Cardiac cycle - what is it? Cardiac cycle: systole, diastole, contractions Contraction of the atria and ventricles 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 to flow 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?

To move blood through the vessels, it is necessary to create a pressure drop, since the blood flow is carried out from a high level to a low one. This is possible due to the contraction (systole) of the ventricles. During diastole (relaxation), they are filled with blood, the more it is received, the stronger the muscle fibers work, pushing the contents into large vessels.

In diseases of the myocardium, endocrine and nervous pathology, the synchronism and duration of parts of the cardiac cycle are disturbed.

Read in this article

Cardiac cycle - systole and diastole

Alternate contraction and relaxation of cardiomyocytes ensures synchronous work of the whole heart. The cardiac cycle consists of:

• pauses- general relaxation (diastole) of all parts of the myocardium, the atrioventricular valves are open, the blood passes into the cavity of the heart;
• atrial systole- movement of blood into the ventricles;
• ventricular contractions- ejection of the main vessels.

atrial

The impulse for myocardial contraction occurs in the sinus node. After the openings of the vessels overlap, the atrial cavity becomes closed. At the moment of coverage of the entire muscle layer by excitation, the fibers are compressed and blood is pushed out into the ventricles. The valve flaps are opened under pressure. The atria then relax.

Normally, the atrial contribution to the total filling of the ventricles is insignificant, since they are already 80% filled during the pause period. But with an increase in the frequency of contractions (flicker, flutter, fibrillation, supraventricular form of tachycardia), their role in filling increases significantly.

Ventricular

The first period of contractions is called myocardial tension. It lasts until the valves of the valves of the large vessels leaving the ventricles open. It consists of 2 parts: non-simultaneous contraction (asynchronous) and isometric. The latter means the involvement of all myocardial cells in the work. The blood flow closes the atrial valves, and the ventricle is completely closed from all sides.

The second stage (expulsion) begins with the opening of the valvular cusps of the pulmonary trunk and aorta. It also has two periods - fast and slow. At the end of cardiac output, the pressure increases already in the vascular network, and when it becomes equal to the heart, the systole stops and diastole begins.

difference between systole and diastole

For the heart muscle, relaxation is no less important than contraction. By apt definition, diastole makes systole. This period is also active. During its time, actin and myosin filaments separate in the heart muscle, which, according to the Frank-Starling law, determines the strength of cardiac output - the greater the stretch, the greater the contraction.

The ability to relax depends on the fitness of the heart muscle; in athletes, due to the long diastole, the frequency of contractions decreases, and the blood flow through the coronary vessels increases at this time. During the relaxation period, two phases are distinguished:

• protodiastolic(the reverse movement of blood closes the valvular valves of the vessels);
• isometric- expansion of the ventricles.

This is followed by filling, and then atrial systole begins. Upon their completion, the cavities of the ventricles are ready for the subsequent contraction.

Systole, diastole, pause time

If the heart rate is normal, then the approximate duration of the entire cycle is 800 milliseconds. Of these, individual stages account for (ms):

• atrial contraction 100, relaxation 700;
• ventricular systole 330 - asynchronous voltage 50, isometric 30, expulsion 250;
• ventricular diastole 470 - relaxation 120, filling 350.

Expert opinion

Alena Ariko

Expert in cardiology

That is, most of the life (470 to 330) the heart is in a state of active rest. In response to stress, the frequency of contractions increases precisely due to a decrease in relaxation time. An accelerated pulse is considered one of the risk factors for diseases of the circulatory system, since the myocardium does not have time to recover and accumulate energy for the next stroke, which leads to a weakening of the heart.

What are the phases of systole and diastole?

To the factors that determine the extensibility and subsequent contractility of the myocardium, relate:

• wall elasticity;
• the thickness of the heart muscle, its structure (cicatricial changes, inflammation, dystrophy due to malnutrition);
• cavity size;
• structure and patency of valves, aorta, pulmonary artery;
• activity of the sinus node and the speed of propagation of the excitation wave;
• condition of the pericardial sac;
• blood viscosity.

Watch the video about the cardiac cycle:

Reasons for violation of indicators

Violation of myocardial contractility and weakening of systole cause ischemic and dystrophic processes -,. Due to the narrowing of the openings of the valves or the difficulty in ejection of blood from the ventricles, the amount of residual blood in their cavities increases, and a reduced volume enters the vasculature.

Such changes are characteristic of congenital and, hypertrophic cardiomyopathy, narrowing of the main vessels.

Violation of the formation of an impulse or its movement along the conduction system changes the sequence of myocardial excitation, the synchrony of systole and diastole of parts of the heart, and reduces cardiac output. Arrhythmias change the duration of the phases of the cardiac cycle, the efficiency of ventricular contractions and the possibility of their complete relaxation.

Diseases that are accompanied by diastolic and then systolic dysfunction also include:

• systemic autoimmune pathologies;
• endocrine regulation disorders - diseases of the thyroid gland, pituitary gland, adrenal glands;
• - imbalance between parts of the autonomic nervous system.

Cardiac cycle on ECG and ultrasound

To investigate the synchrony of the work of the heart and changes in the individual phases of the cardiac cycle allows the ECG. On it you can see the following periods:

• tooth P - atrial systole, the rest of the time their diastole continues;
• the ventricular complex 0.16 seconds after P reflects the process of ventricular systole;
• occurs a little earlier than systole ends and relaxation begins (ventricular diastole).

Doppler ultrasound helps to visualize and measure the parameters of the heart. This diagnostic method provides information about the rate of blood entering the ventricles, its expulsion, the movement of the valve leaflets, and the magnitude of cardiac output.

Systole means contraction, and diastole means relaxation of the heart. They sequentially and cyclically replace each other. In turn, each part of the cardiac cycle is divided into phases. In time, most of it falls on diastole, the usefulness of contractions of muscle fibers depends on it.

With pathology of the myocardium, valves, conduction system, systolic and diastolic functions are violated. Changes in the work of the heart can also occur under the influence of a violation of hormonal or nervous regulation.

Read also

The doctor will tell a lot about systolic and diastolic pressure, more precisely, the difference between them. The scores can differ significantly. For example, a small difference, like a big one, will definitely interest a doctor. It will not be left without attention if the systolic is higher / lower, low diastolic with normal systolic, etc.

The heart is the main organ of the human body. Its important function is to sustain life. The processes taking place 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 cyclicity 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 general relaxation that follows, 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 orifices 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 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, 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.

The following properties are characteristic of the myocardium: excitability, the ability to contract, conduction and automaticity. To understand the phases of contractions of the heart muscle, it is necessary to remember two basic terms: systole and diastole. Both terms are of Greek origin and are opposite in meaning, in translation systello means "to tighten", diastello - "to expand".

Here a natural question arises: why does the blood not rush back into the atrium? This is exactly what would have happened, but she cannot do this: the first thing that begins to be pushed into the atrium is the free edges of the atrioventricular valve cusps floating in the ventricles. It would seem that under such pressure they should have twisted into the atrial cavity. But this does not happen, since tension increases not only in the myocardium of the ventricles, the fleshy crossbars and papillary muscles also tighten, pulling the tendon filaments, which protect the valve flaps from “falling out” into the atrium. Thus, by closing the leaflets of the atrioventricular valves, that is, by the slamming of the communication between the ventricles and the atria, the period of tension in the systole of the ventricles ends.

After the voltage reaches its maximum, it starts ventricular myocardium, it lasts for 0.25 s, during this period the actual ventricular systole. For 0.13 s, blood is ejected into the openings of the pulmonary trunk and aorta, the valves are pressed against the walls. This happens due to an increase in pressure up to 200 mm Hg. in the left ventricle and up to 60 mm Hg. in the right. This phase is called . After it, in the remaining time, there is a slower release of blood under less pressure - . At this point, the atria are relaxed and begin to receive blood from the veins again, thus layering the ventricular systole on the atrial diastole occurs.

In the following 0.08 s after the protodiastolic period, the myocardium enters . During this phase, the cusps of the mitral and tricuspid valves are still closed, and blood, therefore, does not enter the ventricles. But calmness ends when the pressure in the ventricles becomes lower than the pressure in the atria (0 or even slightly less in the first and from 2 to 6 mm Hg in the second), which inevitably leads to the opening of the atrioventricular valves. During this time, the blood has time to accumulate in the atria, the diastole of which began earlier. For 0.08 s, it safely migrates to the ventricles, is carried out . Blood for another 0.17 s gradually continues to flow into the atria, a small amount of it enters the ventricles through the atrioventricular openings - . The last thing the ventricles undergo during their diastole is an unexpected flow of blood from the atria during their systole, lasting 0.1 s and amounting to ventricular diastole. Well, then the cycle closes and begins again.

The first "fat", the so-called I tone, is generated by ventricular systole. For simplicity, you can remember that this is the result of the slamming of the atrioventricular valves: mitral and tricuspid. At the moment of rapid tension of the myocardium, the valves close the atrioventricular orifices in order not to release blood back into the atria, their free edges close, and a characteristic “blow” is heard. To be more precise, the tensing myocardium, trembling tendon filaments, and the oscillating walls of the aorta and pulmonary trunk are involved in the formation of the first tone.

II tone - the result of diastole. It occurs when the semilunar leaflets of the valves of the aorta and the pulmonary trunk block the path of blood, which decides to return to the relaxed ventricles, and “knock”, connecting the edges in the lumen of the arteries. This, perhaps, is all.

However, there are changes in the sound picture when the heart is in trouble. With heart disease, sounds can become very diverse. Both tones known to us can change (become quieter or louder, split in two), additional tones appear (III and IV), various noises, squeaks, clicks, sounds called “swan cry”, “whooping cough”, etc.

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.