The science of cardiology studies the heart. The average heart weight is 250-300 grams. The heart has a cone shape. It consists mainly of strong elastic tissue - the heart muscle, which contracts rhythmically throughout life and drives blood through the arteries and capillaries to the body tissues. The average heart rate is about 70 times per minute.

Departments of the heart

The human heart is divided by partitions into four chambers, which fill with blood at different times. The lower thick-walled chambers of the heart are called ventricles. They act as a pump and, after receiving blood from the upper chambers, send it into the arteries by contraction. The process of contraction of the ventricles is the heartbeat. The upper chambers are called atria, which, thanks to the elastic walls, easily stretch and accommodate the blood coming from the veins between contractions.

The left and right chambers of the heart are separate from each other, each consisting of an atrium and a ventricle. Oxygen-poor blood flowing from the body’s tissues first enters the right side and then goes to the lungs. On the contrary, the left section receives oxygenated blood from the lungs and is redirected to all tissues of the body. Due to the fact that the left ventricle performs the most difficult work, which is to pump blood through the systemic circulation, it differs from other chambers of the heart in its massiveness and greater wall thickness - almost 1.5 cm.

In each half of the heart, the atria and ventricles are connected to each other by an opening closed by a valve. The valves open exclusively towards the ventricles. This process is assisted by tendon threads, which are attached at one end to the valve leaflets, and at the opposite end to the papillary muscles located on the walls of the ventricles. Such muscles are outgrowths of the wall of the ventricles and contract simultaneously with them, putting the tendon threads under tension and preventing blood from flowing back into the atrium. Tendon threads prevent the valves from turning toward the atria during the ventricles.

In the places where the aorta leaves the left ventricle and the pulmonary artery leaves the right ventricle, semilunar valves are placed in the form of pockets. Through them, blood passes into the aorta and pulmonary artery, but movement back into the ventricles is impossible due to the fact that the semilunar valves straighten and close when filled with blood.

The main task of the human heart is to create and maintain a difference in blood pressure in the arteries and veins. It is the difference in pressure that underlies the movement of blood. When the heart stops, blood circulation automatically levels out and stops, thus death occurs. To keep blood moving through the arteries and veins, the body uses many functions of the heart. What role each function plays will be discussed in today’s review.

ATTENTION!

Before considering the functions of the cardiovascular system, the structure of the heart should be briefly discussed.

The heart in its structure has cavities and chambers consisting of atria and ventricles, which are separated by a septum. Due to the latter, venous and aortic blood does not mix. The atrium and ventricle of each cavity communicate with each other through valves. The chambers are lined with endocardium, and their folds create valves.

Venous blood, saturated with carbon dioxide, collects in the vena cava, which originates in the right atrium. Next, it goes to the right ventricle. Arterial blood is formed in the pulmonary trunk and delivered to the lungs. Blood moves into the left chamber: the atrium and the left ventricle.

Valves play an important role in pumping blood because... like pumps. Automatic operation of the valves allows maintaining blood pressure. During normal heart function, the frequency of its contractions is, on average, 70 beats per minute. It is worth noting that the work of the organ departments - the atria and ventricles - is performed in a sequential manner.

Contraction of the heart muscle is called systolic function, and relaxation is called diastolic function.

The heart muscle or myocardium is the basis of the mass of the organ. The myocardium has a complex structure in the form of layers. The thickness in each part of the human heart can vary from 6 to 11 mm. This muscle works due to electrical impulses, the conductivity of which is ensured by the organ in an independent mode. It is these signals that encourage the heart to work automatically. Outside, the organ is located in a membrane (pericardium), which consists of 2 layers - external and internal (epicardium). In the space between the layers there is 15 ml of serous fluid, due to which sliding occurs during contraction and relaxation.

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A brief overview of the structure of the main organ of the human body allows us to talk about the functions of the heart, which are:

1. Automaticity - the production of electrical signals even in the absence of external irritation.
2. Conduction – excitation of the fibers of the heart and myocardium.
3. Excitability is the ability of cells and myocardium to be irritated under the influence of external factors.
4. Contractility is the ability of the heart muscle to contract and relax.

The combined concept of the above functions is the autowave function. The pumping function of the heart is ensured and maintained due to the activity of the organ. But in addition to the main task, the heart also performs secondary ones - pumping and endocrine. These functions will be discussed in detail below.

Pressure function

Blood is pumped into the vessels due to periodic contraction of the heart cells of the muscles of the atria and stomachs. The myocardium, contracting, creates high pressure and pushes blood out of the chambers. Due to the fact that the myocardium has a layered structure, the right and left atria and ventricles receive an impulse to contract (automatically) and then relax the muscle. This is called the heart rate. Due to it, the heart fills with blood, carrying it to other organs.

The pumping function of the heart is due to several reasons:

• Based on the remaining inert force caused by the previous contraction of the muscle walls.
• Muscle contraction, which causes compression of the veins in the limbs. Each vein has valves that direct blood along only one vector of movement, i.e. to the heart. Systematic compression ensures blood is pumped to the organ.
• Blood flow to the organ due to inhalation and exhalation of the chest cavity. As a person inhales, the vena cava in the chest stretches and the pressure in the atria becomes low. Therefore, the blood begins to move stronger towards the heart.

Due to the pumping function, the human heart has different pressures in the vessels and moves in one direction due to the valve system.

endocrine function

The endocrine function of the heart in modern medicine has received a new name - neuroendocrine. This function is responsible for the regulation and coordination of all systems and organs of the human body. The endocrine system adapts the body to constant changes occurring both in the external and internal environment. The result of normal operation of the system is the preservation of homeostasis (author’s note - maintaining balance in the work of all organs and systems).

Based on research conducted in recent years, doctors have identified two new factors:

• The endocrine function of the heart directly interacts with the immune system.
• The heart is the main endocrine gland.

In turn, other systems provide endocrine function:

• glands and hormones;
• transport route;
• tissues and organs that are provided with normal receptor mechanisms.

In other words, this system is aimed at maintaining stability within the body. In addition, the endocrine function, together with human immunity and the central nervous system, ensures reproductive functions, and is also responsible for the growth of new cells and the disposal of “internal waste”.

Based on this, it should be noted that all systems of the human body, brought by nature to automaticity, allow the heart to beat and maintain life.

Pumping function

The cardiac cycle occurs from one muscle contraction to the next. A contraction is created due to the excitation of the myocardium by the heart’s own impulse (function of automatism). This excitation (irritation) is gradually transmitted to the atria and causes a systolic state (author's note - blood pressure). The reaction is then transmitted to the ventricles, causing a systolic state and squeezing blood into the aorta and pulmonary arteries. After this release, the walls of the myocardium relax, the pressure level decreases, and the main organ prepares for the next impulse. Thus, the pumping function of the heart occurs.

Right and left ventricles of the heart

The ventricles are responsible for the hemodynamic task of the human heart. This occurs due to consistent and rhythmic contractions of the left and right atria and ventricles in an automatic mode, which alternate with a state of relaxation of the muscle walls.

The ventricle of the right atrium is located in the front of the human heart and occupies it almost completely. Its structure has denser walls, because Unlike the left ventricle, it contains three layers of myocardium. Based on this, the right ventricle has three sections: inlet, outlet and muscular section. The inner part of the muscular section has a smooth surface, but on the side of the wall there are fleshy crossbars (trabeculae), which are the beginning of the papillary muscles: anterior, posterior and septal. In medical practice, cases have been recorded when there were more of these muscles.

The left ventricle is located in the posterior lower part of the heart. This ventricle is smaller than the right one. But in structure they have minor differences, which are as follows:

• the walls are thinner, due to the presence of only 2 layers of myocardium;
• weakly defined septum.

Despite the slight differences, the functions of the ventricles of the heart are different. Scientists have not yet been able to fully study the chambers of the heart, but the forecast that the main organ is able to very quickly adapt to overload has already received worldwide recognition.

Speaking about the hemodynamic function of the stomachs, it should be noted. The right stomach is the chamber of the organ from which blood circulation begins, directed in a small circle. And the left ventricle is presented in the form of one of the chambers and is the source for the systemic circulation. The left ventricle carries out uninterrupted conduction of blood throughout the body.

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In order to ensure adequate nutrition of internal organs, the heart pumps an average of seven tons of blood per day. Its size is equal to a clenched fist. Throughout life, this organ makes approximately 2.55 billion beats. The final formation of the heart occurs by the 10th week of intrauterine development. After birth, the type of hemodynamics changes dramatically - from feeding on the mother’s placenta to independent, pulmonary breathing.

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Muscle fibers (myocardium) are the predominant type of heart cells. They make up its bulk and are located in the middle layer. The outside of the organ is covered with epicardium. It wraps at the level of the attachment of the aorta and pulmonary artery, heading downwards. In this way, the pericardial sac is formed. It contains about 20 - 40 ml of clear liquid, which prevents the leaves from sticking together and being injured during contractions.

The inner membrane (endocardium) folds in half at the transition of the atria into the ventricles, the mouths of the aortic and pulmonary trunk, forming valves. Their valves are attached to a ring of connective tissue, and the free part moves with the blood flow. In order to prevent the parts from everting into the atrium, threads (chords) are attached to them, extending from the papillary muscles of the ventricles.

The heart has the following structure:

• three membranes - endocardium, myocardium, epicardium;
• pericardial sac;
• chambers with arterial blood - left atrium (LA) and ventricle (LV);
• sections with venous blood - right atrium (RA) and ventricle (RV);
• valves between the LA and LV (mitral) and tricuspid on the right;
• two valves separate the ventricles and large vessels (aortic on the left and pulmonary artery on the right);
• the septum divides the heart into right and left halves;
• efferent vessels, arteries - pulmonary (venous blood from the pancreas), aorta (arterial from the left ventricle);
• afferent veins - pulmonary (with arterial blood) enter the LA, vena cava flow into the RA.

Internal anatomy and structural features of valves, atria, ventricles

Each part of the heart has its own function and anatomical features. In general, the LV is more powerful (compared to the right), as it forces blood into the arteries, overcoming the high resistance of the vascular walls. The PP is more developed than the left, it receives blood from the whole body, and the left one only from the lungs.

Which side of a person's heart is on?

In humans, the heart is located on the left side in the center of the chest. The main part is located in this area - 75% of the total volume. One third extends beyond the midline into the right half. In this case, the axis of the heart is inclined (oblique direction). This situation is considered classic, as it occurs in the vast majority of adults. But options are also possible:

• dextrocardia (right side);
• almost horizontal - with a wide, short chest;
• close to vertical - for thin people.

Where is a person's heart located?

The human heart is located in the chest between the lungs. It is adjacent to the sternum from the inside, and is limited below by the diaphragm. It is surrounded by the pericardium, the pericardium. Pain in the heart area appears on the left near the mammary gland. The top is projected there. But with angina, patients feel pain behind the sternum, and it spreads along the left side of the chest.

Where is the heart located in the human body?

The heart in the human body is located in the center of the chest, but its main part goes into the left half, and only one third is located on the right side. For most people it has an angle of inclination, but for overweight people its position is closer to horizontal, and for thin people it is closer to vertical.

Location of the heart in the human chest

In humans, the heart is located in the chest in such a way that its anterior and lateral surfaces are in contact with the lungs, and its posterior and inferior surfaces are in contact with the diaphragm. The base of the heart (from above) passes into large vessels - the aorta, pulmonary artery. The apex is the lowest part, it approximately corresponds to the 4-5 space between the ribs. It can be found in this area by lowering an imaginary perpendicular from the center of the left collarbone.

The external structure of the heart refers to its chambers; it contains two atria and two ventricles. They are separated by partitions. The pulmonary veins, the vena cava, enter the heart, and the arteries of the lungs, the aorta, carry the blood out. Between the large vessels, at the border of the atria and ventricles of the same name, there are valves:

• aortic;
• pulmonary artery;
• mitral (left);
• tricuspid (between the right parts).

The heart is surrounded by a cavity containing a small amount of fluid. It is formed by the pericardial layers.

If you clench your fist, you can imagine exactly the appearance of a heart. In this case, the part that is located at the wrist joint will be its base, and the acute angle between the first and thumb will be its apex. What is important is that its size is also very close to a clenched fist.

This is what a human heart looks like

Borders of the heart and their projection onto the surface of the chest

The boundaries of the heart are found by percussion, by tapping; radiography or echocardiography helps to determine them more accurately. The projections of the cardiac contour onto the surface of the chest are:

• right – 10 mm to the right of the sternum;
• left – 2 cm inward from the perpendicular from the center of the collarbone;
• apex – 5th intercostal space;
• base (upper) – 3rd rib.

What tissues make up the heart?

The heart consists of the following types of tissue:

• muscle - the main one, is called the myocardium, and the cells are cardiomyocytes;
• connective – valves, chords (threads that hold the valves), outer (epicardial) layer;
• epithelium – inner lining (endocardium).

Surfaces of the human heart

The human heart has the following surfaces:

• ribs, sternum – anterior;
• pulmonary – lateral;
• diaphragmatic – lower.

Apex and base of the heart

The apex of the heart is directed down and to the left, its localization is the 5th intercostal space. It represents the top of the cone. The wide part (base) is located on top, closer to the collarbones, and is projected at the level of the 3rd rib.

Human heart shape

The shape of a healthy person's heart is like a cone. Its tip is directed at an acute angle down and to the left of the center of the sternum. The base contains the mouths of large vessels and is located at the level of the 3rd rib.

Right atrium

Receives blood from the vena cava. Next to them is the foramen ovale, which connects the RA and LA in the fetal heart. In a newborn, it closes after the pulmonary blood flow opens, and then completely heals. During systole (contraction), venous blood passes into the pancreas through the tricuspid valve. The RA has a fairly powerful myocardium and a cubic shape.

Left atrium

Arterial blood from the lungs passes into the LA through 4 pulmonary veins and then flows through the opening into the LV. The walls of the LA are 2 times thinner than those of the right one. The shape of the LP is similar to a cylinder.

Right ventricle

It looks like an inverted pyramid. The capacity of the pancreas is about 210 ml. It can be divided into two parts - the arterial (pulmonary) cone and the ventricular cavity itself. In the upper part there are two valves: the tricuspid and the pulmonary trunk.

Left ventricle

It looks like an inverted cone, its lower part forms the top of the heart. The thickness of the myocardium is the largest - 12 mm. There are two openings at the top - for connecting to the aorta and LA. Both of them are covered by valves - the aortic and mitral.

Why are the walls of the atria thinner than the walls of the ventricles?

The thickness of the walls of the atrium is less, they are thinner, since they only need to push blood into the ventricles. The right ventricle follows them in strength; it throws its contents into the neighboring lungs, and the left one is the largest in terms of the size of its walls. It pumps blood to the aorta, where there is high pressure.

Tricuspid valve

The right atrioventricular valve consists of a sealed ring that limits the opening and leaflets; there may be not 3, but from 2 to 6.

Half of the people have a tricuspid configuration.

The function of this valve is to prevent the reflux of blood into the RA during RV systole.

Pulmonary valve

It prevents blood from passing back into the pancreas after it contracts. The composition contains valves similar in shape to a crescent. In the middle of each there is a knot that seals the closure.

Mitral valve

It has two doors, one is in the front and the other is in the back. When the valve is open, blood flows from the LA to the LV. When the ventricle contracts, its parts close together to allow blood to pass into the aorta.

Aortic valve

Formed by three semilunar-shaped flaps. Like the pulmonary one, it does not contain threads that hold the valves in place. In the area where the valve is located, the aorta expands and has depressions called sinuses.

Adult heart weight

Depending on the physique and total body weight, the weight of the heart in an adult varies from 200 to 330 g. In men, it is on average 30-50 g heavier than in women.

Diagram of blood circulation

Gas exchange occurs in the alveoli of the lungs. They receive venous blood from the pulmonary artery emerging from the pancreas. Despite the name, the pulmonary arteries carry venous blood. After the release of carbon dioxide and oxygen saturation through the pulmonary veins, the blood passes into the left atrium. This is how a small circle of blood flow, called pulmonary, is formed.

The large circle covers the entire body as a whole. From the LV, arterial blood spreads to all vessels, nourishing the tissues. Deprived of oxygen, venous blood flows from the vena cava into the RA, then into the RV. The circles close together, ensuring a continuous flow.

In order for blood to enter the myocardium, it must first pass into the aorta and then into the two coronary arteries. They are named so because of the shape of the branches, reminiscent of a crown (crown). Venous blood from the heart muscle predominantly enters the coronary sinus. It opens into the right atrium. This circle of blood circulation is considered the third, coronary.

Watch the video about the structure of the human heart:

What is special about the structure of a child’s heart?

Until the age of six, the heart is spherical due to the large atria. Its walls are easily stretched, they are much thinner than those of adults. A network of tendon threads is gradually formed, fixing the valve leaflets and papillary muscles. Full development of all heart structures ends by age 20.

The position of the newborn's heart in the chest is initially oblique, adjacent to the anterior surface. This is caused by an increase in the volume of lung tissue and a decrease in the mass of the thymus gland.

Until two years of age, the heart impulse forms the right ventricle, and then part of the left. The atria are the leaders in growth rate up to 2 years, and the ventricles after 10 years. Up to ten years, the LV is ahead of the right.

Basic functions of the myocardium

The heart muscle differs in structure from all others, as it has several unique properties:

• Automatism is excitation under the influence of one’s own bioelectric impulses. They first form in the sinus node. He is the main pacemaker, generating about 60 - 80 signals per minute. The underlying cells of the conducting system are nodes of the 2nd and 3rd order.
• Conduction - impulses from the site of formation can spread from the sinus node to the RA, LA, atrioventricular node, and along the ventricular myocardium.
• Excitability - in response to external and internal stimuli, the myocardium is activated.
• Contractility is the ability to contract when excited. This function creates the pumping capabilities of the heart. The force with which the myocardium reacts to an electrical stimulus depends on the pressure in the aorta, the degree of stretching of the fibers in diastole, and the volume of blood in the chambers.

The functioning of the heart goes through three stages:

1. Contraction of the RA, LA and relaxation of the RV and LV with the opening of the valves between them. Transition of blood into the ventricles.
2. Ventricular systole - the valves of the blood vessels open, blood flows into the aorta and pulmonary artery.
3. General relaxation (diastole) - blood fills the atria and presses on the valves (mitral and tricuspid) until they open.

During the period of contraction of the ventricles, the valves between them and the atria are closed by blood pressure. In diastole, the pressure in the ventricles drops, it becomes lower than in large vessels, then parts of the pulmonary and aortic valves close so that the blood flow does not return.

Heart cycle

There are 2 stages in the heart cycle: contraction and relaxation. The first is called systole and also includes 2 phases:

• compression of the atria to fill the ventricles (lasts 0.1 sec.);
• the work of the ventricular part and the release of blood into large vessels (about 0.5 sec.).

Then comes relaxation - diastole (0.36 sec). Cells change polarity to respond to the next impulse (repolarization), and the blood vessels of the myocardium bring nutrition. During this period, the atria begin to fill.

The heart ensures the movement of blood through the large and small circles thanks to the coordinated work of the atria, ventricles, great vessels and valves. The myocardium has the ability to generate an electrical impulse and conduct it from the nodes of automaticity to the cells of the ventricles. In response to the signal, muscle fibers become active and contract. The cardiac cycle consists of a systolic and a diastolic period.

Useful video

Watch the video about the work of the human heart:

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Coronary circulation plays an important function. Its features, pattern of movement in a small circle, blood vessels, physiology and regulation are studied by cardiologists if problems are suspected.

The complex conduction system of the heart has many functions. Its structure, which contains nodes, fibers, sections, as well as other elements, helps in the overall functioning of the heart and the entire hematopoietic system in the body.

Because of training, an athlete's heart is different from that of an ordinary person. For example, by stroke volume, rhythm. However, a former athlete or when taking stimulants may develop diseases - arrhythmia, bradycardia, hypertrophy. To prevent this, you should take special vitamins and medications.

If any abnormality is suspected, a heart x-ray is prescribed. It can reveal a normal shadow, an increase in the size of an organ, and defects. Sometimes radiography with contrast of the esophagus is performed, as well as in one to three and sometimes even four projections.

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.

The shape of the heart is not the same from person to person. 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 various 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 of a physical or chemical nature, accompanied by changes in the physical and chemical properties of the tissue.

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

When the heart rhythm fails, fibrillation occurs - 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 of the myocardium.

TICKET 34 (LARGE AND SMALL CIRCULATION)

Circulation- blood circulation in the body. Blood can perform its functions only by circulating in the body.

Circulatory system: heart(central circulatory organ) and blood vessels(arteries, veins, capillaries).

Structure of the heart

Heart- a hollow four-chambered muscular organ. The size of the heart is approximately the size of the fist. The average weight of the heart is 300 g. The outer lining of the heart is pericardium. It consists of two leaves: one forms pericardial sac, the other - the outer shell of the heart - epicardium. Between the pericardial sac and the epicardium there is a cavity filled with fluid to reduce friction during heart contraction. Middle layer of the heart - myocardium. It consists of striated muscle tissue of a special structure (cardiac muscle tissue). In it, neighboring muscle fibers are interconnected by cytoplasmic bridges. Intercellular connections do not interfere with the conduction of excitation, due to which the heart muscle is able to contract quickly. In nerve cells and skeletal muscles, each cell fires separately. Inner lining of the heart - endocardium. It lines the cavity of the heart and forms the valves - valves

The human heart consists of four chambers: 2 atria(left and right) and 2 ventricle(left and right). The muscular wall of the ventricles (especially the left) is thicker than the wall of the atria. Venous blood flows in the right half of the heart, arterial blood flows in the left.

Between the atria and ventricles there are flap valves(between the left - two-leaf, between the right - three-leaf). Between the left ventricle and the aorta and between the right ventricle and the pulmonary artery there are semilunar valves(consist of three sheets resembling pockets). Heart valves allow blood to flow in only one direction: from the atria to the ventricles, and from the ventricles to the arteries.

Work of the heart

The heart contracts rhythmically: contractions alternate with relaxations. Contraction of parts of the heart is called systole, and relaxation - diastole. Cardiac cycle- a period covering one contraction and one relaxation. It lasts 0.8 s and consists of three phases: Phase I- contraction (systole) of the atria - lasts 0.1 s; II phase- contraction (systole) of the ventricles - lasts 0.3 s; III phase- general pause - both the atria and ventricles are relaxed - lasts 0.4 s. At rest, the heart rate of an adult is 60-80 times per minute. The myocardium is formed by a special striated muscle tissue that contracts involuntarily. Characteristic of the heart muscle automatic- the ability to contract under the influence of impulses arising in the heart itself. This is due to special cells located in the heart muscle, in which excitations rhythmically appear -

Rice. 1. Diagram of the structure of the heart (vertical section):

1 - muscular wall of the right ventricle, 2 - papillary muscles, from which tendon threads arise (3), attached to valve (4), located between the atrium and ventricle, 5 - right atrium, 6 - opening of the inferior vena cava; 7 - superior vena cava, 8 - septum between the atria, 9 - openings of the four pulmonary veins; 10 - right atrium, 11 - muscular wall of the left ventricle, 12 - septum between the ventricles

The automatic contraction of the heart continues even when isolated from the body. In this case, the excitation received at one point passes to the entire muscle and all its fibers contract simultaneously.

There are three phases in the work of the heart. First - atrial contraction, second - contraction of the ventricles - systole, third - simultaneous relaxation of the atria and ventricles - diastole, or a pause in the last phase, both atria are filled with blood from the veins and it freely passes into the ventricles. The blood entering the ventricles presses on the atrial valves from the lower side, and they close. When both ventricles contract, blood pressure increases in their cavities and it enters the aorta and pulmonary artery (into the systemic and pulmonary circulation). After contraction of the ventricles, their relaxation occurs. The pause is followed by contraction of the atria, then the ventricles, etc.

The period from one atrial contraction to another is called cardiac cycle. Each cycle lasts 0.8 s. Of this time, contraction of the atria accounts for 0.1 s, contraction of the ventricles accounts for 0.3 s, and the total pause of the heart lasts 0.4 s. If the heart rate increases, the time of each cycle decreases. This occurs mainly due to a shortening of the overall cardiac pause. With each contraction, both ventricles eject the same amount of blood into the aorta and pulmonary artery (on average about 70 ml), which is called stroke volume of blood.

The work of the heart is regulated by the nervous system depending on the influence of the internal and external environment: the concentration of potassium and calcium ions, thyroid hormone, state of rest or physical work, emotional stress. Two types of centrifugal nerve fibers belonging to the autonomic nervous system approach the heart as a working organ. One pair of nerves (sympathetic fibers) when irritated, it increases and increases heart rate. When another pair of nerves is irritated (branches of the vagus nerve) impulses entering the heart weaken its activity.

The work of the heart is connected with the activities of other organs. If excitation is transmitted to the central nervous system from working organs, then from the central nervous system it is transmitted to the nerves that enhance the function of the heart. Thus, through a reflexive process, a correspondence is established between the activities of various organs and the work of the heart. The heart beats 60-80 times per minute.

The walls of arteries and veins consist of three layers: interior(thin layer of epithelial cells), average(a thick layer of elastic fibers and smooth muscle cells) and outer(loose connective tissue and nerve fibers). Capillaries consist of a single layer of epithelial cells.

Arteries- vessels through which blood flows from the heart to organs and tissues. The walls consist of three layers. The following types of arteries are distinguished: elastic arteries (large vessels closest to the heart), muscular arteries (medium and small arteries that resist blood flow and thereby regulate blood flow to the organ) and arterioles (the last branches of the artery that turn into capillaries).

Capillaries- thin vessels in which fluids, nutrients and gases are exchanged between blood and tissues. Their wall consists of a single layer of epithelial cells.

Vienna- vessels through which blood flows from organs to the heart. Their walls (like those of arteries) consist of three layers, but they are thinner and poorer in elastic fibers. Therefore, the veins are less elastic. Most veins have valves that prevent blood from flowing back.