Constituting only 0.5% of the total body weight, the heart is the most important organ in the body. human body, without normal functioning which makes it impossible for all other systems to fully operate. The structure and functions of the heart are one of the most complex subsections of the science of the structure of the body; moreover, a lot of miraculous qualities from the field of psychology and even theology are attributed to this organ.

Where the human heart is located, what it consists of and how it works is described in detail on this page.

What does the human heart consist of and where is it located (with photo)

Speaking about the structure of the human heart, philosophers and doctors of antiquity called it the “royal muscle,” meaning the importance of this organ for humans.

Here you will learn how the heart works and how it works in the body healthy person.

The heart, located asymmetrically in the chest cavity between the lungs, is a hollow muscular organ. Outside, it is enclosed in a closed cavity - the pericardium. The heart wall consists of three layers: the outer or epicardium, the middle - the myocardium, and the inner - the endocardium. The epicardium envelops the outside of the heart. The endocardium lines the inside of the heart chambers and its valves. The predominant part of the heart wall is the myocardium - a muscular layer formed by cardiac striated muscle tissue. The myocardium of the atria and ventricles is separated, which creates the possibility of their separate contraction. The structure and function of the heart is based on sequential contraction and relaxation various departments and are associated with the presence of a conductive system through which the impulse propagates.

Look at the photo where the human heart is located and how it works.

The atrioventricular conduction system of the heart consists of the sinoatrial node, which controls the rhythm of the heart (pacemaker), the atrioventricular node, the atrioventricular bundle, its legs and branches. One of the structural features of the heart is that the conduction system is formed by cardiac conductive fibers and is rich in innervated autonomic nerves. The atria are connected to each other by the sinoatrial node, and the atria and ventricles are connected by the atrioventricular bundle.

This is how the human heart works: it is divided into four cavities (right and left atria and right and left ventricles); the atria are divided interatrial septum, and the ventricles - interventricular septa. The superior and inferior vena cava and the coronary sinus of the heart, carrying venous blood, flow into the right atrium.

How do human heart valves work?

Now that you know how the heart works, learn about how it works. The basic principle of the functioning of the heart is as follows: blood from the right atrium, during its contraction, enters the right ventricle through the right atrioventricular orifice, along the edge of which is located the atrioventricular (tricuspid) valve, consisting of three leaflets, which are formed by folds of the endocardium and covered with endothelium. From the free edges of the valves, tendinous chords begin, attached at their ends to three papillary muscles located on inner surface right ventricle.

How do the heart valves of a healthy person work? The papillary muscles, together with the chordae tendineae, hold the valves and, during contraction (systole) of the ventricle, prevent the backflow of blood into the atrium.

Now it’s time to find out how the heart works when the ventricle contracts. In this case, the blood is pushed into the pulmonary trunk through the opening of the pulmonary trunk, in the area of ​​which there is a valve consisting of three semilunar valves that freely pass blood from the ventricle into the pulmonary trunk. By touching their ends, they, like filled pockets, close the hole and prevent the reverse flow of blood. This occurs after the ventricle has emptied.

Four pulmonary veins open into the left atrium (two on each side). The myocardium of the left ventricle is 2-3 times thicker than the myocardium of the right. This is due to great job produced by the left ventricle. From the cavity of the left atrium, the oval-shaped left atrioventricular orifice, equipped with the left atrioventricular bicuspid valve (mitral), leads into the left ventricle. From the ventricle, blood is directed into the aortic opening, equipped with a valve consisting of three semilunar valves, which have the same structure as the pulmonary valve. On the inner surface of the left ventricle, like the right, there are two papillary muscles, from which thin chordae tendineae extend, attaching to the leaflets of the left atrioventricular valve.

The right and left coronary arteries, the branches of which are connected to each other, supply the heart with blood. They branch into capillaries in all three layers of the heart wall. Blood collects in the cardiac veins, then the sinus venosus, which flows directly into the right atrium.

It is the coronary arteries that most often suffer from atherosclerosis: their lumen narrows to the point of complete blockage, which leads to the development.

At the age of 30-40 years, a slight increase in the amount of connective tissue usually begins in the myocardium, fat deposits appear in it, muscle cells are replaced connective tissue. As a person ages adipose tissue accumulates under the epicardium, thickening of the endocardium occurs.

These changes can be significantly slowed down or even prevented through regular physical activity and proper nutrition.

The development of body muscles affects the size of the heart. Thus, the size and mass of the heart in persons engaged in physical labor and in athletes is greater than in representatives of mental labor. Moreover, sports in which physical stress is long-term (for example, cycling, rowing, marathon running, skiing), leads to myocardial hypertrophy and an increase in heart size. Jogging, swimming, short-distance running, boxing, athletics, football and some other sports lead to less pronounced enlargement of the heart muscles.

Physiology of the human heart

When talking about how the human heart works, we must not forget that it is the most powerful motor in the world. During a person's life, the heart makes 2 to 3 billion contractions! The resulting force is capable of lifting the train to its highest level. high point Europe - Elbrus. The heart has an unusually high reliability and a huge margin of safety, which is theoretically designed to last a human life for 150 years.

Every day a healthy heart pumps 2000 liters of blood. Although the average human heart weighs only 300 g, it beats at a rate of 100,800 beats per day, and in a year it makes an astonishing 36,792,000 beats.

The myocardium, being muscle tissue, has the properties of excitability, conductivity and contractility.

The conduction system of the heart ensures sequential contractions and relaxations of its parts. Moreover, both contraction and relaxation of the heart muscle occurs automatically.

Automatism (from Greek automates - self-acting, spontaneous) The heart is its ability to contract rhythmically under the influence of impulses arising within itself (in the cells of its conduction system).

The generator of these impulses is the sinoatrial node. Excitation spreads throughout the myocardium. The atria contract first, and then the ventricles. A healthy myocardium contracts throughout a person’s life and does not experience fatigue.

Remember what the heart is made of, and now imagine what controls this complex system. The activity of the heart is “directed” by the heart centers located in medulla oblongata and pons, which act through the autonomic nervous system. Sympathetic nerves have positive influence(increased heart rate and increase in their strength), parasympathetic - negative (decrease in heart rate and decrease in their strength).

The cerebral cortex regulates the activity of the heart centers through the hypothalamus. Cardiac contraction muscle cells provides the pumping function of the heart. The movement of blood through the vessels occurs mainly due to this function of the heart and muscle contraction.

The physiology of the heart is like a pump pumping blood into the vessels. Each striated muscle fiber is a kind of “peripheral heart”, the contraction of which promotes the movement of blood through the microvasculature. Muscles, contracting, promote the movement of blood through the veins of the lower half of the body against gravity.

Valuable advice! Physical activity facilitates the work of the heart, and physical inactivity requires increased work, which is one of the important factors violation of its function.

Having learned what the human heart is made of and how it works, it’s time to learn about the heart rhythm.

Heart rhythm: the process of contraction and relaxation of the heart muscle

The rhythm of the heart is not an empty phrase, it is truly a rhythmic process. The work of the human “engine” alternates between contraction of the heart muscle (systole) and relaxation (diastole). During general relaxation of the heart (diastole), blood from the vena cava and pulmonary veins enters the right and left atria, respectively. After this, contraction (systole) of the atria occurs. The process of heart contraction begins at the junction of the superior vena cava into the right atrium and spreads through both atria, as a result of which blood from the atria is pumped through the atrioventricular openings into the ventricles. Then a wave of ventricular contractions begins in the walls of the heart, which spreads to both ventricles, and blood is pumped into the openings of the pulmonary trunk and aorta; at this time, the atrioventricular valves close. After this there is a pause. Atrial systole lasts 0.1 s, ventricular systole - 0.3 s, total pause - 0.4 s. These three phases make up the cardiac cycle - the set of processes occurring in the heart during one complete cycle of contraction and relaxation. So, during one cardiac cycle the atria contract for 0.1 s and rest for 0.7 s; ventricles, respectively - 0.3 and 0.5 s.

Due to changes in pressure in the cavities of the heart, the valves of the heart, pulmonary artery and aorta open or close. At the beginning of ventricular systole, the atrioventricular valves close and the semilunar valves of the aorta and pulmonary artery open. During ventricular diastole, atrial systole occurs, the atrioventricular valves open and the ventricles fill with blood. The return of blood from the aorta and pulmonary trunk is prevented by the semilunar valves.

During the day, the contraction of the heart muscle lasts 8 hours and rests for 16 hours. This is a vivid example of a rational regime of work and rest.

Adequate physical activity ensures optimal and high functional reserves of the heart. At the same time, the blood supply to the heart itself does not exceed 5% total number expelled blood. With intense physical work this figure increases 3-4 times. The amount of blood ejected by each ventricle during systole ranges from 70 to 100 ml. This figure also increases with physical activity.

Adult heart weight and normal beat rate

The size of a healthy person’s heart correlates with the size of his body, and also depends on the intensity of physical activity and metabolism. Approximate weight hearts in women - 250 g, in men - 300 g. That is, the average weight of the heart of an adult is 0.5% of body weight, while at rest the heart consumes about 25-30 ml of oxygen (09) per minute - about 10% of total consumption 09 at rest. With intense muscular activity, the consumption of 02 by the heart increases by 3-4 times. Depending on the load coefficient useful action(efficiency) of the heart ranges from 15 to 40%. Let us recall that the efficiency of a modern diesel locomotive reaches 14-15%. Blood flows from the area high pressure in the low pressure area.

In humans, the heart rate per minute is about 125 beats per minute at the age of 1 year, at 2 years - 105, at 3 years - 100, at 4 - 97. At the age of 5 to 10 years, the normal heart rate is 90 , from 10 to 15 - 75-78, from 15 to 50 - 70, from 50 to 60 - 74, from 60 to 80 years - 80 beats/min. Some interesting figures: during the day the heart beats about 108,000 times, during life - 2,800,000,000-3,100,000,000 times; 225-250 million liters pass through the heart. blood.

The heart adapts to the constantly changing conditions of human life: daily routine, physical activity, food, ecology, stressful situations etc. At rest, the ventricles of an adult are pushed into vascular system about 5 liters of blood per minute. This indicator - minute volume of blood circulation (MBV) - increases 5-6 times during heavy physical work. The ratio between IOC at rest and during maximally intense muscular work indicates the functional reserves of the heart, and therefore the functional reserves of health.

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This transport system of the body is called the cardiovascular or circulatory system. The blood also carries hormones, enzymes and other substances, which ensures the functioning of the body as a whole.

Circulation

Blood vessels are closed in two circles of blood circulation - large and small. Systemic circulation serves for delivery necessary substances all organs and tissues, and pulmonary circulation- to enrich the blood flowing from the organs with oxygen in the lungs and remove carbon dioxide from it. Each circuit of blood circulation begins and ends in the heart, which is why it has four chambers. Two chambers that push blood into the systemic and pulmonary circulation are ventricles hearts, two chambers receiving blood, - atria(Fig. 1). The vessels through which blood flows from the heart are called arteries, and the vessels through which blood returns to the heart are called veins. Oxygen-enriched blood is usually called arterial; it flows through the arteries of the systemic circulation and the veins of the pulmonary circulation. Oxygen-poor venous blood moves in the veins of the systemic circulation and in the arteries of the pulmonary circulation.

Location of the heart

The heart is located in the chest cavity, behind the sternum. The left half of the chest cavity contains 2/3 of the heart, and only 1/3 lies on the right. Such asymmetry is characteristic only of man and arose in connection with the vertical position of his body. The upper border of the heart (base) is projected onto the sternum at the level of the third ribs, the apex of the heart is located on the left between the fifth and sixth ribs, almost in line with the nipple. The boundaries of the heart change with age and depend on gender and body type. Thus, in newborns, the heart is almost entirely located in the left half of the chest cavity and lies horizontally. With heart diseases, for example, with its defects, the cavities of the heart increase and, accordingly, its boundaries shift.

Structure of the heart

The heart is a hollow, cone-shaped muscular organ weighing about 300 g in men and 220 g in women. Radiographs show that the size of the heart corresponds to the size of a hand folded into a fist. Extended upper part the heart, where the large vessels are located, is called the base, and the narrowed bottom part, facing forward and to the left, is the apex of the heart.

Inside, the heart is divided by a longitudinal septum into two halves that do not communicate with each other - right and left. Venous blood flows in the right half of the heart, arterial blood flows in the left. Each half of the heart consists of two chambers: the upper one - the atrium and the lower one - the ventricle. The atria communicate with the corresponding ventricles through the atrioventricular orifices (right and left). Through these openings, blood is forced into the ventricles during contraction of the atria.

The right atrium receives blood from throughout the body through the two largest veins: superior and inferior vena cava. This is where it flows coronary sinus heart, collecting venous blood from the tissues of the heart itself. When the atrial muscle contracts (atrial systole), blood from the right atrium enters the right ventricle. Exits from the right ventricle pulmonary trunk, through which at the moment of contraction of the ventricles (ventricular systole), venous blood enters the lungs. From the side of the right ventricular cavity, the right atrioventricular orifice closes during ventricular systole tricuspid valve(Fig. 2). The edges of the valve leaflets are connected to the papillary muscles on the inner wall of the ventricle using special tendon strands, this prevents them from turning towards the atrium and prevents the reverse flow of blood from the ventricle into the atrium.

At the mouth of the pulmonary trunk there is also a valve that looks like three pockets (semilunar valves), opening in the direction of blood flow at the time of ventricular systole. When the ventricles relax (diastole), the pouches fill with blood, their edges close, which prevents the return of blood from the pulmonary trunk to the heart.

Into the left atrium in fours pulmonary veins oxygenated blood comes from the lungs. In the phase of atrial systole, it passes into the left ventricle. The valve opening between the left atrium and the left ventricle has two leaflets and is called mitral valve. It is designed like a tricuspid valve. Exits from the left ventricle aorta, carrier arterial blood to all organs and tissues. The aorta begins big circle blood circulation The aortic opening is closed by a valve of three semilunar valves, the mechanism of action of which is the same as that of the pulmonary valve. A view of the heart valves is shown in Fig. 3.

Sometimes heart valves, damaged due to certain diseases (for example, rheumatism), cannot close tightly enough, then the work of the heart is disrupted, and heart defects occur.

The walls of the heart chambers vary significantly in thickness: in the atria it is 2-3 mm, in the left ventricle - on average 15 mm, in the right - about 6 mm. This is due to the development of the muscular lining of the heart, which is determined by the force with which blood must be pushed out of this chamber. The left ventricle of the heart has the thickest walls, as it pushes blood into the systemic circulation, the vessels of which blood passes through on average in 22 seconds. Blood moves through the vessels of the pulmonary circulation for 4-5 seconds.

The heart wall consists of three membranes: the inner - endocardium, the middle - myocardium and the outer - epicardium. Endocardium lines the cavities of the heart from the inside, and its outgrowths (folds) form the heart valves. Myocardium- the middle, muscular layer of the heart, consisting of special muscle fibers, their contraction occurs involuntarily.

The myocardium is divided into two sections: the atrial myocardium, consisting of two layers, and the ventricular myocardium, formed by three layers of muscle fibers. The muscle fibers of the atria and ventricles are not connected to each other, since different sides are attached to the fibrous rings located at the base of the atrioventricular valves. This allows the atria and ventricles to contract independently. The sequence of contractions of the atria and ventricles is ensured by the so-called conduction system of the heart, consisting of muscle fibers of a special structure. The latter form nodes and bundles in the myocardium of the atria and ventricles.

Epicard, covering the heart from the outside, is the inner leaf of a special serous membrane heart, tightly fused with the myocardium. The outer layer of the serous membrane is part of the pericardium - the pericardial sac. Between the leaves there is a slit-like cavity containing serous fluid. Pericardium separates the heart from neighboring organs, A serous fluid in its cavity helps reduce friction during cardiac contractions.

The heart is fed from two coronary (coronary) arteries. They arise from the aorta at the level of its valve. Blood enters these arteries during relaxation (diastole) of the ventricles, when the semilunar valves of the aortic valve close and the entrance to the coronary vessels opens. Numerous branches arise from these arteries, which provide nutrition to the wall of the heart. If the vessels in the thickness of the myocardium are clogged with atherosclerotic deposits or blood clot(thrombus) or when their walls contract spastically, the area of ​​the heart “served” by these vessels ceases to be supplied with blood. This is how myocardial infarction develops.

How does the heart work?

The presence of valves in the heart likens it to a pump, ensuring the difference in blood pressure between the arteries and veins and its flow in one direction. When the heart stops, the pressure in the arteries and veins quickly equalizes and blood circulation stops.

The heart contracts under the influence of impulses arising within itself, namely, in the nodes of the conduction system. This ability of the heart to contract rhythmically is called automatism. The nerves that innervate the heart do not cause its contractions, but only regulate their strength and frequency, adapting the intensity of blood circulation to the needs of the body. For example, during physical work the heart contracts stronger and more often than under resting conditions. Adrenaline, which enters the blood during emotional stress(anger, fear, pain, joy).

As already mentioned, contraction of the heart muscles is called systole, and relaxation is called diastole. The atria and ventricles do not contract simultaneously, but sequentially. At a normal heart rate - an average of 70 beats per minute - a full cycle of cardiac activity lasts 0.8 seconds. At one time, the famous physiologist I.M. Sechenov calculated that the ventricles work 8 hours a day, and this was the rationale for the eight-hour working day. During muscular work, as well as when body temperature rises or environment the heart rate can increase sharply, reaching 200 beats per minute - this is tachycardia. A decrease in the number of heartbeats is called bradycardia. Heart rate can be judged by the pulse.

Heart study

Information about changes in heart rhythm and the presence of pathology can be obtained by electrocardiography - registration electrical activity hearts. The electrocardiogram (ECG) records fluctuations - waves corresponding to the cycle of cardiac activity. An increase or decrease in the intervals between individual ECG waves indicates changes in the functioning of the heart. Electrocardiography plays a leading role in the diagnosis of myocardial infarction, especially in determining the location, extent and depth of the lesion.

Physical training leads to improvement of the body, including the heart muscle. The thickness of the myocardium increases. The heart of athletes therefore has a relatively larger size and works more economically. In trained people, during physical activity, the heart rate increases to a lesser extent than in untrained people. Healthy Heart- the key to successful and active life until old age.

The human heart is a four-chambered muscular organ whose functions are to pump blood into circulatory system, starting and ending with a heart. In 1 minute it is capable of pumping 5 - 30 liters; per day it pumps, like a pump, 8 thousand liters of blood, which in 70 years will amount to 175 million liters.

Anatomy

The heart is located behind the sternum, slightly shifted to the left - approximately 2/3 is on the left side chest. The mouth of the trachea, where it branches into two bronchi, is located higher. Behind it is the esophagus and the descending aorta.

The anatomy of the human heart does not change with age; its structure in adults and children does not differ (see photo). But the location changes somewhat, and in newborns the heart is located entirely on the left side of the chest.

The mass of the human heart is on average 330 grams in men, 250 grams in women; the shape of this organ resembles a streamlined cone with a wide base the size of a fist. Its front part lies behind the sternum. And the lower part borders on the diaphragm - a muscular partition that separates chest cavity from the abdominal.

The shape and size of the heart are determined by age, gender, and existing myocardial diseases. On average, its length in an adult reaches 13 cm, and the width of the base is 9-10 cm.

The size of the heart depends on age. Children's heart less than that of an adult, but its relative mass is higher, and its weight in a newborn is approximately 22 g.

Heart - driving force human blood circulation, as can be seen from the diagram, is a hollow organ (see figure), divided longitudinally by a muscular septum in half, and the halves are divided into atria/ventricles.

The atria are smaller in size and separated from the ventricles by valves:

• on the left side - bicuspid (mitral);
• on the right - tricuspid (tricuspid).

From the left ventricle, blood enters the aorta, then passes through the systemic circulation (BCC). From the right - into the pulmonary trunk, then passes along the lesser circle (ICC).

Cardiac membranes

The human heart is enclosed in the pericardium, which consists of 2 layers:

• external fibrous, preventing overextension;
• internal, which consists of two leaves:
  • visceral (epicardium), which fuses with cardiac tissue;
  • pariental, fused with fibrous tissue of the pericardium.

Between the visceral and pariental sheets of the pericardium there is a space filled with pericardial fluid. This anatomical feature The structure of the human heart is designed to soften mechanical shocks.

In the picture, which shows a heart in cross-section, you can see what its structure is and what it consists of.

The following layers are distinguished:

• myocardium;
• epicardium, the layer adjacent to the myocardium;
• endocardium, which consists of a fibrous outer pericardium and a parietal layer.

Musculature of the heart

The walls consist of striated muscles, innervated by autonomic nervous system. Muscles are represented by two types of fibers:

• contractile - the bulk;
• conducting electrochemical impulses.

The non-stop contractile work of the human heart is ensured by the structural features of the heart wall and the automaticity of the pacemakers.

• The atrium wall (2-5 mm) consists of 2 muscle layers - pepper fibers and longitudinal ones.
• The wall of the heart ventricle is more powerful and consists of three layers that carry out contractions in different directions:
  • layer of oblique fibers;
  • ring fibers;
  • longitudinal layer of papillary muscles.

Coordination of the work of the heart chambers is carried out using the conduction system. The thickness of the myocardium depends on the load that falls on it. The wall of the left ventricle (15 mm) is thicker than the right (about 6 mm), since it pushes blood into the BCC and performs a larger volume of work.

The muscle fibers that make up the contractile tissue of the human heart receive oxygen-rich blood through the coronary vessels.

The lymphatic system of the myocardium is represented by a network of lymphatic capillaries located in the thickness of the muscle layers. Lymphatic vessels go along the course of the coronary veins and arteries that supply the myocardium.

Lymph flows into lymph nodes, which are located near the aortic arch. From there, the lymphatic fluid drains into the thoracic duct.

Duty cycle

At a heart rate (heart rate) of 70 pulses/minute, the work cycle is completed in 0.8 seconds. Blood is expelled from the ventricles of the heart during a contraction called systole.

Systoles take:

• atrial – 0.1 seconds, then relaxation 0.7 seconds;
• ventricles - 0.33 seconds, then diastole 0.47 seconds.

Each beat of the pulse consists of two systoles - the atria and the ventricles. During ventricular systole, blood is pushed into the circulation. When the atria are compressed, up to 1/5 of their total volume enters the ventricles. The value of atrial systole increases with the acceleration of the heart rate, when, due to the contraction of the atria, the ventricles have time to fill with blood.

When the atria relax, blood passes:

• into the right atrium - from the vena cava;
• to the left - from the pulmonary veins.

The human circulatory system is designed in such a way that inhalation promotes blood flow into the atria, as a suction effect is created in the heart due to the pressure difference. This process occurs in the same way as when you inhale, air enters the bronchi.

Atrial compression

The atria are compressed, the ventricles are not working yet.

• At the initial moment, the entire myocardium is relaxed, the valves sag.
• As the compression of the atria increases, blood is expelled into the ventricles.

Atrial contraction ends when the impulse reaches the atrioventricular (AV) node and ventricular contraction begins. At the end of atrial systole, the valves close, the internal chords (tendons) prevent the valve leaflets from diverging or everting into the heart cavity (the phenomenon of prolapse).

Ventricular compression

The atria are relaxed, only the ventricles contract, expelling the volume of blood contained in them:

• left – into the aorta (BCC);
• right - into the pulmonary trunk (PT).

The time of atrial activity (0.1 s) and ventricular work (0.3 s) does not change. An increase in the frequency of contractions occurs due to a decrease in the duration of rest of the heart - this condition is called diastole.

General pause

In phase 3, the muscles of all cardiac chambers are relaxed, the valves are relaxed, and blood from the atria flows freely into the ventricles.

By the end of phase 3, the ventricles are 70% filled with blood. The force of compression of the muscle walls during systole depends on how completely the ventricles are filled with blood in diastole.

Heart sounds

Myocardial contractile activity is accompanied by sound vibrations called heart sounds. These sounds are clearly distinguishable by auscultation (listening) with a phonendoscope.

Heart sounds are distinguished:

1. systolic - long, dull, arising:
   1. when atrioventricular valves collapse;
   2. emitted by the walls of the ventricles;
   3. tension of the cardiac chords;
2. diastolic – high, shortened, created by the collapse of the valves of the pulmonary trunk and aorta.

Automation system

A person’s heart works throughout their life as a single system. The work of the human heart is coordinated by a system consisting of specialized muscle cells (cardiomycetes) and nerves.

Abbreviations are regulated:

• autonomic nervous system;
  • the vagus nerve slows down the rhythm;
  • sympathetic nerves accelerate the myocardium.
• centers of automation.

The center of automatism is a structure consisting of cardiomycetes that set the rhythm of the heart. The center of 1st order automaticity is the sinus node. On the diagram of the structure of the human heart, it is located at the point where the superior vena cava enters the right atrium (see captions).

The sinus node sets the normal atrial rhythm of 60-70 impulses/minute, then the signal is conducted to the atrioventricular node (AV), the legs of His are automatic systems of 2-4 orders, setting the rhythm with a lower heart rate.

Additional automation centers are provided in case of malfunction or failure of the sinus pacemaker. The functioning of the centers of automaticity is ensured by conducting cardiomycetes.

In addition to conductors, there are:

• working cardiomycetes - make up the bulk of the myocardium;
• secretory cardiomycetes - they produce natriuretic hormone.

The sinus node is the main center for controlling the work of the heart; when there is a pause in its work for more than 20 seconds, cerebral hypoxia, fainting, and Morgagni-Adams-Stokes syndrome develop, which we discussed in the article “Bradycardia.”

The work of the heart and blood vessels – complex process, and this article only briefly discusses what function the heart performs and the features of its structure. The reader can learn more about the physiology of the human heart and the characteristics of blood circulation in the materials on the site.

ANATOMICAL STRUCTURE OF THE HEART

Anatomically, the heart is a muscular organ. Its size is small, about the size of a clenched fist. The heart works throughout a person's life. It pumps about 5-6 liters of blood per minute. This volume increases when a person moves, physically strains, and decreases during rest.

We can say that the heart is a muscular pump that ensures the continuous movement of blood through the vessels. Together, the heart and blood vessels make up the cardiovascular system. This system consists of the systemic and pulmonary circulation. From the left side of the heart, blood first moves through the aorta, then through large and small arteries, arterioles, and capillaries. In the capillaries, oxygen and other substances necessary for the body enter the organs and tissues, and from there carbon dioxide, metabolic products, are removed. After this, the blood turns from arterial to venous and again begins to move towards the heart. First along the venules, then through smaller and larger veins. Through the inferior and superior vena cava, blood again enters the heart, only this time into the right atrium. A large circle of blood circulation is formed.

Venous blood from the right side of the heart is sent through the pulmonary arteries to the lungs, where it is enriched with oxygen and returns to the heart.

Inside, the heart is divided by partitions into four chambers. The two atria are divided by the interatrial septum into the left and right atria. The left and right ventricles of the heart are separated by the interventricular septum. Normally, the left and right parts of the heart are completely separate. The atria and ventricles have different functions. The atria store blood that flows into the heart. When the volume of this blood is sufficient, it is pushed into the ventricles. And the ventricles push blood into the arteries, through which it moves throughout the body. The ventricles have to do more hard work, therefore the muscle layer in the ventricles is much thicker than in the atria. The atria and ventricles on each side of the heart are connected by the atrioventricular orifice. Blood moves through the heart in only one direction. In the systemic circle of blood circulation from the left side of the heart (left atrium and left ventricle) to the right, and in the small circle from the right to the left.

The correct direction is ensured by the valve apparatus of the heart:

tricuspid

pulmonary

mitral

aortic valves.

They open in right moment and close, preventing blood flow in the opposite direction.

Tricuspid valve

It is located between the right atrium and the right ventricle. It consists of three doors. If the valve is open, blood flows from the right atrium to the right ventricle. When the ventricle fills, its muscle contracts and, under the influence of blood pressure, the valve closes, preventing blood from flowing back into the atrium.

Pulmonary valve

When the tricuspid valve is closed, the exit of blood in the right ventricle is possible only through the pulmonary trunk into the pulmonary arteries. The pulmonary valve is located at the entrance to the pulmonary trunk. It opens under blood pressure when the right ventricle contracts, blood flows into the pulmonary arteries, then under the influence of reverse blood flow when the right ventricle relaxes, it closes, preventing blood from flowing back from the pulmonary trunk into the right ventricle.

Bivalve or mitral valve

Located between the left atrium and left ventricle. Consists of two doors. If it is open, blood flows from the left atrium into the left ventricle; when the left ventricle contracts, it closes, preventing the blood from flowing back.

Aortic valve

Closes the entrance to the aorta. It also consists of three valves, which look like crescents. Opens when the left ventricle contracts. In this case, blood enters the aorta. When the left ventricle relaxes, it closes. Thus, venous blood (poor in oxygen) from the superior and inferior vena cava enters the right atrium. When the right atrium contracts, it moves through the tricuspid valve into the right ventricle. Contracting, the right ventricle ejects blood through the pulmonary valve into the pulmonary arteries (pulmonary circulation). Enriched with oxygen in the lungs, the blood turns into arterial and moves through the pulmonary veins to the left atrium, then to the left ventricle. When the left ventricle contracts, arterial blood through aortic valve under high pressure it enters the aorta and spreads throughout the body (systemic circulation).

The heart muscle is called the myocardium

There are contractile and conductive myocardium.

The contractile myocardium is the actual muscle that contracts and produces the work of the heart. In order for the heart to contract in a certain rhythm, it has a unique conduction system. The electrical impulse to contract the heart muscle occurs in the sinoatrial node, which is located in the upper part of the right atrium and spreads through the conduction system of the heart, reaching each muscle fiber.

Structure and functions of the heart

The heart is a hollow four-chamber muscular organ that pumps blood into the arteries and receives venous blood, located in the chest cavity. The shape of the heart resembles a cone. It works throughout life. Right half The heart (right atrium and right ventricle) is completely separated from its left half (left atrium and left ventricle).

The heart is four-chambered; two atria and two ventricles provide blood circulation. The septum divides the heart into right and left side, which prevents blood from mixing. Leaf valves allow blood to flow in one direction: from the atria to the ventricles. Semilunar valves ensure the movement of blood in one direction: from the ventricles to the systemic and pulmonary circulation. The walls of the stomachs are thicker than the walls of the atria because perform a heavy load, push blood into the systemic and pulmonary circulation. The walls of the left ventricle are thicker and more powerful because it carries out a greater load than the right one, pushing blood into the systemic circulation.

The atria and ventricles are connected to each other by valves. Between the left atrium and the left ventricle the valve has two leaflets and is called bicuspid, between the right atrium and the right ventricle there is a tricuspid valve.

The heart is covered with a thin and dense membrane, forming a closed sac - the pericardial sac. Between the heart and the pericardial sac there is a fluid that moisturizes the heart and reduces friction during its contractions.

The average heart weight is about 300 grams. Trained people have larger heart sizes than untrained people.

The activity of the heart is a rhythmic change of three phases of the cardiac cycle: contraction of the atria (0.1 s.), contraction of the ventricles (0.3 s.) and general relaxation of the heart (0.4 s.), the entire cardiac cycle is (0.8 s.)

The pressure of blood on the walls of blood vessels is called blood pressure, it is created by the force of contraction of the ventricles of the heart.

The heart works automatically throughout your life.

The structure of heart cells is determined by the function they perform.

The regulation and coordination of the contractile function of the heart is carried out by its conduction system.

Sensitive fibers from the receptors of the walls of the heart and its vessels go as part of the cardiac nerves and cardiac branches to the corresponding centers of the spinal cord and brain.

Nervous regulation of the heart. The central nervous system constantly controls the functioning of the heart through nerve impulses. Inside the cavities of the heart itself and in the walls large vessels There are nerve endings - receptors that perceive pressure fluctuations in the heart and blood vessels. Impulses from the receptors cause reflexes that affect the functioning of the heart. There are two types of nervous influences on the heart: some are inhibitory, which reduce the heart rate, others are accelerating.

Humoral regulation. Along with nervous control, the activity of the heart is regulated by chemicals constantly entering the blood.

The atria and ventricles can be in two states: contracted and relaxed. Contraction and relaxation of the atria and ventricles of the heart occur in a certain sequence and are strictly coordinated in time. The cardiac cycle consists of contraction of the atria, contraction of the ventricles, relaxation of the ventricles and atria (general relaxation). The duration of the cardiac cycle depends on the heart rate. In a healthy person at rest, the heart contracts 60-80 times per minute. Therefore, the time of one cardiac cycle is less than 1 s. Let's consider the work of the heart using the example of one cardiac cycle. The cardiac cycle begins with atrial contraction, which lasts 0.1 s. At this moment, the ventricles are relaxed, the leaflet valves are open, and the semilunar valves are closed. During contraction of the atria, all the blood from them enters the ventricles. Contraction of the atria is replaced by their relaxation. Then ventricular contraction begins, which lasts 0.3 s. At the onset of ventricular contraction, the semilunar and tricuspid valves remain closed. Contraction of the muscles of the ventricles leads to an increase in pressure inside them. The pressure in the cavities of the ventricles becomes higher than the pressure in the cavities of the atria. According to the laws of physics, blood tends to move from a zone of higher pressure to a zone where it is lower, i.e. towards the atria. Blood moving towards the atria meets the valve leaflets on its way. The valves cannot turn inside the atria; they are held in place by tendon threads.

Blood enclosed in the closed cavities of the ventricles has only one path left - into the aorta and pulmonary artery. Contraction of the ventricles is replaced by their relaxation, which lasts 0.4 s. At this moment, blood flows freely from the atria and veins into the cavity of the ventricles. The semilunar valves are closed. The peculiarities of the cardiac cycle include the ability to maintain the working activity of the heart throughout life. Let us remember that out of the total duration of the cardiac cycle of 0.8 s, the cardiac pause accounts for 0.4 s. This interval between contractions is sufficient to fully restore the heart’s performance. During each contraction of the ventricles, a certain portion of blood is pushed into the vessels. Its volume is 70-80 ml. In 1 minute, the heart of an adult at rest pumps 5-5.5 liters of blood. The heart pumps about 10,000 liters of blood per day, and over 70 years - approximately 200,000,000 liters of blood. During physical activity, the amount of blood pumped by the heart in 1 minute in a healthy, untrained person increases to 15-20 liters. For athletes, this value reaches 30-40 l/min. Systematic training leads to an increase in the mass and size of the heart and increases its power.

2. HEART VALVE APPARATUS

Blood circulation in the human body occurs through two interconnected circulatory circles in the cavities of the heart. And the heart plays the role of the main circulatory organ - the role of a pump. From the structure of the heart described above, the mechanism of interaction between the parts of the heart is not entirely clear. What prevents the mixing of arterial and venous blood? This important function is played by the so-called valvular apparatus of the heart.

Heart valves are divided into three types:

Lunar;

Casement;

Mitral.

2.1. Semilunar valves

Along the anterior edge of the mouth of the inferior vena cava from the side of the atrium cavity there is a semilunar-shaped muscular valve of the inferior vena cava, valvula venae cavae inferioris, which comes to it from the oval fossa, fossa ovalis, the atrial septum. This valve in the fetus directs blood from the inferior vena cava through the foramen ovale into the cavity of the left atrium. The valve often contains one large outer and several small tendon threads.

Both vena cava form an obtuse angle between themselves; in this case, the distance between their mouths reaches 1.5-2 cm. Between the confluence of the superior vena cava and the inferior vena cava, on the inner surface of the atrium, there is a small intervenous tubercle, tuberculum intervenosum.

semilunar valves

The opening of the pulmonary trunk, ostium tranci pulmonalis, is located in front and to the left, it leads into the pulmonary trunk, truncus pulmonalis; three semilunar valves formed by the duplication of the endocardium are attached to its edge: anterior, right and left, valvula semilunares sinistra, valvula semilunares anterior, valvula semilunares dextra, their free edges protrude into the pulmonary trunk.

All these three valves together form the pulmonary valve, valva trunci pulmonalis.

Almost in the middle of the free edge of each valve there is a small, inconspicuous thickening - the nodule of the semilunar valve, nodulus valvulae semilunaris, from which a dense cord extends to both sides of the edge of the valve, called the lunula of the semilunar valve, lunula valvulae semilunaris. The semilunar valves form depressions on the side of the pulmonary trunk - pockets, which together with the valves prevent the reverse flow of blood from the pulmonary trunk into the cavity of the right ventricle.

2.2. Tricuspid and mitral valves

Along the circumference of the atrioventricular orifice, the right atrioventricular valve, tricuspid valve, valva atrioventricularis dextra (valva tricuspidalis), formed by a duplication of the inner lining of the heart - the endocardium, is attached, which prevents the reverse flow of blood from the cavity of the right ventricle into the cavity of the right atrium.

Mitral and tricuspid atrioventricular valves

In the thickness of the valve there is a small amount of connective, elastic tissue and muscle fibers; the latter are associated with the muscles of the atrium.

The tricuspid valve is formed by three triangular-shaped valves (blades-teeth), cuspis: septal valve, cuspis septalis, posterior valve, cuspis posterior, anterior valve, cuspis anterior; all three leaflets protrude into the cavity of the right ventricle with their free edges.

Of the three leaflets, one large one, the septal leaflet, cuspis septalis, is located closer to the ventricular septum and is attached to the medial part of the right atrioventricular foramen. The posterior valve, cuspus posterior, is smaller in size and is attached to the posterior-outer periphery of the same opening. The anterior leaflet, cuspus anterior, the smallest of all three leaflets, is strengthened at the anterior periphery of the same opening and faces the arterial cone. Often, a small additional tooth may be located between the septal and posterior valves.

The free edges of the valves have small notches. With their free edges, the valves face the cavity of the ventricle.

Attached to the edges of the valves are thin tendon strings of unequal length and thickness, chordae tendineae, which usually begin from the papillary muscles, mm. papillares; some of the threads are fixed to the surface of the valves facing the ventricular cavity.

Part of the tendon strings, mainly at the apex of the ventricle, does not arise from the papillary muscles, but directly from the muscular layer of the ventricle (from the fleshy crossbars). A series of tendinous strings, not connected to the papillary muscles, are directed from the ventricular septum to the septal valve. Small areas of the free edge of the valves between the tendon strings are significantly thinned.

The tendon strings of the three papillary muscles are attached to the three leaflets of the tricuspid valve so that each of the muscles is connected by its threads to two adjacent leaflets.

In the right ventricle, three papillary muscles are distinguished: one, permanent, large papillary muscle, the tendon threads of which are attached to the posterior and anterior valves; this muscle extends from the anterior wall of the ventricle - the anterior papillary muscle, m. papillaris anterior; the other two, insignificant in size, are located in the area of ​​the septum - the septal papillary muscle, m. papillaris septalis (not always present), and back wall ventricle - posterior papillary muscle, m. papillarisposterior.

The left atrioventricular (mitral) valve, valva atrioventricularis sinister (v. mitralis), is attached around the circumference of the left atrioventricular orifice; the free edges of its valves protrude into the ventricular cavity. They, like the tricuspid valve, are formed by doubling the inner layer of the heart, the endocardium. This valve, when the left ventricle contracts, prevents the passage of blood from its cavity back into the cavity of the left atrium.

The valve is distinguished by an anterior leaflet, cuspus anterior, and a posterior leaflet, cuspus posterior, in the spaces between which there are sometimes two small teeth.

The anterior leaflet, strengthening on the anterior sections of the circumference of the left atrioventricular orifice, as well as on the connective tissue base of the aortic opening closest to it, is located to the right and more anteriorly than the posterior one. The free edges of the anterior leaflet are fixed by tendon strings, chordae tendineae, to the anterior papillary muscle, i.e. papillaris anterior, which starts from the anterior left wall of the ventricle. The anterior valve is slightly larger than the posterior one. Due to the fact that it occupies the area between the left atrioventricular orifice and the aortic orifice, its free edges are adjacent to the aortic orifice.

The posterior flap is attached to the posterior section of the circumference of the indicated opening. It is smaller than the anterior one and, in relation to the hole, is located somewhat posteriorly and to the left. Through the chordae tendinae, it is fixed primarily to the posterior papillary mouse, m.papillaris posterior, which begins on the posterior left wall of the ventricle.

The small teeth, lying in the spaces between the large ones, are fixed with the help of tendon threads either to the papillary muscles or directly to the wall of the ventricle.

In the thickness of the teeth of the mitral valve, as in the thickness of the teeth of the tricuspid valve, there are connective tissue, elastic fibers and a small number of muscle fibers associated with the muscular layer of the left atrium.

The anterior and posterior papillary muscles can each be divided into several papillary muscles. From the ventricular septum, as in the right ventricle, they begin very rarely.

On the side of the inner surface, the wall of the posterior left part of the left ventricle is covered a large number projections - fleshy crossbars, trabeculae carneae. Repeatedly splitting and joining again, these fleshy crossbars intertwine and form a network denser than in the right ventricle; there are especially many of them at the apex of the heart in the area of ​​the interventricular septum.

2.3. Aortic valves

The anterior-right section of the cavity of the left ventricle is the arterial cone, conus arteriosus, communicated by the aortic opening, ostium aortae, with the aorta. The conus arteriosus of the left ventricle lies in front of the anterior leaflet of the mitral valve and behind the conus arteriosus of the right ventricle; heading up and to the right, he crosses it. Because of this, the opening of the aorta lies somewhat posterior to the opening of the pulmonary trunk. The inner surface of the conus arteriosus of the left ventricle, like the right, is smooth.

Three semilunar valves of the aorta are attached around the circumference of the aortic opening, which, according to their position in the opening, are called the right, left and posterior semilunar valves, valvulae semilunares dextra, sinistra et posterior. All of them together form the aortic valve, valva aortae.

aortic valves

The semilunar valves of the aorta are formed, like the semilunar valves of the pulmonary trunk, by a duplication of the endocardium, but are more developed. The aortic valve nodule, nodulus valvulae aortae, embedded in the thickness of each of them, is thicker and harder. Located on each side of the nodule, the semilunar valves of the aorta, lunulae valvularum aortae, are stronger.

In addition to the heart, semilunar valves are also found in the veins. Their task is to prevent the reverse flow of blood.

vein valves

The structure of contractile (working) cardiomyocytes. The cells have an elongated (100-150 µm) shape, close to cylindrical. Their ends are connected to each other, so that the chains of cells form the so-called functional fibers (up to 20 microns thick). In the area of ​​cell contacts, so-called intercalary discs are formed (see p. 418). Cardiomyocytes can branch and form a spatial network. Their surfaces are covered with a basement membrane, into which reticular and collagen fibers are woven from the outside. The nucleus of the cardiomyocyte (sometimes there are two of them) is oval and lies in the central part of the cell (Fig. 125). A few organelles are concentrated at the poles of the nucleus general meaning, with the exception of the agranular endoplasmic reticulum and mitochondria. Special organelles that provide contraction are called myofibrils. They are weakly separated from each other and can split. Their structure is similar to the structure of myofibrils of myosymplast of skeletal muscle fiber. Each mitochondrion is located throughout the entire sar-comere. T-tubules located at the level of the Z-line are directed from the surface of the plasmalemma into the depths of the cardiomyocyte. Their membranes are close together and contact the membranes of the smooth endoplasmic (sarcoplasmic) reticulum. The loops of the latter are elongated along the surface of the myofibrils and have lateral thickenings (L-systems), which together with the T-tubules form triads or dyads. The cytoplasm contains inclusions of glycogen and lipids, especially many inclusions of myoglobin. The mechanism of contraction of cardiomyocytes is the same as that of myosymplast.

Refractoriness (from the French refractaire - unresponsive), in physiology - the absence or decrease in excitability of a nerve or muscle after previous excitation. Refractoriness underlies inhibition. The refractory period lasts from several ten-thousandths (in many nerve fibers) to several tenths (in muscle fibers) of a second. It is replaced by a phase of increased excitability (see Exaltation).

Structure

The myocardium is formed by cardiac striated muscle tissue, which is a tight junction of muscle cells - cardiomyocytes, which form the main part of the myocardium. Different from other types muscle tissue(skeletal muscle, smooth muscle) with a special histological structure that facilitates the propagation of the action potential between cardiomyocytes.

Peculiarities

A functional feature of the myocardium is rhythmic automatic contractions, alternating with relaxations, which occur continuously throughout the life of the body. The sequential contraction and relaxation of various parts of the heart is associated with its structure and the presence of the cardiac conduction system through which the impulse propagates. The myocardium of the atria and ventricles is separated, which makes their independent contraction possible.

The “all or nothing” law is an empirical law that establishes the relationship between the strength of the current stimulus and the magnitude of the response of the excitable structure. Excitable tissue gives a maximum response, constant in its parameters, “all” at any strength of irritation. An example is the action potential of a neuron.

Heartperson- this is a cone-shaped hollow muscular organ that receives blood from the venous trunks flowing into it and pumps it into the arteries that are adjacent to the heart. The heart cavity is divided into 2 atria and 2 ventricles. The left atrium and left ventricle together form the “arterial heart,” named for the type of blood passing through it; the right ventricle and right atrium combine to form the “venous heart,” named for the same principle. Contraction of the heart is called systole, relaxation is called diastole.

Heart shape is not the same different people. It is determined by age, gender, physique, health, and other factors. In simplified models, it is described by a sphere, ellipsoids, and the intersection figures of an elliptical paraboloid and a triaxial ellipsoid. The measure of elongation (factor) of the shape is the ratio of the largest longitudinal and transverse linear dimensions of the heart. With a hypersthenic body type, the ratio is close to one, and with an asthenic body type, it is about 1.5. The length of the heart of an adult varies from 10 to 15 cm (usually 12-13 cm), width at the base 8-11 cm (usually 9-10 cm) and anteroposterior size 6-8.5 cm (usually 6.5-7 cm) . The average heart weight in men is 332 g (from 274 to 385 g), in women - 253 g (from 203 to 302 g).

Heart human is a romantic organ. In our country it is considered the seat of the soul. “I feel it in my heart,” people say. Among African aborigines it is considered the organ of the mind.

A healthy heart is a strong, continuously working organ, about the size of a fist and weighing about half a kilogram.

Consists of 4 chambers. A muscular wall called the septum divides the heart into left and right halves. Each half has 2 chambers.

The upper chambers are called atria, the lower chambers are called ventricles. The two atria are separated by the interatrial septum, and the two ventricles are separated by the interventricular septum. The atrium and ventricle of each side of the heart are connected by the atrioventricular orifice. This opening opens and closes the atrioventricular valve. The left atrioventricular valve is also known as the mitral valve, and the right atrioventricular valve is also known as the tricuspid valve. The right atrium receives all the blood returning from the upper and lower parts of the body. Then, through the tricuspid valve, it sends it to the right ventricle, which in turn pumps blood through the pulmonary valve to the lungs.

In the lungs, the blood is enriched with oxygen and returns to the left atrium, which sends it through the mitral valve to the left ventricle.

The left ventricle pumps blood through the arteries through the aortic valve throughout the body, where it supplies the tissues with oxygen. Oxygen-depleted blood returns through the veins to the right atrium.

The blood supply to the heart is carried out by two arteries: the right coronary artery and the left coronary artery, which are the first branches of the aorta. Each of the coronary arteries emerges from the corresponding right and left aortic sinuses. Valves are used to prevent blood flow in the opposite direction.

Types of valves: bicuspid, tricuspid and semilunar.

Semilunar valves have wedge-shaped leaflets that prevent blood from returning as it leaves the heart. There are two semilunar valves in the heart. One of these valves prevents backflow in the pulmonary artery, the other valve is located in the aorta and serves a similar purpose.

Other valves prevent blood from flowing from the lower chambers of the heart to the upper chambers. The bicuspid valve is located in the left side of the heart, the tricuspid valve is in the right. These valves have a similar structure, but one of them has two leaflets, and the other, respectively, three.

To pump blood through the heart, alternating relaxations (diastole) and contractions (systole) occur in its chambers, during which the chambers fill with blood and push it out accordingly.

The natural pacemaker, called the sinus node or Kis-Flyak node, is located in the upper part of the right atrium. This is an anatomical formation that controls and regulates heart rate in accordance with the activity of the body, time of day and many other factors affecting a person. The heart's natural pacemaker produces electrical impulses that pass through the atria, causing them to contract, to the atrioventricular (that is, atrioventricular) node, located at the border of the atria and ventricles. Then the excitation spreads through the conducting tissues into the ventricles, causing them to contract. After this, the heart rests until the next impulse, which begins a new cycle.

Basic heart function is to ensure blood circulation by communicating kinetic energy to the blood. To ensure the normal existence of the body in different conditions the heart can operate in a fairly wide range of frequencies. This is possible due to some properties, such as:

Automaticity of the heart- this is the ability of the heart to contract rhythmically under the influence of impulses originating in itself. Described above.

Excitability of the heart- this is the ability of the heart muscle to be excited by various stimuli physical or chemical nature, accompanied by changes in physical - chemical properties fabrics.

Cardiac conductivity- carried out in the heart electrically due to the formation of an action potential in pacemaker cells. The place where excitation transfers from one cell to another is the nexus.

Cardiac contractility– The force of contraction of the heart muscle is directly proportional to the initial length of the muscle fibers

Myocardial refractoriness- a temporary state of non-excitability of tissues

On failure heart rate flickering occurs, fibrillation - rapid asynchronous contractions of the heart, which can lead to death.

Blood pumping is achieved through alternating contraction (systole) and relaxation (diastole) of the myocardium. The fibers of the heart muscle contract due to electrical impulses (excitation processes) formed in the membrane (shell) of the cells. These impulses appear rhythmically in the very heart. The ability of the heart muscle to independently generate periodic excitation impulses is called automaticity.

Muscle contraction in the heart is a well-organized periodic process. The function of periodic (chronotropic) organization of this process is provided by the conduction system.

As a result of the rhythmic contraction of the heart muscle, the periodic expulsion of blood into the vascular system is ensured. The period of contraction and relaxation of the heart constitutes the cardiac cycle. It consists of atrial systole, ventricular systole and a general pause. During atrial systole, the pressure in them increases from 1-2 mm Hg. Art. up to 6-9 mm Hg. Art. in the right and up to 8-9 mm Hg. Art. in the left. As a result, blood is pumped through the atrioventricular openings into the ventricles. In humans, blood is expelled when the pressure in the left ventricle reaches 65-75 mmHg. Art., and in the right - 5-12 mm Hg. Art. After this, ventricular diastole begins, the pressure in them quickly drops, as a result of which the pressure in large vessels becomes higher and the semilunar valves slam shut. As soon as the pressure in the ventricles drops to 0, the leaflet valves open and the ventricular filling phase begins. Ventricular diastole ends with the filling phase caused by atrial systole.

The duration of the phases of the cardiac cycle is not constant and depends on the heart rate. With a constant rhythm, the duration of the phases may be disrupted due to cardiac dysfunction.

The strength and frequency of heart contractions can change in accordance with the needs of the body, its organs and tissues for oxygen and nutrients. Regulation of heart activity is carried out by neurohumoral regulatory mechanisms.

The heart also has its own regulatory mechanisms. Some of them are related to the properties of the myocardial fibers themselves - the relationship between the magnitude of the heart rhythm and the force of contraction of its fiber, as well as the dependence of the energy of contraction of the fiber on the degree of its stretching during diastole.

The elastic properties of the myocardial material, manifested outside the process of active coupling, are called passive. The most likely carriers of elastic properties are the supporting-trophic skeleton (especially collagen fibers) and actomyosin bridges, which are present in a certain amount in passive muscle. The contribution of the supporting-trophic skeleton to the elastic properties of the myocardium increases during sclerotic processes. The bridging component of stiffness increases with ischemic contracture and inflammatory diseases myocardium.

TICKET 34 (LARGE AND SMALL CIRCULATION)