The effect of physical activity on the human heart. The effect of physical activity on the human heart Changes in the activity of the heart during physical work
Physical loads cause restructuring of various body functions, the features and degree of which depend on the power, the nature of motor activity, the level of health and fitness. The effect of physical activity on a person can only be judged on the basis of a comprehensive consideration of the totality of reactions of the whole organism, including the reaction from the central nervous system (CNS), cardiovascular system (CVS), respiratory system, metabolism, etc. It should be emphasized that the severity changes in body functions in response to physical activity depends, first of all, on the individual characteristics of a person and his level of fitness. At the heart of the development of fitness, in turn, is the process of adaptation of the body to physical stress. Adaptation is a set of physiological reactions that underlies the body's adaptations to changing environmental conditions and is aimed at maintaining the relative constancy of its internal environment - homeostasis.
The concepts of “adaptation, adaptability”, on the one hand, and “training, fitness”, on the other hand, have many common features, the main of which is the achievement of a new level of performance. Adaptation of the body to physical stress consists in the mobilization and use of the functional reserves of the body, the improvement of the existing physiological mechanisms of regulation. No new functional phenomena and mechanisms are observed in the process of adaptation, just the existing mechanisms begin to work more perfectly, more intensively and more economically (decrease in heart rate, deepening of breathing, etc.).
The adaptation process is associated with changes in the activity of the entire complex of functional systems of the body (cardiovascular, respiratory, nervous, endocrine, digestive, sensorimotor, and other systems). Different types of physical exercises impose different requirements on individual organs and systems of the body. A properly organized process of performing physical exercises creates conditions for improving the mechanisms that maintain homeostasis. As a result, the shifts that occur in the internal environment of the body are compensated faster, cells and tissues become less sensitive to the accumulation of metabolic products.
Among the physiological factors that determine the degree of adaptation to physical activity, indicators of the state of systems that provide oxygen transport, namely, the blood system and the respiratory system, are of great importance.
Blood and circulatory system
The body of an adult contains 5-6 liters of blood. At rest, 40-50% of it does not circulate, being in the so-called "depot" (spleen, skin, liver). During muscular work, the amount of circulating blood increases (due to the exit from the “depot”). It is redistributed in the body: most of the blood rushes to actively working organs: skeletal muscles, heart, lungs. Changes in the composition of the blood are aimed at meeting the increased need for oxygen in the body. As a result of an increase in the number of red blood cells and hemoglobin, the oxygen capacity of the blood increases, i.e., the amount of oxygen carried in 100 ml of blood increases. When playing sports, the mass of blood increases, the amount of hemoglobin increases (by 1–3%), the number of erythrocytes increases (by 0.5–1 million in cubic mm), the number of leukocytes and their activity increase, which increases the body's resistance to colds and infectious diseases. diseases. As a result of muscle activity, the blood coagulation system is activated. This is one of the manifestations of the urgent adaptation of the body to the effects of physical exertion and possible injuries, followed by bleeding. By programming such a situation “in advance”, the body increases the protective function of the blood coagulation system.
Motor activity has a significant impact on the development and condition of the entire circulatory system. First of all, the heart itself changes: the mass of the heart muscle and the size of the heart increase. In trained people, the mass of the heart is on average 500 g, in untrained people - 300.
The human heart is extremely easy to train and needs it like no other organ. Active muscular activity contributes to the hypertrophy of the heart muscle and an increase in its cavities. Athletes have 30% more heart volume than non-athletes. An increase in the volume of the heart, especially its left ventricle, is accompanied by an increase in its contractility, an increase in systolic and minute volumes.
Physical activity contributes to a change in the activity of not only the heart, but also blood vessels. Active motor activity causes the expansion of blood vessels, a decrease in the tone of their walls, and an increase in their elasticity. During physical exertion, the microscopic capillary network is almost completely opened, which at rest is only 30-40% active. All this allows you to significantly accelerate blood flow and, consequently, increase the supply of nutrients and oxygen to all cells and tissues of the body.
The work of the heart is characterized by a continuous change of contractions and relaxations of its muscle fibers. Contraction of the heart is called systole, relaxation is called diastole. The number of heartbeats in one minute is the heart rate (HR). At rest, in healthy untrained people, the heart rate is in the range of 60-80 beats / min, in athletes - 45-55 beats / min and below. Decrease in heart rate as a result of systematic exercise is called bradycardia. Bradycardia prevents “wear and tear of the myocardium and is of great health importance. During the day, during which there were no trainings and competitions, the sum of the daily pulse in athletes is 15–20% less than in people of the same sex and age who do not go in for sports.
Muscular activity causes an increase in heart rate. With intense muscular work, the heart rate can reach 180-215 beats / min. It should be noted that the increase in heart rate is directly proportional to the power of muscle work. The greater the power of work, the higher the heart rate. However, with the same power of muscular work, the heart rate in less trained individuals is much higher. In addition, during the performance of any motor activity, the heart rate changes depending on gender, age, well-being, training conditions (temperature, air humidity, time of day, etc.).
With each contraction of the heart, blood is ejected into the arteries at high pressure. As a result of the resistance of the blood vessels, its movement in them is created by pressure, called blood pressure. The greatest pressure in the arteries is called systolic or maximum, the smallest - diastolic or minimum. At rest, systolic pressure in adults is 100–130 mm Hg. Art., diastolic - 60-80 mm Hg. Art. According to the World Health Organization, blood pressure up to 140/90 mm Hg. Art. is normotonic, above these values - hypertonic, and below 100-60 mm Hg. Art. - hypotonic. During exercise, as well as after exercise, blood pressure usually rises. The degree of its increase depends on the power of the performed physical activity and the level of fitness of the person. Diastolic pressure changes less pronounced than systolic. After a long and very strenuous activity (for example, participation in a marathon), diastolic pressure (in some cases, systolic) may be less than before muscle work. This is due to the expansion of blood vessels in the working muscles.
Important indicators of the performance of the heart are systolic and minute volume. Systolic volume of blood (stroke volume) is the amount of blood ejected by the right and left ventricles with each contraction of the heart. The systolic volume at rest in trained is 70-80 ml, in untrained - 50-70 ml. The greatest systolic volume is observed at a heart rate of 130–180 beats/min. With a heart rate over 180 beats / min, it is greatly reduced. Therefore, the best opportunities for training the heart have physical activity in the mode of 130-180 beats / min. Minute blood volume - the amount of blood ejected by the heart in one minute, depends on the heart rate and systolic blood volume. At rest, the minute volume of blood (MBC) averages 5-6 liters, with light muscular work it increases to 10-15 liters, with strenuous physical work in athletes it can reach 42 liters or more. An increase in the IOC during muscle activity provides an increased need for blood supply to organs and tissues.
Respiratory system
Changes in the parameters of the respiratory system during the performance of muscle activity are assessed by respiratory rate, lung capacity, oxygen consumption, oxygen debt and other more complex laboratory studies. Respiratory rate (change of inhalation and exhalation and respiratory pause) - the number of breaths per minute. The respiratory rate is determined by the spirogram or by the movement of the chest. The average frequency in healthy individuals is 16-18 per minute, in athletes - 8-12. During exercise, the respiratory rate increases by an average of 2–4 times and amounts to 40–60 respiratory cycles per minute. As breathing increases, its depth inevitably decreases. The depth of breathing is the volume of air in a quiet breath or exhalation during one respiratory cycle. The depth of breathing depends on the height, weight, size of the chest, the level of development of the respiratory muscles, the functional state and the degree of fitness of the person. Vital capacity (VC) is the largest volume of air that can be exhaled after a maximum inhalation. In women, VC averages 2.5-4 liters, in men - 3.5-5 liters. Under the influence of training, VC increases, in well-trained athletes it reaches 8 liters. The minute volume of respiration (MOD) characterizes the function of external respiration and is determined by the product of the respiratory rate and the tidal volume. At rest, the MOD is 5–6 l, with strenuous physical activity it increases to 120–150 l/min or more. During muscle work, tissues, especially skeletal muscles, require significantly more oxygen than at rest, and produce more carbon dioxide. This leads to an increase in MOD, both due to increased respiration and due to an increase in tidal volume. The harder the work, the relatively more MOD (Table 2.2).
Table 2.2
Mean indicators of cardiovascular response
and respiratory systems for physical activity
|
Options |
With intense physical activity |
|
|
Heart rate |
50–75 bpm |
160–210 bpm |
|
systolic blood pressure |
100–130 mmHg Art. |
200–250 mmHg Art. |
|
Systolic blood volume |
150–170 ml and above |
|
|
Minute blood volume (MBV) |
30–35 l/min and above |
|
|
Breathing rate |
14 times/min |
60–70 times/min |
|
Alveolar ventilation (effective volume) |
120 l/min and more |
|
|
Minute breathing volume |
120–150 l/min |
Maximum oxygen consumption(MIC) is the main indicator of the productivity of both the respiratory and cardiovascular (in general - cardio-respiratory) systems. MPC is the maximum amount of oxygen that a person is able to consume within one minute per 1 kg of weight. MIC is measured in milliliters per minute per 1 kg of body weight (ml/min/kg). MPC is an indicator of the body's aerobic capacity, i.e., the ability to perform intense muscular work, providing energy costs due to oxygen absorbed directly during work. The value of the IPC can be determined by mathematical calculation using special nomograms; it is possible in laboratory conditions when working on a bicycle ergometer or climbing a step. BMD depends on age, state of the cardiovascular system, body weight. To maintain health, it is necessary to have the ability to consume oxygen by at least 1 kg - for women at least 42 ml / min, for men - at least 50 ml / min. When less oxygen enters the tissue cells than is necessary to fully meet the energy needs, oxygen starvation, or hypoxia, occurs.
oxygen debt- this is the amount of oxygen that is required for the oxidation of metabolic products formed during physical work. With intense physical exertion, as a rule, metabolic acidosis of varying severity is observed. Its cause is the “acidification” of the blood, i.e., the accumulation of metabolic metabolites in the blood (lactic, pyruvic acids, etc.). To eliminate these metabolic products, oxygen is needed - an oxygen demand is created. When the oxygen demand is higher than the current oxygen consumption, an oxygen debt is formed. Untrained people are able to continue working with an oxygen debt of 6–10 liters, athletes can perform such a load, after which an oxygen debt of 16–18 liters or more arises. Oxygen debt is liquidated after the end of work. The time of its elimination depends on the duration and intensity of the previous work (from several minutes to 1.5 hours).
Digestive system
Systematically performed physical activity increases metabolism and energy, increases the body's need for nutrients that stimulate the release of digestive juices, activates intestinal motility, and increases the efficiency of digestion processes.
However, with intense muscular activity, inhibitory processes can develop in the digestive centers, which reduce the blood supply to various parts of the gastrointestinal tract and digestive glands due to the fact that it is necessary to provide blood to the hard-working muscles. At the same time, the very process of active digestion of abundant food within 2-3 hours after its intake reduces the efficiency of muscle activity, since the digestive organs in this situation appear to be more in need of increased blood circulation. In addition, a full stomach raises the diaphragm, thereby complicating the activity of the respiratory and circulatory organs. That is why the physiological pattern requires taking food 2.5-3.5 hours before the start of the workout, and 30-60 minutes after it.
excretory system
During muscular activity, the role of the excretory organs, which perform the function of preserving the internal environment of the body, is significant. The gastrointestinal tract removes the remnants of digested food; gaseous metabolic products are removed through the lungs; sebaceous glands, releasing sebum, form a protective, softening layer on the surface of the body; the lacrimal glands provide moisture that wets the mucous membrane of the eyeball. However, the main role in the release of the body from the end products of metabolism belongs to the kidneys, sweat glands and lungs.
The kidneys maintain the necessary concentration of water, salts and other substances in the body; remove the end products of protein metabolism; produce the hormone renin, which affects the tone of blood vessels. With great physical exertion, the sweat glands and lungs, by increasing the activity of the excretory function, significantly help the kidneys in removing decay products from the body, which are formed during intensive metabolic processes.
Nervous system in movement control
When controlling movements, the central nervous system performs a very complex activity. To perform clear targeted movements, it is necessary to continuously receive signals to the central nervous system about the functional state of the muscles, about the degree of their contraction and relaxation, about the posture of the body, about the position of the joints and the angle of bend in them. All this information is transmitted from the receptors of the sensory systems, and especially from the receptors of the motor sensory system, located in muscle tissue, tendons, and articular bags. From these receptors, according to the principle of feedback and the mechanism of the CNS reflex, complete information is received about the performance of a motor action and about its comparison with a given program. With repeated repetition of a motor action, the impulses from the receptors reach the motor centers of the CNS, which accordingly change their impulses going to the muscles in order to improve the learned movement to the level of a motor skill.
motor skill- a form of motor activity developed by the mechanism of a conditioned reflex as a result of systematic exercises. The process of forming a motor skill goes through three phases: generalization, concentration, automation.
Phase generalization characterized by the expansion and intensification of excitation processes, as a result of which extra muscle groups are involved in the work, and the tension of the working muscles turns out to be unreasonably large. In this phase, movements are constrained, uneconomical, inaccurate and poorly coordinated.
Phase concentration characterized by a decrease in excitation processes due to differentiated inhibition, concentrating in the desired areas of the brain. Excessive intensity of movements disappears, they become accurate, economical, performed freely, without tension, stably.
In phase automation the skill is refined and consolidated, the performance of individual movements becomes as if automatic and does not require consciousness control, which can be switched to the environment, the search for solutions, etc. An automated skill is distinguished by high accuracy and stability of all its constituent movements.
Question 1 Phases of the cardiac cycle and their changes during exercise. 3
Question 2 Motility and secretion of the large intestine. Absorption in the large intestine, the influence of muscle work on the processes of digestion. 7
Question 3 The concept of the respiratory center. Mechanisms of regulation of respiration. 9
Question 4 Age features of the development of the motor apparatus in children and adolescents 11
List of used literature.. 13
Question 1 Phases of the cardiac cycle and their changes during exercise
In the vascular system, blood moves due to a pressure gradient: from high to low. Blood pressure is determined by the force with which the blood in the vessel (cavity of the heart) presses in all directions, including on the walls of this vessel. The ventricles are the structure that creates this gradient.
Cyclically repeated change of states of relaxation (diastole) and contraction (systole) of the heart is called the cardiac cycle. With a heart rate of 75 per minute, the duration of the entire cycle is about 0.8 s.
It is more convenient to consider the cardiac cycle, starting from the end of the total diastole of the atria and ventricles. In this case, the heart departments are in the following state: the semilunar valves are closed, and the atrioventricular valves are open. Blood from the veins enters freely and completely fills the cavities of the atria and ventricles. The blood pressure in them is the same as in the nearby veins, about 0 mm Hg. Art.
The excitation that originated in the sinus node first of all goes to the atrial myocardium, since its transmission to the ventricles in the upper part of the atrioventricular node is delayed. Therefore, atrial systole occurs first (0.1 s). At the same time, the contraction of muscle fibers located around the mouths of the veins overlaps them. A closed atrioventricular cavity is formed. With the contraction of the atrial myocardium, the pressure in them rises to 3-8 mm Hg. Art. As a result, part of the blood from the atria through the open atrioventricular openings passes into the ventricles, bringing the blood volume in them to 110-140 ml (end-diastolic ventricular volume - EDV). At the same time, due to the incoming additional portion of blood, the cavity of the ventricles is somewhat stretched, which is especially pronounced in their longitudinal direction. After this, ventricular systole begins, and at the atria - diastole.
After an atrioventricular delay (about 0.1 s), excitation along the fibers of the conducting system spreads to ventricular cardiomyocytes, and ventricular systole begins, lasting about 0.33 s. The systole of the ventricles is divided into two periods, and each of them - into phases.
The first period - the period of tension - continues until the semilunar valves open. To open them, the blood pressure in the ventricles must be raised to a level greater than in the corresponding arterial trunks. At the same time, the pressure, which is recorded at the end of ventricular diastole and is called diastolic pressure, in the aorta is about 70-80 mm Hg. Art., and in the pulmonary artery - 10-15 mm Hg. Art. The voltage period lasts about 0.08 s.
It begins with an asynchronous contraction phase (0.05 s), since not all ventricular fibers begin to contract at the same time. The cardiomyocytes located near the fibers of the conducting system are the first to contract. This is followed by the isometric contraction phase (0.03 s), which is characterized by the involvement of the entire ventricular myocardium in the contraction.
The onset of ventricular contraction leads to the fact that, with the semilunar valves still closed, blood rushes to the area of \u200b\u200blowest pressure - back towards the atria. The atrioventricular valves in its path are closed by the blood flow. Tendon threads keep them from dislocation into the atria, and contracting papillary muscles create even more emphasis. As a result, for some time there are closed cavities of the ventricles. And until the contraction of the ventricles raises the blood pressure in them above the level necessary for the opening of the semilunar valves, a significant shortening of the length of the fibers does not occur. Only their inner tension increases.
The second period - the period of expulsion of blood - begins with the opening of the valves of the aorta and pulmonary artery. It lasts 0.25 s and consists of phases of fast (0.1 s) and slow (0.13 s) expulsion of blood. The aortic valves open at a pressure of about 80 mm Hg. Art., and pulmonary - 10 mm Hg. Art. The relatively narrow openings of the arteries are not able to immediately pass the entire volume of ejected blood (70 ml), and therefore the developing contraction of the myocardium leads to a further increase in blood pressure in the ventricles. In the left, it rises to 120-130 mm Hg. Art., and in the right - up to 20-25 mm Hg. Art. The resulting high pressure gradient between the ventricle and the aorta (pulmonary artery) contributes to the rapid ejection of part of the blood into the vessel.
However, the relatively small capacity of the vessels, in which there was blood before, leads to their overflow. Now the pressure is rising already in the vessels. The pressure gradient between the ventricles and vessels gradually decreases, as the rate of blood ejection slows down.
Due to the lower diastolic pressure in the pulmonary artery, the opening of the valves and the expulsion of blood from the right ventricle begin somewhat earlier than from the left. And a lower gradient leads to the fact that the expulsion of blood ends a little later. Therefore, the systole of the right ventricle is 10-30 ms longer than the systole of the left.
Finally, when the pressure in the vessels rises to the level of pressure in the cavity of the ventricles, the expulsion of blood ends. By this time, the contraction of the ventricles stops. Their diastole begins, lasting about 0.47 s. Usually, by the end of systole, about 40-60 ml of blood remains in the ventricles (end-systolic volume - ESC). The cessation of expulsion leads to the fact that the blood in the vessels slams the semilunar valves with a reverse current. This state is called the proto-diastolic interval (0.04 s). Then there is a drop in tension - an isometric period of relaxation (0.08 s).
By this time, the atria are already completely filled with blood. Atrial diastole lasts about 0.7 s. The atria are filled mainly with passively flowing blood through the veins. But it is possible to single out an "active" component, which manifests itself in connection with the partial coincidence of their diastole with the ventricular systole. With the contraction of the latter, the plane of the atrioventricular septum shifts towards the apex of the heart, which creates a suction effect.
When the tension in the ventricular walls decreases and the pressure in them drops to 0, the atrioventricular valves open with blood flow. The blood filling the ventricles gradually straightens them. The period of filling the ventricles with blood can be divided into phases of fast and slow filling. Before the start of a new cycle (atrial systole), the ventricles, like the atria, have time to completely fill with blood. Therefore, due to the flow of blood during atrial systole, the intraventricular volume increases by about 20-30%. But this contribution increases significantly with the intensification of the work of the heart, when the total diastole is shortened, and the blood does not have time to fill the ventricles sufficiently.
During physical work, the activity of the cardiovascular system is activated and, thus, the increased need of working muscles for oxygen is more fully satisfied, and the heat generated with the blood flow is removed from the working muscle to those parts of the body where it is returned. 3-6 minutes after the start of light work, a stationary (sustained) increase in the heart rate occurs, which is due to the irradiation of excitation from the motor cortex to the cardiovascular center of the medulla oblongata and the flow of activating impulses to this center from the chemoreceptors of the working muscles. Activation of the muscular apparatus enhances blood supply in the working muscles, which reaches a maximum within 60-90 seconds after the start of work. With light work, a correspondence is formed between blood flow and the metabolic needs of the muscle. In the course of light dynamic work, the aerobic pathway of ATP resynthesis begins to dominate, using glucose, fatty acids and glycerol as energy substrates. In heavy dynamic work, the heart rate increases to a maximum as fatigue develops. Blood flow in working muscles increases 20-40 times. However, the delivery of O 3 to the muscles lags behind the needs of muscle metabolism, and part of the energy is generated due to anaerobic processes.
Question 2 Motility and secretion of the large intestine. Absorption in the large intestine, the effect of muscle work on digestion
The motor activity of the large intestine has features that ensure the accumulation of chyme, its thickening due to the absorption of water, the formation of feces and their removal from the body during defecation.
The temporal characteristics of the process of movement of contents through the sections of the gastrointestinal tract are judged by the movement of an X-ray contrast agent (for example, barium sulphate). After taking it, it begins to enter the caecum after 3-3.5 hours. Within 24 hours, the colon is filled, which is released from the contrast mass after 48-72 hours.
The initial sections of the colon are characterized by very slow small pendulum contractions. With their help, the chyme is mixed, which accelerates the absorption of water. In the transverse colon and sigmoid colon, large pendulum contractions are observed, caused by the excitation of a large number of longitudinal and circular muscle bundles. The slow movement of the contents of the colon in the distal direction is carried out due to rare peristaltic waves. The retention of chyme in the large intestine is promoted by anti-peristaltic contractions, which move the contents in a retrograde direction and thereby promote the absorption of water. Condensed dehydrated chyme accumulates in the distal colon. This segment of the intestine is separated from the overlying, filled with liquid chyme, constriction caused by contraction of circular muscle fibers, which is an expression of segmentation.
When the transverse colon is filled with condensed dense contents, irritation of the mechanoreceptors of its mucous membrane increases over a large area, which contributes to the emergence of powerful reflex propulsive contractions that move a large amount of contents into the sigmoid and rectum. Therefore, such reductions are called mass reductions. Eating accelerates the occurrence of propulsive contractions due to the implementation of the gastrocolic reflex.
The listed phase contractions of the large intestine are carried out against the background of tonic contractions, which normally last from 15 s to 5 min.
The basis of the motility of the large intestine, as well as the small intestine, is the ability of the membrane of smooth muscle elements to spontaneous depolarization. The nature of contractions and their coordination depend on the influence of efferent neurons of the intraorgan nervous system and the autonomic part of the central nervous system.
Absorption of nutrients in the large intestine under normal physiological conditions is insignificant, since most of the nutrients have already been absorbed in the small intestine. The size of water absorption in the large intestine is large, which is essential in the formation of feces.
Small amounts of glucose, amino acids, and some other easily absorbed substances can be absorbed in the large intestine.
Juice secretion in the large intestine is mainly a reaction in response to local mechanical irritation of the mucous membrane by chyme. Colon juice consists of dense and liquid components. The dense component includes mucous lumps, consisting of desquamated epitheliocytes, lymphoid cells and mucus. The liquid component has a pH of 8.5-9.0. Juice enzymes are contained mainly in desquamated epitheliocytes, during the decay of which their enzymes (pentidases, amylase, lipase, nuclease, cathepsins, alkaline phosphatase) enter the liquid component. The content of enzymes in the juice of the colon and their activity is much lower than in the juice of the small intestine. But the available enzymes are sufficient to complete the hydrolysis in the proximal colon of the remnants of undigested nutrients.
The regulation of juice secretion of the mucous membrane of the large intestine is carried out mainly due to enteral local nervous mechanisms.
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Physical activity that requires more energy than is produced at rest is physical load. During physical activity, the internal environment of the body changes, as a result of which homeostasis is disturbed. Muscles' need for energy is provided by a complex of adaptive processes in various tissues of the body. The chapter discusses physiological parameters that change under the influence of a sharp physical load, as well as cellular and systemic mechanisms of adaptation that underlie repeated or chronic muscle activity.
ASSESSMENT OF MUSCLE ACTIVITY
A single episode of muscular work or "acute load" causes responses of the body that are different from those that occur during chronic exercise, in other words during workout. Forms of muscular work can also vary. The amount of muscle mass involved in the work, the intensity of efforts, their duration and the type of muscle contractions (isometric, rhythmic) affect the responses of the body and the characteristics of adaptive reactions. The main changes that occur in the body during exercise are associated with increased energy consumption by skeletal muscles, which can increase from 1.2 to 30 kcal/min, i.e. 25 times. Since it is impossible to directly measure ATP consumption during physical activity (it occurs at the subcellular level), an indirect estimate of energy costs is used - measurement oxygen taken in during respiration. On fig. Figure 29-1 shows the oxygen consumption before, during and after light steady work.
Rice. 29-1. Oxygen consumption before, during and after light exercise.
Oxygen uptake and hence ATP production increase until a steady state is reached in which ATP production is adequate to its consumption during muscle work. A constant level of oxygen consumption (ATP formation) is maintained until the intensity of work changes. Between the start of work and the increase in oxygen consumption to some constant level, there is a delay called oxygen debt or deficiency. oxygen deficiency- the period of time between the start of muscular work and the increase in oxygen consumption to a sufficient level. In the first minutes after the contraction, there is an excess of oxygen uptake, the so-called oxygen debt(See Fig. 29-1). The "excess" of oxygen consumption in the recovery period is the result of many physiological processes. During dynamic work, each person has his own limit of maximum muscle load, at which oxygen uptake does not increase. This limit is called maximum oxygen uptake (VO 2ma J. It is 20 times the oxygen consumption at rest and cannot be higher, but with proper training it can be increased. Maximum oxygen uptake, ceteris paribus, decreases with age, bed rest, and obesity.
Responses of the cardiovascular system to physical activity
With an increase in energy costs during physical work, more energy production is required. Oxidation of nutrients produces this energy, and the cardiovascular system delivers oxygen to working muscles.
Cardiovascular system under dynamic load conditions
Local control of blood flow ensures that only working muscles with increased metabolic demands receive more blood and oxygen. If only the lower extremities work, the muscles of the legs receive an increased amount of blood, while the blood flow to the muscles of the upper extremities remains unchanged or reduced. At rest, skeletal muscle receives only a small fraction of cardiac output. At dynamic load both total cardiac output and relative and absolute blood flow to the working skeletal muscles are greatly enhanced (Table 29-1).
Table 29-1.Distribution of blood flow at rest and under dynamic load in an athlete
Region | Rest, ml/min | % |
% |
|
Internal organs | ||||
kidneys | ||||
coronary vessels | ||||
Skeletal muscles | 1200 | 22,0 | ||
Leather | ||||
Brain | ||||
Other organs | ||||
Total cardiac output | 25,65 |
During dynamic muscle work, systemic regulation (cardiovascular centers in the brain, with their autonomic effector nerves to the heart and resistive vessels) is involved in the control of the cardiovascular system along with local regulation. Already before the start of muscle activity, her
the program is formed in the brain. First of all, the motor cortex is activated: the overall activity of the nervous system is approximately proportional to the muscle mass and its working intensity. Under the influence of signals from the motor cortex, the vasomotor centers reduce the tonic effect of the vagus nerve on the heart (as a result, the heart rate increases) and switch arterial baroreceptors to a higher level. In actively working muscles, lactic acid is formed, which stimulates the muscle afferent nerves. Afferent signals enter the vasomotor centers, which increase the influence of the sympathetic system on the heart and systemic resistive vessels. Simultaneously muscle chemoreflex activity inside the working muscles lowers Po 2, increases the content of nitric oxide and vasodilating prostaglandins. As a result, a complex of local factors dilates arterioles, despite an increase in sympathetic vasoconstrictor tone. Activation of the sympathetic system increases cardiac output, and local factors in the coronary vessels ensure their expansion. High sympathetic vasoconstrictor tone limits blood flow to the kidneys, visceral vessels, and inactive muscles. Blood flow in inactive areas can drop by up to 75% under heavy work conditions. An increase in vascular resistance and a decrease in blood volume help maintain blood pressure during dynamic exercise. In contrast to reduced blood flow in visceral organs and inactive muscles, the self-regulatory mechanisms of the brain keep blood flow at a constant level, regardless of the load. Skin vessels remain constricted only until there is a need for thermoregulation. During overexertion, sympathetic activity can limit vasodilation in working muscles. Prolonged work at high temperatures is associated with increased blood flow in the skin and intense sweating, leading to a decrease in plasma volume, which can cause hyperthermia and hypotension.
Responses of the cardiovascular system to isometric exercise
Isometric exercise (static muscle activity) causes slightly different cardiovascular responses. Blood-
muscle current and cardiac output increase relative to rest, but high mean intramuscular pressure limits the increase in blood flow relative to rhythmic work. In a statically contracted muscle, intermediate metabolic products appear very quickly under conditions of too little oxygen supply. Under conditions of anaerobic metabolism, lactic acid production increases, the ADP/ATP ratio increases, and fatigue develops. Maintaining only 50% of the maximum oxygen consumption is already difficult after the 1st minute and cannot continue for more than 2 minutes. A long-term stable voltage level can be maintained at 20% of the maximum. Factors of anaerobic metabolism under conditions of isometric load trigger muscle chemoreflex responses. Blood pressure rises significantly, and cardiac output and heart rate are lower than during dynamic work.
Reactions of the heart and blood vessels to one-time and constant muscle loads
A single intense muscular work activates the sympathetic nervous system, which increases the frequency and contractility of the heart in proportion to the effort expended. Increased venous return also contributes to the performance of the heart in dynamic work. This includes a "muscle pump" that compresses the veins during rhythmic muscle contractions, and a "respiratory pump" that increases intrathoracic pressure oscillations from breath to breath. The maximum dynamic load causes the maximum heart rate: even blockade of the vagus nerve can no longer increase the heart rate. Stroke volume reaches its ceiling during moderate work and does not change when moving to the maximum level of work. An increase in blood pressure, an increase in the frequency of contractions, stroke volume and myocardial contractility that occur during work increase myocardial oxygen demand. The linear increase in coronary blood flow during work can reach a value that is 5 times higher than the initial level. Local metabolic factors (nitric oxide, adenosine, and activation of ATP-sensitive K-channels) act vasodilator on coronary
stem vessels. Oxygen uptake in the coronary vessels at rest is high; it increases during operation and reaches 80% of the delivered oxygen.
Adaptation of the heart to chronic muscle overload largely depends on whether the work performed carries the risk of pathological conditions. Examples are left ventricular volume expansion when work requires high blood flow and left ventricular hypertrophy is created by high systemic blood pressure (high afterload). Consequently, in people adapted to prolonged, rhythmic physical activity, which is accompanied by relatively low blood pressure, the left ventricle of the heart has a large volume with a normal thickness of its walls. People accustomed to prolonged isometric contractions have increased left ventricular wall thickness at normal volume and elevated pressure. A large volume of the left ventricle in people engaged in constant dynamic work causes a decrease in the rhythm and an increase in cardiac output. At the same time, the tone of the vagus nerve increases and decreasesβ -adrenergic sensitivity. Endurance training partially alters myocardial oxygen consumption, thus affecting coronary blood flow. Oxygen uptake by the myocardium is approximately proportional to the ratio "heart rate times mean arterial pressure", and since training decreases heart rate, coronary blood flow under the conditions of a standard fixed submaximal load decreases in parallel. Exercise, however, increases peak coronary blood flow by thickening myocardial capillaries and increases capillary exchange capacity. Training also improves endothelial-mediated regulation, optimizes responses to adenosine and control of intracellular free calcium in coronary SMCs. Preservation of endothelial vasodilating function is the most important factor that determines the positive effect of chronic physical activity on coronary circulation.
The effect of exercise on blood lipids
Constant dynamic muscle work is associated with an increase in the level of circulating high-density lipoproteins.
(HDL) and a decrease in low-density lipoprotein (LDL). As a result, the ratio of HDL to total cholesterol increases. Such changes in cholesterol fractions are observed at any age, provided that physical activity is regular. Body weight decreases and insulin sensitivity increases, which is typical for sedentary people who have begun regular exercise. In people who are at risk of coronary heart disease due to very high lipoprotein levels, exercise is a necessary addition to dietary restrictions and a means of losing weight, which helps to reduce LDL. Regular exercise improves fat metabolism and increases cellular metabolic capacity, favoringβ -oxidation of free fatty acids, and also improves lipoprotease function in muscle and adipose tissue. Changes in lipoprotein lipase activity, together with an increase in lecithin-cholesterol acyltransferase activity and apolipoprotein A-I synthesis, increase circulation
HDL.
Regular physical activity in the prevention and treatment of certain cardiovascular diseases
Changes in the ratio of HDL to total cholesterol that occur with regular physical activity reduce the risk of atherosclerosis and coronary artery disease in active people compared to sedentary people. It has been established that the cessation of active physical activity is a risk factor for coronary artery disease, which is as significant as hypercholesterolemia, high blood pressure and smoking. The risk is reduced, as noted earlier, due to a change in the nature of lipid metabolism, a decrease in the need for insulin and an increase in insulin sensitivity, as well as due to a decrease inβ -adrenergic reactivity and increased vagal tone. Regular exercise often (but not always) reduces resting BP. It has been established that a decrease in blood pressure is associated with a decrease in the tone of the sympathetic system and a drop in systemic vascular resistance.
Increased breathing is an obvious physiological response to exercise.
Rice. 29-2 shows that minute ventilation at the beginning of work increases linearly with increasing work intensity and then, after reaching some point near the maximum, becomes super-linear. Due to the load, it increases the absorption of oxygen and the production of carbon dioxide by working muscles. Adaptation of the respiratory system consists in extremely accurate maintenance of the homeostasis of these gases in the arterial blood. During light to moderate work, arterial Po 2 (and hence oxygen content), Pco 2 and pH remain unchanged at rest. The respiratory muscles involved in increasing ventilation and, above all, in increasing the tidal volume, do not create a feeling of shortness of breath. With a more intense load, already halfway from rest to maximum dynamic work, lactic acid, which is formed in working muscles, begins to appear in the blood. This is observed when lactic acid is formed faster than it is (removed) metabolized-
Rice. 29-2. Dependence of minute ventilation on the intensity of physical activity.
sya. This point, which depends on the type of work and the state of training of the subject, is called anaerobic or lactic threshold. The lactate threshold for a particular person doing a particular job is relatively constant. The higher the lactate threshold, the higher the intensity of continuous work. The concentration of lactic acid gradually increases with the intensity of work. At the same time, more and more muscle fibers switch to anaerobic metabolism. Almost completely dissociated lactic acid causes metabolic acidosis. During work, healthy lungs respond to acidosis by further increasing ventilation, lowering arterial Pco 2 levels, and maintaining arterial blood pH at normal levels. This response to acidosis, which promotes non-linear lung ventilation, can occur during strenuous work (see Fig. 29-2). Within certain operating limits, the respiratory system fully compensates for the decrease in pH caused by lactic acid. However, during the hardest work, the ventilation compensation becomes only partial. In this case, both pH and arterial Pco 2 may fall below baseline. The inspiratory volume continues to increase until the stretch receptors limit it.
The control mechanisms of pulmonary ventilation that ensure muscle work include neurogenic and humoral influences. The rate and depth of breathing are controlled by the respiratory center of the medulla oblongata, which receives signals from central and peripheral receptors that respond to changes in pH, arterial Po 2 and Pto 2 . In addition to signals from chemoreceptors, the respiratory center receives afferent impulses from peripheral receptors, including muscle spindles, Golgi stretch receptors, and pressure receptors located in the joints. Central chemoreceptors perceive an increase in alkalinity with the intensification of muscle work, which indicates the permeability of the blood-brain barrier for CO 2 , but not for hydrogen ions.
Training does not change the magnitude of the functions of the respiratory system
The impact of training on the respiratory system is minimal. Diffusion capacity of the lungs, their mechanics and even pulmonary
volumes change very little during training. The widely held assumption that exercise improves vital capacity is incorrect: even loads designed specifically to increase respiratory muscle strength only increase vital capacity by 3%. One of the mechanisms of adaptation of the respiratory muscles to physical activity is a decrease in their sensitivity to shortness of breath during exercise. However, the primary respiratory changes during exercise are secondary to reduced lactic acid production, which reduces the need for ventilation during heavy work.
Muscle and bone responses to exercise
The processes that occur during the work of the skeletal muscle are the primary factor in its fatigue. The same processes, repeated during training, promote adaptation, which increases the amount of work and delays the development of fatigue during such work. Skeletal muscle contractions also increase the stress effect on the bones, causing specific bone adaptation.
Muscle fatigue does not depend on lactic acid
Historically, it has been thought that an increase in intracellular H+ (decrease in cellular pH) played a major role in muscle fatigue by directly inhibiting actinmyosin bridges and thereby leading to a decrease in contractile force. Although very hard work can reduce the pH value< 6,8 (pH артериальной крови может падать до 7,2), имеющиеся данные свидетельствуют, что повышенное содержание H+ хотя и является значительным фактором в снижении мышечной силы, но не служит исключительной причиной утомления. У здоровых людей утомление коррелирует с накоплением АДФ на фоне нормального или слегка редуцированного содержания АТФ. В этом случае соотношение АДФ/АТФ бывает высоким. Поскольку полное окисление глюкозы, гликогена или свободных жирных кислот до CO 2 и H 2 O является основным источником энергии при продолжительной работе, у людей с нарушениями гликолиза или электронного транспорта снижена способность к продолжительной
work. Potential factors in the development of fatigue may occur centrally (pain signals from a tired muscle are fed back to the brain and reduce motivation and possibly reduce impulses from the motor cortex) or at the level of a motor neuron or neuromuscular junction.
Endurance training increases the oxygen capacity of the muscles
Skeletal muscle adaptation to training is specific to the form of muscle contraction. Regular exercise under conditions of low load contributes to an increase in oxidative metabolic capacity without muscle hypertrophy. Strength training causes muscle hypertrophy. Increased activity without overload increases the density of capillaries and mitochondria, the concentration of myoglobin and the entire enzymatic apparatus for energy production. Coordination of the energy-producing and energy-using systems in muscle is maintained even after atrophy when the remaining contractile proteins are adequately maintained metabolically. Local adaptation of the skeletal muscle to perform long-term work reduces dependence on carbohydrates as an energy fuel and allows greater use of fat metabolism, prolongs endurance and reduces the accumulation of lactic acid. The decrease in the content of lactic acid in the blood, in turn, reduces the ventilation dependence on the severity of work. As a result of the slower accumulation of metabolites inside the trained muscle, the chemosensory impulse flow in the feedback system in the CNS decreases with increasing load. This weakens the activation of the sympathetic system of the heart and blood vessels and reduces myocardial oxygen demand at a fixed level of work.
Muscle hypertrophy in response to stretch
Common forms of physical activity involve a combination of muscle contractions with shortening (concentric contraction), lengthening the muscle (eccentric contraction), and no change in its length (isometric contraction). Under the action of external forces that stretch the muscle, a smaller amount of ATP is required for the development of force, since part of the motor units
out of work. However, since the forces exerted on individual motor units are greater during eccentric work, eccentric contractions can easily cause muscle damage. This is manifested in muscle weakness (occurs on the first day), soreness, swelling (lasts 1-3 days) and an increase in the level of intramuscular enzymes in plasma (2-6 days). Histological evidence of damage may persist for up to 2 weeks. The injury is followed by an acute phase response that includes complement activation, an increase in circulating cytokines, and the mobilization of neurotrophils and monocytes. If adaptation to training with stretching elements is sufficient, then soreness after repeated training is minimal or absent altogether. Stretch training injury and its response complex is likely to be the most important stimulus for muscle hypertrophy. The immediate changes in actin and myosin synthesis that cause hypertrophy are mediated at the post-translational level; a week after exercise, messenger RNA for these proteins changes. Although their exact role remains unclear, the activity of S6 protein kinase, which is closely associated with long-term changes in muscle mass, is increased. Cellular mechanisms of hypertrophy include the induction of insulin-like growth factor I and other proteins that are members of the fibroblast growth factor family.
The contraction of skeletal muscles through the tendons has an effect on the bones. Because bone architecture changes under the influence of osteoblast and osteoclast activation induced by loading or unloading, physical activity has a significant specific effect on bone mineral density and geometry. Repetitive physical activity can create unusually high tension, leading to insufficient bone restructuring and bone fracture; on the other hand, low activity causes osteoclast dominance and bone loss. The forces acting on the bone during exercise depend on the mass of the bone and the strength of the muscles. Therefore, bone density is most directly related to the forces of gravity and the strength of the muscles involved. This assumes that the load for the purpose
prevent or mitigate osteoporosis must take into account the mass and strength of the applied activity. Because exercise can improve gait, balance, coordination, proprioception, and reaction time, even in the elderly and frail, staying active reduces the risk of falls and osteoporosis. Indeed, hip fractures are reduced by about 50% when older people exercise regularly. However, even when physical activity is optimal, the genetic role of bone mass is much more important than the role of exercise. Perhaps 75% of population statistics are related to genetics and 25% are the result of various levels of activity. Physical activity also plays a role in treatment osteoarthritis. Controlled clinical trials have shown that appropriate regular exercise reduces joint pain and disability.
Dynamic strenuous work (requiring more than 70% of the maximum O 2 intake) slows down the emptying of the liquid contents of the stomach. The nature of this effect has not been elucidated. However, a single load of varying intensity does not change the secretory function of the stomach, and there is no evidence of the effect of the load on the factors contributing to the development of peptic ulcers. It is known that intense dynamic work can cause gastroesophageal reflux, which impairs esophageal motility. Chronic physical activity increases the rate of gastric emptying and the movement of food masses through the small intestine. These adaptive responses constantly increase energy expenditure, promote faster food processing, and increase appetite. Experiments on animals with a model of hyperphagia show a specific adaptation in the small intestine (increase in the surface of the mucosa, the severity of microvilli, a greater content of enzymes and transporters). The intestinal blood flow slows down in proportion to the intensity of the load, and the sympathetic vasoconstrictor tone increases. In parallel, the absorption of water, electrolytes and glucose slows down. However, these effects are transient and the syndrome of reduced absorption as a consequence of acute or chronic loading is not observed in healthy people. Physical activity is recommended for faster recovery
formation after surgery on the ileum, with constipation and irritable bowel syndrome. Constant dynamic loading significantly reduces the risk of colon cancer, possibly because the amount and frequency of food consumed increases and, consequently, the movement of feces through the colon is accelerated.
Exercise improves insulin sensitivity
Muscular work suppresses insulin secretion due to the increased sympathetic effect on the pancreatic islet apparatus. During work, despite a sharp decrease in the level of insulin in the blood, there is an increased consumption of glucose by the muscles, both insulin-dependent and non-insulin-dependent. Muscle activity mobilizes glucose transporters from intracellular storage sites to the plasma membrane of working muscles. Because muscle exercise increases insulin sensitivity in people with type 1 (insulin-dependent) diabetes, less insulin is required when their muscle activity increases. However, this positive result can be insidious, as work accelerates the development of hypoglycemia and increases the risk of hypoglycemic coma. Regular muscle activity reduces the need for insulin by increasing the sensitivity of insulin receptors. This result is achieved by regularly adapting to smaller loads, and not just by repeating episodic loads. The effect is quite pronounced after 2-3 days of regular physical training, and it can be lost just as quickly. Consequently, healthy people who lead a physically active lifestyle have significantly higher insulin sensitivity than their sedentary counterparts. Increased sensitivity of insulin receptors and less release of insulin after regular physical activity serve as an adequate therapy for type 2 diabetes (non-insulin dependent) - a disease characterized by high secretion of insulin and low sensitivity to insulin receptors. In people with type 2 diabetes, even a single episode of physical activity significantly affects the movement of glucose transporters to the plasma membrane in skeletal muscle.
Chapter summary
Physical activity is an activity that involves muscle contractions, flexion and extension movements of the joints and has an exceptional effect on various body systems.
The quantitative assessment of the dynamic load is determined by the amount of oxygen absorbed during operation.
Excess oxygen consumption in the first minutes of recovery after work is called oxygen debt.
During muscle exercise, blood flow is predominantly directed towards the working muscles.
During work, blood pressure, heart rate, stroke volume, heart contractility are increased.
In people accustomed to prolonged rhythmic work, the heart, with normal blood pressure and normal left ventricular wall thickness, ejects large volumes of blood from the left ventricle.
Long-term dynamic work is associated with an increase in high-density lipoproteins in the blood and a decrease in low-density lipoproteins. In this regard, the ratio of high-density lipoproteins and total cholesterol increases.
Muscle loading plays a role in the prevention and recovery from certain cardiovascular diseases.
Pulmonary ventilation increases during work in proportion to the need for oxygen and removal of carbon dioxide.
Muscle fatigue is a process caused by the performance of a load, leading to a decrease in its maximum strength and independent of lactic acid.
Regular muscle activity at low loads (endurance training) increases muscle oxygen capacity without muscle hypertrophy. Increased activity at high loads causes muscle hypertrophy.
What kind of physical activity can be used for people at high risk of developing heart disease?
Before starting training, patients of the "risk" group should consult with their doctor in order not to harm their health.
People suffering from the following diseases should avoid strenuous exercise and strenuous exercise:
- diabetes
- hypertension;
- angina pectoris
- ischemic heart disease;
- heart failure.
What effect does sport have on the heart?
Sports can affect the heart in different ways, both strengthen its muscles and lead to serious diseases. In the presence of cardiovascular pathologies, sometimes manifested in the form of chest pain, it is necessary to consult a cardiologist.It's no secret that athletes often suffer from heart disease due to influence big physical stress on the heart. That is why they are advised to include training before a serious load in the regime. This will serve as such a "warm-up" of the muscles of the heart, balance the pulse. In no case should you abruptly quit training, the heart is used to moderate loads, if they don’t, hypertrophy of the heart muscles can occur.
The influence of professions on the work of the heart
Conflicts, stress, lack of normal rest negatively affects the work of the heart. A list of professions that negatively affect the heart was compiled: athletes take the first place, politicians the second; the third is teachers.Professions can be divided into two groups according to their influence on the work of the most important organ - the heart:
- Professions are associated with an inactive lifestyle, physical activity is practically absent.
- Work with increased psycho-emotional and physical stress.
Ticket 2
Systole of the ventricles of the heart, its periods and phases. The position of the valves and pressure in the cavities of the heart during systole.
Ventricular systole- the period of contraction of the ventricles, which allows you to push the blood into the arterial bed.
In the contraction of the ventricles, several periods and phases can be distinguished:
· Voltage period- characterized by the onset of contraction of the muscle mass of the ventricles without a change in the volume of blood inside them.
· Asynchronous reduction- the beginning of excitation of the ventricular myocardium, when only individual fibers are involved. The pressure change in the ventricles is enough to close the atrioventricular valves at the end of this phase.
· Isovolumetric contraction- almost the entire myocardium of the ventricles is involved, but there is no change in the volume of blood inside them, since the efferent (semilunar - aortic and pulmonary) valves are closed. Term isometric contraction not entirely accurate, since at this time there is a change in the shape (remodeling) of the ventricles, tension of the chords.
· Period of exile characterized by the expulsion of blood from the ventricles.
· Rapid Exile- the period from the opening of the semilunar valves to the achievement of systolic pressure in the cavity of the ventricles - during this period the maximum amount of blood is ejected.
· slow exile- the period when the pressure in the cavity of the ventricles begins to decrease, but is still greater than the diastolic pressure. At this time, the blood from the ventricles continues to move under the action of the kinetic energy imparted to it, until the pressure in the cavity of the ventricles and the efferent vessels is equalized.
In a state of calm, the ventricle of the heart of an adult ejects from 60 ml of blood for each systole (stroke volume). The cardiac cycle lasts up to 1 s, respectively, the heart makes from 60 contractions per minute (heart rate, heart rate). It is easy to calculate that even at rest, the heart pumps 4 liters of blood per minute (minute volume of the heart, MCV). During the maximum load, the stroke volume of the heart of a trained person can exceed 200 ml, the pulse can exceed 200 beats per minute, and the blood circulation can reach 40 liters per minute. ventricular systole the pressure in them becomes higher than the pressure in the atria (which begin to relax), which leads to the closure of the atrioventricular valves. The external manifestation of this event is the I heart sound. Then the pressure in the ventricle exceeds the aortic pressure, as a result of which the aortic valve opens and the expulsion of blood from the ventricle into the arterial system begins.
2. Centrifugal nerves of the heart, the nature of the influences coming through them on the activity of the heart. the concept of the tone of the nucleus of the vagus nerve.
The activity of the heart is regulated by two pairs of nerves: vagus and sympathetic. The vagus nerves originate in the medulla oblongata, and the sympathetic nerves originate from the cervical sympathetic ganglion. Vagus nerves inhibit cardiac activity. If you start to irritate the vagus nerve with an electric current, then there is a slowdown and even a stop of heart contractions. After the cessation of irritation of the vagus nerve, the work of the heart is restored. Under the influence of impulses entering the heart through the sympathetic nerves, the rhythm of cardiac activity increases and each heartbeat increases. This increases the systolic, or shock, blood volume. The vagus and sympathetic nerves of the heart usually act in concert: if the excitability of the center of the vagus nerve increases, then the excitability of the center of the sympathetic nerve decreases accordingly.
During sleep, in a state of physical rest of the body, the heart slows down its rhythm due to an increase in the influence of the vagus nerve and a slight decrease in the influence of the sympathetic nerve. During physical activity, the heart rate increases. In this case, there is an increase in the influence of the sympathetic nerve and a decrease in the influence of the vagus nerve on the heart. In this way, an economical mode of operation of the heart muscle is ensured.
The change in the lumen of the blood vessels occurs under the influence of impulses transmitted to the walls of the vessels along vasoconstrictor nerves. Impulses from these nerves originate in the medulla oblongata in vasomotor center. An increase in blood pressure in the aorta causes stretching of its walls and, as a result, irritation of the pressoreceptors of the aortic reflexogenic zone. Excitation arising in the receptors along the fibers of the aortic nerve reaches the medulla oblongata. The tone of the nuclei of the vagus nerves reflexively increases, which leads to inhibition of cardiac activity, as a result of which the frequency and strength of heart contractions decrease. At the same time, the tone of the vasoconstrictor center decreases, which causes the expansion of the vessels of the internal organs. The inhibition of the heart and the expansion of the lumen of the blood vessels restore the increased blood pressure to normal values.
3. The concept of general peripheral resistance, hemodynamic factors that determine its value.
It is expressed by the equation R=8*L*nu\n*r4, where L is the length of the vascular bed, nu-viscosity is determined by the ratio of plasma volumes and formed elements, plasma protein content and other factors. The least constant of these parameters is the radius of the vessels, and its change in any part of the system can significantly affect the value of the OPS. If the resistance decreases in some limited region - in a small muscle group, organ, then this may not affect the OPS, but it significantly changes the blood flow in this region, because. organ blood flow is also determined by the above formula Q=(Pn-Pk)\R, where Pn can be considered as the pressure in the artery supplying the given organ, Pk is the pressure of the blood flowing through the vein, R is the resistance of all vessels in the given region. In connection with the increase in the age of a person, the total vascular resistance gradually increases. This is due to an age-related decrease in the number of elastic fibers, an increase in the concentration of ash substances, and a limitation in the extensibility of blood vessels that pass through the “path from fresh grass to hay” throughout life.
No. 4. Renal-adrenal system of regulation of vascular tone.
The system of regulation of vascular tone is activated during orthostatic reactions, blood loss, muscle load and other conditions in which the activity of the sympathetic nervous system increases. The system includes the JGA of the kidneys, the zona glomeruli of the adrenal glands, the hormones secreted by these structures, and the tissues where they are activated. Under the above conditions, the secretion of renin increases, which converts plasma angiltensinogen into angiotensin-1, the latter in the lungs turns into a more active form of angiotensin-2, which is 40 times greater than HA in vasoconstrictive action, but has little effect on the vessels of the brain, skeletal muscles and hearts. Angiotensin also stimulates the zona glomeruli of the adrenal glands, promoting the secretion of aldosterone.
Ticket3
1. The concept of eu, hypo, hyperkinetic types of hemodynamics.
The most characteristic feature of type I, first described by V.I. Kuznetsov, is isolated systolic hypertension, which, as it turns out during the study, is caused by a combination of two factors: an increase in the cardiac output of blood circulation and an increase in the elastic resistance of large muscle-type arteries. The last sign is probably associated with excessive tonic tension of the smooth muscle cells of the arteries. However, there is no spasm of arterioles, peripheral resistance is reduced to such an extent that the effect of cardiac output on mean hemodynamic pressure is leveled.
In hemodynamic type II, which occurs in 50-60% of young people with borderline hypertension, an increase in cardiac output and stroke volume is not compensated by an adequate expansion of resistive vessels. The discrepancy between minute volume and peripheral resistance leads to an increase in mean hemodynamic pressure. It is especially significant that in these patients the peripheral resistance remains higher than in the control, even when the differences in the values of the minute volume of the heart disappear.
Finally, hemodynamic type III, which we found in 25-30% of young people, is characterized by an increase in peripheral resistance with a normal cardiac output. We have well-tracked observations showing that, at least in some patients, the normal kinetic type of hypertension is formed from the very beginning without a preceding phase of hyperkinetic circulation. True, in some of these patients, in response to the load, a pronounced reaction of the hyperkinetic type is noted, that is, there is a high readiness to mobilize cardiac output.
2.Intracardiac fur. Regulation of the work of the heart. Relationship between intra and extracardiac mechanisms of regulation.
It has also been proven that intracardiac regulation provides a hemodynamic connection between the left and right parts of the heart. Its significance lies in the fact that if a large amount of blood enters the right side of the heart during exercise, then its left side prepares to receive it in advance by increasing active diastolic relaxation, which is accompanied by an increase in the initial volume of the ventricles. Let's consider intracardiac regulation with examples. Suppose, due to an increase in the load on the heart, blood flow to the atria increases, which is accompanied by an increase in the frequency of heart contraction. The scheme of the reflex arc of this reflex is as follows: the flow of a large amount of blood in the atria is perceived by the corresponding mechanoreceptors (volume receptors), information from which is sent to the cells of the leading node, in the area of \u200b\u200bwhich the neurotransmitter norepinephrine is released. Under the influence of the latter, depolarization of the pacemaker cells develops. Therefore, the development time of slow diastolic spontaneous depolarization is shortened. Therefore, the heart rate increases.
If significantly less blood enters the heart, then the receptor effect from the mechanoreceptors turns on the cholinergic system. As a result, the mediator acetylcholine is released in the cells of the sinoatrial node, causing hyperpolarization of atypical fibers. As a result, the time for the development of slow spontaneous diastolic depolarization increases, and the heart rate, respectively, decreases.
If blood flow to the heart increases, then not only the heart rate increases, but also the systolic output due to intracardiac regulation. What is the mechanism of increasing the force of contractions of the heart? It appears as follows. Information at this stage comes from the atrial mechanoreceptors to the contractile elements of the ventricles, apparently through the intercalary neurons. So, if the blood flow to the heart increases during exercise, then this is perceived by the atrial mechanoreceptors, which includes the adrenergic system. As a result, norepinephrine is released in the corresponding synapses, which, through (most likely) the calcium (possibly cAMP, cGMP) cellular regulatory system, causes an increased release of calcium ions to the contractile elements, increasing the conjugation of muscle fibers. It is also possible that norepinephrine reduces the resistance in the nexuses of reserve cardiomyocytes and connects additional muscle fibers, due to which the force of heart contractions also increases. If the blood flow to the heart decreases, then the cholinergic system is activated through the atrial mechanoreceptors. As a result, the mediator acetylcholine is released, which inhibits the release of calcium ions into the interfibrillar space, and the conjugation weakens. It can also be assumed that under the influence of this mediator, the resistance in the nexuses of working motor units increases, which is accompanied by a weakening of the contractile effect.
3. Systemic blood pressure, its fluctuations depending on the phase of the cardiac cycle, gender, age and other factors. Blood pressure in different parts of the circulatory system.
Systemic pressure in the initial sections of the circulatory system - in large arteries. its value depends on the changes occurring in any part of the system. The value of systemic blood pressure depends on the phase of the cardiac cycle. The main hemodynamic factors affecting the value of systemic arterial pressure are determined from the following formula:
P=Q*R(r,l,nu). Q-intensity and frequency of contractions of the heart., tone of the veins. R-tone of arterial vessels, elastic properties and thickness of the vascular wall.
Blood pressure also changes in connection with the phases of respiration: on inspiration, it decreases. BP is a relatively mild state: its value can fluctuate throughout the day: during physical work of greater intensity, systolic pressure can increase by 1.5-2 times. It also increases with emotional and other types of stress. The highest values of systemic blood pressure at rest are recorded in the morning; many people also have a second peak at 15-18 hours. Under normal conditions, in a healthy person during the day, blood pressure fluctuates by no more than 20-25 mm Hg st. With age, systolic blood pressure gradually increases - 50-60 years to 139 mm Hg st, while diastolic pressure also slightly increases. normal values of blood pressure is extremely important, since increased blood pressure among people over 50 years of age occurs in 30%, and among women in 50% of those examined. At the same time, not everyone makes any complaints, despite the increasing risk of complications.
4. Vasoconstrictive and vasodilating nerve effects. The mechanism of their action on vascular tone.
In addition to local vasodilating mechanisms, skeletal muscles are supplied with sympathetic vasoconstrictor nerves, as well as (in some animal species) sympathetic vasodilating nerves. Sympathetic vasoconstrictor nerves. The mediator of the sympathetic vasoconstrictor nerves is norepinephrine. The maximum activation of sympathetic adrenergic nerves leads to a decrease in blood flow in the vessels of the skeletal muscles by 2 and even 3 times compared with the rest level. Such a reaction is of great physiological importance in the development of circulatory shock and in other cases when it is vital to maintain a normal or even high level of systemic arterial pressure. In addition to norepinephrine secreted by the endings of the sympathetic vasoconstrictor nerves, large amounts of norepinephrine and adrenaline are secreted into the bloodstream by the cells of the adrenal medulla, especially during heavy physical exertion. Norepinephrine circulating in the blood has the same vasoconstrictive effect on the vessels of the skeletal muscles, as does the mediator of the sympathetic nerves. However, adrenaline most often causes a moderate expansion of muscle vessels. The fact is that adrenaline interacts mainly with beta-adrenergic receptors, the activation of which leads to vasodilation, while norepinephrine interacts with alpha-adrenergic receptors and always causes vasoconstriction. Three main mechanisms contribute to the dramatic increase in skeletal muscle blood flow during exercise: (1) excitation of the sympathetic nervous system, causing general changes in the circulatory system; (2) an increase in blood pressure; (3) increase in cardiac output.
Sympathetic vasodilatory system. Influence of the CNS on the sympathetic vasodilating system. Sympathetic nerves of skeletal muscles, along with vasoconstrictor fibers, contain sympathetic vasodilating fibers. In some mammals, such as cats, these vasodilator fibers secrete acetylcholine (rather than norepinephrine). In primates, epinephrine is thought to have a vasodilating effect by interacting with beta-adrenergic receptors in skeletal muscle vessels. Descending pathways through which the central nervous system controls vasodilating influences. The main area of the brain that exercises this control is the anterior hypothalamus. Perhaps the sympathetic vasodilator system is not of great functional importance. It is doubtful that the sympathetic vasodilating system plays a significant role in the regulation of blood circulation in humans. Complete blockade of the sympathetic nerves of skeletal muscles practically does not affect the ability of these tissues to self-regulate blood flow depending on metabolic needs. On the other hand, experimental studies show that at the very beginning of physical activity, it is the sympathetic vasodilatation of skeletal muscles that possibly leads to an outstripping increase in blood flow even before the need for oxygen and nutrients in skeletal muscles increases.
Ticket
1. heart sounds, their origin. Principles of phonocardiography and the advantages of this method over auscultation.
Heart sounds- a sound manifestation of the mechanical activity of the heart, determined by auscultation as alternating short (percussive) sounds that are in a certain connection with the phases of the systole and diastole of the heart. T. s. are formed in connection with the movements of the valves of the heart, chords, heart muscle and vascular wall, generating sound vibrations. The auscultated loudness of tones is determined by the amplitude and frequency of these oscillations (see. Auscultation). Graphic registration T. with. with the help of phonocardiography showed that, in terms of its physical nature, T. s. are noises, and their perception as tones is due to the short duration and rapid attenuation of aperiodic oscillations.
Most researchers distinguish 4 normal (physiological) T. s., of which I and II tones are always heard, and III and IV are not always determined, more often graphically than during auscultation ( rice. ).
I tone is heard as a fairly intense sound over the entire surface of the heart. It is maximally expressed in the region of the apex of the heart and in the projection of the mitral valve. The main fluctuations of the I tone are associated with the closure of the atrioventricular valves; participate in its formation and movements of other structures of the heart.
II tone is also auscultated over the entire region of the heart, as much as possible - at the base of the heart: in the second intercostal space to the right and left of the sternum, where its intensity is greater than the first tone. The origin of the II tone is mainly associated with the closure of the valves of the aorta and pulmonary trunk. It also includes low-amplitude low-frequency oscillations resulting from the opening of the mitral and tricuspid valves. On PCG, as part of the II tone, the first (aortic) and second (pulmonary) components are distinguished
Ill tone - low-frequency - is perceived during auscultation as a weak, dull sound. On FKG it is determined on a low-frequency channel, more often in children and athletes. In most cases, it is recorded at the apex of the heart, and its origin is associated with fluctuations in the muscular wall of the ventricles due to their stretching at the time of rapid diastolic filling. Phonocardiographically, in some cases, a left and right ventricular III tone is distinguished. The interval between II and left ventricular tone is 0.12-15 With. The so-called mitral valve opening tone is distinguished from the III tone - a pathognomonic sign of mitral stenosis. The presence of the second tone creates an auscultatory picture of the “quail rhythm”. Pathological III tone appears when heart failure and causes proto- or mesodiastolic gallop rhythm (see. gallop rhythm). Ill tone is better heard with a stethoscopic head of a stethophonendoscope or by direct auscultation of the heart with an ear tightly attached to the chest wall.
IV tone - atrial - is associated with atrial contraction. With synchronous recording with an ECG, it is recorded at the end of the P wave. This is a weak, rarely heard tone, recorded on the low-frequency channel of the phonocardiograph, mainly in children and athletes. Pathologically enhanced IV tone causes a presystolic gallop rhythm during auscultation. The fusion of III and IV pathological tones in tachycardia is defined as "summation gallop".
Phonocardiography is one of the methods of diagnostic examination of the heart. It is based on the graphic recording of sounds accompanying heart contractions using a microphone that converts sound vibrations into electrical vibrations, an amplifier, a frequency filter system and a recording device. Register mainly tones and murmurs of the heart. The resulting graphic image is called a phonocardiogram. Phonocardiography significantly complements auscultation and makes it possible to objectively determine the frequency, shape and duration of recorded sounds, as well as their change in the process of dynamic monitoring of the patient. Phonocardiography is used mainly for the diagnosis of heart defects, phase analysis of the cardiac cycle. This is especially important for tachycardia, arrhythmias, when it is difficult to decide in which phase of the cardiac cycle certain sound phenomena occurred with the help of one auscultation.
The harmlessness and simplicity of the method make it possible to conduct studies even in a patient who is in serious condition, and with the frequency necessary to solve diagnostic problems. In the departments of functional diagnostics, for the implementation of phonocardiography, a room with good sound insulation is allocated, in which the temperature is maintained at 22-26 ° C, since at a lower temperature the subject may experience muscle tremors that distort the phonocardiogram. The study is carried out in the supine position of the patient, while holding the breath in the exhalation phase. The analysis of phonocardiography and the diagnostic conclusion on it is carried out only by a specialist, taking into account auscultatory data. For the correct interpretation of phonocardiography, synchronous recording of a phonocardiogram and an electrocardiogram is used.
Auscultation is called listening to sound phenomena that occur in the body.
Usually these phenomena are weak and use direct and mediocre auscultation to capture them; the first is called listening with the ear, and the second is listening with the help of special auditory instruments - a stethoscope and a phonendoscope.
2. Hemodynamic mechanisms of regulation of the activity of the heart. The law of the heart, its meaning.
Hemodynamic, or myogenic, mechanisms of regulation ensure the constancy of the systolic blood volume. The strength of the contractions of the heart depends on its blood supply, i.e. on the initial length of muscle fibers and the degree of their stretching during diastole. The more stretched the fibers, the greater the blood flow to the heart, which leads to an increase in the strength of heart contractions during systole - this is the "law of the heart" (Frank-Starling's law). This type of hemodynamic regulation is called heterometric.
It is explained by the ability of Ca2 + to leave the sarcoplasmic reticulum. The more the sarcomere is stretched, the more Ca2+ is released and the greater the force of contractions of the heart. This self-regulation mechanism is activated when the body position changes, with a sharp increase in the volume of circulating blood (during transfusion), as well as with pharmacological blockade of the sympathetic nervous system by beta-sympatholytics.
Another type of myogenic self-regulation of the work of the heart - homeometric does not depend on the initial length of cardiomyocytes. The strength of heart contractions can increase with an increase in the frequency of heart contractions. The more often it contracts, the higher the amplitude of its contractions ("Bowditch's ladder"). With an increase in pressure in the aorta to certain limits, the counterload on the heart increases, and there is an increase in the strength of heart contractions (Anrep phenomenon).
Intracardiac peripheral reflexes belong to the third group of regulatory mechanisms. In the heart, regardless of the nervous elements of extracardiac origin, the intraorgan nervous system functions, forming miniature reflex arcs, which include afferent neurons, the dendrites of which begin on stretch receptors on the fibers of the myocardium and coronary vessels, intercalary and efferent neurons (Dogel cells I, II and III order), the axons of which can end on myocardiocytes located in another part of the heart.
Thus, an increase in blood flow to the right atrium and stretching of its walls leads to an increase in the contraction of the left ventricle. This reflex can be blocked using, for example, local anesthetics (novocaine) and ganglionic blockers (beisohexonium).
heart law, Starling's law, the dependence of the energy of contraction of the heart on the degree of stretching of its muscle fibers. The energy of each heart contraction (systole) changes in direct proportion to
| diastolic volume. Hearts law established by the English physiologist E. Starling in 1912-18 on cardiopulmonary drug. Starling found that the volume of blood ejected by the heart into the arteries with each systole increases in proportion to the increase in venous return of blood to the heart; the increase in the strength of each contraction is associated with an increase in the volume of blood in the heart by the end of diastole and, as a result, an increase in the stretching of the myocardial fibers. Hearts law does not determine the entire activity of the heart, but explains one of the mechanisms of its adaptation to the changing conditions of the organism's existence. In particular, Hearts law underlies the maintenance of a relative constancy of stroke volume with an increase in vascular resistance in the arterial part of the cardiovascular system. This self-regulating mechanism, due to the properties of the heart muscle, is inherent not only in an isolated heart, but also participates in the regulation of the activity of the cardiovascular system in the body; controlled by nervous and humoral influences |
3. Volumetric blood flow velocity, its value in different parts of the sss. Hemodynamic factors that determine its value.
Q-volume velocity of blood flow is the amount of blood flowing through the cross section of the system per unit time. This total value is the same in all sections of the system. Blood circulation, if we consider it as a whole. THOSE. the amount of blood ejected from the heart in a minute is equal to the amount of blood returning to it and passing through the total cross section of the circulatory circle in any of its parts during the same time. , B) from the functional load on it. The brain and heart receive significantly more blood (15 and 5 - at rest; 4 and 5 - physical load), liver and gastrointestinal tract (20 and 4); muscles (20 and 85); bones, bone marrow, adipose tissue (15 and 2) . Functional hyperpia is achieved by many mechanisms. Under the influence of chemical, humoral, and nervous influences in a working organ, vasodilation occurs, the resistance to blood flow in them decreases, which leads to a redistribution of blood and, under conditions of constant blood pressure, can cause a deterioration in the blood supply to the heart, liver, and other organs . In the conditions of physical The load is an increase in systemic blood pressure, sometimes quite significant (up to 180-200), which prevents a decrease in blood flow in the internal organs and ensures an increase in blood flow in a working organ. Hemodynamically can be expressed by the formula Q=P*p*r4/8*nu*L
4. The concept of acute, Q-volumetric velocity of blood flow is the amount of blood flowing through the cross section of the system per unit time. This total value is the same in all sections of the system. Blood circulation, if we consider it as a whole. THOSE. the amount of blood ejected from the heart in a minute is equal to the amount of blood returning to it and passing through the total cross section of the circulatory circle in any of its parts during the same time. , B) from the functional load on it. The brain and heart receive significantly more blood (15 and 5 - at rest; 4 and 5 - physical load), liver and gastrointestinal tract (20 and 4); muscles (20 and 85); bones, bone marrow, adipose tissue (15 and 2) . Functional hyperpia is achieved by many mechanisms. Under the influence of chemical, humoral, and nervous influences in a working organ, vasodilation occurs, the resistance to blood flow in them decreases, which leads to a redistribution of blood and, under conditions of constant blood pressure, can cause a deterioration in the blood supply to the heart, liver, and other organs . In the conditions of physical The load is an increase in systemic blood pressure, sometimes quite significant (up to 180-200), which prevents a decrease in blood flow in the internal organs and ensures an increase in blood flow in a working organ. Hemodynamically can be expressed by the formula Q=P*p*r4/8*nu*L
4. The concept of acute, subacute, chronic regulation of blood pressure.
Acute neuroreflex mechanism initiated by blood vessel baroreceptors. The baroreceptors of the aortic and carotid zones have the most powerful influence on the deprossor zone of the hemodynamic center. the imposition of a plaster bandage in the form of a muff on such a zone excludes the excitation of baroreceptors, therefore it was concluded that they do not respond to pressure itself, but to the stretching of the vessel wall under the influence of blood pressure. This is also facilitated by the structural features of the sections of the vessels where there are baroreceptors: they are thinned, they have few muscle and many elastic fibers. The depressant effects of baroreceptors are also used in practical medicine: pressure on the neck in the region. projection of the carotid artery can help stop an attack of tachycardia, and percutaneous irritation in the carotid zone is used to reduce blood pressure. On the other hand, the adaptation of baroreceptors as a result of a prolonged increase in blood pressure, as well as the development of sclerotic changes in the walls of blood vessels and a decrease in their extensibility, can become factors contributing to the development of hypertension. Transection of the depressor nerve in dogs produces this effect in a relatively short time. In rabbits, transection of the nerve a, which begins in the aortic zone, the receptors of which are more active with significant rises in blood pressure, causes death from a sharp increase in blood pressure and disturbances in cerebral blood flow. To maintain the stability of blood pressure, the baroreceptors of the heart itself are even more important than the vascular ones. Novocainization of epicardial receptors can lead to the development of hypertension. Brain baroreceptors change their activity only in terminal states of the body. Baroreceptor reflexes are suppressed under the action of nociceptive ones, in particular, those associated with impaired coronary blood flow, as well as during activation of chemoreceptors, emotional stress and physical activity. One of the mechanisms of reflex suppression in physical. The load is an increase in venous return of blood to the heart, as well as the implementation of the Bainbridge unloading reflex and heterometric regulation.
Subacute regulation - hell on hemodynamic mechanisms implemented through changes in bcc. in decapitated animals with a destroyed spinal cord, 30 minutes after blood loss or injection of fluid into the vessels in the amount of 30% of the bcc, the blood pressure is restored to a level close to similar. These mechanisms include: 1) changes in the movement of fluid from capillaries to tissues and vice versa; 2) changes in blood deposition in the venous section; 3) changes in renal filtration and reabsorption (an increase in blood pressure by only 5 mm Hg, other things being equal, can cause diuresis)
Chronic regulation of blood pressure is provided by the renal-adrenal system, the elements of which and the nature of their influence on each other are shown in the diagram, where positive influences are marked with arrows with a + sign, and negative -
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1. Diastole of the ventricles of the heart, its periods and phases. valvular position and pressure in the cavities of the heart during diastole.
By the end of ventricular systole and the beginning of diastole (from the moment the semilunar valves close), the ventricles contain a residual, or reserve, volume of blood (end-systolic volume). At the same time, a sharp drop in pressure in the ventricles begins (the phase of isovolumic, or isometric, relaxation). The ability of the myocardium to quickly relax is the most important condition for filling the heart with blood. When the pressure in the ventricles (initial diastolic) becomes less than the pressure in the atria, the atrioventricular valves open and the rapid filling phase begins, during which blood accelerates from the atria to the ventricles. During this phase, up to 85% of their diastolic volume enters the ventricles. As the ventricles fill, their rate of filling with blood decreases (slow filling phase). At the end of ventricular diastole, atrial systole begins, resulting in another 15% of their diastolic volume entering the ventricles. Thus, at the end of diastole, an end-diastolic volume is created in the ventricles, which corresponds to a certain level of end-diastolic pressure in the ventricles. End-diastolic volume and end-diastolic pressure make up the so-called preload of the heart, which is the determining condition for stretching the myocardial fibers, i.e., the implementation of the Frank-Starling law.
2. Cardiovascular center, its localization. Structural and functional features.
Vasomotor center
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 - 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.
3.Functional classification of blood vessels.
Cushioning vessels - aorta, pulmonary artery and their large branches, i.e. elastic vessels.
Vessels of distribution - medium and small arteries of the muscular type of regions and organs. their function is to distribute blood flow to all organs and tissues of the body. With an increase in tissue demand, the diameter of the vessel adjusts to increased blood flow in accordance with the change in linear velocity due to an endothelium-dependent mechanism. With an increase in shear stress (the force of friction between the layers of blood and the endothelium of the vessel, which prevents the movement of blood.) of the parietal layer of blood, the apical membrane of endotheliocytes is deformed, and they synthesize vasodilators (nitric oxide), which reduce the tone of the smooth muscles of the vessel, i.e., the vessel expands. In violation of this mechanism, the distribution vessels can become a limiting link, preventing a significant increase in blood flow in the organ, despite its metabolic demand, for example, coronary and cerebral vessels affected by atherosclerosis.
Vessels of resistance - an artery with a diameter of less than 100 microns, arterioles, precapillary sphincters, sphincters of the main capillaries. These vessels account for about 60% of the total resistance to blood flow, hence their name. They regulate the blood flow of the systemic, regional and microcirculatory levels. The total vascular resistance of different regions forms the systemic diastolic blood pressure, changes it and keeps it at a certain level as a result of general neurogenic and humoral changes in the tone of these vessels. Multidirectional changes in the tone of resistance vessels in different regions provide a redistribution of volumetric blood flow between regions. In a region or organ, they redistribute blood flow between microregions, i.e. control microcirculation. Resistance vessels of a microregion distribute blood flow between the exchange and shunt circuits, determine the number of functioning capillaries.
Exchange vessels are capillaries. Partially, the transport of substances from the blood to tissues also occurs in arterioles and venules. Oxygen easily diffuses through the wall of arterioles, and through hatches - venules, protein molecules diffuse from the blood, which later enter the lymph. Water, water-soluble inorganic and low-molecular organic substances (ions, glucose, ureas) pass through the pores. In some organs (skeletal muscles, skin, lungs, central nervous system), the capillary wall is a barrier (histo-hematic, hemato-encephalic). And external. Secretion capillaries have fenestra (20-40 nm) that ensure the activity of these organs.
Shunting vessels- Shunting vessels are arteriovenous anastomoses that are present in some tissues. When these vessels are open, blood flow through the capillaries either decreases or stops completely. Most typical for the skin: if heat transfer is required to decrease, blood flow through the capillary system stops, and blood is shunted from the arterial system to the venous system.
Capacitive (accumulating) vessels - in which changes in the lumen, even so small that they do not significantly affect the overall resistance, cause pronounced changes in the distribution of blood and the amount of blood flow to the heart (venous part of the system). These are postcapillary venules, venules, small veins, venous plexuses and specialized formations - sinusoids of the spleen. Their total capacity is about 50% of the total volume of blood contained in the cardiovascular system. The functions of these vessels are associated with the ability to change their capacity, which is due to a number of morphological and functional features of capacitive vessels.
Vessels of blood return to the heart - These are medium, large and hollow veins that act as collectors through which regional outflow of blood is provided, returning it to the heart. The capacity of this section of the venous bed is about 18% and changes little under physiological conditions (by less than 1/5 of the original capacity). Veins, especially superficial ones, can increase the volume of blood contained in them due to the ability of the walls to stretch with an increase in transmural pressure.
4. features of hemodynamics in the pulmonary circulation. blood supply to the lungs and its regulation.
Of considerable interest for pediatric anesthesiology is the study of hemodynamics of the pulmonary circulation. This is primarily due to the special role of pulmonary hemodynamics in maintaining homeostasis during anesthesia and surgery, as well as its multicomponent dependence on blood loss, cardiac output, methods of artificial lung ventilation, etc.
In addition, the pressure in the pulmonary arterial bed differs significantly from the pressure in the arteries of a large circle, which is associated with the peculiarity of the morphological structure of the pulmonary vessels.
This leads to the fact that the mass of circulating blood in the pulmonary circulation can increase significantly without causing an increase in pressure in the pulmonary artery due to the opening of non-functioning vessels and shunts.
In addition, the pulmonary-arterial bed has greater extensibility due to the abundance of elastic fibers in the walls of blood vessels and resists during the operation of the right ventricle 5-6 times less than the resistance encountered during contraction of the left ventricle. Under physiological conditions, pulmonary blood flow through the system small circle is equal to the blood flow in the systemic circulation
In this regard, the study of the hemodynamics of the pulmonary circulation can provide new interesting information about the complex processes that occur during surgical interventions, especially since this issue remains poorly understood in children.
A number of authors note an increase in pressure in the pulmonary artery and an increase in pulmonary vascular resistance in chronic suppurative lung diseases in children.
It should be noted that the syndrome of hypertension of the pulmonary circulation develops as a result of narrowing of the pulmonary arterioles in response to a decrease in oxygen tension in the alveolar air.
Since during operations using mechanical ventilation, and especially during operations on the lungs, a decrease in the oxygen tension of the alveolar air can be observed, the study of the hemodynamics of the pulmonary circulation is of additional interest.
Blood from the right ventricle is sent through the pulmonary artery and its branches to the capillary networks of the respiratory tissue of the lung, where it is enriched with oxygen. Upon completion of this process, blood from the capillary networks is collected by the branches of the pulmonary vein and sent to the left atrium. It should be remembered that in the pulmonary circulation, blood, which we usually call venous, moves through the arteries, and arterial blood flows in the veins.
The pulmonary artery enters the root of each lung and branches further along with the bronchial tree, so that each branch of the tree is accompanied by a branch of the pulmonary artery. Small branches that reach the respiratory bronchioles supply blood to the terminal branches, which bring blood to the capillary networks of the alveolar ducts, sacs and alveoli.
Blood from the capillary networks in the respiratory tissue is collected in the smallest branches of the pulmonary vein. They begin in the parenchyma of the lobules and are surrounded by thin connective tissue membranes. They enter the interlobular septa, where they open into the interlobular veins. The latter, in turn, are directed along the partitions to those areas where the tops of several lobules converge. Here the veins come into close contact with the branches of the bronchial tree. Starting from this place and to the root of the lung, the veins go along with the bronchi. In other words, with the exception of the area inside the lobules, the branches of the pulmonary artery and vein follow along with the branches of the bronchial tree; inside the lobules, however, only the arteries go along with the bronchioles.
Oxygenated blood is supplied to parts of the lung itself by bronchial arteries. The latter also pass into the lung tissue in close connection with the bronchial tree and feed the capillary networks in its walls. They also supply blood to the lymph nodes scattered throughout the bronchial tree. In addition, the branches of the bronchial arteries run along the interlobular septa and supply oxygenated blood to the capillaries of the visceral pleura.
Naturally, there are differences between the blood in the arteries of the pulmonary circulation and the arteries of the systemic circulation - both the pressure and the oxygen content in the former are lower than in the latter. Therefore, anastomoses between the two circulatory systems in the lung will create unusual physological problems.
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1. Bioelectric phenomena in the heart. Teeth and interval ekg. Properties of the heart muscle assessed with ecg.
2. change in the work of the heart during physical activity. Fur. And meaning.
Work of the heart during exercise
The frequency and strength of heart contractions during muscular work increase significantly. Muscular work while lying down speeds up the pulse less than sitting or standing.
The maximum blood pressure increases to 200 mm Hg. and more. An increase in blood pressure occurs in the first 3-5 minutes from the start of work, and then in strong trained people with prolonged and intense muscular work, it is kept at a relatively constant level due to the training of reflex self-regulation. In weak and untrained people, blood pressure begins to fall already during work due to lack of training or insufficient training of reflex self-regulation, which leads to disability due to a decrease in blood supply to the brain, heart, muscles and other organs.
In people trained for muscular work, the number of heart contractions at rest is less than in untrained people, and, as a rule, no more than 50-60 per minute, and in especially trained people - even 40-42. It can be assumed that this decrease in heart rate is due to the pronounced in those involved in physical exercises that develop endurance. With a rare rhythm of heartbeats, the duration of the phase of isometric contraction and diastole is increased. The duration of the exile phase is almost unchanged.
Resting systolic volume in trained is the same as in untrained, but as training increases, it decreases. Consequently, their minute volume also decreases at rest. However, in trained systolic volume at rest, as in untrained, it is combined with an increase in ventricular cavities. It should be noted that the cavity of the ventricle contains: 1) systolic volume, which is ejected during its contraction, 2) reserve volume, which is used during muscle activity and other conditions associated with increased blood supply, and 3) residual volume, which is almost never used even when the most intense work of the heart. In contrast to the untrained, the trained have a particularly increased reserve volume, and the systolic and residual volumes are almost the same. A large reserve volume in trained people allows you to immediately increase the systolic blood output at the beginning of work. Bradycardia, prolongation of the isometric tension phase, a decrease in systolic volume, and other changes indicate the economical activity of the heart at rest, which is referred to as controlled myocardial hypodynamia. During the transition from rest to muscle activity, the trained hyperdynamia of the heart immediately manifests itself, which consists in an increase in heart rate, an increase in systole, a shortening or even disappearance of the isometric contraction phase.
The minute volume of blood after training increases, which depends on the increase in systolic volume and the strength of cardiac contraction, the development of the heart muscle and the improvement of its nutrition.
During muscular work and in proportion to its value, the minute volume of the heart in a person increases to 25-30 dm 3 , and in exceptional cases up to 40-50 dm 3 . This increase in minute volume occurs (especially in trained people) mainly due to systolic volume, which in humans can reach 200-220 cm 3 . A less significant role in the increase in cardiac output in adults is played by an increase in heart rate, which especially increases when systolic volume reaches the limit. The more fitness, the relatively more powerful work a person can perform with an optimal increase in heart rate up to 170-180 in 1 min. An increase in the pulse above this level makes it difficult for the heart to fill with blood and its blood supply through the coronary vessels. With the most intense work in a trained person, the heart rate can reach up to 260-280 per minute.
During muscular work, the blood supply to the heart muscle itself also increases. If 200-250 cm 3 of blood flows through the coronary vessels of the human heart at rest per 1 min, then during intense muscular work the amount of blood flowing through the coronary vessels reaches 3.0-4.0 dm 3 per 1 min. With an increase in blood pressure by 50%, 3 times more blood flows through the dilated coronary vessels than at rest. Expansion of the coronary vessels occurs reflexively, as well as due to the accumulation of metabolic products and the flow of adrenaline into the blood.
An increase in blood pressure in the aortic arch and carotid sinus reflexively dilates the coronary vessels. The coronary vessels expand the fibers of the sympathetic nerves of the heart, excited both by adrenaline and acetylcholine.
In trained people, heart mass increases in direct proportion to the development of their skeletal muscles. In trained men, the volume of the heart is greater than that of untrained men, 100-300 cm 3, and in women - by 100 cm 3 or more.
During muscular work, the minute volume increases and blood pressure increases, and therefore the work of the heart is 9.8-24.5 kJ per hour. If a person performs muscular work for 8 hours a day, then the heart during the day produces work of approximately 196-588 kJ. In other words, the heart per day performs work equal to that which a person weighing 70 kg expends when climbing 250-300 meters. The performance of the heart increases during muscular activity, not only due to an increase in the volume of systolic ejection and an increase in heart rate, but also a greater acceleration of blood circulation, since the rate of systolic ejection increases by 4 times or more.
The increase and intensification of the work of the heart and the narrowing of the blood vessels during muscular work occurs reflexively due to irritation of the receptors of the skeletal muscles during their contractions.
3. Arterial pulse, its origin. Sphygmography.
The arterial pulse is called the rhythmic oscillations of the arterial walls, due to the passage of the pulse wave. A pulse wave is a propagating oscillation of the arterial wall as a result of a systolic rise in blood pressure. A pulse wave occurs in the aorta during systole, when a systolic portion of blood is ejected into it and its wall is stretched. Since the pulse wave moves along the wall of the arteries, the speed of its propagation does not depend on the linear velocity of the blood flow, but is determined by the morphofunctional state of the vessel. The greater the rigidity of the wall, the greater the speed of propagation of the pulse wave and vice versa. Therefore, in young people it is 7-10 m / s, and in old people, due to atherosclerotic changes in blood vessels, it increases. The simplest method of studying the arterial pulse is palpation. Usually the pulse is felt on the radial artery by pressing it against the underlying radius.
The pulse diagnostic method originated many centuries before our era. Among the literary sources that have come down to us, the most ancient are the works of ancient Chinese and Tibetan origin. Ancient Chinese include, for example, “Bin-hu Mo-xue”, “Xiang-lei-shi”, “Zhu-bin-shih”, “Nan-jing”, as well as sections in the treatises “Jia-i-ching”, "Huang-di Nei-jing Su-wen Lin-shu", etc.
The history of pulse diagnosis is inextricably linked with the name of the ancient Chinese healer - Bian Qiao (Qin Yue-Ren). The beginning of the path of the pulse diagnosis technique is associated with one of the legends, according to which Bian Qiao was invited to treat the daughter of a noble mandarin (official). The situation was complicated by the fact that even doctors were strictly forbidden to see and touch persons of noble rank. Bian Qiao asked for a thin string. Then he suggested tying the other end of the cord to the wrist of the princess, who was behind the screen, but the court healers disdainfully treated the invited doctor and decided to play a trick on him by tying the end of the cord not to the princess’s wrist, but to the paw of a dog running nearby. A few seconds later, to the surprise of those present, Bian Qiao calmly declared that these were impulses not of a person, but of an animal, and this animal tossed with worms. The skill of the doctor aroused admiration, and the cord was transferred with confidence to the princess's wrist, after which the disease was determined and treatment was prescribed. As a result, the princess quickly recovered, and his technique became widely known.
Sphygmography(Greek sphygmos pulse, pulsation + graphō write, depict) - a method for studying hemodynamics and diagnosing some forms of pathology of the cardiovascular system, based on graphic registration of pulse oscillations in the wall of a blood vessel.
Sphygmography is carried out using special attachments to an electrocardiograph or other registrar, which make it possible to convert the mechanical vibrations of the vessel wall perceived by the pulse receiver (or the accompanying changes in the electrical capacitance or optical properties of the studied area of the body) into electrical signals, which, after preliminary amplification, are fed to the recording device. The recorded curve is called a sphygmogram (SG). There are both contact (applied to the skin over the pulsating artery) and non-contact, or remote, pulse receivers. The latter are usually used to register a venous pulse - phlebosphygmography. The recording of pulse oscillations of a limb segment with the help of a pneumatic cuff or strain gauge applied around its perimeter is called volumetric sphygmography.
4. Features of blood pressure regulation in individuals with hypo and hyperkinetic types of blood circulation. The place of hemodynamic and humoral mechanisms in the self-regulation of blood pressure.
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1.minute volume of blood circulation and systolic blood volume. Their sizes. Definition methods.
The minute volume of blood circulation characterizes the total amount of blood pumped by the right and left parts of the heart for one minute in the cardiovascular system. The unit of minute volume of blood circulation is l/min or ml/min. To neutralize the influence of individual anthropometric differences on the value of the IOC, it is expressed as a cardiac index. The cardiac index is the value of the minute volume of blood circulation divided by the body surface area in m. The dimension of the cardiac index is l / (min m2).
The most accurate method for determining the minute volume of blood flow in humans was proposed by Fick (1870). It consists in an indirect calculation of the IOC, which is performed knowing the difference between the oxygen content in the arterial and. When using the Fick method, it is necessary to take mixed venous blood from the right half of the heart. Venous blood from a person is taken from the right half of the heart using a catheter inserted into the right atrium through the brachial vein. The Fick method, being the most accurate, has not been widely used in practice due to technical complexity and laboriousness (the need for cardiac catheterization, puncture of the artery, determination of gas exchange). venous blood, the volume of oxygen consumed by a person per minute.
By dividing the minute volume by the number of heartbeats per minute, you can calculate systolic volume blood.
Systolic blood volume- The volume of blood pumped by each ventricle into the main vessel (aorta or pulmonary artery) with one contraction of the heart is referred to as the systolic, or shock, volume of blood.
The greatest systolic volume is observed at a heart rate of 130 to 180 beats/min. At a heart rate above 180 beats/min, systolic volume begins to decline strongly.
With a heart rate of 70 - 75 per minute, the systolic volume is 65 - 70 ml of blood. In a person with a horizontal position of the body at rest, the systolic volume ranges from 70 to 100 ml.
The capital volume of blood is most simply calculated by dividing the minute volume of blood by the number of heartbeats per minute. In a healthy person, the systolic blood volume ranges from 50 to 70 ml.
2. Afferent link in the regulation of the activity of the heart. Influence of excitation of various reflexogenic zones on the activity of the SS center of the medulla oblongata.
The afferent link of K.'s own reflexes is represented by angioceptors (baro- and chemoreceptors) located in various parts of the vascular bed and in the heart. In places they are collected in clusters forming reflexogenic zones. The main ones are the zones of the aortic arch, carotid sinus, and vertebral artery. The afferent link of conjugated reflexes To. is located outside the vascular bed, its central part includes various structures of the cerebral cortex, hypothalamus, medulla oblongata and spinal cord. The vital nuclei of the cardiovascular center are located in the medulla oblongata: the neurons of the lateral part of the medulla oblongata through the sympathetic neurons of the spinal cord have a tonic activating effect on the heart and blood vessels; neurons of the medial part of the medulla oblongata inhibit the sympathetic neurons of the spinal cord; the motor nucleus of the vagus nerve inhibits the activity of the heart; neurons on the ventral surface of the medulla oblongata stimulate the activity of the sympathetic nervous system. Through hypothalamus the connection of the nervous and humoral links of the regulation of K is carried out.
3. main hemodynamic factors that determine the magnitude of systemic blood pressure.
Systemic blood pressure, the main hemodynamic factors that determine its value One of the most important parameters of hemodynamics is systemic blood pressure, i.e. pressure in the initial sections of the circulatory system - in large arteries. Its magnitude depends on the changes taking place in any department of the system. Along with the systemic, there is the concept of local pressure, i.e. pressure in small arteries, arterioles, veins, capillaries. This pressure is less, the longer the path traveled by the blood to this vessel when it leaves the ventricle of the heart. So, in the capillaries, the blood pressure is greater than in the veins, and is equal to 30-40 mm (beginning) - 16-12 mm Hg. Art. (end). This is explained by the fact that the longer the blood travels, the more energy is spent on overcoming the resistance of the vessel walls, as a result, the pressure in the vena cava is close to zero or even below zero. The main hemodynamic factors affecting the value of systemic arterial pressure are determined from the formula: Q \u003d P p r4 / 8 Yu l, Where Q is the volumetric blood flow velocity in a given organ, r is the radius of the vessels, P is the difference in pressure on "inspiration" and " exhale" from the organ. The value of systemic arterial pressure (BP) depends on the phase of the cardiac cycle. Systolic blood pressure is created by the energy of heart contractions in the systole phase, is 100-140 mm Hg. Art. Its value depends mainly on the systolic volume (ejection) of the ventricle (CO), total peripheral resistance (R) and heart rate. Diastolic blood pressure is created by the energy accumulated in the walls of large arteries as they stretch during systole. The value of this pressure is 70-90 mm Hg. Art. Its value is determined, to a greater extent, by the values of R and heart rate. The difference between systolic and diastolic pressure is called pulse pressure, because. it determines the range of the pulse wave, which is normally equal to 30-50 mm Hg. Art. The energy of systolic pressure is spent: 1) to overcome the resistance of the vascular wall (lateral pressure - 100-110 mm Hg); 2) to create the speed of moving blood (10-20 mm Hg - shock pressure). An indicator of the energy of a continuous flow of moving blood, the resulting “value of all its variables, is the artificially allocated average dynamic pressure. It can be calculated according to the formula of D. Hinema: Rmean = Rdiastolic 1/3Rpulse. The value of this pressure is 80-95 mm Hg. Art. Blood pressure also changes in connection with the phases of respiration: on inspiration, it decreases. BP is a relatively mild constant: its value can fluctuate during the day: during physical work of great intensity, systolic pressure can increase by 1.5-2 times. It also increases with emotional and other types of stress. On the other hand, the blood pressure of a healthy person may decrease relative to its average value. This is observed during non-REM sleep and - briefly - during orthostatic perturbation associated with the transition of the body from a horizontal to a vertical position.
4.Features of blood flow in the brain and its regulation.
The role of the brain in the regulation of blood circulation can be compared with the role of a powerful monarch, dictator: an adequate supply of blood, oxygen to the brain and myocardium is calculated on the value of systemic blood pressure at any moment of life. At rest, the brain uses 20% of the oxygen consumed by the whole body and 70% of glucose; cerebral blood flow is 15% of myoc, although the mass of the brain is equal to only 2% of body weight.
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1. The concept of extrasystole. The possibility of its occurrence in different phases of the cardiac cycle. Compensatory pause, the reasons for its development.
Extrasystole is a heart rhythm disorder caused by premature contraction of the entire heart or its individual parts due to increased activity of ectopic automatism foci. It belongs to the most common heart rhythm disturbances in both men and women. According to some researchers, extrasystole periodically occurs in almost all people.
Rarely occurring extrasystoles do not affect the state of hemodynamics, the general condition of the patient (sometimes patients experience unpleasant sensations of interruptions). Frequent extrasystoles, group extrasystoles, extrasystoles emanating from various ectopic foci can cause hemodynamic disorders. They are often harbingers of paroxysmal tachycardia, atrial fibrillation, ventricular fibrillation. Such extrasystoles, of course, can be attributed to urgent conditions. Especially dangerous are the conditions when the ectopic focus of excitation temporarily becomes the pacemaker of the heart, i.e., an attack of alternating extrasystoles occurs, or an attack of paroxysmal tachycardia.
Modern research suggests that this type of heart rhythm disorder is often found in people who are considered to be practically healthy. So, N. Zapf and V. Hutano (1967) during a single examination of 67,375 people found extrasystole in 49%. K. Averill and Z. Lamb (1960), examining 100 people repeatedly during the day by teleelectrocardiography, revealed extrasystole in 30%. Therefore, the notion that interruptions are a sign of heart muscle disease has now been rejected.
G. F. Lang (1957) indicates that extrasystole in approximately 50% of cases is the result of extracardiac influences.
In the experiment, extrasystole causes irritation of various parts of the brain - the cerebral cortex, thalamus, hypothalamus, cerebellum, medulla oblongata.
There is an emotional extrasystole that occurs during emotional experiences and conflicts, anxiety, fear, anger. Extrasystolic arrhythmia may be one of the manifestations of general neurosis, altered cortico-visceral regulation. The role of the sympathetic and parasympathetic parts of the nervous system in the genesis of cardiac arrhythmias is evidenced by reflex extrasystole that occurs during exacerbation of gastric and duodenal ulcers, chronic cholecystitis, chronic pancreatitis, diaphragmatic hernias, and operations on the abdominal organs. The cause of reflex extrasystole can be pathological processes in the lungs and mediastinum, pleural and pleuropericardial adhesions, cervical spondylarthrosis. Conditional extrasystole is also possible.
Thus, the state of the central and autonomic nervous system plays an important role in the occurrence of extrasystoles.
Most often, the occurrence of extrasystole is promoted by organic changes in the myocardium. It should be borne in mind that often even minor organic changes in the myocardium in combination with functional factors and, above all, with discoordinated influences of the extracardiac nerves, can lead to the appearance of ectopic foci of excitation. In various forms of coronary heart disease, the cause of extrasystole may be changes in the myocardium or a combination of organic changes in the myocardium with functional ones. So, according to E.I. Chazov (1971), M.Ya. Ruda, A.P. Zysko (1977), L.T. moreover, the most common rhythm disturbance is extrasystole (ventricular extrasystole is observed in 85-90% of hospitalized
