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Coronary artery what. Structure and functions of coronary veins and arteries

Coronary arteries originate at the ostium aorta, the left one supplies the left ventricle and the left atrium, partly the interventricular septum, the right one supplies the right atrium and right ventricle, part of the interventricular septum and the posterior wall of the left ventricle. At the apex of the heart, branches of various arteries penetrate inside and supply blood to the inner layers of the myocardium and the papillary muscles; collaterals between the branches of the right and left coronary arteries are poorly developed. Venous blood from the basin of the left coronary artery flows into the venous sinus (80-85% of the blood), and then into the right atrium; 10-15% of venous blood enters the right ventricle through the veins of Tebesium. Blood from the basin of the right coronary artery flows through the anterior cardiac veins into the right atrium. At rest, 200-250 ml of blood flows per minute through the human coronary arteries, which is about 4-6% minute emission hearts.

The density of the myocardial capillary network is 3-4 times greater than in skeletal muscle, and is equal to 3500-4000 capillaries per 1 mm 3, and the total area of the diffusion surface of the capillaries is 20 m 2. This creates good conditions for oxygen transport to myocytes. The heart consumes 25-30 ml of oxygen per minute at rest, which is approximately 10% of the body's total oxygen consumption. At rest, half of the diffusion area of the heart capillaries is used (this is more than in other tissues), 50% of the capillaries do not function and are in reserve. Coronary blood flow at rest is a quarter of the maximum, i.e. there is a reserve for increasing blood flow by 4 times. This increase occurs not only due to the use of reserve capillaries, but also due to an increase in the linear velocity of blood flow.

Blood supply to the myocardium depends on the phase cardiac cycle, while two factors influence blood flow: myocardial tension, which compresses the arterial vessels, and blood pressure in the aorta, which creates the driving force for coronary blood flow. At the beginning of systole (during the period of tension), blood flow in the left coronary artery completely stops as a result of mechanical obstacles (the branches of the artery are pinched by the contracting muscle), and in the expulsion phase, blood flow is partially restored due to the high blood pressure in the aorta, which counteracts the mechanical force compressing the vessels. In the right ventricle, blood flow in the tension phase suffers slightly. In diastole and at rest, coronary blood flow increases in proportion to the work done in systole to move the blood volume against pressure forces; This is also facilitated by the good distensibility of the coronary arteries. Increased blood flow leads to the accumulation of energy reserves ( ATP And creatine phosphate) and oxygen deposition myoglobin; these reserves are used during systole, when oxygen supply is limited.

Brain

Supplied with blood from the internal pool sleepy and the vertebral arteries, which form the circle of Willis at the base of the brain. Six cerebral branches depart from it, going to the cortex, subcortex and midbrain. The medulla oblongata, pons, cerebellum and occipital lobes of the cerebral cortex are supplied with blood from the basilar artery, formed by the fusion of the vertebral arteries. Venules and small veins of brain tissue do not have a capacitive function, since, being in the brain substance enclosed in the bone cavity, they are inextensible. Venous blood flows from the brain through jugular vein and a number of venous plexuses associated with the superior vena cava.

The brain is capillary per unit volume of tissue in approximately the same way as the heart muscle, but there are few reserve capillaries in the brain; almost all capillaries function at rest. Therefore, an increase in blood flow in the microvessels of the brain is associated with an increase linear speed blood flow, which can increase 2 times. The structure of brain capillaries is of the somatic (solid) type with low permeability to water and water-soluble substances; this creates a blood-brain barrier. Lipophilic substances, oxygen and carbon dioxide are easily diffuse through the entire surface of the capillaries, and oxygen even through the wall of the arterioles. High capillary permeability for fat-soluble substances such as ethanol, ether etc., can create their concentrations, at which not only the work is disrupted neurons, but their destruction also occurs. Water-soluble substances necessary for the functioning of neurons ( glucose, amino acids), are transported from the blood to the central nervous system through endothelium capillaries by special carriers according to the concentration gradient (facilitated diffusion). Many organic compounds circulating in the blood, for example catecholamines And serotonin, do not penetrate the blood-brain barrier, as they are destroyed by specific enzyme systems capillary endothelium. Thanks to the selective permeability of the barrier, the brain creates its own composition of the internal environment.

The energy demands of the brain are high and generally relatively constant. The human brain consumes approximately 20% of the body's total energy expenditure at rest, although the brain's mass makes up only 2% of the body's mass. Energy is spent on the chemical work of synthesis of various organic compounds and on the operation of pumps to transport ions against the concentration gradient. In this regard, for the normal functioning of the brain, the constancy of its blood flow is of exceptional importance. Any change in blood supply not related to brain function can disrupt the normal activity of neurons. Thus, a complete cessation of blood flow to the brain after 8-12 s leads to loss of consciousness, and after 5-7 min, irreversible phenomena begin to develop in the cerebral cortex; after 8-12 min, many cortical neurons die.

The blood flow through the vessels of the brain in humans at rest is 50-60 ml/min per 100 g of tissue, in gray matter - approximately 100 ml/min per 100 g, in white matter - less: 20-25 ml/min per 100 g. Cerebral blood flow in general, it accounts for approximately 15% of the cardiac output. The brain is characterized by good myogenic and metabolic autoregulation of blood flow. Autoregulation of cerebral blood flow consists in the ability of cerebral arterioles to increase their diameter in response to a decrease in blood pressure and, conversely, to reduce their lumen in response to its increase, due to which local cerebral blood flow remains almost constant with changes in systemic blood pressure from 50 to 160 mm Hg. Art. . It has been experimentally shown that the mechanism of autoregulation is based on the ability of cerebral arterioles to maintain a constant tension of their own walls. (According to Laplace's law, wall tension is equal to the product of the radius of the vessel and the intravascular pressure).

Applications

Physical basis of blood movement in the vascular system. Pulse wave

To maintain electric current in a closed circuit, a current source is required that creates the potential difference necessary to overcome the resistance in the circuit. Similarly, to maintain fluid movement in a closed hydrodynamic system, a “pump” is required to create the pressure difference necessary to overcome the hydraulic resistance. In the circulatory system, the role of such a pump is played by the heart.

As a visual model cordially- vascular system consider a closed, liquid-filled system of many branched tubes with elastic walls. The movement of liquid occurs under the action of a rhythmically operating pump in the form of a pear with two valves (Fig. 9.1).

Rice. 9.1. Vascular system model

When the bulb is compressed (contraction of the left ventricle), the outlet valve K 1 opens and the fluid contained in it is pushed into tube A (aorta). Due to the stretching of the walls, the volume of the tube increases and it accommodates excess liquid. After this, valve K 1 closes. The walls of the aorta begin to gradually contract, driving excess fluid into the next link of the system (arteries). Their walls also first stretch, accepting excess liquid, and then contract, pushing the liquid into subsequent links of the system. At the final stage of the circulatory cycle, the fluid collects in tube B (vena cava) and returns to the pump through the inlet valve K 2. Thus, this model qualitatively correctly describes the blood circulation pattern.

Let us now consider the phenomena occurring in the systemic circulation in more detail. The heart is a rhythmically operating pump, in which the working phases - systole (contraction of the heart muscle) - alternate with idle phases - diastole (muscle relaxation). During systole, the blood contained in the left ventricle is pushed into the aorta, after which the aortic valve closes. The volume of blood that is pushed into the aorta during one contraction of the heart is called stroke volume(60-70 ml). The blood entering the aorta stretches its walls, and the pressure in the aorta increases. This pressure is called systolic(SAD, R s). Increased pressure spreads along the arterial part of the vascular system. This propagation is due to the elasticity of the artery walls and is called a pulse wave.

Pulse wave - a wave of increased (above atmospheric) pressure spreading through the aorta and arteries, caused by the ejection of blood from the left ventricle during systole.

The pulse wave propagates at a speed v p = 5-10 m/s. The magnitude of the velocity in large vessels depends on their size and the mechanical properties of the wall tissue:

where E is the elastic modulus, h is the thickness of the vessel wall, d is the diameter of the vessel, ρ is the density of the substance of the vessel.

The profile of the artery in different phases of the wave is shown schematically in Fig. 9.2.

Rice. 9.2. Profile of an artery during the passage of a pulse wave

After the pulse wave passes, the pressure in the corresponding artery drops to a value called diastolic pressure(DBP or P d). Thus, the change in pressure in large vessels is pulsating in nature. Figure 9.3 shows two cycles of blood pressure changes in the brachial artery.

Rice. 9.3. Change in blood pressure in the brachial artery: T - duration of the cardiac cycle; T s ≈ 0.3T - duration of systole; Td ≈ 0.7T - duration of diastole; P s - maximum systolic pressure; P d - minimum diastolic pressure

The pulse wave will correspond to a pulsation of blood flow speed. In large arteries it is 0.3-0.5 m/s. However, as the vascular system branches, the vessels become thinner and their hydraulic resistance quickly (proportional to

but R 4) is increasing. This leads to a decrease in the range of pressure fluctuations. In the arterioles and beyond there are practically no pressure fluctuations. As the branching occurs, not only the range of pressure fluctuations decreases, but also its average value. The nature of the pressure distribution in different parts of the vascular system is shown in Fig. 9.4. The excess pressure above atmospheric pressure is shown here.

Rice. 9.4. Pressure distribution in different parts of the human vascular system (on the x-axis is the relative proportion of the total blood volume in a given area)

The duration of the human circulatory cycle is approximately 20 seconds, and during the day the blood makes 4200 revolutions.

The cross-sections of the vessels of the circulatory system undergo periodic changes throughout the day. This is due to the fact that the length of the vessels is very large (100,000 km) and 7-8 liters of blood are clearly not enough to fill them to their maximum. Therefore, those organs that are in this moment work at maximum load. The cross-section of the remaining vessels decreases at this moment. For example, after eating, the digestive organs function most energetically, and a significant part of the blood is directed to them; There is not enough energy for normal brain function, and the person experiences drowsiness.

The influx of blood through the arteries of the heart and its outflow through the venous network constitutes the third circle of blood circulation. The peculiarities of coronary blood flow ensure that it increases 4-5 times during exercise. For regulation vascular tone important has oxygen content in the blood and autonomic tone nervous system.

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Diagram of the coronary circle

The coronary arteries of the heart originate from the root of the aorta near the valve flaps. They arise from the right and left aortic sinuses.

The right branch supplies almost the entire right ventricle and the posterior wall of the left, a small section of the septum.

The rest of the myocardium is supplied by the left coronary branch. It has from two to four departing arteries, of which the most important are the descending and circumflex.

The first is a direct continuation of the left coronary artery and runs to the apex, and the second is located at right angles to the main one, goes from front to back, going around the heart.

The options for the structure of the coronary network are:

three main arteries (an independent posterior branch is added);
one vessel instead of two (it goes around the base of the aorta);
double arteries running in parallel.

Myocardial nutrition is determined by the posterior interventricular artery. It can arise from the right or left circumflex branch.

Depending on this, the type of blood supply is called right or left, respectively. Almost 70% of people have the first option, 20% have a mixed system, and the rest have a left type of dominance.

Venous outflow passes through three vessels - the large, small and middle veins. They take approximately 65% of the blood from the tissues, dump it into the venous sinus, and then through it into the right atrium. The rest passes through the smallest veins of Viessen-Tebesius and the anterior venous branches.

Thus, schematically, the movement of blood passes through: the aorta - the common coronary artery - its right and left branches - arterioles - capillaries - venules - veins - coronary sinus - the right half of the heart.

Physiology and features of coronary circulation

At rest, about 4% of the total blood ejected into the aorta is spent on feeding the heart. With high physical or emotional stress, it increases 3-4 times, and sometimes more. The speed of blood movement through the coronary arteries depends on:

predominance of the tone of the sympathetic or parasympathetic nervous system;
intensity of metabolic processes.

Main income arterial blood to the cardiac muscle of the left ventricle occurs during the period of relaxation of the heart, only a small part (about 14 - 17%) enters during systole, as with all internal organs. For the right ventricle, phase dependence cardiac cycle not that significant. During cardiac contraction, venous blood flows away from the myocardium under the influence of muscle compression.

Cardiac muscle differs from skeletal muscle. The features of its blood circulation are:

the number of vessels in the myocardium is twice as large as in the rest of the muscle tissue;
blood nutrition is better with diastolic relaxation; the more frequent the contractions, the worse the flow of oxygen and energy compounds;
although the arteries have many connections, they are not enough to compensate for the blocked vessel, which leads to a heart attack;
Arterial walls, due to their high tone and distensibility, can provide increased blood flow in the myocardium during exercise.

Arteries and veins of the heart

Regulation of the small coronary circle

The coronary arteries react most strongly to oxygen deficiency. When under-oxidized metabolic products are formed, they stimulate the expansion of the vascular lumen.

Oxygen starvation can be absolute - with spasm of an arterial branch or thrombus or embolus, blood flow is reduced. With a relative deficiency, problems with cell nutrition arise only when there is an increased need, when it is necessary to increase the frequency and strength of contractions, but there is no reserve opportunity for this. This occurs when in response to physical activity or emotional stress.

The coronary arteries of the heart also receive impulses from the autonomic nervous system. The vagus nerve, the parasympathetic department and its conductor (mediator) acetylcholine dilates blood vessels. Simultaneously with the decrease in arterial tone, and decreases.

Action sympathetic division, the release of stress hormones is not so clear. Stimulation of alpha-adrenergic receptors constricts blood vessels, and beta-adrenergic stimulation dilates them. The end result of this multidirectional effect is the activation of coronary blood flow with good patency of the arterial pathways.

Research methods

The state of coronary circulation can be assessed using and. They imitate the response of the arteries to increased oxygen demands. Normally, when a high frequency of contractions is achieved (with the help of a treadmill or medications), there are no signs of ischemia on the cardiogram.

This proves that blood flow increases and fully provides intensive work hearts. With coronary insufficiency, changes in the ST segment appear - a decrease of 1 mm or more from the isoelectric line.

If an ECG helps to study functional features blood flow, then for research anatomical structure the arteries of the heart are carried out. The introduction of a contrast agent is usually used when it is necessary to perform operations to restore myocardial nutrition.

Angiography of the coronary arteries helps to identify areas of narrowing, their significance for the development of ischemia, the prevalence of atherosclerotic changes, as well as the condition of the bypass blood supply routes - collateral vessels.

Watch the video about the blood supply to the myocardium and methods for diagnosing the heart:

To expand diagnostic capabilities, coronary angiography is performed simultaneously with multispiral computed tomography. This method allows you to create a three-dimensional model of the coronary arteries, down to the smallest branches. MSCT angiography reveals:

the site of narrowing of the artery;
number of affected branches;
structure of the vascular wall;
the reason for the decrease in blood flow is thrombosis, embolism, cholesterol plaque, spasm;
anatomical features of the coronary vessels;
consequences .

The arteries and veins of the heart make up the third circle of blood circulation. It has structural and functional features that are aimed at increasing blood flow during exercise. Regulation of arterial tone is carried out by the concentration of oxygen in the blood, as well as by mediators of the sympathetic and parasympathetic nervous system.

To study the coronary vessels, ECG, stress tests, coronary angiography with X-ray or tomographic control are used.

Myocardial vasculature

Due to the impermeability of the inner walls of the heart (endocardium) and the large thickness of the myocardium, the heart is not deprived of the opportunity to use the blood contained in its own chambers to obtain oxygen and nutrition. Therefore, it has its own blood supply system, consisting of the coronary vessels of the heart. Two main coronary (coronary) arteries are responsible for the general distribution of blood:

left (LCA or LCA);
and right (PCA or RCA).

Both of them begin their journey from the corresponding sinuses at the base of the aorta, located behind the valves aortic valve, as shown in the diagram of the coronary arteries. When the heart is relaxed, blood flows into its pockets and then enters the coronary arteries. Since the LCA and RCA lie on the surface of the heart, they are called epicardial, their branches running deep in the myocardium are called subepicardial. Most people have two coronary arteries, but about 4% also have a third, called posterior (it is not shown on the diagram of the arteries of the heart).

The main trunk of the LCA has a lumen diameter, often exceeding 4.5 millimeters, and is one of the shortest and most important vessels body. It typically measures 1 to 2 cm in length, but may be as little as 2 mm in length before the division point. The left coronary artery divides into two branches:

anterior descending or interventricular (LAD);
envelope (OB).

The left anterior descending (anterior interventricular branch) usually begins as a continuation of the LMCA. Its size, length and extent are key factors in the balance of blood supply to the IVS (interventricular septum), LV (left ventricle), and most of both the left and right atria. Passing along the longitudinal cardiac groove, it goes to the apex of the heart (in some cases it continues beyond it to the posterior surface). The lateral branches of the LAD lie on the anterior surface of the LV, feeding its walls.

The bed of the OB, usually diverted from the LCA at a right angle, passing along the transverse groove, reaches the edge of the heart, goes around it, passes to the posterior wall of the LV and, in the form of the posterior descending artery, reaches the apex. One of the main branches of OB is the branch blunt edge(VTK), supplying the lateral wall of the LV.

The lumen (RCA) is about 2.5 mm or more. Anatomical structure RCA is individual and determines the types of blood supply to the myocardium. The most important role is nutrition of the areas of the heart responsible for regulating heart rhythm.

Types of blood supply to the heart

Blood flow to the anterior and lateral surfaces of the myocardium is quite stable and is not subject to individual changes. Depending on where the coronary arteries and their branches are located in relation to the posterior part or surface of the myocardial diaphragm , there are three types of blood supply to the heart:

Average. Consists of well-developed LAD, OB and RCA. The blood supply vessels entirely to the LV and from two-thirds to half of the IVS are branches of the LMCA. The pancreas and the rest of the IVS receive nutrition from the RCA. This is the most common type.
Left. In this case, blood flow in the LV, the entire IVS and part of the posterior wall of the RV is carried out by the LCA network.
Right. Isolated when the pancreas and back wall The LVs are supplied by the RCA.

These structural changes dynamic, they can only be accurately determined using coronary angiography. Exists important feature, characteristic of cardiac circulation, consisting in the presence of collaterals. This is the name given to alternative routes formed between the main vessels that can be activated at the moment when, for some reason, the working one is blocked in order to take over the functions of the one that has become unusable. The collateral network is most developed in elderly people suffering from coronary pathologies.

That is why in critical situations associated with blockage of the main myocardial vessels, young people are at greatest risk.

Disorders of the coronary arteries

Coronary arteries with abnormal structure are not uncommon. People do not have complete identity in the structure of blood circulation either with the standards of anatomy or with each other. Differences arise for many reasons. They can be divided into two groups:

hereditary;
purchased.

The former may be the result of abnormal variability, while the latter include the consequences of injuries, operations, inflammation and other diseases. The range of consequences from violations can be enormous: from asymptomatic to life-threatening. Anatomical changes in the coronary vessels include their position, direction, number, size and length. If congenital abnormalities are significant, they make themselves felt even in early age and are subject to treatment by a pediatric cardiologist.

But more often such changes are discovered by chance or against the background of another disease. Blockage or rupture of one of the coronary vessels leads to consequences of poor circulation proportional to the size of the damaged vessel. The normal functioning of the main myocardial vessels and problems in their functioning are always reflected in typical clinical symptoms and ECG recordings.

Problems with blood supply to the myocardium make themselves felt when physical or emotional stress is exceeded. This is especially important to remember because some coronary anomalies can cause sudden cardiac arrest in the absence of underlying medical conditions.

Cardiac ischemia

CAD occurs when the arteries that supply blood to the heart muscle become fragile and narrowed due to deposits in the walls. It causes oxygen starvation myocardium. In the 21st century, IHD is the most common type of heart disease and main reason death in many countries. The main signs and consequences of a reduction in coronary blood flow:

If the reduction or absence of blood flow in coronary vessels occurs due to stenotic damage to the vessel, then blood supply can be restored using:

If the lack of blood flow is caused by blood clots (thrombosis), then the administration of drugs that dissolve the clots is used. Aspirin and antiplatelet drugs are used to prevent recurrence of thrombosis.

The arteries of the heart arise from the aortic bulb and surround the heart like a crown, which is why they are called coronary arteries.

Right coronary artery goes to the right under the appendage of the right atrium, lies in the coronary sulcus and goes around the right surface of the heart. The branches of the right coronary artery supply blood to the walls of the right ventricle and atrium, the posterior part of the interventricular septum, the papillary muscles of the left ventricle, the sinoatrial and atrioventricular nodes of the conduction system of the heart.

Left coronary artery thicker than the right and located between the beginning of the pulmonary trunk and the appendage of the left atrium. The branches of the left coronary artery supply blood to the walls of the left ventricle, the papillary muscles, most of the interventricular septum, the anterior wall of the right ventricle, and the walls of the left atrium.

The branches of the right and left coronary arteries form two arterial rings around the heart: transverse and longitudinal. They provide blood supply to all layers of the walls of the heart.

There are several types of blood supply to the heart:

right coronary type - most parts of the heart are supplied with blood by the branches of the right coronary artery;
left coronary type - most of the heart receives blood from the branches of the left coronary artery;
uniform type - blood is evenly distributed throughout the arteries;
middle right type - transitional type of blood supply;
middle-left type - transitional type of blood supply.

It is believed that among all types of blood supply, the middle-right type is predominant.

Veins of the heart more numerous than arteries. Most of the large veins of the heart gather in coronary sinus- one common wide venous vessel. The coronary sinus is located in the coronary sulcus on the posterior surface of the heart and opens into the right atrium. The tributaries of the coronary sinus are 5 veins:

great vein hearts;
middle vein of the heart;
small vein hearts;
posterior vein of the left ventricle;
oblique vein of the left atrium.

In addition to these five veins that empty into the coronary sinus, the heart has veins that open directly into the right atrium: anterior veins of the heart, And smallest veins of the heart.

Autonomic innervation of the heart.

Parasympathetic innervation hearts

Preganglionic parasympathetic cardiac fibers are part of the branches that arise from the vagus nerves on both sides in the neck. Fibers from the right vagus nerve innervate predominantly the right atrium and especially abundantly the sinoatrial node. The atrioventricular node is mainly approached by fibers from the left vagus nerve. As a result, the right vagus nerve predominantly affects the heart rate, and the left one affects atrioventricular conduction. Parasympathetic innervation of the ventricles is weakly expressed and exerts its influence indirectly, due to the inhibition of sympathetic effects.

Sympathetic innervation of the heart

Sympathetic nerves, unlike the vagus nerves, are almost evenly distributed throughout all parts of the heart. Preganglionic sympathetic cardiac fibers originate in the lateral horns of the upper thoracic segments spinal cord. In the cervical and superior thoracic ganglia of the sympathetic trunk, in particular in the stellate ganglion, these fibers switch to postganglionic neurons. The processes of the latter approach the heart as part of several cardiac nerves.

In most mammals, including humans, ventricular activity is controlled primarily by sympathetic nerves. As for the atria and, especially, the sinoatrial node, they are under constant antagonistic influences from the vagus and sympathetic nerves.

Afferent nerves of the heart

The heart is innervated not only by efferent fibers, but also by a large number of afferent fibers running as part of the vagus and sympathetic nerves. Most of the afferent pathways belonging to vagus nerves, are myelinated fibers with sensory endings in the atria and left ventricle. When recording the activity of single atrial fibers, two types of mechanoreceptors were identified: B-receptors that respond to passive stretch, and A-receptors that respond to active tension.

Along with these myelinated fibers from specialized receptors, there is another large group sensory nerves extending from the free endings of the dense subendocardial plexus of soft fibers. This group of afferent pathways is part of the sympathetic nerves. It is believed that these fibers are responsible for sharp pains with segmental irradiation, observed with coronary disease heart (angina pectoris and myocardial infarction).

Heart development. Anomalies of the position and structure of the heart.

Heart development

The complex and unique structure of the heart, corresponding to its role as a biological engine, takes shape in the embryonic period. In the embryo, the heart goes through stages when its structure is similar to the two-chambered heart of fish and the incompletely occluded heart of reptiles. The heart rudiment appears during the neural tube period in an embryo of 2.5 weeks, having a length of only 1.5 mm. It is formed from cardiogenic mesenchyme ventral to the head end of the foregut in the form of paired longitudinal cellular strands in which thin endothelial tubes are formed. In the middle of the 3rd week, in an embryo 2.5 mm long, both tubes merge with each other, forming a simple tubular heart. At this stage, the heart rudiment consists of two layers. The inner, thinner layer represents the primary endocardium. Outside there is a thicker layer consisting of the primary myocardium and epicardium. At the same time, the pericardial cavity, which surrounds the heart, expands. At the end of the 3rd week, the heart begins to contract.

Due to its rapid growth the heart tube begins to bend to the right, forming a loop, and then takes an S-shape. This stage is called the sigmoid heart. At the 4th week, several parts can be distinguished in the heart of an embryo 5 mm long. The primary atrium receives blood from the veins converging to the heart. At the junction of the veins, an extension is formed called the venous sinus. From the atrium, blood enters the primary ventricle through the relatively narrow atrioventricular canal. The ventricle continues into the bulbus cordis, followed by the truncus arteriosus. At the junction of the ventricle with the bulb and the bulb with the truncus arteriosus, as well as on the sides of the atrioventricular canal, there are endocardial tubercles from which the heart valves develop. The structure of the embryonic heart is similar to the two-chambered heart of an adult fish, the function of which is to supply venous blood to the gills.

During the 5th and 6th weeks, significant changes occur in relative position parts of the heart. Its venous end moves cranially and dorsally, and the ventricle and bulb move caudally and ventrally. The coronary and interventricular grooves appear on the surface of the heart, and it acquires general outline definitive external form. During the same period, internal transformations begin, which lead to the formation of a four-chambered heart, characteristic of higher vertebrates. The heart develops septa and valves. The division of the atria begins at an embryo of 6 mm in length. In the middle of its posterior wall, the primary septum appears, it reaches the atrioventricular canal and merges with the endocardial tubercles, which by this time increase and divide the canal into the right and left parts. The septum primum is not complete; first the primary and then the secondary interatrial foramina are formed in it. Later, a secondary septum is formed, in which there is an oval opening. Through the foramen ovale, blood passes from the right atrium to the left. The hole is covered by the edge of the septum primum, which forms a valve that prevents the reverse flow of blood. Complete fusion of the primary and secondary septa occurs at the end of the intrauterine period.

During the 7th and 8th weeks embryonic development partial reduction of the venous sinus occurs. Its transverse part is transformed into the coronary sinus, the left horn is reduced to a small vessel - the oblique vein of the left atrium, and the right horn forms part of the wall of the right atrium between the places where the superior and inferior vena cava flow into it. The common pulmonary vein and the trunks of the right and left pulmonary veins are drawn into the left atrium, as a result of which two veins from each lung open into the atrium.

At 5 weeks, the bulb of the heart merges with the ventricle in the embryo, forming the arterial cone belonging to the right ventricle. The arterial trunk is divided by the spiral septum developing in it into the pulmonary trunk and the aorta. From below, the spiral septum continues towards the interventricular septum in such a way that the pulmonary trunk opens into the right, and the beginning of the aorta into the left ventricle. Endocardial tubercles located in the bulb of the heart take part in the formation of the spiral septum; due to them, the valves of the aorta and pulmonary trunk are also formed.

The interventricular septum begins to develop at the 4th week, its growth occurs from bottom to top, but until the 7th week the septum remains incomplete. In its upper part there is an interventricular foramen. The latter is closed by the growing endocardial tubercles, in this place the membranous part of the septum is formed. The atrioventricular valves are formed from the endocardial tubercles.

As the heart chambers divide and valves form, the tissues that make up the heart wall begin to differentiate. The atrioventricular conduction system is distinguished in the myocardium. The pericardial cavity is separated from common cavity bodies. The heart moves from the neck to the chest cavity. The embryonic and fetal hearts have relatively big sizes, since it ensures not only the movement of blood through the vessels of the fetal body, but also placental blood circulation.

Throughout the prenatal period, communication is maintained between the right and left halves of the heart through the foramen ovale. Blood entering the right atrium through the inferior vena cava is directed through the valves of this vein and the coronary sinus to the foramen ovale and through it into the left atrium. From the superior vena cava blood is flowing into the right ventricle and ejected into the pulmonary trunk. The pulmonary circulation of the fetus does not function, since the narrow pulmonary vessels provide great resistance to the flow of blood. Only 5-10% of the blood entering the pulmonary trunk passes through the fetal lungs. The rest of the blood is drained ductus arteriosus into the aorta and enters the systemic circulation, bypassing the lungs. Thanks to the foramen ovale and the ductus arteriosus, the balance of blood flow through the right and left halves of the heart is maintained.

To get acquainted with the anatomy and physiology of the cardiovascular system, you need to visit the section "Anatomy of the cardiovascular system."

The blood supply to the heart is carried out through two main vessels - the right and left coronary arteries, starting from the aorta immediately above the semilunar valves.

Left coronary artery

The left coronary artery begins from the left posterior sinus of Vilsalva, goes down to the anterior longitudinal groove, leaving the pulmonary artery to its right, and to the left the left atrium and the appendage surrounded by fatty tissue, which usually covers it. It is a wide but short trunk, usually no more than 10-11 mm long.

The left coronary artery is divided into two, three, in rare cases into four arteries, of which highest value for pathology they have an anterior descending (LAD) and circumflex branch (OB), or arteries.

The anterior descending artery is a direct continuation of the left coronary artery.

Along the anterior longitudinal cardiac groove it is directed to the region of the apex of the heart, usually reaches it, sometimes bends over it and passes to the posterior surface of the heart.

Several smaller lateral branches depart from the descending artery at an acute angle, which are directed along the anterior surface of the left ventricle and can reach the obtuse edge; in addition, numerous septal branches depart from it, piercing the myocardium and branching in the anterior 2/3 of the interventricular septum. The lateral branches supply the anterior wall of the left ventricle and give branches to the anterior papillary muscle of the left ventricle. The superior septal artery gives off a branch to the anterior wall of the right ventricle and sometimes to the anterior papillary muscle of the right ventricle.

Throughout its entire length, the anterior descending branch lies on the myocardium, sometimes plunging into it to form muscle bridges 1-2 cm long. Throughout the rest of its length, its anterior surface is covered with fatty tissue of the epicardium.

The circumflex branch of the left coronary artery usually departs from the latter at the very beginning (the first 0.5-2 cm) at an angle close to a straight line, passes in the transverse groove, reaches the obtuse edge of the heart, goes around it, passes to the posterior wall of the left ventricle, sometimes reaches posterior interventricular groove and in the form of the posterior descending artery goes to the apex. Numerous branches extend from it to the anterior and posterior papillary muscles, the anterior and posterior walls of the left ventricle. One of the arteries supplying the sinoauricular node also departs from it.

Right coronary artery

The right coronary artery begins in anterior sinus Vilsalva. It is first located deep in the adipose tissue to the right of pulmonary artery, goes around the heart along the right atrioventricular groove, passes to the posterior wall, reaches the posterior longitudinal groove, then in the form of a posterior descending branch descends to the apex of the heart.

The artery gives 1-2 branches to the anterior wall of the right ventricle, partially to the anterior part of the septum, both papillary muscles of the right ventricle, the posterior wall of the right ventricle and the posterior part of the interventricular septum; a second branch also departs from it to the sinoauricular node.

Main types of blood supply to the myocardium

There are three main types of blood supply to the myocardium: middle, left and right.

This division is based mainly on variations in the blood supply to the posterior or diaphragmatic surface of the heart, since the blood supply to the anterior and lateral sections is quite stable and is not subject to significant deviations.

At average type all three main coronary arteries are well developed and fairly evenly developed. The blood supply to the entire left ventricle, including both papillary muscles, and the anterior 1/2 and 2/3 of the interventricular septum is carried out through the left coronary artery system. The right ventricle, including both right papillary muscles and the posterior 1/2-1/3 of the septum, receives blood from the right coronary artery. This appears to be the most common type of blood supply to the heart.

At left type blood supply to the entire left ventricle and, in addition, to the entire septum and partially to the posterior wall of the right ventricle is carried out due to the developed circumflex branch of the left coronary artery, which reaches the posterior longitudinal sulcus and ends here in the form of the posterior descending artery, giving some branches to the posterior surface of the right ventricle .

Right type observed with weak development of the circumflex branch, which either ends before reaching the obtuse edge, or passes into the coronary artery of the obtuse edge, without spreading to the posterior surface of the left ventricle. In such cases, the right coronary artery, after the origin of the posterior descending artery, usually gives several more branches to the posterior wall of the left ventricle. In this case, the entire right ventricle, the posterior wall of the left ventricle, the posterior left papillary muscle and partly the apex of the heart receive blood from the right coronary arteriole.

Blood supply to the myocardium is carried out directly:

A) capillaries lying between the muscle fibers that weave around them and receive blood from the coronary artery system through the arterioles;

B) a rich network of myocardial sinusoids;

C) Viessant-Tebesius vessels.

As pressure in the coronary arteries increases and the work of the heart increases, blood flow in the coronary arteries increases. Lack of oxygen also leads to a sharp increase in coronary blood flow. The sympathetic and parasympathetic nerves appear to have little effect on the coronary arteries, exerting their main action directly on the heart muscle.

Outflow occurs through veins that collect in the coronary sinus

Venous blood in coronary system collects in large vessels, usually located near the coronary arteries. Some of them merge, forming a large venous canal - the coronary sinus, which runs along the posterior surface of the heart in the groove between the atria and ventricles and opens into the right atrium.

Intercoronary anastomoses play important role in the coronary circulation, especially in pathological conditions. There are more anastomoses in the hearts of people suffering from coronary artery disease, so closure of one of the coronary arteries is not always accompanied by necrosis in the myocardium.

IN normal hearts anastomoses were found only in 10-20% of cases, and of small diameter. However, their number and magnitude increase not only with coronary atherosclerosis, but also with valvular heart defects. Age and gender by themselves do not have any effect on the presence and degree of development of anastomoses.