Topic: Nervous regulation of the respiratory system. Respiratory center, regulation of breathing
The rhythmic sequence of inhalation and exhalation, as well as changes in the nature of respiratory movements depending on the state of the body (rest, work of varying intensity, emotional manifestations etc.) are regulated by the respiratory center located in the medulla oblongata. The respiratory center is a set of neurons that ensure the activity of the respiratory apparatus and its adaptation to changing conditions of external and internal environment.
The studies of Russian physiologist N.A. were of decisive importance in determining the localization of the respiratory center and its activity. Mislavsky, who in 1885 showed that the respiratory center in mammals is located in the oblong pulp, at the bottom of the fourth ventricle in the reticular formation. The respiratory center is a paired, symmetrically located formation, which includes inhalation and exhalation parts.
Research results by N.A. Mislavsky formed the basis of modern ideas about the localization, structure and function of the respiratory center. They were confirmed in experiments using microelectrode technology and the removal of biopotentials from various structures of the medulla oblongata. It has been shown that in the respiratory center there are two groups of neurons: inspiratory and expiratory. Some peculiarities in the functioning of the respiratory center have been discovered. At calm breathing Only a small part of the respiratory neurons are active, and therefore there is a reserve of neurons in the respiratory center that is used for increased need body in oxygen. It has been established that there are functional relationships between the inspiratory and expiratory neurons of the respiratory center. They are expressed in the fact that when the inspiratory neurons that provide inspiration are excited, the activity of the expiratory neurons nerve cells inhibited, and vice versa. Thus, one of the reasons for the rhythmic, automatic activity of the respiratory center is the interconnected functional relationships between these groups of neurons. There are other ideas about the localization and organization of the respiratory center, which are supported by a number of Soviet and foreign physiologists. It is believed that the centers of inhalation, exhalation and convulsive breathing are localized in the medulla oblongata. In the upper part of the cerebral pons (pons) there is a pneumotaxic center, which controls the activity of the lower inhalation and exhalation centers and ensures the correct alternation of cycles breathing movements.
The respiratory center, located in the medulla oblongata, sends impulses to the motor neurons of the spinal cord that innervate the respiratory muscles. The diaphragm is innervated by axons of motor neurons located at the level of the III-IV cervical segments of the spinal cord. Motor neurons, the processes of which form the intercostal nerves innervating the intercostal muscles, are located in the anterior horns (III-XII) of the thoracic segments of the spinal cord.
Regulation of the activity of the respiratory center
Regulation of the activity of the respiratory center is carried out with the help of humoral, reflex mechanisms and nerve impulses coming from the overlying parts of the brain.
Humoral mechanisms. A specific regulator of the activity of neurons in the respiratory center is carbon dioxide, which acts on respiratory neurons directly and indirectly. In the neurons of the respiratory center, during their activity, metabolic products (metabolites) are formed, including carbon dioxide, which has a direct effect on inspiratory nerve cells, exciting them. In the reticular formation of the medulla oblongata, near the respiratory center, chemoreceptors sensitive to carbon dioxide were found. As the voltage increases carbon dioxide in the blood, chemoreceptors are excited, and nerve impulses travel to inspiratory neurons, which leads to an increase in their activity. In the laboratory of M.V. Sergievsky obtained data that carbon dioxide increases the excitability of neurons in the cerebral cortex. In turn, the cells of the cerebral cortex stimulate the activity of neurons in the respiratory center. In the mechanism of the stimulating effect of carbon dioxide on the respiratory center important place belongs to chemoreceptors vascular bed. In the area of the carotid sinuses and aortic arch, chemoreceptors were found that are sensitive to changes in the tension of carbon dioxide and oxygen in the blood.
The experiment showed that washing the carotid sinus or aortic arch, isolated humorally, but with preserved nerve connections, a liquid with a high content of carbon dioxide is accompanied by stimulation of respiration (Heymans reflex). In similar experiments, it was found that an increase in oxygen tension in the blood inhibits the activity of the respiratory center.
Mechanism of influence of carbon dioxide on the activity of neurons in the respiratory center is complex. Carbon dioxide has direct action on respiratory neurons, indirectly (excitation of cells of the cerebral cortex, neurons of the reticular formation), as well as reflex due to irritation of special chemoreceptors of the vascular bed. Consequently, depending on the gas composition of the internal environment of the body, the activity of the neurons of the respiratory center changes, which is reflected in the nature of respiratory movements. With optimal levels of carbon dioxide and oxygen in the blood, respiratory movements are observed, reflecting moderate degree excitation of neurons of the respiratory center. These breathing movements of the chest are called eipnea.
Excessive carbon dioxide and lack of oxygen in the blood increase the activity of the respiratory center, which causes frequent and deep respiratory movements - hyperpnea. An even greater increase in the amount of carbon dioxide in the blood leads to disruption of the breathing rhythm and the appearance of shortness of breath - dyspnea. A decrease in the concentration of carbon dioxide and excess oxygen in the blood inhibit the activity of the respiratory center. In this case, breathing becomes shallow, rare, and may stop breathing - apnea.
Periodic breathing is a type of breathing in which a series of respiratory movements alternate with pauses. The duration of pauses ranges from 5 to 20 s or even more. At periodic breathing Cheyne-Stokes type after a pause, weak respiratory movements appear, subsequently intensifying. When the maximum is reached, a weakening of breathing is observed again, and then it stops - a new pause occurs. At the end of the pause, the cycle repeats again. Cycle duration is 30-60 s.
With a decrease in the excitability of the respiratory center due to lack of oxygen, other types of periodic breathing are also observed.
The mechanism of the first breath of a newborn. In the mother's body, gas exchange of the fetus occurs through the umbilical vessels, which are in close contact with the mother's placental blood. After the birth of the child and separation of the placenta, this connection is broken. Metabolic processes in the body of a newborn lead to the formation and accumulation of carbon dioxide, which, like the lack of oxygen, humorally stimulates the respiratory center. In addition, a change in the child’s living conditions leads to excitation of extero- and proprioceptors, which is also one of the mechanisms involved in the taking of the newborn’s first breath.
Reflex mechanisms. There are constant and non-permanent (episodic) reflex influences on the functional state of the respiratory center.
Constant reflex influences arise as a result of irritation of alveolar receptors (Hering-Breuer reflex), lung root and pleura (pulmothoracic reflex), chemoreceptors of the aortic arch and carotid sinuses (Heymans reflex), proprioceptors of the respiratory muscles.
The most important reflex is the Hering-Breuer reflex. The alveoli of the lungs contain mechanoreceptors for stretching and collapsing, which are sensitive nerve endings vagus nerve. Stretch receptors are excited during normal and maximum inspiration, i.e., any increase in the volume of the pulmonary alveoli excites these receptors. Collapse receptors become active only under pathological conditions (with maximum alveolar collapse).
In experiments on animals, it was found that when the volume of the lungs increases (blowing air into the lungs), a reflex exhalation is observed, while pumping air out of the lungs leads to a rapid reflex inhalation. These reactions did not occur during transection vagus nerves.
The Hering-Breuer reflex is one of the mechanisms of self-regulation of the respiratory process, ensuring a change in the acts of inhalation and exhalation. When the alveoli are stretched during inhalation, nerve impulses from stretch receptors travel along the vagus nerve 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 the implementation of active inhalation. In addition, the activity of inspiratory neurons increases with increasing concentration of carbon dioxide in the blood, which also contributes to the manifestation of inhalation.
Thus, self-regulation of breathing is carried out on the basis of the interaction of the nervous and humoral mechanisms of regulation of the activity of neurons of the respiratory center.
The pulmothoracic reflex occurs when the receptors embedded in the lung tissue and pleura. This reflex appears 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 final effect of the reflex is a change in the tone of the respiratory muscles, resulting in an increase or decrease in the average volume of the lungs.
The respiratory center constantly receives nerve impulses from the proprioceptors of the respiratory muscles. During inhalation, the proprioceptors of the respiratory muscles are excited and nerve impulses from them enter the inspiratory part of the respiratory center. Influenced nerve impulses the activity of inspiratory neurons is inhibited, which promotes the onset of exhalation.
Variable reflex influences on the activity of respiratory neurons are associated with the excitation of a variety of extero- and interoreceptors. Variable reflex effects that influence the activity of the respiratory center include reflexes that arise when the receptors of the mucous membrane of the upper respiratory tract, nasal mucosa, nasopharynx, temperature and pain receptors skin, proprioceptors skeletal muscles. For example, when suddenly inhaling ammonia vapor, chlorine, sulfur dioxide, tobacco smoke and some other substances irritate the receptors of the mucous membrane nasal membranes, pharynx, larynx, which leads to a reflex spasm of the glottis, and sometimes even the muscles of the bronchi and a reflex holding of breath.
When the epithelium of the respiratory tract is irritated by accumulated dust, mucus, as well as ingested chemical irritants and foreign bodies, sneezing and coughing are observed. Sneezing occurs when receptors in the nasal mucosa are irritated, while coughing occurs when receptors in the larynx, trachea, and bronchi are stimulated.
The influence of cerebral cortex cells on the activity of the respiratory center. To assess the role of the cerebral cortex in the regulation of breathing great importance have data obtained using the conditioned reflex method. If in humans or animals the sound of a metronome is accompanied by inhalation of a gas mixture with increased content carbon dioxide, this will lead to an increase in pulmonary ventilation. After 10-15 combinations, isolated activation of the metronome (conditioned signal) causes stimulation of respiratory movements, i.e., a conditioned respiratory reflex has been formed to a certain number of metronome beats per unit of time.
Increased and deepening of breathing that occurs before the start of physical work or sports competitions, are also carried out through the mechanism of conditioned reflexes. These changes in respiratory movements reflect shifts in the activity of the respiratory center and have adaptive significance, helping to prepare the body for work that requires a lot of energy and increased oxidative processes.
According to M.E. Marshak, cortical regulation of breathing provides the necessary level of pulmonary ventilation, pace and breathing rhythm, constancy of the level of carbon dioxide in the alveolar air and arterial blood.
According to M.V. Sergievsky, regulation of the activity of the respiratory center is represented by three levels.
First level of regulation - spinal cord. Here are the centers of the diaphragmatic and intercostal nerves causing contraction of the respiratory muscles. However, this level of breathing regulation cannot ensure a rhythmic change in the phases of the respiratory cycle, since a huge number of afferent impulses from breathing apparatus, bypassing spinal cord, are sent directly to medulla.
Second level of regulation - medulla. Here is the respiratory center, which processes a variety of afferent impulses coming from the respiratory apparatus, as well as from the main reflexogenic vascular zones. This level of regulation ensures a rhythmic change in the phases of breathing and the activity of spinal motor neurons, the axons of which innervate the respiratory muscles.
Third level of regulation - upper parts of the brain, including cortical neurons. Only with the participation of the cerebral cortex is it possible to adequately adapt the reactions of the respiratory system to changing environmental conditions.
The respiratory center is a paired cluster of neurons (cells) of the brain, united common function. Due to its work, the respiratory muscles contract and relax in a certain sequence, and the breathing process itself adapts to environment and the state of the body.
This anatomical structure is located in the pons and medulla oblongata. In addition to this anatomical section, important centers such as chewing, swallowing, salivation and others are also located here. Damage to the human medulla oblongata most often leads to death from paralysis of the respiratory muscles, disconnection of the breathing process, and, as a consequence, an increase in respiratory failure.
There are several significant sections in the respiratory center. The inspiratory section is responsible for regulating inhalation, and the expiratory section is responsible for regulating exhalation. Damage to any one department blocks this function on the side where the lesion is located. The expiratory section is located in the ventral nucleus of the medulla oblongata, while the inspiratory section is located in the dorsal nucleus. The process of coordinating inhalation and exhalation is controlled by the pneumotaxic center, which is located in the area of the pons. This department has an automatic function, that is, it independently generates a nerve impulse. This center is stimulated by inhalation, which should be followed by timely exhalation. The bridge also contains a section that regulates the tone of the respiratory center.
The work of the respiratory center
The function of the respiratory center is controlled by a combination of factors. Let's look at their components:
- Automatism of the center's neurons, which independently produce impulses to perform respiratory movements. This process is controlled by the gas composition of the blood, its acid-base state, metabolic characteristics of the body and physical activity, as well as environmental conditions.
- Carbon dioxide causes stimulation of the respiratory center. When there is a lack of oxygen in the surrounding air, little of it is supplied with inhalation, so compensation occurs: an increase in the frequency and depth of breathing.
- The gas composition of the blood directly affects the functioning of the respiratory center. With a lack of oxygen (hypoxia), the acid-base state of the blood shifts towards acidic (acidosis). Fabrics can't cope with their functional responsibilities, since there is not enough oxygen for their activities. In this regard, the breathing rate increases, but it is superficial, i.e. not effective enough.
- In the human body there are several reflexogenic zones, stimulation of which changes the breathing rhythm. Sharp irritation of the heat or cold receptors of the skin can lead to a reflex cessation of breathing. When sneezing or swallowing, respiratory activity stops briefly. The vascular sinocarotid zone, like the respiratory center, is sensitive to changes in the gas composition of the environment.
Normal breathing cycle
Based on the information received, the respiratory cycle can be depicted as follows:
Activation of inspiratory neurons due to an increase in carbon dioxide concentration - the nerve impulse is directed from the ventral nuclei along nerve fibers into the motor receptors of the phrenic and intercostal nerves - an increase in lung volume and chest- inhalation - irritation of the stretch receptors of the alveoli - direction of the nerve impulse to the expiratory section of the respiratory center - irritation of the section - exhalation.
This scheme is called the breathing circuit. The rhythmicity of these cycles is controlled by the pneumotaxic center.
External respiration is one of the essential functions body. Cessation of breathing causes inevitable death of a person within 3-5 minutes. Oxygen reserves in the body are very small, so it is necessary to constantly supply it through the system external respiration. This circumstance explains the formation in the process of evolution of such a regulatory mechanism, which should ensure high reliability of the performance of respiratory movements. The activity of the respiratory regulation system is based on maintaining a constant level of such body indicators as RP), P0 and pH. The basic principle of regulation is self-regulation: deviations of these indicators from normal level immediately triggers a chain of processes aimed at their restoration.
In addition, breathing is involved in thought, in the expression of emotions (laughter), and is also interconnected with some other functions of the body (digestion, thermoregulation, etc.).
In the respiratory regulation system, internal and external links of self-regulation can be distinguished. Internal links are associated with the state of the blood ( buffer properties, hemoglobin content) and of cardio-vascular system, external - with external respiration mechanisms. Adjustable parameters of the external respiration system are the depth and frequency of respiratory movements.
The main regulated object is the respiratory muscles, which belong to the skeletal muscle. In addition to them, the object of breathing regulation must include the unstrained muscles of the pharynx, trachea and bronchi, which affect the condition of the respiratory tract. Transportation of gases in the blood and gas exchange in tissues carry out the formation of the cardiovascular system, the regulation of the function of which was discussed in the corresponding section.
Breathing is regulated reflexively, which covers the following elements:
1) receptors that perceive information and afferent pathways that transmit it to nerve centers;
2) nerve centers;
3) effectors (paths for transmitting commands from centers) and the regulated objects themselves.
Respiratory center
The respiratory center is located in the area brain stem. It consists of several sections, often called separate respiratory centers. The location of each of them was established in experiments on animals using brain resection and implantation of electrodes.
Both halves of the medulla oblongata contain at least two clusters of neurons that manifest their activity at the moment of inhalation or exhalation - the dorsal and ventral nuclei (Fig. 86). If the excitation of a neuron coincides with inhalation, it is classified as inspiratory; if it coincides with exhalation, it is classified as expiratory. The neurons of these nuclei are in wide contact with reticular formation trunk, through which afferent signals from peripheral receptors arrive to the respiratory center.
Today there is still no unified theory of the functioning and structure of the respiratory center. Therefore, one of the hypotheses is presented below.
Dorsal nucleus contains neurons that are excited during inspiration. There are two main types of neurons in it:
a) IA neurons (excited only during inhalation);
b) f-neurons (excited simultaneously with Ia and igid pause time).
IA neurons are typical inspiratory neurons. Nerve impulses from them are transmitted to the motor neurons of the diaphragm located in the spinal cord (3rd and 4th cervical segments). At the same time, the excitation of Ia neurons is transmitted to Iβ neurons. However, these neurons do not transmit their impulses to the motor neuron IA of the diaphragm; their excitation leads to inhibition of the activity of inspiratory IA neurons.
The group of neurons belonging to the ventral nucleus, located 4-6 mm anterior and lateral to the previous ones, has a large length. Top part the ventral nucleus contains inspiratory neurons, and the lower one contains expiratory neurons. Most of the nerve fibers of these nuclei go to thoracic segments the spinal cord to the motor neuron and to the intercostal muscles and abdominal muscles (in accordance with the muscles of inhalation or exhalation). Only 20-25% of the fibers branch in the region of the diaphragmatic nuclei.
In addition to the centers of the medulla oblongata in the anterior part of the pons, another nucleus was found immediately behind the chotirigorbi plate, which is involved in the regulation of breathing - pneumotaxic center.
Rice. 86. 1 - dorsal nucleus; 2 - ventral nucleus; WITH- apneustic center; 4 - pneumotaxic center; 5 - brain bridge
Duration of topic study: 10 hours;
of which 4 hours per lesson; independent work 6 hours
Location training room
Purpose of the lesson: Study the neurohumoral mechanisms of breathing regulation; features of breathing under various conditions and states of the body. Mastering research methods functional state respiratory system.
Tasks:
know the multi-level organization and operating features central office regulation of breathing;
know the essence of the concept of “respiratory center”;
be able to correctly characterize the role of respiratory motor neurons of the spinal cord and proprioceptors of the intercostal muscles in the adaptation of the body.
The topic is closely related to the materials of the previous lesson. For clinical practice, professional selection of people (cosmonauts, climbers, divers, etc.), data relating to the regulation of breathing in various functional states of the body, in pathology and when the body is in special conditions environment. Methods for assessing the functional state of the respiratory system are widely used in the clinic for diagnostic purposes.
Regulation of pulmonary blood flow Oxygen (more precisely, a change in PaO2) causes either vasodilation or vasoconstriction. Vasodilation. Under the influence of an increase in PaO2 (for example, when placed in a chamber with a high oxygen content - hyperbaric oxygenation or when inhaling 100% oxygen - an oxygen cushion), pulmonary vascular resistance (RPV) decreases and perfusion increases. Vasoconstriction. Under the influence of reduced PaO2 (for example, when climbing mountains), RPV increases and perfusion decreases. Biologically active substances (vasoconstrictors and vasodilators) affecting the SMC of blood vessels are numerous, but their effects are local and short-term. Carbon dioxide (increased PaCO2) also has a slight, transient and local vasoconstrictor effect on the lumen of blood vessels. Pulmonary vasodilators: prostacyclin, nitric oxide, acetylcholine, bradykinin, dopamine, β-adrenergic ligands. Vasoconstrictors: thromboxane A2, α-adrenergic ligands, angiotensins , leukotrienes, neuropeptides, serotonin, endothelin, histamine, Pg, increased PaCO2.
The function of nervous regulation of breathing is performed by respiratory neurons - many nerve cells located in the stem part of the brain. Control of respiratory movements (efferent nerve impulses to the respiratory muscles) is carried out both involuntarily (the automatic rhythm of the respiratory neurons of the brainstem, in the figure - “rhythm generator”), and voluntarily (in this case, the efferent nerve impulses enter the respiratory muscles, bypassing the respiratory neurons brain stem). Adequate functioning of these and other respiratory control circuits ensures normal breathing (eupnea).
The regulation of breathing is aimed at performing two tasks: firstly, the automatic generation of the frequency and force of contraction of the respiratory muscles, and secondly, the adjustment of the rhythm and depth of respiratory movements to the real needs of the body (primarily, to changes in metabolic parameters in the form of DPO2, DPCO2 and Arterial blood DpH and DPCO2 and DpH intercellular fluid brain).
The respiratory regulation system consists of 3 main blocks: receptor (chemo- and baroreceptors that record and transmit information to the brain), regulatory or control (a set of respiratory neurons) and effector (respiratory muscles that directly ventilate the lungs). Thus, the entire respiratory regulation system consists of several interconnected regulatory circuits.
Nerve centers located in the brain stem (mainly as part of the medulla oblongata). The breathing regulation scheme provides for the presence of a rhythm generator for respiratory movements and a center for integrating sensory information. The terms “rhythm generator” and “sensory information integrator” should be understood as abstract integral concepts, rather than specific ones. nerve structures, since the correspondence of anatomical structures to the concepts under consideration is not established in all cases. The rhythm generator includes neurons located primarily in the medulla oblongata, as well as the pons and some other parts of the brain stem. Different groups of neurons generate a different spectrum of bursts of impulses - action potentials (AP) - on different phases respiratory movements, including either predominantly during inspiration (inspiratory neurons) or predominantly during exhalation (expiratory neurons).
The entire set of respiratory neurons is divided from an anatomical point of view into the ventral and dorsal respiratory groups (VDG and DRG, respectively). Both the VDG and DDH are presented bilaterally, i.e. duplicated. The dorsal respiratory group (DRG) contains predominantly inspiratory nerve cells (including neurons of an important complex of nuclei of the autonomic nervous system - the nuclei of the solitary tract, which receive sensory information from the internal organs of the thoracic and abdominal cavities along the nerve fibers of the glossopharyngeal and vagus nerves). The ventral respiratory group (VRG) contains both inspiratory and expiratory neurons. In the rostro-caudal direction, the EDH consists of a rostral part - the Bötzinger complex (contains mainly expiratory nerve cells, including the retrofacial nucleus), intermediate (contains mainly inspiratory neurons of the double and paraduplicate nuclei) and caudal (expiratory neurons of the retroduplicate nucleus) parts. Direction of impulses from respiratory neurons: 1. from nerve cells of the DRG to the EDH, as well as to premotor neurons, then to motor neurons and to the main inspiratory muscles; 2. from the intermediate part of the EDH ultimately to the main and auxiliary inspiratory muscles; 3. from the caudal part of the EDH to the accessory expiratory muscles. Incoming signals. The rhythm generator receives impulses descending from the cerebral cortex, as well as nerve signals from the nerve cells of the sensory information integrator and directly from the central chemoreceptors. Output signals. Nerve impulses from the rhythm generator are sent to the motor nerve cells of the corresponding cranial nerve nuclei (VII, IX–XII) that innervate the respiratory muscles and to the motor neurons of the anterior horns of the spinal cord (their axons as part of the spinal nerves are directed to the respiratory muscles).
The mechanism of rhythmic activity of the generator has not been established. Several models have been proposed that take into account the individual characteristics of the electrogenic membrane of groups of the same type of nerve cells (for example, the presence of different ion channels), the spectrum of synaptic connections (including those carried out using different neurotransmitters), the presence of pacemaker (with pacemaker properties) respiratory neurons (those have been discovered) or pacemaker properties of local neural networks. There is also no clarity on the question of whether rhythmic activity is a property of a limited group of nerve cells or a property of the entire set of respiratory neurons. The sensory information integrator receives sensitive information from a variety of chemo- and mechanoreceptors located in the respiratory organs and respiratory muscles, along the main blood vessels (peripheral chemoreceptors), as well as in the medulla oblongata (central chemoreceptors). In addition to these direct signals, the integrator receives a lot of information mediated by various brain structures (including from the higher parts of the central nervous system). The impulse from the nerve cells of the integrator, directed to the neurons of the rhythm generator, modulates the nature of the discharges from them. Sensitive structures, signals from which directly or indirectly (through the sensory information integrator) influence the rhythmic activity of the rhythm generator, include peripheral and central chemoreceptors, baroreceptors of the arterial wall, mechanoreceptors of the lungs and respiratory muscles. The most significant influence on the activity of the rhythm generator is the control of pH and blood gases carried out by peripheral and central chemoreceptors.
Peripheral chemoreceptors(carotid and aortic bodies) record pH, PO2 (PaO2) and PCO2 in arterial blood; they are especially sensitive to a decrease in PO2 (hypoxemia) and, to a lesser extent, to an increase in PCO2 (hypercapnia) and a decrease in pH (acidosis). Carotid sinus - expansion of the lumen of the internal carotid artery immediately at the place of its branch from the common carotid artery. In the wall of the artery in the area of expansion there are numerous baroreceptors that record blood pressure values and transmit this information to the central nervous system along nerve fibers passing as part of the sinus nerve (Hering) - branch glossopharyngeal nerve.Carotid body located in the area of bifurcation of the common carotid artery. The glomerulus of the carotid body consists of 2–3 type I cells (glomus cells) surrounded by supporting cells (type II). Type I cells form synapses with the terminals of afferent nerve fibers. The carotid body consists of clusters of cells (glomeruli, glomus) immersed in a dense network of blood capillaries (the intensity of perfusion of the bodies is the highest in the body, 40 times more than the perfusion of the brain). Each glomerulus contains 2–3 chemosensitive glomus cells that form synapses with the terminal branches of the nerve fibers of the sinus nerve, a branch of the glossopharyngeal nerve. The corpuscles also contain nerve cells of the sympathetic and parasympathetic divisions of the autonomic nervous system. Preganglionic sympathetic and parasympathetic nerve fibers terminate on these neurons and glomus cells, and postganglionic nerve fibers from the superior cervical sympathetic ganglion also terminate on glomus cells [the terminals of these fibers contain light (acetylcholine) or granular (catecholamine) synaptic vesicles]. Glomus cells are connected to each other by gap junctions, their plasmalemma contains voltage-gated ion channels, the cells can generate APs and contain various synaptic vesicles containing acetylcholine, dopamine, norepinephrine, substance P and methionine-enkephalin. The mechanism of registration of DPO2, DPCO2 and DpH has not been fully established, but it leads to blockade of K+ channels, which causes depolarization of the plasmalemma of glomus cells, the opening of voltage-dependent Ca2+ channels, intracellular increase and secretion of neurotransmitters. Aortic(para-aortic) bodies are scattered along the inner surface of the aortic arch and contain glomus chemosensitive cells that form synapses with afferents of the vagus nerve. Central chemoreceptors(nerve cells of the brain stem) record pH and PCO2 in the intercellular fluid of the brain; they are especially sensitive to an increase in PCO2 (hypercapnia), and some of them to a decrease in pH (acidosis). It is important that the central chemoreceptors are located medially from the blood-brain barrier, i.e. they are separated from the blood in the general circulation system (in particular, they are in a more acidic environment).
Blood-brain barrier formed by endothelial cells of the blood capillaries of the brain. The basement membrane surrounding the endothelium and pericytes, as well as the astrocytes, whose stalks completely surround the outside of the capillary, are not components of the barrier. The blood-brain barrier insulates the brain from temporary changes in blood composition. The continuous endothelium of the capillaries, the cells of which are interconnected by chains of tight junctions, is the basis of the blood-brain barrier. The blood-brain barrier functions as a filter. Neutral substances (for example, O2 and CO2) and lipid-soluble substances (for example, nicotine, ethanol, heroin), but the permeability of ions (for example, Na +, Cl –, H +, HCO - 3) is low.
pH and PCO2. Since the permeability of the barrier to CO2 is high (unlike H+ and
HCO - 3), and CO2 easily diffuses through cell membranes, it follows that inside the barrier (in the interstitial fluid, in the cerebrospinal fluid, in the cytoplasm of cells) relative acidosis is observed and that an increase in PCO2 leads to a greater decrease in the pH value than in the blood. In other words, under conditions of acidosis, the chemosensitivity of neurons to DPCO2 and DpH increases.
Acidosis-sensitive (chemosensitive to DPco2 and DpH) neurons, the activity of which influences pulmonary ventilation, are found in the ventrolateral part of the medulla, in the nucleus ambiguus, nuclei of the solitary tract of the medulla oblongata, as well as in the hypothalamus and in the locus coeruleus and in the raphe pons nuclei. Many of these chemosensitive neurons are serotonergic nerve cells.
Baroreceptors in the walls of arteries and veins. These mechanoreceptors respond to changes in pressure in the lumen and in the wall of blood vessels; they are formed by the terminals of fibers passing through the vagus and glossopharyngeal nerves. Baroreceptors are especially numerous in the aortic arch, carotid arteries, pulmonary trunk, pulmonary arteries and in the wall of large veins of the systemic and pulmonary circulation. Baroreceptors are involved in the reflex regulation of blood circulation and respiration; an increase in blood pressure can lead to reflex hypoventilation or even respiratory arrest (apnea), and a decrease in blood pressure can cause hyperventilation.
Receptors airways and respiratory department they record changes in lung volumes, the presence of foreign particles and irritating substances and transmit information along the nerve fibers of the vagus and glossopharyngeal (from the upper airways) nerves to the neurons of the dorsal respiratory group. Receptors in this group include slowly adapting stretch receptors, rapidly adapting irritant receptors and J receptors. Slowly adapting stretch receptors located among the SMC walls of the airways. They respond to an increase in the volume of lung tissue (inflating lung tissue), recording the stretching of the wall of the airways, and conduct packets of impulses along myelinated nerve fibers. A feature of these mechanoreceptors is their slow adaptability (when the receptors are excited, the impulse activity continues long time). These receptors are excited when the lumen of the airways expands (bronchodilation) and trigger the Hering-Breuer reflex (when the lung is inflated, the tidal volume decreases and the respiratory rate increases; in other words, the Hering-Breuer reflex is aimed at suppressing the duration of inhalation and increasing the duration of exhalation). At the same time and reflexively, tachycardia occurs (increased heart rate). In newborns, this reflex controls tidal volume during normal breathing (eupnea). In healthy adults, the reflex is activated only with hyperpnea - a significant increase in tidal volume (over 1 l), for example, with significant physical exertion. In obstructive diseases, increased lung volume constantly stimulates stretch receptors, which leads to a delay in the next inhalation against the background of prolonged difficult exhalation . Rapidly adapting (irritant) receptors located between the epithelial cells of the mucous membrane of large airways. They (like the slowly adapting stretch receptors) respond to strong inflation of the lung tissue, but mainly to the action of caustic gases (for example, ammonia) that irritate the tissue during inhalation. tobacco smoke, dust, cold air, as well as the presence of histamine in the wall of the airways (released from mast cells when allergic reactions), Pg and bradykinins (therefore they are also called irritant - irritant - receptors). Excitation from the receptors spreads along the myelinated afferent nerve fibers of the vagus nerve. A feature of these receptors is their rapid adaptability (when the receptors are excited, the impulse activity practically stops within one second). When irritant receptors are excited, the resistance of the airways increases, and reflexively, breath holding and coughing occur. J receptors(from the English “juxtacapillary” - peri-capillary) are located in the interalveolar septa and are both chemo- and mechanoreceptors. J-receptors are excited when the lung tissue is overstretched, as well as when exposed to various exo- and endogenous chemical compounds (capsaicin, histamine, bradykinin, serotonin, Pg). Packets of impulses from these receptors are sent to the central nervous system along the unmyelinated nerve fibers (C - fibers) of the vagus nerve. Stimulation of these receptors leads to a reflex holding of breath with the subsequent appearance of frequent and shallow breathing, narrowing of the lumen of the airways (bronchoconstriction), increased secretion of mucus, as well as a drop in blood pressure and a decrease in heart rate (bradycardia). Dyspnea. J-receptors respond to blood overflow of the pulmonary capillaries and an increase in the volume of interstitial fluid of the alveoli, which is possible with left ventricular failure and leads to dyspnea (shortness of breath).
Extrapulmonary receptors
Receptors of the face and nasal cavity. Their stimulation when immersed in water reflexively causes respiratory arrest, bradycardia, and sneezing. Receptors of the nasopharynx and pharynx. When they are excited, a strong inspiratory effort (“sniffing”) develops, moving foreign material from the nasopharynx to the pharynx. These receptors are also important for swallowing, when the laryngeal fissure closes at the same time (however, newborns can breathe and swallow at the same time). Laryngeal receptors. Their irritation reflexively causes respiratory arrest (apnea), coughing and strong expiratory movements necessary to prevent foreign material from entering the respiratory tract (aspiration). Mechanoreceptors of joints and muscles(including neuromuscular spindles). The information coming from them is necessary for the reflex regulation of muscle contraction. Excitation of these receptors to some extent causes the sensation of shortness of breath (dyspnea), which occurs when breathing requires great effort (for example, with airway obstruction). Pain and temperature receptors. Changes in ventilation can occur in response to stimulation of various afferent nerves. Thus, in response to pain, breath holding is often observed, followed by hyperventilation.
CNS and pulmonary ventilation. The central nervous system functions not only as a rhythm generator and a modulator of this central generator (“sensory information integrator” in the figure), not only influences the activity of the rhythm generator in connection with the performance of other functions of the airways (voice formation and smell), but also modulates the parameters of the respiratory rhythm when performing other functions controlled by the central nervous system (for example, chewing, swallowing, vomiting, defecation, thermoregulation, various emotions, awakening from sleep, and so on). These parts of the central nervous system include, in particular, the pontine reticular formation, the limbic lobe of the cerebrum, the hypothalamus of the diencephalon, and the cerebral cortex. Sleep and breathing. Breathing during sleep is less strictly controlled than during wakefulness; at the same time, sleep has a powerful effect on breathing parameters and, first of all, on the sensitivity of chemoreceptors to D PCO2 and on the breathing rhythm. During the slow-wave sleep phase, the breathing rhythm generally becomes more regular than during wakefulness, but the sensitivity of chemoreceptors to D PCO2 decreases, as do the efferent influences on the respiratory muscles and pharyngeal muscles. During the REM sleep phase, sensitivity to DP PCO2 further decreases, but the breathing rhythm becomes irregular (up to the absence of any rhythm). Barbiturates suppress the activity of the rhythm generator and increase periods of apnea during sleep. Respiratory disorders during sleep, or sleep apnea syndrome (distinguish between pathological snoring syndrome, sleep apnea-hypopnea syndrome and obesity-hypoventilation syndrome) can be caused by obstructive (obesity, small size of the oropharynx) or non-obstructive (CNS pathology) causes. Sleep apnea is usually mixed, combining obstructive and neurological disorders. Patients may have hundreds of these episodes during sleep in one night. Obstructive sleep apnea- one of the many sleep disorders (frequency - 8–12% of the general adult population). More than half of the cases are severe and can lead to sudden death during sleep.
Adequate performance of the external respiration function is essential for maintaining many parameters of homeostasis and, first of all, blood oxygen saturation (PaO2) and the content of carbon dioxide in the blood - CO2 (PaCO2) and pH (DPo2, DPco2 and DpH), especially the concept of hypoxia and hypercapnia.
Acid-base balance
ASR is assessed by pH value, as well as by standard basic indicators.
pH- hydrogen index - negative decimal logarithm of the molar value in the medium. The pH of body fluids depends on the content of organic and inorganic acids and bases in them. An acid is a substance that acts as a proton donor in solution. A base is a substance that acts as a proton acceptor in solution.
Normally, the body produces almost 20 times more acidic foods, than basic (alkaline). In this regard, the body is dominated by systems that ensure the neutralization, excretion and secretion of excess compounds with acidic properties. These systems include chemical buffer systems and physiological mechanisms for regulating ASR. Chemical buffer systems are represented by bicarbonate, phosphate, protein and hemoglobin buffers. Operating principle buffer systems consists of transforming strong acids and strong bases into weak ones. These reactions are realized both intra- and extracellularly (in the blood, intercellular, spinal cord and other liquid environments), but on a larger scale - in cells. The hydrocarbonate buffer system is the main buffer of blood and interstitial fluid and makes up about half of the buffer capacity of blood and more than 90% of plasma and interstitial fluid. The hydrocarbonate buffer of the extracellular fluid consists of a mixture of carbonic acid - H2CO3 and sodium bicarbonate - NaHCO3. In cells, the carbonic acid salt contains potassium and magnesium. The functioning of the bicarbonate buffer is associated with the function of external respiration and kidneys. The external respiration system maintains the optimal level of Pco2 in the blood (and, as a result, the concentration of H2CO3), and the kidneys maintain the content of the HCO3– anion. Acidosis is characterized by a relative or absolute excess of acids in the body. In the blood during acidosis, there is an absolute or relative increase in [H+] and a decrease in pH below normal (<7,39; компенсированный ацидоз при значениях рН 7,38–7,35; при рН 7,34 и ниже - некомпенсированный ацидоз). Respiratory acidosis develops with a decrease in the volume of alveolar ventilation (hypoventilation), increased formation of CO2 in the body and with excessive intake of CO2 into the body. Hypoventilation of the lungs leads to hypercapnia (increased PCO2 in the blood). With respiratory acidosis, the denominator of the ratio / (i.e., the concentration of carbonic acid) increases. Respiratory acidosis occurs due to the accumulation of excess CO2 in the blood and a subsequent increase in the concentration of carbonic acid in it. Such changes are observed with obstruction of the airways (with bronchial asthma, bronchitis, emphysema, aspiration of foreign bodies), impaired compliance of the lungs (for example, with pneumonia or hemothorax, atelectasis, pulmonary infarction, paresis of the diaphragm), an increase in the functional “dead” space (for example , with hypoperfusion of lung tissue), dysregulation of breathing (for example, with encephalitis, cerebrovascular accidents, poliomyelitis). Increased production of endogenous CO2. Increased production of CO2 in the body (not compensated by ventilation of the lungs) after some time leads to the development of respiratory acidosis. Such changes are observed when catabolic processes are activated in patients with fever, sepsis, prolonged convulsions of various origins, heat stroke, as well as with parenteral administration of large amounts of carbohydrates (for example, glucose). The inclusion of excess carbohydrates in metabolism is also accompanied by increased production of CO2. Thus, in this situation, the accumulation of CO2 in the body is the result of inadequate (insufficient) ventilation of the lungs. Excessive intake of CO2 into the body (with subsequent formation of carbonic acid) is observed when a breathing gas mixture with an inadequately increased CO2 content is supplied (for example, in spacesuits, submarines, aircraft) or when a large number of people are in a confined space (for example, in a mine or small room).
Metabolic acidosis- one of the most common and dangerous forms of violation of the control system. With metabolic acidosis, the numerator of the ratio / (i.e., the concentration of bicarbonates) decreases. One of the characteristic manifestations is a compensatory increase in alveolar ventilation. In severe metabolic acidosis (including ketoacidosis due to acetone, acetoacetic and b-hydroxybutyric acids, which can occur with diabetes mellitus, prolonged fasting, prolonged febrile states, alcohol intoxication, extensive burns and inflammation), deep and noisy breathing may develop - periodic Kussmaul breathing (“acidotic breathing”). The reason for the development of such breathing: an increase in the H+ content in the blood plasma (and in other biological fluids) is a stimulus for inspiratory neurons. However, as Pco2 decreases and damage to the nervous system increases, the excitability of the respiratory center decreases and periodic breathing develops. Alkalosis is characterized by a relative or absolute excess of bases in the body. In the blood with alkalosis, there is an absolute or relative decrease in [H+] or an increase in pH (>7.39; 7.40–7.45 - compensated alkalosis at pH values of 7.40–7.45; at pH 7.46 and above - uncompensated alkalosis). Respiratory alkalosis develops with an increase in the volume of alveolar ventilation (hyperventilation). With hyperventilation (increased effective alveolar ventilation), the volume of ventilation in the lungs exceeds that necessary for adequate removal of CO2 produced in the body. Hyperventilation of the lungs leads to hypocapnia (decrease in PCO2 in the blood), a decrease in the level of carbonic acid in the blood and the development of gas (respiratory) alkalosis. With respiratory alkalosis, the denominator of the ratio / (i.e., the concentration of carbonic acid) decreases. Respiratory alkalosis develops with altitude and mountain sickness; neurotic and hysterical states; brain damage (concussion, stroke, neoplasm); lung diseases (for example, pneumonia, asthma), hyperthyroidism; severe feverish reaction; drug intoxication (for example, salicylates, sympathomimetics, progestogens); renal failure; excessive and prolonged pain or thermal irritation; hyperthermic and a number of other conditions. In addition, the development of gas alkalosis is possible if the regime is violated artificial ventilation lungs (ventilation), leading to hyperventilation. Metabolic alkalosis characterized by an increase in blood pH and an increase in bicarbonate concentration. This condition is characterized by hypoxia, which develops due to hypoventilation of the lungs (caused by a decrease in [H+] in the blood and, as a consequence, a decrease in the functional activity of inspiratory neurons) and due to an increase in the affinity of Hb for oxygen due to a decrease in the H+ content in the blood, which leads to a decrease in dissociation HbO2 and oxygen supply to tissues.
Breathing (external respiration in the lungs, transport of gases in the blood and tissue respiration) is aimed at supplying cells, tissues, organs and the body with oxygen. Insufficient performance of the respiratory function leads to the development of oxygen starvation - hypoxia.
Hypoxia(oxygen starvation, oxygen deficiency) - a condition that occurs as a result of insufficient oxygen supply to the body and/or impaired oxygen absorption during tissue respiration. Hypoxemia(a decrease in blood tension and oxygen levels compared to the normal level) is often combined with hypoxia. Anoxia (lack of oxygen and cessation of biological oxidation processes) and anoxemia (lack of oxygen in the blood) are not observed in a whole living organism; these conditions relate to experimental or special (perfusion of individual organs) situations.
Altitude sickness observed when climbing mountains, where the body is exposed not only to low oxygen content in the air and low barometric pressure, but also to more or less pronounced physical activity, cooling, increased insolation and other factors of mid- and high altitudes.
Altitude sickness develops in people raised to high altitudes in open aircraft, on lift chairs, and also when the pressure in the pressure chamber decreases. In these cases, the body is affected mainly by reduced PO2 in the inhaled air and barometric pressure.
Decompression sickness observed with a sharp decrease in barometric pressure (for example, as a result of depressurization of aircraft at an altitude of more than 10,000–11,000 m). In this case, a life-threatening condition is formed, different from mountain and altitude sickness sharp or even lightning-fast current.
Hypercapnia- excess carbon dioxide in body fluids. If the alveolar PCO2 level rises from 60 to 75 mm Hg. breathing becomes deep and frequent, and dyspnea (subjective feeling of shortening of breathing) becomes more severe. As soon as PCO2 increases from 80 to 100 mm Hg, lethargy and apathy, sometimes a semi-comatose state, occurs. Death can occur at PCO2 levels between 120 and 150 mmHg. Adaptation (adaptation) of the respiratory system to muscular work, to the conditions of an unusual environment (low and high barometric pressure, hypoxia, polluted environment, etc.), as well as the correct diagnosis and treatment of respiratory disorders, are determined by the depth of understanding of the basic physiological principles of respiration and gas exchange. A number of respiratory diseases are the result of inadequate ventilation, while others are the result of impaired diffusion across the airborne barrier. Effect of increased barometric pressure(hyperbaria). The pressure when immersed in water increases by 1 atm for every 10 m of depth (the amount of dissolved gases increases accordingly). The creation of pressure chambers made it possible to study the effect of both increased barometric pressure and high gas pressures on the human body without deep-sea diving. At PO2 about 3000 mmHg. (about 4 atm) the total amount of oxygen not bound to Hb, but physically dissolved in the blood, is 9 ml/100 ml of blood. The BRAIN is especially sensitive to acute oxygen poisoning. After 30 minutes of exposure to an environment with an O2 pressure of 4 atm, convulsive seizures occur, followed by coma. The toxic effect of O2 on the nervous system is caused by the action of the so-called. active forms of oxygen (singlet - 1O2, superoxide radical - O2–, hydrogen peroxide - H2O2, hydroxyl radical - OH–). Breathing a gas mixture with a high concentration of O2 for several hours can cause lung damage. The first pathological changes are found in the endothelial cells of the pulmonary capillaries. In healthy volunteers, when breathing pure oxygen at normal atmospheric pressure, after 24 hours, unpleasant sensations occur in the chest, aggravated by deep breathing. In addition, their lung vital capacity decreases by 500–800 ml. This causes the so-called absorption atelectasis, caused by the intense transition of O2 into the venous blood and the rapid collapse of the alveoli. Postoperative atelectasis often occurs in patients breathing gas mixtures with a high O2 content. Especially high probability Collapse of the lung parenchyma occurs in its lower parts, where the lung parenchyma is expanded to the least extent.
During diving, the partial pressure of N2 increases, causing this poorly soluble gas to accumulate in tissues. During ascent, nitrogen is slowly removed from the tissues. If decompression occurs too quickly, nitrogen bubbles will form. A large number of blisters is accompanied by pain, especially in the joints ( decompression sickness). In severe cases, visual impairment, deafness and even paralysis may occur. To treat decompression sickness, the victim is placed in a special high-pressure chamber.
Basic knowledge of students necessary to achieve the objectives of the lesson:
Know:
Organization of the respiratory center and the role of its different parts in the regulation of breathing.
Mechanisms of breathing regulation (neuro-reflex and neuro-humoral) and experiments proving them (the experiment of Frederick and Heymans).
Types of lung ventilation various states body.
Be able to:
Draw diagrams of the organization of the respiratory center and the central respiratory mechanism.
Draw pneumograms for various functional states of the body.
Draw a diagram of the Donders model.
Questions for self-preparation for the lesson.
Respiratory center. Modern ideas about its structure and function. Automation of the respiratory center.
Spinal level of breathing regulation. The role of proprioceptors of the respiratory muscles in the regulation of breathing.
The role of the medulla oblongata and the pons in maintaining periodicity and optimal levels of pulmonary ventilation.
The role of the hypothalamus of the limbic system and the cerebral cortex in the regulation of breathing during various adaptive reactions of the body.
Humoral regulation of respiration: experiments recording the role of oxygen and carbon dioxide.
Breathing under conditions of high and low atmospheric pressure. Caisson disease. Mountain sickness.
The mechanism of the first breath of a newborn.
Educational, practical and research work:
Task No. 1
Watch the video “Regulating Breathing” and answer the following questions.
What are modern ideas about the structure of the respiratory center?
What determines the correct change of inhalation and exhalation?
What is apnea, dyspnea, hyperpnea?
What effect does excess carbon dioxide and lack of oxygen in the blood have on the respiratory center?
What is hypercapnia, hypocapnia?
What is hypoxia?
What is hypoxemia?
What is the role of chemoreceptors in the regulation of breathing?
What is the role of lung mechanoreceptors in regulating the frequency and depth of breathing?
What causes a baby's first breath?
Under what conditions and why can decompression sickness occur?
What is the cause of altitude or mountain sickness and how does it manifest itself?
What protective breathing reflexes You know?
Task No. 2
Analyze situational tasks:
After an arbitrary breath-hold, breathing, regardless of the will of the subject, automatically resumes. Why?
Why on high altitudes, when a spacesuit depressurizes, can an astronaut’s blood “boil”?
How can you tell whether a child who died suddenly was breathing immediately after birth or not?
A seriously ill patient was admitted to the hospital. The doctor has carbogen at his disposal (95% O 2 and 6% CO 2) and pure oxygen. What will the doctor choose and why?
Experiments were carried out on dogs with brain transection to different levels: 1) transection between the cervical and thoracic spinal cord; 2) transection between the medulla oblongata and the spinal cord. What changes were observed in the dogs in these experiments? Explain your answers.
1.Lecture material.
2.Human physiology: Textbook/Ed. V.M.Smirnova
3.Normal physiology. Textbook./ V.P. Degtyarev, V.A. Korotich, R.P. Fenkina,
4. Human physiology: In 3 volumes. Per. from English/Under. Ed. R. Schmidt and G. Tevs
5. Workshop on physiology / Ed. M.A. Medvedev.
6. Physiology. Basics and functional systems: Course of lectures / Ed. K. V. Sudakova.
7.Normal physiology: Course of physiology of functional systems. /Ed. K.V. Sudakova
8. Normal physiology: Textbook / Nozdrachev A.D., Orlov R.S.
9.Normal physiology: tutorial: in 3 volumes. V. N. Yakovlev et al.
10. Yurina M.A. Normal physiology (educational manual).
11. Yurina M.A. Normal physiology (short course of lectures)
12. Human physiology / Edited by A.V. Kositsky.-M.: Medicine, 1985.
13. Normal physiology / Ed. A.V. Korobkova.-M.; Higher school, 1980.
14. Fundamentals of human physiology / Ed. B.I. Tkachenko.-St. Petersburg; 1994.
15. Physiology of humans and animals / Ed. A.B. Kogan. Part 1 chapter
16. Fundamentals of physiology / Ed. P. Sterki. Chapter 17.
Breathing is regulated by the respiratory center, which is located in the spinal cord, medulla oblongata, pons, hypothalamus, and cerebral cortex.
The leading role in the organization of breathing belongs to the center of the medulla oblongata, which consists of the centers of inspiration (inspiratory neurons) and exhalation (expiratory neurons). Destruction of this area leads to respiratory arrest. Here are the neurons that ensure the rhythm of inhalation and exhalation. This is due to the fact that the respiratory center has the property of automaticity, i.e. its neurons are capable of rhythmically self-excitation. Automaticity is preserved even if nerve impulses do not arrive to the respiratory center through centripetal neurons. Automation may vary depending on humoral factors, nerve impulses arriving through centripetal neurons and under the influence of overlying parts of the brain. From the respiratory center, nerve impulses travel through centrifugal neurons to the intercostal muscles, diaphragm, and other muscles.
Regulation of breathing is carried out with the help of humoral, reflex mechanisms and nerve impulses coming from the overlying parts of the brain.
A specific regulator of the activity of neurons in the respiratory center is carbon dioxide, which acts on respiratory neurons directly and indirectly. Carbon dioxide directly excites the inspiratory cells of the respiratory center. In the mechanism of the stimulating effect of carbon dioxide on the respiratory center, an important place belongs to the chemoreceptors of the vascular bed. In the area of the carotid sinuses and aortic arch, chemoreceptors were found that are sensitive to changes in carbon dioxide tension in the blood. By the way, the first breath of a newborn is explained by the effect of carbon dioxide accumulated in its tissues on the respiratory center (after cutting the umbilical cord and separation from the mother’s body). This action is both direct and indirect, reflex - through the chemoreceptors of the carotid sinus and aortic arch. Excess carbon dioxide in the blood causes shortness of breath. Lack of oxygen in the blood deepens breathing. It has been established that an increase in oxygen tension in the blood inhibits the activity of the respiratory center.
Reflex mechanisms. There are constant and non-permanent reflex influences on the functional state of the respiratory center. Constant reflex influences arise as a result of irritation of the receptors of the alveoli (E. Hering - I. Breuer reflex), the root of the lung and pleura (pleuropulmonary reflex), chemoreceptors of the aortic arch and carotid sinuses (K. Heymans reflex), and proprioceptors of the respiratory muscles.
The reflex of E. Hering and I. Breuer is called the inhalation inhibition reflex when the lungs are stretched. When you inhale, impulses arise that inhibit inhalation and stimulate exhalation, and when you exhale, impulses arise that reflexively stimulate inhalation. Regulation of respiratory movements is carried out according to the principle feedback. When the vagus nerves are cut, the reflex turns off, breathing becomes rare and deep.
Variable reflex influences on the activity of respiratory neurons are associated with the excitation of a variety of exteroceptors and interoreceptors. For example, when suddenly inhaling vapors of ammonia, chlorine, tobacco smoke and some other substances, irritation of the receptors of the mucous membrane of the nose, pharynx, and larynx occurs, which leads to a reflex spasm of the glottis (sometimes even the muscles of the bronchi) and a reflex holding of breath. Strong temperature effects on the skin stimulate the respiratory center and increase ventilation of the lungs. Sudden cooling depresses the respiratory center. Breathing is affected by pain and impulses from vascular baroreceptors: for example, increased blood pressure depresses the respiratory center, which is manifested by a decrease in the depth and frequency of breathing.
When the epithelium of the respiratory tract is irritated by accumulated dust, mucus, chemical irritants and foreign bodies, sneezing and coughing occur (protective innate reflexes). Sneezing occurs when receptors in the nasal mucosa are irritated, while coughing occurs when receptors in the larynx, trachea, and bronchi are stimulated.
The first level of regulation is the spinal cord. The centers of the phrenic and intercostal nerves are located here, causing contraction of the respiratory muscles. However, this level of breathing regulation cannot ensure a rhythmic change in the phases of the respiratory apparatus.
The second level of regulation is the medulla oblongata. Here is the respiratory center, which processes a variety of afferent impulses coming from the respiratory apparatus, as well as from the main reflexogenic vascular zones. This level of regulation ensures a rhythmic change in the phases of breathing and the activity of spinal motor neurons, the axons of which innervate the respiratory muscles.
The third level of regulation – upper sections brain, including cortical neurons. Only with the participation of the cerebral cortex is it possible to adequately adapt the reactions of the respiratory system to changing environmental conditions.
TASKS FOR SELF-CONTROL OF KNOWLEDGE
QUESTIONS FOR SELF-PREPARATION:
1. Overall plan structure and significance of the respiratory system.
2. Structure of the nasal cavity.
3. Structure of the larynx.
4. The structure of the trachea and main bronchi.
5. Structure of the lungs.
6. Pleural cavities and sinuses.
7. Boundaries of the lungs and pleura
8. The concept of the mediastinum. Mediastinal organs.
9. Stages of the breathing process.
10. External respiration apparatus.
11. Respiratory cycle.
12. Mechanisms of inhalation and exhalation.
13. Concept of pulmonary volumes and pulmonary ventilation.
14. Composition of atmospheric, alveolar and exhaled air.
15. Gas exchange in the lungs.
16. Transport of gases by blood.
17. Gas exchange between blood and tissues.
18. Respiratory center. Regulation of breathing.
Task No. 1. Choose one correct statement:
1. B respiratory system Excluded:
A) esophagus
B) larynx
2. The entrance to the larynx closes during swallowing:
B) thyroid cartilage
C) epiglottis
D) tongue soft palate
3. The highest frequency of respiratory movements will be at the concentration of carbon dioxide in the blood:
4. The tidal volume of the lungs is equal to:
A) 1500 – 2000 ml
B) 300 – 700 ml
C) 1000 – 1500 ml
D) 3000 – 3500 ml
5. The olfactory area is:
A) superior nasal passage
B) middle meatus
C) lower nasal meatus
D) vestibule of the nose
6. The most large cartilage larynx:
A) cricoid
B) thyroid
C) supraglottic
D) arytenoid
7. The bifurcation of the trachea is located at the level:
A) VIII thoracic vertebra
B) III thoracic vertebra
C) V thoracic vertebra
D) II thoracic vertebra
8. Number of segments of the upper lobe right lung:
9. Each pulmonary lobe contains:
A) 18 acini
B) 30 acini
C) 10 acini
D) 5 acini
10. Increasing the depth of breathing is called:
A) hyperventilation
B) hyperpnea
C) tachypnea
Task No. 2. Answer the questions of situational problems
No. 1. The subject's vital capacity is 3600 ml, expiratory reserve volume is 1500 ml, inspiratory reserve volume is 1600 ml, respiratory rate is 16 per minute. What is the minute volume of breathing of the subject?
No. 2. Two athletes close in age and physical development, participate in the 1000 meter race. At the end of the distance, the minute volume of breathing of the first is 120 liters, the frequency of respiratory movements is 80 per minute, the minute volume of breathing of the second is 120 liters, with a frequency of respiratory movements of 40 per minute. Which of the athletes being examined is more trained? Calculate the tidal volume of both athletes.
No. 3. When examining the functional state of the student’s external respiration apparatus, it was revealed: tidal volume – 600 ml, inspiratory reserve volume – 1800 ml, exhalation reserve volume – 1900 ml. What is the vital capacity of a student's lungs?
STANDARD ANSWERS
Task No. 1: 1-A, 2-C, 3-D, 4-B, 5-A, 6-B, 7-C, 8-D, 9-A, 10-B.
Task No. 2. No. 1: The minute volume of the subject is 8000 ml, if the tidal volume is 500 ml.
No. 2: The second athlete is more trained: he has a larger tidal volume, so his respiratory rate is half as fast. The tidal volume of the first athlete is 1.5 liters; the second athlete - 3 liters. No. 3: Vital capacity of the lungs – 4300 ml.
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