The airways are divided into upper and lower. The upper ones include the nasal passages, nasopharynx, the lower larynx, trachea, bronchi. The trachea, bronchi and bronchioles are the conduction zone of the lungs. The terminal bronchioles are called the transition zone. They have a small number of alveoli, which contribute little to gas exchange. The alveolar ducts and alveolar sacs belong to the exchange zone.
Physiological is nasal breathing. When cold air is inhaled, a reflex expansion of the vessels of the nasal mucosa and a narrowing of the nasal passages occur. This contributes to better heating of the air. Its hydration occurs due to moisture secreted by the glandular cells of the mucosa, as well as lacrimal moisture and water filtered through the capillary wall. Purification of the air in the nasal passages occurs due to the deposition of dust particles on the mucosa.
Protective respiratory reflexes occur in the airways. When inhaling air containing irritating substances, there is a reflex slowdown and a decrease in the depth of breathing. At the same time, the glottis narrows and the smooth muscles of the bronchi contract. When the irritant receptors of the epithelium of the mucous membrane of the larynx, trachea, bronchi are stimulated, impulses from them arrive along the afferent fibers of the upper laryngeal, trigeminal and vagus nerves to the inspiratory neurons of the respiratory center. There is a deep breath. Then the muscles of the larynx contract and the glottis closes. 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 leaves the lungs at high speed. There is a cough. All these processes are coordinated by the cough center of the medulla oblongata. 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.
There are anatomical, functional and alveolar dead space. Anatomical is the volume of the airways - the nasopharynx, larynx, trachea, bronchi, bronchioles. It does not undergo gas exchange. Alveolar dead space refers to the volume of alveoli that are not ventilated or there is no blood flow in their capillaries. Therefore, they also do not participate in gas exchange. Functional dead space is the sum of anatomical and alveolar. In a healthy person, the volume of alveolar dead space is very small. Therefore, the size of the anatomical and functional spaces is almost the same and is about 30% of the respiratory volume. On average 140 ml. In violation of 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 processes of respiration. The air in it is warmed, humidified, cleaned of dust and microorganisms. Here respiratory protective reflexes are formed - coughing, sneezing. It senses smells and produces sounds.
Depending on the state of the body (sleep, physical work, temperature change, etc.), the frequency and depth of breathing change reflexively. Arcs of respiratory reflexes pass through the respiratory center. Consider such reflexes as sneezing and coughing.
Dust or substances with a pungent odor, entering the nasal cavity, irritate the receptors located in its mucous membrane. There is a protective reflex - 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 during a runny nose causes the same reaction. Cough is a sharp reflex exhalation through the mouth, which 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 the arterial blood, which enters the tissues through the vessels of the systemic circulation, is greater than in the tissue fluid. As a result, oxygen freely passes from the blood into the tissue fluid and into the tissues. Carbon dioxide, which is formed during numerous chemical transformations, on the contrary, passes from the tissues into the tissue fluid, and from it into the blood. Thus, the blood is saturated with carbon dioxide.
Breathing regulation. The activity of the respiratory system is controlled by the respiratory center. It is located in the medulla oblongata. The impulses coming from here coordinate muscle contractions during inhalation and exhalation. From this center, along the nerve fibers through the spinal cord, impulses arrive that cause, in a certain order, the contraction of the muscles responsible for inhalation and exhalation.
The excitation of the center itself depends on the excitations coming from various receptors and on the chemical composition of the blood. Thus, jumping into cold water or dousing with cold water causes a deep breath and holding the breath. Strongly odorous substances can also cause breath holding. This is due to the fact that 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 the larynx, trachea, bronchi - cough. This is a defensive reaction of the body. When sneezing, coughing, foreign particles that have entered the respiratory tract are removed from the body.
When inhaled vapors of substances that irritate the receptors of the mucous membrane of the respiratory tract (chlorine, ammonia) occur reflex spasm muscles of the larynx, bronchi and breath holding.
Short sharp exhalations should also be attributed to protective reflexes - coughing and sneezing. Cough occurs when the bronchi are irritated. There is a deep inhalation followed by an intensified sharp exhalation. The glottis opens, air is released, accompanied by the sound of coughing. sneezing occurs when irritation of the mucous membranes of the nasal cavity. There is a sharp exhalation, as when coughing, but the tongue blocks the back of the mouth and the air exits through the nose. When sneezing and coughing, foreign particles, mucus, etc. are removed from the respiratory tract.
Manifestations of a person's emotional state (laughter and crying) are nothing more than long breaths followed by short, sharp exhalations. A yawn is a long inhale and a long, gradual exhale. Yawning is needed in order to ventilate the lungs before going to bed, as well as increase blood oxygen saturation.
RESPIRATORY DISEASES
The organs of the respiratory system are subject to many infectious diseases. Among them are distinguished airborne and drip-dust infections. The first are transmitted by direct contact with the patient (when coughing, sneezing or talking), the second - by contact with objects that the patient used. The most common viral infections (influenza) and acute respiratory diseases (ARI, SARS, tonsillitis, tuberculosis, bronchial asthma).
Flu and SARS transmitted by airborne droplets. The patient has a fever, chills, body aches, headache, cough and runny nose. Often after these diseases, especially influenza, there are serious complications as a result of disruption of the internal organs - lungs, bronchi, heart, etc.
Pulmonary tuberculosis causes a bacterium Koch's wand(named after the scientist who described it). This pathogen is widely distributed in nature, but the immune system actively suppresses its development. However, under adverse conditions (dampness, malnutrition, reduced immunity), the disease can turn into an acute form, leading to physical destruction of the lungs.
Common lung disease bronchial asthma. With this disease, the muscles of the walls of the bronchi are reduced, an asthma attack develops. The cause of asthma is an allergic reaction to: household dust, animal hair, plant pollen, etc. A number of drugs are used to stop suffocation. Some of them are administered as aerosols and act directly on the bronchi.
The respiratory organs are also affected oncological diseases, most often in chronic smokers.
Used for early diagnosis of lung disease fluorography- a photographic image of the chest, translucent x-rays.
Runny nose, which is an inflammation of the nasal passages, is called rhinitis. Rhinitis can give complications. From the nasopharynx, inflammation through the auditory tubes reaches the middle ear cavity and causes inflammation - otitis.
Tonsillitis- inflammation of the palatine tonsils (gland). Acute tonsillitis - angina. Most often, tonsillitis is caused by bacteria. Angina is also terrible for its complications on the joints and heart. Inflammation of the back of the throat is called pharyngitis. If it affects the vocal cords (hoarse voice), then this laryngitis.
Growth of lymphoid tissue at the exit from the nasal cavity into the nasopharynx is called adenoids. If the adenoids impede the passage of air from the nasal cavity, then they have to be removed.
The most common lung disease is bronchitis. In bronchitis, the lining of the airways becomes inflamed and swells. The lumen of the bronchi narrows, breathing becomes difficult. The accumulation of mucus leads to a constant desire to cough up. The main cause of acute bronchitis is viruses and microbes. Chronic bronchitis leads to irreversible damage to the bronchi. The cause of chronic bronchitis is long-term exposure to harmful impurities: tobacco smoke, pollution derivatives, exhaust gases. Smoking is especially dangerous, since the tar formed during the combustion of tobacco and paper is not removed from the lungs and settles on the walls of the airways, killing mucosal cells. If the inflammatory process extends to the lung tissue, then it develops pneumonia, or pneumonia.
Breathing is easy and free, as the pleura sheets slide freely over each other. With inflammation of the pleura, friction during respiratory movements increases sharply, breathing becomes difficult and painful. This bacterial disease is called pleurisy.
Questions for self-study
1. The main functions of the respiratory system.
2. The structure of the nasal cavity.
3. The structure of the larynx.
4. Mechanism of sound production.
5. The structure of the trachea and bronchi.
6. The structure of the right and left lungs. borders of the lungs.
7. The structure of the alveolar tree. Pulmonary acinus.
The respiratory system performs a number of important functions:
1. I. The function of external respiration is associated with the absorption of oxygen from the inhaled air, saturation of the blood with it and removal of carbon dioxide from the body.
2. II. Non-respiratory functions:
1. Inactivation of a number of hormones occurs in the lungs (for example, serotonin).
2. The lungs are involved in the regulation of blood pressure, because. The endothelium of the capillaries of the lungs synthesizes a factor that promotes the conversion of angiotensin I to angiotensin II.
3. The lungs are involved in the processes of blood clotting, because. the endothelium of the capillaries of the lungs synthesizes heparin and its antipode thromboplastin.
4. In the lungs, erythropoietins are produced, which regulate the differentiation of erythrocytes in the red bone marrow.
5. The lungs are involved in lipid metabolism due to macrophages, which capture cholesterol from the blood and leave the body through the airways, providing physiological prevention of atherosclerosis.
6. Lungs - blood depot.
7. Lungs are involved in immune responses, because. along the airways there are lymphoid nodules that together form broncho-associated lymphoid tissue.
8. The lungs take part in water-salt metabolism.
The protective mechanisms of the respiratory system include filtering large particles in the upper and small particles in the lower respiratory tract, warming and moistening the inhaled! air, absorption of toxic vapors and gases by the vascular network of the upper respiratory tract. Temporary cessation of breathing, reflex shallow breathing, laryngo- or bronchospasm limit the depth of penetration and the amount of foreign matter. However, spasm or a decrease in the depth of breathing can only provide temporary protection. Prevention of aspiration of food, secretions and foreign bodies is ensured by an intact swallowing mechanism and closure of the epiglottis.
Protective reflexes (sneezing, coughing)
The mucous membrane of the respiratory tract is simply dotted with receptors of nerve endings that analyze everything that happens in the respiratory tract. When various foreign bodies and irritating substances enter the mucous membrane of the respiratory tract, as well as when it becomes inflamed, the body responds with protective reflexes - sneezing and coughing.
Sneezing occurs when the receptors of the nasal mucosa are irritated and is a sharp exhalation through the nose, aimed at removing the irritant from the mucosa.
Coughing is a more complex act. In order to produce it, a person needs to take a deep breath, hold his breath, and then exhale sharply, while the glottis is often closed, which leads to a characteristic sound. Cough occurs when irritation of the mucous membrane of the larynx, trachea and bronchi.
The main task of the protective removal of irritating objects from the surface of the mucous membranes, but sometimes a cough is not beneficial, but only aggravates the course of the disease. And then antitussive drugs are used
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1.Hypothalamo-neurohypophyseal system. Hormones of the posterior pituitary gland. The mechanism of action of vasopressin on the epithelial cells of the renal tubules.
Hypothalamo-neurohypophyseal system through majorneurosecretory cells concentrated in the supraoptic and paraventricular hypothalamic nuclei, controls some of the visceral functions of the body. The processes of these cells, through which the neurosecretion is transported, form the hypothalamic-pituitary tract, ending in the neurohypophysis. The pituitary hormone vasopressin is predominantly secreted from the axon endings of the neurosecretory cells of the supraoptic nucleus. It reduces the amount of urine excreted and increases its osmotic concentration, which gave reason to call it also antidiuretic hormone (ADH). There is a lot of vasopressin in the blood of camels and little in guinea pigs, which is due to the ecological conditions of their existence.
Oxytocin is synthesized by neurons in the paraventricular nucleus and released in the neurohypophysis. It targets the smooth muscles of the uterus, stimulates labor activity.
Vasopressin and oxytocin are chemically nanopeptides, identical in 7 amino acid residues. Receptors for them have been identified in target cells.
52. 2. Features of coronary blood flow and its regulation
For the full-fledged work of the myocardium, a sufficient supply of oxygen is necessary, which is provided by the coronary arteries. They begin at the base of the aortic arch. The right coronary artery supplies most of the right ventricle, the interventricular septum, the posterior wall of the left ventricle, the remaining sections are supplied by the left coronary artery. The coronary arteries are located in the groove between the atrium and the ventricle and form numerous branches. The arteries are accompanied by coronary veins that drain into the venous sinus.
Features of coronary blood flow: 1) high intensity; 2) the ability to extract oxygen from the blood; 3) the presence of a large number of anastomoses; 4) high tone of smooth muscle cells during contraction; 5) a significant amount of blood pressure.
At rest, every 100 g of heart mass consumes 60 ml of blood. When switching to an active state, the intensity of coronary blood flow increases (in trained people it rises to 500 ml per 100 g, and in untrained people - up to 240 ml per 100 g).
At rest and activity, the myocardium extracts up to 70-75% of oxygen from the blood, and with an increase in oxygen demand, the ability to extract it does not increase. The need is met by increasing the intensity of blood flow.
Due to the presence of anastomoses, arteries and veins are connected to each other bypassing the capillaries. The number of additional vessels depends on two reasons: the fitness of the person and the ischemia factor (lack of blood supply).
Coronary blood flow is characterized by relatively high blood pressure. This is due to the fact that the coronary vessels start from the aorta. The significance of this lies in the fact that conditions are created for a better transition of oxygen and nutrients into the intercellular space.
During systole, up to 15% of blood enters the heart, and during diastole - up to 85%. This is due to the fact that during systole, contracting muscle fibers compress the coronary arteries. As a result, a portioned ejection of blood from the heart occurs, which is reflected in the magnitude of blood pressure.
Regulation of coronary blood flow is carried out using three mechanisms - local, nervous, humoral.
Autoregulation can be carried out in two ways - metabolic and myogenic. The metabolic method of regulation is associated with a change in the lumen of the coronary vessels due to substances formed as a result of metabolism.
Expansion of coronary vessels occurs under the influence of several factors: 1) lack of oxygen leads to an increase in the intensity of blood flow; 2) an excess of carbon dioxide causes an accelerated outflow of metabolites; 3) adenosyl promotes the expansion of the coronary arteries and increased blood flow.
A weak vasoconstrictor effect occurs with an excess of pyruvate and lactate. Myogenic effect of Ostroumov-Beilis is that smooth muscle cells begin to contract to stretch when blood pressure rises and relax when it is lowered. As a result, the blood flow velocity does not change with significant fluctuations in blood pressure.
Nervous regulation of coronary blood flow is carried out mainly by the sympathetic division of the autonomic nervous system and is activated with an increase in the intensity of coronary blood flow. This is due to the following mechanisms: 1) 2-adrenergic receptors predominate in the coronary vessels, which, when interacting with norepinephrine, lower the tone of smooth muscle cells, increasing the lumen of the vessels; 2) when the sympathetic nervous system is activated, the content of metabolites in the blood increases, which leads to the expansion of the coronary vessels, as a result, an improved blood supply to the heart with oxygen and nutrients is observed.
Humoral regulation is similar to the regulation of all types of vessels.
83. Determination of the erythrocyte sedimentation rate
For work, a Panchenkov tripod is used. The capillary from this rack is flushed with 5% sodium citrate to prevent blood clotting. Then they collect citrate to the mark "75" and blow it onto a watch glass. In the same capillary up to the "K" mark, blood is collected from a finger. Blood is mixed on a watch glass with citrate and again drawn up to the “K” mark (the ratio of diluting fluid and blood is 1: 4). The capillary is installed in a tripod and after an hour the result is evaluated by the height of the formed plasma column in mm.
In men, the norm of ESR is 1-10 mm in one hour, in women, the norm is 2-15 mm in one hour. In the case of an increase in ESR, an inflammatory process develops in the body, immunoglobulins begin to increase in the blood, proteins are in an acute phase, because of this, ESR increases, if it is very high, then inflammation in the body is intense
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Ticket 43
7. Neuromuscular synapse. End plate potential formation (EPP). Differences between PEP and action potential
Synapses with chemical transmission of excitation have a number of common properties: excitation through synapses is carried out only in one direction, which is due to the structure of the synapse (the mediator is released only from the presynaptic membrane and interacts with the receptors of the postsynaptic membrane); the transmission of excitation through the synapses is slower than through the nerve fiber (synaptic delay); synapses have low lability and high fatigue, as well as high sensitivity to chemical (including pharmacological) substances; in synapses, the rhythm of excitation is transformed.
Excitation is transmitted with the help of mediators (intermediaries), Picks - these are chemicals that, depending on their nature, are divided into the following groups; monoamines (acetylcholine, dopamine, norepinephrine, serotonin), amino acids (gamma-aminobutyric acid - GABA, glugamic acid, glycine, etc.) and neuropeptides (substance P, endorphins, neurotensin, angiotensin, vasopressin, somatostatin, etc.). The mediator is located in the vesicles of the presynaptic thickening, where it can enter either from the central region of the neuron using axonal transport or due to the reuptake of the mediator from the synaptic cleft. It can also be synthesized in synaptic terminals from its cleavage products.
An action potential (AP) comes to the end of the nerve fiber; synaptic vesicles release a mediator (acetylcholine) into the sypaptic cleft; acetylcholine (ACh) binds to receptors on the postsynaptic membrane; the potential of the postsynaptic membrane decreases from minus 85 to minus 10 mV (EPSP occurs). Under the action of a current flowing from a depolarized site to a non-depolarized one, an action potential arises on the membrane of the muscle fiber.
EPSP-excitatory postsynaptic potential.
Differences between PKP and PD:
1. PKP is 10 times longer than PD.
2. PKP occurs on the postsynaptic membrane.
3. PKP has a larger amplitude.
4. The PCR value depends on the number of acetylcholine molecules associated with the postsynaptic membrane receptors, i.e. in contrast to the action potential, the EPP is gradual.
54. Features of blood flow in the cortical and medulla of the kidneys, their significance for the function of urination. Mechanisms of regulation of renal blood flow
The kidney is one of the most highly supplied organs with blood - 400 ml / 100 g / min, which is 20-25% of cardiac output. The specific blood supply to the cortex significantly exceeds the blood supply to the medulla of the kidney. In humans, 80-90% of the total renal blood flow flows through the renal cortex. Medullary blood flow is small only in comparison with cortical blood flow, however, if compared with other tissues, it is, for example, 15 times higher than in resting skeletal muscle.
Hydrostatic blood pressure in the capillaries of the glomeruli is much higher than in the somatic capillaries, and is 50-70 mm Hg. This is due to the proximity of the kidneys to the aorta and the difference in the diameters of the afferent and efferent vessels of the cortical nephrons. An essential feature of blood flow in the kidneys is its autoregulation, which is especially pronounced with changes in systemic arterial pressure in the range from 70 to 180 mm Hg.
Metabolism in the kidneys is more intense than in other organs, including the liver, brain and myocardium. Its intensity is determined by the amount of blood supply to the kidneys. This feature is typical for the kidneys, since in other organs (brain, heart, skeletal muscles), on the contrary, the intensity of metabolism determines the amount of blood flow.
Breathing reflexes
Of great biological importance, especially in connection with the deterioration of environmental conditions and air pollution, are protective respiratory reflexes - sneezing and coughing. Sneezing - irritation of the receptors of the nasal mucosa, for example, dust particles or gaseous narcotic substances, tobacco smoke, water causes bronchial constriction, bradycardia, a decrease in cardiac output, narrowing of the lumen of the vessels of the skin and muscles. Various chemical and mechanical irritations 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 irritation of the mechano- and chemoreceptors of the pharynx, larynx, trachea and bronchi. At the same time, after inhalation, the expiratory muscles contract strongly, intrathoracic and intrapulmonary pressure rise 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 occurrence of respiratory movements and their regulation in accordance with the changes that occur in the body. Impulses from D. c. enter the motor neurons of the anterior horns of the cervical and thoracic spinal cord, from which excitation is transmitted to the respiratory muscles. D.'s activity of c. it is regulated humorally, i.e., by the composition of the blood and tissue fluid washing 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 an inhalation center and an exhalation center.
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 the medulla oblongata in the form of two elongated columns near the 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 surface of the medulla oblongata, are designated as the 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 area n. ambiguus caudal to obex level, n. retroambigualis directly rostral to obex and are represented by the Betzinger complex, which is located immediately 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, nucleus of the hypoglossal nerve), which innervate the muscles of the larynx and pharynx.
Interaction of neurons of inspiratory and expiratory zones
Respiratory neurons whose activity causes inspiration or expiration are called inspiratory or expiratory neurons, respectively. There are reciprocal relationships 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 the "early" inspiratory neurons, then the "late" inspiratory neurons are activated. Also, expiratory neurons are sequentially fired, which inhibit inspiratory neurons and stop inspiration. 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.
Representation of autorhythm of breathing. Influence of blood pH on the process of respiration.
If there is a decrease in arterial blood pH from the normal level of 7.4, ventilation of the lungs increases. As the pH rises above normal, ventilation decreases, although to a lesser extent.
autorhythmia- these are waves of excitation and the corresponding "movements" of the animal, occurring with a certain periodicity. autorhythmia - spontaneous activity of the central nervous system, which is carried out without any influence of afferent stimulation and manifests itself in rhythmic and coordinated movements of the body.
Pneumotoxic center of the varoli mota. Interaction with the respiratory center of the medulla oblongata
The pons contains the nuclei of the respiratory neurons that form the pneumotaxic center. It is believed that the respiratory neurons of the bridge are involved in the mechanism of inhalation and exhalation and regulate the amount of tidal volume. The respiratory neurons of the medulla oblongata and the pons varolii are interconnected by ascending and descending nerve pathways and function in concert. Having received impulses from the inspiratory center of the medulla oblongata, the pneumotaxic center sends them to the expiratory center of the medulla oblongata, stimulating the latter. Inspiratory neurons are inhibited. Brain destruction between the medulla oblongata and the pons prolongs the inspiratory phase.
Spinal cord; motoneurons 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 of - motor neurons are located, forming the phrenic nerve. The phrenic nerve, a mixed nerve that provides sensory innervation to the pleura and pericardium, is part of the cervical plexus; formed by the anterior branches of the C3-C5 nerves. It 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 pericardium). Passing along these nerves from the brain, impulses cause periodic contractions of the diaphragm during breathing.
The motor neurons innervating the intercostal muscles are located in the anterior horns at levels - (- - motor neurons of the inspiratory muscles, - - expiratory). The motor branches of the intercostal nerves innervate the autochthonous muscles (inspiration) of the chest and abdominal muscles. It has been established that some regulate predominantly respiratory, while others regulate postural tonic activity of the intercostal muscles.
The role of the cerebral cortex in the regulation of respiration. Certain zones of the cerebral cortex carry out voluntary regulation of respiration in accordance with the characteristics 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 brain stem, cortical zones also affect the state of respiratory function, providing its arbitrary regulation. They are located in the cortex of the somatomotor divisions and mediobasal structures of the brain. There is an opinion that the motor and premotor areas of the cortex, at the will of a person, facilitate, activate breathing, and the cortex of the mediobasal parts of the cerebral hemispheres slows down, restrains respiratory movements, affecting the state of the emotional sphere, as well as the degree of balance of autonomic functions. These parts of the cerebral cortex also influence the adaptation of the respiratory function to complex movements associated with behavioral responses, and adapt breathing to the current expected metabolic shifts.
Regulation of blood pressure, blood flow
In the ventrolateral parts of the medulla oblongata, formations are concentrated that correspond in their characteristics to those ideas that are invested in the concept of "vasomotor center". Nerve elements are concentrated here, which play a key role in tonic and reflex regulation of blood circulation. In the ventral parts of the medulla oblongata there are neurons, the 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 neurons in the caudal part of the ventral parts of the medulla oblongata to the cells of its rostral part have been proven, which indicates the possibility of tonic inhibition of the activity of these cells. The connections between the structures of the ventral parts of the medulla oblongata and the nucleus of the solitary tract, which plays a key role in the processing of afferentation from the chemo- and baroreceptors of the vessels, are functionally significant.
In the medulla oblongata 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 nuclei of the vagus nerve constantly send impulses, thanks to which a constant tone is maintained: the arteries and arterioles are constantly somewhat narrowed, and cardiac activity is slowed down.
VF Ovsyannikov (1871) found that the nerve center that provides a certain degree of narrowing of the arterial bed - the vasomotor center - is located in the medulla oblongata. The localization of this center was determined by transection of the brain stem at different levels. If the transection is made in a dog or cat above the quadrigemina, then blood pressure does not change. If the brain is cut between the medulla oblongata and the spinal cord, then the maximum blood pressure in the carotid artery drops to 60-70 mm Hg. 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 part of the vasomotor center causes narrowing of the arteries and rise, and irritation of the second part causes the expansion of the arteries and a drop in blood pressure.
It is believed that the depressor part of the vasomotor center causes vasodilation, lowering the tone of the pressor part and thus reducing the effect of the vasoconstrictor nerves.
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 individual parts of the body. The spinal centers are able, some time after the vasoconstrictor center of the medulla oblongata is turned off, to slightly increase 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 various zones of the hypothalamus are stimulated with electric current, both vasoconstriction and vasodilation can be caused. The impulse is transmitted along the fibers of the posterior longitudinal bundle. Part of the fibers pass through the area, do not switch and go to the vasomotor neurons. Information comes from osmoreceptors, they capture the state of water inside and outside the cell contained in the hypothalamus. Activation of osmoreceptors causes a hormonal effect - the release of vasopressin, and this substance has a strong vasoconstrictor effect, it has a holding property.
NES (neuroendocrine regulation) is of particular importance in the regulation of visceral (“relating to internal organs”) functions of the body. It has been established that the efferent effects of the CNS on visceral functions are realized in the norm and in pathology by both vegetative and endocrine apparatuses (Speckmann, 1985). Unlike the cortex, the hypothalamus, obviously, is constantly involved in controlling the work of the visceral systems of the body. Ensures the stability of the internal environment. Control over the action of the sympathetic and parasympathetic systems innervating the internal organs, blood vessels, smooth muscles, glands of internal and external secretion, is carried out by the “visceral brain”, which is represented by the central autonomic apparatuses (vegetative nuclei) of the hypothalamic region (O.G. Gazenko et al., 1987). In turn, the hypothalamus is under
control of certain areas of the cortex (in particular, 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 cerebral cortex. 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 of blood vessels
Afferent impulses from baroreceptors arrive at the vasomotor center of the medulla oblongata. These impulses have an inhibitory effect on the sympathetic centers and excitatory on the parasympathetic. As a result, the tone of the 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 blood pressure values, their inhibitory effects are manifested even at “normal” pressure. In other words, baroreceptors have a constant 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, with vessels dilating to varying degrees in different areas. With a drop in pressure, the impulses from baroreceptors decrease and reverse processes develop, ultimately leading to an increase in pressure. Excitation of chemoreceptors leads to a decrease in the frequency of heart 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 consequences 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 baroreceptors, signals from which enter the central nervous system. Then the feedback signals are sent to the centers of the autonomic nervous system, and from them to the vessels. As a result, the pressure drops to a normal level. Baroreceptors respond extremely quickly to changes in blood pressure.
Chemoreceptors are sensitive to the chemical components of the blood. arterial chemoreceptors respond to changes in the concentration of oxygen, carbon dioxide, hydrogen ions, nutrients and hormones in the blood, the level of osmotic pressure; chemoreceptors maintain homeostasis.
