The thickness of the muscular wall of the heart is greatest. Heart

Outer shell of the heart Fig. 701. Heart, cor. The sternocostal (anterior) surface.] (The pericardium is removed at the place of its transition to the epicardium.) (Diagram). Rice. 700. X-ray image hearts and large vessels in various projections (diagram).

The right and left fibrous rings are interconnected in a common plate, which completely, with the exception of a small area, isolates the atrial musculature from the ventricular musculature. In the middle of the fibrous plate connecting the ring, there is an opening through which the atrial musculature is connected to the ventricular musculature by means of the atrioventricular bundle.

In the circumference of the openings of the aorta and the pulmonary trunk (see Fig.) There are also fibrous rings connected to each other; the aortic ring is connected to the fibrous rings of the atrioventricular openings.

The muscular membrane of the atria

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

Surface layer is common to both atria and is a muscle bundle that runs 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 (see Fig.), Passing to inner surface 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, between the bundles of the superficial layer of muscles, there is a depression covered with an epicardium, limited by the mouth of the inferior vena cava, the projection of the interatrial septum and the mouth of the venous sinus (see Fig.). At this site, the nerve trunks enter the atrial septum, which innervate the atrial septum and the ventricular septum - the atrioventricular bundle (Fig.).

The deep muscle layer of the right and left atria is not common to both atria. It distinguishes between circular and vertical muscle bundles.

Circular muscle bundles in large numbers lie 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 beginning of the left ear.

Vertical muscle bundles are located perpendicular to the fibrous rings of the atrioventricular openings, attaching to them with their ends. Some of the vertical muscle bundles enter the thickness of the atrioventricular valves.

Comb muscles, mm. pectinati are also formed by beams of a deep layer. They are most developed on the inner surface of the antero-right wall of the right atrial cavity, as well as on the right and left auricles; in the left atrium they are less pronounced. In the intervals between the comb muscles, the wall of the atria and auricles is especially thinned.

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

The muscular membrane of the ventricles

In the muscular membrane (see Fig.) (Myocardium), three muscle layers are distinguished: outer, middle and deep. The outer and deep layers, passing from one ventricle to another, are common in both ventricles; the middle, although connected to the other two layers, 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 sternocostal (front) surface of the heart, the outer bundles go from right to left, and along the diaphragmatic (bottom) - from left to right. At the apex of the left ventricle, those and other bundles of the outer layer form the so-called curl heart, vortex cordis(see fig.,), and penetrate deep into the walls of the heart, passing into a deep muscle layer.

The deep layer consists of bundles that rise from the apex of the heart to its base. They are cylindrical, and some of the beams are oval, they 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 trabeculae. Only the interventricular septum immediately under the arterial openings is devoid of these crossbeams.

A number of such short, but more powerful muscle bundles, partially associated with both the middle and the outer layer, protrude freely into the cavity of the ventricles, forming cone-shaped papillary muscles of various sizes (see Fig.,,).

The papillary muscles with tendinous chords hold the valve cusps when they are slammed by the blood flow, heading from the contracted ventricles (with systole) into the relaxed atria (with diastole). Meeting obstacles from the side of the valves, blood rushes not into the atria, but into the openings of the aorta and pulmonary trunk, the lunar valves of which are pressed by the blood flow to the walls of these vessels 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, therefore the walls of the left ventricle are much thicker than the walls of the right. 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.

Interventricular septum, septum interventriculare(see Fig.), formed by all three muscle layers of both ventricles, but more muscle layers of the left ventricle. The thickness of the septum reaches 10-11 mm, somewhat inferior to the thickness of the wall of the left ventricle. The interventricular septum is convex towards the cavity of the right ventricle and represents a well-developed muscle layer for 4/5. This much larger part of the interventricular septum is called muscle part, pars muscularis.

The upper (1/5) part of the interventricular septum is membranous part, pars membranacea... The septal flap of the right atrioventricular valve is attached to the membranous part.

Rice. 703. Cross sections of the heart at different levels (I-VII).

The heart is the main organ of the blood supply and lymph formation system in the body. It is presented in the form of a large muscle with several hollow chambers. Thanks to its ability to contract, it sets the blood in motion. In total, there are three membranes of the heart: epicardium, endocardium and myocardium. We will consider the structure, purpose and functions of each of them in this material.

The structure of the human heart - anatomy

The heart muscle consists of 4 chambers - 2 atria and 2 ventricles. The left ventricle and the left atrium form the so-called arterial part of the organ, based on the nature of the blood located here. In contrast, the right ventricle and right atrium make up the venous portion of the heart.

The blood organ is presented in the form of a flattened cone. It contains the base, the apex, the lower and the anteroposterior surfaces, as well as two edges - the left and right. The apex of the heart has a rounded shape and is entirely formed by the left ventricle. The atria are located in the base area, and the aorta lies in its front part.

Heart size

It is believed that in an adult, formed human individual, the dimensions of the heart muscle are equal to the dimensions of a clenched fist. In fact, on average, the length of this organ in a mature person is 12-13 cm.The heart is 9-11 cm across.

The heart mass of an adult male is about 300 g. In women, the average heart weight is about 220 g.

Phases of the heart

There are several separate phases of contraction of the heart muscle:

1. At the beginning, atrial contraction occurs. Then, with some delay, the contraction of the ventricles starts. During the course this process blood naturally tends to fill the reduced pressure chambers. Why, after this, there is no reverse outflow into the atria? The fact is that the blood is blocked by the gastric valves. Therefore, she can only move in the direction of the aorta, as well as the vessels of the pulmonary trunk.
2. The second phase is relaxation of the ventricles and atria. The process is characterized by a short-term decrease in the tone of the muscle structures from which these chambers are formed. The process causes a decrease in pressure in the ventricles. Thus, the blood begins to move in the opposite direction. However, this is prevented by the closing pulmonary and arterial valves. During relaxation, the ventricles are filled with blood from the atria. On the contrary, the atria are filled with bodily fluid from the large and

What is responsible for the work of the heart?

As you know, the functioning of the heart muscle is not an arbitrary act. The organ remains active continuously, even when the person is in a state of deep sleep. There are hardly any people who pay attention to heart rate during activity. But this is achieved due to a special structure built into the heart muscle itself - a system for generating biological impulses. It is noteworthy that the formation of this mechanism occurs even in the first weeks of intrauterine fetus. Subsequently, the impulse generation system does not allow the heart to stop throughout life.

V calm state the number of contractions of the heart muscle during a minute is about 70 beats. Within one hour, the number reaches 4200 hits. Considering that in the course of one contraction, the heart throws out circulatory system 70 ml of liquid, it is easy to guess that up to 300 liters of blood pass through it in an hour. How much blood does this organ pump over its entire life? This figure averages 175 million liters. Therefore, it is not surprising that the heart is called the ideal motor, which practically does not fail.

Shell of the heart

In total, 3 separate membranes of the heart muscle are distinguished:

1. The endocardium is the inner lining of the heart.
2. The myocardium is an internal muscle complex formed by a thick layer of filamentous fibers.
3. Epicardium is the thin outer shell of the heart.
4. The pericardium is an auxiliary cardiac membrane, which is a kind of bag that contains the whole heart.

Myocardium

The myocardium is a multi-tissue muscular membrane of the heart, which is formed by striated fibers, loose connective structures, nerve processes, as well as a branched network of capillaries. Here are P-cells that form and conduct nerve impulses... In addition, myocardium contains myocyte and cardiomyocyte cells, which are responsible for contraction blood organ.

The myocardium consists of several layers: inner, middle and outer. The internal structure consists of muscle bundles that are located longitudinally in relation to each other. In the outer layer, the bundles of muscle tissue are located obliquely. The latter go to the very top of the heart, where they form the so-called curl. The middle layer consists of circular muscle bundles, separate for each of the ventricles of the heart.

Epicard

The presented shell of the heart muscle has the smoothest, thinnest and somewhat transparent structure. The epicardium forms the outer tissues of the organ. In fact, the shell acts as an inner layer of the pericardium - the so-called bursa of the heart.

The surface of the epicardium is formed from mesothelial cells, under which there is a connective, loose structure, represented by connective fibers. In the region of the apex of the heart and in its grooves, the considered membrane includes adipose tissue. The epicardium grows together with the myocardium in the places of the least accumulation of fat cells.

Endocardium

Continuing to consider the lining of the heart, let's talk about the endocardium. The presented structure is formed by elastic fibers, which are composed of smooth muscle and connective cells... Endocardial tissue lines all hearts. On the elements extending from the blood organ: the aorta, pulmonary veins, the pulmonary trunk of the endocardial tissue passes smoothly, without clearly distinguishable boundaries. In the thinnest parts of the atria, the endocardium fuses with the epicardium.

Pericardium

The pericardium is the outer part of the heart and is also called the pericardial sac. The specified structure is presented in the form of a cut oblique cone. The inferior base of the pericardium is located on the diaphragm. To the top, the shell goes more into left side rather than to the right. This peculiar bag surrounds not only the heart muscle, but also the aorta, the mouth of the pulmonary trunk and adjacent veins.

The pericardium forms early in human individuals intrauterine development... This happens about 3-4 weeks after the formation of the embryo. Violations of the structure of this shell, its partial or complete absence, often leads to congenital heart defects.

Finally

In the presented material, we examined the structure of the human heart, the anatomy of its chambers and membranes. As you can see, the heart muscle has an extremely complex structure... Surprisingly, despite its intricate structure, this organ functions continuously throughout life, failing only in the event of the development of serious pathologies.

STRUCTURE OF THE WALLS OF THE HEART

The walls of the heart consist of 3 layers: inner - endocardium, middle - myocardium4 and outer - epicardium, which is a visceral leaf of the pericardial sac, pericardium.

The thickness of the walls of the heart is formed mainly by the middle layer, the myocardium, myocardium, consisting of muscle tissue. Outer layer, epicardium, represents the visceral layer of the serous pericardium. The inner leaflet, endocardium, endocardium, lines the heart cavity.

Myocardium myocardium, or muscle of the heart, although it has a transverse striation, it differs from skeletal muscles in that it does not consist of separate bundles, but is a network of interconnecting fibers with a mid-location of the nuclei. In the musculature of the heart, two sections are distinguished: the muscular layers of the atrium and the muscular layers of the ventricles. The fibers of both begin from two fibrous rings - anuli fibrosi, one of which surrounds ostium atrioventriculare dextrum, the other - ostium atrioventriculare sinistrurn. Since the fibers of one section, as a rule, do not pass into the fibers of another, the result is the possibility of contraction of the atria separately from the ventricles. In the atria, the superficial and deep muscle layers are distinguished: the superficial one consists of circularly or transversely located fibers, the deep one consists of longitudinal fibers, which with their ends start from the fibrous rings and cover the atrium in a loop. Around the circumference of the large venous trunks that flow into the atria, there are circular fibers covering them, like sphincters. The fibers of the surface layer cover both atria, the deep ones belong separately to each atrium.

Ventricular musculature even more complex Three layers can be distinguished in it: a thin surface layer is composed of longitudinal fibers that start from the right annulus fibrosus and go obliquely downward, passing to the left ventricle; at the apex of the heart, they form a curl, vortex cordis, bending here in a loop-like manner in depth and forming an internal longitudinal layer, the fibers of which are attached to the fibrous rings with their upper ends. The fibers of the middle layer, located between the longitudinal outer and inner, go more or less circularly, and, unlike the surface layer, do not pass from one ventricle to another, but are independent for each ventricle separately (Fig. 206, 207).

An important role in the rhythmic work of the heart and in the coordination of the activity of the muscles of the individual chambers of the heart is played by the so-called conduction system of the heart. Although the musculature of the atria is separated from the musculature of the ventricles by fibrous rings, there is a connection between them through the conducting system, which is a complex neuromuscular formation. The muscle fibers that make up it (Purkinje fibers) have a special structure: they are poor in myofibrils and rich in sarcoplasm, therefore they are lighter. They are sometimes visible to the naked eye in the form of light-colored filaments and represent a less differentiated part of the original syncytium, although they exceed in size the ordinary muscle fibers of the heart. In the conducting system, nodes and beams are distinguished (Fig. 208).

1. Atrioventricular bundle, fasciculus atrioventricularis, begins with a thickening of the nodus atrioventricularis (Ashof-Tavara node), located in the wall of the right atrium, near the cuspis septalis of the tricuspid valve. The fibers of the node, directly connected with the musculature of the atrium, continue into the septum between the ventricles in the form of a bundle of His (noted a little earlier by Kent). In the septum of the ventricles, the bundle of His is divided into two legs - crus dextrum and sinistrum, which go into the walls of the same ventricles and branch under the endocardium in their muscles. The atrioventricular bundle is very important for the work of the heart, since a wave of contraction from the atria to the ventricles is transmitted through it, due to which the regulation of the rhythm of the systole - of the atria and ventricles - is established.

2. Sinus node, nodus sinuatriali s, or sinus-atrial bundle of Kis-Flak, is located in the section of the right atrial wall corresponding to the sinus venosus of cold-blooded animals (in the sulcus terminalis, between the superior vena cava and the right ear). It is associated with the muscles of the atrium and is important for their rhythmic contraction.

Consequently, the atria are connected by a sinusoatrial bundle, and the atria and ventricles are connected by an atrioventricular one. Usually, irritation from the right atrium is transmitted from the sinus node to the atrioventricular node, and from it along the bundle of His to both ventricles.

Epicardium, epicardium, covers the outside of the myocardium and is an ordinary serous membrane, lined on the free surface by mesothelium.

Endocardium, endocardium, lines the inner surface of the cavities of the heart. It, in turn, consists of a layer connective tissue with a large number of elastic fibers and smooth muscle cells, from another layer of connective tissue located outside with an admixture of elastic fibers and from the inner endothelial layer, than the endocardium differs from the epicardium. The endocardium by its origin corresponds to the vascular wall, and the listed layers correspond to the 3 vascular membranes. All heart valves are folds (duplicates) of the endocardium.

The described structural features of the heart determine the characteristics of its vessels, which form, as it were, a separate circle of blood circulation - the heart.

Arteries of the heart(fig. 209, 210) - aa. coronariae dextra et sinistra, coronary arteries, right and left, start from the bulbus aortae below the upper edges of the semilunar valves.

Therefore, during systole, the entrance to the coronary arteries is covered with valves, and the arteries themselves are compressed by the contracted muscle of the heart. As a result, during systole, the blood supply to the heart decreases; blood enters the coronary arteries during diastole, when the inlets of these arteries, located in the aortic opening, are not closed by semilunar valves.
Right coronary artery, a. coronaria dextra, leaves the aorta, respectively, with the right semilunar valve and lies between the aorta and the auricle of the right atrium, outward from which it goes around the right edge of the heart along the coronary groove and passes to its posterior surface. Here it continues into the interventricular branch, r. interventricularis posterior. The latter descends along the posterior interventricular groove to the apex of the heart, where it anastomoses with the branch of the left coronary artery.

Branches of the right coronary artery vascularize: the right atrium, part of the anterior and the entire posterior wall of the right ventricle, a small area back wall left ventricle, atrial septum, posterior third of the interventricular septum, papillary muscles of the right ventricle and posterior papillary muscle of the left ventricle.

Left coronary artery, a. coronaria sinistra , coming out of the aorta at the left lunar valve, it also lies in the coronary sulcus anterior to the left atrium. Between the pulmonary trunk and the left ear, it gives two branches: a thinner one - the anterior, interventricular, ramus interventriclaris anterior, and a larger one - the left, envelope, ramus circumflexus.

The first descends along the anterior interventricular groove to the apex of the heart, where it anastomoses with the branch of the right coronary artery, as discussed above. The second, continuing the main trunk of the left coronary artery, bends around the coronary groove on the left side of the heart and also connects to the right coronary artery... As a result, an arterial ring is formed along the entire coronary groove, located in the horizontal plane, from which branches extend perpendicularly to the heart. The ring is a functional device for collateral circulation hearts. The branches of the left coronary artery vascularize the left atrium, the entire anterior and most of the posterior wall of the left ventricle, part of the anterior wall of the right ventricle, the anterior 2/3 of the interventricular septum, and the anterior papillary muscle of the left ventricle.

Observed different options the development of coronary arteries, as a result of which there are different ratios of the blood supply basins.

From this point of view, three forms of blood supply to the heart are distinguished: uniform with the same development of both coronary arteries, left coronary and right coronary. In addition to the coronary arteries, “additional” arteries from the bronchial arteries, from the lower surface of the aortic arch near the arterial ligament, come to the heart, which is important to take into account so as not to damage them during operations on the lungs and esophagus and thereby not worsen the blood supply to the heart.

(Fig. 211, 212): from the trunks of the coronary arteries and their large branches, respectively, to the 4 chambers of the heart, the atrial arteries (aa. atriales) and their ears (aa. auriculares), the arteries of the ventricles (aa. ventriculares), the arteries of the septa between them ( aa.Septi anterior et posterior).

Having penetrated into the thickness of the myocardium, they branch out according to the number, location and arrangement of its layers: first in the outer layer, then in the middle (in the ventricles) and, finally, in the inner layer, after which they penetrate into the papillary muscles (aa.papillares) and even into the atrioventricular valves. Intramuscular arteries in each layer follow the course of muscle bundles and anastomose in all layers and parts of the heart.

Some of these arteries have a highly developed layer of smooth muscles in their wall, when contracted, the lumen of the vessel is completely closed, which is why these arteries are called "closing". A temporary spasm of the "closing" arteries can lead to the cessation of blood flow to this part of the heart muscle and cause myocardial infarction. A case of an accessory coronary artery of the heart, extending from the truncus pulmonalis, is described.

Veins of the heart do not open into the vena cava, but directly into the heart cavity.

Intramuscular veins are located in all layers of the myocardium and, accompanying the arteries, correspond to the course of muscle bundles. Small arteries (up to the 3rd order) are accompanied by double veins, large ones - single. Venous outflow goes along three paths: 1) into the coronary sinus, 2) into the anterior veins of the heart, and 3) into the small veins (Tebosia - Viessen), which flow directly into the right part of the heart. There are more of these veins in the right half of the heart than in the left, and therefore the coronary veins are more developed on the left.

The predominance of the veins of Tebesia in the walls of the right ventricle with a small outflow through the veins of the coronary sinus indicates that they play an important role in the redistribution of venous blood in the region of the heart.

1. Veins of the coronary sinus system, sinus coronarius cordis. It is the remnant of the left Cuvier's duct and lies in the posterior part of the coronary sulcus of the heart between the left atrium and the left ventricle. With its right, thicker end, it flows into the right atrium near the septum between the ventricles, between the valve of the inferior vena cava and the atrial septum. The following veins flow into sinus coronarius:

a) v. cordis magna, starting at the apex of the heart, rises along the anterior interventricular groove of the heart, turns to the left and, going around the left side of the heart, continues into sinus coronarius; b) v. posterior ventriculi sinistri - one or more venous trunks on the posterior surface of the left ventricle, flowing into the sinus coronarius or into v. cordis magna; c) v. obliqua atrii sinistri - a small branch located on the posterior surface of the left atrium (the remnant of the germinal v. cava superior sinistra); it begins in the fold of the pericardium, enclosing the connective tissue cord, plica venae cavae sinistrae, also representing the remainder of the left vena cava; d) v. cordis media lies in the posterior interventricular groove of the heart and, having reached the transverse groove, flows into the sinus coronarius; e) v. cordis parva is a thin branch located in the right half of the transverse groove of the heart and usually flows into v. cordis media, in the place where this vein reaches the transverse groove.

2. Anterior veins of the heart, vv. cordis anteriores, - small veins, are located on the anterior surface of the right ventricle and flow directly into the right atrial cavity.

3. Small veins of the heart, vv. cordis minimae, - very small venous trunks, do not appear on the surface of the heart, but, having collected from the capillaries, flow directly into the cavities of the atria and ventricles.

In the heart, there are 3 networks of lymphatic capillaries: under the endocardium, inside the myocardium and under the epicardium. Among the discharge vessels, two main lymphatic collectors of the heart are formed. The right collector arises at the beginning of the posterior interventricular sulcus; it takes lymph from the right ventricle and atrium and reaches the left upper anterior mediastinal nodes lying on the aortic arch near the beginning of the left common carotid artery.

The left collector is formed in the coronary groove at the left edge of the pulmonary trunk, where it receives the vessels carrying lymph from the left atrium, left ventricle, and partly from the anterior surface of the right ventricle; then it goes to the tracheobronchial, or tracheal nodes, or nodes of the root of the left lung.

Both collectors flow into the nodes of the anterior mediastinum, into the left tracheal or tracheobronchial nodes.

Nerves, providing innervation to the heart muscles, which have a special structure and function, are complex and form numerous plexuses. The entire nervous system is composed of: 1) suitable trunks, 2) plexuses in the heart itself, and 3) nodal fields associated with the plexus.

Functionally, the nerves of the heart are divided into 4 types: slowing down and accelerating, weakening and strengthening. Morphologically, these nerves are n. vagus and tr. sympathicus. Sympathetic nerves (mainly postganglionic fibers) branch off from the three upper cervical and five upper thoracic sympathetic nodes: n. cardiacus cervicitis superior - from ganglion cervicale superius, n. cardiacus cervicalis medius - From ganglion cervicale medium, n. cardiacus cervicalis inferior - from ganglion cervicale inferius or ganglion cervicothoracicum s. ganglion stellatum and nn. cardiaci thoracici from the chest nodes of the sympathetic trunk.

Heart branches vagus nerve start from his cervical(rami cardiaci superiores), breast (rami cardiaci medii) and from n. laryngeus recurrens vagi (rami cardiaci inferiores). The nerves approaching the heart are divided into two groups - superficial and deep. The surface group belongs to upper section to sleepy and subclavian arteries, in the lower - to the aorta and pulmonary trunk. The deep group, composed mainly of the branches of the vagus nerve, lies on the anterior surface of the lower third of the trachea. These branches touch lymph nodes located in the tracheal region, and with an increase in the nodes, for example, with pulmonary tuberculosis, they can be compressed by them, which leads to a change in the heart rhythm. From the listed sources, two nerve plexuses are formed.

1) superficial, plexus cardiacus superficialis, between the aortic arch (under it) and the bifurcation of the pulmonary trunk;

2) deep, plexus cardiacus profundus, between the aortic arch (behind it) and the tracheal bifurcation.

These plexuses continue in the plexus coronarius dexter et sinister, surrounding the vessels of the same name, as well as in the plexus located between the epicardium and the myocardium. Intra-organ branching of the nerves extends from the last plexus. The plexuses contain numerous groups of ganglion cells, nerve nodes.

Afferent fibers start from receptors and go along with efferent fibers in the vagus and sympathetic nerves.

The heart (cor) is a hollow muscular organ enclosed in a serous membrane (pericardium), consisting of muscle and connective tissue fibers, richly innervated and having an intense blood supply. The contracting heart provides continuous movement of blood through the blood vessels to all organs and tissues, and thus - metabolism and vital activity human body... The contraction of the heart is called systole, and its relaxation is called diastole (Fig. 368). The time of systole and diastole depends on the rhythm of the heart contractions. At a frequency of 75 per minute, atrial systole lasts 0.1 s, alternating with ventricular systole, which lasts 0.3 s. During the period of ventricular systole, atrial diastole occurs (0.7 s), and then ventricular diastole occurs. After a general pause, atrial systole reappears and a new cycle of cardiac activity begins.

368. Diagram explaining the mechanism of closure of the atrioventricular openings and the direction of blood flow during diastole (A) and systole (B).

The heart cavity is divided into two atria and two ventricles, communicated by the atrioventricular openings. These openings for unilateral blood flow are provided with cuspid valves, which are formed by folds due to the inner lining of the heart. In the right opening there is a valve with three flaps; in the left opening, the valve is formed by two flaps. Venous blood passes through the right atrium and right ventricle, arterial blood passes through the left atrium and left ventricle.

The heart has an average weight of 280 g, length 13 cm, width 10.5 cm, thickness 7 cm. All these parameters are subject to significant fluctuations depending on age, body weight, gender and physical activity.

The shape of the heart is conical: there is a wider base (basis cordis) with large blood vessels and a narrow free part - the apex (apex cordis), facing down, forward and left.

369. Heart and large vessels. The pericardium is removed (front view).

1 - a. subclavia sinistra;
2 - a. carotis communis;
3 - arcus aortae;
4 - a. pulmonalis dextra;
5 - truncus pulmonalis;
6 - auricula sinistra;
7 - conus arteriosus;
8 - sulcus interventricularis anterior;
9 - ventriculus sinister;
10 - apex cordis;
11 - ventriculus dexter;
12 - sulcus coronarius;
13 - auricula dextra;
14 - aorta descendens;
15 - v. cava superior;
16 - the place of transition of the epicardium to the pericardium;
17 - truncus brachiocephalicus.

Surface of the heart... The front convex surface faces the ribs and sternum and is called facies sternocostalis (Fig. 369). From the left edge of the base of the heart diagonally to the notch of the apex runs the anterior interventricular groove (sulcus interventricularis anterior), which is the border between the right and left ventricles. In fact, this groove is not visible, since it is filled with arterial and venous vessels covered with fatty tissue. 2/3 of the area of ​​the anterior wall belongs to the right ventricle.

The lower flattened surface of the heart faces the diaphragm (facies diaphragmatica) in the area of ​​its tendon part. It also contains the posterior interventricular sulcus (sulcus interventricularis posterior), which joins at the apex in the incisura cordis with the anterior interventricular sulcus. The posterior sulcus also contains an artery, vein and adipose tissue. 2/3 of the posterior surface of the heart belongs to the left ventricle. On the border of the atria and ventricles, the coronary groove (sulcus coronarius) runs across the heart on the diaphragmatic surface, in which the venous coronary sinus (sinus coronarius) lies. This groove on the anterior surface of the heart is absent.

Distinguish between the edges of the heart: the right one is sharper and the left one is more dull.

Heart wall structure... The wall of the heart consists of the epicardium - the outer layer, myocardium - the middle layer and the endocardium - the inner layer.

The outer layer of the heart is formed by the visceral layer of the serous membrane of the heart and is covered with mesothelium. The connective tissue base of the outer layer of the heart consists of intertwined elastic and collagen fibers.

The middle layer is represented by striated, muscle fibers that make up the bulk of the heart wall. The nuclei of the striated muscle fibers of the heart are located in their thickness and this property makes them related to smooth muscles. The connective tissue layers between muscle fibers and bundles create a strong frame of the heart wall that resists blood pressure during systole. The muscles of the atria and ventricles are isolated from each other by fibrous layers that represent the supporting structures of the heart. The muscle of the atrium relative to the muscle of the ventricles is thinner, better developed around the mouths of the vessels in the form of circular bundles that prevent the return of blood to the veins (Fig. 370). For the right and left atria, there are also common (ring) muscle bundles.

370. The muscular layer of the atrium (back view). 1 - striated muscles surrounding the mouth of the left pulmonary veins; 2 - striated muscles surrounding the mouth of the right pulmonary veins; 3 - right pulmonary veins; 4 - superior vena cava; 5 - the muscles of its mouth; 6 - muscles of the right atrium; 7 - inferior vena cava: 8 - the mouth of the venous sinus of the heart; 9 - muscles of the left atrium; 10 - left pulmonary veins.

The muscle layers of the ventricles are more developed and complexly constructed, conventionally divided into the outer longitudinal, circular and inner longitudinal layers. The muscle fibers of the outer layer are common to both ventricles, starting from the fibrous rings of the heart (anuli fibrosi) and spiraling towards its apex (Fig. 371). Then, from the apex of the heart, they return as part of the inner layer to the fibrous rings. The nipple muscles (mm. Papillares) and fleshy trabeculae (trabeculae carneae) are formed from the fibers of the inner layer. The circular muscle fibers of each ventricle represent an independent layer.

371. The muscular layer of the heart (by RD Sinelnikov).

1 - vv. pulmonales;
2 - auricula sinistra;
3 - external muscular sip of the left ventricle;
4 - middle muscle layer;
5 - deep muscle layer;
6 - sulcus interventricularis anterior;
7 - valva trunci pulmonalis;
8 - valva aortae;
9 - atrium dextrum;
10 - v. cava superior.

The inner layer of the heart - the endocardium - consists of collagen and elastic fibers and is lined with endothelium from the side of the heart cavity. The inner layer covers all the depressions and bulges of the chambers of the heart, forms the valve leaflets and tendon filaments of the mastoid muscles.

Supporting formations of the heart. The supporting formations of the heart are represented by fibrous rings (anuli fibrosi), which are invisible on its surface. These rings separate the atria from the ventricles and are located in the plane of the heart valves (Fig. 372). The pulmonary trunk and aorta, striated muscle fibers of the atria and ventricles begin from the fibrous rings. The bases of the cusps of all valves are connected directly with the fibrous rings of the heart.

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The heart is surrounded on the outside by a pericardial sac - pericardium.

The wall of the heart consists of three membranes:

• outdoor - epicardium,
• middle - myocardium,
• internal - endocardium.

Between the epicardium and the pericardium there is a slit-like space in which there is no a large number of serous fluid, which acts as a lubricant and facilitates the sliding of the surfaces of the epicardium and pericardium relative to each other during the contraction of the heart.

The walls of the cavities of the heart vary considerably in thickness:
in the atria they are relatively thin (2–5 mm),
in the left ventricle (15 mm on average) is usually 2.5 times thicker than in the right (about 6 mm).

Epicard

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Epicardium (epicardium) - the inner layer of the serous sac, or pericardium. The surfaces of the epicardium and pericardium, facing the pericardial cavity, are covered with mesothelium. The connective tissue, which forms the basis of these two membranes, contains a large number of collagen and elastic fibers. It contains numerous blood and lymphatic capillaries and nerve endings. The epicardium firmly grows together with the myocardium and at the roots of large vessels entering and leaving the heart passes into the pericardium. In the area of ​​the furrows and near the vessels in the epicardium, significant amounts of adipose tissue are sometimes found.

Myocardium

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Myocardium (myocardium) - the most powerful membrane formed by the striated muscle, which, unlike the skeletal muscle, consists of cells - cardiomyocytes, connected in chains (fibers). The cells are firmly connected with each other through intercellular contacts - desmosomes. Between the fibers there are thin layers of connective tissue and a well-developed network of blood and lymphatic capillaries.

Distinguish between contractile and conducting cardiomyocytes: their structure was studied in detail in the course of histology. The contractile cardiomyocytes of the atria and ventricles differ from each other: in the atria they are branched, and in the ventricles they are cylindrical. The biochemical composition and the set of organelles in these cells also differ. Atrial cardiomyocytes produce substances that reduce blood clotting and regulate blood pressure. Contractions of the heart muscle are involuntary.

Rice. 2.4. "Skeleton" of the heart from above (diagram):

Rice. 2.4. "Skeleton" of the heart from above (diagram):
fibrious rings:
1 - pulmonary trunk;
2 - aorta;
3 - left and
4 - right atrioventricular foramen

In the thickness of the myocardium there is a strong connective tissue "skeleton" of the heart (Fig. 2.4). It is formed mainly by the fibrous rings, which are embedded in the plane of the atrioventricular openings. Of these, dense connective tissue passes into the fibrous rings around the openings of the aorta and the pulmonary trunk. These rings prevent the holes from stretching as the heart muscle contracts. Muscle fibers of both the atria and the ventricles originate from the "skeleton" of the heart, due to which the atrial myocardium is isolated from the ventricular myocardium, which makes it possible to contract them separately. The "skeleton" of the heart also serves as a support for the valve apparatus.

Rice. 2.5. Heart muscle (left)

Rice. 2.5. Heart muscle (left):
1 - right atrium;
2 - superior vena cava;
3 – right and
4 – left pulmonary veins;
5 - left atrium;
6 - left ear;
7 - circular,
8 - outer longitudinal and
9 - internal longitudinal muscle layers;
10 - the left ventricle;
11 - anterior longitudinal groove;
12 - semilunar valves of the pulmonary trunk
13 - semilunar aortic valves

The musculature of the atria has two layers: the superficial one consists of transverse (circular) fibers common to both atria, and the deep one consists of vertically located fibers, independent for each atrium. Some of the vertical bundles are included in the cusps of the mitral and tricuspid valves. In addition, circular muscle bundles lie around the openings of the vena cava and pulmonary veins, as well as at the edge of the oval fossa. Deep muscle bundles also form the comb muscles.

The musculature of the ventricles, especially the left, is very powerful and consists of three layers. The superficial and deep layers are common to both ventricles. The fibers of the first, starting from the fibrous rings, descend obliquely to the apex of the heart. Here they bend, pass into a deep longitudinal layer and rise to the base of the heart. Some of the shorter fibers form the fleshy beams and papillary muscles. The middle circular layer is independent in each ventricle and serves as a continuation of the fibers of both the outer and deep layers. In the left ventricle, it is much thicker than in the right, and therefore the walls of the left ventricle are more powerful than the right. All three muscle layers form the interventricular septum. Its thickness is the same as that of the walls of the left ventricle, only in the upper part it is much thinner.

In the heart muscle, special, atypical fibers are distinguished, poor in myofibrils, staining on histological preparations much weaker. They are referred to as the so-called conduction system of the heart(fig. 2.6).

Rice. 2.6. Conductive system of the heart:

A dense plexus of non-fleshy nerve fibers and groups of neurons of the autonomic nervous system are located along them. In addition, the fibers of the vagus nerve end here. The centers of the conducting system are two nodes - sinus-atrial and atrioventricular.

Rice. 2.6. Conductive system of the heart:
1 - sinus-atrial and
2 - atrioventricular nodes;
3 - bundle of His;
4 - the legs of the bundle of His;
5 - Purkinje fibers

Sinoatrial node

The sinoatrial node (sinoatrial) is located under the epicardium of the right atrium, between the confluence of the superior vena cava and the right ear. The node is a collection of conducting myocytes surrounded by connective tissue, permeated by a network of capillaries. Numerous nerve fibers that belong to both parts of the autonomic nervous system penetrate into the node. The cells of the node are capable of generating impulses at a frequency of 70 times per minute. Cell function is influenced by certain hormones, as well as sympathetic and parasympathetic influences... From the node along special muscle fibers, excitement spreads through the muscles of the atria. Part of the conducting myocytes forms an atrioventricular bundle, which descends along the interatrial septum to the atrioventricular node.

Atrioventricular node

The atrioventricular node (atrioventricular) lies in the lower part of the interatrial septum. It, like the sinoatrial node, is formed by highly branched and anastomosing conducting cardiomyocytes. The atrioventricular bundle (His bundle) departs from it into the thickness of the interventricular septum. In the septum, the bundle is divided into two legs. Approximately at the level of the middle of the septum, numerous fibers, called Purkinje fibers. They branch in the myocardium of both ventricles, penetrate into the papillary muscles and reach the endocardium. The distribution of fibers is such that myocardial contraction at the apex of the heart begins earlier than at the base of the ventricles.

The myocytes, which form the cardiac conduction system, are connected with the working cardiomyocytes with the help of slit-like intercellular contacts. Due to this, excitation is transmitted to the working myocardium and its contraction. The conducting system of the heart combines the work of the atria and ventricles, the muscles of which are isolated; it ensures the automatism of the heart and heart rate.

Endocardium

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Endocardium - thin shell lining the cavity of the heart. In the atria, the endocardium is thicker than in the ventricles. In its structure and development, the endocardium is similar to the inner membrane of the vessel wall - intima. The deep layer of the endocardium consists of connective tissue with numerous elastic fibers, blood vessels, smooth muscle and fat cells. The endothelium covers the endocardium, lining the cavity of the heart from the inside, and goes directly into the wall of the vessels connected to the heart.

Heart valves, both cuspid and lunar, are folds (duplications, duplications) of the endocardium, which have a connective tissue base with numerous collagen and elastic fibers. At the base of the valves, these fibers pass into the dense connective tissue of the rings surrounding the holes. From the middle layer of each leaflet of the atrioventricular valve, tendon filaments begin, which are also covered by the endocardium. These threads are stretched between the papillary muscles and the ventricular surface of the valve cusps. The cusps of the semilunar valves are thinner than the atrioventricular valves and do not have tendon filaments. Near the edges of such valves, a layer of dense connective tissue is somewhat thickened and forms a knot in their middle part. These thickened strips of fabric touch each other when the valve is closed. The narrow free edge of each leaf ensures complete tightness in a closed valve.

In various diseases, the structure of the valve leaflets can be disrupted. In this case, the flaps are deformed, become denser, their complete closure does not occur; they can shorten or grow together at the edges. As a result of such defects, the valve loses its ability to prevent the reverse flow of blood.