The structure of the lungs. Gas exchange in the lungs and tissues. Lungs - how do they work? Gas exchange in the lungs and tissues occurs due to

Instructions

IN pulmonary breathing The intercostal muscles and the diaphragm are involved - a flat muscle located on the border of the abdominal and thoracic cavities. When the diaphragm contracts, the pressure in the lungs decreases, causing air to rush into them. Exhalation is done passively: the lungs independently push the air out. The breathing process is controlled by a part of the brain - the medulla oblongata. It houses the respiratory control center, which responds to the presence of carbon dioxide in the blood. As soon as its level rises, the center sends a signal to the diaphragm along the nerve pathways, it contracts, and inhalation occurs. In case of damage to the respiratory center, artificial ventilation is used.

The process of gas exchange takes place in the alveoli of the lungs - microscopic bubbles located at the ends of the bronchioles. They consist of squamous (respiratory) alveocytes, large alveocytes and chemoreceptors. The main role in this case belongs to the circulatory system. Oxygen entering the alveoli of the lungs penetrates the walls of the capillaries. A similar process occurs due to the difference in the blood and air in the alveoli. The blood in the veins has less pressure, so oxygen rushes from the alveoli into the capillaries. Carbon dioxide in the alveoli has lower pressure, so venous blood it enters the lumen of the alveoli.

The blood contains red blood cells containing the protein hemoglobin. Oxygen molecules attach to hemoglobin. Oxygenated blood is called arterial blood and is transported to the heart. The heart drives it to tissue cells. In cells, blood gives out oxygen and takes away in return carbon dioxide, which is also carried by hemoglobin. Then it happens reverse process: Blood flows from tissue capillaries to the veins, heart and lungs. In the lungs, venous blood with carbon dioxide enters the alveoli, and carbon dioxide, along with air, is pushed out. Double gas exchange occurs in the alveoli with lightning speed.

The vital capacity of the lungs includes the tidal volume, as well as the inspiratory and expiratory reserve volumes. Tidal volume is the amount of air entering the lungs during 1 breath. If, after a calm inhalation, you take a strong inhalation, an additional amount of air will enter the lungs, which is called the inspiratory volume reserve. After a calm exhalation, you can exhale some more air (expiratory reserve volume). In general, the vital capacity of the lungs is greatest number air that a person can exhale after taking a deep breath.

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Lungs are the most voluminous organ of our body. The structure and mechanism of the lungs are quite interesting. Each inhalation fills our body with oxygen, and exhalation removes carbon dioxide and some toxic substances from the body. We breathe constantly - both in sleep and while awake. The process of inhalation and exhalation is quite complex actions that are carried out by several systems and organs with simultaneous interaction.

Some surprising facts about the lungs

Did you know that the lungs contain 700 million alveoli ( saccular endings in which gas exchange occurs)?
An interesting fact is that the area inner surface alveoli change more than 3 times - when inhaling more than 120 square meters, versus 40 square meters when exhaling.
The area of ​​the alveoli is more than 50 times greater than the area of ​​the skin.

Lung anatomy

Conventionally, the lung can be divided into 3 sections:
1. Air section ( bronchial tree) - through which air, like a system of channels, reaches the alveoli.
2. The section in which gas exchange occurs is the alveolar system.
3. The circulatory system of the lung deserves special attention.

For a more detailed study of the structure of the lung, we will consider each of the presented systems separately.

Bronchial tree - like an air system

It is represented by the branches of the bronchi, visually resembling corrugated tubes. As the bronchial tree branches, the lumen of the bronchi narrows, but they become more and more numerous. The terminal branches of the bronchi, called bronchioles, have a lumen of less than 1 millimeter in size, but their number is several thousand.

Structure of the bronchial wall

The wall of the bronchi consists of 3 layers:
1. Inner layer – slimy. Lined with columnar ciliated epithelium. A feature of this mucous layer is the presence of ciliated bristles on the surface, which create unidirectional movement of mucus on the surface and contribute to the mechanical removal of dust particles or other microscopic particles into external environment. The mucosal surface is always moisturized and contains antibodies and immune cells.

2. Middle shell – musculocartilaginous. This shell acts as a mechanical frame. Cartilaginous rings create the appearance of a corrugated hose. Cartilage tissue bronchi prevents the lumen of the bronchi from collapsing due to changes in air pressure in the lungs. Also, cartilaginous rings connected by flexible connective tissue provide mobility and flexibility of the bronchial tree. As the caliber of the bronchi decreases, the muscular component begins to predominate in the middle layer. Using a smooth muscle tissue The lungs have the opportunity to regulate air flow, limit the spread of infection and foreign bodies.

3. Outer shell – adventitia. This membrane provides a mechanical connection between the bronchial tree and surrounding organs and tissues. Consists of collagen connective tissue.

The branching of the bronchi is very reminiscent of the appearance of an overturned tree. Hence the name - bronchial tree. The beginning of the airways of the bronchial tree can be called the lumen of the trachea. The trachea in its lower part bifurcates into two main bronchi, which direct air flows each to its own lung ( right and left). Inside the lung, branching continues to the lobar bronchi ( 3 in the left lung and 2 in the right), segmental, etc. The airway system of the bronchial tree ends in terminal bronchioles, which give rise to the respiratory part of the lung ( gas exchange occurs between the blood and the air in the lungs).

Respiratory part of the lung

Branching aerial lung systems reaches the level of bronchioles. Each bronchiole, the diameter of which does not exceed 1 mm, gives rise to 13 - 16 respiratory bronchioles, which in turn give rise to respiratory passages ending in alveoli ( grape-shaped sacs), in which the main gas exchange occurs.

The structure of the pulmonary alveoli

The pulmonary alveolus looks like a bunch of grapes. Consists of the respiratory bronchioles, respiratory passages and air sacs. The inner surface of the alveoli is lined with single-layer squamous epithelium, closely connected with the endothelium of the capillaries, enveloping the alveoli like a network. It is precisely due to the fact that the lumen of the alveoli is separated from the lumen of the capillary by a very thin layer that active gas exchange is possible between the pulmonary and circulatory systems.

The inner surface of the alveoli is covered with a special organic substance - surfactant.
This substance contains organic components that prevent the alveoli from collapsing during exhalation; it contains antibodies and immune cells that provide protective functions. The surfactant also prevents blood from penetrating into the lumen of the alveoli.

Location of the lung in the chest

The lung is mechanically fixed to the surrounding tissues only at the junction with the main bronchi. The rest of its surface has no mechanical connection with the surrounding organs.

How then does the lung expand during breathing?

The fact is that the lung is located in a special cavity chest called pleural. This cavity is lined with a single layer of mucous tissue - pleura. The same fabric lines the outer surface lung These mucous membranes come into contact with each other, maintaining the possibility of sliding. Thanks to the secreted lubricant, gliding is possible when inhaling and exhaling outer surface lung along the inner surface of the chest and diaphragm.

Muscles involved in the act of breathing

In fact, inhalation and exhalation is a rather complex and multi-level process. To consider it, it is necessary to become familiar with the musculoskeletal system involved in the process of external respiration.

Muscles involved in external respiration
Diaphragm - This is a flat muscle, stretched like a trampoline along the edge of the costal arch. The diaphragm separates the thoracic cavity from the abdominal cavity. The main function of the diaphragm is active breathing.
Intercostal muscles – are represented by several layers of muscles, through which the upper and lower edges of adjacent ribs are connected. As a rule, these muscles are involved in deep breath and long exhalation.

Mechanics of breathing

When inhaling, a number of simultaneous movements occur, which lead to the active injection of air into the airways.
As the diaphragm contracts, it flattens. IN pleural cavity negative pressure is created due to the vacuum. Negative pressure in the pleural cavity is transmitted to the tissues of the lung, which obediently expands, creating negative pressure in the respiratory and airways. As a result, atmospheric air rushes into the area low blood pressure- into the lungs. Having passed through the airways, fresh air mixes with the residual portion of lung air ( air remaining in the lumen of the alveoli and respiratory tract after exhalation). As a result, the concentration of oxygen in the air of the alveoli increases, and the concentration of carbon dioxide decreases.

When you inhale deeply, a certain part of the oblique intercostal muscles relaxes and a perpendicular portion of the muscles contracts, which increases the intercostal distances, increasing the volume of the chest. Therefore, it becomes possible to increase the volume of inhaled air by 20 - 30%.

Exhalation is mostly a passive process. A calm exhalation does not require tension of any muscles - only relaxation of the diaphragm is required. The lung, due to its elasticity and elasticity, itself displaces the bulk of the air. Only with forced exhalation can the abdominal muscles and intercostal muscles tense. For example, when sneezing or coughing, the abdominal muscles contract, increasing intra-abdominal pressure, which is transmitted through the diaphragm to the lung tissue. Specific part intercostal muscles, when contracted, lead to a decrease in the intercostal spaces, which reduces the volume of the chest, leading to increased exhalation.

Circulatory system of the lung

The pulmonary vessels originate from the right ventricle of the heart, from which blood enters the pulmonary trunk. It distributes blood to the right and left pulmonary arteries of the respective lungs. IN lung tissue Vessels branch parallel to the bronchi. Moreover, arteries and veins run parallel to the bronchus in close proximity. At the level of the respiratory part of the lung, arterioles branch into capillaries, which envelop the alveoli with a dense vascular network. Active gas exchange occurs in this network. As a result of the passage of blood at the level of the respiratory part of the lung, red blood cells are enriched with oxygen. Leaving the alveolar structures, the blood continues its movement, but towards the heart - to its left sections.

How does gas exchange occur in the lungs?

The portion of air received during inhalation changes the gas composition of the alveolar cavity. Oxygen levels increase, carbon dioxide levels decrease.
The alveoli are shrouded in a fairly dense network the smallest vessels– capillaries, which, passing red blood cells through them at a slow speed, promote active gas exchange. Red blood cells loaded with hemoglobin, passing through the capillary network of the alveoli, add oxygen to the hemoglobin.

At the same time, carbon dioxide is removed from the blood - it leaves the blood and passes into the cavity of the airways. You can find out more about how the process of gas exchange in red blood cells occurs at the molecular level in the article: “Red blood cells - how do they work? "
Through the lungs, during breathing, continuous gas exchange occurs between atmospheric air and blood. The task of the lungs is to provide the body with the necessary amount of oxygen, simultaneously removing what is formed in the tissues of the body and transported to lungs with blood carbon dioxide.

How is the breathing process controlled?

Breathing is a semi-automatic process. We are able to hold our breath for a certain time or speed up our breathing voluntarily. However, during the day, the frequency and depth of breathing is determined mainly automatically by the central nervous system. At the level of the medulla oblongata there are special centers that regulate the frequency and depth of breathing depending on the concentration of carbon dioxide in the blood. This center in the brain is connected to the diaphragm through nerve trunks and ensures its rhythmic contraction during the act of breathing. If the breathing control center or the nerves connecting this center with the diaphragm are damaged, maintaining external respiration is possible only with the help of artificial ventilation lungs.

In fact, the lungs have much more functions: maintaining the acid-base balance of the blood (maintaining the pH of the blood within 7.35-7.47), immune defense, purification of blood from microthrombi, regulation of blood coagulation, removal of toxic volatile substances. However, the purpose of this article was to highlight respiratory function lung, the basic mechanisms leading to external respiration.

Subject:Respiratory system

Lesson: Structure of the lungs. Gas exchange in the lungs and tissues

The human lungs are a paired cone-shaped organ (see Fig. 1). On the outside they are covered with pulmonary pleura, the chest cavity is covered with parietal pleura. Between the 2 layers of the pleura there is pleural fluid, which reduces the friction force during inhalation and exhalation.

Rice. 1.

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-layered, which facilitates gas exchange. They are formed by epithelium. They secrete surfactant, which prevents alveoli from sticking together, and substances that kill microorganisms. Spent biologically active substances are digested by phagocytes or excreted in the form of sputum.

Rice. 3.

Oxygen from the alveolar air passes into the blood, and carbon dioxide from the blood passes into the alveolar air (see Fig. 3).

This occurs due to partial pressure, since each gas dissolves in a liquid precisely due to its partial pressure.

If the partial pressure of gas in environment higher than its pressure in the liquid, 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. 4.

The mechanisms of carbon dioxide release are similar to the mechanisms of oxygen intake. Carbon dioxide forms an unstable compound with hemoglobin - carbohemoglobin, the dissociation of which occurs in the lungs.

Rice. 5.

Carbon monoxide forms a stable compound with hemoglobin, the dissociation of which does not occur. And such hemoglobin can no longer perform its function - to carry oxygen throughout the body. As a result, a person may 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 burning.

Additional information

A lot of people breathe quickly (more than 16 times per minute), while making shallow breathing movements. As a result of such breathing, air enters only the upper parts of the lungs, and lower parts air stagnation occurs. In such an environment, intensive reproduction of bacteria and viruses occurs.

For self-check To ensure proper breathing, you will need a stopwatch. It will be necessary to determine how much breathing movements a person does in a minute. In this case, it is necessary to monitor the process of inhalation and inhalation.

If the abdominal muscles tense when breathing, this is abdominal breathing. If the volume of the chest changes, this breast type breathing. If both of these mechanisms are used, then in humans mixed type breathing.

If a person makes up to 14 breathing movements per minute, this is an excellent result. If a person makes 15 - 18 movements, this is good result. And if there are more than 18 movements, this is a bad result.

References

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-Graf.

Homework

1. Kolesov D.V., Mash R.D., Belyaev I.N. Biology. 8. - M.: Bustard. - P. 141, tasks 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 you explain why nitrogen, carbon dioxide and other air components do not enter the blood when inhaled.

Oxygen passes from the alveoli into the blood of the pulmonary capillaries, and carbon dioxide - in the opposite direction due to a simple physical process diffusion; each of these gases moves from an area of ​​higher concentration to an area of ​​lower concentration. The extremely thin alveolar epithelium does not provide significant resistance to the diffusion of gases, and since the concentration of oxygen in the alveoli is usually higher than in the blood, flowing to the lungs through pulmonary artery oxygen diffuses from the alveoli into the capillaries. On the contrary, the concentration of carbon dioxide in the blood of the pulmonary artery in normal conditions higher than in the pulmonary alveoli, and therefore carbon dioxide diffuses from the pulmonary capillaries into the alveoli. Unlike the cells lining the intestine, which can absorb a particular substance from the intestinal lumen and transfer it to the blood, where its concentration may be higher, the alveolar epithelium is not able to transport oxygen and carbon dioxide against a concentration gradient.

Since the cells of the alveoli cannot force oxygen to pass into the blood, when its concentration in the alveoli falls below a certain level, the blood passing through the lungs in this case cannot receive enough oxygen for the body and symptoms of “altitude sickness” appear - nausea, headache and hallucinations. Altitude sickness begins to occur at an altitude of about 4500 m, and in some people at lower altitudes. Human body can adapt to life at high altitudes by increasing the number of red blood cells in the blood; however, humans cannot live significantly above 6000 m without an additional source of oxygen. At an altitude of approximately 11 km, the pressure is so low that even when breathing pure oxygen a person cannot satisfy his need for this gas. Therefore, aircraft flying at such altitudes must be pressurized, and they must be equipped with pumps to maintain air pressure in the cabin equal to the pressure at sea level, i.e. 760 mm Hg. Art.

In the tissues of the entire body, where internal respiration occurs, oxygen passes from capillaries to cells, and carbon dioxide from cells to capillaries by diffusion. Due to the continuous breakdown of glucose and other substances in cells, carbon dioxide is constantly formed and oxygen is used. Therefore, the oxygen concentration in the cells is always lower, and the carbon dioxide concentration is higher than in the capillaries.

Throughout its journey from the lungs through the blood to the tissues, oxygen moves from an area of ​​higher concentration to an area of ​​lower concentration and is finally used by the cells; Carbon dioxide moves from the cells where it is formed, through the blood to the lungs and then outward - always towards an area of ​​lower concentration.

The carbon dioxide tension in the venous blood flowing to the lungs is higher, and the oxygen tension is lower, than their pressure in the alveolar air. Therefore, as blood flows through the capillaries of the lungs, it gives off carbon dioxide and absorbs oxygen. The exchange of gases between the blood and alveolar air is facilitated by the huge number of alveoli, reaching 750 million in humans, and their large surface, amounting to 100 m2 on inhalation and 30 m2 on exhalation. The membrane separating the blood from the alveolar air is only 0.004 mm thick and consists of two layers of cells - capillary endothelial cells and alveolar epithelial cells, which freely allow gases to pass through.

Gas exchange in the lungs occurs as a result of the diffusion of carbon dioxide from the blood into the alveolar air and oxygen from the alveolar air into the blood. Diffusion of gases occurs due to the difference between the partial pressure of these gases in the alveolar air and their tension in the blood. Evidence of this was obtained by measuring the partial pressure of oxygen and carbon dioxide in the alveolar air and the tension of these gases in the venous and arterial blood.

To determine the voltage of gases in the blood, a Krogh microtonometer is used ( rice. 59), which is a modification of the device proposed by K. A. Timiryazev. The microtonometer is connected between the central and peripheral ends of a blood vessel—an artery or vein. Blood from the blood vessel flows through tube A into the microtonometer ampoule B, where there is a small air bubble, and from there through tube C back to blood vessel (rice. 59). Since the volume of an air bubble is negligible compared to the mass of flowing blood, to establish gas equilibrium between an air bubble and blood requires the transfer of such a small amount of gases into the bubble that their tension in the blood does not change. The bubble is drawn from time to time by piston D into capillary E, where its volume is measured. After dynamic equilibrium of gases is established, the volume of the bubble becomes constant, it is removed and the gas content in it is determined. Partial pressures of gases are calculated from their percentages. Since the gases in the air bubble were in equilibrium with the blood gases, it is clear that by draining the gas content in the bubble, one can thereby measure the voltage in the blood. Rice. 59. Krogh microtonometer (explanations in the text).

It has been established that the oxygen tension in arterial blood is 100 mmHg. Art., and carbon dioxide - 40 mm; in venous blood, the oxygen tension is 40 mmHg, and the carbon dioxide tension is 46 mmHg. Art.

From these figures it follows that the difference between the tension of gases in the venous blood and their pressure in the alveolar air is approximately 110-40 = 70 mm Hg for oxygen, and 46-40 = 6 mm Hg for carbon dioxide. Art.

For short time When blood stays in the pulmonary capillaries, the tension of gases in the blood is almost equal to their partial pressure in the alveolar air. This is evident from the fact that the carbon dioxide tension in arterial blood is almost the same as in the alveolar air, and the oxygen tension is 2-10 mm lower.

It has been experimentally established that with a voltage difference of only 1 mm Hg. Art. in a healthy adult at rest, 25-60 ml of oxygen per minute can enter the blood. Because average value Oxygen consumption in humans at rest is approximately 250-300 ml per minute, therefore, a pressure difference of 70 mm is more than sufficient to ensure that the required amount of oxygen enters the blood. With such a difference in oxygen pressure in the alveolar air and the tension of this gas in the venous blood, a significant increase in the flow of oxygen into the blood can be ensured, which is necessary, for example, when physical work or sports exercises, when the minute volume of blood ejected by the heart increases significantly and the flow of blood through the lungs accelerates.

Since the rate of diffusion of carbon dioxide from the blood is 25 times greater than that of oxygen, carbon dioxide also has time to be released from the blood in the required quantities due to the existing difference between the CO2 tension in the venous blood and its pressure in the alveolar air.

. Holden noticed that the ventilation of different parts of the lungs is not the same. It is known that the outer zone of the lung tissue is most extensible, extending 25-30 mm deep into the lung; The intermediate zone is less extensible - the lung tissue, covering the branches of the bronchi and blood vessels. The least extensible is the internal zone, located in the root of the lung, among the large bronchi, vessels and connective tissue. In a person at rest, the most extensible outer zone of the lung tissue primarily participates in the act of breathing.