BLOOD AND LYMPHO CIRCULATION

The delivery of oxygen and nutrients to the tissues and cells of mammals and humans, as well as the excretion of their metabolic products, are provided by blood circulating through a closed cardiovascular system, consisting of the heart and two circulation circles: large and small. The systemic circulation begins from the left ventricle of the heart, from which arterial blood enters the aorta. Passing through the arteries, arterioles, capillaries of all organs except the lungs, it gives them oxygen and nutrients, and takes away carbon dioxide and metabolic products. Then the blood is collected in venules and veins and through the superior and inferior vena cava enters the right atrium.

The lesser circulation begins in the right ventricle of the heart, from where venous blood is directed to the pulmonary artery. After passing through the pulmonary capillaries, the blood is freed from carbon dioxide, oxygenated and, already as an arterial blood, enters through the pulmonary veins into the left atrium.

Physiology of the heart Properties of the heart muscle

The heart muscle has the following properties: 1) automation - the ability of the heart to contract rhythmically under the influence of impulses that arise in itself; 2) excitability - the ability of the heart to come into a state of excitation under the influence of an irritant; 3) conductivity - the ability of the heart muscle to conduct excitation; 4) contractility - the ability to change its shape and size under the influence of an irritant, as well as a tensile force or blood.

Automation

The substratum of automatism in the heart is a specific buccal tissue, or conduction system of the heart which consists of sinoatrial(sinoatrial) (CA) node, located in the wall of the right atrium at the confluence of the superior vena cava into it, atrioventricular(atrioventricular) knot, located in the interatrial septum at the border of the atria and ventricles. The bundle starts from the atrioventricular node Gisa. Having passed into the thickness of the interventricular septum, it is divided into the right and left legs, ending in terminal branches - Purkinje fibers. The apex of the heart does not have automaticity, but only contractility, since it lacks elements of the conduction system of the heart.

AT normal conditions pacemaker, or pacemaker is the sinoatrial node. The frequency of discharges of the sinoatrial node at rest is 70 per minute. The atrioventricular node is a second-order pacemaker with a frequency of 40-50 per minute. He takes on the role of a pacemaker if, for some reason, excitation from the SA cannot pass to the atria in case of atrioventricular blockade or in violation of the ventricular conduction system. If all the main pacemakers are affected, then very rare impulses (20 imp/s) can occur in the Purkinje fibers - this is a 3rd order pacemaker.

Therefore, there is heart automaticity gradient, according to which the degree of automation is higher, the closer the given section of the conducting system is to the sinus node.

Electrical activity of myocardial cells and the conduction system of the heart

The action potential of cardiomyocytes begins with a rapid reversion of the membrane potential, which is -90mV and created due to the K + potential, to the peak of AP (+30mV) (Fig. 11). This is phase of rapid depolarization, due to a short significant increase in the permeability for Na "1", which rushes like an avalanche into the cell. The fast depolarization phase is very short and is only 1-2ms. The initial input of Na + is rapidly inactivated, however, membrane depolarization continues due to the activation of slow sodium-calcium channels, and the input of Ca 2+ leads to the development PD plateau - this is a specific feature of myocardial cells. During this period, fast sodium channels are inactivated and the cell becomes absolutely unexcitable. This is phase of absolute refractoriness. At the same time, potassium channels are activated, and K + ions leaving the cell create phase of rapid repolarization membranes.

The acceleration of the repolarization process occurs due to the closure of calcium channels. At the end of the repolarization period, potassium channels are gradually closed and sodium channels are reactivated. This leads to the restoration of the excitability of the cardiomyocyte and the appearance of a relative refractory phase. The duration of AP of a cardiomyocyte is 200 - 400ms.

R
is. 11. Schemes of action potentials of various parts of the heart, the contraction curve and phases of excitability of the heart muscle: BUT - myocardial cell action potential diagram (/), contraction curve (II) and phases of excitability (III) heart muscle; 1 - action potential of myocardial cells: / - rapid depolarization; 2 - peak, 3 - plateau, 4 - fast repolarization; II - contraction curve: a - contraction phase, b - relaxation phase; III - excitability curve: 5 - absolute refractory phase, b - relative refractory phase, 7 - phase of supernormal excitability; B - scheme of the action potential of the pacemaker cell (sinoauricular node): MDP - maximum diastolic potential; DMD - slow diastolic depolarization

The potassium-sodium pump, which creates the resting potential or the membrane potential of the myocardiocyte, can be inactivated by the action of cardiac glycosides (digitalis, strophanthin), which also lead to an increase in the intracellular concentration of Na +, a decrease in the intensity of the exchange of intracellular Ca 2+ to extracellular Na + , and the accumulation of Ca 2 + in a cage. As a result, myocardial contractility becomes greater. It can be increased both by increasing the extracellular concentration of Ca 2+ and by using substances (adrenaline, norepinephrine) that accelerate the entry of Ca 2+ during PD. If Ca 2+ is removed from the external environment or Ca 2+ entry is blocked during PD with the help of calcium antagonist substances such as verapamil, nifedipine, etc., then the contractility of the heart decreases.

The cells of the conduction system of the heart and, in particular, the pacemaker cells with automaticity, in contrast to the cells of the working myocardium-cardiomyocytes, can spontaneously depolarize to a critical level. In such cells, the phase of repolarization is followed by the phase slow diastolic depolarization. (MDD), which leads to a decrease in MP to a threshold level and the emergence of PD. DMD is a local, non-propagating excitation, in contrast to PD, which is

spreading excitement.

Thus, pacemaker cells differ from cardiomyocytes: 1) by a low level of MP - about 50-70 mV, 2) by the presence of DMD, 3) by a form of AP close to the peak-like potential, 4) by a low amplitude of AP - 30-50 mV without the phenomenon of reversion (overshoot).

Features of the electrical activity of pacemaker cells are due to a number of processes occurring on their membrane. First, these cells, even under “resting” conditions, have an increased permeability for Na + ions, which leads to a decrease in MP. Secondly, during the period of repolarization, only slow sodium-calcium channels open on the membrane, since fast sodium channels are already inactivated due to low MP. In the cells of the sinoatrial node, during the period of repolarization, open potassium channels are quickly inactivated, but sodium permeability increases, against which DMD and then PD occur. The action potential of the sinoatrial node extends to all other parts of the conduction system of the heart.

Thus, the sinoatrial node imposes its rhythm on all the "slave" departments of the conducting system. If the excitation does not come from the main pacemaker, then the "latent" pacemakers, i.e. automatized heart cells take on the function of a new pacemaker, DMD and PD are also born in them, and the heart continues its work.

Physiology of circulation

The main properties of the heart muscle

The main properties of the heart muscle include automatism, excitability, conductivity, contractility.

The ability to rhythmically contract without any visible irritation under the influence of impulses arising in the organ itself is a characteristic feature of the heart. This property is called automatism.

The appearance of impulses is associated with the function of atypical muscle cells - pacemakers embedded in the nodes of the heart. First node conduction system is located at the confluence of the vena cava into the right atrium - sinoatrial node. It is the main center of heart automation - pacemaker of the first order.

From the node, the excitation spreads to the working cells of the atrial myocardium both diffusely and along special intracardiac conducting bundles. Both streams reach second node– atrioventricular. It is located in the thickness of the cardiac septum on the border of the atria and ventricles. This node is pacemaker of the second order. Excitation through the atrioventricular node under normal conditions can only pass in one direction.

When the excitation passes through the atrioventricular node, the impulses are delayed by 0.02-0.04 s. This phenomenon has been named atrioventricular delay. Its functional significance lies in the fact that ventricular systole has time to complete during the delay, and their fibers will be in the refractory phase.

Third level is located in bundle of His and Purkinje fibers. The bundle of His originates from the atrioventricular node and forms two legs, one of which goes to the left, the other to the right ventricle. These legs branch into thinner pathways ending in Purkinje fibers that are in direct contact with myocardial working cells.

The centers of automation located in the conduction system of the ventricles are called pacemakers of the third order. Thus, the excitation along the legs of the bundle of His is directed to the apex of the heart and from there, along the branches of the legs and Purkinje fibers, it returns to the base of the heart. As a result of this, the contraction of the heart as a whole is carried out in a certain sequence: first, the atria contract, then the tops of the ventricles and their bases.

in the areas of the nodes are nerve cells. Their accumulations and numerous fibers form a dense nervous network. These nerve cells belong to the cardiac part of the metasympathetic nervous system.

To ensure the work of the heart necessary condition is an anatomical integrity of its conducting system. In the event that, for some reason, excitation does not occur in the first-order pacemaker or its transmission is blocked, the second-order pacemaker takes on the role of the pacemaker. If it is impossible to transfer excitation to the ventricles, they begin to contract in the rhythm of pacemakers of the third order. With transverse blockade, the atria and ventricles contract each in their own rhythm.

Damage to the pacemakers leads to complete cardiac arrest.

Cells of atypical muscle tissue are functionally heterogeneous. true pacemakers have the ability to spontaneously generate an action potential. The rest of the cells are potential pacemakers. They are discharged as a result of the excitement that has come to them. Potential pacemakers characterized by slow diastolic depolarization and a lower rate of discharges.

In contrast to the fibers of the contractile myocardium, the membrane of these cells during diastole acquires a greater ion permeability, which leads to the development slow diastolic depolarization– pacemaker potential. At this moment, a local non-propagating excitation occurs. In potential pacemakers, this phase reaches the threshold level later than in true pacemakers. With the achievement of the diastolic threshold level, a propagating AP occurs.

The ionic mechanism of the pacemaker potential is that during the repolarization phase cell membrane becomes more permeable to intracellular K +. As a result of the penetration of Na + and Ca + into the cell and a decrease in the rate of exit from the K + cell, a slow diastolic depolarization occurs. When the potential level decreases, a sharp increase in membrane permeability occurs, first for Na + and later for Ca + . This ion current leads to the appearance of the AP peak. The total AP amplitude is about 100 mV. With the closure of ion channels, a positive charge outer surface membrane is restored. The appearance of AP in the pacemaker cell is accompanied by the occurrence of depolarization in the slave working cardiomyocytes adjacent to it, which do not have automatism, and the spread of excitation.

Excitability of the heart muscle. Under the influence of electrical, chemical, thermal and other stimuli, the heart is able to come to state of arousal. The excitation process is based on the appearance of a negative electric potential in the initially excited area.

At rest, the membrane of cardiomyocytes is almost impermeable to Na + and partially to K +. As a result of the diffusion process, K + ions, leaving the cell, increase the positive charge on its surface. Inner side membrane becomes negative. Under the action of an irritant of any nature, the arrival of excitation from a neighboring cell or a pacemaker, Na + enters the cell. At this moment, a negative electric charge appears on the surface of the membrane and a potential reversion develops. The emerging potential depolarizes the membranes of neighboring cells, they have their own AP. Thus, the spread of excitation in the whole organ occurs.

This process is the same in the working myocardium and in pacemakers.

The action potential of a working myocardial cell lasts 0.3 s, which is about 150 times longer than in a skeletal muscle cell. During the development of AP, the cell is unexcitable to subsequent stimuli. Its refractory period is almost 100 times longer than the reflex period of skeletal muscle. This feature is extremely important for the function of the heart as an organ, since in response to frequent repeated irritations, the myocardium can respond with only one action potential and one contraction. All this creates conditions for the rhythmic contraction of the organ.

The long absolute refractory period of the heart muscle protects it from rapid re-excitation until the previous wave of depolarization has ended. This prevents a violation of the pumping function of the heart, the rhythmic alternation of systole and diastole. It excludes the possibility of tetanic contraction of the heart.

Contractility of the heart muscle. The heart does not respond to pre-threshold stimuli at all, but as soon as the strength of the stimulus reaches the threshold level, the maximum contraction of the myocardium occurs. A further increase in the strength of the irritating current does not change the magnitude of the contraction. Thus, the threshold irritation is at the same time the maximum. This feature of the contraction of the heart muscle is called the all-or-nothing law.

The subordination of the heart muscle to the all-or-nothing law is explained by its structural organization. In the heart muscle, individual muscle fibers are connected to each other by intercalated discs with very low electrical resistance. Therefore, when the impulse reaches the threshold value, excitation synchronously covers the entire muscle as a whole.

The contractility of the heart muscle is determined by the structural features of its fibers and the ratio between the length and tension of the sarcomere. Changes in the contractile force of the myocardium, which occur periodically, are carried out through two mechanisms of self-regulation: heterometric and homeometric.

At the core heterometric mechanism lies the change in the initial dimensions of the length of the myocardial fibers, which occurs when the value of the inflow of venous blood changes. In other words, than stronger heart stretched during diastole, the more it contracts during systole. This feature is called law of the heart frank– Starling.

homeometric mechanism is based on the direct action of biologically active substances on the metabolism of muscle fibers, the production of energy in them. Adrenaline and norepinephrine increase Ca + entry into the cell at the time of the development of the action potential, thereby causing an increase in heart contractions.

A series of successive events in a myocardial cell, starting with a membrane action potential and ending with a shortening of myofibrils, is called conjugation of excitation and contraction (electromechanical conjugation). The contraction of the heart muscle occurs in the same way as the skeletal one.

The structures responsible for conjugation of excitation and contraction of the myocardium include cross tube system especially strongly developed in the ventricles, and also longitudinal tube system, which is an intracellular reservoir of Ca +.

Cycle of the heart. Despite the great complexity of the processes underlying cardiac activity, the heart is built on the principle rhythm pump. Like any pump for pumping liquid, it is equipped with two types of valves located at the inlet and outlet of the ventricles.

In the relaxed state of the cone during diastole blood flows freely through the gap formed by the outgrowths. In the moment systole cone and a decrease in the diameter of the tube, the outgrowths tightly close and separate the cavity of the ventricle from the aorta.

The atria and ventricles separate flap valves(in the left half - bivalve, or mitral, in the right - tricuspid). During ventricular systole, these valves prevent backflow of blood into the atria. the valves of the aorta and pulmonary artery form pocket-like depressions facing the cavity of the vessel, surrounding the mouth of the vessels in the form of crescents, which is why they received the name semilunar valves. During ventricular systole, the valves are open and pressed against the inner walls of the vessels. At the time of diastole, blood rushing back from the aorta and pulmonary artery closes the valves. Closing the valves does not require special contraction energy, this act occurs as a result of a change in pressure in the cavities of the heart.

The contraction of the heart muscle is called systole her relaxation. diastole. With each systole of the ventricles, blood is ejected from the left ventricle into the aorta, from the right ventricle into the pulmonary artery, during diastole they are filled with blood coming from the atria. Blood enters the atria from the veins. Under normal conditions, systole and diastole are clearly coordinated in time. The period, including one contraction and subsequent relaxation of the heart, constitutes a cardiac cycle. Its total duration in humans is approximately 0.8 s. The cardiac cycle has three phases: atrial systole, ventricular systole, and a general pause.

The beginning of each cycle is atrial systole, lasting 0.1 s. During systole, the pressure in the atrial cavities increases, which leads to the expulsion of blood into the ventricles. The ventricles at this moment are relaxed, the atrioventricular valve flaps hang down and blood flows freely from the atria to the ventricles.

At the end of atrial systole, ventricular systole, the duration of which is 0.3 s. At the time of ventricular systole, the atria are already relaxed. Ventricular systole begins with an asynchronous contraction of their fibers resulting from the spread of excitation through the myocardium.

Due to the increase in intraventricular pressure, the atrioventricular valves quickly close. At this moment, the semilunar valves are also closed, so the ventricular cavity is closed and the volume of blood in the cavity remains constant. As a result of excitation, the tension of muscle fibers increases without changing their length. (isometric tension), which leads to an even greater increase in blood pressure. The wall of the left ventricle is stretched and hits the inner surface of the chest. Thus arises heart impulse.

When the blood pressure in the ventricles exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open, their petals press against the inner walls and come period of exile lasting approximately 0.25 s. With a drop in pressure, the semilunar valves close, thereby preventing the reverse flow of blood from the aorta and pulmonary artery, and the ventricular myocardium begins to relax. When the pressure in the ventricles is less than in the atria, the atrioventricular valves open, the ventricles fill with blood, which will be ejected in the next cycle, and whole heart diastole. It continues until the next atrial systole. This phase or general break, is of great importance, since during this period Ca + is withdrawn from myofibrils by the tubules of the sarcoplasmic reticulum.

The heart is rightfully the most important human organ, because it pumps blood and is responsible for the circulation of dissolved oxygen and other nutrients throughout the body. Stopping it for a few minutes can cause irreversible processes, dystrophy and death of organs. For the same reason, diseases and cardiac arrest are one of the most common causes of death.

What tissue forms the heart

The heart is a hollow organ about the size of a human fist. It is almost completely formed by muscle tissue, so many doubt: is the heart a muscle or an organ? The correct answer to this question is an organ formed by muscle tissue.

The heart muscle is called the myocardium, its structure differs significantly from the rest of the muscle tissue: it is formed by cardiomyocyte cells. Cardiac muscle tissue has a striated structure. It contains thin and thick fibers. Microfibrils are clusters of cells that form muscle fibers, collected in bundles of different lengths.

Properties of the heart muscle - ensuring the contraction of the heart and pumping blood.

Where is the heart muscle located? In the middle, between two thin shells:

• epicardium;
• Endocardium.

The myocardium accounts for the maximum amount of heart mass.

Mechanisms that provide reduction:

There are two phases in the heart cycle:

• Relative, in which cells respond to strong stimuli;
• Absolute - when for a certain period of time the muscle tissue does not respond even to very strong stimuli.

Compensation mechanisms

The neuroendocrine system protects the heart muscle from overload and helps maintain health. It provides the transmission of "commands" to the myocardium when it is necessary to increase the heart rate.

The reason for this may be:

• A certain state of internal organs;
• Reaction to environmental conditions;
• Irritants, including nervous.

Usually in these situations, in large numbers adrenaline and norepinephrine are produced, in order to “balance” their action, an increase in the amount of oxygen is required. The faster the heart rate, the more oxygenated blood is carried throughout the body.

Features of the structure of the heart

The heart of an adult weighs approximately 250-330 g. In women, the size of this organ is smaller, as is the volume of pumped blood.

It consists of 4 chambers:

• two atria;
• Two ventricles.

The pulmonary circulation often passes through the right heart, and the large circle passes through the left. Therefore, the walls of the left ventricle are usually larger: so that in one contraction the heart can push out a larger volume of blood.

The direction and volume of the ejected blood is controlled by valves:

• Bicuspid (mitral) - on the left side, between the left ventricle and the atrium;
• Three-leaved - on the right side;
• Aortic;
• Pulmonary.

Pathological processes in the heart muscle

With small malfunctions in the work of the heart, a compensatory mechanism is activated. But conditions are not uncommon when pathology develops, dystrophy of the heart muscle.

This leads to:

• oxygen starvation;
• Loss of muscle energy and a number of other factors.

Muscle fibers become thinner, and the lack of volume is replaced by fibrous tissue. Dystrophy usually occurs "in conjunction" with beriberi, intoxication, anemia, and disruption of the endocrine system.

The most common causes of this condition are:

• Myocarditis (inflammation of the heart muscle);
• atherosclerosis of the aorta;
• Increased blood pressure.

If it hurts heart: the most common diseases

There are quite a lot of heart diseases, and they are not always accompanied by pain in this particular organ.

Often in this area are given pain arising in other organs:

• Stomach
• Lungs;
• With chest trauma.

Causes and nature of pain

Pain in the region of the heart is:

1. sharp penetrating when it hurts even to breathe. They indicate an acute heart attack, heart attack and other dangerous conditions.
2. Aching occurs as a reaction to stress, with hypertension, chronic diseases of the cardiovascular system.
3. Spasm, which gives into the hand or shoulder blade.

Often heart pain is associated with:

Emotional experiences.

But often occurs at rest.

All pain in this area can be divided into two main groups:

1. Anginal or ischemic- associated with insufficient blood supply to the myocardium. Often occur at the peak of emotional experiences, also in some chronic diseases of angina pectoris, hypertension. It is characterized by a sensation of squeezing or burning of varying intensity, often radiating to the hand.
2. Cardiac disturb the patient almost constantly. They have a weak whining character. But the pain can become sharp with a deep breath or physical exertion.

The cardiac cycle is understood as successive alternations of contraction (systole) and relaxation (diastole) of the cavities of the heart, as a result of which blood is pumped from the venous to the arterial bed.

There are three phases in the cardiac cycle: 1. Atrial systole and ventricular diastole;

2. Atrial diastole and ventricular systole;

3. General diastole of the atria and ventricles.

Cardiac push is the beat of the heart against the chest. It is detected during an external examination of the animal and palpation on the left side of the chest. A cardiac impulse occurs due to the fact that during ventricular systole the heart tenses, becomes denser and more elastic, rises (because in the chest cavity the heart seems to be suspended on large blood vessels), and in cats and dogs it slightly rotates around its axis , hitting the chest wall with the tip (apical heart beat). During a clinical examination of the animal, attention is paid to the topography of the cardiac impulse, to its strength and frequency.

Frequency and Rhythm heart contractions. Under the frequency of contractions understand the number of cardiac cycles in 1 minute. The frequency of contractions can be determined by the number of heart beats, i.e. ventricular systole for 1 minute. An increase in heart rate is tachycardia, a slowdown is bradycardia.

The rhythm of cardiac activity is understood as the correct coordination during cardiac cycles. Cardiac activity can be rhythmic (same intervals) and non-rhythmic. Changes in heart rate are called arrhythmias. Arrhythmias can be physiological and pathological. In healthy animals, physiological arrhythmias are observed during the respiratory cycle and are called respiratory arrhythmias. Physiological arrhythmia can be in young animals (during puberty). Both types of arrhythmia do not require special treatment.

Heart sounds These are sounds that occur during the work of the heart. The main source of sound phenomena is the operation of the valve apparatus, sounds occur during the slamming of the valves. Heart sounds can be heard by applying a listening device, a stethoscope or phonendoscope, to the chest. Heart sounds are heard in those places where the valves are projected onto the surface of the chest. These four points (according to the number of valves) are called the points of best audibility. When analyzing heart tones, pay attention to their topography. strength, frequency. rhythm and the presence or absence of additional - pathological - sounds, which are called noises. The study of heart sounds is the main clinical method for studying the state of the valvular apparatus of the heart. The atrioventricular valves close at the beginning of ventricular systole, and the semilunar valves close at the beginning of ventricular diastole. There are two main heart sounds: the first (systolic), the second (diastolic).

The first tone is systolic, coincides with the systole of the ventricles, it is low, deaf, lingering. The second tone is diastolic, coinciding with the beginning of ventricular diastole, the sound is short, high, sonorous, jerky. The third and fourth tones merge with the main ones when listening and therefore do not differ.

Electrocardiography

ECG is a method of recording electrical potentials that occur during the work of the heart. Recording the biocurrents of the heart is called an electrocardiogram.

In veterinary practice, ECG is used various ways placement of electrodes, or leads. The standard way to conduct biopotentials is to apply electrodes to the limbs:

1. First lead: pasterns of the left and right thoracic limbs - atrial potentials are recorded.

2. The second lead: metacarpus of the right thoracic and metatarsus of the left pelvic limb - excitation of the ventricles is recorded.

3. The third lead: the metacarpus of the left thoracic and metatarsus of the left pelvic limb - the lead of the left ventricle is recorded.

The ECG consists of a flat isopotential line. which corresponds to the resting potential, and five teeth - P, Q, R, S, T. Three teeth (P, R, T) going up from the isopotential line are positive, and two teeth (Q. S). downward from it - negative.

• The R wave is the sum of atrial potentials. Occurs during the period of propagation of excitation through the atria.
• The P-Q interval is the time of passage of excitation from the atria to the ventricles.
• Q wave - excitation of the inner layers of the ventricular muscle, right papillary muscle, septum. apex of the left and base of the right ventricle.
• The R wave is the spread of excitation to the muscles of both ventricles.
• S wave - excitation coverage of the ventricles.
• The S-T interval reflects the absence of a potential difference in a period. when the myocardium is engulfed in excitation. Normally isopotential.
• The T wave is the phase of recovery (repolarization) of the ventricular myocardium.
• QRS - the time during which the excitation has time to completely cover the muscles of the ventricles.
• QRST is the excitation and recovery time of the ventricular myocardium.
• The interval of T-P excitation in the ventricles has already ended, but in the atria it has not yet begun. It is called the electrical diastole of the heart.
• The R-R interval (or R-R) corresponds to the full cycle of cardiac activity.

When analyzing the ECG, the height of the teeth, their direction from the isopotential line and the duration of the intervals are taken into account.

ECG in combination with other clinical research methods is used to diagnose heart diseases, especially these. which are associated with a disorder of the excitability of the conduction of the heart muscle.

Physiology of blood circulation.

The circulatory system is the continuous movement of blood through a closed system of heart cavities and a network of blood vessels that provide all the vital functions of the body.

The heart is the primary pump that energizes the movement of the blood. This is a complex point of intersection of different blood streams. In a normal heart, these flows do not mix. The heart begins to contract about a month after conception, and from that moment its work does not stop until the last moment of life.

During the time equal to the average life expectancy, the heart performs 2.5 billion contractions, and at the same time it pumps 200 million liters of blood. This is a unique pump that is about the size of a man's fist, and the average weight for a man is 300g and for a woman is 220g. The heart looks like a blunt cone. Its length is 12-13 cm, width 9-10.5 cm, and anterior-posterior size is 6-7 cm.

The system of blood vessels makes up 2 circles of blood circulation.

The systemic circulation begins in the left ventricle with the aorta. The aorta provides delivery of arterial blood to various organs and tissues. At the same time, parallel vessels depart from the aorta, which bring blood to different organs. arteries become arterioles, and arterioles become capillaries. Capillaries provide the entire amount of metabolic processes in tissues. There, the blood becomes venous, it flows from the organs. It flows to the right atrium through the inferior and superior vena cava.

The pulmonary circulation begins in the right ventricle with the pulmonary trunk, which divides into the right and left pulmonary arteries. Arteries carry venous blood to the lungs, where gas exchange will take place. The outflow of blood from the lungs is carried out through the pulmonary veins (2 from each lung), which carry arterial blood to the left atrium. The main function of the small circle is transport, the blood delivers oxygen, nutrients, water, salt to the cells, and removes carbon dioxide and end products of metabolism from the tissues.

Circulation- this is the most important link in the processes of gas exchange. Thermal energy is transported with blood - this is heat exchange with the environment. Due to the function of blood circulation, hormones and other physiologically active substances are transferred. This ensures the humoral regulation of the activity of tissues and organs. Modern ideas about the circulatory system were outlined by Harvey, who in 1628 published a treatise on the movement of blood in animals. He came to the conclusion that the circulatory system is closed. Using the method of clamping blood vessels, he established direction of blood flow. From the heart, the blood moves through the arterial vessels, through the veins, the blood moves to the heart. The division is based on the direction of the flow, and not on the content of the blood. The main phases of the cardiac cycle have also been described. The technical level did not allow detecting capillaries at that time. The discovery of the capillaries was made later (Malpighet), which confirmed Harvey's assumptions about the closedness of the circulatory system. The gastro-vascular system is a system of channels associated with the main cavity in animals.

The evolution of the circulatory system.

Circulatory system in shape vascular tubes appears in worms, but in worms, hemolymph circulates in the vessels and this system is not yet closed. The exchange is carried out in the gaps - this is the interstitial space.

Then there is isolation and the appearance of two circles of blood circulation. The heart in its development goes through stages - two-chamber- in fish (1 atrium, 1 ventricle). The ventricle pushes out venous blood. Gas exchange takes place in the gills. Then the blood goes to the aorta.

Amphibians have three hearts chamber(2 atria and 1 ventricle); The right atrium receives venous blood and pushes the blood into the ventricle. The aorta comes out of the ventricle, in which there is a septum and it divides the blood flow into 2 streams. The first stream goes to the aorta, and the second one goes to the lungs. After gas exchange in the lungs, blood enters the left atrium, and then into the ventricle, where the blood mixes.

In reptiles, the differentiation of heart cells into the right and left halves ends, but they have a hole in the interventricular septum and the blood mixes.

In mammals, the complete division of the heart into 2 halves . The heart can be considered as an organ that forms 2 pumps - the right one - the atrium and the ventricle, the left one - the ventricle and the atrium. There is no more mixing of the blood ducts.

A heart located in a person in the chest cavity, in the mediastinum between the two pleural cavities. The heart is bounded anteriorly by the sternum and posteriorly by the spine. In the heart, the apex is isolated, which is directed to the left, down. The projection of the apex of the heart is 1 cm inward from the left midclavicular line in the 5th intercostal space. The base is directed up and to the right. The line connecting the apex and base is the anatomical axis, which is directed from top to bottom, from right to left and from front to back. The heart lies asymmetrically in the chest cavity. 2/3 to the left of the midline, the upper border of the heart is the upper edge of the 3rd rib, and the right border is 1 cm outward from the right edge of the sternum. It practically lies on the diaphragm.

The heart is a hollow muscular organ that has 4 chambers - 2 atria and 2 ventricles. Between the atria and ventricles are atrioventricular openings, which will be atrioventricular valves. Atrioventricular openings are formed by fibrous rings. They separate the ventricular myocardium from the atria. The exit site of the aorta and pulmonary trunk are formed by fibrous rings. Fibrous rings - the skeleton to which its membranes are attached. There are semilunar valves in the openings in the exit area of ​​the aorta and pulmonary trunk.

The heart has 3 shells.

Outer shell- pericardium. It is built from two sheets - outer and inner, which fuses with the inner shell and is called the myocardium. A space filled with fluid forms between the pericardium and epicardium. Friction occurs in any moving mechanism. For easier movement of the heart, he needs this lubricant. If there are violations, then there are friction, noise. In these areas, salts begin to form, which immure the heart into a “shell”. This reduces the contractility of the heart. Currently, surgeons remove by biting this shell, freeing the heart, so that the contractile function can be carried out.

The middle layer is muscular or myocardium. It is the working shell and makes up the bulk. It is the myocardium that performs the contractile function. The myocardium refers to striated striated muscles, consists of individual cells - cardiomyocytes, which are interconnected in a three-dimensional network. Tight junctions are formed between cardiomyocytes. The myocardium is attached to the rings of fibrous tissue, the fibrous skeleton of the heart. It has attachment to the fibrous rings. atrial myocardium forms 2 layers - the outer circular, which surrounds both atria and the inner longitudinal, which is individual for each. In the area of ​​confluence of the veins - hollow and pulmonary, circular muscles are formed that form sphincters, and when these circular muscles contract, blood from the atrium cannot flow back into the veins. Myocardium of the ventricles formed by 3 layers - outer oblique, inner longitudinal, and between these two layers is located a circular layer. The myocardium of the ventricles begins from the fibrous rings. The outer end of the myocardium goes obliquely to the apex. At the top, this outer layer forms a curl (vertex), it and the fibers pass into the inner layer. Between these layers are circular muscles, separate for each ventricle. The three-layer structure provides shortening and reduction of the clearance (diameter). This makes it possible to expel blood from the ventricles. The inner surface of the ventricles is lined with endocardium, which passes into the endothelium of large vessels.

Endocardium- inner layer - covers the valves of the heart, surrounds the tendon filaments. On the inner surface of the ventricles, the myocardium forms a trabecular meshwork and the papillary muscles and papillary muscles are connected to the valve leaflets (tendon filaments). It is these threads that hold the valve leaflets and do not allow them to twist into the atrium. In the literature tendon threads are called tendon strings.

Valvular apparatus of the heart.

In the heart, it is customary to distinguish between atrioventricular valves located between the atria and ventricles - in the left half of the heart it is a bicuspid valve, in the right - a tricuspid valve, consisting of three wings. The valves open into the lumen of the ventricles and pass blood from the atria into the ventricle. But with contraction, the valve closes and the ability of blood to flow back into the atrium is lost. In the left - the magnitude of the pressure is much greater. Structures with fewer elements are more reliable.

At the exit site of large vessels - the aorta and pulmonary trunk - there are semilunar valves, represented by three pockets. When filling with blood in the pockets, the valves close, so the reverse movement of blood does not occur.

The purpose of the valvular apparatus of the heart is to ensure one-way blood flow. Damage to the valve leaflets leads to valve insufficiency. In this case, a reverse blood flow is observed as a result of a loose connection of the valves, which disrupts hemodynamics. The boundaries of the heart are changing. There are signs of development of insufficiency. The second problem associated with the area of ​​​​the valves, stenosis of the valves - (for example, the venous ring is stenotic) - the lumen decreases. When they talk about stenosis, they mean either atrioventricular valves or the place where the vessels originate. Above the semilunar valves of the aorta, from its bulb, the coronary vessels depart. In 50% of people, the blood flow in the right is greater than in the left, in 20% the blood flow is greater in the left than in the right, 30% have the same outflow in both the right and left coronary arteries. Development of anastomoses between the pools of the coronary arteries. Violation of the blood flow of the coronary vessels is accompanied by myocardial ischemia, angina pectoris, and complete blockage leads to necrosis - a heart attack. Venous outflow of blood is surface system veins, the so-called coronary sinus. There are also veins that open directly into the lumen of the ventricle and right atrium.

Cardiac cycle.

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

The cardiac cycle consists of 3 phases:

Atrial systole - 0.1 s

Ventricular systole - 0.3 s

Total pause 0.4 s

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

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

Ventricular systole is the most difficult phase of the cardiac cycle, lasting 0.3 s. secreted in systole stress period. it lasts 0.08 s and period of exile. Each period is divided into 2 phases -

stress period

1. asynchronous contraction phase - 0.05 s

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

period of exile

1. fast ejection phase 0.12s

2. slow phase 0.13 s.

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

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

The structure of the heart muscle.

The heart muscle has cellular structure and the cellular structure of the myocardium was established as early as 1850 by Kelliker, but long time it was believed that the myocardium is a network - sencidia. And only electron microscopy confirmed that each cardiomyocyte has its own membrane and is separated from other cardiomyocytes. The contact area of ​​cardiomyocytes is intercalated disks. Currently, cardiac muscle cells are divided into cells of the working myocardium - cardiomyocytes of the working myocard of the atria and ventricles and into cells of the conduction system of the heart. Allocate:

- transitional cells

- Purkinje cells

Working myocardial cells belong to striated muscle cells and cardiomyocytes have an elongated shape, length reaches 50 microns, diameter - 10-15 microns. The fibers are composed of myofibrils, the smallest working structure of which is the sarcomere. The latter has thick - myosin and thin - actin branches. On thin filaments there are regulatory proteins - tropanin and tropomyosin. Cardiomyocytes also have a longitudinal system of L tubules and transverse T tubules. However, T tubules, unlike T tubules skeletal muscle, depart at the level of membranes Z (in skeletal ones - at the border of disk A and I). Neighboring cardiomyocytes are connected with the help of an intercalary disk - the area of ​​\u200b\u200bcontact of the membranes. In this case, the structure of the intercalary disk is heterogeneous. In the intercalary disk, a slot area (10-15 Nm) can be distinguished. The second zone of tight contact is the desmosomes. In the region of desmosomes, a thickening of the membrane is observed, tonofibrils (threads connecting neighboring membranes) pass here. Desmosomes are 400 nm long. There are tight contacts, they are called nexuses, in which the outer layers of neighboring membranes merge, now they are found - conexons - fastening due to special proteins - conexins. Nexuses - 10-13%, this area has a very low electrical resistance 1.4 Ohm per kV.cm. This makes it possible to transmit an electrical signal from one cell to another, and therefore cardiomyocytes are included simultaneously in the excitation process. The myocardium is a functional sensidium.

Physiological properties of the heart muscle .

Cardiomyocytes are isolated from each other and contact in the area of ​​the intercalated discs, where the membranes of adjacent cardiomyocytes come into contact.

Connexons are connections in the membrane of neighboring cells. These structures are formed at the expense of connexin proteins. The connexon is surrounded by 6 such proteins, a channel is formed inside the connexon, which allows the passage of ions, thus electricity spreads from one cell to another. “f area has a resistance of 1.4 ohms per cm2 (low). Excitation covers cardiomyocytes simultaneously. They function like functional sensations. Nexuses are very sensitive to lack of oxygen, to the action of catecholamines, to stressful situations, to physical activity. This can cause a disturbance in the conduction of excitation in the myocardium. Under experimental conditions, the violation of tight junctions can be obtained by placing pieces of myocardium in a hypertonic sucrose solution. Important for the rhythmic activity of the heart conducting system of the heart- this system consists of a complex of muscle cells that form bundles and nodes, and the cells of the conducting system differ from the cells of the working myocardium - they are poor in myofibrils, rich in sarcoplasm and contain a high content of glycogen. These features under light microscopy make them lighter with little transverse striation and they have been called atypical cells.

The conduction system includes:

1. Sinoatrial node (or Kate-Flak node), located in the right atrium at the confluence of the superior vena cava

2. The atrioventricular node (or Ashoff-Tavar node), which lies in the right atrium on the border with the ventricle, is the posterior wall of the right atrium

These two nodes are connected by intra-atrial tracts.

3. Atrial tracts

- anterior - with the branch of Bachman (to the left atrium)

- middle tract (Wenckebach)

- posterior tract (Torel)

4. The Hiss bundle (departs from the atrioventricular node. Passes through the fibrous tissue and provides a connection between the atrial myocardium and the ventricular myocardium. Passes into the interventricular septum, where it is divided into the right and left pedicle of the Hiss bundle)

5. The right and left legs of the Hiss bundle (they run along the interventricular septum. The left leg has two branches - anterior and posterior. Purkinje fibers will be the final branches).

6. Purkinje fibers

In the conducting system of the heart, which is formed by modified types of muscle cells, there are three types of cells. pacemaker (P), transitional cells and Purkinje cells.

1. P -cells. They are located in the sino-arterial node, less in the atrioventricular nucleus. These are the smallest cells, they have few t-fibrils and mitochondria, there is no t-system, l. system is underdeveloped. The main function of these cells is to generate an action potential due to the innate property of slow diastolic depolarization. In them, there is a periodic decrease in the membrane potential, which leads them to self-excitation.

2. transition cells carry out the transfer of excitation in the region of the atrioventricular nucleus. They are found between P cells and Purkinje cells. These cells are elongated and lack the sarcoplasmic reticulum. These cells have a slow conduction rate.

3. Purkinje cells wide and short, they have more myofibrils, the sarcoplasmic reticulum is better developed, the T-system is absent.

Electrical properties of myocardial cells.

Myocardial cells, both working and conducting systems, have resting membrane potentials and outside the membrane of the cardiomyocyte is charged "+", and inside "-". This is due to ionic asymmetry - there are 30 times more potassium ions inside the cells, and 20-25 times more sodium ions outside. This is ensured by the constant operation of the sodium-potassium pump. Measurement of the membrane potential shows that the cells of the working myocardium have a potential of 80-90 mV. In the cells of the conducting system - 50-70 mV. When cells of the working myocardium are excited, an action potential arises (5 phases). 0 - depolarization, 1 - slow repolarization, 2 - plateau, 3 - fast repolarization, 4 - resting potential.

0. When excited, the process of depolarization of cardiomyocytes occurs, which is associated with the opening of sodium channels and an increase in the permeability for sodium ions, which rush inside the cardiomyocytes. With a decrease in the membrane potential of about 30-40 millivolts, slow sodium-calcium channels open. Through them, sodium and additionally calcium can enter. This provides a process of depolarization or overshoot (reversion) of 120 mV.

1. The initial phase of repolarization. There is a closing of sodium channels and some increase in the permeability to chloride ions.

2. Plateau phase. The depolarization process is slowed down. Associated with an increase in the release of calcium inside. It delays charge recovery on the membrane. When excited, potassium permeability decreases (5 times). Potassium cannot leave cardiomyocytes.

3. When the calcium channels close, a phase of rapid repolarization occurs. Due to the restoration of polarization to potassium ions, the membrane potential returns to its original level and diastolic potential occurs

4. Diastolic potential is constantly stable.

The cells of the conduction system have distinctive potential features.

1. Reduced membrane potential during the diastolic period (50-70mV).

2. The fourth phase is not stable. There is a gradual decrease in the membrane potential to the threshold critical level of depolarization and gradually continues to slowly decrease in diastole, reaching a critical level of depolarization, at which self-excitation of P-cells occurs. In P-cells, there is an increase in the penetration of sodium ions and a decrease in the output of potassium ions. Increases the permeability of calcium ions. These shifts in ionic composition lead to the fact that the membrane potential in P-cells decreases to a threshold level and the p-cell self-excites, giving rise to an action potential. The Plateau phase is poorly expressed. Phase zero smoothly transitions to the TB repolarization process, which restores the diastolic membrane potential, and then the cycle repeats again and P-cells go into a state of excitation. The cells of the sino-atrial node have the greatest excitability. The potential in it is especially low and the rate of diastolic depolarization is the highest. This will affect the excitation frequency. P-cells of the sinus node generate a frequency of up to 100 beats per minute. The nervous system (sympathetic system) suppress the action of the node (70 strokes). The sympathetic system can increase automaticity. Humoral factors - adrenaline, norepinephrine. Physical factors - the mechanical factor - stretching, stimulate automaticity, warming also increases automaticity. All this is used in medicine. The event of direct and indirect heart massage is based on this. The area of ​​the atrioventricular node also has automaticity. The degree of automaticity of the atrioventricular node is much less pronounced and, as a rule, it is 2 times less than in the sinus node - 35-40. In the conduction system of the ventricles, impulses can also occur (20-30 per minute). In the course of the conductive system, a gradual decrease in the level of automaticity occurs, which is called the gradient of automaticity. The sinus node is the center of first-order automation.

Staneus - scientist. The imposition of ligatures on the heart of a frog (three-chamber). The right atrium has a venous sinus, where the analogue of the human sinus node lies. Staneus applied the first ligature between the venous sinus and the atrium. When the ligature was tightened, the heart stopped its work. The second ligature was applied by Staneus between the atria and the ventricle. In this zone there is an analogue of the atria-ventricular node, but the 2nd ligature has the task of not separating the node, but its mechanical excitation. It is applied gradually, exciting the atrioventricular node and at the same time there is a contraction of the heart. The ventricles get contracted again under the action of the atria-ventricular node. With a frequency of 2 times less. If you apply a third ligature that separates the atrioventricular node, then cardiac arrest occurs. All this gives us the opportunity to show that the sinus node is the main pacemaker, the atrioventricular node has less automation. In a conducting system, there is a decreasing gradient of automation.

Physiological properties of the heart muscle.

The physiological properties of the heart muscle include excitability, conductivity and contractility.

Under excitability heart muscle is understood as its property to respond to the action of stimuli with a threshold or above the threshold force by the process of excitation. Excitation of the myocardium can be obtained by the action of chemical, mechanical, temperature irritations. This ability to respond to the action of various stimuli is used during heart massage (mechanical action), the introduction of adrenaline, and pacemakers. A feature of the reaction of the heart to the action of an irritant is what acts according to the principle " All or nothing". The heart responds with a maximum impulse already to the threshold stimulus. The duration of myocardial contraction in the ventricles is 0.3 s. This is due to the long action potential, which also lasts up to 300ms. The excitability of the heart muscle can drop to 0 - an absolutely refractory phase. No stimuli can cause re-excitation (0.25-0.27 s). The heart muscle is completely unexcitable. At the moment of relaxation (diastole), the absolute refractory turns into a relative refractory 0.03-0.05 s. At this point, you can get re-stimulation on over-threshold stimuli. The refractory period of the heart muscle lasts and coincides in time as long as the contraction lasts. Following relative refractoriness, there is a short period of increased excitability - excitability becomes higher than the initial level - super normal excitability. In this phase, the heart is especially sensitive to the effects of other stimuli (other stimuli or extrasystoles may occur - extraordinary systoles). The presence of a long refractory period should protect the heart from repeated excitations. The heart performs a pumping function. The gap between normal and extraordinary contraction is shortened. The pause can be normal or extended. An extended pause is called a compensatory pause. The cause of extrasystoles is the occurrence of other foci of excitation - the atrioventricular node, elements of the ventricular part of the conducting system, cells of the working myocardium. This may be due to impaired blood supply, impaired conduction in the heart muscle, but all additional foci are ectopic foci of excitation. Depending on the localization - different extrasystoles - sinus, pre-medium, atrioventricular. Ventricular extrasystoles are accompanied by an extended compensatory phase. 3 additional irritation - the reason for the extraordinary reduction. In time for an extrasystole, the heart loses its excitability. They receive another impulse from the sinus node. A pause is needed to restore a normal rhythm. When a failure occurs in the heart, the heart skips one normal beat and then returns to a normal rhythm.

Conductivity- the ability to conduct excitation. The speed of excitation in different departments is not the same. In the atrial myocardium - 1 m / s and the time of excitation takes 0.035 s

Excitation speed

Myocardium — 1 m/s 0.035

Atrioventricular node 0.02 - 0-05 m/s. 0.04 s

Conduction of the ventricular system - 2-4.2 m/s. 0.32

In total from the sinus node to the myocardium of the ventricle - 0.107 s

Myocardium of the ventricle - 0.8-0.9 m / s

Violation of the conduction of the heart leads to the development of blockades - sinus, atriventricular, Hiss bundle and its legs. The sinus node may turn off. Will the atrioventricular node turn on as a pacemaker? Sinus blocks are rare. More in atrioventricular nodes. The lengthening of the delay (more than 0.21 s) excitation reaches the ventricle, albeit slowly. Loss of individual excitations that occur in the sinus node (For example, only two out of three reach - this is the second degree of blockade. The third degree of blockade, when the atria and ventricles work inconsistently. Blockade of the legs and bundle is a blockade of the ventricles. accordingly, one ventricle lags behind the other).

Contractility. Cardiomyocytes include fibrils, and the structural unit is sarcomeres. There are longitudinal tubules and T tubules of the outer membrane, which enter inward at the level of the membrane i. They are wide. The contractile function of cardiomyocytes is associated with the proteins myosin and actin. On thin actin proteins - the troponin and tropomyosin system. This prevents the myosin heads from bonding to the myosin heads. Removal of blockage - calcium ions. T tubules open calcium channels. An increase in calcium in the sarcoplasm removes the inhibitory effect of actin and myosin. Myosin bridges move the filament tonic toward the center. The myocardium obeys 2 laws in the contractile function - all or nothing. The strength of the contraction depends on the initial length of the cardiomyocytes - Frank Staraling. If the cardiomyocytes are pre-stretched, they respond with a greater force of contraction. Stretching depends on filling with blood. The more, the stronger. This law is formulated as "systole - there is a function of diastole." This is an important adaptive mechanism that synchronizes the work of the right and left ventricles.

Features of the circulatory system:

1) the closure of the vascular bed, which includes the pumping organ of the heart;

2) the elasticity of the vascular wall (the elasticity of the arteries is greater than the elasticity of the veins, but the capacity of the veins exceeds the capacity of the arteries);

3) branching of blood vessels (difference from other hydrodynamic systems);

4) a variety of vessel diameters (the diameter of the aorta is 1.5 cm, and the capillaries are 8-10 microns);

5) a fluid-blood circulates in the vascular system, the viscosity of which is 5 times higher than the viscosity of water.

Types of blood vessels:

1) the main vessels of the elastic type: the aorta, large arteries extending from it; there are many elastic and few muscle elements in the wall, as a result of which these vessels have elasticity and extensibility; the task of these vessels is to transform the pulsating blood flow into a smooth and continuous one;

2)resistance or resistive vessels vessels - vessels muscular type, in the wall there is a high content of smooth muscle elements, the resistance of which changes the lumen of the vessels, and hence the resistance to blood flow;

3) exchange vessels or "exchange heroes" are represented by capillaries, which ensure the flow of the metabolic process, the performance of the respiratory function between blood and cells; the number of functioning capillaries depends on the functional and metabolic activity in the tissues;

4) shunt vessels or arteriovenular anastomoses directly connect arterioles and venules; if these shunts are open, then blood is discharged from the arterioles into the venules, bypassing the capillaries; if they are closed, then the blood flows from the arterioles into the venules through the capillaries;

5) capacitive vessels are represented by veins, which are characterized by high extensibility, but low elasticity, these vessels contain up to 70% of all blood, significantly affect the amount of venous return of blood to the heart.

The movement of blood obeys the laws of hydrodynamics, namely, it occurs from an area of ​​​​higher pressure to an area of ​​\u200b\u200blower pressure.

The amount of blood flowing through a vessel is directly proportional to the pressure difference and inversely proportional to the resistance:

Q=(p1—p2) /R= ∆p/R,

where Q-blood flow, p-pressure, R-resistance;

An analogue of Ohm's law for a section of an electrical circuit:

where I is the current, E is the voltage, R is the resistance.

Resistance is associated with the friction of blood particles against the walls of blood vessels, which is referred to as external friction, there is also friction between particles - internal friction or viscosity.

Hagen Poiselle's law:

where η is the viscosity, l is the length of the vessel, r is the radius of the vessel.

Q=∆ppr 4 /8ηl.

These parameters determine the amount of blood flowing through the cross section of the vascular bed.

For the movement of blood, it is not the absolute values ​​\u200b\u200bof pressure that matters, but the pressure difference:

p1=100 mm Hg, p2=10 mm Hg, Q=10 ml/s;

p1=500 mm Hg, p2=410 mm Hg, Q=10 ml/s.

The physical value of blood flow resistance is expressed in [Dyne*s/cm 5 ]. Relative resistance units were introduced:

If p \u003d 90 mm Hg, Q \u003d 90 ml / s, then R \u003d 1 is a unit of resistance.

The amount of resistance in the vascular bed depends on the location of the elements of the vessels.

If the values ​​of the resistances arising in series-connected vessels are considered, then the total resistance will be equal to the sum of the vessels in the individual vessels:

In the vascular system, blood supply is carried out due to the branches extending from the aorta and running in parallel:

R=1/R1 + 1/R2+…+ 1/Rn,

that is, the total resistance is equal to the sum of the reciprocal values ​​of the resistance in each element.

Physiological processes are subject to general physical laws.

Cardiac output.

Cardiac output is the amount of blood pumped out by the heart per unit of time. Distinguish:

Systolic (during 1 systole);

Minute volume of blood (or MBV) - is determined by two parameters, namely systolic volume and heart rate.

The value of the systolic volume at rest is 65-70 ml, and is the same for the right and left ventricles. At rest, the ventricles eject 70% of the end-diastolic volume, and by the end of systole, 60-70 ml of blood remains in the ventricles.

V system avg.=70ml, ν avg.=70 beats/min,

V min \u003d V syst * ν \u003d 4900 ml per minute

It is difficult to determine V min directly; an invasive method is used for this.

An indirect method based on gas exchange has been proposed.

Fick method (method for determining the IOC).

IOC \u003d O2 ml / min / A - V (O2) ml / l of blood.

1. O2 consumption per minute is 300 ml;
2. O2 content in arterial blood = 20 vol %;
3. O2 content in venous blood = 14% vol;
4. Arterio-venous oxygen difference = 6 vol% or 60 ml of blood.

IOC = 300 ml / 60 ml / l = 5 l.

The value of systolic volume can be defined as V min/ν. The systolic volume depends on the strength of contractions of the ventricular myocardium, on the amount of blood filling of the ventricles in diastole.

The Frank-Starling Law establishes. that systole is a function of diastole.

The value of the minute volume is determined by the change in ν and the systolic volume.

During exercise, the value of the minute volume can increase to 25-30 l, the systolic volume increases to 150 ml, ν reaches 180-200 beats per minute.

The reactions of physically trained people relate primarily to changes in systolic volume, untrained - frequency, in children only due to frequency.

Regulation of the activity of the heart

Other from the section: ▼

The function of the heart, that is, the strength and frequency of its contractions, varies depending on the state of the body and the conditions in which the body is located. These changes are provided by regulatory mechanisms, which can be divided into myogenic (associated with the physiological properties of the structures of the seria), humoral (the influence of various physiologically active substances, produced directly in the heart and body) and nervous (carried out with the help of intra- and extracardiac systems).

myogenic mechanisms. Frank-Starling law. Due to the properties of contractile myofilaments, the myocardium can change the force of contraction depending on the degree of filling of the heart cavities. With a constant heart rate, the force of heart contractions increases with an increase in venous blood flow. This is observed, for example, with an increase in end-diastolic volume from 130 to 180 ml.

It is believed that the Frank-Starling mechanism is based on the initial arrangement of actin and myosin filaments in the sarcomiri. Sliding threads relative to each other is carried out with mutual overlap due to the created transverse bridges. If these threads are stretched, then the number of possible "steps" will increase, therefore, the strength of the next contraction will also increase (positive inotropic effect). But further stretching can lead to the fact that the actin AND myosin filaments will no longer overlap and will not be able to form bridges for contraction. So

excessive stretching of muscle fibers will lead to a decrease in the force of contraction, i.e. negative inotropic effect. This is observed with an increase in end-diastolic volume above 180 ml.

Frank-Starling mechanism provides an increase in SV with an increase in venous blood flow to the corresponding department (right or left) of the heart. It contributes to the strengthening of heart contractions with an increase in the resistance of the ejection of blood into the vessels. The latter circumstance may be due to an increase in diastolic pressure in the aorta (pulmonary artery) or narrowing of these vessels (coarctation). In this case, one can imagine sequence of development of changes. An increase in pressure in the aorta leads to a sharp increase in coronary blood flow, during which cardiomyocytes are mechanically stretched and, according to the Frank-Starling mechanism, in their increased contraction, an increase in blood VR. This phenomenon is called the Anrep effect.

The Frank-Starling mechanism and the Anrep effect provide autoregulation of heart function under many physiological conditions (for example, during exercise). In this case, the IOC can be increased by 13-15 l / min.

Chronoinotropy. The dependence of the force of contraction of the heart on the frequency of its activity (the Bowditch ladder) is a fundamental property of the myocardium. The heart of a person and most animals, with the exception of rats, in response to an increase in the rhythm, reacts with an increase in the strength of contractions and, conversely, with a decrease in the rhythm, the force of contractions decreases. The mechanism of this phenomenon is associated with the accumulation or decrease in the concentration of Ca2 + in the myoplasm, as well as an increase or decrease in the number of cross-bridges, which leads to positive or

negative effects of the heart.

humoral mechanisms. Influence of the endocrine function of the heart.

In the heart, especially in its atria, biologically active compounds (digitalis-like factors, catecholamines, arachidonic acid products) and hormones, in particular, atrial natriuretic and renin-angiotensin compounds, are formed. Both hormones are involved in the regulation of myocardial contractile activity, IOC. The last of them has specific receptors, upon exposure to which myocardial hypertrophy develops.

Effect of ions on heart function. The vast majority of regulatory influences on the functional state of the heart is associated with the membrane mechanisms of the conduction system and cardiomyocytes. The membranes are primarily responsible for the penetration of ions. The state of membrane channels, carriers, and pumps that use ATP energy affect the concentration of ions in the myoplasm. A significant role in the transmembrane exchange of ions belongs to the concentration gradient, which is determined primarily by their concentration in the blood, and therefore in the intercellular fluid. An increase in the extracellular concentration of ions leads to an increase in their passive entry into cardiocytes, a decrease leads to "washout". It is likely that the cardiogenic effect of ions served as one of the reasons for the formation of complex regulatory systems in the course of evolution, which ensures their homeostasis in the blood.

Influence of Ca2 +. If the content of Ca2 + in the blood decreases, then the excitability and contractility of the heart decreases, and with an increase, on the contrary, it increases. The mechanism of this phenomenon is associated with the level of Ca2 + in the cells of the conducting system and the working myocardium, depending on which positive or negative effects of the activity of the heart develop.

Influence of K +. With a decrease in the concentration of K + (less than 4 mmol / l) in the blood, the pacemaker activity and heart rate increase. As its concentration increases, these indicators decrease. A twofold increase in the content of K + in the blood can lead to cardiac arrest. This effect is used in clinical practice to stop the heart during surgery. The mechanism of these changes is associated with a decrease in the ratio between external and intracellular K + an increase in membrane permeability to K + a decrease in the resting potential.

Influence of Na+. A decrease in the content of Na + in the blood can lead to cardiac arrest. This effect is based on a violation of the gradient transmembrane transport of Na +, Ca2 + and a combination of excitability with contractility. A slight increase in the level of Na + due to the Na + -, Ca2 + exchanger will lead to an increase in myocardial contractility.

Influence of hormones. A number of real ones (adrenaline, norepinephrine, glucagon, insulin, etc.). And tissue (angiotensin II, histamine, serotonin, etc.). Hormones stimulate the function of the heart. The mechanism of action, for example, of norepinephrine, serotonin and histamine is associated with the corresponding receptors: p-adrenergic receptors, Hg-histamine and serotonin. As a result of their interaction, the concentrations of adenylate cyclase and cAMP increase, calcium channels are activated, intracellular Ca2 + accumulates, which leads to an improvement in the activity of the heart.

In addition, hormones that activate adenylate cyclase, the formation of cAMP, can act on the myocardium indirectly, through increased glycogen breakdown and glucose oxidation. By intensifying the formation of ATP, hormones such as adrenaline and glucagon also cause a positive hegiotropic reaction.

On the contrary, stimulation of cGMP formation inactivates Ca2 + channels, which causes Negative influence on the function of the heart. Thus, the mediator of the parasympathetic nervous system acetylcholine, as well as bradykinin, act on cardiomyocytes. But other than that, acetylcholine? K +-permeability and thus predetermines hyperpolarization. The consequence of these influences is a decrease in the rate of depolarization, a reduction in the duration of AP, and a decrease in the force of contraction.

Influence of metabolites. The heart needs energy to function properly. Therefore, all changes in coronary blood flow, trophic function of the blood affect the work of the myocardium.

During hypoxia, intracellular acidosis, slow Ca2 + channels are blocked on the membrane of cardiomyocytes, thereby suppressing contractile activity. In this effect, there are elements of self-protection of the heart, since not spent on reducing ATP ensures the viability of cardiomyocytes. And if hypoxia is eliminated, then the preserved cardiomyocyte will begin to perform a pumping function.

An increase in the concentration of creatine phosphate, free fatty acids, lactic acid as an energy source in the heart is accompanied by an increase in myocardial activity. By decomposing lactic acid, the heart not only receives additional energy, but also helps to maintain a constant blood pH.

Basic physiological properties of the heart muscle.

The cardiac muscle (myocardium), like skeletal muscles, has the properties of excitability, conductivity, and contractility. Its physiological features include an extended refractory period and automatism.

1) excitability called the ability of the heart muscle to come into an active state - excitation. Cardiac muscle is less excitable than skeletal muscle. for the occurrence of excitation in the heart muscle, a stronger stimulus is needed than for the skeletal muscle. It is maximally reduced both by the threshold and by the stronger irritation.

2) Conductivity called the ability to spread excitation from one area of ​​\u200b\u200bmuscle tissue to another. The speed of propagation of excitation through the fibers of the heart muscle is 5 times less than through the fibers of the skeletal muscles, and is respectively 0.8-1 m/s and 4.7-5 m/s (through the conducting system of the heart - 2-4.2 m /with).

3) Contractility called the ability of the heart muscle to develop tension and shorten when excited. It has its own characteristics. The atrial muscles contract first, followed by the papillary muscles and the subendocardial layer of the ventricular muscles. In the future, the contraction also covers the inner layer of the muscles of the ventricles, thereby ensuring the movement of blood from the cavities of the ventricles into the aorta and pulmonary trunk. To carry out the contraction, the heart receives energy, which is released during the breakdown of ATP and CP (creatine phosphate).

4) Refractory period- this is the period of immunity of the muscles of the heart to the action of other stimuli. Unlike other tissues, the heart has a significantly pronounced and prolonged refractory period. There are absolute and relative refractory periods. During the absolute refractory period, the heart muscle does not respond by contraction even to a strong stimulus. During the relative refractory period, the heart muscle gradually returns to baseline and may respond by contraction to stimulation above the threshold. The relative refractory period is observed during diastole of the atria and ventricles of the heart. Due to the pronounced refractory period, which lasts longer than the systole period (0.1-0.3 seconds), the heart muscle is not capable of prolonged (tetanic) contraction and performs work like a single muscle contraction.

5) Automatism- the ability of the heart muscle to come into a state of excitation and rhythmic contraction without external influences. Provided by a conductive system without external influences. Provided by the conduction system, consisting of the sinoatrial, atrioventricular nodes and the atrioventricular bundle. The myocardium does not have the function of automatism. The main driver of the heart rhythm (pacemaker) is the sinoatrial node, which generates electrical impulses at a frequency of 60-80 per minute (the so-called sinus rhythm). This is the center of automatism of the first order. Normally, it suppresses the automatic activity of the remaining (ectopic) pacemakers of the heart. The center of automatism of the II order is the zone of transition of the atrioventricular node to the bundle of V. His (but not the node itself: V.V. Murashko, A.V. Strutynsky, 1991), which can produce electrical impulses with a frequency of 40-50 per minute ( atrioventricular rhythm). Finally, the centers of automatism of the III order (25-45 impulses per minute) are the lower part of the bundle of V. His, its branches and fibers of J. Purkinje (idioventricular rhythm).