lungs will supply the body and its structures with the oxygen necessary for oxidation.
Mechanism of gas exchange
It implies the presence of at least two substances whose circulation in the body provides metabolic processes. In addition to the above oxygen, gas exchange in the lungs, blood and tissues occurs with another compound - carbon dioxide. It is formed in dissimilation reactions. Being a toxic substance of metabolism, it must be removed from the cytoplasm of cells. Let's consider this process in more detail.
Carbon dioxide diffuses through the cell membrane into the interstitial fluid. From it, he enters the blood capillaries - venules. Further, these vessels merge, forming the inferior and superior vena cava. They collect blood saturated with CO 2. And send it to the right atrium. With the reduction of its walls, a portion of venous blood enters the right ventricle. From here begins the pulmonary (small) circle of blood circulation. Its task is to saturate the blood with oxygen. Venous in the lungs becomes arterial. And CO 2, in turn, leaves the blood and is removed through. To understand how this happens, you must first study the structure of the lungs. Gas exchange in the lungs and tissues is carried out in special structures - the alveoli and their capillaries.
The structure of the lungs
These are paired organs located in the chest cavity. The left lung has two lobes. The right one is larger. It has three parts. Through the gates of the lungs, two bronchi enter into them, which, branching, form the so-called tree. Air moves along its branches during inhalation and exhalation. On small, respiratory bronchioles are vesicles - alveoli. They are collected in acini. Those, in turn, form the lung parenchyma. It is important that each respiratory vesicle is densely braided with a capillary network of small and large circles of blood circulation. Bearing branches pulmonary arteries supplying venous blood from the right ventricle, carbon dioxide is transported into the lumen of the alveolus. And the efferent pulmonary venules take oxygen from the alveolar air.
It enters through the pulmonary veins into the left atrium, and from it into the aorta. Its branches in the form of arteries provide the cells of the body with the oxygen necessary for internal respiration. It is in the alveoli that the blood from the venous becomes arterial. Thus, gas exchange in tissues and lungs is directly carried out by blood circulation through the small and big circles circulation. This happens due to continuous contractions of the muscular walls of the heart chambers.
external respiration
It is also called ventilation. Represents the exchange of air between the external environment and the alveoli. A physiologically correct breath through the nose provides the body with a portion of air of this composition: about 21% O 2, 0.03% CO 2 and 79% nitrogen. It enters the alveoli. They have their own portion of air. Its composition is as follows: 14.2% O 2, 5.2% CO 2, 80% N 2. Inhalation, like exhalation, is regulated in two ways: nervous and humoral (carbon dioxide concentration). By stimulating the respiratory center medulla oblongata, nerve impulses are transmitted to the respiratory intercostal muscles and the diaphragm. The volume of the chest increases. The lungs, passively moving following the contractions of the chest cavity, expand. The air pressure in them becomes lower than atmospheric pressure. Therefore, a portion of the air from the upper respiratory tract enters the alveoli.
Exhalation follows inhalation. It is accompanied by relaxation of the intercostal muscles and elevation of the arch of the diaphragm. This leads to a decrease in lung volume. The air pressure in them becomes higher than atmospheric pressure. And air with an excess of carbon dioxide rises into the bronchioles. Further, along the upper respiratory tract, it follows in nasal cavity. The composition of the exhaled air is as follows: 16.3% O 2 , 4% CO 2 , 79 N 2 . At this stage, external gas exchange occurs. Pulmonary gas exchange, carried out by the alveoli, provides the cells with oxygen necessary for internal respiration.
Cellular respiration
Included in the system of catabolic reactions of metabolism and energy. These processes are studied both by biochemistry and anatomy, and gas exchange in the lungs and tissues is interconnected and is impossible without each other. So, it supplies oxygen to the interstitial fluid and removes carbon dioxide from it. And the internal, carried out directly in the cell by its organelles - mitochondria, which provide oxidative phosphorylation and the synthesis of ATP molecules, uses oxygen for these processes.
Krebs cycle
cycle three carboxylic acids is leading in It combines and coordinates the reactions of the oxygen-free stage and processes involving transmembrane proteins. It also acts as a supplier of building cellular material (amino acids, simple sugars, higher carboxylic acids), formed in its intermediate reactions and used by the cell for growth and division. As you can see, in this article, gas exchange in tissues and lungs was studied, and its biological role in the life of the human body.
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