Heart - main body blood supply and lymph formation systems in the body. It is presented in the form of a large muscle with several hollow chambers. Thanks to its ability to contract, it moves the blood. There are three linings of the heart: epicardium, endocardium and myocardium. The structure, purpose and functions of each of them will be considered 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 left atrium form the so-called arterial part of the organ, based on the nature of the blood found here. In contrast, the right ventricle and right atrium make up the venous part of the heart.
The circulatory organ is presented in the shape of a flattened cone. It has a base, apex, lower and anterosuperior surfaces, as well as two edges - left and right. The apex of the heart has a rounded shape and is formed entirely by the left ventricle. The atria are located in the base area, and the aorta lies in its anterior part.
Heart sizes
It is believed that in an adult, mature human individual, the size of the heart muscle is equal to the size of a clenched fist. In fact, the average length of this organ in a mature person is 12-13 cm. The diameter of the heart is 9-11 cm.
The weight of an adult man's heart is about 300 g. In women, the heart weighs on average about 220 g.
Phases of the heart
There are several separate phases of contraction of the heart muscle:
- At the beginning, contraction of the atria occurs. Then, with some slowdown, ventricular contraction begins. During this process, blood naturally tends to fill the chambers with low blood pressure. Why doesn’t it flow back into the atria after this? The fact is that the blood is blocked by the gastric valves. Therefore, it can only move in the direction of the aorta, as well as the vessels of the pulmonary trunk.
- 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 fill with blood that comes 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 a voluntary act. The organ remains active continuously, even when the person is in a state of deep sleep. There are hardly people who pay attention to their 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 in the first weeks of intrauterine conception of the fetus. Subsequently, the impulse generation system does not allow the heart to stop throughout life.
IN calm state The number of contractions of the heart muscle during a minute is about 70 beats. Within one hour the number reaches 4200 beats. Considering that during one contraction the heart ejects circulatory system 70 ml of liquid, it’s easy to guess that up to 300 liters of blood passes 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 an ideal engine that practically does not fail.
The membranes of the heart
In total, there are 3 separate membranes of the heart muscle:
- Endocardium is the inner lining of the heart.
- The myocardium is an internal muscle complex formed by a thick layer of thread-like fibers.
- The epicardium is the thin outer layer of the heart.
- The pericardium is an auxiliary cardiac membrane, which is a kind of bag that contains the entire heart.
Myocardium
The myocardium is a multi-tissue muscular layer of the heart that is formed by striated fibers, loose connective structures, nerve processes, and a branched network of capillaries. Here are P-cells that form and conduct nerve impulses. In addition, the myocardium contains myocytes and cardiomyocytes, which are responsible for the contraction of the blood organ.
The myocardium consists of several layers: inner, middle and outer. Internal structure consists of muscle bundles that are located longitudinally in relation to each other. In the outer layer there are bunches muscle tissue 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 membrane of the heart muscle has the smoothest, thinnest and somewhat transparent structure. The epicardium forms the outer tissue of the organ. In fact, the membrane acts as the inner layer of the pericardium - the so-called cardiac sac.
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 lining in question includes adipose tissue. The epicardium fuses with the myocardium in the areas of least accumulation of fat cells.
Endocardium
Continuing to consider the membranes of the heart, let's talk about the endocardium. The presented structure is formed by elastic fibers, which consist of smooth muscle and connective cells. Endocardial tissue lines all hearts. The endocardial tissues move smoothly onto the elements extending from the blood organ: aorta, pulmonary veins, pulmonary trunk, without clearly distinguishable boundaries. In the thinnest parts of the atria, the endocardium fuses with the epicardium.
Pericardium
Pericardium - outer heart, which is also called the pericardial sac. This structure is presented in the form of an obliquely cut cone. The inferior base of the pericardium is placed on the diaphragm. Towards the top the shell extends further 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 approximately 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 defects hearts.
Finally
In the material presented, 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, malfunctioning only in the event of the development of serious pathologies.
Outer shell hearts Fig. 701. Heart, cor. Sternocostal (anterior) surface.] (The pericardium is removed at the point of its transition into the epicardium.) (diagram). 
Rice. 700. X-ray image of the heart and large vessels in various projections (diagram).
The right and left fibrous rings are interconnected into a common plate, which completely, with the exception of a small area, isolates the atrium muscles from the ventricular muscles. In the middle of the fibrous plate connecting the ring there is a hole through which the muscles of the atria are connected to the muscles of the ventricles through the atrioventricular bundle.
In the circumference of the openings of the aorta and pulmonary trunk (see Fig.) there are also interconnected fibrous rings; The aortic ring is connected to the fibrous rings of the atrioventricular orifices.
Muscular membrane of the atria
There are two muscle layers in the walls of the atria: superficial and deep (see Fig.).
Surface layer is common to both atria and consists of muscle bundles running predominantly 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 interauricular bundle (see Fig.), passing onto 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, between the bundles of the superficial layer of muscles, there is a depression covered with the 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.). In this area, the atrial septum includes nerve trunks that innervate the atrial septum and the ventricular septum - the atrioventricular bundle (Fig.).
The deep layer of muscles of the right and left atria is not common to both atria. It distinguishes between circular and 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, extending onto 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 appendage.
Vertical muscle bundles are located perpendicular to the fibrous rings of the atrioventricular orifices, attaching to them at their ends. Some of the vertical muscle bundles are included in the thickness of the leaflets of the atrioventricular valves.
Pectineus muscles, mm. pectinati, are also formed by deep layer bundles. They are most developed on the inner surface of the anterior-right wall of the cavity of the right atrium, as well as the right and left ears; in the left atrium they are less pronounced. In the spaces between the pectineus muscles, the wall of the atria and auricles is especially thin.
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.
Muscular tunic of the ventricles
In the muscular layer (see Fig.) (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 to the other two layers, surrounds each ventricle separately.
The outer, relatively thin layer consists of oblique, partly round, 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. Along the sternocostal (anterior) surface of the heart, the external bundles go from right to left, and along the diaphragmatic (lower) surface - from left to right. At the apex of the left ventricle, both bundles of the outer layer form the so-called curl of the heart, vortex cordis(see Fig.,), and penetrate deep into the walls of the heart, moving into the 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 bundles are oval in shape; they are repeatedly split and reconnected, forming loops of varying sizes. The shorter of these bundles do not reach the base of the heart, but are directed obliquely from one wall of the heart to the other in the form of fleshy trabeculae. Only the interventricular septum immediately below the arterial openings is devoid of these crossbars.
A number of such short but more powerful muscle bundles, partly associated with both the middle and outer layers, protrude freely into the cavity of the ventricles, forming cone-shaped papillary muscles of various sizes (see Fig. , , ).
Papillary muscles with chordae tendineae hold the valve leaflets when they are slammed shut by the flow of blood flowing from the contracted ventricles (during systole) to the relaxed atria (during diastole). Encountering obstacles from the valves, the blood rushes not into the atria, but into the openings of the aorta and pulmonary trunk, the semilunar 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, so the walls of the left ventricle are much thicker than the walls of the right. The bundles of the middle muscular 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.) is formed by all three muscle layers of both ventricles, but there are 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 along 4/5 represents a well-developed muscle layer. This much larger part of the interventricular septum is called muscular part, pars muscularis.
The upper (1/5) part of the interventricular septum is membranous part, pars membranacea. The septal leaflet of the right atrioventricular valve is attached to the membranous part.
Rice. 703. Transverse sections of the heart on different levels(I-VII). The heart wall includes three membranes: the inner - endocardium, average – myocardium and external - epicardium.
Endocardium, endocardium , relatively thin shell, lines the chambers of the heart from the inside. The endocardium is divided into: endothelium, subendothelial layer, muscle-elastic layer and outer connective tissue layer. The endothelium is represented by only one layer of flat cells. The endocardium, without a sharp border, passes onto large pericardial vessels. The leaflets of the leaflet valves and the flaps of the semilunar valves represent a duplication of the endocardium.
Myocardium, myocardium , the most significant shell in terms of thickness and the most important in function. The myocardium is a multi-tissue structure consisting of cardiac muscle tissue (typical cardiomyocytes), loose and fibrous connective tissue, atypical cardiomyocytes (cells of the conduction system), blood vessels and nerve elements.
set of contractile muscle cells(cardiomyocytes) makes up the heart muscle. The heart muscle has a special structure, occupying an intermediate position between striated (skeletal) and smooth muscles. The fibers of the heart muscle are capable of rapid contractions and are interconnected by jumpers, resulting in the formation of a wide-loop network. The muscles of the atria and ventricles are anatomically separate. They are connected only by a system of conducting fibers. The atrial myocardium has two layers: superficial, the fibers of which run transversely, covering both atria, and deep - separate for each atrium. The latter consists of vertical bundles starting from the fibrous rings in the area of the atrioventricular orifices and of circular bundles located at the mouths of the vena cava and pulmonary veins.
The ventricular myocardium is much more complex than the atrial myocardium. There are three layers: outer (superficial), middle and inner (deep). The bundles of the superficial layer, common to both ventricles, start from the fibrous rings and go obliquely - from top to bottom to the apex of the heart. Here they curl back, go deep, forming a curl of the heart in this place, vortex cordis . Without interruption, they pass into the inner (deep) layer of the myocardium. This layer has longitudinal direction, forms fleshy trabeculae and papillary muscles.
Between the superficial and deep layers lies the middle - circular layer. It is separate for each of the ventricles and is better developed on the left. Its bundles also start from the fibrous rings and run almost horizontally. Between all muscle layers there are numerous connecting fibers.
In the wall of the heart, in addition to muscle fibers, there are connective tissue formations - this is the heart’s own “soft skeleton”. It acts as a supporting structure from which muscle fibers originate and where valves are fixed. The soft skeleton of the heart includes fibrous rings, anuli fibrosi , fibrous triangles, trigonum fibrosum , and membranous part of the interventricular septum , pars membranacea septum interventriculare . Fibrous rings , anulus fibrosus dexter , anulus fibrosus sinister , They surround the right and left atrioventricular orifices and support the tricuspid and bicuspid valves.
The projection of these rings onto the surface of the heart corresponds to the coronary sulcus. Similar fibrous rings are located around the mouth of the aorta and pulmonary trunk.
Fibrous triangles connect the right and left fibrous rings and the connective tissue rings of the aorta and pulmonary trunk. Inferiorly, the right fibrous triangle is connected to the membranous part of the interventricular septum.
Atypical cells of the conduction system, forming and conducting impulses, ensure the automaticity of contraction of typical cardiomyocytes. Automatism- the ability of the heart to contract under the influence of impulses that arise within itself.
Thus, within the muscular lining of the heart, three functionally interconnected apparatuses can be distinguished:
1. Contractile, represented by typical cardiomyocytes;
2. Supporting, formed by connective tissue structures around natural openings and penetrating into the myocardium and epicardium;
3. Conductive, consisting of atypical cardiomyocytes - cells of the conduction system.
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Structure of the heart wall
Recard
The heart wall consists of a thin inner layer - the endocardium (endocardium), a middle developed layer - the myocardium (myocardium) and an outer layer - the epicardium (epicardium).
The endocardium lines the entire inner surface of the heart with all its formations.
The myocardium is formed by cardiac striated muscle tissue and consists of cardiac cardiomyocytes. The muscle fibers of the atria and ventricles begin from the right and left (anuli fibrosi dexter et sinister) fibrous rings, which are part of the soft skeleton of the heart. The fibrous rings surround the corresponding atrioventricular orifices, providing support for their valves.
The myocardium consists of three layers. The outer oblique layer at the apex of the heart passes into the curl of the heart (vortex cordis) and continues into the deep layer. The middle layer is formed by circular fibers. The epicardium is built on the principle of serous membranes and is a visceral layer of the serous pericardium. The epicardium covers the outer surface of the heart on all sides and the initial sections of the vessels extending from it, passing along them into the parietal plate of the serous pericardium.
The normal contractile function of the heart is ensured by its conduction system, the centers of which are:
1) sinoatrial node (nodus sinuatrialis), or Keys-Fleck node;
2) the atrioventricular node (nodus atrioventricularis), or the Fshoff-Tavara node, which passes down into the atrioventricular bundle (fasciculus atrioventricularis), or the bundle of His, which is divided into the right and left legs (cruris dextrum et sinistrum).
The pericardium is a fibrous-serous sac in which the heart is located. The pericardium is formed by two layers: the outer (fibrous pericardium) and the inner (serous pericardium). The fibrous pericardium passes into the adventitia of the large vessels of the heart, and the serous one has two plates - parietal and visceral, which pass into each other at the base of the heart. Between the plates there is a pericardial cavity (cavitas pericardialis), it contains a small amount of serous fluid.
Innervation: branches of the right and left sympathetic trunks, branches of the phrenic and vagus nerves.
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The inner lining of the heart, or endocardium
Endocardium, endocardium(see Fig. 704. 709), is formed from elastic fibers, among which connective tissue and smooth muscle cells are located. On the side of the heart cavity, 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 fleshy trabeculae, pectineal and papillary muscles, as well as their tendinous outgrowths.
The endocardium passes onto the inner lining of the vessels leaving the heart and flowing into it - the vena cava and pulmonary veins, the aorta and the pulmonary trunk - 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 chordae tendineae and fleshy trabeculae.
In the thinnest areas of the atrium walls, where in their muscle layer Gaps are formed, the endocardium comes into close contact and even fuses with the epicardium. In the area of the fibrous rings of the atrioventricular orifices, 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 leaves of each of the valves and semilunar valves is connected to the fibrous rings and thus fixes the valves to them.
The membranes of the heart
The heart is located in the pericardium, the pericardium. The heart wall consists of three layers: the outer layer is the epicardium, the middle layer is the myocardium, and the inner layer is the endocardium.
The outer lining of the heart. Epicard
The epicardium is a smooth, thin and transparent membrane. It is the internal plate of the pericardium (pericardium). The connective tissue base of the epicardium in various parts of the heart, especially in the grooves and in the apex, includes adipose tissue. With the help of this connective tissue, the epicardium is fused with the myocardium most tightly in places of the least accumulation or absence of adipose tissue.
The muscular lining of the heart, or myocardium
The middle, muscular layer of the heart (myocardium), or cardiac muscle, is a powerful and significant part of the heart wall 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 outside outer surface hearts, their location corresponds to the region of the coronary 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 orifice: on the right, left and behind and has a horseshoe shape.
With its anterior sections, the left fibrous ring is attached to the aortic root, forming connective tissue plates around its posterior periphery triangular shape– 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 section, isolates the atrial muscles from the ventricular muscles. In the middle of the fibrous plate connecting the ring there is a hole through which the muscles of the atria are connected to the muscles of the ventricles through the impulse-conducting neuromuscular atrioventricular bundle.
In the circumference of the openings of the aorta and pulmonary trunk there are also interconnected fibrous rings; the aortic ring is connected to the fibrous rings of the atrioventricular orifices.
Muscular membrane of the atria
There are two muscle layers in the walls of the atria: superficial and deep.
The superficial layer is common to both atria and represents muscle bundles running predominantly 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 interauricular bundle, passing onto 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 boundaries of the inferior vena cava, left atrium and venous sinus, between the bundles of the superficial layer of muscles there is a depression covered with 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 atrium muscles with the ventricular muscles - the atrioventricular bundle.
The deep layer of muscles of the right and left atria is not common to both atria. It distinguishes between 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, extending onto 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 orifices, attaching to them at their ends. Some of the vertical muscle bundles are included in the thickness of the cusps of the mitral and tricuspid valves.
The pectineus 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 spaces between the pectineus muscles, the wall of the atria and auricles is especially thin.
On the inner surface of both ears there are very short and thin tufts, the so-called fleshy bars. Crossing in different directions, they form a very thin loop-like network.
Muscular tunic of the ventricles
In the muscular layer (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, surrounds each ventricle separately.
The outer, relatively thin, layer consists of oblique, partly round, 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. Along the anterior surface of the heart, the external bundles run from right to left, and along the posterior surface, from left to right. At the apex of the left ventricle, these and other bundles of the outer layer form the so-called whirlpool of the heart and penetrate deep into the walls of the heart, passing into the deep muscle layer.
The deep layer consists of bundles that rise from the apex of the heart to its base. They have a cylindrical, partly oval shape, are repeatedly split and reconnected, forming loops of varying sizes. The shorter of these bundles do not reach the base of the heart, but are directed obliquely from one wall of the heart to the other, in the form of fleshy crossbars. The crossbars are located in large numbers throughout 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, protrude freely into the cavity of the ventricles, forming papillary muscles of varying sizes, cone-shaped.
There are three papillary muscles in the cavity of the right ventricle, and two in the cavity of the left ventricle. From the top of each of the papillary muscles, tendon strings begin, 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 tendinous strings are associated with the papillary muscles. A number of them begin directly from the fleshy crossbars formed by the deep muscular layer and are most often attached to the lower, ventricular, surface of the valves.
The papillary muscles with tendinous strings hold the leaflet valves when they are slammed shut by the blood flow going 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 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, so the walls of the left ventricle are much thicker than the right. The bundles of the middle muscular 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, one can distinguish bundles that lie closer to the outer layer and located closer to the deep layer.
The interventricular septum is formed by all three muscular layers of both ventricles. However, the muscle layers of the left ventricle play 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 musculature of the atria is isolated from the musculature of the ventricles. An exception is the bundle of fibers that begins 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 there is an initial, thickened part called the atrioventricular node, which passes into a thinner trunk - the atrioventricular bundle; the bundle is directed to the interventricular septum, passes between both fibrous rings and at the superoposterior part of the muscular part of the septum is divided into right and left legs .
The right leg, short and thinner, follows the septum from the cavity of the right ventricle to the base of the anterior papillary muscle and, in the form of a network of thin fibers (Purkinje), spreads in the muscular layer of the ventricle.
The left leg, wider and longer than the right, 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 crumbles into a thin network of fibers that form the anterior, middle and posterior bundles, spreading in the myocardium of the left ventricle.
At the point where the superior vena cava enters the right atrium, between the vein and the right ear, the sinoatrial node is located.
These bundles and nodes, accompanied by nerves and their branches, represent the conduction system of the heart, which serves to transmit impulses from one part of the heart to another.
The inner lining of the heart, or endocardium
The inner lining of the heart, or endocardium, is formed of collagen and elastic fibers, among which are connective tissue and smooth muscle cells.
On the side of the heart cavities, 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, pectineal and papillary muscles, as well as their tendinous outgrowths.
The endocardium passes onto the inner lining of the vessels leaving the heart and flowing into it - the vena cava and pulmonary veins, the aorta and the pulmonary trunk - 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 thinnest areas of the atrium walls, where gaps form in the muscle layer, the endocardium comes into close contact and even fuses with the epicardium. In the area of fibrous rings, atrioventricular orifices, as well as the 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 leaves of each of the leaflets and semilunar valves is connected to the fibrous rings and thus fixes the valves to them.
Pericardial sac or pericardium
The pericardial sac, 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 sternum angle. In width it extends more to the left side than to the right.
The pericardial sac is divided into: the anterior (sternocostal) part, the posteroinferior (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 corresponding to the body of the sternum, the V–VI costal cartilages, the intercostal spaces and the left portion of the xiphoid process.
The lateral sections of the sternocostal part of the pericardial sac are covered by the right and left layers of the mediastinal pleura, separating it in the anterior sections from the anterior chest wall. The areas of the mediastinal pleura covering the pericardium are called the pericardial part of the mediastinal pleura.
The middle of the sternocostal part of the bursa, 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, with their bases facing upward (towards the notch of the sternum) and downwards (towards the diaphragm ).
In the area of the upper triangle, the sternocostal part of the pericardium is separated from the sternum by loose connective and adipose tissue, which in children contains thymus. The compacted part of this fiber forms the so-called superior sternocervical ligament, which fixes the anterior wall of the pericardium to the manubrium 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 distinguished, the lower sterno-pericardial ligament, which fixes the lower section 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 the azygos vein, from which this part of the pericardium is separated by a layer of loose connective tissue and a thin fascial layer.
The lower section of the same part of the pericardium, which is its base, fuses tightly with the tendon center of the diaphragm; slightly spreading to the anterior left 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 through loose connective tissue and can be separated by careful preparation. In the thickness of this loose tissue, connecting the mediastinal pleura with the pericardium, passes the phrenic nerve and the accompanying pericardio-phrenic vessels.
The pericardium consists of two parts - the inner, serous (serous pericardium) and the outer, fibrous (fibrous pericardium).
The serous pericardial sac consists of two serous sacs, as if nested one inside the other - the outer one, loosely 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 pericardium, and the serous cover of the heart is the splanchnic plate (epicardium) of the serous pericardium.
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 ligaments to the inner surface of the sternum.
The epicardium passes into the pericardium at the base of the heart, in the area of the confluence of large vessels: the vena cava and pulmonary veins and the exit of the aorta and pulmonary trunk.
Between the epicardium and pericardium there is slit-shaped a space (cavity of the pericardium) containing a small amount of fluid from the pericardium, which wets the serous surfaces of the pericardium, causing one serous plate to slide over another during heart contractions.
As stated, the parietal plate of the serous pericardial sac passes into the splanchnic plate (epicardium) at the point of entry and exit from the heart of large blood vessels.
If, after removing the heart, we examine the pericardial sac from the inside, then 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 to it. By 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 transition of the epicardium into the parietal plate, several various shapes and the size of the sinuses. The largest of them 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 epicardial layer; behind them are the atria and next to the right is the superior vena cava. Epicardium from the side back wall the initial sections of the aorta and pulmonary trunk passes upward 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 root of the aorta and the pulmonary trunk in front and the atria behind, a passage is formed - a sinus, clearly visible when the aorta and pulmonary trunk are pulled anteriorly, and the superior vena cava - posteriorly. This sinus is bounded above by the pericardium, behind by the superior vena cava and the anterior surface of the atria, in front by the aorta and pulmonary trunk; on the right and left the transverse sinus is open.
Oblique sinus of the pericardial sac. It is located below and behind the heart and represents a space limited 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 with epicardium. In the upper blind pocket of this sinus there is a large number of nerve ganglia and trunks of the cardiac plexus.
Between the epicardium, which covers the initial part of the aorta (up to the level of the brachiocephalic trunk from it), and the parietal plate extending from it at this place, a small pocket is formed - an aortic protrusion. On the pulmonary trunk, the transition of the epicardium into the indicated parietal plate occurs at the level (sometimes below) of the ligament arteriosus. On the superior vena cava, this transition occurs below the place where the azygos vein enters 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, there runs from left to right a fold of the pericardial sac, 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.
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Myocardium (myocardium) – the most powerful membrane formed by striated muscle, which, unlike skeletal muscle, consists of cells - cardiomyocytes, connected into chains (fibers). Cells are tightly connected to each other using intercellular contacts - desmosomes. Between the fibers lie thin layers of connective tissue and a well-developed network of blood and lymphatic capillaries.
There are contractile and conductive cardiomyocytes: their structure was studied in detail in the histology course. 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 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):
fibrous rings:
1 – pulmonary trunk;
2 – aorta;
3 – left and
4 – right atrioventricular orifices
In the thickness of the myocardium there is a strong connective tissue “skeleton” of the heart (Fig. 2.4). It is formed mainly by fibrous rings, which are laid in the plane of the atrioventricular orifices. Of these, dense connective tissue passes into fibrous rings around the openings of the aorta and pulmonary trunk. These rings prevent the holes from stretching when the heart muscle contracts. The muscle fibers of both the atria and ventricles originate from the “skeleton” of the heart, due to which the atrial myocardium is isolated from the ventricular myocardium, which makes it possible for them to contract 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
– external longitudinal and
9
– internal longitudinal muscle layers;
10
– left ventricle;
11
– anterior longitudinal groove;
12
– semilunar valves of the pulmonary trunk
13
– semilunar valves of the aorta
The musculature of the atria has two layers: the superficial one consists of transverse (circular) fibers, common to both atria, and the deep one - from vertically located fibers, independent for each atrium. Some of the vertical bundles enter the leaflets of the mitral and tricuspid valves. In addition, around the openings of the vena cava and pulmonary veins, as well as at the edge of the fossa ovale, there are circular muscle bundles. Deep muscle bundles also form the pectineus muscles.
The musculature of the ventricles, especially the left one, 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 bars 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, 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 the wall of the left ventricle, only in the upper part it is much thinner.
In the heart muscle there are special, atypical fibers, poor in myofibrils, stained histological preparations much weaker. They belong to the so-called conduction system of the heart(Fig. 2.6).
Rice. 2.6. Conducting system of the heart: Along them there is a dense plexus of soft nerve fibers and groups of autonomic neurons. nervous system. In addition, this is where the fibers end vagus nerve. The centers of the conduction system are two nodes - the sinus-atrial and atrioventricular.
Rice. 2.6. Conducting system of the heart:
1
– sinoatrial and
2
– atrioventricular nodes;
3
– bundle of His;
4
– bundle branches;
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 appendage. The node is a cluster of conducting myocytes surrounded by connective tissue, penetrated by a network of capillaries. Numerous nerve fibers belonging 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, excitation spreads through the muscles of the atria. Some of the conducting myocytes form the 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 (bundle of His) extends from it into the thickness of the interventricular septum. At the septum, the bundle is divided into two legs. At approximately the level of the middle of the septum, numerous fibers extend from them, called Purkinje fibers. They branch in the myocardium of both ventricles, penetrate 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.
Myocytes that form the conduction system of the heart are connected to working cardiomyocytes using gap-like intercellular contacts. Thanks to this, excitation is transferred to the working myocardium and its contraction. The conduction system of the heart combines the work of the atria and ventricles, the muscles of which are separate; it ensures the automaticity of the heart and heart rhythm.
Surgery after a heart attack
The walls of the heart consist of 3 layers: internal - endocardium, average - myocardium and external - epicardium, which is a visceral layer pericardium, pericardium.
The thickness of the walls of the heart is formed mainly by the middle layer, myocardium, myocardium, consisting of cardiac striated muscle tissue. Outer shell, epicardium, represents the serous covering. The inner lining, endocardium, lines the cavities of the heart.
Myocardium, myocardium, or muscle tissue of the heart, although it has transverse striations, it differs from skeletal muscles in that it is not composed of individual multinuclear fibers, but is a network of mononuclear cells - cardiomyocytes. IN heart muscles there are two departments: muscular layers of the atrium and muscular layers of the ventricles. The fibers of both start from two fibrous rings - anulifibrosi, of which one surrounds ostium atrioventriculare dextrum, other - ostium atrioventriculare sinistrum. 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, there are superficial and deep muscle layers: the superficial one consists of circularly or transversely located fibers, the deep one - of longitudinal ones, which with their ends start from the fibrous rings and cover the atrium in a loop. Along the circumference of the large venous trunks flowing into the atria, there are circular fibers covering them, like sphincters. The fibers of the superficial layer cover both atria, the deep fibers belong separately to each atrium.
The musculature of the ventricles is even more complex. In it one can distinguish three layers: the thin superficial layer is composed of longitudinal fibers that start from the right fibrous ring and go obliquely downwards, moving 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. Middle layer fibers, located between the longitudinal outer and inner ones, go more or less circularly, and, unlike the superficial layer, they do not pass from one ventricle to another, but are independent for each ventricle.
The heart wall includes three membranes: the inner - endocardium, average – myocardium and external - epicardium.
Endocardium, endocardium , a relatively thin membrane that lines the chambers of the heart from the inside. The endocardium is divided into: endothelium, subendothelial layer, muscle-elastic layer and outer connective tissue layer. The endothelium is represented by only one layer of flat cells. The endocardium, without a sharp border, passes onto large pericardial vessels. The leaflets of the leaflet valves and the flaps of the semilunar valves represent a duplication of the endocardium.
Myocardium, myocardium , the most significant shell in terms of thickness and the most important in function. The myocardium is a multi-tissue structure consisting of cardiac muscle tissue (typical cardiomyocytes), loose and fibrous connective tissue, atypical cardiomyocytes (cells of the conduction system), blood vessels and nerve elements. The collection of contractile muscle cells (cardiomyocytes) makes up the heart muscle. The heart muscle has a special structure, occupying an intermediate position between striated (skeletal) and smooth muscles. The fibers of the heart muscle are capable of rapid contractions and are interconnected by jumpers, resulting in the formation of a wide-loop network. The muscles of the atria and ventricles are anatomically separate. They are connected only by a system of conducting fibers. The atrial myocardium has two layers: superficial, the fibers of which run transversely, covering both atria, and deep - separate for each atrium. The latter consists of vertical bundles starting from the fibrous rings in the area of the atrioventricular orifices and of circular bundles located at the mouths of the vena cava and pulmonary veins.
The ventricular myocardium is much more complex than the atrial myocardium. There are three layers: outer (superficial), middle and inner (deep). The bundles of the superficial layer, common to both ventricles, start from the fibrous rings and go obliquely - from top to bottom to the apex of the heart. Here they curl back, go deep, forming a curl of the heart in this place, vortex cordis . Without interruption, they pass into the inner (deep) layer of the myocardium. This layer has a longitudinal direction and forms fleshy trabeculae and papillary muscles.
Between the superficial and deep layers lies the middle - circular layer. It is separate for each of the ventricles and is better developed on the left. Its bundles also start from the fibrous rings and run almost horizontally. Between all muscle layers there are numerous connecting fibers.
In the wall of the heart, in addition to muscle fibers, there are connective tissue formations - this is the heart’s own “soft skeleton”. It acts as a supporting structure from which muscle fibers originate and where valves are fixed. The soft skeleton of the heart includes fibrous rings, anuli fibrosi , fibrous triangles, trigonum fibrosum , and membranous part of the interventricular septum , pars membranacea septum interventriculare . Fibrous rings , anulus fibrosus dexter , anulus fibrosus sinister , They surround the right and left atrioventricular orifices and support the tricuspid and bicuspid valves.
The projection of these rings onto the surface of the heart corresponds to the coronary sulcus. Similar fibrous rings are located around the mouth of the aorta and pulmonary trunk.
Fibrous triangles connect the right and left fibrous rings and the connective tissue rings of the aorta and pulmonary trunk. Inferiorly, the right fibrous triangle is connected to the membranous part of the interventricular septum.
Atypical cells of the conduction system, forming and conducting impulses, ensure the automaticity of contraction of typical cardiomyocytes. Automatism- the ability of the heart to contract under the influence of impulses that arise within itself.
Thus, within the muscular lining of the heart, three functionally interconnected apparatuses can be distinguished:
1. Contractile, represented by typical cardiomyocytes;
2. Supporting, formed by connective tissue structures around natural openings and penetrating into the myocardium and epicardium;
3. Conductive, consisting of atypical cardiomyocytes - cells of the conduction system.
