Pulp cardiac reflex. Intraoperative complications. Conjugate reflexes of the cardiovascular system

8.10. CONNECTED REFLEXES OF THE CARDIOVASCULAR SYSTEM

This concept was introduced into physiology by V. N. Chernigovsky. Conjugate (intersystem) reflexes are reflex influences on the cardiovascular system from the reflexogenic zones of other organs or from the cardiovascular system to other body systems. They do not directly participate in the regulation of systemic blood pressure. The following reflexes can serve as an example of conjugate reflexes.

Danini-Aschner reflex (eye-heart reflex) is a decrease in heart rate (HR) that occurs when pressure is applied to the lateral surface of the eyes.

Goltz reflex - a decrease in heart rate or even complete cardiac arrest when the mechanoreceptors of the abdominal organs or peritoneum are irritated, which is taken into account during surgical interventions in the abdominal cavity. In Goltz's experiment, beating the frog's stomach and intestines leads to cardiac arrest.

Tom reflex - RU - bradycardia with strong pressure or shock to the epigastric region. A blow to the stomach (below the xiphoid process of the sternum - the solar plexus area) in a person can lead to cardiac arrest, short-term loss of consciousness and even death. For boxers, such a blow is prohibited. The Goltz and Tom-Ru reflexes are carried out with the help of the vagus nerve and, apparently, have a common reflexogenic zone.

Reflex from mechano- and thermoreceptors of the skin when they are irritated consists of inhibition or stimulation of cardiac activity. The degree of their expression can be very strong. For example, there are known cases of death due to cardiac arrest when diving into cold water (sharp cooling of the abdominal skin).

Reflex from proprioceptors occurs during physical activity and is expressed in an increase in heart rate due to a decrease in: the tone of the vagus nerves. This reflex is adaptive - it improves the supply of working muscles with oxygen and nutrients, and removes metabolites. Conditioned reflexes changes in cardiac activity are also classified as associated reflexes, for example, a pre-launch state, which is accompanied by pronounced emotions and the release of adrenaline into the blood.

8.11. LYMPHATIC SYSTEM

The lymphatic system is a collection of lymphatic vessels and lymph nodes located along their course, ensuring the absorption of intercellular fluid and substances and their return to the bloodstream. The lymphatic system maintains the balance of various substances and fluids in the body.

Lymphatic vessels begin with capillaries, which are an extensive branched network of small thin-walled vessels, unevenly represented in different parts of the body "(for example, there are none in the brain, few in the muscles). The lymphatic system begins with the thinnest terminals, closed at one end ny lymphatic capillaries. Their walls are highly permeable; protein molecules and other large particles easily pass inside along with tissue fluid. In structural and functional terms, lymphatic vessels are similar to veins and are also equipped with valves that prevent the reverse flow of lymph. valves (valve segments), hereafter called lymphangions(ANzNp), provide the pumping function of the lymphatic system (R. S. Orlov). Lymphatic vessels flow into the venous system. In particular, the thoracic duct flows into the angle formed by the left (external jugular and subclavian) veins at their confluence.

Lymphatic nodes, located on the path of lymphatic vessels, due to the presence of smooth muscle elements in them, they are able to contract. The bacteria contained in the lymph are phago-

quoted by lymph node cells. At the same time, an inflammatory process develops in the lymph nodes, they increase in size and become painful. Functions of the lymphatic system.

Drainage function consists in removing metabolic products and excess water from the interstitium, filtered from the blood capillaries and not completely reabsorbed. If lymph flow stops, tissue swelling and dystrophic disorders develop.

Protective function consists in ensuring the transport of antigens and antibodies, in the transfer of plasma cells from the lymphoid organs to ensure humoral immunity - in the formation of an immune response to the antigen, in the cooperation of various immunocompetent cells (lymphocytes, macrophages), in the implementation of cellular immunity.

Return of proteins and electrolytes into the blood (about 40 g of protein returns to the blood per day).

Transport from the digestive system products of hydrolysis of nutrients (mainly lipids) into the blood.

Hematopoietic function is that in the lymphoid tissue the processes of differentiation and formation of new lymphocytes that begin in the bone marrow continue.

Lymph is a transparent liquid, slightly yellowish in color, salty taste, with a cloying odor. It consists of lymphoplasm and formed elements, mainly lymphocytes. The chemical composition of lymphoplasm is close to blood plasma.

Lymph is formed as a result of filtration of fluid from the capillaries into the interstitium, from where it diffuses into the lymphatic capillaries. Proteins, chylomicrons and other particles enter the cavity of the lymphatic capillary through pinocytosis. The filtration rate in all blood capillaries (except for the glomeruli) is 14 ml/min, which is 20 liters per day; the reabsorption rate is about 12.5 ml/min, i.e. 18 liters per day. Consequently, about 2 liters of fluid per day enters the lymphatic capillaries. The lymphatic vessels of an adult weighing 70 kg on an empty stomach contain 2-3 liters of lymph.

The direct driving force of lymph, like blood, in any part of the vascular bed there is hydrostatic pressure gradient. The valve apparatus of the lymphatic vessels prevents the reverse flow of lymph. In working organs, lymph flow increases. The hydrostatic pressure gradient in the lymphatic system is created by several factors. 1. The main one is the contractile activity of the lymphatic

vessels and nodes. The lymphangion has a muscle-containing part and an area with weak development of muscle elements (the area of attachment of the valves). The functions of lymphatic vessels are characterized by phasic rhythmic contractions (10-20 per minute), slow waves (2-5 per minute) and tone. 2. Suction action of the chest(as well as for the movement of blood through the veins). 3. Reduction of ske-flight muscles, pulsation of nearby large arterial vessels, increased intra-abdominal pressure.

Regulation of contractile activity of lymphangions carried out using nervous, humoral and myogenic mechanisms. Myogenic regulation lymphangions are carried out thanks to the automaticity of smooth muscles, while an increase in their stretching leads to an increase in the force of contraction and has an activating effect on neighboring lymphangions. Nervous regulation contractile activity of lymphangions, according to R. S. Orlov et al. (1982), is carried out with the help of the intramural nervous system and the sympathetic nervous system, which activates α-adrenergic receptors, which leads to an increase in phasic contractions. Catecholamines cause multidirectional reactions of lymphatic microvessels. The effect depends on the dose of the drug, apparently for the same reason as in the blood vessels. Cholinergic effects are ambiguous, but, as a rule, low concentrations of acetylcholine reduce the frequency of spontaneous phasic contractions of lymphangion pacemakers. Hormonal regulation contractions of lymphangions has not been studied enough. It is known, for example, that vasopressin increases lymph flow, while oxytocin inhibits it.

Chapter 9 DIGESTIVE SYSTEM

9.1. CONCEPTS. CHARACTERISTICS OF SMOOTH MUSCLE

Most of the body's smooth muscles are found in the digestive system.

Digestive system It is a convoluted tube starting with the mouth and ending with the anus, with adjacent salivary glands, liver and pancreas. There is also the concept digestive tract, which includes the oral part, pharynx, food-

water, stomach, small and large intestines (intestines). The stomach and intestines make up gastrointestinal tract (Gastrointestinal tract).

The wall of the digestive tract has the same structure and includes V itself mucous, submucosal, muscular and serous membranes. The digestive tract communicates with the outside world. However, the wall of the digestive tract reliably protects the internal environment of the body from the entry of microbes and foreign particles from the external environment.

Digestion - This is a set of processes that ensure the breakdown of proteins, fats and carbohydrates of food in the digestive tract into relatively simple compounds - nutrients. Nutrients - this is water, mineral salts, vitamins and products of the breakdown of proteins, fats and carbohydrates of food in the digestive tract into compounds that are not species-specific, but retain energy and plastic value, capable of being absorbed into the blood and lymph and assimilated by the body (A. A. Kromin). The source of nutrients is food. Importance of the digestive system - providing cells and tissues of the body with initial plastic and energy materials used in the metabolic process.

For nutrients to enter the body, food must be subjected to physical processing (crushing, mixing, swelling and dissolving), chemical processing - hydrolysis. Hydrolysis is the process of breakdown of polymers (depolymerization) - proteins, fats and carbohydrates under the influence of hydrolytic enzymes of the digestive glands into monomers. The glands of the digestive tract produce three groups of hydrolytic enzymes: proteases (break down proteins into amino acids) lipases (break down fats and lipids into monoglycerides and fatty acids) and carbohydrases (break down carbohydrates into monosaccharides). It is these products of food breakdown (digestion) that are the nutrients of a living organism.

Smooth muscle. The walls of many internal organs are smooth (non-striated) muscles (stomach, intestines, esophagus, gall bladder, etc.). Their activity is not controlled arbitrarily. Therefore, smooth muscles and the heart muscle are called involuntary. Slow, often rhythmic contractions of the smooth muscle walls of the internal organs ensure the movement of the contents of these organs. Tonic contraction of the walls of blood vessels maintains an optimal level of blood pressure and blood supply to organs and tissues, lymph outflow from skeletal muscles and internal organs. Smooth muscles are built from spindle-shaped mononuclear muscle cells, the thickness of which is

is 2-10 µm, length - from 50 to 400 µm. The fibers are interconnected nexuses, which conduct excitement well, therefore smooth muscle functions as a syncytium - a functional formation in which excitation can be directly transmitted from one cell to another. This property distinguishes smooth muscle from skeletal muscle and is similar to cardiac muscle. However, for the occurrence of PD, it is necessary to excite a certain number of muscle fibers; excitation of one muscle fiber is not enough. Thus, the functional unit of smooth muscle is not a single cell, as in skeletal muscle, but a muscle bundle.

Many smooth muscle fibers have automaticity. The resting potential in smooth muscle cells is 30-70 mV. The duration of peak-like APs is 5-80 ms; APs with a plateau, characteristic of the smooth muscles of the uterus, urethra and some vessels, last from 30 to 500 ms. Ca 2+ plays the main role in the generation of smooth muscle action potential.

The process of contraction of smooth muscle fibers occurs by the same mechanism of sliding of actin and myosin filaments as in skeletal muscles. However, in smooth muscle cells weak The sarcoplasmic reticulum is more pronounced. In this regard, the trigger for muscle contraction is the entry of Ca 2+ ions into the cell from the intercellular environment during the generation of AP. Ca 2+ ions affect protein calmodulin, which activates myosin light chain kinases. This ensures the transfer of the phosphate group to myosin and immediately triggers the activation of cross bridges, i.e. reduction. The troponin-tropomyosin system appears to be absent in smooth muscle. The force of contraction genies smooth muscles have less force than skeletal muscle contractions. Contraction speed smooth muscles is small - 1-2 orders of magnitude lower than that of skeletal muscles.

The characteristic properties of smooth muscle are car tires and plasticity (smooth muscle can be relaxed in a shortened and stretched state). Due to the plasticity of smooth muscle, the pressure in the hollow internal organs can change little when they are filled significantly.

9.2. FUNCTIONS OF THE DIGESTIVE SYSTEM. STATE OF HUNGER AND SATURATION

The digestive system performs digestive and non-digestive functions.

Digestive functions.

Motor (motor) function - This is the contractile activity of the digestive tract, which ensures the grinding of food, its mixing with digestive secretions and the movement of food contents in the distal direction.

Secretion - synthesis by a secretory cell of a specific product - secretion and its release from the cell. The secretion of the digestive glands ensures the digestion of food.

Suction - transport of nutrients into the internal environment of the body.

Non-digestive functions of the digestive system.

Protective function carried out using several mechanisms. ]. The mucous membranes of the digestive tract prevent the penetration of undigested food, foreign substances and bacteria into the internal environment of the body (barrier function). 2. Digestive juices have a bactericidal and bacteriostatic effect. 3. The local immune system of the digestive tract (tonsils of the pharyngeal ring, lymphatic follicles in the intestinal wall, Peyer's patches, plasma cells of the mucous membrane of the stomach and intestines, vermiform appendix) blocks the action of pathogenic microorganisms. 4. The digestive tract produces natural antibodies upon contact with obligate intestinal microflora.

Metabolic function consists in the circulation of endogenous substances between the blood and the digestive tract, providing the possibility of their reuse in metabolic processes or digestive activity. Under conditions of physiological hunger, endogenous proteins are periodically released from the blood into the cavity of the gastrointestinal tract in the composition of digestive juices, where they undergo hydrolysis, and the resulting amino acids are absorbed into the blood and included in metabolism. A significant amount of water and inorganic salts dissolved in it circulates between the blood and the digestive tract.

Excretory (excretory) function consists of removing from the blood with the secretions of the glands into the cavity of the digestive tract metabolic products (for example, urea, ammonia) and various foreign substances that enter the bloodstream (salts of heavy metals, medicinal substances, isotopes, dyes) introduced into organism for diagnostic purposes.

Endocrine function consists in the secretion of hormones of the digestive system, the main of which are:

sulin, glucagon, gastrin, serotonin, cholecystokinin, secretin, vasoactive intestinal peptide, motilin.

State of hunger. The feeling of hunger occurs after the evacuation of chyme from the stomach and duodenum, the muscle wall of which acquires increased tone and the impulse from the mechanoreceptors of the empty organs increases. (sensory stage state of hunger). When nutrients in the blood decrease, metabolic stage states of hunger. The lack of nutrients in the blood (“hungry” blood) is perceived by the chemoreceptors of the vascular bed and directly by the hypothalamus, which are selectively sensitive to the lack of certain nutrients in the blood. In this case, it is formed food mo- tification (caused by the dominant food need, the body’s motivation for eating behavior - searching, obtaining and eating food). Irritation by electric current of the hypothalamic hunger center in animals causes hyperphagia - continuous eating of food, and its destruction - aphagia (refusal of food). The hunger center of the lateral hypothalamus is in a reciprocal (mutually inhibitory) relationship with the saturation center of the ventromedial hypothalamus. When this center is stimulated, aphagia is observed, and when it is destroyed, hyperphagia is observed.

State of saturation. After taking in enough food to satisfy nutritional needs, the stage begins sensory saturation, which is accompanied by a positive emotion. True stage saturation occurs much later - 1.5-2 hours after eating, when nutrients begin to enter the blood.

9.3. DIGESTION IN THE ORAL CAVITY. ACT OF SWALLOWING

Mechanical and chemical processing occurs in the oral cavity.
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A.Mechanical restoration food in the oral cavity is carried out with the help of chewing.

The chewing process is voluntary. Efferent impulses are transmitted along the corticobulbar pathway to the motor nucleus of the masticatory center in the medulla oblongata and further along the centrifugal fibers of the trigeminal, facial and hypoglossal nerves to the masticatory muscles, causing their rhythmic contractile activity. Chewing process under experimental conditions can be carried out involuntarily (automatic movements). Decerebrate animals perform rhythmic chewing

movements when food is placed in their mouth. Careful grinding of food during chewing to particles with a diameter of several millimeters plays a very important role.

It greatly facilitates subsequent digestion and absorption.

Chewing stimulates salivation, which shapes the sense of taste and the digestion of carbohydrates.

Chewing has a reflex stimulating effect on the secretory and motor activity of the gastrointestinal tract.

Chewing ensures the formation of a bolus of food suitable for swallowing and digestion.

B.Chemical food processing in the oral cavity it is carried out with the help of saliva, which is produced in the parotid, submandibular, sublingual salivary glands, as well as in the glands of the tongue and palate. 0.5-2.0 liters of saliva are secreted per day. The saliva of different glands varies somewhat. Mixed saliva 99.5% consists of water, has a pH of 5.8-7.4. One third of the dry residue consists of mineral components of saliva, two thirds are organic substances: proteins, amino acids, nitrogen-containing compounds of non-protein nature (urea, ammonia, creatinine, creatine). The viscosity and slimy properties of saliva are due to the presence of mucopolysaccharides (mucin). Saliva performs several functions.

Provides physical processing of food: 1) wetting food and thereby facilitating its grinding and homogenization during chewing; 2) dissolution of substances, without which taste perception is impossible; 3) licking of food during chewing, which is necessary for the formation of a food bolus and its swallowing.

Chemical processing of food - digestion of carbohydrates - carried out by salivary enzymes: a-amylase (breaks down starch and glycogen to maltose and glucose) and a-glucosidase (maltase hydrolyzes maltose to monosaccharides). Due to the short stay of food in the oral cavity (15-20 s), the main hydrolytic effect (carbohydrases of saliva) is realized in the stomach.

Saliva also performs a protective function. Muromi-daza (lysozyme) of saliva has a bactericidal effect; Proteinases, which resemble trypsin in their substrate specificity, disinfect the contents of the oral cavity. Salivary nucleases are involved in the degradation of viral nucleic acids.

IN.Regulation of the secretion of the salivary glands is carried out through conditioned and unconditioned reflexes. Branch

saliva begins a few seconds after eating. During the process of eating, tactile, temperature and taste receptors of the oral mucosa are excited. Streams of afferent impulses enter through the sensory fibers of the trigeminal, facial, glossopharyngeal and vagus nerves into the bulbar section of the salivary center, which is represented by the superior and inferior salivary nuclei. Afferent- nal impulses also enter the overlying parts of the central nervous system, including the cortical part of the taste analyzer. Excitation of parasympathetic nerves (the chorda tympani innervates the submandibular and sublingual glands, the glossopharyngeal nerve innervates the parotid gland) causes abundant secretion of liquid saliva with a high concentration of salts and low mucin content. Stimulation of sympathetic nerves (preganglionic neurons, localized in the II-V thoracic segments of the spinal cord) causes the release of a small amount of thick saliva with a high concentration of enzymes and mucin. As a result of chewing, the bolus of food is prepared for swallowing.

G.The act of swallowing consists of three phases.

During the first (oral) phase of swallowing With the help of the tongue, the food bolus is transferred behind the anterior arches of the pharyngeal ring, and chewing stops. This phase is voluntary. The larynx rises with the help of contraction of the mylohyoid muscle.

Second (pharyngeal) phase of swallowing involuntary, occurs due to irritation of the mechanoreceptors of the mucous membrane of the root of the tongue, anterior arches and soft palate by the food bolus. When these receptors are pharmacologically switched off, swallowing becomes impossible. The act of swallowing cannot be induced if there is no food, water or saliva in the oral cavity. The second phase of the act of swallowing ends with the entry of a bolus of food from the pharynx into the esophagus. The duration of the first two phases of the act of swallowing is about 1 s.

The third (esophageal) phase of the act of swallowing also involuntary, ensures the entry of the food bolus into the stomach. After the food bolus enters the initial part of the esophagus, a peristaltic wave, primary in the proximodistal direction, appears in it, ensuring the movement of the food bolus along the esophagus. The contraction of the circular striated muscles above the bolus and their relaxation below the bolus creates a proximodistal pressure gradient. In the thoracic region, the striated muscles of the esophagus are replaced by smooth ones, but the peristaltic wave spreads along the entire length of the esophagus. The duration of passage of water through the esophagus is 1 s, mucous mass - 5 s, solid food - 9-10 s.

D.Regulation of motor function of the esophagus carried out mainly by the vagus nerve. Moreover, the striated muscles of the upper part of the esophagus are controlled by it Report

2009. Smirnov V.M., Dubrovsky V.I. Physiologyphysicaleducation And sports: Textbook. -M.: Vlados-Press, 2002 ... Hygienic fundamentals physical culture and sports Main: 1. Weinbaum Y.S. Hygiene physicaleducation And sports: Textbook. help...

Relevance. Many surgeons and anesthesiologists encounter during dental and neurosurgical operations (for example, with injuries in the middle third of the face, with the removal of vestibular schwanoma, etc.) with the occurrence (due to the trigeminocardiac reflex) of intraoperative bradycardia and hypotension, which lead to hypoperfusion of the brain and the development of ischemic foci in it.

Trigeminal cardiac reflex(trigemincardiac reflex, TCR) - a decrease in heart rate and a drop in blood pressure by more than 20% from baseline values during surgical manipulations in the region of the branches of the trigeminal nerve (Schaller, et al., 2007).

There are central and peripheral types of the trigeminal-cardiac reflex, the anatomical boundary between which is the trigeminal (Gasserian) node. The central type develops during surgical manipulations at the base of the skull. The peripheral type, in turn, is divided into the ophthalmocardiac reflex (OCR) and the maxillomandibular cardiac reflex (maxillomandibulocardiac reflex - MCR), this division is mainly due to the area of surgical interests of various specialists.

Cardiac dysfunction, arterial hypotension, apnea and gastroesophageal reflux as a manifestation of the trigemincardiac reflex (TCR) were first described by Kratschmer in 1870 (Kratschmer, 1870) with irritation of the nasal mucosa in experimental animals. Later in 1908, Aschner and Dagnini described the orbital-cardiac reflex (oculocardiac reflex). But most clinicians view the orbitocardiac reflex as the originally described peripheral subtype of the trigeminocardiac reflex (Blanc, et al., 1983). However, we can say with confidence that back in 1854 N.I. Pirogov predetermined and anatomically substantiated the development of the reflex. He outlined a detailed description of the autonomic innervation of the ocular complex in his work “Topographic anatomy, illustrated by sections drawn through the frozen human body in three directions.” In 1977 Kumada et al. (Kumada, et al., 1977) described similar reflexes during electrical stimulation of the trigeminal complex in laboratory animals. In 1999, anesthesiologist Schaller et al. (Schaller, et al., 1999) initially described the central type of trigeminal cardiac reflex, after irritation of the central part of the trigeminal nerve during surgery in the area of the cerebellopontine angle and brain stem. It was then that Schaller combined the concept of central and peripheral afferent stimulation of the trigeminal nerve, which is recognized to this day, although detailed anatomical justifications are presented in the work of N.I. Pirogov.

Stimulation of any branch of the trigeminal nerve causes an afferent flow of signals (i.e., from the periphery to the center) through the trigeminal ganglion to the sensory nucleus of the trigeminal nerve, crossing the efferent pathways from the motor nucleus of the vagus nerve. Efferent pathways contain fibers that innervate the myocardium, which in turn closes the reflex arc (Lang, et al., 1991, Schaller, 2004).

Clinical manifestations of the trigeminal cardiac reflex are associated with a high risk of developing life-threatening conditions, such as bradycardia and the culmination of bradycardia - asystole, as well as the development of asystole without previous bradycardia or apnea (Campbell, et al., 1994, Schaller, 2004).

The general prerequisites for the development of the reflex are hypercapnia, hypoxia, “superficial” anesthesia, young age, as well as prolonged exposure to external stimuli on the nerve fiber. The presence of a large number of external stimuli, such as mechanical compression, chemical intraoperative solutions (H2O2 3%), long-term use of painkillers contribute to additional sensitization of the nerve fiber and the development of cardiac manifestations of the reflex (Schaller, et al., 2009, Spiriev, et al., 2011 ) [: article “Trigeminal-cardiac reflex in surgery of midface injuries” Shevchenko Yu.L., Epifanov S.A., Balin V.N., Apostolidi K.G., Mazaeva B.A. National Medical and Surgical Center named after. N.N. Pirogova, 2013].

© Laesus De Liro

(r. cardiocardialis) vegetative P: a change in the activity of the heart or its parts when the pressure in the cavities of the heart changes (for example, a drop in pressure in the left ventricle causes a reflex increase in frequency and intensification of its contractions).

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Baroreceptor reflex. Baroreceptors are receptors that sense stretching of the arterial wall and are located in the carotid sinuses and aortic arch. Afferent impulses from the receptors of the carotid sinuses enter the brain through the nerves of the carotid sinuses, which are branches of the glossopharyngeal (ίΧ pair of cranial nerves), and from the baroreceptors of the aortic arch - through the aortic nerves, which are branches of the vagus nerves (X pair of cranial nerves).

The efferent arm of the baroreceptor reflex is formed by sympathetic and parasympathetic fibers. With an increase in mean arterial pressure in the area of the carotid sinuses and aortic arch, nerve activity in efferent sympathetic fibers decreases and activity in efferent parasympathetic fibers increases. As a result, vasomotor tone in the resistive and capacitive vessels of the whole body decreases, the heart rate decreases, the atrioventricular conduction time increases and the contractility of the atria and ventricles decreases. When the pressure drops, the opposite effect is observed. The synchronous action of the sympathetic and parasympathetic divisions is observed only under physiological conditions, when blood pressure fluctuates near the normal pressure range. If blood pressure drops sharply to an abnormal level, then reflex regulation is carried out exclusively due to efferent sympathetic activity (since the tone of the vagus nerve practically disappears), and vice versa, if blood pressure rises sharply to an abnormally high level, sympathetic tone is completely inhibited, and reflex regulation is carried out only due to changes in the efferent activity of the vagus

Bainbridge reflex. The increase in circulating blood volume, leading to dilation of the ostia of the vena cava and atria, leads to an increase in heart rate, despite the concomitant increase in blood pressure. Afferent impulses during this reflex are transmitted along the vagus nerves.

Chemoreceptor reflex Peripheral arterial chemoreceptors respond to a decrease in p0 2 and pH of arterial blood and to an increase in pCO 2. Chemoreceptors are located in the arch of the aorga and the carotid bodies surrounding the carotid sinuses. Stimulation of arterial chemoreceptors causes hyperventilation of the lungs, bradycardia and vasoconstriction. However, the amplitude of cardiovascular responses depends on concomitant changes in pulmonary ventilation; if stimulation of chemoreceptors causes a moderate degree of hyperventilation, then the cardiac response is likely to be bradycardia. On the contrary, with severe hyperventilation caused by stimulation of chemoreceptors, the heart rate usually increases.

An extreme example of such a reflex reaction is a situation where it is impossible to increase ventilation of the lungs in response to stimulation of chemoreceptors. Thus, in patients undergoing artificial ventilation, stimulation of carotid chemoreceptors causes a sharp increase in the activity of the vagus nerve, leading to severe bradycardia and disruption of atrioventricular conduction.

Pulmonary reflexes. Due to the presence of baroreceptors in the pulmonary artery, filling the lungs with air causes a reflex increase in heart rate, which is eliminated by denervation of both lungs; the afferent and efferent pathways of this reflex are located in the vagus nerves.

Stretching of the pulmonary veins leads to a reflex increase in heart rate; The efferent pathway of the reflex lies in the sympathetic nerves.

The pulmonary depressor chemoreflex is activated from the chemoreceptors of the lung tissue (decreased systolic pressure and bradycardia).

Oculocardial Aschner reflex. Compression of the eyeballs causes a profound slowing of the heart rate.

Strictly speaking, irritation of various areas and parts of the body can change the rhythm of heart contractions. Impulses arising in all visceral afferent devices, i.e. in all tissues (except skin), lead to bradycardia. Irritation of internal organs can cause a sharp, sometimes dramatic depression in heart rate. For example, cardiac arrest can be caused by irritation of the nerve endings in the upper respiratory tract. Bradycardia is caused by finger pressure on the area of the carotid sinuses, inserting a needle into the brachial artery with the patient in an upright position can cause a similar effect, the gastrointestinal tract is equipped with a large number of afferent nerve endings and receptors, the fibers of which reach the medulla oblongata as part of the vagus nerve, resulting in nausea and vomiting is usually accompanied by a slowing of heart contractions, regardless of whether they are caused by mechanical irritation of the root of the tongue, pharynx, or exposure to toxic agents. Painful stimulation of skeletal muscles causes bradycardia.

Reflex regulation of heart activity

It is carried out with the participation of the centers of the vagus and sympathetic nerves (the second level of the hierarchy) and the centers of the hypothalamic region (the first level of the hierarchy). Reflex reactions can both inhibit (slow down and weaken) and excite (accelerate and strengthen) heart contractions.

Reflex changes in heart function occur when various receptors are stimulated. These receptors are excited when blood pressure changes in the vessels or when exposed to humoral (chemical) stimuli. The areas where such receptors are concentrated are called vascular reflexogenic zones .

The most significant role is played by reflexogenic zones located in the aortic arch and in the area of the branch of the carotid artery. Here are the endings of the centripetal nerves, the irritation of which reflexively causes a decrease in heart rate. These nerve endings are baroreceptors. Their natural irritant is the stretching of the vascular wall when the pressure in the vessels where they are located increases. The flow of afferent nerve impulses from these receptors increases the tone of the vagus nerve nuclei, which leads to a slowdown in heart contractions. The higher the blood pressure in the vascular reflexogenic zone, the more often afferent impulses occur.

Receptors have also been found in the heart itself: the endocardium, myocardium and epicardium; their irritation reflexively changes both the work of the heart and the tone of blood vessels.

In the right atrium and at the mouths of the vena cava there are mechanoreceptors that respond to stretching (with an increase in pressure in the atrium cavity or in the vena cava). Volleys of afferent impulses from these receptors pass along the centripetal fibers of the vagus nerves to a group of neurons in the reticular formation of the brainstem, called "cardiovascular center". Afferent stimulation of these neurons leads to the activation of neurons of the sympathetic division of the autonomic nervous system and causes a reflex increase in heart rate. Impulses going to the central nervous system from the mechanoreceptors of the atria also affect the functioning of other organs

A classic example of the vagal reflex was described in the 60s of the last century: light tapping on the stomach and intestines of a frog causes the heart to stop or slow down. The vagal reflexes also include the Aschner ocular reflex (a decrease in heart rate by 10-20 per minute when pressing on the eyeballs).

Reflex acceleration and increased cardiac activity are observed during painful stimulation and emotional states: rage, anger, joy, as well as during muscle work.

Changes in cardiac activity are caused by impulses traveling to the heart through the sympathetic nerves, as well as by a weakening of the tone of the vagus nerve nuclei.

Own reflexes:

Zion-Ludwig

1. Increased blood pressure.

2. Irritation of high pressure baroreceptors in the receptor zone of the aortic arch.

3. An increase in the frequency of impulses in afferent nerve fibers running as part of the depressor nerve (vagus branch).

4. Activation of the depressor zone of the vasomotor center in the anterior parts of the medulla oblongata at the lower angle of the rhomboid fossa (giant cell reticular nucleus, reticular ventral nucleus, caudal and oral pontine nuclei, posterior nucleus of the X nerve).

5. Activation of the nuclei of the vagus nerve (parasympathetic nervous system) through the mediator acetylcholine on m-chr leads to a decrease in the heart rate (suppression of adenylate cyclase activity and opening of K channels in the cardiomyocytes of the SA node), a decrease in the speed of propagation of excitations along the conduction system of the heart, and the strength of atrial contractions and ventricles.

6. Decrease in stroke and minute blood volumes.

7. Lower blood pressure

Hering's pressor reflex

1. Decreased blood pressure (for example, as a result of bleeding).

2. Irritation of baroreceptors of the carotid sinus of the carotid arteries.

3. Change in the frequency of excitations coming from this receptor zone along the nerve fibers as part of the glossopharyngeal nerve (Hering’s nerve) to the vasomotor center.

4. Activation of the pressor zone of the vasomotor center, located in the posterolateral parts of the medulla oblongata at the level of the lower angle of the rhomboid fossa (nucleus of the solitary tract, lateral and paramedian reticular nucleus, chemoreceptor zone of the respiratory center). The neurons of this zone have efferent output to the sympathetic centers: Th-5 - for the heart (and Th1, -L2 - for the vessels).

Activation of the centers of the sympathetic nervous system causes positive chrono-, ino-, dromotropic effects with the help of the mediator norepinephrine and β1-adrenoreceptors.

6. Increase in stroke and minute blood volumes.

7. Increased blood pressure.

Parin reflex

Formed in response to changes in blood pressure in the arteries of the small circle.

1. With an increase in blood pressure, the baroreceptors of the arteries of the pulmonary circulation are irritated.

2. The increased frequency of impulses along the afferent fibers of the vagus nerve enters the depressor section of the vasomotor center of the medulla oblongata.

3. Neurons of this zone have efferent output to the parasympathetic neurons of the posterior nucleus of the X nerve for the heart (IX and VII nerves for some vessels of the head) and have an inhibitory effect on the spinal sympathetic neurons innervating the heart and blood vessels .

4. Decrease in the frequency and force of heart contraction.

5. Decrease in stroke and minute blood volume.

6. Decrease in blood pressure in the arteries of the pulmonary circulation.

Bainbridge vasocardial reflex

1. Atrial receptors are excited when the myocardium is stretched: A-receptors when the atrial muscles contract, B-receptors when it is passively stretched (increased intra-atrial pressure).

2. Impulses from atrial receptors arrive through sensory fibers vagus nerves to circulatory centers medulla oblongata and other parts of the central nervous system.

3. Signals from A receptors (as opposed to B receptors) are likely to increase sympathetic tone. It is the excitation of these receptors that explains tachycardia, which often (but not always) occurs in experiments with very strong stretching of the atria, caused by the rapid introduction of a large volume of fluid into the bloodstream (Bainbridge reflex).

Henry-Gower reflex, which is an increase in urine output in response to stretching of the left atrium wall. delay in the release of antidiuretic hormone when blood flow to the right side of the heart increases when a person remains in a horizontal position for a long time; manifested by increased diuresis.

Associated reflexes:

Goltz reflex ( manifests itself in the form of bradycardia (until complete cardiac arrest) in response to irritation of the mechanoreceptors of the peritoneum or abdominal organs)
Danini-Aschner reflex (somatovisceral) - manifests itself in the form of bradycardia when pressing on the eyeballs (increase in pulse by 10-12)