Cycle of the heart. Cardiac cycle - what is it? At a calm state of a person, the duration of diastole of the heart

Lesson Objectives

Educational: study of the structure of the heart; the formation of new concepts in students about the cardiac cycle and automatism of the work of the heart, ideas about the features of the regulation of heart contractions.

Developing: the development of students' general biological ideas about the relationship between the structure and function of the heart.

Educational: the formation of a scientific worldview on specific examples of scientific discoveries, the success of medicine.

Equipment: a collapsible model of the heart, a table depicting the structure of the heart, the cardiac cycle, task cards, scissors, glue, felt-tip pens; tape recorder, computer, projector.

Conduct form: lesson in the museum - correspondence tour.

Decor: on the board “Route sheet for the exposition of the Cardiology Museum”, epigraph: “The heart, like a millstone, gives flour when enough grain is covered, but is erased when it is not added” (K. Weber).

During the classes

I. Motivational stage (preparation for active perception of the topic)

The sound of a heartbeat is heard. The teacher reads an excerpt from E. Mezhelaitis's poem "Heart".

What is a heart?
Is the stone hard?
An apple with crimson skin?
Maybe between the ribs and the aorta
Is a ball beating, similar to the earth's ball?
One way or another, everything earthly
fit within it,
Because he has no rest
Everything has a thing to do.

Many literary works are dedicated to the heart. Everyone probably remembers the “brave heart of Danko” from the story of M. Gorky, “Old Woman Izergil”; Gauf's fairy tale "Frozen". A warm heart and a cold one, disinterested and greedy, sympathetic, kind and cruel, brave, proud and evil... What is my heart like? This will be discussed in our lesson, which will take place in the museum.

To get into the museum, you need to get a ticket, which is issued only to those who complete the task.

Exercise 1 (individual survey)

Fill the gaps.

Blood, intercellular substance and lymph form ... ( internal environment of the body).

Liquid connective tissue - ... ( blood).

The protein dissolved in plasma, necessary for blood clotting, is ... ( fibrinogen).

Blood plasma without fibrinogen is called ... ( blood serum).

Non-nuclear blood cells containing hemoglobin - ... ( erythrocytes).

The state of the body in which the number of erythrocytes in the blood decreases or the content of hemoglobin in them is ... ( anemia).

A person who gives his blood for a transfusion is ... ( donor).

The protective reaction of the body, for example against infections - ... ( inflammation).

The ability of organisms to defend themselves against pathogenic bacteria and viruses is ... ( immunity).

Weakened or killed microorganisms - pathogens introduced into the human body to increase the activity of the immune system, - ... ( vaccine).

Proteins produced by lymphocytes upon contact with a foreign organism or protein - ... ( antibodies).

The circulatory organs include ... ( heart and blood vessels).

Vessels through which blood flows from the heart - ... ( arteries).

The smallest blood vessels in which the exchange of substances between blood and tissues takes place - ... ( capillaries).

The path of blood from the left ventricle to the right atrium is ... ( systemic circulation).

Task 2 (group work on problematic issues)

In one popular book on physiology, it is figuratively said: “Every second in the Red Sea, millions of ships are wrecked and sink to the bottom. But millions of new ships leave the harbors again to sail. What is meant by "ships" and "harbours"? ( Ships are red blood cells, harbors are red marrow.)

I.P. Pavlov said: “There is an “emergency” reaction in the body, in which the body sacrifices some part to save the whole.” What is it about? ( About phagocytosis.)

It is known that about 25 g of blood is replaced in a person per day. How much blood is produced in 70 years? ( About 640 kg.)

Consider micropreparations of human and frog blood. State the similarities and differences.

II. Learning new material (story with elements of conversation)

Museum director. I am glad that you are interested in the exhibits of our museum. Our museum is called Cardiology. Cardiology is a branch of medicine that studies the structure, functions and diseases of the cardiovascular system, as well as developing methods for their diagnosis, treatment and prevention. The museum was founded in 2005, on the basis of the 8th grade of school No. 5. Our employees will introduce you to the museum.

Guide (beating heart display). Listen. Whatever you do - sleep, eat, run - there is always a muffled, rhythmic knock. It's your heart beating. Clench your hand into a fist - you will see how big it is. The heart is a muscular organ that constantly contracts and forces blood to move through your body.

The heart is located in the chest cavity behind the sternum, slightly shifted from the middle to the left, its weight is about 300 g.

It is covered with a thin and dense membrane that forms a closed sac - the pericardial sac, or pericardium.

Student. I would like to know what is the role of the pericardial sac?

Guide. The pericardial sac contains a serous fluid that lubricates the heart and reduces friction during its contractions.

The wall of the heart has three layers. The epicardium is the outer serous layer that covers the heart (fuses with the pericardium). The myocardium is the middle muscular layer formed by the striated cardiac muscle. Each muscle fiber contains 1-2 nuclei, many mitochondria. Endocardium is the inner epithelial layer.

Let's see what the heart is made of. Conventionally, it is divided by a partition into two halves: left and right. The left one consists of the left ventricle and the left atrium. Between them is a bicuspid valve - it has only two cusps (it is also called the mitral valve). The right half of the heart consists of the right ventricle and the right atrium. They are also separated from each other by a valve, but this valve has three leaflets and is therefore called a tricuspid (tricuspid) valve. The valves open and close the passage between the atria and ventricles, forcing blood to flow in one direction.

Between the ventricles and arteries are semilunar valves, each of which consists of three pockets. The valves of the heart and blood vessels ensure the movement of blood in exactly one direction: through the arteries from the heart, through the veins to the heart, from the atria to the ventricles.

The external structure of the heart

The walls of the chambers of the heart vary in thickness depending on the work being done. When the walls of the atria contract, little work is done: blood is supplied to the ventricles, so the walls of the atria are relatively thin. The right ventricle pushes blood through the pulmonary circulation, and the left ventricle ejects blood into the systemic circulation, so its walls are 2-3 times thicker than the walls of the right one.

Metabolic processes are extremely intensive in the heart: muscle tissue cells contain many mitochondria, and the tissue is well supplied with blood. The mass of the heart is about 0.5% of body weight, while 10% of the blood ejected by the aorta goes to the coronary or coronary vessels that feed the heart itself. Aorta (Greek) - "straight artery."

Student. What causes rapid contraction of the heart chamber?

Guide. Muscle fibers branch and connect with each other at the ends, forming a complex network, due to which the rapid contraction of the chamber as a single structure is ensured.

Student. How does the heart work?

Guide. The heart is a tireless motor that knows no weekends, no holidays, no vacations. During the day, the heart contracts almost 100 thousand times, and pumps about 300 liters of blood in 1 hour (demonstration “heart-pump”). For one beat, the heart expends so much energy that it would be enough to lift a load weighing 200 g to a height of 1 m, and in 1 minute the heart could lift this load to the height of a 20-story building.

Internal structure of the heart

Now consider the work of the heart on the example of one cardiac cycle.

A cardiac cycle is a sequence of events that occurs during a single heartbeat that lasts less than 1 second. The cardiac cycle consists of three phases.

During contraction (systole) of the atria, which lasts about 0.1 s, the ventricles are relaxed, the cuspid valves are open, and the semilunar valves are closed. Contraction (systole) of the ventricles lasts about 0.3 s. At the same time, the atria are relaxed, the cusp valves are closed (the tendon filaments do not allow them to bend, and blood flows into the atrium), blood rushes into the pulmonary artery and aorta. Complete relaxation of the heart - cardiac pause, or diastole - lasts about 0.4 s.

Voronezh scientists Yu.D. Safonov and L.I. Yakimenko determined that during one cardiac cycle, the valves and the heart muscle are involved in 40 consecutive movements. The optimal mode of the heart: the atria work 0.1 s and rest 0.7 s, and the ventricles work 0.3 s and rest 0.5 s.

Independent work: Complete the Cardiac Cycle table.

Table. Cardiac cycle

A task (for tourists). The man is 80 years old. Determine how many years his heart ventricles rested, considering that the average heart rate was 70 beats per minute. ( 46 years old.)

Student. What is the reason for the high efficiency of the heart?

Guide. It is provided by the following factors:

- a high level of metabolic processes occurring in the heart;
- increased supply of blood to the muscles of the heart;
- a strict rhythm of the activity of the heart (the phases of work and rest of each department strictly alternate).

Student. The demands placed on the body by the cardiovascular system are constantly changing. The heart responds to this by changing the rate of contractions. What affects the work of the heart?

Guide. Let us recall the methods of regulation of functions in the body known to us.

Firstly, it is nervous regulation, and secondly, it is humoral regulation of heart activity. The central nervous system constantly controls the work of the heart through nerve impulses. In the medulla oblongata is the center of blood circulation, from which a pair of parasympathetic nerves emerge, reducing the frequency and strength of contractions. Strong excitation of the vagus nerve causes cardiac arrest (Goltz experiment). For example, a blow to the stomach can be fatal; irritation of the abdominal organs slows down heart contractions. Sympathetic nerves emerge from the cervical sympathetic ganglion, accelerating and intensifying heart contractions. Thus, the heart has a dual innervation: parasympathetic and sympathetic.

Humoral regulation of heart activity is provided by substances circulating in the blood. The work of the heart is inhibited: acetylcholine, sodium salts, an increase in blood pH. Adrenaline enhances the work of the heart (in case of cardiac arrest, it is injected directly into the heart muscle), potassium salts, and a decrease in pH. Hormones - secrets of the endocrine glands - thyroxine (thyroid gland), insulin (pancreas), corticosteroid hormones (adrenal glands), pituitary hormones affect cardiac activity.

Nervous and humoral regulation are closely interrelated and constitute a single mechanism for the regulation of heart contractions.

Student. Why does the heart contract even outside the body?

Guide. It has its own "built-in" mechanism that ensures the contraction of muscle fibers. The impulses travel from the atria to the ventricles. This ability of the heart to contract rhythmically without external stimuli, but only under the influence of impulses arising in it, is called automatism.

Automatism is provided by special muscle cells. They are innervated by the endings of autonomic neurons. In these cells, the membrane potential can reach 90 mV, which leads to the generation of an excitation wave. Changes in these potentials can be recorded with special equipment - their recording is an electrocardiogram.

Thus, the heart beats (on average) 70 times per minute, 100,000 times a day, 40 million times a year, and about 2.5 billion times in a lifetime. At the same time, it pumps the following volumes of blood: in 1 minute - 5.5 liters, in a day - 8 thousand liters, in 70 years - about 200 million liters.

Student. What were the important events in the history of cardiology in our country?

Guide. In 1902 A.A. Kulyabko revived the child's heart 20 hours after his death, and later prof. S.S. Bryukhonenko revived the heart even 100 hours after death. In 1897–1941 315 heart surgeries were performed. In 1948 A.N. Bakulev performed the first operation on the mitral valve. In 1961, the Institute of Cardiovascular Surgery was established. A.N. Bakulev. In 1967, a surgeon from Cape Town, prof. Christian Barnard performed the first human heart transplant operation, and exactly 20 years later, the same operation was carried out by prof. IN AND. Shumakov in the USSR.

Generalization and systematization of knowledge

Exercise 1. Match terms and concepts

Terms

• Pericardium.
• Epicardium.
• Myocardium.
• Endocardium.
• arteries.
• Aorta.
• capillaries.
• Right atrium.
• Ventricles.
• Valves.
• Heart.
• Cardiology.

Concepts

• Pericardium.
• Outer serous layer.
• middle muscle layer.
• The inner layer.
• Vessels that carry blood from the heart, "smooth air carriers", "air veins".
• The largest arterial vessel in the human body.
• The thinnest (from lat. capillaros- hair) blood vessels.
• Chamber of the heart (from lat. atrium- front yard), where the hollow veins flow.
• Parts of the heart that push blood into the arteries.
• Education (from him. clappe- cover, valve, closing of the lumen), preventing the passage of blood from the ventricles to the atria.
• The main organ of the circulatory system.
• A branch of medicine that studies the structure, functions and diseases of the cardiovascular system, as well as developing methods for their diagnosis, treatment and prevention.

Task 2. Test (mutual check)

Answers: A - 7, B - 2, C - 12, D - 1, D - 9, E - 3, F - 8, H - 6, I - 4, K - 10, L - 15, M - 5, H - 14, O - 13, P - 11.

Independent work following the excursion

Creative task: design and defense of the methodological manual "The Heart of a Man".

Summarizing

Homework

Study the material on the structure and work of the heart in the textbook, solve the problem.

A task. It is known that the human heart contracts on average 70 times per minute, ejecting about 150 cm3 of blood with each contraction. How much blood does your heart pump in 6 lessons at school?

Cardiac cycle

This is a period of time during which there is a complete contraction and relaxation of all parts of the heart. Contraction is systole, relaxation is diastole. The duration of the cycle will depend on the heart rate. The normal frequency of contractions ranges from 60 to 100 beats per minute, but the average frequency is 75 beats per minute. To determine the duration of the cycle, we divide 60s by the frequency. (60s / 75s = 0.8s).

Atrial systole - 0.1 s

Ventricular systole - 0.3 s

Total pause 0.4 s

State of the heart at the end of the general pause. The cuspid valves are open, the semilunar valves are closed, and blood flows from the atria to the ventricles. By the end of the general pause, the ventricles are 70-80% filled with blood. The cardiac cycle begins with

atrial systole, the atria contract to complete the filling of the ventricles with blood. It is the contraction of the atrial myocardium and the increase in blood pressure in the atria - in the right up to 4-6, and in the left up to 8-12mm, it ensures the injection of additional blood into the ventricles and the atrial systole completes the filling of the ventricles with blood. Blood cannot flow back, as the circular muscles contract. The ventricles will contain the final diastolic volume blood. On average, 120-130 ml, but in people engaged in physical activity up to 150-180 ml, which ensures more efficient work, this department goes into a state of diastole. Next comes ventricular systole.

Ventricular systole- the most difficult phase of the cycles, duration 0,#-0,#3 s. secreted in systole stress period, it lasts 0.08 s and period of exile. Each period is divided into 2 phases -

stress period -

1. asynchronous contraction phase - 0.05 s and

2. phases of isometric contraction - 0.03 s. This is the isovalumin contraction phase.

Exile period -

1. fast ejection phase 0.12s and

2. slow phase 0.!3 s.

Ventricular systole begins with a phase of asynchronous contraction. Some cardiomyocytes are excited and are involved in the process of excitation. But the resulting tension in the myocardium of the ventricles provides an increase in pressure in it. This phase ends with the closing of the flap valves and the cavity of the ventricles is closed. The ventricles are filled with blood and their cavity is closed, and the cardiomyocytes continue to develop a state of tension. The length of the cardiomyocyte cannot change. It has to do with the properties of the liquid. Liquids do not compress. In a closed space, when there is a tension of cardiomyocytes, it is impossible to compress the liquid. The length of cardiomyocytes does not change. Isometric contraction phase. Cut at low length. This phase is called the isovaluminic phase. In this phase, the volume of blood does not change. The space of the ventricles is closed, the pressure rises, in the right up to 5-12 mm Hg. in the left 65-75 mm Hg, while the pressure of the ventricles becomes greater than the diastolic pressure in the aorta and pulmonary trunk and the excess pressure in the ventricles over the blood pressure in the vessels leads to the opening of the semilunar valves. The semilunar valves open and blood begins to flow into the aorta and pulmonary trunk.

The exile phase begins, when the ventricles contract, the blood is pushed into the aorta, into the pulmonary trunk, the length of cardiomyocytes changes, the pressure increases and at the height of systole in the left ventricle 115-125 mm, in the right 25-30 mm. Initially, the fast ejection phase, and then the ejection becomes slower. During the systole of the ventricles, 60 - 70 ml of blood is pushed out, and this amount of blood is the systolic volume. Systolic blood volume = 120-130 ml, i.e. there is still enough blood in the ventricles at the end of systole end systolic volume and this is a kind of reserve, so that if necessary - to increase systolic output. The ventricles complete systole and begin to relax. The pressure in the ventricles begins to fall and the blood that is ejected into the aorta, the pulmonary trunk rushes back into the ventricle, but on its way it meets the pockets of the semilunar valve, which, when filled, close the valve. This period is called proto-diastolic period- 0.04s. When the semilunar valves close, the cuspid valves also close, period of isometric relaxation ventricles. It lasts 0.08s. Here, the voltage drops without changing the length. This causes a pressure drop. Blood accumulated in the ventricles. The blood begins to press on the atrioventricular valves. They open at the beginning of ventricular diastole. There comes a period of blood filling with blood - 0.25 s, while a fast filling phase is distinguished - 0.08 and a slow filling phase - 0.17 s. Blood flows freely from the atria into the ventricle. This is a passive process. The ventricles will be filled with blood by 70-80% and the filling of the ventricles will be completed by the next systole.

The cardiac muscle has a cellular structure and the cellular structure of the myocardium was established back in 1850 by Kelliker, but for a long time it was believed that the myocardium is a network of sensations. And only electron microscopy confirmed that each cardiomyocyte has its own membrane and is separated from each other. Contact area - insert discs. Currently, cardiac muscle cells are subdivided into cells of the working myocardium - cardiomyocytes of the working atrial myocardium and ventricles - cells of the conduction system of the heart, in which

The cardiac cycle is a complex and very important process. It includes periodic contractions and relaxations, which are called "systole" and "diastole" in medical language. The most important human organ (heart), which is in second place after the brain, resembles a pump in its work.

Due to excitation, contraction, conductivity, as well as automatism, it supplies blood to the arteries, from where it goes through the veins. Due to the different pressures in the vascular system, this pump works without interruption, so the blood moves without stopping.

What it is

Modern medicine tells in sufficient detail what the cardiac cycle is. It all starts with systolic atrial work, which takes 0.1 s. Blood flows to the ventricles while they are in a state of relaxation. As for the cusp valves, they open, and the semilunar valves, on the contrary, close.

The situation changes when the atria relax. The ventricles begin to contract, it takes 0.3 s.

When this process is just beginning, all the valves of the heart remain in the closed position. The physiology of the heart is such that as the muscles of the ventricles contract, pressure is created that gradually builds up. This indicator also increases where the atria are located.

If we recall the laws of physics, it becomes clear why blood tends to move from a cavity in which there is high pressure to a place where it is less.

On the way there are valves that do not allow blood to reach the atria, so it fills the cavities of the aorta and arteries. The ventricles stop contracting, there comes a moment of relaxation for 0.4 s. In the meantime, blood flows into the ventricles without problems.

The task of the cardiac cycle is to maintain the work of the main organ of a person throughout his life.

A strict sequence of phases of the cardiac cycle fits into 0.8 s. The cardiac pause takes 0.4 s. To fully restore the work of the heart, such an interval is quite enough.

The duration of the heart

According to medical data, the heart rate is from 60 to 80 in 1 minute if a person is in a calm state - both physically and emotionally. After human activity, heart beats become more frequent depending on the intensity of the load. By the level of the arterial pulse, you can determine how many heart contractions occur in 1 minute.

The walls of the artery fluctuate, as they are affected by high blood pressure in the vessels against the background of the systolic work of the heart. As mentioned above, the duration of the cardiac cycle is no more than 0.8 s. The process of contraction in the atrium lasts 0.1 s, where the ventricles - 0.3 s, the remaining time (0.4 s) is spent on relaxing the heart.

The table shows the exact data of the cycle of heart beats.

Phases

Medicine describes 3 main phases that make up the cycle:

1. At first, the atria contract.
2. Systole of the ventricles.
3. Relaxation (pause) of the atria and ventricles.

Each phase has its own time limit. The first phase takes 0.1 s, the second 0.3 s, and the last phase takes 0.4 s.

At each stage, certain actions occur that are necessary for the proper functioning of the heart:

• The first phase involves complete relaxation of the ventricles. As for the flap valves, they open. The semilunar valves are closed.
• The second phase begins with the atria relaxing. The semilunar valves open and the leaflets close.
• When there is a pause, the semilunar valves, on the contrary, open, and the leaflets are in the open position. Some of the venous blood fills the atrial region, while the rest is collected in the ventricle.

Of great importance is the general pause before a new cycle of cardiac activity begins, especially when the heart is filled with blood from the veins. At this moment, the pressure in all chambers is almost the same due to the fact that the atrioventricular valves are in the open state.

In the region of the sinoatrial node, excitation is observed, as a result of which the atria contract. When contraction occurs, ventricular volume is increased by 15%. After systole ends, the pressure drops.

Heart contractions

For an adult, the heart rate does not go beyond 90 beats per minute. Children have a faster heart rate. The heart of an infant gives out 120 beats per minute, in children under 13 years old this figure is 100. These are general parameters. Everyone has slightly different values ​​- less or more, they are influenced by external factors.

The heart is entwined with nerve threads that control the cardiac cycle and its phases. The impulse coming from the brain increases in the muscle as a result of a serious stressful condition or after physical exertion. It can be any other changes in the normal state of a person under the influence of external factors.

The most important role in the work of the heart is played by its physiology, or rather, the changes associated with it. If, for example, the composition of the blood changes, the amount of carbon dioxide changes, there is a decrease in the level of oxygen, then this leads to a strong impulse of the heart. The process of its stimulation is intensifying. If changes in physiology have affected the vessels, then the heart rate, on the contrary, decreases.

The activity of the heart muscle is determined by various factors. The same applies to the phases of cardiac activity. Among these factors is the central nervous system.

For example, elevated body temperatures contribute to an accelerated heart rate, while low ones, on the contrary, slow down the system. Hormones also affect heart contractions. Together with the blood, they enter the heart, thereby increasing the frequency of strokes.

In medicine, the cardiac cycle is considered a rather complex process. It is influenced by many factors, some directly, others indirectly. But together, all these factors help the heart to work properly.

The structure of heart contractions is no less important for the human body. She keeps him alive. An organ like the heart is complex. It has a generator of electrical impulses, a certain physiology, controls the frequency of strokes. That is why it works throughout the life of the body.

Only 3 main factors can influence it:

• human life;
• hereditary predisposition;
• ecological state of the environment.

Numerous body processes are under the control of the heart, especially metabolic processes.. In a matter of seconds, he can show violations, inconsistencies with the established norm. That is why people should know what the cardiac cycle is, what phases it consists of, what their duration is, and also physiology.

You can determine possible violations by evaluating the work of the heart. And at the first sign of failure, contact a specialist.

Phases of heartbeats

As already mentioned, the duration of the cardiac cycle is 0.8 s. The stress period provides for 2 main phases of the cardiac cycle:

1. When asynchronous reductions occur. The period of heart beats, which is accompanied by systolic and diastolic work of the ventricles. As for the pressure in the ventricles, it remains practically the same.
2. Isometric (isovolumic) contractions are the second phase, which begins some time after asynchronous contractions. At this stage, the pressure in the ventricles reaches the parameter at which the atrioventricular valves close. But this is not enough for the semilunar valves to open.

Pressure indicators increase, thus, the semilunar valves open. This encourages blood to flow out of the heart. The entire process takes 0.25 s. And it has a phase structure consisting of cycles.

• Rapid exile. At this stage, the pressure increases and reaches maximum values.
• Slow exile. The period when the pressure parameters decrease. After the contractions are over, the pressure will quickly subside.

After the systolic activity of the ventricles ends, the period of diastolic work begins. Isometric relaxation. It lasts until the pressure rises to optimal parameters in the atrial region.

At the same time, the atrioventricular cusps open. The ventricles fill with blood. There is a transition to the fast filling phase. Blood circulation is carried out due to the fact that different pressure parameters are observed in the atria and ventricles.

In other chambers of the heart, the pressure continues to fall. After diastole, a phase of slow filling begins, the duration of which is 0.2 s. During this process, the atria and ventricles continuously fill with blood. When analyzing cardiac activity, you can determine how long the cycle lasts.

Diastolic and systolic work take almost the same time. Therefore, the human heart works half of its life, and rests the other half. The total duration time is 0.9 s, but due to the overlapping processes, this time is 0.8 s.

Details

The heart acts as a pump. atrium- containers that receive blood, which continuously flows to the heart; they contain important reflexogenic zones, where volumoreceptors are located (to assess the volume of incoming blood), osmoreceptors (to assess the osmotic pressure of blood), etc .; in addition, they perform an endocrine function (secretion of atrial natriuretic hormone and other atrial peptides into the blood); pumping function is also characteristic.
Ventricles perform mainly a pumping function.
valves heart and large vessels: atrioventricular flap valves (left and right) between the atria and ventricles; semilunar valves of the aorta and pulmonary artery.
The valves prevent backflow of blood. For the same purpose, there are muscular sphincters at the confluence of the hollow and pulmonary veins into the atria.

CARDIAC CYCLE.

Electrical, mechanical, biochemical processes that occur during one complete contraction (systole) and relaxation (diastole) of the heart are called the cycle of cardiac activity. The cycle consists of 3 main phases:
(1) atrial systole (0.1 sec),
(2) ventricular systole (0.3 sec),
(3) total pause or total diastole of the heart (0.4 sec).

General diastole of the heart: the atria are relaxed, the ventricles are relaxed. Pressure = 0. Valves: atrioventricular valves open, semilunar valves closed. There is a filling of the ventricles with blood, the volume of blood in the ventricles increases by 70%.
Atrial systole: blood pressure 5-7 mm Hg. Valves: atrioventricular valves open, semilunar valves closed. There is an additional filling of the ventricles with blood, the volume of blood in the ventricles increases by 30%.
Ventricular systole consists of 2 periods: (1) the tension period and (2) the ejection period.

Ventricular systole:

Direct ventricular systole

1)stress period

• asynchronous reduction phase
• isometric contraction phase

2)period of exile

• rapid ejection phase
• slow ejection phase

Asynchronous reduction phase: excitation spreads through the myocardium of the ventricles. Individual muscle fibers begin to contract. The pressure in the ventricles is about 0.

Isometric contraction phase: all fibers of the ventricular myocardium are reduced. The pressure in the ventricles increases. The atrioventricular valves close (because the pressure in the ventricles becomes greater than in the precardia). The semilunar valves are still closed (because the pressure in the ventricles is still less than in the aorta and pulmonary artery). The volume of blood in the ventricles does not change (at this time there is neither inflow of blood from the atria, nor outflow of blood into the vessels). Isometric mode of contraction (the length of the muscle fibers does not change, the tension increases).

Period of exile: all ventricular myocardial fibers continue to contract. The blood pressure in the ventricles becomes greater than the diastolic pressure in the aorta (70 mm Hg) and pulmonary artery (15 mm Hg). The semilunar valves open. Blood flows from the left ventricle to the aorta, from the right ventricle to the pulmonary artery. Isotonic mode of contraction (muscle fibers shorten, their tension does not change). The pressure rises to 120 mm Hg in the aorta and to 30 mm Hg in the pulmonary artery.

DIASTOLIC PHASES OF THE VENTRICULAR.

ventricular diastole

• isometric relaxation phase
• rapid passive filling phase
• slow passive filling phase
• rapid active filling phase (due to atrial systole)

Electrical activity in different phases of the cardiac cycle.

Left atrium: P wave => atrial systole (wave a) => additional filling of the ventricles (plays an essential role only with increased physical activity) => atrial diastole => venous blood flow from the lungs to the left. atrium => atrial pressure (wave v) => wave c (P due to the closing of the miter valve - towards the atrium).
Left ventricle: QRS => gastric systole => biliary pressure > atrial P => mitral valve closure. Aortic valve still closed => isovolumetric contraction => gastric P > aortic P (80 mm Hg) => aortic valve opening => blood ejection, decreased V ventricle => inertial blood flow through the valve =>↓ P in the aorta
and stomach.

Ventricular diastole. R in the stomach.<Р в предсерд. =>opening of the miter valve => passive filling of the ventricles even before atrial systole.
EDV = 135 ml (when the aortic valve opens)
CSR = 65 ml (when the mitral valve opens)
UO = BDO - KSO = 70 ml
EF \u003d UO / KDO \u003d normal 40-50%

The heart is the main organ of the human body. Its important function is to sustain life. The processes occurring in this organ excite the heart muscle, starting a process in which contractions and relaxation alternate, which is a vital cycle to maintain rhythmic blood circulation.

The work of the heart is essentially a change of cyclic periods and continues without stopping. The viability of the body depends primarily on the quality of the work of the heart.

According to the mechanism of action, the heart can be compared to a pump that pumps blood flows from the veins into the arteries. These functions are provided by the special properties of the myocardium, such as excitability, the ability to contract, serve as a conductor, and work in automatic mode.

A feature of myocardial movement is its continuity and cyclicality due to the presence of a pressure difference at the ends of the vascular system (venous and arterial), one of the indicators of which in the main veins is 0 mm Hg, while in the aorta it can reach up to 140 mm.

Cycle length (systole and diastole)

In order to understand the essence of the cyclic function of the heart, one should understand what is systole and what is diastole. The first is characterized by the release of the heart from the blood fluid, thus. contraction of the heart muscle is called systole, while diastole is accompanied by the filling of the cavities with blood flow.

The process of alternating systole and diastole of the ventricles and atria, as well as the subsequent general relaxation, is called the cycle of cardiac activity.

Those. The opening of the leaf valves occurs at the time of systole. When the leaflet contracts during diastole, blood rushes to the heart. The pause period is also of great importance, as the flap valves are closed during this rest time.

Table 1. Cycle duration in humans and animals in comparison

The duration of systole is in humans, essentially the same period as diastole, while in animals this period lasts somewhat longer.

The duration of different phases of the heart cycle is determined by the frequency of contractions. Their increase affects the length of all phases, to a greater extent, this applies to diastole, which becomes noticeably smaller. At rest, healthy organisms have a heart rate of up to 70 cycles per minute. At the same time, they can have a duration of up to 0.8 s.

Before contractions, the myocardium is relaxed, its chambers are filled with blood fluid from the veins. The difference of this period is the full opening of the valves, and the pressure in the chambers - in the atria and ventricles remains at the same level. The myocardial excitation impulse originates from the atria.

Then it provokes an increase in pressure and, due to the difference, the blood flow is gradually pushed out.

The cyclical work of the heart is distinguished by a unique physiology, because. it independently provides itself with an impulse for muscle activity, through the accumulation of electrical stimulation.

Phase structure with table

To analyze changes in the heart, you also need to know what phases this process consists of. There are such phases as: contraction, expulsion, relaxation, filling. What are the periods, sequence and place in the cycle of the heart of individual types of each of them can be seen in Table 2.

Table 2. Cardiac cycle indicators

K ardiocycle is divided into several phases with a specific purpose and duration, ensuring the correct direction blood flow in order precisely established by nature.

Cycle phase names:

Video: Cardiac cycle

Heart sounds

The activity of the heart is characterized by emitted cyclic sounds, they resemble tapping. The components of each beat are two easily distinguishable tones.

One of them arises from contractions in the ventricles, the impulse of which arises from the slamming valves that close the atrioventricular openings during myocardial tension, preventing the blood flow from penetrating back into the atria.

The sound at this time appears directly when the free edges are closed. The same blow is produced with the participation of the myocardium, the walls of the pulmonary trunk and aorta, tendon filaments.

The next tone occurs during the period of diastole from the movement of the ventricles, being at the same time a consequence of the activity of the semilunar valves, which prevent the blood flow from penetrating back, acting as a barrier. The knock becomes audible at the moment of connection in the lumen of the edges of the vessels.

In addition to the two most prominent tones in the cycle of the heart, there are two more, called the third and fourth. If a phonendoscope is enough to hear the first two, then the rest can be registered only with a special device.

Listening to heart beats is extremely important for diagnosing its condition and possible changes that make it possible to judge the development of pathologies. Some ailments of this organ are characterized by a violation of the cycle, a bifurcation of beats, a change in their volume, accompanied by additional tones or other sounds, including squeaks, clicks, noises.

Video: Auscultation of the heart. Basic tones

Cardiac cycle- a unique physiological reaction of the body created by nature, necessary to maintain its vital activity. This cycle has certain patterns, which include periods of muscle contraction and relaxation.

According to the results of the phase analysis of the activity of the heart, it can be concluded that its two main cycles are intervals of activity and rest, i.e. between systole and diastole, essentially about the same.

An important indicator of the health of the human body, determined by the activity of the heart, is the nature of its sounds, in particular, noises, clicks, etc. should cause a wary attitude.

In order to avoid the development of pathologies in the heart, it is necessary to undergo a timely diagnosis in a medical institution, where a specialist will be able to assess changes in the cardiac cycle according to its objective and accurate indicators.