What is characteristic of a general pause in the cardiac cycle. Cardiac cycle and its phase structure. Systole. Diastole. Asynchronous contraction phase. Isometric contraction phase. Fundamentals of cardiac morphophysiology

CYCLE OF THE HEART

Cardiac cycle- a concept reflecting the sequence of processes occurring in one contraction hearts and its subsequent relaxation. Each cycle includes three large stages: systole atria , systoleventricles And diastole . Term systole means muscle contraction. Highlight electrical systole- electrical activity that stimulates myocardium and calls mechanical systole- contraction of the heart muscle and reduction of the heart chambers in volume. Term diastole means muscle relaxation. During the cardiac cycle, blood pressure increases and decreases; accordingly, high pressure at the time of ventricular systole is called systolic, and low during their diastole - diastolic.

The repetition rate of the cardiac cycle is called heart rate, it is asked heart pacemaker.

Periods and phases of the cardiac cycle

Schematic relationship between the phases of the cardiac cycle, ECG, FKG, sphygmograms. The ECG waves, numbers of FCG tones and parts of the sphygmogram are indicated: a - anacrota, d - dicrota, j - catacrota. The phase numbers correspond to the table. The time scale scale is preserved.

A summary table of the periods and phases of the cardiac cycle with approximate pressures in the chambers of the heart and the position of the valves is given at the bottom of the page.

Ventricular systole

Ventricular systole- the period of contraction of the ventricles, which allows blood to be pushed into the arterial bed.

Several periods and phases can be distinguished in the contraction of the ventricles:

Voltage period- characterized by the beginning of contraction of the muscle mass of the ventricles without changing the volume of blood inside them.

• Asynchronous reduction- the beginning of excitation of the ventricular myocardium, when only individual fibers are involved. The change in ventricular pressure is sufficient to close the atrioventricular valves at the end of this phase.

  Isovolumetric contraction- almost the entire myocardium of the ventricles is involved, but there is no change in the volume of blood inside them, since the efferent (semilunar - aortic and pulmonary) valves are closed. Term isometric contraction is not entirely accurate, since at this time there is a change in the shape (remodeling) of the ventricles and tension of the chordae.

Exile period- characterized by the expulsion of blood from the ventricles.

• Quick expulsion- the period from the moment the semilunar valves open until systolic pressure is reached in the ventricular cavity - during this period the maximum amount of blood is ejected.

  Slow expulsion- the period when the pressure in the ventricular cavity begins to decrease, but is still higher than the diastolic pressure. At this time, the blood from the ventricles continues to move under the influence of the kinetic energy imparted to it, until the pressure in the cavity of the ventricles and efferent vessels equalizes.

In a state of calm, the ventricle of an adult’s heart pumps out 60 ml of blood (stroke volume) for each systole. The cardiac cycle lasts up to 1 s, respectively, the heart makes 60 contractions per minute (heart rate, heart rate). It is easy to calculate that even at rest, the heart pumps 4 liters of blood per minute (cardiac minute volume, MCV). During maximum exercise, the stroke volume of a trained person’s heart can exceed 200 ml, the pulse can exceed 200 beats per minute, and blood circulation can reach 40 liters per minute.

Diastole

Diastole- the period of time during which the heart relaxes to accept blood. In general, it is characterized by a decrease in pressure in the ventricular cavity, closure of the semilunar valves and opening of the atrioventricular valves with the movement of blood into the ventricles.

Ventricular diastole

• Protodiastole- the period of the beginning of myocardial relaxation with a drop in pressure lower than in the efferent vessels, which leads to the closure of the semilunar valves.

  Isovolumetric relaxation- similar to the phase of isovolumetric contraction, but exactly the opposite. The muscle fibers lengthen, but without changing the volume of the ventricular cavity. The phase ends with the opening of the atrioventricular (mitral and tricuspid) valves.

Filling period

• Fast filling- the ventricles quickly restore their shape in a relaxed state, which significantly reduces the pressure in their cavity and sucks blood from the atria.

  Slow filling- the ventricles have almost completely restored their shape, blood flows due to the pressure gradient in the vena cava, where it is 2-3 mm Hg higher. Art.

Atrial systole

It is the final phase of diastole. At a normal heart rate, the contribution of atrial contraction is small (about 8%), since during the relatively long diastole the blood already has time to fill the ventricles. However, with an increase in contraction frequency, the duration of diastole generally decreases and the contribution of atrial systole to ventricular filling becomes very significant.

In order to understand how certain cardiac diseases arise, manifest themselves and are treated, any medical student, and especially a doctor, must know the basics of normal physiology of the cardiovascular system. Sometimes it seems that the heartbeat is based on simple contractions of the heart muscle. But in fact, the heart rhythm mechanism contains more complex electro-biochemical processes that lead to the mechanical work of smooth muscle fibers. Below we will try to figure out what maintains regular and uninterrupted heartbeats throughout a person’s life.

The electro-biochemical prerequisites for the cycle of cardiac activity begin to be laid in the prenatal period, when intracardiac structures are formed in the fetus. Already in the third month of pregnancy, the child’s heart has a four-chamber basis with almost complete formation of intracardiac structures, and it is from this moment that full cardiac cycles occur.

To make it easier to understand all the nuances of the cardiac cycle, it is necessary to define such concepts as the phases and duration of heart contractions.

The cardiac cycle is understood as one complete contraction of the myocardium, during which a sequential change occurs over a certain period of time:

• Atrial systolic contraction,
• Ventricular systolic contraction,
• General diastolic relaxation of the entire myocardium.

Thus, in one cardiac cycle, or in one complete cardiac contraction, the entire volume of blood that is in the cavity of the ventricles is pushed into the large vessels extending from them - into the lumen of the aorta on the left and the pulmonary artery on the right. Thanks to this, all internal organs receive blood in a continuous mode, including the brain (systemic circulation - from the aorta), as well as the lungs (pulmonary circulation - from the pulmonary artery).

Video: heart contraction mechanism

How long does a cardiac cycle last?

The normal length of the heartbeat cycle is determined genetically, remaining almost the same for the human body, but at the same time can vary within normal limits in different individuals. Typically, the duration of one complete heartbeat is 800 milliseconds, which include contraction of the atria (100 milliseconds), contraction of the ventricles (300 milliseconds) and relaxation of the cardiac chambers (400 milliseconds). In this case, the heart rate in a calm state ranges from 55 to 85 beats per minute, that is, the heart is capable of completing the specified number of cardiac cycles per minute. The individual duration of the cardiac cycle is calculated using the formula Heart rate:60.

What happens during the cardiac cycle?

cardiac cycle from a bioelectrical point of view (the impulse originates in the sinus node and spreads throughout the heart)

The electrical mechanisms of the cardiac cycle include the functions of automaticity, excitation, conduction and contractility, that is, the ability to generate electricity in myocardial cells, conduct it further along electrically active fibers, as well as the ability to respond with mechanical contraction in response to electrical excitation.

Thanks to such complex mechanisms, the heart's ability to contract correctly and regularly is maintained throughout a person's life, while at the same time subtly responding to constantly changing environmental conditions. For example, systole and diastole occur faster and more actively if a person is in danger. At the same time, under the influence of adrenaline from the adrenal cortex, the ancient, evolutionarily established principle of the three “Bs” is activated - fight, fear, run, the implementation of which requires greater blood supply to the muscles and brain, which, in turn, directly depends on the activity of the cardiovascular system, in particular, from the accelerated alternation of phases of the cardiac cycle.

hemodynamic reflection of the cardiac cycle

If we talk about hemodynamics (blood movement) through the chambers of the heart during a full heart contraction, it is worth noting the following features. At the beginning of cardiac contraction, after electrical stimulation is received by the muscle cells of the atria, biochemical mechanisms are activated in them. Each cell contains myofibrils made from the proteins myosin and actin, which begin to contract under the influence of microcurrents of ions into and out of the cell. The set of contractions of myofibrils leads to contraction of the cell, and the set of contractions of muscle cells leads to contraction of the entire cardiac chamber. At the beginning of the cardiac cycle, the atria contract. In this case, blood, through the opening of the atrioventricular valves (tricuspid on the right and mitral on the left), enters the cavity of the ventricles. After the electrical excitation has spread to the walls of the ventricles, systolic contraction of the ventricles occurs. The blood is expelled into the above vessels. After the expulsion of blood from the ventricular cavity, general diastole of the heart occurs, while the walls of the heart chambers are relaxed, and the cavities are passively filled with blood.

Normal cardiac cycle phases

One complete cardiac contraction consists of three phases, called atrial systole, ventricular systole and total diastole of the atria and ventricles. Each phase has its own characteristics.

First phase The cardiac cycle, as already described above, consists of the outpouring of blood into the cavity of the ventricles, which requires the opening of the atrioventricular valves.

Second phase The cardiac cycle includes periods of tension and expulsion, in which in the first case there is an initial contraction of the muscle cells of the ventricles, and in the second there is an outpouring of blood into the lumen of the aorta and pulmonary trunk, followed by the movement of blood throughout the body. The first period is divided into asynchronous and isovolumetric contractile types, with the muscle fibers of the ventricular myocardium contracting individually and then in a synchronous manner, respectively. The expulsion period is also divided into two types - rapid expulsion of blood and slow expulsion of blood, in the first case the maximum volume of blood is released, and in the second - a not so significant volume, since the remaining blood moves into large vessels under the influence of a slight difference in pressure between the ventricular cavity and the lumen of the aorta (pulmonary trunk).

Third phase, is characterized by rapid relaxation of the muscle cells of the ventricles, as a result of which blood quickly and passively (also under the influence of the pressure gradient between the filled cavities of the atria and the “empty” ventricles) begins to fill the latter. As a result, the heart chambers are filled with a volume of blood sufficient for the next cardiac output.

Cardiac cycle in pathology

The duration of the cardiac cycle can be influenced by many pathological factors. So, in particular, an accelerated heart rate due to a decrease in the time of one heartbeat occurs during fever, intoxication of the body, inflammatory diseases of internal organs, infectious diseases, shock conditions, as well as injuries. The only physiological factor that can cause a shortening of the cardiac cycle is physical activity. In all cases, the decrease in the duration of one complete heartbeat is due to the increasing need of body cells for oxygen, which is ensured by more frequent heartbeats.

An increase in the duration of cardiac contraction, leading to a decrease in heart rate, occurs when the conduction system of the heart is disrupted, which, in turn, is clinically manifested by arrhythmias of the bradycardia type.

How can you evaluate the cardiac cycle?

It is entirely possible to directly examine and evaluate the usefulness of one complete heartbeat using functional diagnostic methods. The “gold” standard in this case is, which allows you to record and interpret indicators such as stroke volume and ejection fraction, which are normally 70 ml of blood per cardiac cycle, and 50-75%, respectively.

Thus, the normal functioning of the heart is ensured by a continuous alternation of the described phases of heart contractions, successively replacing each other. If any deviations occur in the normal physiology of the cardiac cycle, they develop. As a rule, this is a sign of increasing pain, and in both cases it suffers. In order to know how to treat these types of cardiac dysfunction, it is necessary to clearly understand the basics of the normal cycle of cardiac activity.

Video: lectures on the cardiac cycle

October 23, 2017 No comments

A functional measure of the pumping function of the heart is considered to be the cardiac cycle, which includes 2 phases - systole and diastole.

Diastole phase

At the beginning of diastole, immediately after the closure of the aortic valve, the pressure in the left ventricle is less than the aortic pressure, but higher than the atrial pressure, because The aortic and mitral valves are closed. This is a short isovolumic period of diastole (period of isometric relaxation of the ventricle). Ventricular pressure then drops below atrial pressure, causing the mitral valve to open and blood to flow from the atrium into the ventricle.

There are three periods in the filling of the ventricle:

1) the early (fast) filling phase, during which the greatest flow of blood accumulated in the atrium into the ventricle occurs. Ventricular filling then slows; in this case, the atrium acts as a rope for returning blood to the heart (diastasis);

2) diastasis [(Greek diastasis - separation) in cardiology is an indicator of the contractile function of the left atrium, representing the pressure difference in the left atrium at the end and beginning of diastole] and

3) contraction of the atrium, which ensures filling of the ventricle to its end-diastolic volume.

During this phase, the blood partially flows retrograde through the openings of the pulmonary veins due to the absence of valves in them.

During diastole, blood flows from the peripheral vessels of the systemic circulation are directed to the right atrium, and from the pulmonary circulation to the left. Blood moves from the atria to the ventricles when the tricuspid and mitral valves open.

In the early diastole phase, blood flows freely from the venous vessels into the atria and, when the tricuspid and mitral valves open, fills the right and left ventricles, respectively. The contraction of the atria (atrial systole) that occurs at the end of ventricular diastole provides additional active blood flow into the ventricular chambers. This final flow of blood accounts for 20-30% of the total volume of diastolic filling of the ventricles.

Systole phase

Then the process of contraction of the ventricles begins - systole. During systole, intraventricular cavity pressure increases and when it exceeds the pressure in the atria, the mitral and tricuspid valves are forced to close. During the contraction of the ventricles, there is a short period of time when all four valves (orifices) of the heart are closed.

This is determined by the fact that the pressure in the ventricles can be high enough to close the mitral and tricuspid valves, but not high enough to open the aortic and pulmonary valves. When all heart valves are closed, ventricular volumes do not change. This short period at the beginning of ventricular systole is called the period of isovolumic contraction.

As the ventricles continue to contract, the pressure in them begins to exceed the pressure in the aorta and pulmonary artery, which ensures the opening of the aortic and pulmonary valves and the ejection of blood from the ventricles (the period of heterometric contraction, or the ejection phase). When systole ends and the pressure in the ventricles falls below the pressure in the pulmonary artery and aorta, the pulmonary and aortic valves close.

Although the cardiac cycles of the right and left hearts are completely identical, the physiology of the two systems is different. This difference is functional in nature and in modern cardiology it is differentiated on the basis of compliance (from English, compliance - conformity, agreement) of systems. In the aspect of the issue under discussion, "compliance" is a measure of the relationship between pressure (P) and volume (V) in a closed hemodynamic system. Compliance reflects the regulatory component of the system. There are systems with high and low compliance. The right heart system, which carries blood through the right heart (right atrium and ventricle) and in the vessels of the pulmonary artery, is characterized by high compliance. In this “venous system”, significant fluctuations in blood volume, including its increase, in the right ventricle under normal physiological conditions do not significantly affect the pressure in the vessels of the pulmonary circulation.

Thanks to the high compliance of the right ventricle and the vessels of the pulmonary artery system, a full systolic ejection of blood from the right ventricle into the pulmonary artery is ensured, in which the pressure is very low - in the range from 25 to 30 mm Hg. Art., which is approximately 1/4-1/5 of the level of normal systemic blood pressure (100-140 mm Hg).

Thus, the normally thin-walled, i.e., relatively low-power, right ventricle copes with pumping large volumes of blood due to its high functional compatibility (high compliance) with the pulmonary artery. If this compliance had not been formed in evolution, then under conditions of increased blood supply to the right ventricle (for example, non-closure of the interventricular septum with discharge of blood from the left ventricle to the right, hypervolemia), pulmonary hypertension would have developed (i.e., increased pressure in the pulmonary artery) - severe form of pathology with a high risk of death.

In contrast to the right heart and pulmonary circulation, the left heart and systemic circulation are a low-compliance system. The structures included in this “high pressure” arterial system differ significantly from the system of the right heart: the left ventricle is thicker and more massive than the right; the aortic and mitral valves are thicker than the pulmonary and tricuspid valves; systemic arteries of the muscular type, i.e. arterioles, are rather “thick-walled tubes”.

Normally, even a slight decrease in cardiac output leads to a noticeable increase in the tone of arterioles - resistive vessels (“faucets of the vascular system,” as I.M. Sechenov called them) and, accordingly, an increase in the level of systemic diastolic blood pressure, which mainly depends on the tone arterioles On the contrary, an increase in cardiac output is accompanied by a decrease in the tone of resistive vessels and a decrease in diastolic pressure.

These facts, i.e., multidirectional changes in blood volume and blood pressure, indicate that the “arterial system” of the left heart is a system with low compliance. So, the main factor determining blood flow in the venous system of the right heart is blood volume, and in the arterial system of the left heart - vascular tone, i.e. blood pressure.

Cardiac cycle - This is the systole and diastole of the heart, periodically repeating in a strict sequence, i.e. a period of time involving one contraction and one relaxation of the atria and ventricles.

In the cyclical functioning of the heart, two phases are distinguished: systole (contraction) and diastole (relaxation). During systole, the cavities of the heart are emptied of blood, and during diastole they are filled. The period that includes one systole and one diastole of the atria and ventricles and the following general pause is called cardiac cycle.

Atrial systole in animals lasts 0.1-0.16 s, and ventricular systole lasts 0.5-0.56 s. The total pause of the heart (simultaneous diastole of the atria and ventricles) lasts 0.4 s. During this period the heart rests. The entire cardiac cycle lasts for 0.8-0.86 s.

The work of the atria is less complex than the work of the ventricles. Atrial systole ensures the flow of blood into the ventricles and lasts 0.1 s. Then the atria enter the diastole phase, which lasts for 0.7 s. During diastole, the atria fill with blood.

The duration of the various phases of the cardiac cycle depends on the heart rate. With more frequent heart contractions, the duration of each phase, especially diastole, decreases.

Phases of the cardiac cycle

Under cardiac cycle understand the period covering one contraction - systole and one relaxation - diastole atria and ventricles - general pause. The total duration of the cardiac cycle at a heart rate of 75 beats/min is 0.8 s.

Heart contraction begins with atrial systole, lasting 0.1 s. The pressure in the atria rises to 5-8 mm Hg. Art. Atrial systole is replaced by ventricular systole lasting 0.33 s. Ventricular systole is divided into several periods and phases (Fig. 1).

Rice. 1. Phases of the cardiac cycle

Voltage period lasts 0.08 s and consists of two phases:

• phase of asynchronous contraction of the ventricular myocardium - lasts 0.05 s. During this phase, the excitation process and the subsequent contraction process spread throughout the ventricular myocardium. The pressure in the ventricles is still close to zero. By the end of the phase, the contraction covers all myocardial fibers, and the pressure in the ventricles begins to increase rapidly.
• isometric contraction phase (0.03 s) - begins with the slamming of the atrioventricular valves. In this case, I, or systolic, heart sound occurs. The displacement of the valves and blood towards the atria causes an increase in pressure in the atria. The pressure in the ventricles increases quickly: up to 70-80 mm Hg. Art. in the left and up to 15-20 mm Hg. Art. in the right.

The leaflet and semilunar valves are still closed, the volume of blood in the ventricles remains constant. Due to the fact that the fluid is practically incompressible, the length of the myocardial fibers does not change, only their tension increases. Blood pressure in the ventricles increases rapidly. The left ventricle quickly becomes round and hits the inner surface of the chest wall with force. In the fifth intercostal space, 1 cm to the left of the midclavicular line, the apical impulse is detected at this moment.

Towards the end of the period of tension, the rapidly increasing pressure in the left and right ventricles becomes higher than the pressure in the aorta and pulmonary artery. Blood from the ventricles rushes into these vessels.

Exile period blood from the ventricles lasts 0.25 s and consists of a fast phase (0.12 s) and a slow ejection phase (0.13 s). At the same time, the pressure in the ventricles increases: in the left one up to 120-130 mm Hg. Art., and in the right up to 25 mm Hg. Art. At the end of the slow ejection phase, the ventricular myocardium begins to relax and diastole begins (0.47 s). The pressure in the ventricles drops, blood from the aorta and pulmonary artery rushes back into the ventricular cavities and “slams” the semilunar valves, and a second, or diastolic, heart sound occurs.

The time from the beginning of ventricular relaxation to the “slamming” of the semilunar valves is called protodiastolic period(0.04 s). After the semilunar valves close, the pressure in the ventricles drops. The leaflet valves are still closed at this time, the volume of blood remaining in the ventricles, and therefore the length of the myocardial fibers, does not change, which is why this period is called the period isometric relaxation(0.08 s). Towards the end, the pressure in the ventricles becomes lower than in the atria, the atrioventricular valves open and blood from the atria enters the ventricles. Begins period of filling the ventricles with blood, which lasts 0.25 s and is divided into phases of fast (0.08 s) and slow (0.17 s) filling.

Vibration of the walls of the ventricles due to the rapid flow of blood to them causes the appearance of the third heart sound. Towards the end of the slow filling phase, atrial systole occurs. The atria pump additional blood into the ventricles ( presystolic period, equal to 0.1 s), after which a new cycle of ventricular activity begins.

Vibration of the walls of the heart, caused by contraction of the atria and additional flow of blood into the ventricles, leads to the appearance of the IV heart sound.

During normal listening of the heart, loud I and II tones are clearly audible, and quiet III and IV tones are detected only with graphical recording of heart sounds.

In humans, the number of heartbeats per minute can fluctuate significantly and depends on various external influences. When performing physical work or sports activity, the heart can contract up to 200 times per minute. In this case, the duration of one cardiac cycle will be 0.3 s. An increase in the number of heartbeats is called tachycardia, at the same time, the cardiac cycle decreases. During sleep, the number of heart contractions decreases to 60-40 beats per minute. In this case, the duration of one cycle is 1.5 s. A decrease in the number of heartbeats is called bradycardia, while the cardiac cycle increases.

Structure of the cardiac cycle

Cardiac cycles follow at a frequency set by the pacemaker. The duration of a single cardiac cycle depends on the frequency of heart contractions and, for example, at a frequency of 75 beats/min it is 0.8 s. The general structure of the cardiac cycle can be represented in the form of a diagram (Fig. 2).

As can be seen from Fig. 1, with a cardiac cycle duration of 0.8 s (beat frequency 75 beats/min), the atria are in a systole state of 0.1 s and in a diastole state of 0.7 s.

Systole- phase of the cardiac cycle, including contraction of the myocardium and expulsion of blood from the heart into the vascular system.

Diastole- phase of the cardiac cycle, including relaxation of the myocardium and filling of the cavities of the heart with blood.

Rice. 2. Scheme of the general structure of the cardiac cycle. Dark squares show the systole of the atria and ventricles, light squares show their diastole.

The ventricles are in systole for about 0.3 s and in diastole for about 0.5 s. At the same time, the atria and ventricles are in diastole for about 0.4 s (total diastole of the heart). Ventricular systole and diastole are divided into periods and phases of the cardiac cycle (Table 1).

Table 1. Periods and phases of the cardiac cycle

Asynchronous contraction phase - the initial stage of systole, during which a wave of excitation spreads across the ventricular myocardium, but there is no simultaneous contraction of cardiomyocytes and the pressure in the ventricles is from 6-8 to 9-10 mm Hg. Art.

Isometric contraction phase - the stage of systole, during which the atrioventricular valves close and the pressure in the ventricles quickly increases to 10-15 mmHg. Art. in the right and up to 70-80 mm Hg. Art. in the left.

Rapid expulsion phase - the stage of systole, during which there is an increase in pressure in the ventricles to a maximum value of 20-25 mm Hg. Art. in the right and 120-130 mm Hg. Art. in the left and blood (about 70% of systolic output) enters the vascular system.

Slow expulsion phase- the stage of systole, in which blood (the remaining 30% of systolic output) continues to flow into the vascular system at a slower rate. The pressure gradually decreases in the left ventricle from 120-130 to 80-90 mmHg. Art., in the right - from 20-25 to 15-20 mm Hg. Art.

Protodiastolic period- the transition period from systole to diastole, during which the ventricles begin to relax. The pressure decreases in the left ventricle to 60-70 mm Hg. Art., in temperament - up to 5-10 mm Hg. Art. Due to greater pressure in the aorta and pulmonary artery, the semilunar valves close.

Isometric relaxation period - stage of diastole, during which the ventricular cavities are isolated by closed atrioventricular and semilunar valves, they relax isometrically, the pressure approaches 0 mmHg. Art.

Rapid filling phase - the stage of diastole, during which the atrioventricular valves open and blood rushes into the ventricles at high speed.

Slow filling phase - the stage of diastole, during which blood slowly flows through the vena cava into the atria and through the open atrioventricular valves into the ventricles. At the end of this phase, the ventricles are 75% filled with blood.

Presystolic period - the stage of diastole coinciding with atrial systole.

Atrial systole - contraction of the atrial muscles, in which the pressure in the right atrium rises to 3-8 mm Hg. Art., in the left - up to 8-15 mm Hg. Art. and each ventricle receives about 25% of the diastolic blood volume (15-20 ml).

Table 2. Characteristics of the phases of the cardiac cycle

Contraction of the myocardium of the atria and ventricles begins following their excitation, and since the pacemaker is located in the right atrium, its action potential initially spreads to the myocardium of the right and then the left atrium. Consequently, the myocardium of the right atrium responds with excitation and contraction somewhat earlier than the myocardium of the left atrium. Under normal conditions, the cardiac cycle begins with atrial systole, which lasts 0.1 s. The non-simultaneous coverage of the myocardial excitation of the right and left atria is reflected by the formation of the P wave on the ECG (Fig. 3).

Even before atrial systole, the AV valves are open and the cavities of the atria and ventricles are already largely filled with blood. Stretch Rate the thin walls of the atrial myocardium with blood is important for irritation of mechanoreceptors and the production of atrial natriuretic peptide.

Rice. 3. Changes in cardiac performance in different periods and phases of the cardiac cycle

During atrial systole, pressure in the left atrium can reach 10-12 mm Hg. Art., and in the right - up to 4-8 mm Hg. Art., the atria additionally fill the ventricles with a volume of blood that at rest is about 5-15% of the volume located in the ventricles by this time. The volume of blood entering the ventricles during atrial systole can increase during physical activity and amount to 25-40%. The volume of additional filling can increase to 40% or more in people over 50 years of age.

The flow of blood under pressure from the atria promotes stretching of the ventricular myocardium and creates conditions for their more efficient subsequent contraction. Therefore, the atria play the role of a kind of amplifier of the contractile capabilities of the ventricles. With this atrial function (for example, with atrial fibrillation), the efficiency of the ventricles decreases, a decrease in their functional reserves develops, and the transition to insufficiency of myocardial contractile function accelerates.

At the moment of atrial systole, an a-wave is recorded on the venous pulse curve; in some people, when recording a phonocardiogram, a 4th heart sound may be recorded.

The volume of blood located after atrial systole in the ventricular cavity (at the end of their diastole) is called end-diastolic. It consists of the volume of blood remaining in the ventricle after the previous systole ( end-systolic volume), the volume of blood that filled the cavity of the ventricle during its diastole before atrial systole, and the additional volume of blood that entered the ventricle during atrial systole. The amount of end-diastolic blood volume depends on the size of the heart, the volume of blood flowing from the veins and a number of other factors. In a healthy young person at rest, it can be about 130-150 ml (depending on age, gender and body weight, it can fluctuate from 90 to 150 ml). This volume of blood slightly increases the pressure in the ventricular cavity, which during atrial systole becomes equal to the pressure in them and can fluctuate in the left ventricle within 10-12 mm Hg. Art., and in the right - 4-8 mm Hg. Art.

For a period of time 0.12-0.2 s, corresponding to the interval PQ on the ECG, the action potential from the SA node spreads to the apical region of the ventricles, in the myocardium of which the excitation process begins, quickly spreading in the directions from the apex to the base of the heart and from the endocardial surface to the epicardial. Following the excitation, myocardial contraction or ventricular systole begins, the duration of which also depends on the heart rate. Under resting conditions it is about 0.3 s. Ventricular systole consists of periods voltage(0.08 s) and exile(0.25 s) blood.

Systole and diastole of both ventricles occur almost simultaneously, but occur under different hemodynamic conditions. A further, more detailed description of the events occurring during systole will be considered using the example of the left ventricle. For comparison, some data for the right ventricle are provided.

The period of ventricular tension is divided into phases asynchronous(0.05 s) and isometric(0.03 s) contractions. The short-term phase of asynchronous contraction at the beginning of systole of the ventricular myocardium is a consequence of the non-simultaneous coverage of excitation and contraction of various parts of the myocardium. Excitation (corresponds to the wave Q on the ECG) and myocardial contraction occurs initially in the area of ​​the papillary muscles, the apical part of the interventricular septum and the apex of the ventricles and spreads to the remaining myocardium in about 0.03 s. This coincides in time with the registration of the wave on the ECG Q and the ascending part of the tooth R to its top (see Fig. 3).

The apex of the heart contracts before its base, so the apical part of the ventricles is pulled towards the base and pushes the blood in the same direction. At this time, areas of the ventricular myocardium that are not affected by excitation can stretch slightly, so the volume of the heart practically does not change, the blood pressure in the ventricles does not yet change significantly and remains lower than the blood pressure in large vessels above the tricuspid valves. Blood pressure in the aorta and other arterial vessels continues to fall, approaching the minimum diastolic pressure value. However, the tricuspid vascular valves remain closed.

At this time, the atria relax and the blood pressure in them decreases: for the left atrium, on average, from 10 mm Hg. Art. (presystolic) up to 4 mm Hg. Art. By the end of the phase of asynchronous contraction of the left ventricle, the blood pressure in it rises to 9-10 mm Hg. Art. Blood, under pressure from the contracting apical part of the myocardium, picks up the leaflets of the AV valves, they close, taking a position close to horizontal. In this position, the valves are held by tendon threads of the papillary muscles. The shortening of the size of the heart from its apex to the base, which, due to the unchanged size of the tendon filaments, could lead to eversion of the valve leaflets into the atria, is compensated by contraction of the papillary muscles of the heart.

At the moment of closure of the atrioventricular valves, the 1st systolic sound heart, the asynchronous phase ends and the isometric contraction phase begins, which is also called the isovolumetric (isovolumic) contraction phase. The duration of this phase is about 0.03 s, its implementation coincides with the time interval in which the descending part of the wave is recorded R and the beginning of the tooth S on the ECG (see Fig. 3).

From the moment the AV valves close, under normal conditions the cavity of both ventricles becomes sealed. Blood, like any other fluid, is incompressible, so contraction of myocardial fibers occurs at their constant length or in an isometric mode. The volume of the ventricular cavities remains constant and myocardial contraction occurs in an isovolumic mode. The increase in tension and force of myocardial contraction under such conditions is converted into rapidly increasing blood pressure in the cavities of the ventricles. Under the influence of blood pressure on the area of ​​the AV septum, a short-term shift occurs towards the atria, is transmitted to the inflowing venous blood and is reflected by the appearance of a c-wave on the venous pulse curve. Within a short period of time - about 0.04 s, the blood pressure in the cavity of the left ventricle reaches a value comparable to its value at this moment in the aorta, which decreased to a minimum level - 70-80 mm Hg. Art. Blood pressure in the right ventricle reaches 15-20 mm Hg. Art.

The excess of blood pressure in the left ventricle over the diastolic blood pressure in the aorta is accompanied by the opening of the aortic valves and the change from the period of myocardial tension to the period of blood expulsion. The reason for the opening of semilunar valves of blood vessels is the blood pressure gradient and the pocket-like feature of their structure. The valve leaflets are pressed against the walls of the vessels by the flow of blood expelled into them by the ventricles.

Exile period blood lasts about 0.25 s and is divided into phases quick expulsion(0.12 s) and slow exile blood (0.13 s). During this period, the AV valves remain closed, the semilunar valves remain open. The rapid expulsion of blood at the beginning of the period is due to a number of reasons. About 0.1 s has passed since the onset of cardiomyocyte excitation and the action potential is in the plateau phase. Calcium continues to flow into the cell through open slow calcium channels. Thus, the tension of the myocardial fibers, which was already high at the beginning of expulsion, continues to increase. The myocardium continues to compress the decreasing blood volume with greater force, which is accompanied by a further increase in its pressure in the ventricular cavity. The blood pressure gradient between the ventricular cavity and the aorta increases and blood begins to be expelled into the aorta at high speed. During the rapid ejection phase, more than half of the stroke volume of blood expelled from the ventricle during the entire ejection period (about 70 ml) is ejected into the aorta. By the end of the phase of rapid expulsion of blood, the pressure in the left ventricle and aorta reaches its maximum - about 120 mm Hg. Art. in young people at rest, and in the pulmonary trunk and right ventricle - about 30 mm Hg. Art. This pressure is called systolic. The phase of rapid expulsion of blood occurs during the period of time when the end of the wave is recorded on the ECG S and isoelectric part of the interval ST before the beginning of the tooth T(see Fig. 3).

Under the condition of rapid expulsion of even 50% of the stroke volume, the rate of blood flow into the aorta in a short time will be about 300 ml/s (35 ml/0.12 s). The average rate of blood outflow from the arterial part of the vascular system is about 90 ml/s (70 ml/0.8 s). Thus, more than 35 ml of blood enters the aorta in 0.12 s, and during the same time about 11 ml of blood flows out of it into the arteries. Obviously, in order to accommodate for a short time a larger volume of inflowing blood compared to outflow, it is necessary to increase the capacity of the vessels receiving this “excess” volume of blood. Part of the kinetic energy of the contracting myocardium will be spent not only on the expulsion of blood, but also on stretching the elastic fibers of the wall of the aorta and large arteries to increase their capacity.

At the beginning of the phase of rapid expulsion of blood, stretching of the vessel walls is relatively easy, but as more blood is expelled and the vessels are stretched more and more, the resistance to stretching increases. The stretching limit of the elastic fibers is exhausted and the hard collagen fibers of the vessel walls begin to undergo stretching. The flow of blood is prevented by the resistance of peripheral vessels and the blood itself. The myocardium needs to spend a large amount of energy to overcome these resistances. The potential energy of muscle tissue and elastic structures of the myocardium itself, accumulated during the phase of isometric tension, is exhausted and the force of its contraction decreases.

The rate of blood expulsion begins to decrease and the rapid expulsion phase is replaced by the slow blood expulsion phase, which is also called phase of reduced expulsion. Its duration is about 0.13 s. The rate of decrease in ventricular volume decreases. At the beginning of this phase, blood pressure in the ventricle and aorta decreases at almost the same rate. By this time, the slow calcium channels close, and the plateau phase of the action potential ends. Calcium entry into cardiomyocytes decreases and the myocyte membrane enters phase 3—terminal repolarization. Systole, the period of blood expulsion, ends and ventricular diastole begins (corresponding in time to phase 4 of the action potential). The implementation of reduced expulsion occurs during the period of time when a wave is recorded on the ECG T, and the end of systole and the beginning of diastole occur at the end of the tooth T.

During the systole of the ventricles of the heart, more than half of the end-diastolic volume of blood (about 70 ml) is expelled from them. This volume is called stroke volume of blood. Stroke blood volume can increase with increasing myocardial contractility and, conversely, decrease with insufficient contractility (see below for indicators of the pumping function of the heart and myocardial contractility).

The blood pressure in the ventricles at the beginning of diastole becomes lower than the blood pressure in the arterial vessels leaving the heart. The blood in these vessels experiences the forces of stretched elastic fibers of the vessel walls. The lumen of the vessels is restored and a certain amount of blood is displaced from them. Part of the blood flows to the periphery. The other part of the blood is displaced in the direction of the ventricles of the heart, and during its reverse movement fills the pockets of the tricuspid vascular valves, the edges of which are closed and held in this state by the resulting difference in blood pressure.

The time interval (about 0.04 s) from the beginning of diastole to the closure of the vascular valves is called protodiastolic interval. At the end of this interval, the 2nd diastolic beat of the heart is recorded and audible. When recording an ECG and a phonocardiogram simultaneously, the onset of the 2nd sound is recorded at the end of the T wave on the ECG.

Diastole of the ventricular myocardium (about 0.47 s) is also divided into periods of relaxation and filling, which, in turn, are divided into phases. From the moment the semilunar vascular valves close, the ventricular cavities become 0.08 closed, since the AV valves still remain closed at this time. Relaxation of the myocardium, caused mainly by the properties of the elastic structures of its intra- and extracellular matrix, is carried out under isometric conditions. In the cavities of the ventricles of the heart, less than 50% of the end-diastolic volume of blood remains after systole. The volume of the ventricular cavities does not change during this time, the blood pressure in the ventricles begins to decrease rapidly and tends to 0 mmHg. Art. Let us remember that by this time blood continued to return to the atria for about 0.3 s and the pressure in the atria gradually increased. At the moment when the blood pressure in the atria exceeds the pressure in the ventricles, the AV valves open, the phase of isometric relaxation ends and the period of filling the ventricles with blood begins.

The filling period lasts about 0.25 s and is divided into fast and slow filling phases. Immediately after the opening of the AV valves, blood quickly flows along a pressure gradient from the atria into the ventricular cavity. This is facilitated by a certain suction effect of the relaxing ventricles, associated with their straightening under the action of elastic forces that arise during compression of the myocardium and its connective tissue framework. At the beginning of the rapid filling phase, sound vibrations in the form of the 3rd diastolic heart sound can be recorded on the phonocardiogram, which are caused by the opening of the AV valves and the rapid passage of blood into the ventricles.

As the ventricles fill, the difference in blood pressure between the atria and ventricles decreases, and after about 0.08 s, the rapid filling phase is replaced by a slow filling phase of the ventricles with blood, which lasts about 0.17 s. The filling of the ventricles with blood in this phase is carried out mainly due to the preservation in the blood moving through the vessels of the residual kinetic energy imparted to it by the previous contraction of the heart.

0.1 s before the end of the phase of slow filling of the ventricles with blood, the cardiac cycle ends, a new action potential arises in the pacemaker, the next atrial systole occurs and the ventricles are filled with end-diastolic volumes of blood. This period of time of 0.1 s, which completes the cardiac cycle, is sometimes also called periodadditionalfilling ventricles during atrial systole.

An integral indicator characterizing mechanical is the volume of blood pumped by the heart per minute, or minute blood volume (MBV):

IOC = heart rate. UO,

where heart rate is the heart rate per minute; SV - stroke volume of the heart. Normally, at rest, the IOC for a young man is about 5 liters. Regulation of the IOC is carried out by various mechanisms through changes in heart rate and (or) stroke volume.

The influence on heart rate can be exerted through changes in the properties of cardiac pacemaker cells. The influence on stroke volume is achieved through the effect on the contractility of myocardial cardiomyocytes and the synchronization of its contraction.

Lesson Objectives

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

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

Educational: the formation of a scientific worldview using specific examples of scientific discoveries and medical successes.

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

Form of conduct: lesson at the museum - correspondence excursion.

Decor: on the board “Route sheet for the exhibition of the Museum “Cardiology””, epigraph: “The heart is like a millstone, yielding flour when enough grain is poured in, but erased when it is not poured in” (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 the poem “Heart” by E. Mezhelaitis.

What is a heart?
Is the stone hard?
An apple with crimson-red skin?
Maybe between the ribs and the aorta
Is there a beating ball that looks like a globe on Earth?
One way or another, everything earthly
Fits within its boundaries
Because he has no peace
There's something to do with everything.

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

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

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

Non-nuclear formed elements of blood containing hemoglobin - ... ( red blood cells).

A condition of the body in which the number of red blood cells in the blood or the hemoglobin content in them decreases - ... ( anemia).

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

The body’s protective reaction, for example against infections - ... ( inflammation).

The ability of organisms to protect themselves from 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 are ... ( antibodies).

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

The vessels through which blood flows from the heart are... ( arteries).

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

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

Task 2 (group work on problematic issues)

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

I.P. Pavlov said: “The body has an “extraordinary” reaction in which the body sacrifices some part to save the whole.” What does this mean? ( 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? ( Approximately 640 kg.)

Consider microscopic specimens of human and frog blood. Point out 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 staff will introduce you to the museum.

Guide (display of a pulsating heart on the screen). Listen. No matter what you do - sleep, eat, run - there is always a muffled, rhythmic knocking sound. This is your heart beating. Make a fist with your hand and you will see how big it is. The heart is a muscular organ that constantly contracts and forces blood to move throughout your body.

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

It is covered with a thin and dense membrane, forming 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 serous fluid that moisturizes the heart and reduces friction during its contractions.

The heart wall has three layers. The epicardium is the outer serous layer covering the heart (fused with the pericardium). Myocardium is the middle muscle layer formed by striated cardiac muscle. Each muscle fiber contains 1–2 nuclei and many mitochondria. Endocardium is the inner epithelial layer.

Let's figure out 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 the bicuspid valve - it has only two leaflets (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 tricuspid (tricupsidal). The valves open and close the passage between the atria and ventricles, causing 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 strictly in one direction: through the arteries from the heart, through the veins to the heart, from the atria to the ventricles.

External structure of the heart

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

Metabolic processes occur extremely intensively in the heart: muscle cells contain many mitochondria, and the tissue is well supplied with blood. The heart's mass makes up about 0.5% of the body's mass, with 10% of the blood ejected by the aorta going into the coronary or coronary vessels that supply the heart itself. Aorta (Greek) – “straight artery”.

Student. What ensures rapid contraction of the heart chamber?

Guide. The muscle fibers branch and interconnect at their ends, forming a complex network, which ensures rapid contraction of the chamber as a single structure.

Student. How does the heart work?

Guide. The heart is a tireless motor that knows no days off, no holidays, no vacations. During the day, the heart contracts almost 100 thousand times, and in 1 hour it pumps about 300 liters of blood (demonstration of the “heart-pump”). The heart expends so much energy per beat 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 let’s look at the work of the heart using 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 leaflet valves are open, and the semilunar valves are closed. Contraction (systole) of the ventricles lasts about 0.3 s. In this case, the atria are relaxed, the leaflet valves are closed (the tendon threads prevent them from bending and blood from flowing 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 heart muscle are involved in 40 consecutive movements. The optimal operating mode of the heart: the atria work for 0.1 s and rest for 0.7 s, and the ventricles work for 0.3 s and rest for 0.5 s.

Independent work: fill out the table “Cardiac cycle”.

Table. Cardiac cycle

Task (for excursionists). The man is 80 years old. Determine how many years the ventricles of his heart rested, assuming that the average heart rate was 70 beats per minute. ( 46 years old.)

Student. What causes the high performance of the heart?

Guide. It is ensured by the following factors:

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

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

Guide. Let us recall the methods known to us for regulating functions in the body.

Firstly, this is nervous regulation, and secondly, it is the humoral regulation of heart activity. The central nervous system constantly controls the functioning of the heart through nerve impulses. In the medulla oblongata there is a circulatory center, from which a pair of parasympathetic nerves emerge, which reduce the frequency and strength of contractions. Strong stimulation of the vagus nerve causes cardiac arrest (Goltz's 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, speeding up and intensifying heart contractions. Thus, the heart has double innervation: parasympathetic and sympathetic.

Humoral regulation of heart activity is ensured by substances circulating in the blood. The work of the heart is inhibited by: acetylcholine, sodium salts, increased blood pH. The work of the heart is enhanced by adrenaline (in case of cardiac arrest it is injected directly into the heart muscle), potassium salts, and a decrease in pH. Hormones that influence cardiac activity are the secretions of the endocrine glands: thyroxine (thyroid gland), insulin (pancreas), corticosteroid hormones (adrenal glands), pituitary hormones.

Nervous and humoral regulation are closely interconnected and constitute a single mechanism for regulating heart contractions.

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

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

Automaticity 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 thousand times per day, 40 million times per year, and about 2.5 billion times throughout life. At the same time, it pumps the following volumes of blood: in 1 minute - 5.5 liters, in 24 hours - 8 thousand liters, in 70 years - about 200 million liters.

Student. What important events were 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 named after. A.N. Bakuleva. In 1967, Cape Town surgeon Prof. Christian Barnard performed the first human heart transplant operation, and exactly 20 years later the same operation was performed by Prof. IN AND. Shumakov in the USSR.

Generalization and systematization of knowledge

Exercise 1. Match the 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.
• Inner layer.
• Vessels carrying blood from the heart are “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 vena cava flows.
• The parts of the heart that push blood into the arteries.
• Education (from German. clappe- cover, valve, closing the lumen), preventing the passage of blood from the ventricles into 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, G – 6, I – 4, K – 10, L – 15, M – 5, N – 14, O – 13, P – 11.

Independent work based on the results of the excursion

Creative task: design and defense of the teaching aid “The Human Heart”.

Summarizing

Homework

Study the material about the structure and function of the heart in the textbook, solve the problem.

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