The breathing process of inhalation and exhalation is carried out. Breath. Reflexes of the respiratory center and reflex influence on breathing

The human breathing process: what it is and how it happens

Every few seconds we do inhale, which carries vital nutrients to the body oxygen. This process occurs automatically and without the participation of consciousness. How so elementary at first glance process capable of supporting life?

The breathing process gives rise to the environment. The air we breathe, i.e. which inhale, is nothing more than a mixture of gases. In number: nitrogen, carbon dioxide and oxygen, which is vital for us.

Entering the body through the nose and mouth, air passes through the larynx, trachea and bronchi. After which it will enter the alveolar sacs located in the lungs. In the alveoli due to air pressure occurs exchange oxygen with blood. In this process of gas exchange, the diaphragm and intercostal muscles play a role pumping station.

Human activity(especially during physical and mental stress) and breathing intensity are interrelated. Remember how you took a difficult test. Most people are worried and intensitybreathing increases. When breathing shallowly, the brain receives less oxygen, and it becomes more difficult to concentrate. How does the body perceive physical activity, for example, football on the grass after school? Increased intensity of loads requires influx energy to the muscles, which requires additional oxygen. The man begins rapidlybreathe, as a result of which more oxygen from the air enters the body, and the mechanism also turns on thermoregulation by natural cooling.

Breathing intensity may also change in other cases. Remember a situation when you were captured emotions or anger. Feeling anger triggers a number of processes in the body that increase internal temperature and give vent to feelings. Have you ever seen someone lose their temper? However breath able stress over a long period of time is fraught with consequences. If the body's cells do not receive enough oxygen, then it is disrupted synthesis nutrients begin to accumulate in the blood toxins. There is evidence that hypoxic(oxygen-poor) environment increases risk cancer. But don't be upset ability There is much more to a person's ability to control their breathing than it seems. And volume inhalation and degree assimilationoxygen it is possible to increase. For thousands of years people, starting from the ancient Indian yogis and ending with modern specialists pulmonologists, are studying the processes of breathing. Special methods for organ training breathing owned by both yogis and doctors.

In fact, breathing process comes down to pumping air from where pressure above, to where it is below. The deeper the breath, the more into the body through blood supplies oxygen necessary for cells to synthesize all substances. This is most easily achieved by deep inhale. Intensity breathing mainly depends on the pressure of air entering the lungs. In case of coughing, sneezing or hiccups, the pressure changes automatically.

Let's do a simple experiment. Close with your thumb right hand right nostril and try to breathe only through the left. Notice how much more difficult began to breathe. Not only do the diaphragm muscles work with greater tension, but this process is also distracting. Reducing the cross-section of air flows increases the pressure at which oxygen flows from the alveoli into the blood. Slow breathing through one nostril to increase the volume of incoming oxygen and activate the parasympathetic nervous system(which is responsible for the functions of the body at rest) is a common practice of yoga.

Here's another one example. Imagine how it breathes dog, sticking out his tongue. Try breathing like this themselves: first with the tongue hanging out, and then with the mouth closed. You will immediately feel voltage abdominal muscles that push air out when you exhale. If you put your palm to your lip, you will feel how by force air comes out when you exhale. Such breathing is difficult due to the need for stronger reductions diaphragm and intercostal muscles. The body reacts immediately to the greater pressure produced during exhalation change temperature. It is not surprising that on a hot day dogs resort to this method to cool down.

Breathing managed by the center in oblongbrain, which supports this process during sleep. Fortunately, the participation of consciousness is not required for this. However, during the day there are many factors affecting breathing. more. It is especially affected by stress and troubles, in connection with which it is useful to control breathing. By monitoring your breathing and controlling its intensity, you can regulate how amount inhaled air and assimilation oxygen. It protects against stress, improves tone and strengthens immune system. So what if one more time will hear: “Relax and take a deep breath,” then you will already know what this is for.

The act of breathing consists of rhythmically repeating 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. During its contraction, the diaphragm lowers (flattens), which leads to an increase in the vertical size of the thoracic cavity. When the external intercostal and some other muscles contract, the ribs rise, and the anteroposterior and transverse dimensions of the thoracic cavity increase. Thus, as a result of muscle contraction, the volume of the chest increases. Due to the fact that there is no air in the pleural cavity and the pressure in it is negative, simultaneously with the increase in the volume of the chest, the lungs expand. As the lungs expand, the air pressure inside them decreases (it becomes lower than atmospheric pressure) and atmospheric air rushes through the respiratory tract into the lungs. Consequently, when inhaling, the following occurs sequentially: muscle contraction - an increase in the volume of the chest - expansion of the lungs and a decrease in pressure inside the lungs - the flow of air through the airways into the lungs.

Exhalation occurs after inhalation. The muscles involved in the act of inhalation relax (the diaphragm rises), the ribs fall as a result of contraction of the internal intercostal and other muscles and due to their heaviness. The volume of the chest decreases, the lungs compress, the pressure in them increases (becomes higher than atmospheric pressure), and air rushes out through the airways.

The mechanism of breathing regulation is very complex. In a schematic presentation, it boils down to the following. In the medulla oblongata there is a cluster of nerve cells that regulate breathing - the respiratory center. The respiratory center has two sections: the inhalation section and the exhalation section. The function of both departments is interconnected: when the inhalation department is excited, the exhalation department is inhibited, and, conversely, the excitation of the exhalation department is accompanied by inhibition of the inhalation department. In addition to the respiratory center located in the medulla oblongata, special clusters of nerve cells in the pons and diencephalon are involved in the regulation of breathing. The respiratory center exerts its influence on the respiratory muscles, on which the change in chest volume during inhalation and exhalation depends, not directly, but through spinal cord. In the spinal cord there are groups of cells, the processes of which (nerve fibers) go as part of the spinal nerves to the respiratory muscles. When the respiratory center (inspiratory department) is excited, nerve impulses are transmitted to the spinal cord, and from there along the nerves to the respiratory muscles, causing them to contract; As a result, the chest expands and inhalation occurs. The cessation of the transmission of impulses from the respiratory center (during inhibition of the inspiratory department) to the spinal cord, and from it to the respiratory muscles is accompanied by relaxation of these muscles; As a result, the chest collapses and exhalation occurs.

In the respiratory center, there is an alternating change in the state of excitation and inhibition (inhalation and exhalation departments), which causes rhythmic alternations of inhalation and exhalation. Changes in the state of the respiratory center depend on nervous and humoral influences. In this case, an important role belongs to the receptors of the lungs and carbon dioxide in the blood. During inhalation, the lungs stretch and due to this, the endings of the vagus nerve embedded in the lung tissue are irritated. Nerve impulses generated in the receptors are transmitted along the vagus nerve to the respiratory center, causing stimulation of the exhalation department and at the same time inhibition of the inhalation department. As a result, the transmission of impulses from the respiratory center to the spinal cord stops and exhalation occurs. When you exhale, the lung tissue collapses, the lung receptors are not irritated, and nerve impulses from the receptors do not enter the respiratory center. As a result, the exhalation section comes into a state of inhibition, at the same time the inhalation section is excited and inhalation occurs. Then everything repeats again. In this way, automatic self-regulation of breathing is carried out: inhalation causes exhalation, and exhalation causes inhalation.

Carbon dioxide is a specific respiratory pathogen. When carbon dioxide accumulates in the blood to a certain concentration, special receptors in the walls of blood vessels are irritated. The impulses generated in the receptors are transmitted along nerve fibers to the respiratory center (inspiratory department) and cause its excitation, which is accompanied by deepening and increased breathing. In addition, carbon dioxide also has a direct effect on the respiratory center: an increase in the concentration of carbon dioxide in the blood washing the respiratory center causes its excitation. A decrease in the concentration of carbon dioxide in the blood is accompanied, on the contrary, by a decrease in the excitability of the respiratory center (inspiratory department).

If, as a result of intense muscular work or for other reasons, an excess amount of carbon dioxide accumulates in the blood, then due to excitation of the respiratory center, breathing becomes rapid - shortness of breath occurs. As a result, carbon dioxide is quickly eliminated from the body and its content in the blood becomes normal. The respiratory rate also becomes normal. The accumulation of carbon dioxide automatically causes its rapid elimination and thereby a decrease in the excitability of the respiratory center (inhalation department).

Along with excess carbon dioxide, excitation of the respiratory center is also caused by a lack of oxygen, as well as some other substances entering the blood, in particular special medicinal substances. It should be noted that the reflex effect on the respiratory center is exerted not only by irritation of the receptors of the walls of blood vessels and the receptors of the lungs themselves, but also by other influences (for example, irritation of the nasal mucosa with ammonia, skin irritation cold water and etc.).

Breathing is subordinated to the cerebral cortex, evidence of which is that a person can voluntarily hold his breath (albeit for a very long time). a short time) or change its depth and frequency. Evidence of cortical regulation of breathing is also increased breathing during emotional states.

Breathing is associated with protective acts: coughing and sneezing. They are carried out reflexively, and the centers of these reflexes are located in the medulla oblongata.

A cough occurs in response to irritation of the mucous membrane of the larynx, pharynx or bronchi (when particles of dust, food, etc. get there). When you cough after a deep breath, air is forcefully pushed out of the respiratory tract and causes the vocal cords to move (a characteristic sound appears). What irritated you is removed along with the air Airways.

Sneezing occurs in response to irritation of the nasal mucosa according to the same principle as coughing.

Coughing and sneezing are protective breathing reflexes.

Performance evaluation criteria respiratory system .

Three types of breathing are defined: chest, abdominal (diaphragmatic) and mixed. With chest breathing, as you inhale, the collarbones rise noticeably and the ribs move. With this type of breathing, lung volume increases mainly due to the movement of the upper and lower ribs. With the abdominal type of breathing, the increase in lung volume occurs mainly due to the movement of the diaphragm - as you inhale, it goes down, slightly displacing the organs abdominal cavity. Therefore, during inhalation during abdominal breathing, the abdominal wall protrudes slightly. Athletes, as a rule, have a mixed type of breathing, where both mechanisms of increasing chest volume are involved.

Percussion(effleurage) allows you to determine the change (if any) in lung density. Changes in the lungs are usually a consequence of certain diseases (pneumonia, tuberculosis, etc.).

Auscultation(listening) determines the condition of the airways (bronchi, alveoli). With various diseases of the respiratory system, very characteristic sounds are heard - various wheezing, increased or decreased breathing noise, etc.

The study of external respiration is carried out according to indicators characterizing ventilation, gas exchange, content and partial pressure of oxygen and carbon dioxide in arterial blood and other parameters. To study the function of external respiration, spirometers, spirographs and special devices of open and closed type are used.

Respiratory system parameters.

Residual air(OV) - the volume of air remaining in the lungs that have not returned to their original position.

Breathing rate(RR) - number of breaths in 1 minute. RR is determined by spirogram or chest movement. The average respiratory rate in a healthy person is 16-18 per minute, in athletes it is 8-12. Under conditions of maximum load, the respiratory rate increases to 40-60 per minute.

Breathing depth(DO) - the volume of air during a quiet inhalation or exhalation during one respiratory cycle. The depth of breathing depends on the height, weight, gender and functional state of the athlete. In healthy individuals, DO is 300-800 ml.

Minute breathing volume(MOD) characterizes the function of external respiration.

In a calm state, the air in the trachea, bronchi, bronchioles and non-perfused alveoli does not participate in gas exchange, since it does not come into contact with the active pulmonary blood flow - this is the so-called “dead” space. The part of the tidal volume that participates in gas exchange with pulmonary blood is called the alveolar volume. From a physiological point of view, alveolar ventilation is the most essential part of external respiration, since it is the volume of air inhaled in 1 minute that exchanges gases with the blood of the pulmonary capillaries.

MOR is measured by the product of BH and DO. In healthy individuals, RR is 16-18 per minute, and DO ranges from 350-750 ml; in athletes, RR is 8-12 ml, and DO is 900-1300 ml. An increase in MOP (hyperventilation) is observed due to excitation of the respiratory center, difficulty in oxygen diffusion, etc.

At rest, MOD is 5-6 l, with intense physical activity can increase 20-25 times and reach 120-150 liters per minute or more. The increase in MOR is directly dependent on the power of the work performed, but only up to a certain point, after which the increase in load is no longer accompanied by an increase in MOR.

Even with the heaviest load, the MOP never exceeds 70-80% of the maximum ventilation level. Calculation of the proper MOD value is based on the fact that healthy individuals absorb approximately 40 ml of oxygen from each liter of ventilated air (this is the so-called oxygen utilization factor).

Ventilation equivalent(VE) is the relationship between MOD and the amount of oxygen consumption. At rest, 1 liter of oxygen in the lungs is absorbed from 20-25 liters of air. During heavy physical activity, the ventilation equivalent increases and reaches 30-35 liters. Under the influence of endurance training, the ventilatory equivalent at a standard load decreases. This indicates more economical breathing in trained individuals.

Vital capacity of the lungs(VC) consists of the tidal volume of the lungs, the inspiratory reserve volume and the expiratory reserve volume. Vital capacity depends on gender, age, body size and fitness. Vital capacity is on average 2.5-4 l in women, and 3.5-5 l in men. Under the influence of training, vital capacity increases; in well-trained athletes it reaches 8 liters.

Total lung capacity(REL) is the sum of vital capacity and residual lung volume, that is, the air that remains in the lungs after maximum exhalation and can only be determined indirectly. In young healthy people, 75-80% of the TLC is vital capacity, and the rest is the residual volume. In athletes, the proportion of vital capacity in the structure of the total capacity increases, which has a positive effect on the efficiency of ventilation.

Maximum lung ventilation(MVL) is the maximum possible amount of air that can be ventilated through the lungs per unit of time. Typically, forced breathing is carried out for 15 s and multiplied by 4. This will be the value of the MVL. Large fluctuations in MVL reduce the diagnostic value of determining the absolute value of these values. Therefore, the resulting value of MVL is brought to the proper value.

The volume of air remaining in the lungs after maximum exhalation(OO) most fully and accurately characterizes gas exchange in the lungs.

One of the main indicators of external respiration is gas exchange (analysis of respiratory gases - carbon dioxide and oxygen in the alveolar air), that is, the absorption of oxygen and the excretion of carbon dioxide. Gas exchange characterizes external respiration at the stage “alveolar air - blood of pulmonary capillaries”. It is studied by gas chromatography.

The Rosenthal functional test allows one to judge the functional capabilities of the respiratory muscles. The test is carried out on a spirometer, where the vital capacity of the subject is determined 4-5 times in a row with an interval of 10-15 s. Normally, they get the same results. A decrease in vital capacity throughout the study indicates fatigue of the respiratory muscles.

Pneumotonometric indicator(PTP, mmHg) makes it possible to assess the strength of the respiratory muscles, which is the basis of the ventilation process. PTP decreases with physical inactivity, with long breaks in training, with overwork, etc. The study is carried out using a V.I. pneumotonometer. Dubrovsky and I.I. Deryabina (1972). The subject exhales (or inhales) into the mouthpiece of the device. Normally, in healthy individuals, the average PTP in men during exhalation is 328 ± 17.4 mm Hg. Art., on inspiration - 227 ± 4.1 mm Hg. Art., in women, respectively, - 246 ± 1.8 and 200 ± 7.0 mm Hg. Art. With lung diseases, physical inactivity, and fatigue, these indicators decrease.

The Stange and Genchi tests give some idea of ​​the body's ability to withstand a lack of oxygen.

Stange test. The maximum time you hold your breath after a deep breath is measured. In this case, the mouth should be closed and the nose should be pinched with the fingers. Healthy people hold their breath for an average of 40-50 seconds; highly qualified athletes - up to 5 minutes, and female athletes - from 1.5 to 2.5 minutes.

Genchi test. After a shallow inhalation, exhale and hold your breath. In healthy people, the breath holding time is 25-30 seconds. Athletes are able to hold their breath for 60-90 seconds. With chronic fatigue, the time you hold your breath decreases sharply.

Respiration is a set of physiological processes that ensure the supply of oxygen to the body, its use by tissues and the removal of carbon dioxide from the body.

The entire process of breathing in the body can be represented as a set of sequential processes:

Exchange of air between the external environment and the alveoli of the lungs (external respiration or ventilation);

Exchange of gases between alveolar air and blood flowing through the pulmonary capillaries (diffusion of gases in the lungs);

Transport of gases by blood;

Exchange of gases between blood and tissues in tissue capillaries (diffusion of gases in tissues);

The consumption of oxygen by cells and the release of carbon dioxide by them (cellular respiration).

External breathing provided by the trachea, bronchi, bronchioles and alveoli. Gas exchange between the lungs and environment carried out by inhalation and exhalation. Inhalation and exhalation is the respiratory cycle.

Inhalation mechanism is an active process. When inhaling, the volume of the chest increases due to contraction of the muscles of the diaphragm and external intercostal muscles. When the muscles of the diaphragm contract, its dome flattens, the diaphragm lowers, displacing the abdominal organs downward. As a result of the lowering of the diaphragm, the vertical (↕) size of the thoracic cavity increases. The external intercostal muscles, contracting, increase the size of the chest in the transverse (frontal - ↔) and anteroposterior (sagittal - /) directions.

An increase in the volume of the chest, and, consequently, the lungs, leads to a drop in pressure in them, which causes atmospheric air to enter them through the respiratory tract. This is explained by the fact that air tends to move from the area high pressure to an area of ​​low pressure.

Exhalation mechanism. As soon as the inhalation is completed, the muscles of the chest relax and it returns to its normal size. At the same time, the volume of the lungs decreases, the pressure in them increases, air from the alveoli rushes out through the airways. Thus, a calm exhalation, unlike inhalation, occurs passively. During physical activity, exhalation becomes active.

The amount of air in the lungs after maximum inspiration is the total lung capacity, the value of which in an adult is 4-6 liters.

In total lung capacity there are four components:

Tidal volume;

Inspiratory reserve volume;

Expiratory reserve volume;

Residual volume.

Tidal volume(DO) is the volume of air that a person inhales and exhales during quiet breathing. In an adult, the tidal volume is approximately 400-500 ml.

Inspiratory reserve volume(ROVD) is the maximum volume of air that a person can inhale after a quiet breath. The size of the ROVD is 1.5-1.8 liters.

Expiratory reserve volume(ROvyd) is the maximum volume of air that a person can additionally exhale after a quiet exhalation. ROvyd can be equal to 1 - 1.5 liters.

Residual volume(OO) is the volume of air that remains in the lungs after maximum exhalation - 1-1.2 liters.

The sum of the tidal volume, the reserve volume of inhalation and exhalation is the vital capacity of the lungs (VC), equal to 3.5 - 5 liters.

Breathing -complex process of oxygen entering the body, using it in biological oxidation and removing carbon dioxide ,

The respiratory system includes:

Airways,

Organs of gas exchange - lungs,

The ventilation system for the lungs is the chest, respiratory muscles, respiratory center.

In humans, not only the lungs take part in breathing, but also the entire surface of the body - from the thick epithelium on the heels to the hairy scalp. The skin of the chest, back and abdomen “breathe” the most. Interestingly, in terms of breathing intensity, these areas significantly predominate over the lungs. However, the total surface of human skin is approximately 2 m2, while the surface of the lungs, if you expand 700,000,000 alveoli, is 90-100 m2 . Overall share skin accounts for less than 1% of gas exchange.

Breathing stages:

1. Pulmonary ventilation.

2. Diffusion of gases from the alveoli into the blood of the pulmonary capillaries.

3. Transport of gases by blood.

4. Diffusion of gases from the blood into the tissues.

5. Tissue or internal respiration.

The first four stages refer to external respiration, the purpose of which is to absorb O2 and remove CO2 from the body.

Pulmonary ventilation - This is the exchange of gases between atmospheric and alveolar air.

The respiratory tract consists of the nasal and oral cavity, nasopharynx, oropharynx, larynx, trachea, which in the chest cavity is divided into 2 bronchi, which, branching, form the bronchial in. Total there are 23-26 such branches. The smallest bronchi are bronchioles. At their ends, alveolar sacs are formed, which are divided into 20 cavities - alveoli with a diameter of 0.15-0.3 mm. The collection of alveoli forms the tissue of the lungs.

Functions in the lungs large system collaterals, which provides ventilation in conditions of blocking the lumen of the bronchi or other obstacles to the flow of air. It is represented by a network of additional connections between particles, segments and acini of the lungs. The basis of collateral ventilation are additional bronchioles that connect the terminal bronchioles of adjacent segments. Within one acinus, collateral ventilation is provided by bronchoalveolar communications in the walls of the alveoli. Adjacent acini are also combined with each other. In only 40% of cases, air can enter the alveoli through such messages.

The mucous membrane of the airways is covered with ciliated epithelium and has glands that secrete mucus. In addition, the mucous membrane has a dense network of blood capillaries. Therefore, the air on its way to the lungs is moistened, warmed by blood and purified by ciliated epithelium. Each lung is covered on the outside pleura, which consists of 2 leaves - parietal and visceral. Between the leaves there is a narrow sealed gap (pleural cavity), which contains a small amount of serous substance.

The alveolar wall consists of single-layer epithelium. Each alveolus is entwined with a dense network of capillaries into which the pulmonary artery branches.

Mechanism of inhalation and exhalation

The respiratory cycle consists of inhalation, exhalation and a respiratory pause. Air enters and leaves the lungs thanks to the work of the intercostal muscles and the diaphragm. As a result of their contraction and relaxation, the volume of the chest cavity changes. Intercostal muscles are divided into 2 groups: external and internal. The diaphragm consists of circular and radial muscle fibers located around the central tendon region.

Inhale - active process. The external intercostal and internal intercartilaginous muscles contract, and the internal intercostal muscles relax. The ribs move forward, moving away from the spine. At the same time, the diaphragm contracts, becomes flatter, and its dome lowers. All this leads to an increase in the volume of the chest cavity. As a result, the pressure in the pleural cavity becomes below atmospheric. The lungs stretch and the pressure in them also becomes lower than atmospheric. Air enters (sucks in) into the lungs and fills the alveoli until the pressure in the lungs is equal to atmospheric pressure, there is a pause between inhalation and exhalation. (Fig. 8.1).

Pressure (in mm Hg. Art.) In the pleural cavity (relative to atmospheric) at the height of quiet inspiration is -9 ...- 6, at the height of deep inspiration - -30 ...- 10, at the height of quiet exhalation - 5, 5- 3.5, at the height of deep exhalation - -3 ...- 1.5.

If the tightness of the pleural cavity is broken, air enters it (pneumothorax), the pressure of the pleural cavity increases and equalizes With atmospheric (becomes equal to 0), the lungs come in and ventilation stops .

Forced inhalation is ensured by the contraction of additional muscles: scalene, december, serratus anterior, trapezius, rhomboid.

Exhalation can be passive, in which it occurs under the influence of elastic traction of the lung tissue and with relaxation of the respiratory muscles that provide inhalation. The volume of the chest cavity changes -

Rice. 8.1. Alveolar ventilation mechanism

As a result, the pressure in the pleural fissure increases and, together with the elastic traction, becomes higher. Intrapulmonary pressure. The alveoli are compressed, the pressure in them becomes greater than atmospheric pressure and air is pushed out of the lungs (see Fig. 8.1). It is convenient to consider the mechanism of inhalation and exhalation using the Donders model, in which the chest and diaphragm are simulated.

Active exhalation is ensured by contraction of the abdominal wall muscles: oblique, transverse, rectus. Elasticity is the ability of the lungs to stretch. The elasticity of the lungs depends significantly on the surface tension of the film of fluid covering the wall of the alveoli. As the volume of the alveoli decreases, surface tension decreases due to the presence surfactant(substance of lipid nature) V liquid covering the surface of the alveoli (Table 8.1). If surface tension did not decrease during exhalation, the alveoli would collapse. Surfactants are produced by type II alveocytes. Surfactant plays an important role during human birth, protecting the lungs from re-collapse. Surfactant deficiency is an important cause respiratory distress syndrome of newborns (hyaline membrane disease) - severe lung disease arising V babies born before their surfactant system began to function. A decrease in surfactant was detected in smokers.

Table 8.1. importance of surfactants

Reduce surface tension in the alveoli,

They create the possibility of expansion of the lung during the first breath of the newborn, prevent the decrease of terminal bronchioles,

Prevents overstretching of the alveoli,

Anti-edematous effect, antioxidant effect,

Provide up to 2/3 of the elastic resistance of adult lung tissues and stability of the structure of the respiratory zone,

Regulate the absorption rate 0, at the gas-liquid phase boundary,

Regulate the intensity of water evaporation from the alveolar surface (regulation of water balance),

They have a bacteriostatic effect, opsonize bacteria,

They cleanse the surface of the alveoli from foreign particles that have entered the lungs.

Act inhalation(inspiration) occurs due to an increase in the volume of the thoracic cavity in three directions - vertical, sagittal and frontal. This occurs due to the raising of the ribs and the lowering of the diaphragm ( rice. 49).

The ribs are connected to the sternum by cartilage, and they are articulated with the spine at two points: the head of the rib is with the vertebral body, and the tubercle of the rib is with the lateral process of the vertebra. In a state of exhalation, the ribs are lowered down; able inhalation the ribs take a more horizontal position, rising upward. In this case, the lower end of the sternum moves forward, due to which the cross-section of the chest becomes larger both transversely and vertically.
longitudinal direction.

Raising the ribs occurs as a result of contraction of the external intercostal (mm. intercostales extcrni) and intercartilaginous (mm. Intercartilagihci) muscles. The external intercostal muscles run from rib to rib in an oblique direction: behind and above, forward and down.

During inhalation, the muscle fibers of the diaphragm contract, causing the dome of the diaphragm to become flatter and lower; the abdominal viscera are pushed down, to the sides and forward; the volume of the chest cavity increases, especially in the vertical direction. Electrophysiological studies of various respiratory muscles have shown that bioelectrical oscillations (action potentials) arise first in the diaphragm, then in the intercostal muscles.

In the first months after birth, breathing movements are carried out mainly due to contraction of the diaphragm. Therefore, if a kitten’s diaphragm is paralyzed by cutting the nn. phrenici, then he dies.

In different people, depending on age and gender, clothing and working conditions, breathing occurs either predominantly through the intercostal muscles - costal, or thoracic, type of breathing, or predominantly through the diaphragm - diaphragmatic, or abdominal, type of breathing.

The type of breathing is not strictly constant and can adapt to the conditions of a given moment. Thus, when carrying large loads on the back, the chest serves as a support for the load, and therefore is fixed motionless by the muscles of the trunk and intercostal spaces along with the spine; breathing occurs solely through the movements of the diaphragm. In pregnant women, the downward displacement of the diaphragm is difficult and therefore the costal type of breathing predominates.

With forced, i.e., increased breathing, for example during shortness of breath, a number of additional or auxiliary respiratory muscles are involved in the act of inhalation: the levator upper ribs (mm. sternocleidomasto-idei, mm. scalcni) and the fixing of the shoulder girdle with the shoulders thrown back (mm . trapecii, mm. rhomboidci, mm. levatores scapulae).

Accessory respiratory muscles include: mm. pectorales major, et minor., mm. serrati anter., which can also raise the ribs.