Gas exchange is carried out using diffusion: CO2 is released from the blood into the alveoli, 02 comes from the alveoli into the venous blood that has come to the pulmonary capillaries from all organs and tissues of the body. In this case, venous blood, rich in CO2 and poor in O2, turns into arterial blood, saturated in O2 and depleted in CO2. Gas exchange between the alveoli and the blood is continuous, but during systole it is more than during diastole.

A. Driving force, providing gas exchange in the alveoli is the difference between the partial pressures of Po 2 and Pco 2 in the alveolar mixture of gases and the voltages of these gases in the blood. Partial pressure of a gas (parIans - partial) is the part of the total pressure of the gas mixture attributable to a given gas. The voltage of a gas in a liquid depends only on the partial pressure of the gas above the liquid, and they are equal to each other.

Po 2 and Pso, in the alveoli and capillaries are equalized.

In addition to the partial pressure-stress gradient, which ensures gas exchange in the lungs, there are a number of other auxiliary factors that play an important role in gas exchange.

B. Factors contributing to the diffusion of gases intolungs.

1. Huge contact surfacepulmonary capillaries and alveoli (60-120m 2). Alveoli are vesicles with a diameter of 0.3-0.4 mm, formed by epithelial cells. Moreover, each capillary contacts 5-7 alveoli.

2. High gas diffusion ratethrough a thin pulmonary membrane of about 1 micron. Alignment of Po 2 in the alveoli and blood in the lungs occurs in 0.25 s; the blood is in the capillaries of the lungs for about 0.5 s, i.e. 2 times more. The diffusion rate of C0 2 is 23 times higher than that of 0 2; there is a high degree of reliability in the processes of gas exchange in the body.

3. Intensive lung ventilation and blood circulation -activation of ventilation of the lungs and blood circulation in them, naturally, promotes the diffusion of gases in the lungs.

4. Correlation between blood flowin this area of \u200b\u200bthe lung and its ventilation. If a portion of the lung is poorly ventilated, then the blood vessels in this area narrow and even completely close. This is carried out using the mechanisms of local self-regulation - through the reactions of smooth muscles: with a decrease in Po 2 in the alveoli, vasoconstriction occurs.

IN. Change in the content of 0 2 and CO 2 in the lungs. Gas exchange in the lung naturally leads to a change in the gas composition in the lung in comparison with the composition of atmospheric air. At rest, a person consumes about 250 ml of O 2 and releases about 230 ml of CO 2. Therefore, in the alveolar air the amount of 0 2 decreases and the amount of CO2 increases (Table 7.2).

Changes in the content of 0 2 and C0 2 in the alveolar mixture of gases are a consequence of the body's consumption of 02 and the release of C0 2. In the exhaled air, the amount of 0 2 increases somewhat, and the C0 2 decreases in comparison with the alveolar gas mixture due to the fact that air of the airway is added to it, which does not participate in gas exchange and, naturally, contains C0 2 and 0 2 in the same quantities, as well as atmospheric air. The blood, enriched with 0 2 and having given off C0 2, from the lungs enters the heart and, with the help of arteries and capillaries, is distributed throughout the body, in various organs and tissues it gives 0 2 and receives C0 2.

TRANSPORTATION OF BLOOD GASES

The gases in the blood are in the form of physical dissolution and chemical bonding.The amount of physically dissolved in the blood 0 2 \u003d 0.3 vol%; C0 2 \u003d 4.5 vol%; 1 \\ [2 \u003d 1 vol%. The total content of O 2 and CO 2 in the blood is many times greater than that of their physically dissolved phases (see Table 7.3). Comparing the amount of dissolved gases in the blood with their total content, we see that O 2 and CO 2 in the blood are mainly in the form of chemical compounds, with the help of which they are transferred.

Oxygen transport

Almost all of 0 2 (about 20 vol% - 20 ml of 0 2 per 100 ml of blood) is transferred by the blood in the form of a chemical compound with hemoglobin. Only 0.3% by volume is transported in the form of physical dissolution. However, this phase is very important, since 0 2 from the capillaries to the tissues and 0 2 from the alveoli into the blood and erythrocytes passes through the blood plasma in the form of a physically dissolved gas.

A. Properties of hemoglobin and its compounds. This red blood pigment, contained in erythrocytes as a carrier of 0 2, has the remarkable property of attaching 0 2 when the blood is in the lung, and giving 0 2 when the blood passes through the capillaries of all organs and tissues of the body. Hemoglobin is a chromoprotein, its molecular weight is 64,500, it consists of four identical groups - hemes. Heme is a protoporphyrin, in the center of which there is an ion of ferrous iron, which plays a key role in the transfer of 0 2. Oxygen forms a reversible bond with heme, and the valence of iron does not change. In this case, reduced hemoglobin (Hb) becomes oxidized Hb0 2, more precisely, Hb (0 2) 4 Each heme attaches one molecule of oxygen, therefore one hemoglobin molecule binds four molecules of 0 2. The hemoglobin content in the blood of men is 130-160 g / l, in women 120-140 g / l. The amount of 0 2, which can be associated in 100 ml of blood, in men is about 20 ml (20 vol%) - blood oxygen capacity, in women it is 1-2% less by volume, since they have less Hb. After the destruction of old erythrocytes in the norm and as a result of pathological processes, the respiratory function of hemoglobin also ceases, since it is partially "lost" through the kidneys, partially phagocytized by the cells of the mononuclear phagocytic system.

Heme can undergo not only oxygenation, but also true oxidation.In this case, iron is converted from bivalent to trivalent. The oxidized heme is called hematin (metheme), and the entire polypeptide molecule as a whole is called methemoglobin. Normally, human blood contains insignificant amounts of methemoglobin, but in case of poisoning with some poisons, with the action of certain drugs, for example, codeine, phenacetin, its content increases. The danger of such conditions lies in the fact that oxidized hemoglobin dissociates very weakly (does not give 0 2 to tissues) and, naturally, cannot add additional molecules of 0 2, that is, it loses its oxygen carrier properties. The compound of hemoglobin with carbon monoxide (CO) - carboxyhemoglobin is also dangerous, since the affinity

Hemoglobin to CO is 300 times more than to oxygen, and HbCO dissociates 10,000 times more slowly than HbO2. Even at extremely low partial pressures of carbon monoxide, hemoglobin is converted into carboxyhemoglobin: Hb + CO \u003d HbCO. Normally, HbCO accounts for only 1% of the total amount of hemoglobin in the blood, in smokers it is much more: by the evening it reaches 20%. If the air contains 0.1% CO, then about 80% of hemoglobin is converted into carboxyhemoglobin and is turned off from transport 0 2. The danger of the formation of large amounts of HbCO lurks passengers on highways. There are many known fatalities when a car engine is turned on in a garage in cold weather for the purpose of heating. First aid to the victim consists in the immediate termination of his contact with carbon monoxide.

B. Oxyhemoglobin formation occurs in the capillaries of the lungs very quickly. The half-saturation time of hemoglobin with oxygen is only 0.01 s (the duration of the stay of blood in the capillaries of the lungs is on average 0.5 s). The main factor providing the formation of oxyhemoglobin is a high partial pressure of 0 2 in the alveoli (100 mm Hg).

The gentle character of the curve for the formation and dissociation of oxyhemoglobin in its upper part indicates that in the case of a significant drop in Po 2 in the air, the content of O 2 in the blood will remain high enough (Fig. 7.6). So, even with a drop in Po 2 in arterial blood to 60 mm Hg. (8.0 kPa) oxygen saturation of hemoglobin is 90% - this is a very important biological fact: the body will still be provided with 0 2 (for example, when climbing mountains, flying at low altitudes - up to 3 km), i.e. there is a high the reliability of the mechanisms for providing the body with oxygen.

The process of saturation of hemoglobin with oxygen in the lungs reflects the upper part of the curve from 75% to 96-98%. In the venous blood flowing into the capillaries of the lungs, Po 2 is 40 mm Hg. and reaches 100 mm Hg in arterial blood, like Po 2 in the alveoli. There are a number of auxiliary factors that contribute to blood oxygenation: 1) elimination of CO2 from carbhemoglobin and its removal (Verigo effect); 2) lowering the temperature in the lungs; 3) an increase in blood pH (Bohr effect). It should also be noted that with age, the binding of 0 2 hemoglobin worsens.

IN. Dissociation of oxyhemoglobin occurs in the capillaries when blood from the lungs reaches the tissues of the body. In this case, hemoglobin not only gives 0 2 to tissues, but also attaches the CO2 formed in the tissues. The main factor providing

the dissociation of oxyhemoglobin is a drop in Po 2, which is rapidly consumed by tissues. The formation of oxyhemoglobin in the lungs and its dissociation in tissues pass within the same upper part of the curve (75-96% saturation of hemoglobin with oxygen). In the intercellular fluid, Po 2 decreases to 5-20 mm Hg, and in cells it drops to 1 mm Hg. and less (when Po 2 in the cell becomes equal to 0.1 mm Hg, the cell dies). Since there is a large gradient of Po 2 (it is about 95 mm Hg in the incoming arterial blood), the dissociation of oxyhemoglobin is fast, and 0 2 passes from the capillaries into the tissue. The duration of half-dissociation is 0.02 s (the time of passage of each erythrocyte through the capillaries of the great circle is about 2.5 s), which is sufficient for the elimination of 0 2 (a huge margin of time).

In addition to the main factor (gradient Po 2) there are also a number of auxiliary factors that contribute to the dissociation of oxyhemoglobin in tissues. These include: 1) the accumulation of CO2 in tissues; 2) acidification of the environment; 3) temperature rise.

Thus, an increase in the metabolism of any tissue leads to an improvement in the dissociation of oxyhemoglobin. In addition, the dissociation of oxyhemoglobin promotes 2,3-diphosphoglycerate - an intermediate product formed in erythrocytes during cleavage

lesion of glucose. With hypoxia, more of it is formed, which improves the dissociation of oxyhemoglobin and the provision of oxygen to the tissues of the body. Accelerates the dissociation of oxyhemoglobin also ATF,but to a much lesser extent, since 2,3-diphosphoglycerate in erythrocytes contains 4-5 times more than ATP.

G. Myoglobin also appends 0 2. In terms of amino acid sequence and tertiary structure, the myoglobin molecule is very similar to the individual subunit of the hemoglobin molecule. However, myoglobin molecules do not combine with each other to form a tetramer, which apparently explains the functional features of O 2 binding. The affinity of myoglobin to 0 2 is greater than that of hemoglobin: already at a voltage of Po 2 3-4 mm Hg. 50% of myoglobin is saturated with oxygen, and at 40 mm Hg. saturation reaches 95%. However, myoglobin is more difficult to give up oxygen. This is a kind of reserve of 0 2, which is 14% of the total amount of 0 2 contained in the body. Oxymyoglobin begins to release oxygen only after the partial pressure of 0 2 drops below 15 mm Hg. Due to this, it plays the role of an oxygen depot in the resting muscle and gives 0 2 only when the reserves of oxyhemoglobin are exhausted, in particular, during muscle contraction, the blood flow in the capillaries can stop as a result of their compression, the muscles during this period use the oxygen stored during relaxation ... This is especially important for the heart muscle, which is mainly powered by aerobic oxidation. Under conditions of hypoxia, the content of myoglobin increases. The affinity of myoglobin with CO is less than that of hemoglobin.

Carbon dioxide transport

The transport of carbon dioxide, like oxygen, is carried out by the blood in the form of physical dissolution and chemical bonds. Moreover, C0 2, like 0 2, is carried by both plasma and erythrocytes (I.M.Sechenov, 1859). However, the ratio of CO2 fractions carried by plasma and erythrocytes differs significantly from those for 02. Below are the average indicators of the content of CO2 in the blood.

Distribution of CO2 in plasma and erythrocytes. Most of CO2 is transported by blood plasma,moreover, about 60% of the total CO 2 is in the form of sodium bicarbonate (NaHCO 3, 34 vol%), i.e. in the form of a chemical bond, 4.5 vol% - in the form of physically dissolved CO 2 and about 1.5% CO, is in the form of H 2 CO 3. In total, the venous blood contains 58 vol% CO2. In the erythrocyte, CO2 is in the form of chemical compounds carbhemoglobin (HHbCO2, 5.5 vol%) and potassium bicarbonate (KHC03, 14 vol%). Carbon dioxide,

formed in the body, is excreted mainly through the lungs (about 98%) and only 0.5% through the kidneys, about 2% through the skin in the form of HC0 3 bicarbonates.

It should be noted that a slight increase in the content of CO2 in the blood has a beneficial effect on the body: it increases the blood supply to the brain and myocardium, stimulates the processes of biosynthesis and regeneration of damaged tissues. An increase in the content of CO2 in the blood also stimulates the vasomotor and respiratory centers.

Formation of carbon dioxide compounds.As a result of oxidative processes and the formation of CO2, its voltage in the cells and, naturally, in the intercellular spaces is much higher (reaches 60-80 mm Hg) than in the arterial blood entering the tissues (40 mm Hg). Therefore, CO2, according to the voltage gradient, passes from the interstitium through the capillary wall into the blood. A small part of it remains in the plasma in the form of physical dissolution. A small amount of Н 2 С0 3 (Н 2 0 + С0 2 -> H 2 C0 3), but this process is very slow, since there is no carbonic anhydrase enzyme in the blood plasma that catalyzes the formation of H 2 C0 3

Carbonic anhydrase is found in various cells of the body, including leukocytes and platelets. C0 2 also enters these cells, where carbonic acid and HCO 3 ~ ions are also formed. However, the role of these cells in the transport of CO2 is insignificant, since they do not contain hemoglobin, their number is much less than that of erythrocytes, their size is very small (platelets have a diameter of 2-3 microns, erythrocytes - 8 microns).

Hemoglobin transports not only 0 2, but also C0 2. In this case, the so-called carbamine bond is formed: HHb + C0 2 \u003d \u003d HHbCO 2 (Hb-NH-COOH-carbhemoglobin, more precisely - carbamino-hemoglobin).

A small amount of CO2 (1-2%) is transported by blood plasma proteins also in the form of carbamine compounds.

Dissociation of carbon dioxide compounds.In the lungs, the reverse processes occur - the release of CO2 from the body (about 850 g of CO2 are released per day). First of all, the release of physically dissolved CO2 from the blood plasma into the alveoli begins, since the partial pressure of Рco 2 in the alveoli (40 mm Hg) is lower than in the venous blood (46 mm Hg). This leads to a decrease in the Pco 2 voltage in the blood. Moreover, the addition of oxygen to hemoglobin leads to a decrease in the affinity of carbon dioxide for hemoglobin and the breakdown of carbhemoglobin (Holden effect). General scheme of the processes of formation and dissociation of all oxygen compounds

and carbon dioxide, occurring during the passage of blood in the capillaries of tissues and lungs, is shown in Fig. 7.7.

In the process of breathing, the pH of the internal environment is regulated due to the removal of CO2 from the body, since H2CO3 dissociates into H2O and CO2. At the same time, acidification of the internal environment of the body is prevented by the constantly formed Н 2 С0 3.

RESPIRATORY REGULATION

The body carries out fine regulation of the tension of 0 2 and CO 2 in the blood - their content remains relatively constant, despite fluctuations in the amount of available oxygen and the need for it, which during intense muscular work can increase 20 times. The frequency and depth of breathing are regulated by the respiratory center, the neurons of which are located in different parts of the central nervous system; the main ones are the medulla oblongata and the bridge. The respiratory center rhythmically sends impulses to the diaphragm and intercostal muscles along the corresponding nerves, which cause respiratory movements. Basically, the rhythm of breathing is involuntary, but it can change in some

within the higher centers of the brain, which indicates the possibility of arbitrary influence on the underlying parts of the respiratory center.

Gas exchange in the lungs

The process of gas exchange between the inhaled air and the alveolar air, between the alveolar air (it is advisable to call it the alveolar gas mixture) and the blood is determined by the composition of gases in these media (Table 8).

Table 8.

Partial pressure of gases

The partial pressure of each gas in the mixture is proportional to its volume. Since the lungs, together with oxygen, carbon dioxide and nitrogen, also contain water vapor, to determine the partial pressure of each gas, it is necessary to adjust the pressure to the pressure of the "dry" gas mixture. If a person is in "dry" air, then the partial pressure of each gas should be calculated taking into account the value of the total pressure. The humidity requires making appropriate corrections with steam. Table 9 shows the values \u200b\u200bof gas pressure for "dry" atmospheric air at a pressure of 101 kPa (760 mm Hg).

Table 9.

Analysis of the vidihuvano gas mixture indicates that different portions of it in terms of the percentage of "main" gases - 02 and CO2 - differ significantly. The composition of the first exhaled portions is closer to atmospheric, since this is the air of dead space. The last portions are close in composition to the alveolar gas mixture. The indicator of the partial pressure of the gas in the alveolar mixture is designated RA.

To determine PA0 and RLS0 in the alveolar mixture, it is necessary to subtract that part of the pressure that falls on water vapor and nitrogen. As a result, it turns out that the level of radioactive waste is 13.6 kPa (102 mm Hg), PAC0 - 5.3 kPa (40 mm Hg).

To determine the intensity of gas exchange in the body, in addition to the partial pressure of gases, it is necessary to know the amount of absorption of 02 and the release of CO2. At rest, an adult in 1 minute absorbs 250-300 ml of oxygen and releases 200-250 ml of carbon dioxide.

Gas exchange between lungs and blood

Pulmonary hemodynamics

The lungs have a double network of capillaries. The lung tissue itself is fed from the vessels of the systemic circulation. This part makes up a very small percentage (1-2%) of the total blood of the lungs.

Normally, the vessels of the small circle contain 10-12% of all blood in the body. These vessels belong to the system with low blood pressure (25-10 mm Hg). The small circle capillaries have a large cross-sectional area (about 80% larger than the large circle). The number of capillaries is extremely

Figure: 80. The relationship of the alveoli with the vessels (for Butler):

1,4 - bronchial capillary; 2 - pleura; FROM - alveolus; 5 - lymphatic capillary; b - pulmonary capillaries

tea is great. It is only slightly less than the number of all capillaries of the great circle (8 and 10 billion, respectively).

Normal gas exchange requires an adequate ratio of ventilation of the alveoli and blood flow in the capillaries, they are entwined (Fig. 80). However, this condition is not always met. Some areas of the lungs are ventilated and perfused not always in the same way. There are poorly or completely unventilated alveoli while maintaining blood flow, and vice versa, well-ventilated alveoli with nonperfused vessels (Fig. 81).

Gas exchange across the aerohematic barrier

Gas exchange in the human lungs takes place over a huge area, which is 50-90 m2. The thickness of the aerohematic barrier is 0.4-1.5 microns. Gases penetrate through it by diffusion along the partial pressure gradient. In a person at rest, in the inflowing venous blood G ^ is 40 mm Hg. Art., aPvCO - about 46 mm Hg. Art.

The gases pass through two layers of cells (alveolar epithelium and capillary endothelium) and the interstitial space between them.

Thus, in the path of each gas there are five cellular and one main membrane, as well as six aqueous solutions. The latter includes the fluid covering the epithelium of the alveoli, the cytoplasm of two

Figure: 81.

1 - adequate; 2 - normal ventilation in case of impaired blood flow; 3 - violation of the aerohematic barrier; 4 - impaired ventilation due to stored blood flow

Figure: 82.

cells of the pulmonary membrane, microcrystalline fluid, blood plasma, erythrocyte cytoplasm. The most "difficult to pass" areas are cell membranes. The rate of passage of all these media by each gas is determined, on the one hand, by the partial pressure gradient, and on the other, by the solubility of gases in lipids, which form the basis of membranes, and in water. Carbon dioxide in lipids and water dissolves 23 times more actively than oxygen. Therefore, despite the lower pressure gradient (for CO2 - 6 mm Hg, and for 02 - 60 mm Hg), CO2 penetrates through the pulmonary membrane faster than 02 (Fig. 82). When blood passes through the capillary, the level of P0 in the alveoli and blood levels out after 0.2-0.25 s, and - after 0.1 s.

The efficiency of gas exchange in the lungs also depends on the blood flow rate. It is such that the erythrocyte passes through the capillary for 0.6 - 1 sec. During this time, PA0 and Pa0 are aligned. But under the condition of an excessive increase in the blood flow velocity, for example, in the case of intense physical activity, the erythrocyte through the pulmonary capillary can slip faster from the critical 0.2-0.25 s, and then the oxygen saturation of the blood decreases.

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-2.jpg" alt \u003d "(! LANG:\u003e Gas exchange between atmospheric air and blood is called external respiration and is carried out by the respiratory organs -"> Газообмен между атмосферным воздухом и кровью называется внешним дыханием и осуществляется органами дыхания - легкими и внелегочными дыхательными путями. Газообмен между легкими и другими органами осуществляет система кровообращения. Клеточное дыхание - биологическое окисление - обеспечивает организм энергией.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-3.jpg" alt \u003d "(! LANG:\u003e STAGES OF BREATHING 1. Ventilation of the lungs. When the intercostal muscles and"> ЭТАПЫ ДЫХАНИЯ 1. Вентиляция лёгких. При сокращении межрёберных мышц и диафрагмы лёгкие растягиваются - вдох, при расслаблении межрёберных мышц и диафрагмы лёгкие сжимаются - выдох.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-4.jpg" alt \u003d "(! LANG:\u003e Respiratory movements External intercostal muscles - raise the ribs. Internal intercostal muscles - lower the ribs."> Дыхательные движения Наружные межреберные мышцы- поднимают ребра. Внутренние межреберные мышцы - опускают ребра. Действие межреберных мышц основано на принципе рычага.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-5.jpg" alt \u003d "(! LANG:\u003e rest inhale exhale">!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-6.jpg" alt \u003d "(! LANG:\u003e Lung vital capacity With calm breathing, 0 enters the lungs in one breath ,"> Жизненная емкость легких При спокойном дыхании за один вдох в легкие входит 0, 3 - 0, 5 л воздуха (дыхательный объем). При самом глубоком дыхании дыхательный объем может достигать 3 -5 л (жизненная емкость легких). Но и тогда после выдоха в легких остается более 1 л воздуха (остаточный объем).!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-7.jpg" alt \u003d "(! LANG:\u003e Lung vital capacity is measured with a spirometer.">!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-8.jpg" alt \u003d "(! LANG:\u003e Dead space is formed by those areas"> Мертвое пространство образовано теми областями органов дыхания, где нет газообмена с кровью. В норме это внелёгочные дыхательные пути и большинство бронхов. Объем заключенного в них воздуха - около 150 мл, что составляет 30% дыхательного объема при спокойном дыхании. Таким образом, в обычных условиях почти треть вдыхаемого воздуха не участвует в газообмене.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-9.jpg" alt \u003d "(! LANG:\u003e 2. Pulmonary respiration (gas exchange in the lungs). Gas exchange between air and"> 2. Лёгочное дыхание (газообмен в лёгких). Газообмен между воздухом и кровью происходит путем диффузии по разности концентраций газов. В мертвом пространстве газообмен не идет. Венозная кровь превращается в артериальную.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-10.jpg" alt \u003d "(! LANG:\u003e 3. Transport of gases. In the capillaries of the lungs (pulmonary circulation) the blood is saturated with oxygen"> 3. Транспорт газов. В капиллярах легких (малый круг кровообращения) кровь насыщается кислородом и избавляется от углекислого газа, превращаясь из венозной в артериальную. Благодаря работе сердца кровь разносится по всем органам (большой круг кровообращения), в капиллярах которых происходят обратные процессы.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-11.jpg" alt \u003d "(! LANG:\u003e Most of the oxygen in the blood is in the form of a compound with hemoglobin (Hb . O 2"> Основная часть кислорода находится в крови в виде соединения с гемоглобином (Hb. O 2) и совсем немного растворено в плазме. Углекислый газ переносится в основном плазмой - в виде ионов НСО 3 - и растворенного СО 2 , в меньшей степени, эритроцитами - в соединении с гемоглобином (Hb. СO 2).!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-12.jpg" alt \u003d "(! LANG:\u003e Gases pass from one medium to another due to the difference in their pressure.">!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-13.jpg" alt \u003d "(! LANG:\u003e Since there is relatively little CO 2 in the alveoli, it leaves the blood plasma in"> Поскольку в альвеолах относительно мало CO 2 , он выходит из плазмы крови в альвеолярный воздух. Это влечет за собой высвобождение CO 2 из соединения с гемоглобином (Hb. СO 2) и из солей угольной кислоты - гидрокарбонатов (НСО 3 -). Кислород диффундирует в обратном направлении- из воздуха в кровь, где интенсивно связывается гемоглобином.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-14.jpg" alt \u003d "(! LANG:\u003e 4. Tissue respiration (gas exchange in tissues). In the process of cellular breathing"> 4. Тканевое дыхание (газообмен в тканях). В процессе клеточного дыхания постоянно потребляется кислород. Поэтому он диффундирует из плазмы крови в межклеточное вещество других тканей и далее - в клетки. Выделяемый клетками CO 2 , наоборот, поступает в кровь, где частично связывается гемоглобином, а большей частью - с водой. Артериальная кровь превращается в венозную.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-16.jpg" alt \u003d "(! LANG:\u003e Respiration regulation">!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-17.jpg" alt \u003d "(! LANG:\u003e NERVOUS REGULATION Involuntary Arbitrary"> НЕРВНАЯ РЕГУЛЯЦИЯ Непроизвольная Произвольная регуляция частоты и регуляция частоты и глубины дыхания. ОСУЩЕСТВЛЯЕТСЯ Дыхательным центром Корой больших продолговатого мозга. полушарий. Воздействие на Мы можем произвольно холодовые, болевые и др. ускорить или остановить рецепторы может дыхание. приостановить дыхание.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-18.jpg" alt \u003d "(! LANG:\u003e HUMORAL REGULATION The rate and depth of breathing accelerates"> ГУМОРАЛЬНАЯ РЕГУЛЯЦИЯ Частоту и глубину дыхания ускоряет замедляет Избыток CO 2 Недостаток CO 2 В результате усиления вентиляции легких дыхание приостанавливается, т. к. концентрация CO 2 в крови снижается.!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-20.jpg" alt \u003d "(! LANG:\u003e REFLEXION">!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-21.jpg" alt \u003d "(! LANG:\u003e BACKGROUND">!}

Src \u003d "https://present5.com/presentation/3/45299511_365066074.pdf-img/45299511_365066074.pdf-22.jpg" alt \u003d "(! LANG:\u003e In F. Cooper's novels, Indians sometimes fled from enemies by plunging into water and breathing"> В романах Ф. Купера индейцы иногда спасались от врагов, погружаясь в воду и дыша при этом через полую камышинку. Однако дышать таким способом можно на глубине, не превышающей 1, 5 м. ПОЧЕМУ? На большей глубине давление настолько возрастает, что вдох сделать невозможно.!}

Breathing is a set of processes that exchange oxygen and carbon dioxide between the body and the external environment. These processes proceed in the following sequence:

1. gas exchange between the lungs and the external environment - pulmonary ventilation, or external respiration;

2. gas exchange between the alveoli and blood - pulmonary respiration;

3. gas exchange between blood and tissues - tissue or cellular respiration;

4. transport of gases by blood.

The respiratory system is a collection of organs that perform air-conducting and gas exchange functions. It includes

· Upper respiratory tract - nasal cavity, nasal and oral part of the pharynx;

• lower respiratory tract - larynx, trachea and bronchi;

· The lungs are a paired organ.

The airways from the inside are covered with ciliated epithelium, the cilia of which are tilted towards the inhaled air. In addition, the epithelium has a dense circulatory network. As a result, the air in the respiratory tract is humidified, cleaned and warmed.

Inhalation and exhalation mechanism

During the act of inhalation, the respiratory intercostal muscles that lift the ribs contract, the muscles of the diaphragm contract at the same time, its dome, directed towards the chest cavity, descends, the abdominal organs move down - an increase in the volume of the chest occurs. An increase in the volume of the chest leads to an increase in the volume of the lungs, which are pressed against the chest wall by atmospheric pressure. An increase in the volume of the lungs leads to a decrease in pressure in their cavity, and therefore the external atmospheric air, due to the pressure difference, enters them.

With the act of exhalation, the intercostal muscles relax (the ribs fall) and the muscles of the diaphragm (the dome of the diaphragm rises and presses on the organs of the chest cavity, in particular, compresses the lungs). As a result, the volume of the chest decreases, and accordingly the volume of the lungs decreases, the pressure in the lung cavity becomes higher than atmospheric pressure and therefore the air is pushed out of the lungs through the respiratory tract.

Gas exchange in the lungs

In the lungs, gas exchange takes place between alveolar air and blood. This gas exchange is facilitated by the small thickness of the so-called air-blood barrier. This barrier between air and blood is formed by the wall of the alveoli and the wall of the pulmonary capillary. Its thickness is 2 layers of cells, which is approximately 2.5 microns. The wall of the alveoli is covered from the inside with a thin film of phospholipid - a surfactant. Surfactant prevents adhesion of the walls of the alveoli, participates in immune defense with the help of class A and M immunoglobulins (Ig A, Ig M).

In alveolar air, the oxygen concentration (partial pressure) is much higher (100 mm Hg) than in venous blood (40 mm Hg), flowing through the pulmonary capillaries. Therefore, oxygen easily leaves the alveoli into the blood, where it quickly combines with the hemoglobin of erythrocytes. At the same time, carbon dioxide, the concentration of which in the venous blood is high (47 mm Hg), diffuses into the alveoli, where the pressure of carbon dioxide is lower (40 mm Hg).

As a result, the partial pressure of oxygen (and the partial pressure of carbon dioxide) in the alveolar air and blood is equalized.

Transport of gases by blood

After diffusion of oxygen into the blood, it combines with the hemoglobin of erythrocytes, turning into a fragile compound oxyhemoglobin. One hemoglobin molecule can attach 4 oxygen molecules to itself. Then the blood carries red blood cells to the tissues, where hemoglobin gives up oxygen and attaches carbon dioxide to itself, turning into a fragile compound, carbhemoglobin. Returning to the lungs, the blood again releases carbon dioxide and takes in oxygen.

An insufficient supply of oxygen to the blood is called hypoxia. It can occur when a person rises to an altitude of 4000-5000 m above sea level. This condition is called altitude sickness.

When breathing stops, asphyxia develops - choking. This condition can occur with drowning, electric shock, or gas poisoning.

Features of the spread of excitement. Soltator and continuous excitation. The speed of the excitation. Antidromic, artodromic, non-decremental, isolated conduction of excitation, a factor of reliability.

All the features of the propagation of excitation in the central nervous system are explained by its neural structure - the presence of chemical synapses, multiple branching of neuronal axons, and the presence of closed neural pathways. These features are as follows.

1. Unilateral propagation of excitation in neural circuits, in reflex arcs. One-way propagation of excitation from the axon of one neuron to the body or dendrites of another neuron (but not back) is explained by the properties of chemical synapses, which conduct excitation in only one direction.

(2) The slow propagation of excitation in the central nervous system in comparison with the nerve fiber is explained by the presence of many chemical synapses on the pathways of the propagation of excitation, in each of which there is a synaptic delay of about 0.5 ms before the onset of EPSP. The time of excitation through the synapse is spent on the release of the mediator into the synaptic cleft, its propagation to the postsynaptic membrane, the emergence of EPSP, and, finally, AP. The total delay in the transmission of excitation in a neuron with the simultaneous arrival of many impulses to it reaches a value of the order of 2 ms. The more synapses in the neuronal chain, the lower the overall speed of propagation of excitation along it. By the latent time of the reflex, more precisely by the central time of the reflex, it is possible to roughly calculate the number of neurons of one or another reflex arc.

3. Irradiation (divergence) of excitation in

The central nervous system is explained by the branching of neuron axons (on average, a neuron forms up to 1000 endings) and their ability to establish numerous connections with other neurons, the presence of intercalary neurons, whose axons also branch (Fig. 7.3, A). Irradiation of excitation can be easily observed in the experiment on a spinal frog, when a weak irritation causes flexion of one limb, and a strong one causes vigorous movements of all limbs and even the trunk. Divergence expands the scope of each neuron. One neuron, sending impulses to the cerebral cortex, can activate up to 5000 neurons.

4. Convergence of excitation (the principle of a common final path) - the convergence of excitation of various origins along several paths to the same neuron or neuronal pool (the principle of the sherrington funnel). It is explained by the presence of many axonal collaterals, intercalary neurons, and also by the fact that there are several times more afferent pathways than efferent neurons. Up to 10,000 synapses can be located on one neuron of the central nervous system, and up to 20,000 synapses in motor neurons of the spinal cord. The phenomenon of convergence of excitation in the central nervous system is widespread. An example is the convergence of excitations on a spinal motoneuron. Thus, primary afferent fibers (Fig. 7.3, B), as well as various descending paths of many overlying centers of the brainstem and other parts of the central nervous system, are suitable for the same spinal motor neuron. The phenomenon of convergence is very important: it provides, for example, the participation of one motor neuron in several different reactions. The motor neuron, which innervates the muscles of the pharynx, participates in the reflexes of swallowing, coughing, sucking, sneezing and breathing, forming a common final path for numerous reflex arcs. In fig. 7.3, A shows two afferent fibers, each of which gives off collaterals to 4 neurons in such a way that 3 neurons out of a total of 5 of them form connections with both afferent fibers. On each of these 3 neurons, two afferent fibers converge.

1. Continuous propagation of APs is carried out in myelin-free fibers of type C, which have a uniform distribution of voltage-dependent ion channels involved in the generation of APs. Conduction of a nerve impulse begins with the stage of electrotonic propagation of the resulting AP. The amplitude of the AP of the nerve fiber (membrane potential + inversion) is about 90 mV, the constant membrane length (Km) in myelin-free fibers is 0.1 - 1.0 mm.

Therefore, AP, propagating at this distance as an electrotonic potential and retaining at least 37% of its amplitude, is able to depolarize the membrane to a critical level and generate new APs throughout its length (Fig. 5.3). At the same time, at the stage of electrotonic propagation of a nerve impulse, ions move along the fiber between the depolarized and polarized sections, providing excitation to the adjacent sections of the fiber. In reality, with an intact nerve fiber, the stage of purely electrotonic propagation of AP (along the membrane) is extremely small, since voltage-dependent channels are in close proximity to each other and, naturally, from the action potential that has arisen and is observed only until depolarization equal to 50% Ecr is achieved. Further, the movement of ions into the cell (nerve fiber) and out of the cell is switched on due to the activation of ion channels.

With the formation of a new AP in a neighboring area in the depolarization phase, a powerful current of sodium ions into the cell occurs due to the activation of sodium channels, leading to regenerative (self-reinforcing) depolarization. This current provides the formation of a new AP of the same amplitude, which, as usual, is the sum of two quantities - the resting membrane potential and inversion. In this regard, the PD is carried out without decrement (without decreasing the amplitude). Thus, the continuous propagation of the nerve impulse goes through the generation of new APs along the relay race, when each section of the membrane acts first as an irritated one (when an electrotonic potential arrives at it), and

then as annoying (after the formation of a new PD).

2. Salypatory type of nerve impulse conduction is carried out in myelin fibers (types A and B), which are characterized by the concentration of voltage-dependent ion channels only in small areas of the membrane (in the interceptions of Ranvier), where their density reaches 12,000 per 1 μm2, which is about 100 times higher than in the membranes of myelin-free fibers. In the area of \u200b\u200bmyelin couplings (inter-nodal segments), which have good insulating properties, there are almost no voltage-dependent channels, and the membrane of the axial cylinder is practically non-excitable there. Under these conditions, the AP, which has arisen in one Ranvier intercept, electrotonically (along the fiber, without the participation of ion channels) spreads to the neighboring intercept, depolarizing the membrane there to a critical level, which leads to the emergence of a new AP, i.e. excitation is carried out abruptly (Fig. 5.4). The constant length of the myelin fiber membrane reaches 5 mm. This means that the AP, propagating electrotonically at this distance, retains 37% of its amplitude (about 30 mV) and can depolarize the membrane to a critical level (the threshold potential in Ranvier interceptions is about 15 mV). Therefore, in case of damage to the interceptions of Ranvier that are closest along the route, the action potential can electrotonically excite the 2nd - 4th and even 5th interceptions.

Non-incremental conduction of arousal. The amplitude of AP in different parts of the nerve is the same, that is, the conduction of excitation along the nerve fiber is carried out without attenuation (without decrement). Thus, information is encoded not by changing the AP amplitude, but by changing their frequency and distribution over time.

· Isolated conduction of excitation. Nerve trunks are usually formed by a large number of nerve fibers, but the APs going along each of them are not transmitted to neighboring ones. This feature of nerve fibers is due to: Ú the presence of sheaths surrounding individual nerve fibers and their bundles (as a result, a barrier is formed that prevents the transition of excitation from fiber to fiber); Ú the resistance of the intercellular fluid (the fluid between the fibers has much less resistance to current than the membrane of the axons; therefore, the current is shunted through the interfiber spaces and does not reach the neighboring fibers).

Gas exchange is a set of processes that ensure the transfer of oxygen from the external environment to the tissues of a living organism, and carbon dioxide from tissues to the external environment.
The movement of gases (lungs - blood - tissues) is carried out under the influence of the difference in the partial pressures and stresses of these gases in each of the body's environments.
The partial pressure of oxygen in the air filling the alveoli of the lungs is about 100 mm Hg. Art., and its tension in the venous blood flowing to the lungs, about 40 mm Hg. Art. Due to the pressure difference, oxygen from the alveoli is directed into the blood, where it binds to the hemoglobin of erythrocytes.

When breathing, almost 30% of the inhaled air is in the airways, and 70% fills the volume of the alveoli. It is this part of the air that provides ventilation of the alveoli, its ratio to the inhaled air is called the coefficient of pulmonary ventilation. Atmospheric air is a mixture of nitrogen (up to 78%), oxygen (up to 21%), carbon dioxide (up to 0.03%), water vapor and minor admixtures of other gases.

In the alveoli, there is no complete replacement of air with atmospheric, therefore, according to Fick's law, gas exchange of O2 between alveolar air and blood occurs due to the presence of a concentration gradient of O2 between these media. Under normal conditions, the partial pressure of oxygen in the alveoli is always greater than its tension in the venous blood (40 mm Hg), and the partial pressure of carbon dioxide, on the contrary, is less than its voltage (46 mm Hg). The pressure of gases in water or in body tissues is denoted by the term "gas tension" and is designated by the symbols Po2, Pco2. Thus, the difference in oxygen concentration on both sides of the alveoli exceeds 60 mm Hg, so it moves into the blood. Carbon dioxide also escapes quickly, because the slight difference in its concentration is compensated for by better solubility in water. In addition, the saturation of blood with gases is affected by the fact that they are mainly in a chemically bound state in it, this contributes to constant diffusion. Oxygen entering the blood plasma from the alveoli moves to erythrocytes, in which it combines with hemoglobin to form oxyhemoglobin (1 g of hemoglobin adds 1.34 ml of oxygen). Oxygen capacity of blood - the maximum amount of oxygen that can be bound in 100 ml of blood, provided that all hemoglobin is converted to oxyhemoglobin. In arterial blood flowing to the tissues, the oxygen tension is higher than in the tissues, and the carbon dioxide voltage, on the contrary, is much lower. As a result, oxygen passes from the blood to the tissues and is included in the cycle of metabolic processes, and carbon dioxide, contained in excess in the tissues, passes into the blood and is then transferred to the lungs. O2 transport begins in the capillaries of the lungs after it chemically binds to hemoglobin. Hemoglobin (Hb) is able to selectively bind O2 and form oxyhemoglobin (HbO2) in the area of \u200b\u200bhigh O2 concentration in the lungs and release molecular O2 in the area of \u200b\u200blow O2 content in tissues. In this case, the properties of hemoglobin do not change and it can perform its function for a long time. The fixation of oxygen and the breakdown of oxyhemoglobin depends on factors that affect this reaction, in particular temperature, the presence of acidic substances and carbon dioxide. An increase in temperature in working organs and tissues, an increase in the concentration of carbon dioxide and organic acids contribute to the breakdown of oxyhemoglobin, the release of oxygen and its transfer into cells. And the opposite conditions, on the contrary, ensure the formation of oxyhemoglobin, for example, in the lungs.

Hemoglobin carries O2 from the lungs to the tissues. This function depends on two of its properties:

1) the ability to change from a reduced form, which is called deoxyhemoglobin, to an oxidized form (Hb + O2 and HbO2) at a high rate (half-period 0.01 s or less) with normal Po2 in alveolar air;

2) the ability to donate O2 in tissues (HbO2 and Hb + O2) depending on the metabolic needs of the body's cells.

The rate of gas transfer through the layer of tissue is directly proportional to the area of \u200b\u200bthe layer and the difference in the partial pressure of the gas on both sides and inversely proportional to the thickness of the layer. During gas exchange between tissues and blood, the thickness of the diffusion barrier is less than 0.5 μm, however, in muscles at rest, the distance between open capillaries is about 50 μm. During work, when the oxygen consumption by the muscles increases, additional capillaries open, which reduces the diffusion distance and increases the diffusion surface. Since CO 2 diffuses into tissues about 20 times faster than O 2, carbon dioxide removal is much easier than oxygen supply. An inadequate supply of oxygen to tissues is called tissue hypoxia.

The gas exchange process occurs continuously as long as there is a difference in the partial pressures and voltages of gases in each of the media participating in gas exchange, the decisive factor determining the continuity of gas exchange is the constancy of the gas composition of the alveolar air.