Non-respiratory functions of the lungs. Respiratory system defense mechanisms

The airways are divided into upper and lower ones. The upper ones include the nasal passages, nasopharynx, the lower larynx, trachea, bronchi. The trachea, bronchi and bronchioles are the conductive zone of the lungs. The terminal bronchioles are called the transition zone. They have a small number of alveoli, which make a small contribution to gas exchange. Alveolar passages and alveolar sacs belong to the exchange zone.

Physiological is nasal breathing... When cold air is inhaled, there is a reflex expansion of the vessels of the nasal mucosa and a narrowing of the nasal passages. This contributes to better heating of the air. Its moistening occurs due to the moisture secreted by the glandular cells of the mucous membrane, as well as tear moisture and water filtering through the wall of the capillaries. Air purification in the nasal passages occurs due to the deposition of dust particles on the mucous membrane.

In the airways, protective respiratory reflexes arise. When air containing irritating substances is inhaled, there is a reflex decrease and a decrease in the depth of breathing. At the same time, the glottis narrows and the smooth muscles of the bronchi contract. When irritating the irritant receptors of the epithelium of the mucous membrane of the larynx, trachea, bronchi, impulses from them come along the afferent fibers of the upper laryngeal, trigeminal and vagus nerves to the inspiratory neurons of the respiratory center. Take a deep breath. Then the muscles of the larynx contract and the glottis is closed. Expiratory neurons are activated and exhalation begins. And since the glottis is closed, the pressure in the lungs increases. At a certain moment, the glottis opens and air with high speed comes out of the lungs. There is a cough. All these processes are coordinated by the medulla oblongata cough center. When dust particles and irritants are exposed to the sensitive endings of the trigeminal nerve, which are located in the nasal mucosa, sneezing occurs. Sneezing also initially activates the inspiratory center. Then there is a forced exhalation through the nose.

Distinguish between anatomical, functional and alveolar dead space. Anatomical is the volume of the airways - nasopharynx, larynx, trachea, bronchi, bronchioles. There is no gas exchange in it. The alveolar dead space refers to the volume of the alveoli that are not ventilated or there is no blood flow in their capillaries. Therefore, they also do not participate in gas exchange. The functional dead space is the sum of the anatomical and alveolar. Have healthy person the volume of alveolar dead space is very small. Therefore, the size of the anatomical and functional spaces is practically the same and amounts to about 30% of the tidal volume. On average 140 ml. In case of impaired ventilation and blood supply to the lungs, the volume of functional dead space is much larger than the anatomical one. At the same time, the anatomical dead space plays an important role in the breathing process. The air in it is warmed, humidified, cleaned of dust and microorganisms. Respiratory protective reflexes are formed here - coughing, sneezing. In it, smells are perceived and sounds are formed.

Sneezing- This is an unconditional reflex, with the help of which dust, foreign particles, mucus, vapors of caustic chemicals, etc. are removed from the nasal cavity. Due to this, the body prevents them from entering other respiratory tract. The receptors for this reflex are located in the nasal cavity, and its center is in the medulla oblongata. Sneezing can also be a symptom infectious disease accompanied by a runny nose. With a stream of air from the nose during cheeking, many viruses and bacteria are thrown out. This frees the body from infectious agents, but promotes the spread of infection. So, when you sneeze, be sure to cover your nose with a handkerchief.

Cough Is also a protective unconditioned reflex aimed at removal through oral cavity dust, foreign particles, if they get into the larynx, pharynx, trachea or bronchi, sputum, which is formed during inflammation respiratory tract... Sensitive receptors for cough are found in the mucous membrane of the respiratory tract. Its center is in the medulla oblongata. Material from the site

In smokers, the protective cough reflex is first intensified through irritation of its receptors with tobacco smoke. Therefore, they are constantly coughing. However, after a while, these receptors die along with the ciliary and secretory cells. The cough disappears, and the phlegm, continuously formed in smokers, is retained in the airways, deprived of protection. This leads to severe inflammatory lesions throughout respiratory system... Arises Chronical bronchitis smoker. A person who smokes snores loudly during sleep due to the accumulation of mucus in the bronchi.

On this page material on topics:

• Respiratory volume Respiratory center Respiratory protective reflexes briefly

• Reflexes of sneezing and coughing

• Sneezed and sputum got into the respiratory tract

• Protective breathing reflexes sneezing and coughing

Questions about this material:

Breathing reflexes

Important biological significance, especially in connection with the deterioration of environmental conditions and atmospheric pollution, have protective respiratory reflexes - sneezing and coughing... Sneezing - irritation of the receptors of the nasal mucosa, for example, dust particles or gaseous drugs, tobacco smoke, water causes narrowing of the bronchi, bradycardia, cardiac output, narrowing of the lumen of the vessels of the skin and muscles. Various chemical and mechanical irritation of the nasal mucosa cause a deep strong exhalation - sneezing, which contributes to the desire to get rid of the irritant. The afferent pathway of this reflex is the trigeminal nerve. Cough - occurs when the mechano- and chemoreceptors of the pharynx, larynx, trachea and bronchi are irritated. In this case, after inhalation, the expiratory muscles are strongly contracted, the intrathoracic and intrapulmonary pressure rises sharply, the glottis opens and air from the respiratory tract is released outward under high pressure and removes the irritating agent. The cough reflex is the main pulmonary reflex of the vagus nerve.

Respiratory center of the medulla oblongata

Respiratory center, a set of several groups of nerve cells (neurons) located in different parts of the central nervous system, mainly in the reticular formation of the medulla oblongata. The constant coordinated rhythmic activity of these neurons ensures the emergence of respiratory movements and their regulation in accordance with the changes occurring in the body. Impulses from D. c. enter the motor neurons of the anterior horns of the cervical and thoracic spinal cord, from which excitement is transmitted to the respiratory muscles. D.'s activity c. it is regulated humorally, that is, by the composition of the blood and tissue fluid that washes it, and reflexively, in response to impulses coming from receptors in the respiratory, cardiovascular, motor and other systems, as well as from the higher parts of the central nervous system. Consists of the center of inhalation and the center of exhalation.

The respiratory center consists of nerve cells (respiratory neurons), which are characterized by periodic electrical activity in one of the phases of respiration. The neurons of the respiratory center are localized bilaterally in medulla oblongata in the form of two elongated pillars near obex - the point where the central canal of the spinal cord flows into the fourth ventricle. These two formations of respiratory neurons, in accordance with their position relative to the dorsal and ventral surfaces of the medulla oblongata, are designated as dorsal and ventral respiratory groups

The dorsal respiratory group of neurons forms the ventrolateral part of the nucleus of the solitary tract. Respiratory neurons of the ventral respiratory group are located in the n region. ambiguus caudal to obex, n. retroambigualis directly rostral to obex and are represented by the Betzinger complex, which is located directly near n. retrofacialis of the ventrolateral parts of the medulla oblongata. The respiratory center includes neurons of the motor nuclei of the cranial nerves (mutual nucleus, the nucleus of the hypoglossal nerve), which innervate the muscles of the larynx and pharynx.

Interaction of neurons in the inspiratory and expiratory zones

Respiratory neurons, the activity of which causes inspiration or expiration, are called, respectively, inspiratory or expiratory. There is a reciprocal relationship between the groups of neurons that control inhalation and exhalation. Excitation of the expiratory center is accompanied by inhibition in the inspiratory center and vice versa. Inspiratory and expiratory neurons, in turn, are divided into "early" and "late". Each respiratory cycle begins with the activation of "early" inspiratory neurons, then the "late" inspiratory neurons are excited. Also, expiratory neurons are sequentially excited, which inhibit the inspiratory neurons and stop inhalation. Modern researchers have shown that there is no clear division into the inspiratory and expiratory sections, but there are clusters of respiratory neurons with a specific function.

The concept of the auto-rhythm of breathing. The effect of blood ph on the respiration process.

If pH decreases arterial blood compared with the normal level of 7.4, ventilation is increased. As the pH rises above the norm, ventilation decreases, although to a somewhat lesser extent.

Autorhythmia- these are waves of excitement and the corresponding "movements" of the animal, occurring with a certain frequency. autorhythmia is a spontaneous activity of the central nervous system, which is carried out without any effect of afferent stimulation and manifests itself in rhythmic and coordinated movements of the body.

Pneumotoxic center of Varoliev's mot. Interaction with the respiratory center of the medulla oblongata

In the pons varoli are the nuclei of the respiratory neurons that form the pneumotaxic center. It is believed that the respiratory neurons of the pons participate in the mechanism of the change of inhalation and exhalation and regulate the value of the tidal volume. Respiratory neurons of the medulla oblongata and pons varoli are connected by ascending and descending nerve pathways and function in concert. Having received impulses from the inspiratory center of the medulla oblongata, the pneumotaxic center also sends them to the expiratory center of the medulla oblongata, exciting the latter. Inspiratory neurons are inhibited. The destruction of the brain between the medulla oblongata and the bridge lengthens the inspiratory phase.

Spinal cord; motor neurons of the nuclei of the intercostal nerves and the nucleus of the phrenic nerve, interaction with the respiratory center of the medulla oblongata. In the anterior horns of the spinal cord, at the level - motor neurons are located, which form the phrenic nerve. Phrenic nerve - mixed nerve, which carries out the sensitive innervation of the pleura and pericardium, is part of the cervical plexus; formed by the anterior branches of the C3-C5 nerves. Departs on both sides of the neck from the cervical plexus of the third, fourth (and sometimes fifth) cervical spinal nerves and goes down to the diaphragm, passing between the lungs and the heart (between the mediastinal pleura and the pericardium). The impulses passing along these nerves from the brain cause periodic contractions of the diaphragm during breathing.

The motor neurons innervating the intercostal muscles are located in the anterior horns at the levels - (- - motor neurons of the inspiratory muscles, - - expiratory). The motor branches of the intercostal nerves innervate the autochthonous (inspiratory) muscles of the chest and abdominal muscles. It has been established that some regulate mainly the respiratory, while others regulate the poznotonic activity of the intercostal muscles.

Role of the bark large hemispheres in the regulation of breathing. Certain zones of the cerebral cortex carry out arbitrary regulation of respiration in accordance with the peculiarities of the influence of environmental factors on the body and the homeostatic shifts associated with this.

In addition to the respiratory center located in the brainstem, the state of the respiratory function is also influenced by the cortical zones, providing its arbitrary regulation. They are located in the cortex of the somatomotor divisions and mediobasal structures of the brain. It is believed that the motor and premotor areas of the cortex, at the will of a person, facilitate and activate respiration, and the cortex of the mediobasal parts of the cerebral hemispheres inhibits, restrains respiratory movements, affecting the state emotional sphere, as well as the degree of balance vegetative functions... These parts of the cerebral cortex also affect the adaptation of the respiratory function to complex movements associated with behavioral responses, and adapt respiration to the current expected metabolic shifts.

Regulation blood pressure, blood flow

In the ventrolateral parts of the medulla oblongata, formations are concentrated, corresponding in their characteristics to those ideas that are put into the concept of "vasomotor center". Here are concentrated nerve elements that play a key role in tonic and reflex regulation of blood circulation. In the ventral regions of the medulla oblongata, neurons are located, a change in the tonic activity of which leads to the activation of sympathetic preganglionic neurons. The structures of these parts of the brain control the release of vasopressin by the cells of the supraoptic and paraventricular nuclei of the hypothalamus.

The projections of the neurons of the caudal part of the ventral parts of the medulla oblongata to the cells of its rostral part have been proved, which indicates the possibility of tonic inhibition of the activity of these cells. The connections between the structures of the ventral regions of the medulla oblongata and the nucleus of the solitary tract, which plays a key role in the processing of afferentation from the vascular chemo- and baroreceptors, are functionally significant.

In the medulla oblongata, there are nerve centers that inhibit the activity of the heart (nucleus of the vagus nerve). In the reticular formation of the medulla oblongata there is a vasomotor center, consisting of two zones: pressor and depressor. Excitation of the pressor zone leads to vasoconstriction, and excitation of the depressor zone leads to their expansion. The vasomotor center and the nucleus of the vagus nerve constantly send impulses, thanks to which a constant tone is maintained: the arteries and arterioles are constantly somewhat narrowed, and the cardiac activity is slowed down.

VF Ovsyannikov (1871) found that the nerve center providing a certain degree of narrowing of the arterial bed - the vasomotor center - is located in the medulla oblongata. The localization of this center is determined by transection of the brainstem at different levels. If the transection is performed in a dog or cat above the quadruple, then the blood pressure does not change. If you cut the brain between the medulla oblongata and the spinal cord, then the maximum blood pressure in carotid artery decreases to 60-70 mm Hg. From this it follows that the vasomotor center is localized in the medulla oblongata and is in a state of tonic activity, i.e., prolonged constant excitation. Elimination of its influence causes vasodilation and a drop in blood pressure.

A more detailed analysis showed that the vasomotor center of the medulla oblongata is located at the bottom of the IV ventricle and consists of two sections - pressor and depressor. Irritation of the pressor section of the vasomotor center causes narrowing of the arteries and lifting, and irritation of the second - expansion of the arteries and a drop in blood pressure.

It is believed that the depressor section of the vasomotor center causes vasodilatation, lowering the tone of the pressor section and thus reducing the effect of the vasoconstrictor nerves.

The influences coming from the vasoconstrictor center of the medulla oblongata come to the nerve centers of the sympathetic part of the autonomic nervous system, located in the lateral horns of the thoracic segments of the spinal cord, which regulate the vascular tone of certain parts of the body. The spinal centers are able, some time after turning off the vasoconstrictor center of the medulla oblongata, to slightly increase the blood pressure, which has decreased due to the expansion of the arteries and arterioles.

In addition to the vasomotor centers of the medulla oblongata and spinal cord, the state of the vessels is influenced by the nerve centers of the diencephalon and cerebral hemispheres.

Hypothalamic regulation of visceral functions

If stimulated with an electric shock different zones hypothalamus, it is possible to cause both vasoconstriction and vasodilation. The pulse is transmitted along the fibers of the posterior longitudinal beam. Some of the fibers pass through the regions, do not switch, and go to the vasomotor neurons. Information comes from osmoreceptors, they capture the state of the water inside and outside the cell contained in the hypothalamus. Osmoreceptor activation causes hormonal effect- the release of vasopressin, and this substance has a strong vasoconstrictor effect, it has a retention property.

NES (neuroendocrine regulation) is of particular importance in the regulation of visceral (“related to internal organs”) functions of the body. It has been established that the efferent effects of the central nervous system on visceral functions are realized in normal and pathological conditions by both autonomic and endocrine apparatus (Speckmann, 1985). In contrast to the cortex, the hypothalamus is obviously constantly involved in the control of the work of the visceral systems of the body. Ensures the consistency of the internal environment. Control over the action of the sympathetic and parasympathetic systems that innervate internal organs, vessels, smooth muscles, glands of internal and external secretion, is carried out by the “visceral brain”, which is represented by the central vegetative apparatus (vegetative nuclei) of the hypothalamic region (OG Gazenko et al., 1987). In turn, the hypothalamus is under

control of certain areas of the cortex (in particular, the limbic) of the cerebral hemispheres.

The coordination of the activity of all three parts of the autonomic nervous system is carried out by segmental and suprasegmental centers (apparatuses) with the participation of the cortex large brain... In the complexly organized part of the diencephalon - the hypothalamic region, there are nuclei that are directly related to the regulation of visceral functions.

Chemo and baroreceptors blood vessels

Afferent impulses from baroreceptors go to the vasomotor center of the medulla oblongata. These impulses have an inhibitory effect on the sympathetic centers and an exciting effect on the parasympathetic. As a result, the tone of sympathetic vasoconstrictor fibers (or the so-called vasomotor tone) decreases, as well as the frequency and strength of heart contractions. Since impulses from baroreceptors are observed in a wide range of values blood pressure, their inhibitory effects are manifested even at "normal" pressure. In other words, baroreceptors have a permanent depressant effect. With an increase in pressure, the impulse from the baroreceptors increases, and the vasomotor center is inhibited more strongly; this leads to even greater vasodilation, and the vessels in different areas expand to varying degrees. With a drop in pressure, impulses from baroreceptors decrease and develop reverse processes, leading, ultimately, to an increase in pressure. Excitation of chemoreceptors leads to a decrease in the frequency of cardiac contractions and vasoconstriction as a result of direct action on the circulatory centers of the medulla oblongata. In this case, the effects associated with vasoconstriction prevail over the effects of a decrease in cardiac output, and as a result, blood pressure rises.

baroreceptors are located in the walls of arteries. An increase in blood pressure leads to stretching of the baroreceptors, signals from which enter the central nervous system... The feedback signals are then directed to the centers of the autonomic nervous system, and from them to the vessels. As a result, the pressure drops to normal level... Baroreceptors respond extremely quickly to changes in blood pressure.

Chemoreceptors are sensitive to blood chemicals. arterial chemoreceptors respond to changes in the concentration in the blood of oxygen, carbon dioxide, hydrogen ions, nutrients and hormones, levels osmotic pressure; thanks to chemoreceptors, homeostasis is maintained.

Reflex influences have a pronounced effect on the activity of the neurons of the respiratory center. Distinguish between permanent and non-permanent (episodic) reflex influences on the respiratory center.

Constant reflex influences arise as a result of irritation of the receptors of the alveoli (Hering-Breuer reflex), the root of the lung and pleura (pulmothoracic reflex), chemoreceptors of the aortic arch and carotid sinuses (Gaimans reflex), mechanoreceptors of the indicated vascular regions, proprioreceptors of the respiratory muscles.

The most important reflex in this group is the Hering-Breuer reflex. The alveoli of the lungs contain mechanoreceptors for stretching and collapse, which are sensitive nerve endings of the vagus nerve. Stretch receptors are excited during normal and maximum inhalation, that is, any increase in the volume of the pulmonary alveoli excites these receptors. Collapse receptors become active only under pathological conditions (with the maximum collapse of the alveoli).

In experiments on animals, it was found that with an increase in the volume of the lungs (blowing air into the lungs), reflex exhalation is observed, while pumping out air from the lungs leads to a rapid reflex inhalation. These reactions did not occur when the vagus nerves were transected. Consequently, nerve impulses enter the central nervous system through the vagus nerves.

The Hering-Breuer reflex refers to self-regulation mechanisms respiratory process, providing a change in the acts of inhalation and exhalation. When the alveoli are stretched during inhalation, nerve impulses from stretch receptors along vagus nerve go to expiratory neurons, which, when excited, inhibit the activity of inspiratory neurons, which leads to passive exhalation. The pulmonary alveoli collapse, and nerve impulses from the stretch receptors no longer reach the expiratory neurons. Their activity decreases, which creates conditions for increasing the excitability of the inspiratory part of the respiratory center and active inhalation. In addition, the activity of inspiratory neurons increases with an increase in the concentration of carbon dioxide in the blood, which also contributes to the implementation of the act of inhalation.

Thus, self-regulation of respiration is carried out on the basis of the interaction of the nervous and humoral mechanisms of regulation of the activity of the neurons of the respiratory center.

The pulmothoracic reflex occurs when the receptors embedded in lung tissue and pleura. This reflex manifests itself when the lungs and pleura are stretched. The reflex arc closes at the level of the cervical and thoracic segments of the spinal cord. The end effect of the reflex is a change in tone respiratory muscles, due to which there is an increase or decrease in the average volume of the lungs.

Nerve impulses from the proprioceptors of the respiratory muscles constantly go to the respiratory center. During inhalation, the proprioceptors of the respiratory muscles are excited and nerve impulses from them are sent to the inspiratory neurons of the respiratory center. Under influence nerve impulses the activity of inspiratory neurons is inhibited, which contributes to the onset of exhalation.

Intermittent reflex influences on the activity of respiratory neurons are associated with the excitation of extero- and interoreceptors of various functions.

Intermittent reflex influences that affect the activity of the respiratory center include reflexes that arise when the receptors of the mucous membrane of the upper respiratory tract, nose, nasopharynx, temperature and pain receptors of the skin, proprioceptors of skeletal muscles, interoreceptors are irritated. So, for example, with sudden inhalation of vapors of ammonia, chlorine, sulfur dioxide, tobacco smoke and some other substances, irritation of the receptors of the mucous membrane of the nose, pharynx, larynx occurs, which leads to reflex spasm of the glottis, and sometimes even the muscles of the bronchi and reflex holding of breath.

When the epithelium of the respiratory tract is irritated by accumulated dust, mucus, as well as trapped chemical irritants and foreign bodies, sneezing and coughing are observed. Sneezing occurs when the receptors of the nasal mucosa are irritated, and coughing occurs when the receptors of the larynx, trachea, and bronchi are excited.

Coughing and sneezing begins with a deep breath, which occurs reflexively. Then there is a spasm of the glottis and at the same time an active exhalation. As a result, the pressure in the alveoli and airways increases significantly. The subsequent opening of the glottis leads to the release of air from the lungs by a push into the airways and out through the nose (when sneezing) or through the mouth (when coughing). Dust, slime, foreign bodies are carried away by this stream of air and are thrown out of the lungs and respiratory tract.

Coughing and sneezing under normal conditions are classified as protective reflexes. These reflexes are called defensive reflexes because they prevent harmful substances into the respiratory tract or facilitate their removal.

Irritation of temperature receptors of the skin, in particular cold ones, leads to reflex holding of breath. Excitation of skin pain receptors, as a rule, is accompanied by increased respiratory movements.

Excitation of skeletal muscle proprioceptors causes stimulation of the act of respiration. In this case, the increased activity of the respiratory center is an important adaptive mechanism that ensures the increased needs of the body for oxygen during muscular work.

Irritation of interoreceptors, for example, mechano-receptors of the stomach during its stretching, leads to inhibition of not only cardiac activity, but also respiratory movements.

When the mechanoreceptors of the vascular reflexogenic zones (aortic arch, carotid sinuses) are excited, changes in the activity of the respiratory center are observed as a result of changes in blood pressure. So, an increase in blood pressure is accompanied by a reflex holding of breath, a decrease leads to the stimulation of respiratory movements.

Thus, the neurons of the respiratory center are extremely sensitive to influences that cause the excitation of extero-, proprio- and interoreceptors, which leads to a change in the depth and rhythm of respiratory movements in accordance with the conditions of the organism's vital activity.

The activity of the respiratory center is influenced by the cerebral cortex. The regulation of respiration by the cerebral cortex has its own qualitative features. In experiments with direct stimulation of individual areas of the cerebral cortex by electric current, a pronounced effect of it on the depth and frequency of respiratory movements was shown. The results of the research of M.V. Sergievsky and his collaborators, obtained with direct stimulation of various parts of the cerebral cortex with electric current in acute, semi-chronic and chronic experiments (implanted electrodes), indicate that the neurons of the cortex do not always have an unambiguous effect on respiration. The final effect depends on a number of factors, mainly on the strength, duration and frequency of the applied stimuli, functional state cerebral cortex and respiratory center.

Important facts were established by E. A. Hasratyan and his collaborators. It was found that animals with removed cerebral cortex lacked adaptive responses external respiration on changes in living conditions. Thus, muscle activity in such animals was not accompanied by stimulation of respiratory movements, but led to prolonged dyspnea and discoordination of respiration.

To assess the role of the cerebral cortex in the regulation of respiration great importance have data obtained using the conditioned reflex method. If the sound of the metronome in humans or animals is accompanied by the inhalation of a gas mixture with an increased content of carbon dioxide, this will lead to an increase in pulmonary ventilation. After 10 ... 15 combinations, the isolated activation of the metronome (conditioned signal) will stimulate respiratory movements - a conditioned respiratory reflex to the selected number of beats of the metronome per unit of time is formed.

The increase and deepening of breathing, which occurs before the start of physical work or sports, are also carried out according to the mechanism of conditioned reflexes. These changes in respiratory movements reflect shifts in the activity of the respiratory center and have an adaptive value, helping to prepare the body for work that requires a lot of energy consumption and intensification of oxidative processes.

According to M.E. Marshak, cortical: regulation of respiration provides the necessary level of pulmonary ventilation, the rate and rhythm of respiration, the constancy of the level of carbon dioxide in the alveolar air and arterial blood.

Breathing adaptation to external environment and the shifts observed in the internal environment of the body is associated with extensive neural information entering the respiratory center, which is pre-processed, mainly in the neurons of the brain pons (pons varoli), midbrain and diencephalon, and in the cells of the cerebral cortex.

Thus, the regulation of the activity of the respiratory center is complex. According to M.V. Sergievsky, it consists of three levels.

The first level of regulation is represented by the spinal cord. The centers of the phrenic and intercostal nerves are located here. These centers cause contraction of the respiratory muscles. However, this level of respiration regulation cannot provide a rhythmic change in the phases of the respiratory cycle, since a huge number of afferent impulses from the respiratory apparatus, bypassing spinal cord, is sent directly to the medulla oblongata.

The second level of regulation is associated with the functional activity of the medulla oblongata. Here is the respiratory center, which perceives a variety of afferent impulses coming from the respiratory apparatus, as well as from the main reflexogenic vascular zones. This level of regulation provides a rhythmic change in the phases of respiration and the activity of spinal motoneurons, the axons of which innervate the respiratory muscles.

The third level of regulation is the upper parts of the brain, which also include cortical neurons. Only in the presence of the cerebral cortex is it possible to adequately adapt the reactions of the respiratory system to the changing conditions of the organism's existence.

Depending on the state of the body (sleep, physical work, temperature changes, etc.), the frequency and depth of breathing reflexively change. The arcs of the respiratory reflexes pass through the respiratory center. Consider reflexes like sneezing and coughing.

Dust or substances with a strong odor getting into nasal cavity, irritate receptors located in its mucous membrane. A protective reflex arises - sneezing - a strong and quick reflex exhalation through the nostrils. Thanks to him, irritating substances are removed from the nasal cavity. The mucus accumulated in the nasal cavity with a cold causes the same reaction. A cough is a sharp reflex exhalation through the mouth that occurs when the larynx is irritated.

Gas exchange in tissues... In the organs of our body, oxidative processes are constantly taking place, for which oxygen is consumed. Therefore, the concentration of oxygen in arterial blood, which enters the tissue through the vessels large circle blood circulation, more than in interstitial fluid. As a result, oxygen freely passes from the blood into the tissue fluid and into the tissues. Carbon dioxide, which is formed in the course of numerous chemical transformations, on the contrary, passes from tissues to tissue fluid, and from it to blood. Thus, the blood is saturated with carbon dioxide.

Respiration regulation. The respiratory center controls the activity of the respiratory system. It is located in the medulla oblongata. The impulses coming from here coordinate muscle contractions during inhalation and exhalation. From this center, impulses are sent along the nerve fibers through the spinal cord, which cause, in a certain order, the muscles responsible for inhaling and exhaling.

The excitation of the center itself depends on excitations coming from various receptors, and on chemical composition blood. So, jump into cold water or douche cold water causes a deep breath and holding the breath. Pungently odorous substances can also cause breath holding. This is because the smell irritates the olfactory receptors in the walls of the nasal cavity. Excitation is transmitted to the respiratory center, and its activity is inhibited. All these processes are carried out reflexively.

Weak irritation of the mucous membrane of the nasal cavity causes sneezing, and of the larynx, trachea, bronchi - coughing. This defensive reaction organism. When sneezing, coughing, foreign particles trapped in the respiratory tract are removed from the body.