What is the middle layer of the heart wall called? The structure of the walls of the heart

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Heart- the central organ of the blood and lymph circulation system. Due to the ability to contract, the heart sets the blood in motion.
Wall of the heart consists of three membranes: endocardium, myocardium and epicardium.

Endocardium. In the inner shell of the heart, the following layers are distinguished: endothelium, lining the inside of the cavity of the heart, and its basement membrane; subendothelial layer, represented by loose connective tissue, in which there are many poorly differentiated cells; muscular-elastic layer, consisting of smooth muscle tissue, between the cells of which elastic fibers are located in the form of a dense network; outer connective tissue layer, consisting of loose connective tissue. The endothelium and subendothelial layers are similar to the inner membrane of the vessels, the musculo-elastic layer is the "equivalent" of the middle membrane, and the outer connective tissue layer is similar to the outer (adventitial) membrane of the vessels.

The surface of the endocardium is ideally smooth and does not interfere with the free movement of blood. In the atrioventricular region and at the base of the aorta, the endocardium forms duplications (folds), called valves. Distinguish between atrioventricular and ventricular-vascular valves. There are fibrous rings at the attachment sites of the valves. Heart valves are dense plates of fibrous connective tissue covered with endothelium. The nutrition of the endocardium occurs by diffusion of substances from the blood located in the cavities of the atria and ventricles.

Myocardium(middle shell of the heart) - a multi-tissue shell, consisting of striated cardiac muscle tissue, intermuscular loose connective tissue, numerous vessels and capillaries, as well as nerve elements. The main structure is the cardiac muscle tissue, which in turn consists of cells that form and conduct nerve impulses, and cells of the working myocardium, providing contraction of the heart (cardiomyocytes). Among the cells that form and conduct impulses in the conduction system of the heart, there are three types: P-cells (pacemaker cells), intermediate cells and Purkinya cells (fibers).

P cells- pacemaker cells located in the center of the sinus node of the conduction system of the heart. They have a polygonal shape and are determined to spontaneous depolarization of the plasmalemma. Myofibrils and organelles general meaning in pacemaker cells are weakly expressed. Intermediate cells are a heterogeneous group of cells that transmit excitation from P-cells to Purkinya cells. Purkinya cells are cells with a small number of myofibrils and a complete absence of the T-system, with a large amount of cytoplasm compared to working contractile myocytes. Purkinya cells transmit excitation from intermediate cells to contractile cells of the myocardium. They are part of the bundle of His of the conduction system of the heart.

An unfavorable effect on pacemaker cells and Purkinya cells is exerted by medicines and other factors that can lead to arrhythmias and heart block. The presence in the heart of its own conducting system is extremely important, since it provides a rhythmic change in systolic contractions and diastole of the heart chambers (atria and ventricles) and the operation of its valvular apparatus.

The bulk of the myocardium make contractile cells - cardiac myocytes, or cardiomyocytes. These are cells of an elongated shape with an ordered system of transversely striated myofibrils located on the periphery. Between the myofibrils are mitochondria with a large number of cristae. In atrial myocytes, the T-system is weakly expressed. The granular endoplasmic reticulum is poorly developed in cardiomyocytes. In the central part of myocytes there is an oval-shaped nucleus. Sometimes there are binuclear cardiomyocytes. Atrial muscle tissue contains cardiomyocytes with osmiophilic secretory granules containing natriuretic peptide.

In cardiomyocytes, inclusions of glycogen, which serves as the energy material of the heart muscle, are determined. Its content in the myocytes of the left ventricle is greater than in other parts of the heart. The myocytes of the working myocardium and the conducting system are interconnected by means of intercalated discs - specialized intercellular contacts. Actin contractile myofilaments are attached in the region of the intercalated discs, desmosomes and gap junctions (nexuses) are present.

Desmosomes contribute to the strong adhesion of contractile myocytes into functional muscle fibers, and the nexuses ensure the rapid propagation of plasma membrane depolarization waves from one muscle cell on the other and the existence of the cardiac muscle fiber as a single metabolic unit. Characteristic for myocytes of the working myocardium is the presence of anastomosing bridges - interconnected fragments of the cytoplasms of muscle cells of different fibers with myofibrils located in them. Thousands of such bridges turn the muscle tissue of the heart into a mesh structure capable of synchronously and efficiently contracting and ejecting the necessary systolic blood volumes from the ventricular cavities. After suffering extensive myocardial infarctions (acute ischemic necrosis of the heart wall), when the muscular tissue of the heart, the system of intercalated discs, anastomosing bridges and the conduction system are diffusely affected, disturbances in the rhythm of the heart, up to fibrillation, occur. In this case, the contractile activity of the heart turns into separate uncoordinated twitches of muscle fibers and the heart is not able to eject the necessary systolic portions of blood into the peripheral circulation.

Myocardium consists in general of highly specialized cells that have lost the ability to divide by mitosis. Mitoses of cardiomyocytes are observed only in certain parts of the atria (Rumyantsev P.P., 1982). At the same time, the myocardium is characterized by the presence of polyploid myocytes, which significantly enhances its working potential. The phenomenon of polyploidy is most often observed in compensatory reactions of the myocardium, when the load on the heart increases, and in pathology (failure of heart valves, lung diseases, etc.).

cardiac myocytes in these cases, they sharply hypertrophy, and the wall of the heart in one or another section thickens. The myocardial connective tissue contains a richly branched network of blood and lymphatic capillaries, which provides the constantly working heart muscle with nutrition and oxygen. In the layers of connective tissue there are dense bundles of collagen fibers, as well as elastic fibers. In general, these connective tissue structures constitute the supporting skeleton of the heart, to which cardiac muscle cells are attached.

Heart- an organ that has the ability to automate contractions. It can function autonomously within certain limits. However, in the body, the activity of the heart is under control. nervous system. In the intramural nerve nodes of the heart there are sensitive vegetative neurons (Type II Dogel cells), small intensely fluorescent cells - MYTH cells and effector autonomic neurons (Type 1 Dogel cells). MYTH cells are considered as intercalary neurons.

epicardium- the outer shell of the heart - is a visceral sheet of the pericardial sac (pericardium). The free surface of the epicardium is lined with mesothelium in the same way as the surface of the pericardium facing the pericardial cavity. Under the mesothelium in the composition of these serous membranes is a connective tissue base of loose fibrous connective tissue.

The heart has complex structure and performs no less complex and important work. Rhythmically contracting, it provides blood flow through the vessels.

The heart is located behind the sternum, in the middle section of the chest cavity and is almost completely surrounded by the lungs. It may move slightly to the side, as it hangs freely on the blood vessels. The heart is located asymmetrically. Its long axis is inclined and forms an angle of 40° with the axis of the body. It is directed from top right forward down to the left and the heart is rotated so that its right section is deviated more forward, and the left - backward. Two thirds of the heart is to the left of the midline and one third (vena cava and right atrium) is to the right. Its base is turned towards the spine, and the apex is turned towards the left ribs, to be more precise, towards the fifth intercostal space.

Sternocostal surface the heart is more convex. It is located behind the sternum and cartilages of the III-VI ribs and is directed forward, up, to the left. A transverse coronal sulcus runs along it, which separates the ventricles from the atria and thereby divides the heart into an upper part, formed by the atria, and a lower part, consisting of the ventricles. Another groove of the sternocostal surface - the anterior longitudinal - runs along the border between the right and left ventricles, while the right one forms a large part of the anterior surface, the left one - a smaller one.

Diaphragmatic surface flatter and adjacent to the tendon center of the diaphragm. A longitudinal posterior groove runs along this surface, separating the surface of the left ventricle from the surface of the right. In this case, the left one makes up a large part of the surface, and the right one - a smaller one.

Anterior and posterior longitudinal grooves merge with the lower ends and form a cardiac notch to the right of the cardiac apex.

Distinguish still side surfaces, located on the right and left and facing the lungs, in connection with which they were called pulmonary.

Right and left edges hearts are not the same. The right edge is more pointed, the left one is more obtuse and rounded due to the thicker wall of the left ventricle.

The boundaries between the four chambers of the heart are not always clearly defined. The reference points are the furrows in which blood vessels hearts covered with adipose tissue and the outer layer of the heart - the epicardium. The direction of these furrows depends on how the heart is located (obliquely, vertically, transversely), which is determined by the type of physique and the height of the diaphragm. In mesomorphs (normostenics), whose proportions are close to average, it is located obliquely, in dolichomorphs (asthenics) with a thin physique, vertically, in brachymorphs (hypersthenics) with wide short forms, transversely.

The heart seems to be suspended from the base on large vessels, while the base remains motionless, and the apex is in a free state and can move.

The structure of the tissues of the heart

The wall of the heart is made up of three layers:

Endocardium - inner layer epithelial tissue lining the cavities of the heart chambers from the inside, exactly repeating their relief.
Myocardium - a thick layer formed by muscle tissue (striated). Cardiac myocytes, of which it consists, are connected by many jumpers connecting them in muscle complexes. This muscle layer ensures the rhythmic contraction of the chambers of the heart. The smallest thickness of the myocardium is in the atria, the largest is in the left ventricle (about 3 times thicker than that of the right), since it needs more force to push blood into big circle blood circulation, in which the resistance to flow is several times greater than in a small one. The atrial myocardium consists of two layers, the ventricular myocardium - of three. The atrial myocardium and the ventricular myocardium are separated by fibrous rings. Conducting system, providing rhythmic contraction of the myocardium, one for the ventricles and atria.
The epicardium is the outer layer, which is the visceral lobe of the heart sac (pericardium), which is a serous membrane. It covers not only the heart, but also the initial sections of the pulmonary trunk and aorta, as well as the final sections of the pulmonary and vena cava.

Anatomy of the atria and ventricles

The heart cavity is divided by a septum into two parts - right and left, which do not communicate with each other. Each of these parts consists of two chambers - the ventricle and the atrium. The partition between the atria is called interatrial, between the ventricles - interventricular. Thus, the heart consists of four chambers - two atria and two ventricles.

Right atrium

In shape, it looks like an irregular cube, in front there is an additional cavity called the right ear. The atrium has a volume of 100 to 180 cc. see. It has five walls, 2 to 3 mm thick: anterior, posterior, superior, lateral, medial.

The superior vena cava (top behind) and the inferior vena cava (bottom) flow into the right atrium. On the lower right is the coronary sinus, where the blood of all cardiac veins flows. Between the openings of the superior and inferior vena cava is intervenous tubercle. In the place where the inferior vena cava flows into the right atrium, there is a fold of the inner layer of the heart - the valve of this vein. The sinus of the vena cava is called the posterior enlarged section of the right atrium, where both of these veins flow.

The right atrial chamber has a smooth inner surface, and only in the right ear with the anterior wall adjacent to it is the surface uneven.

Many pinholes of small veins of the heart open into the right atrium.

Right ventricle

It consists of a cavity and an arterial cone, which is a funnel directed upwards. The right ventricle has the shape of a trihedral pyramid, the base of which is turned up and the apex is turned down. The right ventricle has three walls: anterior, posterior, and medial.

The anterior is convex, the posterior is flatter. The medial is an interventricular septum, consisting of two parts. The largest of them - muscular - is at the bottom, the smaller - membranous - at the top. The pyramid faces the atrium with its base and there are two openings in it: posterior and anterior. The first is between the cavity of the right atrium and the ventricle. The second goes into the pulmonary trunk.

Left atrium

It looks like an irregular cube, is located behind and is adjacent to the esophagus and the descending part of the aorta. Its volume is 100-130 cubic meters. cm, wall thickness - from 2 to 3 mm. Like the right atrium, it has five walls: anterior, posterior, superior, literal, medial. The left atrium continues anteriorly into an accessory cavity called the left auricle, which is directed towards the pulmonary trunk. Four pulmonary veins flow into the atrium (behind and above), in the openings of which there are no valves. The medial wall is the interatrial septum. The inner surface of the atrium is smooth, the pectinate muscles are only in the left ear, which is longer and narrower than the right one, and is markedly separated from the ventricle by an intercept. It communicates with the left ventricle through the atrioventricular orifice.

left ventricle

In shape, it resembles a cone, the base of which is turned upwards. The walls of this chamber of the heart (anterior, posterior, medial) have the greatest thickness - from 10 to 15 mm. There is no clear boundary between the anterior and posterior. At the base of the cone are the opening of the aorta and the left atrioventricular.

The aortic opening is round in shape in front. Its valve consists of three dampers.

Heart size

The size and weight of the heart differ in different people. The average values are as follows:

length is from 12 to 13 cm;
the greatest width is from 9 to 10.5 cm;
anteroposterior size - from 6 to 7 cm;
weight in men - about 300 g;
weight in women - about 220 g.

Functions of the cardiovascular system and the heart

The heart and blood vessels make up the cardiovascular system, the main function of which is transport. It consists in the supply of tissues and organs of nutrition and oxygen and the reverse transportation of metabolic products.

The heart acts as a pump - it ensures the continuous circulation of blood in the circulatory system and the delivery of nutrients and oxygen to organs and tissues. When stressed or physical activity his work immediately restructures: increases the number of cuts.

The work of the heart muscle can be described as follows: its right side (venous heart) receives from the veins the spent blood saturated with carbon dioxide and gives it to the lungs for oxygenation. From the lungs, oxygen-enriched blood is sent to left side heart (arterial) and from there it is pushed into the bloodstream with force.

The heart produces two circles of blood circulation - large and small.

The large one supplies blood to all organs and tissues, including the lungs. It starts in the left ventricle and ends in the right atrium.

The pulmonary circulation produces gas exchange in the alveoli of the lungs. It starts in the right ventricle and ends in the left atrium.

The blood flow is regulated by valves: they do not allow it to flow in the opposite direction.

The heart has such properties as excitability, conduction ability, contractility and automaticity (excitation without external stimuli under the influence of internal impulses).

Thanks to the conduction system, there is a consistent contraction of the ventricles and atria, the synchronous inclusion of myocardial cells in the contraction process.

Rhythmic contractions of the heart provide a portioned flow of blood into the circulatory system, but its movement in the vessels occurs without interruption, due to the elasticity of the walls and the resistance to blood flow that occurs in small vessels.

The circulatory system has a complex structure and consists of a network of vessels for various purposes: transport, shunting, exchange, distribution, capacitive. There are veins, arteries, venules, arterioles, capillaries. Together with the lymphatics, they maintain the constancy of the internal environment in the body (pressure, body temperature, etc.).

Arteries move blood from the heart to the tissues. As they move away from the center, they become thinner, forming arterioles and capillaries. The arterial bed of the circulatory system transports the necessary substances to the organs and maintains a constant pressure in the vessels.

The venous bed is more extensive than the arterial one. Veins move blood from the tissues to the heart. Veins are formed from venous capillaries, which merge, first become venules, then veins. At the heart, they form large trunks. Distinguish superficial veins under the skin, and deep, located in the tissues next to the arteries. The main function of the venous part of the circulatory system is the outflow of blood saturated with metabolic products and carbon dioxide.

To evaluate functionality of cardio-vascular system and admissibility of loads, special tests are carried out, which make it possible to assess the working capacity of the body and its compensatory capabilities. Functional tests of the cardiovascular system are included in the medical physical examination to determine the degree of fitness and general physical fitness. The assessment is given according to such indicators of the work of the heart and blood vessels as arterial pressure, pulse pressure, blood flow velocity, minute and stroke volumes of blood. These tests include Letunov's tests, step tests, Martinet's, Kotov's - Demin's tests.

The heart begins to contract from the fourth week after conception and does not stop until the end of life. It does a gigantic job: it pumps about three million liters of blood per year and about 35 million heartbeats take place. At rest, the heart uses only 15% of its resource, while under load - up to 35%. During an average lifespan, it pumps about 6 million liters of blood. Another interesting fact: The heart provides blood to 75 trillion cells of the human body, except for the cornea of the eyes.

The walls of the chambers of the heart vary considerably in thickness; thus, the thickness of the walls of the atria is 2-3 mm, the left ventricle - an average of 15 mm, which is usually 2.5 times greater than the wall thickness of the right ventricle (about 6 mm). In the wall of the heart, 3 membranes are distinguished: the visceral plate of the pericardium - the epicardium; muscular membrane - myocardium; the inner shell is the endocardium.

epicardium(epicardium) is the serosa. It consists of a thin plate of connective tissue covered with outer surface mesothelium. The epicardium contains vascular and nerve networks.

Myocardium(myocardium) makes up the main mass of the wall of the heart (Fig. 155). It consists of striated cardiac muscle fibers (cardiomyocytes) interconnected by jumpers. The ventricular myocardium is separated from the atrial myocardium by the right and left fibrous rings (annuli fibrosi) located between the atria and ventricles and limiting the atrioventricular openings. The inner semicircles of the fibrous rings turn into fibrous triangles (trigona fibrosa). Myocardial bundles start from fibrous rings and triangles.

Rice. 155. Left ventricle. The direction of muscle bundles in different layers of the myocardium:

1 - superficial myocardial bundles; 2 - internal longitudinal myocardial bundles; 3 - "whirlpool" of the heart; 4 - leaflets of the left atrioventricular valve; 5 - tendon chords; 6 - circular medium myocardial bundles; 7 - papillary muscle

The bundles of muscle fibers of the myocardium have a complex orientation, making up a single whole. To facilitate the idea of the course of myocardial bundles, you need to know the following scheme.

The atrial myocardium is composed of superficial transverse beams and deep loop-like, running almost vertically. Deep bundles form ring thickenings at the mouths of large vessels and protrude into the cavity of the atria and ears in the form comb muscles.

In the myocardium of the ventricles there are muscle bundles in three directions: external longitudinal, medium circular, internal longitudinal. External and internal bundles are common to both ventricles and in the region of the apex of the heart directly pass one into the other. Internal bundles form fleshy trabeculae And papillary muscles. The middle circular muscles form both general and isolated bundles for the left and right ventricles. The interventricular septum is formed over a greater extent by the myocardium [the muscular part (pars muscularis)], and at the top in a small area - a connective tissue plate covered on both sides with an endocardium - a membranous part (pars membranacea).

Endocardium(endocardium) lines the cavity of the heart, including papillary muscles, tendon chords, trabeculae. The valve leaflets are also folds (duplication) of the endocardium, in which the connective tissue layer is located. In the ventricles, the endocardium is thinner than in the atria. It consists of a muscular-elastic layer covered with endothelium.

The myocardium has a special system of fibers that differ from typical (contractile) cardiomyocytes in that they contain more sarcoplasm and fewer myofibrils. These specialized muscle fibers form conduction system of the heart(cardiac stimulation complex) (systema conducente cordis (complexus stimulans cordis))(Fig. 156), which consists of nodes and bundles capable of conducting excitation to various parts of the myocardium. Nerve fibers and groups of nerve cells are located along the bundles and in the nodes. Such a neuromuscular complex allows you to coordinate the sequence of contraction of the wall of the chambers of the heart.

sinoatrial node (nodus sinuatrialis) lies in the wall of the right atrium between the right ear and the superior vena cava, under the epicardium. The length of this node is on average 8-9 mm, width 4 mm, thickness

Rice. 156. Conduction system of the heart:

a - the right atrium and ventricle are opened: 1 - superior vena cava; 2 - sinoatrial node; 3 - oval fossa; 4 - atrioventricular node;

5 - inferior vena cava; 6 - valve of the coronary sinus; 7 - atrioventricular bundle; 8 - his right leg; 9 - branching left leg; 10 - valve of the pulmonary trunk;

b - the left atrium and ventricle are opened: 1 - anterior papillary muscle; 2 - left leg of the atrioventricular bundle; 3 - aortic valve; 4 - aorta; 5 - pulmonary trunk; 6 - pulmonary veins; 7 - inferior vena cava

2-3 mm. Beams depart from it to the atrial myocardium, to the ears of the heart, the mouths of the hollow and pulmonary veins, to the atrioventricular node.

atrioventricular node (nodus atrioventricularis) lies on the right fibrous triangle, above the attachment of the septal leaflet of the tricuspid valve, under the endocardium. The length of this node is 5-8 mm, width 3-4 mm. From it departs into the interventricular septum the atrioventricular bundle (fasc. atrioventricularis) about 10 mm long. The atrioventricular bundle is divided into legs: right (crus dextrum) and left (crus sinistrum). The legs lie under the endocardium, the right one is also in the thickness of the muscular layer of the septum, from the side of the cavities of the corresponding ventricles. The left leg of the bundle is divided into 2-3 branches, branching further to very thin bundles, passing into the myocardium. The right leg, thinner, goes almost to the apex of the heart, where it divides and passes into the myocardium. Under normal conditions

automatic heart rate occurs in the sinoatrial node. From it, impulses are transmitted through bundles to the muscles of the mouths of the veins, the ears of the heart, the atrial myocardium to the atrioventricular node and further along the atrioventricular bundle, its legs and branches to the muscles of the ventricles. Excitation spreads spherically from the inner layers of the myocardium to the outer.

chambers of the heart

Right atrium(atrium dextrum)(Fig. 157, see Fig. 153) has a cubic shape. Below it communicates with the right ventricle through the right atrioventricular orifice. (ostium atrioventriculare dextrum), which has a valve that passes blood from the atrium to the ventricle and prevents it from flowing back

Rice. 157. Heart drug. Opened right atrium:

1 - comb muscles of the right ear; 2 - border ridge; 3 - the mouth of the superior vena cava; 4 - cut of the right ear; 5 - right atrioventricular valve; 6 - the location of the atrioventricular node; 7 - the mouth of the coronary sinus; 8 - valve of the coronary sinus; 9 - flap of the inferior vena cava; 10 - the mouth of the inferior vena cava; 11 - oval fossa; 12 - edge of the oval fossa; 13 - location of the intervenous tubercle

laziness. Anteriorly, the atrium forms a hollow process - the right ear (auricula dextra). The inner surface of the right ear has a number of elevations formed by bundles of pectinate muscles. The crest muscles end, forming an eminence - a border crest (crista terminalis).

Inner wall of the atrium - interatrial septum (septum intertriale) smooth. In its center there is an almost round depression with a diameter of up to 2.5 cm - an oval fossa (fossa ovalis). The edge of the oval fossa (limbus fossae ovalis) thickened The bottom of the fossa is formed, as a rule, by two layers of the endocardium. The embryo has an oval hole in place of the oval fossa (for. ovale), through which the atria communicate. Sometimes the foramen ovale does not close by the time of birth and contributes to the mixing of arterial and venous blood. Such a defect is removed surgically.

Behind, it flows into the right atrium at the top superior vena cava, at the bottom - inferior vena cava. The mouth of the inferior vena cava is limited by a flap (valvula vv. cavae inferioris), which is a fold of the endocardium up to 1 cm wide. The flap of the inferior vena cava in the embryo directs the blood stream to the foramen ovale. Between the mouths of the vena cava, the wall of the right atrium protrudes and forms the sinus of the vena cava (sinus venarum cavarum). On the inner surface of the atrium between the mouths of the vena cava there is an elevation - intervenous tubercle (tuberculum intervenosum). The coronary sinus of the heart flows into the posteroinferior part of the atrium (sinus coronarius cordis), having a small damper (valvula sinus coronaria).

Right ventricle(ventriculus dexter)(Fig. 158, see Fig. 153) has the shape of a trihedral pyramid, with its base facing up. According to the shape of the ventricle, it has 3 walls: anterior, posterior and internal - the interventricular septum (septum interventriculare). The ventricle is divided into two parts: proper ventricle And right arterial cone, located in the upper left part of the ventricle and continuing into the pulmonary trunk.

The inner surface of the ventricle is uneven due to the formation of fleshy trabeculae going in different directions (trabeculae carneae). Trabeculae on the interventricular septum are very weakly expressed.

At the top, the ventricle has 2 openings: on the right and behind - the right atrioventricular; front and left - opening of the pulmonary trunk (ostium trunci pulmonalis). Both openings are closed with valves.

Rice. 158. Internal structures of the heart:

1 - cut plane; 2 - fleshy trabeculae of the right ventricle; 3 - anterior papillary muscle (cut off); 4 - tendon chords; 5 - cusps of the right atrioventricular valve; 6 - right ear; 7 - superior vena cava; 8 - aortic valve flap; 9 - damper knot; 10 - leaflets of the left atrioventricular valve; 11 - left ear; 12 - membranous part of the interventricular septum; 13 - muscular part of the interventricular septum; 14 - anterior papillary muscles of the left ventricle; 15 - posterior papillary muscles

Atrioventricular valves consist of fibrous rings; sashes, atrioventricular openings attached with their base on the fibrous rings, and with free edges facing the ventricular cavity; tendon chords And papillary muscles, formed by the inner layer of the myocardium of the ventricles (Fig. 159).

sashes (cuspes) are folds of the endocardium. There are 3 of them in the right atrioventricular valve, so the valve is called a tricuspid valve. Possibly more folds.

Rice. 159. Heart valves:

a - condition during diastole with remote atria: left atrioventricular valve: 1 - tendon chords; 2 - papillary muscle; 3 - left fibrous ring; 4 - rear sash; 5 - front sash; aortic valve: 6 - rear semilunar damper; 7 - left semilunar valve; 8 - right semilunar valve; pulmonary valve: 9 - left semilunar valve; 10 - right semilunar valve; 11 - front semilunar damper; right atrioventricular valve: 12 - front sash; 13 - partition sash; 14 - rear sash; 15 - papillary muscles with tendon chords extending to the valves; 16 - right fibrous ring; 17 - right fibrous triangle; b - state during systole

Tendon chords (chordae tendineae)- thin fibrous formations running in the form of threads from the edges of the valves to the tops of the papillary muscles.

Papillary muscles (mm. papillares) vary by location. There are usually 3 in the right ventricle: front, back And septal. The number of muscles, as well as valves, can be large.

Pulmonary valve (valva truncipulmonalis) prevents backflow of blood from the pulmonary trunk into the ventricle. It consists of 3 semilunar flaps (valvulae semilunares). In the middle of each semilunar valve there are thickenings - nodules (noduli valvularum semilunarium), contributing to a more hermetic closure of the dampers.

Left atrium(atrium sinistrum) just like the right one, cubic in shape, forms an outgrowth on the left - the left ear (auricula sinistra). The inner surface of the walls of the atrium is smooth, with the exception of the walls of the ear, where there are comb muscles. On the back wall are openings of the pulmonary veins(two on the right and left).

On the interatrial septum from the side of the left atrium is noticeable oval hole, but it is less pronounced than in the right atrium. The left ear is narrower and longer than the right.

left ventricle(ventriculus sinister) conical shape with a base facing upwards, has 3 walls: front, back And internal- interventricular septum. There are 2 holes at the top: left and front - left atrioventricular, right and behind opening of the aorta (ostium aortae). As in the right ventricle, these openings have valves: valva atrioventricularis sinistra et valva aortae.

The inner surface of the ventricle, with the exception of the septum, has numerous fleshy trabeculae.

Left atrioventricular, mitral, valve usually contains two sashes and two papillary muscles- front and back. Both cusps and muscles are larger than in the right ventricle.

The aortic valve is shaped like a pulmonary valve three semilunar valves. The initial part of the aorta at the location of the valve is slightly dilated and has 3 depressions - aortic sinuses (sinus aortae).

Topography of the heart

The heart is located in the lower part of the anterior mediastinum, in the pericardium, between the sheets of the mediastinal pleura. Relative to

to the midline of the body, the heart is located asymmetrically: about 2/3 - to the left of it, about 1/3 - to the right. The longitudinal axis of the heart (from the middle of the base to the top) goes obliquely from top to bottom, from right to left and from back to front. In the pericardial cavity, the heart is suspended on large vessels.

The position of the heart is different: transverse, oblique or vertical. The transverse position is more common in individuals with a wide and short chest and high standing dome of the diaphragm, vertical - in people with a narrow and long chest.

In a living person, the boundaries of the heart can be determined by percussion, as well as radiographically. The frontal silhouette of the heart is projected onto the anterior chest wall, corresponding to its sternocostal surface and large vessels. There are right, left and lower borders of the heart (Fig. 160).

Rice. 160. Projections of the heart, cusp and semilunar valves on the anterior surface of the chest wall:

1 - projection of the valve of the pulmonary trunk; 2 - projection of the left atrioventricular (mitral) valve; 3 - apex of the heart; 4 - projection of the right atrioventricular (tricuspid) valve; 5 - projection of the aortic valve. The auscultation sites of the left atrioventricular (long arrow) and aortic (short arrow) valves are shown.

Right border of the heart in the upper part corresponding to the right surface of the superior vena cava, runs from the upper edge of the II rib at the place of its attachment to the sternum to the upper edge of the III rib, 1 cm to the right of the right edge of the sternum. The lower part of the right border corresponds to the edge of the right atrium and runs from the III to V ribs in the form of an arc spaced from the right edge of the sternum by 1.0-1.5 cm. At the level of the V rib, the right border passes into the lower one.

Inferior border of the heart formed by the edge of the right and partially left ventricles. It runs obliquely down and to the left, crosses the sternum above the base of the xiphoid process, the cartilage of the VI rib and reaches the fifth intercostal space, 1.5-2.0 cm medially from the midclavicular line.

Left border of the heart represented by the aortic arch, pulmonary trunk, left ear, left ventricle. It runs from the bottom

I rib at the place of its attachment to the sternum on the left to the upper edge

II ribs, 1 cm to the left of the edge of the sternum (respectively, the projection of the aortic arch), then at the level of the second intercostal space, 2.0-2.5 cm outward from the left edge of the sternum (respectively, the pulmonary trunk). The continuation of this line at the level of the III rib corresponds to the left heart ear. From the lower edge of the III rib, the left border runs in a convex arc to the fifth intercostal space, 1.5-2.0 cm medially from the midclavicular line, corresponding to the edge of the left ventricle.

Aortic ostium And pulmonary trunk and their valves are projected at the level of the third intercostal space: the mouth of the aorta is behind the left half of the sternum, and the mouth of the pulmonary trunk is at its left edge.

atrioventricular orifices are projected along a line passing from the place of attachment to the sternum of the cartilage of the right V rib to the place of attachment of the cartilage of the left III rib. The projection of the right atrioventricular opening occupies the right half of this line, the left - the left (see Fig. 160).

Sternocostal surface the heart is partially adjacent to the sternum and cartilages of the left III-V ribs. The anterior surface is in contact with the mediastinal pleura and the anterior costal-mediastinal sinuses of the pleura for a longer distance.

Diaphragmatic surface heart is adjacent to the diaphragm, borders on the main bronchi, esophagus, descending aorta and pulmonary arteries.

The heart is placed in a closed fibrous-serous sac (pericardium) and only through it is related to the surrounding organs.

Heart- the central organ of the blood and lymph circulation system. Due to the ability to contract, the heart sets the blood in motion.

Wall of the heart consists of three membranes: endocardium, myocardium and epicardium.

Myocardium(middle shell of the heart) - a multi-tissue shell, consisting of striated cardiac muscle tissue, intermuscular loose connective tissue, numerous vessels and capillaries, as well as nerve elements. The main structure is cardiac muscle tissue, which in turn consists of cells that form and conduct nerve impulses, and cells of the working myocardium that provide contraction of the heart (cardiomyocytes). Among the cells that form and conduct impulses in the conduction system of the heart, there are three types: P-cells (pacemaker cells), intermediate cells and Purkinya cells (fibers).

P cells- pacemaker cells located in the center of the sinus node of the conduction system of the heart. They have a polygonal shape and are determined to spontaneous depolarization of the plasmalemma. Myofibrils and organelles of general importance in pacemaker cells are weakly expressed. Intermediate cells are a heterogeneous group of cells that transmit excitation from P-cells to Purkinya cells. Purkinya cells are cells with a small number of myofibrils and a complete absence of the T-system, with a large amount of cytoplasm compared to working contractile myocytes. Purkinya cells transmit excitation from intermediate cells to contractile cells of the myocardium. They are part of the bundle of His of the conduction system of the heart.

A number of drugs and other factors that can lead to arrhythmias and heart block have an adverse effect on pacemaker cells and Purkinya cells. The presence in the heart of its own conducting system is extremely important, since it provides a rhythmic change in systolic contractions and diastole of the heart chambers (atria and ventricles) and the operation of its valvular apparatus.

Desmosomes contribute to the strong adhesion of contractile myocytes into functional muscle fibers, and nexuses ensure the rapid propagation of plasmolemma depolarization waves from one muscle cell to another and the existence of a cardiac muscle fiber as a single metabolic unit. Characteristic for myocytes of the working myocardium is the presence of anastomosing bridges - interconnected fragments of the cytoplasms of muscle cells of different fibers with myofibrils located in them. Thousands of such bridges turn the muscle tissue of the heart into a mesh structure capable of synchronously and efficiently contracting and ejecting the necessary systolic blood volumes from the ventricular cavities. After suffering extensive myocardial infarctions (acute ischemic necrosis of the heart wall), when the muscular tissue of the heart, the system of intercalated discs, anastomosing bridges and the conduction system are diffusely affected, disturbances in the rhythm of the heart, up to fibrillation, occur. In this case, the contractile activity of the heart turns into separate uncoordinated twitches of muscle fibers and the heart is not able to eject the necessary systolic portions of blood into the peripheral circulation.

Myocardium consists in general of highly specialized cells that have lost the ability to divide by mitosis. Mitoses of cardiomyocytes are observed only in certain parts of the atria (Rumyantsev P.P. 1982). At the same time, the myocardium is characterized by the presence of polyploid myocytes, which significantly enhances its working potential. The phenomenon of polyploidy is most often observed in compensatory reactions of the myocardium, when the load on the heart increases, and in pathology (failure of heart valves, lung diseases, etc.).

Heart- an organ that has the ability to automate contractions. It can function autonomously within certain limits. However, in the body, the activity of the heart is under the control of the nervous system. In the intramural nerve nodes of the heart there are sensitive vegetative neurons (Type II Dogel cells), small intensely fluorescent cells - MYTH cells and effector autonomic neurons (Type 1 Dogel cells). MYTH cells are considered as intercalary neurons.

Inner lining of the heart, or endocardium

Endocardium, endocardium(see Fig. 704. 709), formed from elastic fibers, among which are located connective tissue and smooth muscle cells. From the side of the cavity of the heart, the endocardium is covered with endothelium.

The endocardium lines all the chambers of the heart, is tightly fused with the underlying muscle layer, follows all its irregularities formed by the fleshy trabeculae, pectinate and papillary muscles, as well as their tendon outgrowths.

On the inner shell of the vessels leaving the heart and flowing into it - the hollow and pulmonary veins, the aorta and the pulmonary trunk - the endocardium passes without sharp boundaries. In the atria, the endocardium is thicker than in the ventricles, especially in the left atrium, and thinner where it covers the papillary muscles with tendon chords and fleshy trabeculae.

In the most thinned sections of the walls of the atria, where gaps form in their muscular layer, the endocardium is in close contact and even fuses with the epicardium. In the region of the fibrous rings of the atrioventricular openings, as well as the openings of the aorta and pulmonary trunk, the endocardium, by doubling its leaf - endocardial duplication - forms the leaflets of the atrioventricular valves and the semilunar valves of the pulmonary trunk and aorta. The fibrous connective tissue between both sheets of each of the cusps and semilunar valves is connected to the fibrous rings and thus fixes the valves to them.

shells of the heart

The heart is located in a pericardial sac called the pericardium. The wall of the heart consists of three layers: the outer one - the epicardium, the middle one - the myocardium, and the inner one - the endocardium.

The outer shell of the heart. epicardium

The epicardium is a smooth, thin and transparent membrane. It is the visceral plate of the pericardial sac (pericardium). The connective tissue base of the epicardium in various parts of the heart, especially in the sulci and in the apex, includes adipose tissue. With the help of the specified connective tissue, the epicardium is most tightly fused with the myocardium in places of the least accumulation or absence of adipose tissue.

The muscular layer of the heart, or myocardium

The middle, muscular membrane of the heart (myocardium), or cardiac muscle, is a powerful and significant part of the wall of the heart in thickness.

Between the muscular layer of the atria and the muscular layer of the ventricles lies dense fibrous tissue, due to which fibrous rings, right and left, are formed. From the side of the outer surface of the heart, their location corresponds to the region of the coronal sulcus.

The right fibrous ring, which surrounds the right atrioventricular orifice, is oval in shape. The left fibrous ring does not completely surround the left atrioventricular opening: on the right, on the left and behind, and has a horseshoe shape.

With its anterior sections, the left fibrous ring is attached to the aortic root, forming triangular connective tissue plates around its posterior periphery - the right and left fibrous triangles.

The right and left fibrous rings are interconnected into a common plate, which completely, with the exception of a small area, isolates the muscles of the atria from the muscles of the ventricles. In the middle of the fibrous plate connecting the rings there is a hole through which the muscles of the atria are connected to the muscles of the ventricles through the neuromuscular atrioventricular bundle conducting impulses.

In the circumference of the openings of the aorta and the pulmonary trunk, there are also interconnected fibrous rings; the aortic ring is connected to the fibrous rings of the atrioventricular orifices.

Muscular layer of the atria

In the walls of the atria, two muscle layers are distinguished: superficial and deep.

The surface layer is common to both atria and represents muscle bundles that run mainly in the transverse direction; they are more pronounced on the anterior surface of the atria, forming here a relatively wide muscle layer in the form of a horizontally located inter-auricular bundle passing to the inner surface of both ears.

On the posterior surface of the atria, the muscle bundles of the superficial layer are partially woven into the posterior sections of the septum.

On the posterior surface of the heart, in the gap formed by the convergence of the borders of the inferior vena cava, the left atrium and the venous sinus, between the bundles of the surface layer of muscles there is a depression covered by the epicardium - the neural fossa. Through this fossa, nerve trunks enter the atrial septum from the posterior cardiac plexus, which innervate the atrial septum, the ventricular septum and the muscle bundle that connects the muscles of the atria with the muscles of the ventricles - the atrioventricular bundle.

The deep layer of muscles of the right and left atria is not common to both atria. It distinguishes ring-shaped, or circular, and loop-shaped, or vertical, muscle bundles.

Circular muscle bundles lie in large numbers in the right atrium; they are located mainly around the openings of the vena cava, passing to their walls, around the coronary sinus of the heart, at the mouth of the right ear and at the edge of the oval fossa; in the left atrium, they lie mainly around the openings of the four pulmonary veins and at the neck of the left ear.

Vertical muscle bundles are located perpendicular to the fibrous rings of the atrioventricular holes, attaching to them with their ends. Part of the vertical muscle bundles enters the thickness of the cusps of the mitral and tricuspid valves.

The crest muscles are also formed by bundles of the deep layer. They are most developed on the inner surface of the anterior right wall of the right atrium, as well as the right and left ears; in the left atrium they are less pronounced. In the intervals between the comb muscles, the wall of the atria and ears is especially thinned.

On the inner surface of both ears there are very short and thin bundles, the so-called fleshy crossbars. Crossing in different directions, they form a very thin loop-like network.

Muscular layer of the ventricles

In the muscular membrane (myocardium) there are three muscle layers: outer, middle and deep. The outer and deep layers, passing from one ventricle to another, are common in both ventricles; the middle one, although connected with the other two, outer and deep, layers, but surrounds each ventricle separately.

The outer, relatively thin, layer consists of oblique, partly rounded, partly flattened bundles. The bundles of the outer layer begin at the base of the heart from the fibrous rings of both ventricles and partly from the roots of the pulmonary trunk and aorta. On the front surface of the heart, the outer bundles go from right to left, and on the back - from left to right. At the apex of the left ventricle, both bundles of the outer layer form the so-called whirlpool of the heart and penetrate into the depths of the walls of the heart, passing into the deep muscle layer.

The deep layer consists of bundles that rise from the top of the heart to its base. They have a cylindrical, partly oval shape, are repeatedly split and reconnected, forming loops of various sizes. The shorter of these bundles do not reach the base of the heart, they are directed obliquely from one wall of the heart to another, in the form of fleshy crossbars. The crossbars are located in large numbers along the entire inner surface of both ventricles and have different sizes in different areas. Only the inner wall (septum) of the ventricles, immediately below the arterial openings, is devoid of these crossbars.

A number of such short, but more powerful muscle bundles, partly connected with both the middle and outer layers, freely protrude into the cavity of the ventricles, forming papillary muscles of various sizes and cones.

There are three papillary muscles in the cavity of the right ventricle, and two in the cavity of the left. Tendon strings begin from the top of each of the papillary muscles, through which the papillary muscles are connected to the free edge and partly the lower surface of the cusps of the tricuspid or mitral valves.

However, not all tendon strings are associated with the papillary muscles. A number of them begin directly from the fleshy crossbars formed by the deep muscle layer and are most often attached to the lower, ventricular, surface of the valves.

The papillary muscles with tendinous strings hold the cusp valves when they are slammed by blood flow from the contracted ventricles (systole) to the relaxed atria (diastole). Encountering, however, obstacles from the valves, the blood rushes not into the atria, but into the opening of the aorta and pulmonary trunk, the semilunar valves of which are pressed against the walls of these vessels by the blood flow and thereby leave the lumen of the vessels open.

Located between the outer and deep muscle layers, the middle layer forms a number of well-defined circular bundles in the walls of each ventricle. The middle layer is more developed in the left ventricle, so the walls of the left ventricle are much thicker than the right one. The bundles of the middle muscle layer of the right ventricle are flattened and have an almost transverse and somewhat oblique direction from the base of the heart to the apex.

In the left ventricle, among the bundles of the middle layer, bundles lying closer to the outer layer and located closer to the deep layer can be distinguished.

The interventricular septum is formed by all three muscular layers of both ventricles. However, the muscle layers of the left ventricle take a large part in its formation. Its thickness is almost equal to the thickness of the wall of the left ventricle. It protrudes towards the cavity of the right ventricle. For 4/5, it represents a well-developed muscle layer. This, much larger, part of the interventricular septum is called the muscular part.

The upper (1/5) part of the interventricular septum is thin, transparent and is called the membranous part. The septal leaflet of the tricuspid valve is attached to the membranous part.

The muscles of the atria are isolated from the muscles of the ventricles. An exception is a bundle of fibers starting in the atrial septum in the region of the coronary sinus of the heart. This bundle consists of fibers with a large amount of sarcoplasm and a small amount of myofibrils; the bundle also includes nerve fibers; it originates at the confluence of the inferior vena cava and goes to the ventricular septum, penetrating into its thickness. In the bundle, the initial, thickened part, called the atrioventricular node, is distinguished, passing into a thinner trunk - the atrioventricular bundle, the bundle goes to the interventricular septum, passes between both fibrous rings and at the upper posterior part of the muscular part of the septum is divided into the right and left legs .

The right leg, short and thinner, follows the septum from the side of the cavity of the right ventricle to the base of the anterior papillary muscle and spreads in the muscular layer of the ventricle in the form of a network of thin fibers (Purkinje).

The left leg, wider and longer than the right one, is located on the left side of the ventricular septum, in its initial sections it lies more superficially, closer to the endocardium. Heading to the base of the papillary muscles, it breaks up into a thin network of fibers that form the anterior, middle and posterior bundles, spreading in the myocardium of the left ventricle.

At the confluence of the superior vena cava into the right atrium, between the vein and the right ear is the sinoatrial node.

These bundles and nodes, accompanied by nerves and their branches, are the conduction system of the heart, which serves to transmit impulses from one part of the heart to another.

Inner lining of the heart, or endocardium

The inner shell of the heart, or endocardium, is formed from collagen and elastic fibers, among which are located connective tissue and smooth muscle cells.

From the side of the cavities of the heart, the endocardium is covered with endothelium.

The endocardium lines all the cavities of the heart, is tightly fused with the underlying muscle layer, follows all its irregularities formed by the fleshy crossbars, the pectinate and papillary muscles, as well as their tendon outgrowths.

On the inner shell of the vessels leaving the heart and flowing into it - the hollow and pulmonary veins, the aorta and the pulmonary trunk - the endocardium passes without sharp boundaries. In the atria, the endocardium is thicker than in the ventricles, while it is thicker in the left atrium, less where it covers the papillary muscles with tendon strings and fleshy crossbars.

In the most thinned sections of the walls of the atria, where gaps form in the muscle layer, the endocardium is in close contact and even fuses with the epicardium. In the area of fibrous rings, atrioventricular openings, as well as openings of the aorta and pulmonary trunk, the endocardium, by doubling its leaf, duplicating the endocardium, forms the leaflets of the mitral and tricuspid valves and the semilunar valves of the pulmonary trunk and aorta. The fibrous connective tissue between both sheets of each of the cusps and semilunar valves is connected to the fibrous rings and thus fixes the valves to them.

Pericardial sac or pericardium

The pericardium, or pericardium, has the shape of an obliquely cut cone with a lower base located on the diaphragm and an apex reaching almost to the level of the angle of the sternum. In width, it extends more to the left than to the right.

In the pericardial sac, there are: an anterior (sternocostal) part, a posterior inferior (diaphragmatic) part, and two lateral - right and left - mediastinal parts.

The sternocostal part of the pericardial sac faces the anterior chest wall and is located, respectively, in the body of the sternum, V-VI costal cartilages, intercostal spaces and the left part of the xiphoid process.

The lateral sections of the sternocostal part of the pericardial sac are covered by the right and left sheets of the mediastinal pleura, which separate it in the anterior sections from the anterior chest wall. The areas of the mediastinal pleura covering the pericardium are distinguished under the name of the pericardial part of the mediastinal pleura.

The middle of the sternocostal part of the bag, the so-called free part, is open in the form of two triangular-shaped spaces: the upper, smaller, corresponding to the thymus gland, and the lower, larger, corresponding to the pericardium, facing their bases up (to the notch of the sternum) and down (to the diaphragm ).

In the region of the upper triangle, the sternocostal part of the pericardium is separated from the sternum by loose connective and adipose tissue, in which children have thymus. The compacted part of this fiber forms the so-called superior sterno-periocardial ligament, which fixes here the anterior wall of the pericardium to the handle of the sternum.

In the area of the lower triangle, the pericardium is also separated from the sternum by loose tissue, in which a compacted part is isolated, the lower sterno-periocardio-adrenal ligament, which fixes the lower part of the pericardium to the sternum.

In the diaphragmatic part of the pericardial sac, there is an upper section involved in the formation of the anterior border of the posterior mediastinum, and a lower section covering the diaphragm.

The upper section is adjacent to the esophagus, thoracic aorta and unpaired vein, from which this part of the pericardium is separated by a layer of loose connective tissue and a thin fascial sheet.

The lower section of the same part of the pericardium, which is its base, fuses tightly with the tendon center of the diaphragm; extending slightly to the anterior areas of its muscular part, it is connected to them by loose fiber.

The right and left mediastinal parts of the pericardial sac are adjacent to the mediastinal pleura; the latter is connected to the pericardium by means of loose connective tissue and can be separated by careful preparation. In the thickness of this loose fiber, connecting the mediastinal pleura with the pericardium, passes the phrenic nerve and the accompanying pericardial-bag-diaphragmatic vessels.

The pericardium consists of two parts - internal, serous (serous pericardial sac) and external, fibrous (fibrous pericardial sac).

The serous pericardial sac consists of two serous sacs, as it were, nested one inside the other - the outer one, freely surrounding the heart (the serous sac of the pericardium itself), and the inner one - the epicardium, tightly fused with the myocardium. The serous cover of the pericardium is the parietal plate of the serous pericardial sac, and the serous cover of the heart is the visceral plate (epicardium) of the serous pericardial sac.

The fibrous pericardial sac, which is especially pronounced on the anterior wall of the pericardium, fixes the pericardial sac to the diaphragm, the walls of large vessels and through the ligaments to the inner surface of the sternum.

The epicardium passes into the pericardium at the base of the heart, at the confluence of large vessels: the hollow and pulmonary veins and the exit of the aorta and pulmonary trunk.

Between the epicardium and the pericardium there is a slit-like space (the cavity of the pericardial sac), containing a small amount of pericardial sac fluid, which wets the serous surfaces of the pericardium, thereby causing one serous plate to slide over the other during heart contractions.

As indicated, the parietal plate of the serous pericardial sac passes into the splanchnic plate (epicardium) at the site of entry and exit of large blood vessels from the heart.

If, after the removal of the heart, the pericardial sac is examined from the inside, then the large vessels in relation to the pericardium are located along its posterior wall along approximately two lines - the right, more vertical, and the left, somewhat inclined towards it. On the right line, the superior vena cava, two right pulmonary veins and the inferior vena cava lie from top to bottom, along the left line - the aorta, pulmonary trunk and two left pulmonary veins.

At the site of the transition of the epicardium into the parietal plate, several sinuses of various shapes and sizes are formed. The largest of these are the transverse and oblique sinuses of the pericardial sac.

Transverse sinus of the pericardial sac. The initial sections (roots) of the pulmonary trunk and aorta, adjacent to one another, are surrounded by a common leaf of the epicardium; posterior to them are the atria and next to the right is the superior vena cava. The epicardium from the side of the posterior wall of the initial sections of the aorta and the pulmonary trunk goes up and back to the atria located behind them, and from the latter - down and forward again to the base of the ventricles and the root of these vessels. Thus, between the aortic root and the pulmonary trunk in front and the atria behind, a passage is formed - a sinus, which is clearly visible when the aorta and pulmonary trunk are pulled anteriorly, and the superior vena cava - posteriorly. This sinus is bounded from above by the pericardium, from behind by the superior vena cava and the anterior surface of the atria, from the front by the aorta and the pulmonary trunk; the right and left transverse sinus is open.

Oblique sinus of the pericardial sac. It is located below and behind the heart and represents a space bounded in front by the posterior surface of the left atrium covered with epicardium, behind - by the posterior, mediastinal, part of the pericardium, on the right - by the inferior vena cava, on the left - by the pulmonary veins, also covered by the epicardium. In the upper blind pocket of this sinus there is a large number of nerve nodes and trunks of the cardiac plexus.

Between the epicardium covering the initial part of the aorta (up to the level of the brachiocephalic trunk leaving it), and the parietal plate continuing from it at this place, a small pocket is formed - the aortic protrusion. On the pulmonary trunk, the transition of the epicardium to the specified parietal plate occurs at the level (sometimes below) of the arterial ligament. On the superior vena cava, this transition is carried out below the place where the unpaired vein flows into it. On the pulmonary veins, the junction almost reaches the hilum of the lungs.

On the posterolateral wall of the left atrium, between the left superior pulmonary vein and the base of the left atrium, a fold of the pericardial sac passes from left to right, the so-called fold of the superior left vena cava, in the thickness of which lie the oblique vein of the left atrium and the nerve plexus.

Three layers are distinguished in the wall of the heart: a thin inner layer - the endocardium, a thick muscle layer - the myocardium and a thin outer layer - the epicardium, which is a visceral sheet of the serous membrane of the heart - the pericardium (pericardial sac).

Endocardium (endocardium) lines the cavity of the heart from the inside, repeating its complex relief, and covers the papillary muscles with their tendon chords. The atrioventricular valves, the aortic valve and the pulmonary valve, as well as the valves of the inferior vena cava and the coronary sinus, are formed by duplications of the endocardium, inside which connective tissue fibers are located.

The endocardium is formed by a single layer of flat polygonal endotheliocytes located on a thin basement membrane. The cytoplasm of endotheliocytes contains a large number of micropinocytic vesicles. Endotheliocytes are connected to each other by intercellular contacts, including nexuses. On the border with the myocardium there is a thin layer of loose fibrous connective tissue. The middle layer of the heart wall - myocardium (myocardium), is formed by cardiac striated muscle tissue and consists of cardiac myocytes (cardiomyocytes). Cardiomyocytes are interconnected by a large number of jumpers (intercalary discs), with the help of which they are connected into muscle complexes that form a narrow-loop network. This muscular network provides a complete rhythmic contraction of the atria and ventricles. The thickness of the myocardium is the smallest in the atria, and the largest - in the left ventricle.

The muscle bundles of the atria and ventricles begin from fibrous rings that completely separate the atrial myocardium from the ventricular myocardium. These fibrous rings, like a number of other connective tissue formations of the heart, are part of its soft skeleton. The skeleton of the heart includes: interconnected right and left fibrous rings (annuli fibrosi dexter et sinister), which surround the right and left atrioventricular openings. These rings form the support of the right and left atrioventricular valves (their projection everywhere corresponds to the coronary sulcus of the heart). The right and left fibrous triangles (trigonum fibrosum dextrum et trigonum fibrosum sinistrum) are dense plates that are adjacent to the posterior semicircle of the aorta on the right and left and are formed as a result of the fusion of the left fibrous ring with the connective tissue ring of the aortic opening. The right, most dense, fibrous triangle, which actually connects the left and right fibrous rings and the connective tissue ring of the aorta, is in turn connected to the membranous part of the interventricular septum. In the right fibrous triangle there is a small hole through which the fibers of the atrioventricular bundle of the conduction system of the heart pass.

atrial myocardium separated by fibrous rings from the myocardium of the ventricles. The synchrony of myocardial contractions is provided by the conduction system of the heart, which is the same for the atria and ventricles. In the atria, the myocardium consists of two layers: superficial, common to both atria, and deep, separate for each of them. In the superficial layer, the muscle bundles are located transversely, in the deep layer - longitudinally. Circular muscle bundles loop around the mouths of the veins that flow into the atria, like constrictors. Longitudinally lying muscle bundles originate from the fibrous rings and protrude in the form of vertical strands into the cavities of the auricles of the atria and form the pectinate muscles.

Myocardium of the ventricles consists of three different muscle layers: external (superficial), medium and internal (deep). The outer layer is represented by obliquely oriented muscle bundles, which, starting from the fibrous rings, continue down to the top of the heart, where they form a heart curl (vortex cordis). Then they pass into the inner (deep) layer of the myocardium, the bundles of which are located longitudinally. Due to this layer, papillary muscles and fleshy trabeculae are formed. The outer and inner layers of the myocardium are common to both ventricles. The middle layer located between them, formed by circular (circular) muscle bundles, is separate for each ventricle. The interventricular septum is formed in its greater part (its muscular part) by the myocardium and the endocardium covering it. The basis of the upper section of this septum (its membranous part) is a plate of fibrous tissue.

The outer shell of the heart - the epicardium (epicardium), adjacent to the myocardium from the outside, is a visceral sheet of the serous pericardium. The epicardium is built according to the type of serous membranes and consists of a thin plate of connective tissue covered with mesothelium. The epicardium covers the heart, the initial sections of the ascending aorta and pulmonary trunk, the final sections of the caval and pulmonary veins. Through these vessels, the epicardium passes into the parietal plate of the serous pericardium.