The walls of the heart chambers vary considerably in thickness; so, the thickness of the walls of the atria is 2-3 mm, of the left ventricle - on average 15 mm, which is usually 2.5 times the thickness of the wall of the right ventricle (about 6 mm). In the wall of the heart, 3 membranes are distinguished: the visceral plate of the pericardium - the epicardium; muscular layer - myocardium; the inner shell is the endocardium.
Epicard(epicardium)is the serous membrane. It consists of a thin plate of connective tissue covered from the outer surface with mesothelium. The epicardium contains vascular and nerve networks.
Myocardium(myocardium)constitutes the main mass of the heart wall (Fig. 155). It consists of striated cardiac muscle fibers (cardiomyocytes), interconnected by jumpers. The ventricular myocardium is separated from the atrial myocardium by the right and left fibrous rings (annuli fibrosi),located between the atria and ventricles and limiting the atrioventricular openings. The inner semicircles of the fibrous rings turn into fibrous triangles (trigona fibrosa).The bundles of the myocardium begin from the fibrous rings and triangles.
Figure: 155.Left ventricle. The direction of muscle bundles in different layers of the myocardium:
1 - superficial myocardial bundles; 2 - internal longitudinal bundles of the myocardium; 3 - "whirlpool" of the heart; 4 - cusps of the left atrioventricular valve; 5 - tendon chords; 6 - circular average beams of the myocardium; 7 - papillary muscle
The bundles of myocardial muscle fibers have a complex orientation, making up a single whole. To facilitate the understanding of the course of myocardial bundles, it is necessary to know the following scheme.
The atrial myocardium consists of superficialtransversely directed beams and deeploop-like, running almost vertically. Deep bundles form annular thickenings in the mouths of large vessels and protrude into the cavity of the atria and auricles in the form comb muscles.
In the myocardium of the ventricles, there are muscle bundles of three directions: external longitudinal,average circular,internal longitudinal.The external and internal bundles are common to both ventricles and in the apex of the heart they directly pass one into the other. Internal beams form fleshy trabeculaeand papillary muscles.The middle circular muscles form both common and isolated bundles for the left and right ventricles. The interventricular septum is formed over a greater extent by the myocardium [muscle part (pars muscularis)], and at the top, in a small area, with a connective tissue plate, covered on both sides with an endocardium, is the membranous part (pars membranacea).
Endocardium(endocardium)lines the heart cavity, including papillary muscles, tendon chords, trabeculae. Valve cusps are also folds (duplication) of the endocardium, in which the connective tissue layer is located. In the ventricles, the endocardium is thinner than in the atria. It consists of a muscular-elastic layer covered with endothelium.
In the myocardium there is a special system of fibers that differ from typical (contractile) cardiomyocytes in that they contain more sarcoplasm and fewer myofibrils. These specialized muscle fibers form cardiac conduction system(heart stimulation complex) (systema conducente cordis (complexus stimulans cordis))(Fig. 156), which consists of nodes and bundles capable of conducting excitation to various parts of the myocardium. Nerve fibers and groups of nerve cells are located along the bundles and in the nodes. This neuromuscular complex makes it possible to coordinate the sequence of contraction of the wall of the heart chambers.
Sinoatrial node (nodus sinuatrialis)lies in the wall of the right atrium between the right ear and the superior vena cava, under the epicardium. The length of this knot is on average 8-9 mm, width 4 mm, thickness
Figure: 156.Conductive system of the heart:
a - opened the right atrium and ventricle: 1 - superior vena cava; 2 - sinus-atrial node; 3 - oval fossa; 4 - atrioventricular node;
5 - inferior vena cava; 6 - flap of the coronary sinus; 7 - atrioventricular bundle; 8 - his right leg; 9 - branching left leg; 10 - pulmonary valve;
b - opened the left atrium and ventricle: 1 - anterior papillary muscle; 2 - left leg of the atrioventricular bundle; 3 - aortic valve; 4 - aorta; 5 - pulmonary trunk; 6 - pulmonary veins; 7 - inferior vena cava
2-3 mm. Beams depart from it into the atrial myocardium, to the ears of the heart, the mouths of the hollow and pulmonary veins, to the atrioventricular node.
Atrioventricular node (nodus atrioventricularis)lies on the right fibrous triangle, above the attachment of the septal leaflet of the tricuspid valve, under the endocardium. The length of this node is 5-8 mm, width is 3-4 mm. The atrioventricular bundle departs from it into the interventricular septum (fasc.atrioventricularis)length of about 10 mm. The atrioventricular bundle is divided into legs: right (crus dextrum)and left (crus sinistrum).The legs lie under the endocardium, the right one is also in the thickness of the muscular layer of the septum, from the side of the cavities of the corresponding ventricles. The left leg of the bundle is divided into 2-3 branches, branching further to very thin bundles, passing into the myocardium. The right leg, thinner, goes almost to the apex of the heart, where it divides and passes into the myocardium. Under normal conditions
automatic heart rate occurs in the sinus node. From it, impulses are transmitted along bundles to the muscles of the orifices of the veins, the auricles of the heart, the myocardium of the atria to the atrioventricular node and further along the atrioventricular bundle, its legs and branches to the muscles of the ventricles. Excitation spreads spherically from the inner layers of the myocardium to the outer ones.
Heart chambers
Right atrium(atrium dextrum)(fig. 157, see fig. 153) has a cubic shape. At the bottom, it communicates with the right ventricle through the right atrioventricular opening (ostium atrioventriculare dextrum),which has a valve that allows blood to pass from the atrium to the ventricle and prevents its return
Figure: 157.Heart drug. Opened right atrium:
1 - comb muscles of the right ear; 2 - border ridge; 3 - the mouth of the superior vena cava; 4 - cut of the right ear; 5 - right atrioventricular valve; 6 - the location of the atrioventricular node; 7 - the mouth of the coronary sinus; 8 - flap of the coronary sinus; 9 - the valve of the inferior vena cava; 10 - the mouth of the inferior vena cava; 11 - oval fossa; 12 - edge of the oval fossa; 13 - the location of the intervenous tubercle
laziness. Anteriorly, the atrium forms a hollow process - the right ear (auricula dextra).The inner surface of the right ear has a number of eminences formed by bundles of comb muscles. The comb muscles terminate to form an eminence - borderline ridge (crista terminalis).
Inner wall of the atrium - interatrial septum (septum interatriale)smooth. In its center there is an almost round depression up to 2.5 cm in diameter - an oval fossa (fossa ovalis).Edge of the oval fossa (limbus fossae ovalis)thickened. The bottom of the fossa is formed, as a rule, by two sheets of the endocardium. The embryo has an oval hole at the site of the oval fossa (for. ovale),through which the atria communicate. Sometimes the foramen ovale does not overgrow by the time of birth and promotes mixing of arterial and venous blood. Such a defect is eliminated by surgery.
Behind into the right atrium flows into the top superior vena cava,down below - inferior vena cava.The mouth of the inferior vena cava is limited by a valve (valvula vv. cavae inferioris),which is a fold of the endocardium up to 1 cm wide. The valve of the inferior vena cava in the embryo directs a stream of blood to the oval opening. Between the orifices of the vena cava, the wall of the right atrium protrudes and forms the sinus of the vena cava (sinus venarum cavarum).On the inner surface of the atrium between the mouths of the vena cava there is an elevation - the intervenous tubercle (tuberculum intervenosum).The coronary sinus of the heart flows into the posterior-inferior part of the atrium (sinus coronarius cordis),small damper (valvula sinus coronarii).
Right ventricle(ventriculus dexter)(fig. 158, see fig. 153) has the shape of a trihedral pyramid with the base facing up. According to the shape, the ventricle has 3 walls: the anterior, posterior and internal - the interventricular septum (septum interventriculare).Two parts are distinguished in the ventricle: proper ventricleand right arterial cone,located in the upper left part of the ventricle and continuing into the pulmonary trunk.
The inner surface of the ventricle is uneven due to the formation of fleshy trabeculae running in different directions (trabeculae carneae).Trabeculae on the interventricular septum are very weakly expressed.
Above the ventricle has 2 openings: on the right and behind - the right atrioventricular; front and left - opening of the pulmonary trunk (ostium trunci pulmonalis).Both openings are closed with valves.
Figure: 158.Internal structures of the heart:
1 - cut plane; 2 - fleshy trabeculae of the right ventricle; 3 - anterior papillary muscle (cut off); 4 - tendon chords; 5 - cusps of the right atrioventricular valve; 6 - right ear; 7 - superior vena cava; 8 - aortic valve flap; 9 - damper assembly; 10 - cusps of the left atrioventricular valve; 11 - left ear; 12 - membranous part of the interventricular septum; 13 - the muscular part of the interventricular septum; 14 - anterior papillary muscles of the left ventricle; 15 - posterior papillary muscles
Atrioventricular valvesconsist of fibrous rings; flaps,attaching their base to the fibrous rings of the atrioventricular openings, and the free edges facing the ventricular cavity; tendinous chordsand papillary muscles,formed by the inner layer of the ventricular myocardium (Fig. 159).
Sash (cuspes)represent the folds of the endocardium. In the right atrioventricular valve there are 3 of them, therefore the valve is called tricuspid. More flaps are possible.
Figure: 159.Heart valves:
a - condition during diastole with remote atria: left atrioventricular valve:1 - tendon chords; 2 - papillary muscle; 3 - left fibrous ring; 4 - back flap; 5 - front flap; aortic valve:6 - rear semilunar flap; 7 - left half-moon flap; 8 - the right half-moon flap; pulmonary valve:9 - left half-moon flap; 10 - the right half-moon flap; 11 - front semi-moon flap; right atrioventricular valve:12 - front flap; 13 - partition flap; 14 - back flap; 15 - papillary muscles with tendon chords extending to the valves; 16 - right fibrous ring; 17 - right fibrous triangle; b - state during systole
Tendon chords (chordae tendineae)- thin fibrous formations running in the form of threads from the edges of the valves to the tops of the papillary muscles.
Papillary muscles (mm. papillares)differ by location. There are usually 3 of them in the right ventricle: front, backand partition wall.The number of muscles, like the valves, can be large.
Pulmonary valve (valva truncipulmonalis)prevents the reverse flow of blood from the pulmonary trunk into the ventricle. It consists of 3 semi-moon flaps (valvulae semilunares).In the middle of each semilunar valve there are thickenings - nodules (noduli valvularum semilunarium),contributing to a more hermetic closing of the dampers.
Left atrium(atrium sinistrum)as well as the right, cubic shape, forms an outgrowth on the left - the left ear (auricula sinistra).The inner surface of the atrial walls is smooth, except for the walls of the ear, where there are comb muscles.On the back wall there are pulmonary vein openings(two to the right and two to the left).
On the atrial septum from the left atrium, oval fossa,but it is less pronounced than in the right atrium. The left ear is narrower and longer than the right one.
Left ventricle(ventriculus sinister)conical shape with the base facing upwards, has 3 walls: front, backand internal- the interventricular septum.There are 2 holes at the top: left and front - left atrioventricular,right and back - aortic opening (ostium aortae).As in the right ventricle, these holes have valves: valva atrioventricularis sinistra et valva aortae.
The inner surface of the ventricle, with the exception of the septum, has numerous fleshy trabeculae.
Left atrioventricular, mitral, the valve usually contains two sashand two papillary muscles- front and back. Both the valves and the muscles are larger than those in the right ventricle.
The aortic valve is shaped like a pulmonary valve three lunar flaps.The initial part of the aorta at the location of the valve is slightly expanded and has 3 depressions - the sinuses of the aorta (sinus aortae).
Heart topography
The heart is located in the lower part of the anterior mediastinum, in the pericardium, between the leaves of the mediastinal pleura. In relation to
to the midline of the body, the heart is located asymmetrically: about 2/3 - to the left of it, about 1/3 - to the right. The longitudinal axis of the heart (from the middle of the base to the apex) runs obliquely from top to bottom, right to left, and back to front. In the pericardial cavity, the heart is suspended on large vessels.
The position of the heart is different: transverse, obliqueor vertical.The transverse position is more common in people with a wide and short chest and a high standing of the dome of the diaphragm, vertical - in people with a narrow and long chest.
In a living person, the boundaries of the heart can be determined by percussion, as well as radiographically. The frontal silhouette of the heart is projected onto the anterior chest wall, corresponding to its sternocostal surface and large vessels. Distinguish between the right, left and lower borders of the heart (Fig. 160).
Figure: 160.Projections of the heart, cuspid and semilunar valves on the anterior surface of the chest wall:
1 - projection of the pulmonary valve; 2 - projection of the left atrioventricular (mitral) valve; 3 - apex of the heart; 4 - projection of the right atrioventricular (tricuspid) valve; 5 is a projection of the aortic valve. Auscultation sites of the left atrioventricular (long arrow) and aortic (short arrow) valves are shown
Right border of the heartin the upper part, corresponding to the right surface of the superior vena cava, runs from the upper edge of the II rib at the place of its attachment to the sternum to the upper edge of the III rib, 1 cm to the right from the right edge of the sternum. The lower part of the right border corresponds to the edge of the right atrium and runs from the III to V ribs in the form of an arc, spaced 1.0-1.5 cm from the right edge of the sternum. At the level of the V rib, the right border passes into the lower one.
Lower border of the heartformed by the edge of the right and partially left ventricles. It runs obliquely down and to the left, crosses the sternum over the base of the xiphoid process, the cartilage of the VI rib and reaches the fifth intercostal space, 1.5-2.0 cm medially from the midclavicular line.
Left border of the heartrepresented by the aortic arch, pulmonary trunk, left ear, left ventricle. It runs from the bottom edge
I rib at the place of its attachment to the sternum on the left to the upper edge
II ribs, 1 cm to the left of the edge of the sternum (respectively, the projection of the aortic arch), further at the level of the second intercostal space, 2.0-2.5 cm outward from the left edge of the sternum (corresponding to the pulmonary trunk). The continuation of this line at the level of the III rib corresponds to the left heart ear. From the lower edge of the III rib, the left border runs in a convex arc to the fifth intercostal space, 1.5-2.0 cm medially from the midclavicular line, respectively, to the edge of the left ventricle.
The mouth of the aortaand pulmonary trunkand their valves are projected at the level of the third intercostal space: the mouth of the aorta is behind the left half of the sternum, and the mouth of the pulmonary trunk is at its left edge.
Atrioventricular foramenare projected along a line passing from the place of attachment to the sternum of the cartilage of the right V rib to the place of attachment of the cartilage of the left III rib. The projection of the right atrioventricular opening occupies the right half of this line, the left - the left (see Fig. 160).
Sternocostal surfacethe heart is partly adjacent to the sternum and cartilage of the left III-V ribs. The anterior surface over a greater extent is in contact with the mediastinal pleura and the anterior costal-mediastinal sinuses of the pleura.
Diaphragmatic surfacethe heart is adjacent to the diaphragm, bordered by the main bronchi, esophagus, descending aorta and pulmonary arteries.
The heart is placed in a closed fibrous-serous sac (pericardium) and only through it is related to the surrounding organs.
The heart has a complex structure and performs no less complex and important work. By rhythmically contracting, it provides blood flow through the vessels.
The heart is located behind the sternum, in the middle part of the chest cavity and is almost completely surrounded by the lungs. It may move slightly to the side, as it hangs freely on the blood vessels. The heart is located asymmetrically. Its long axis is inclined and forms an angle of 40 ° with the axis of the body. It is directed from top right to front down to left and the heart is turned so that its right part is deflected more forward, and left - back. Two thirds of the heart is to the left of the midline and one third (vena cava and right atrium) to the right. Its base is turned to the spine, and the apex is turned to the left ribs, more precisely, to the fifth intercostal space.
Sternocostal surfacethe heart is more convex. It is located behind the sternum and cartilage of the III-VI ribs and is directed forward, up, to the left. A transverse coronary groove passes along it, which separates the ventricles from the atria and thereby divides the heart into the upper part, formed by the atria, and the lower, consisting of the ventricles. Another groove of the sternocostal surface - the anterior longitudinal - runs along the border between the right and left ventricles, while the right one forms most of the anterior surface, the left one - a smaller one.
Diaphragmatic surfaceflatter and adjacent to the tendon center of the diaphragm. A longitudinal posterior groove runs along this surface, separating the surface of the left ventricle from the surface of the right. In this case, the left one makes up most of the surface, and the right one - less.
Anterior and posterior longitudinal furrows merge with the lower ends and form a heart notch to the right of the heart apex.
There are also lateral surfaces, located on the right and left and facing the lungs, in connection with which they are called pulmonary.
Right and left edges hearts are not the same. The right edge is more pointed, the left more blunt and rounded due to the thicker wall of the left ventricle.
The boundaries between the four chambers of the heart are not always clearly defined. The landmarks are the grooves in which the blood vessels of the heart are located, covered with fatty tissue and the outer layer of the heart - the epicardium. The direction of these furrows depends on how the heart is located (obliquely, vertically, transversely), which is determined by the body type and the height of the diaphragm. In mesomorphs (normostenics), whose proportions are close to the average, it is located obliquely, in dolichomorphs (asthenics) with a lean physique, it is vertical, in brachimorphs (hypersthenics) with wide short forms - transversely.
The heart seems to be suspended by the base on large vessels, while the base remains motionless, and the apex is in a free state and can be displaced.
Heart tissue structure
The heart wall is made up of three layers:
- The endocardium is the inner layer of epithelial tissue that lines the cavities of the heart chambers from the inside, exactly repeating their relief.
- The myocardium is a thick layer of muscle tissue (striated). The cardiac myocytes, of which it is composed, are connected by many bridges that connect them into muscle complexes. This muscle layer provides rhythmic contraction of the heart chambers. The smallest thickness of the myocardium is in the atria, the largest is in the left ventricle (about 3 times thicker than that of the right), since it needs more force to push blood into the systemic circulation, in which the resistance to flow is several times greater than in the small one. The atrial myocardium consists of two layers, the ventricular myocardium - of three. The atrial myocardium and the ventricular myocardium are separated by fibrous rings. The conducting system, providing rhythmic myocardial contraction, is one for the ventricles and atria.
- Epicardium - the outer layer, which is the visceral lobe of the heart bag (pericardium), which is the serous membrane. It covers not only the heart, but also the initial sections of the pulmonary trunk and aorta, as well as the final sections of the pulmonary and vena cava.
Anatomy of the atria and ventricles
The cardiac cavity is divided by a septum into two parts - right and left, which do not communicate with each other. Each of these parts consists of two chambers - the ventricle and the atrium. The septum between the atria is called the atrial septum, between the ventricles - the interventricular septum. Thus, the heart consists of four chambers - two atria and two ventricles.
Right atrium
It looks like an irregular cube in shape; in front there is an additional cavity called the right ear. The atrium has a volume of 100 to 180 cubic meters. cm. It has five walls, 2 to 3 mm thick: anterior, posterior, superior, lateral, medial.
The superior vena cava flows into the right atrium (from above to behind) and the inferior vena cava (from below). On the bottom right is the coronary sinus, where the blood of all the heart veins flows. There is an intervenous tubercle between the openings of the superior and inferior vena cava. In the place where the inferior vena cava flows into the right atrium, there is a fold of the inner layer of the heart - the valve of this vein. The sinus of the vena cava is called the posterior enlarged section of the right atrium, where both of these veins flow.
The chamber of the right atrium has a smooth inner surface, and only in the right ear with the adjacent anterior wall is the surface uneven.
In the right atrium, many puncture holes of small veins of the heart open.
Right ventricle
It consists of a cavity and an arterial cone, which is an upward funnel. The right ventricle has the shape of a triangular pyramid, the base of which is turned upward and the apex is downward. The right ventricle has three walls: anterior, posterior, and medial.
The front is convex, the back is flatter. The medial septum is a two-part interventricular septum. The largest of them - muscular - is at the bottom, the smaller - membranous - at the top. The pyramid faces the atrium with its base and has two openings: posterior and anterior. The first is between the cavity of the right atrium and the ventricle. The second goes into the pulmonary trunk.
Left atrium
It looks like an irregular cube, is located behind and adjacent to the esophagus and the descending part of the aorta. Its volume is 100-130 cubic meters. cm, wall thickness - from 2 to 3 mm. Like the right atrium, it has five walls: anterior, posterior, superior, literal, medial. The left atrium continues anteriorly into an accessory cavity called the left auricle, which is directed towards the pulmonary trunk. Four pulmonary veins (behind and above) flow into the atrium, in the openings of which there are no valves. The medial wall is the atrial septum. The inner surface of the atrium is smooth, the comb muscles are only in the left ear, which is longer and narrower than the right one, and is noticeably separated from the ventricle by an intercept. It communicates with the left ventricle using the atrioventricular opening.
Left ventricle
In shape, it resembles a cone, the base of which is turned up. The walls of this chamber of the heart (anterior, posterior, medial) have the greatest thickness - from 10 to 15 mm. There is no clear border between the front and back. At the base of the cone is the opening of the aorta and the left atrioventricular.
The aortic opening is round in shape in front. Its valve consists of three flaps.
Heart size
The size and weight of the heart varies from person to person. The average values \u200b\u200bare as follows:
- the length is from 12 to 13 cm;
- greatest width - from 9 to 10.5 cm;
- anteroposterior size - from 6 to 7 cm;
- weight in men - about 300 g;
- weight in women is about 220 g.
Function of the cardiovascular system and heart
The heart and blood vessels make up the cardiovascular system, the main function of which is transport. It consists in the supply of food and oxygen to tissues and organs and the return transportation of metabolic products.
The heart acts as a pump - it ensures continuous blood circulation in the circulatory system and the delivery of nutrients and oxygen to organs and tissues. Under stress or physical exertion, his work is immediately rebuilt: it increases the number of contractions.
The work of the heart muscle can be described as follows: its right side (venous heart) receives waste blood saturated with carbon dioxide from the veins and gives it to the lungs for oxygenation. From the lungs, oxygen-enriched blood is directed to the left side of the heart (arterial) and from there is forced into the bloodstream.
The heart produces two circles of blood circulation - large and small.
The big one supplies blood to all organs and tissues, including the lungs. It starts in the left ventricle and ends in the right atrium.
The small circle of blood circulation produces gas exchange in the alveoli of the lungs. It starts in the right ventricle and ends in the left atrium.
The blood flow is regulated by valves: they prevent it from flowing in the opposite direction.
The heart has such properties as excitability, conductive ability, contractility and automaticity (excitation without external stimuli under the influence of internal impulses).
Thanks to the conducting system, there is a consistent contraction of the ventricles and atria, the synchronous inclusion of myocardial cells in the contraction process.
Rhythmic contractions of the heart provide a portioned flow of blood into the circulatory system, but its movement in the vessels occurs without interruption, which is due to the elasticity of the walls and the resistance to blood flow arising in small vessels.
The circulatory system has a complex structure and consists of a network of vessels for various purposes: transport, shunting, exchange, distribution, capacitive. There are veins, arteries, venules, arterioles, capillaries. Together with the lymphatic, they maintain the constancy of the internal environment in the body (pressure, body temperature, etc.).
Through the arteries, blood moves from the heart to the tissues. With distance from the center, they become thinner, forming arterioles and capillaries. The arterial bed of the circulatory system transports the necessary substances to the organs and maintains constant pressure in the vessels.
The venous channel is more extensive than the arterial one. Through the veins, blood moves from the tissues to the heart. Veins are formed from venous capillaries, which merge, first become venules, then veins. They form large trunks at the heart. Distinguish between superficial veins, located under the skin, and deep, located in the tissues next to the arteries. The main function of the venous part of the circulatory system is the outflow of blood saturated with metabolic products and carbon dioxide.
To assess the functional capabilities of the cardiovascular system and the acceptability of loads, special tests are carried out, which make it possible to assess the body's performance and its compensatory capabilities. Functional tests of the cardiovascular system are included in a medical and physical examination to determine the degree of fitness and general physical fitness. The assessment is given by such indicators of the work of the heart and blood vessels as blood pressure, pulse pressure, blood flow velocity, minute and stroke volumes of blood. These tests include Letunov's tests, step tests, Martine's test, Kotov's - Demin's test.
The heart begins to contract from the fourth week after conception and does not stop until the end of life. It does a gigantic job: in a year it pumps about three million liters of blood and makes about 35 million heartbeats. At rest, the heart uses only 15% of its resource, while under load - up to 35%. Over an average life span, it pumps about 6 million liters of blood. Another interesting fact: The heart supplies 75 trillion cells of the human body with blood, except for the cornea of \u200b\u200bthe eyes.
Three layers are distinguished in the heart wall: a thin inner layer - the endocardium, a thick muscle layer - the myocardium and a thin outer layer - the epicardium, which is the visceral layer of the serous membrane of the heart - the pericardium (pericardial sac).
The endocardium (endocardium) lines the heart cavity from the inside, repeating its complex relief, and covers the papillary muscles with their tendon chords. The atrioventricular valves, the aortic valve and the pulmonary valve, as well as the valves of the inferior vena cava and coronary sinus, are formed by endocardial duplications, within which the connective tissue fibers are located.
The endocardium is formed by a single layer of flat polygonal endothelial cells located on a thin basement membrane. In the cytoplasm of endotheliocytes, a large number of micropinocytic vesicles. Endothelial cells are connected to each other by intercellular contacts, including nexuses. At the border with the myocardium, there is a thin layer of loose fibrous connective tissue. The middle layer of the heart wall - the myocardium, is formed by the cardiac striated muscle tissue and consists of cardiac myocytes (cardiomyocytes). Cardiomyocytes are interconnected by a large number of bridges (insertion disks), with the help of which they are connected into muscle complexes that form a narrow-looped network. This muscle network provides a complete rhythmic contraction of the atria and ventricles. The thickness of the myocardium is the smallest in the atria, and the largest in the left ventricle.
The muscle bundles of the atria and ventricles begin from the fibrous rings that completely separate the atrial myocardium from the ventricular myocardium. These fibrous rings, like a number of other connective tissue formations of the heart, are part of its soft skeleton. The skeleton of the heart includes: interconnected right and left fibrous rings (annuli fibrosi dexter et sinister), which surround the right and left atrioventricular openings. These rings form the support of the right and left atrioventricular valves (their projection everywhere corresponds to the coronary groove of the heart). The right and left fibrous triangles (trigonum fibrosum dextrum et trigonum fibrosum sinistrum) are dense plates, which on the right and left adjoin the posterior semicircle of the aorta and are formed as a result of the fusion of the left fibrous ring with the connective tissue ring of the aortic opening. The right, most dense, fibrous triangle, which actually connects the left and right fibrous rings and the connective tissue ring of the aorta, is in turn connected to the membranous part of the interventricular septum. In the right fibrous triangle there is a small opening through which the fibers of the atrioventricular bundle of the cardiac conduction system pass.
Atrial myocardium separated by fibrous rings from the ventricular myocardium. Synchronization of myocardial contractions is provided by the cardiac conduction system, which is the same for the atria and ventricles. In the atria, the myocardium consists of two layers: superficial, common to both atria, and deep, separate for each of them. In the surface layer, muscle bundles are located transversely, in the deep layer - longitudinally. Circular muscle bundles in a loop-like manner cover the mouths of the veins flowing into the atria, like compressors. Longitudinally lying muscle bundles originate from the fibrous rings and in the form of vertical strands protrude into the cavities of the atrial appendages and form comb muscles.
Ventricular myocardium consists of three different muscle layers: outer (superficial), middle and inner (deep). The outer layer is represented by obliquely oriented muscle bundles, which, starting from the fibrous rings, continue down to the apex of the heart, where they form the curl of the heart (vortex cordis). Then they pass into the inner (deep) layer of the myocardium, the bundles of which are located longitudinally. Due to this layer, papillary muscles and fleshy trabeculae are formed. The outer and inner layers of the myocardium are common to both ventricles. The middle layer between them, formed by circular (circular) muscle bundles, is separate for each ventricle. The interventricular septum is formed for the most part (its muscular part) by the myocardium and the endocardium that covers it. The basis of the upper section of this septum (its membranous part) is a plate of fibrous tissue.
The outer shell of the heart - the epicardium (epicardium), adjacent to the myocardium from the outside, is the visceral layer of the serous pericardium. The epicardium is built like serous membranes and consists of a thin plate of connective tissue covered with mesothelium. The epicardium covers the heart, the initial sections of the ascending part of the aorta and the pulmonary trunk, the final sections of the hollow and pulmonary veins. Through these vessels, the epicardium passes into the parietal plate of the serous pericardium.
The heart is a muscular organ in humans and animals that pumps blood through the blood vessels.
Heart functions - why do we need a heart?
Our blood provides the entire body with oxygen and nutrients. In addition, it also has a cleansing function, helping to remove metabolic waste.
The function of the heart is to pump blood through the blood vessels.
How much blood does a person's heart pump?
The human heart pumps from 7,000 to 10,000 liters of blood in one day. This amounts to approximately 3 million liters per year. It turns out up to 200 million liters in a lifetime!
The amount of blood pumped over a minute depends on the current physical and emotional load - the greater the load, the more blood the body needs. So the heart can pass through itself from 5 to 30 liters in one minute.
The circulatory system consists of about 65 thousand vessels, their total length is about 100 thousand kilometers! Yes, we have not sealed ourselves.
Circulatory system
The human cardiovascular system is formed by two circles of blood circulation. With each heartbeat, blood moves in both circles at once.
Small circle of blood circulation
- Deoxygenated blood from the superior and inferior vena cava enters the right atrium and further into the right ventricle.
- From the right ventricle, blood is pushed into the pulmonary trunk. The pulmonary arteries conduct blood directly to the lungs (up to the pulmonary capillaries), where it receives oxygen and gives off carbon dioxide.
- Having received enough oxygen, the blood returns to the left atrium of the heart through the pulmonary veins.
A large circle of blood circulation
- From the left atrium, blood moves into the left ventricle, from where it is further pumped through the aorta into the systemic circulation.
- Having passed a difficult path, blood through the vena cava again arrives in the right atrium of the heart.
Normally, the amount of blood expelled from the ventricles of the heart is the same with each contraction. So, an equal volume of blood is simultaneously supplied to the large and small circles of blood circulation.
What is the difference between veins and arteries?
- The veins are designed to transport blood to the heart, while the arteries are designed to deliver blood in the opposite direction.
- The blood pressure in the veins is lower than in the arteries. Accordingly, the walls of the arteries are characterized by greater extensibility and density.
- Arteries saturate "fresh" tissue, and veins take "waste" blood.
- In the event of vascular damage, arterial or venous bleeding can be distinguished by its intensity and blood color. Arterial - strong, pulsating, beating with a "fountain", the color of the blood is bright. Venous - bleeding of constant intensity (continuous flow), the color of the blood is dark.
The weight of a human heart is only about 300 grams (on average 250g for women and 330g for men). Despite its relatively low weight, it is undoubtedly the main muscle in the human body and the basis of its life. The size of the heart is indeed approximately equal to the fist of a person. Athletes can have a heart one and a half times larger than that of an ordinary person.
Anatomical structure
The heart is located in the middle of the chest at the level of 5-8 vertebrae.
Normally, the lower part of the heart is located mostly in the left side of the chest. There is a variant of congenital pathology in which all organs are mirrored. It is called transposition of internal organs. The lung, next to which the heart is located (normally - the left), has a smaller size relative to the other half.
The posterior surface of the heart is located near the spinal column, and the anterior surface is reliably protected by the sternum and ribs.
The human heart consists of four independent cavities (chambers) divided by partitions:
- the upper two - the left and right atria;
- and two lower - left and right ventricles.
The right side of the heart includes the right atrium and ventricle. The left half of the heart is represented by the left ventricle and the atrium, respectively.
The inferior and superior vena cava enter the right atrium, and the pulmonary veins enter the left. Of right ventricle the pulmonary arteries (also called the pulmonary trunk) come out. Of left ventricle the ascending aorta rises.
The heart has protection from overstretching and other organs, which is called the pericardium or pericardial sac (a kind of shell, which encloses the organ). It has two layers: an outer dense, strong connective tissue called fibrous membrane of the pericardium and internal ( serous pericardium).
Thus, the heart itself consists of three layers: epicardium, myocardium, endocardium. It is the contraction of the myocardium that pumps blood through the vessels of the body.
The walls of the left ventricle are about three times larger than the walls of the right! This fact is explained by the fact that the function of the left ventricle is to push blood into the systemic circulation, where the resistance and pressure are much higher than in the small.
Heart valve device
Special heart valves allow the blood flow to be constantly maintained in the correct (unidirectional) direction. The valves open and close in turn, letting in blood, then blocking its path. Interestingly, all four valves are located along the same plane.
Between the right atrium and the right ventricle is located tricuspid (tricuspid) valve. It contains three special leaflets that are capable of protecting against the return flow (regurgitation) of blood into the atrium during contraction of the right ventricle.
Works in a similar way mitral valve, only it is located on the left side of the heart and is bicuspid in structure.
Aortic valve prevents the backflow of blood from the aorta to the left ventricle. Interestingly, when the left ventricle contracts, the aortic valve opens as a result of blood pressure on it, so it moves into the aorta. Then, during diastole (the period of relaxation of the heart), the reverse flow of blood from the artery helps to close the valves.
Normally, the aortic valve has three cusps. The most common congenital heart anomaly is bicuspid aortic valve. This pathology occurs in 2% of the human population.
Pulmonary (pulmonary) valve at the moment of contraction of the right ventricle, it allows blood to flow into the pulmonary trunk, and during diastole it does not allow it to flow in the opposite direction. Also consists of three doors.
Heart vessels and coronary circulation
The human heart needs nutrition and oxygen, just like any other organ. The vessels supplying (feeding) the heart with blood are called coronary or coronary... These vessels branch off from the base of the aorta.
The coronary arteries supply the heart with blood, while the coronary veins carry out deoxygenated blood. Those arteries that are on the surface of the heart are called epicardial. Subendocardial arteries are called coronary arteries hidden deep in the myocardium.
Most of the outflow of blood from the myocardium occurs through three cardiac veins: large, medium and small. Forming the coronary sinus, they flow into the right atrium. The anterior and lesser veins of the heart deliver blood directly to the right atrium.
Coronary arteries are classified into two types - right and left. The latter consists of the anterior interventricular and circumflex arteries. The great heart vein branches into the posterior, middle and small veins of the heart.
Even perfectly healthy people have their own unique characteristics of coronary circulation. In reality, the vessels may not look and be located as shown in the picture.
How does the heart develop (form)?
Impulse path
This system ensures the automatism of the heart - the excitation of impulses born in cardiomyocytes without external stimulus. In a healthy heart, the main source of impulses is the sinoatrial (sinus) node. He is the leader and blocks impulses from all other pacemakers. But if any disease occurs that leads to sick sinus syndrome, then other parts of the heart take over its function. So the atrioventricular node (automatic center of the second order) and the bundle of His (AC of the third order) are able to activate when the sinus node is weak. There are cases when secondary nodes enhance their own automatism during normal operation of the sinus node.
Sinus node located in the upper posterior wall of the right atrium in the immediate vicinity of the mouth of the superior vena cava. This node initiates pulses with a frequency of approximately 80-100 times per minute.
Atrioventricular node (AV) located in the lower part of the right atrium in the atrioventricular septum. This septum prevents the propagation of the impulse directly into the ventricles, bypassing the AV node. If the sinus node is weakened, then the atrioventricular node will take over its function and begin to transmit impulses to the heart muscle with a frequency of 40-60 beats per minute.
Further, the atrioventricular node goes into bundle of His (the atrioventricular bundle is subdivided into two legs). The right leg rushes to the right ventricle. The left leg is divided into two more halves.
The situation with the left bundle branch is not fully understood. It is believed that the left leg with the fibers of the anterior branch rushes to the anterior and lateral walls of the left ventricle, and the posterior branch supplies fibers to the posterior wall of the left ventricle and the lower parts of the lateral wall.
In case of weakness of the sinus node and blockade of the atrioventricular node, the His bundle is able to create impulses at a speed of 30-40 per minute.
The conducting system deepens and further branching into smaller branches, eventually passing into purkinje fibers, which penetrate the entire myocardium and serve as a transmission mechanism for the contraction of the ventricular muscles. Purkinje fibers are capable of initiating pulses with a frequency of 15-20 per minute.
Exceptionally trained athletes can have a normal resting heart rate down to the lowest on record - just 28 beats per minute! However, for the average person, even if they lead a very active lifestyle, a heart rate below 50 beats per minute can be a sign of bradycardia. If you have such a low heart rate, then you should be examined by a cardiologist.
Heartbeat
A newborn's heart rate can be around 120 beats per minute. With growing up, the pulse of an ordinary person stabilizes in the range of 60 to 100 beats per minute. Well-trained athletes (we are talking about people with well-trained cardiovascular and respiratory systems) have a heart rate of 40 to 100 beats per minute.
The rhythm of the heart is controlled by the nervous system - the sympathetic intensifies contractions, and the parasympathetic weakens.
Cardiac activity, to a certain extent, depends on the content of calcium and potassium ions in the blood. Other biologically active substances also contribute to the regulation of the heart rhythm. Our heart can begin to beat faster under the influence of endorphins and hormones released when listening to your favorite music or kissing.
In addition, the endocrine system is able to significantly influence the heart rate - both the frequency of contractions and their strength. For example, the release of the adrenal glands by the well-known adrenaline causes an increase in heart rate. The opposite hormone is acetylcholine.
Heart tones
One of the easiest ways to diagnose heart disease is listening to the chest with a stethophonendoscope (auscultation).
In a healthy heart, with standard auscultation, only two heart sounds are heard - they are called S1 and S2:
- S1 - the sound heard when the atrioventricular (mitral and tricuspid) valves are closed during systole (contraction) of the ventricles.
- S2 - the sound heard when the semilunar (aortic and pulmonary) valves are closed during diastole (relaxation) of the ventricles.
Each sound has two components, but for the human ear they merge into one due to the very small time interval between them. If, under normal conditions of auscultation, additional tones become audible, then this may indicate some kind of disease of the cardiovascular system.
Sometimes, additional abnormal sounds called heart murmurs may be heard in the heart. As a rule, the presence of murmurs indicates some kind of heart pathology. For example, a murmur can cause blood to return in the opposite direction (regurgitation) due to malfunction or damage to a valve. However, noise is not always a symptom of the disease. To clarify the reasons for the appearance of additional sounds in the heart, it is worth doing echocardiography (ultrasound of the heart).
Heart disease
It is not surprising that the number of cardiovascular diseases is increasing in the world. The heart is a complex organ that actually rests (if you can call it rest) only in the intervals between heartbeats. Any complex and constantly working mechanism itself requires as much respectful attitude and constant prevention.
Just imagine what a terrible burden falls on the heart, given our lifestyle and poor quality abundant nutrition. Interestingly, deaths from cardiovascular disease are also high in high-income countries.
The huge amounts of food consumed by the population of wealthy countries and the endless pursuit of money, as well as the stress associated with this, destroy our hearts. Another reason for the spread of cardiovascular diseases is physical inactivity - catastrophically low physical activity that destroys the entire body. Or, on the contrary, an illiterate passion for heavy physical exercises, often occurring against a background, the presence of which people do not even suspect and manage to die right during "health-improving" activities.
Lifestyle and heart health
The main factors that increase the risk of developing cardiovascular disease are:
- Obesity.
- High blood pressure.
- Increased blood cholesterol levels.
- Physical inactivity or excessive physical activity.
- Abundant poor quality food.
- Suppressed emotional state and stress.
Make reading this great article a turning point in your life - quit bad habits and change your lifestyle.
The wall of the heart includes three shells: the inner one - endocardium, average - myocardium and outdoor - epicardium.
Endocardium, endocardium , a relatively thin shell that lines the chambers of the heart from the inside. The composition of the endocardium is distinguished: endothelium, subendothelial layer, muscular-elastic and external connective tissue. The endothelium is represented by only one layer of flat cells. The endocardium passes without a sharp border to the large cardiac vessels. The cusps of the cusp valves and the cusp of the semilunar valves represent a duplication of the endocardium.
Myocardium, myocardium , the most significant shell in thickness and 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 conducting system), vessels and nerve elements.
The volume 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, are interconnected by jumpers, as a result of which a wide-mesh network is formed. The musculature of the atria and ventricles is anatomically separate. They are connected only by a system of conductive 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 \u200b\u200bthe atrioventricular openings and from the circular bundles located in 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 (surface), middle and inner (deep). The bundles of the surface layer, common to both ventricles, begin from the fibrous rings, go obliquely - from top to bottom to the apex of the heart. Here they turn back, go into the depths, 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, forms the fleshy trabeculae and papillary muscles.
Between the surface 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 go almost horizontally. There are numerous connecting fibers between all muscle layers.
In the heart wall, 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 begin and where valves are fixed. The soft skeleton of the heart includes fibrous rings, anuli fibrosi , fibrous triangles, trigonum fibrosum , and the membranous part of the interventricular septum , pars membranacea septum interventriculare . Fibrous rings , anulus fibrosus dexter , anulus fibrosus sinister , surround the right and left atrioventricular openings, constitute a support for the tricuspid and bicuspid valves.
The projection of these rings onto the surface of the heart corresponds to the coronal groove. Similar fibrous rings are located in the circumference of the aortic orifice and pulmonary trunk.
Fibrous triangles connect the right and left fibrous rings and connective tissue rings of the aorta and pulmonary trunk. Below, the right fibrous triangle is connected to the membranous part of the interventricular septum.
Atypical cells of the conducting system, which form and conduct impulses, provide the automatic contraction of typical cardiomyocytes. Automatism - the ability of the heart to contract under the influence of impulses that arise in itself.
Thus, in the composition of the muscular membrane of the heart, three functionally interconnected apparatus can be distinguished:
1. Contractile, represented by typical cardiomyocytes;
2. Support, formed by connective tissue structures around natural openings and penetrating into the myocardium and epicardium;
3. Conductive, consisting of atypical cardiomyocytes - cells of the conducting system.
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Heart wall structure
Perecarda
The wall of the heart consists of a thin inner layer - the endocardium (endocardium), the middle developed layer - the myocardium (myocardium) and the 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 start from the right and left (anuli fibrosi dexter et sinister) fibrous rings, which are part of the soft skeleton of the heart. Fibrous rings surround the corresponding atrioventricular openings, 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 the visceral layer of the serous pericardium. The epicardium covers the outer surface of the heart from all sides and the initial sections of the vessels departing from it, passing along them into the parietal plate of the serous pericardium.
The normal contractile function of the heart is provided by its conduction system, the centers of which are:
1) sinus-atrial node (nodus sinuatrialis), or Kis-Fleck's node;
2) the atrioventricular node (nodus atrioventri-cularis), or the Fshoff-Tavara node, passing downward 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 (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 in the region of the heart base. Between the plates there is a pericardial cavity (cavi-tas 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), formed from elastic fibers, among which are connective tissue and smooth muscle cells. From the side of the heart cavity, the endocardium is covered with endothelium.
The endocardium lines all the chambers of the heart, is tightly adhered to the underlying muscle layer, follows all its irregularities formed by fleshy trabeculae, comb and papillary muscles, as well as their tendon outgrowths.
The endocardium passes onto the inner lining of the vessels extending from the heart and flowing into it - the hollow 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 tendinous chords and fleshy trabeculae.
In the most thinned sections of the atrial walls, where gaps are formed in their muscle layer, the endocardium is in close contact and even fuses with the epicardium. In the area of \u200b\u200bthe fibrous rings of the atrioventricular openings, as well as the openings of the aorta and the pulmonary trunk, the endocardium, by doubling its leaf - endocardial duplication - forms the cusps of the atrioventricular valves and the semilunar valves of the pulmonary trunk and aorta. The fibrous connective tissue between both sheets of each of the cusps and semilunar flaps is connected to the fibrous rings and thus fixes the valves to them.
Shell of the heart
The heart is located in the pericardial sac - the pericardium. The wall of the heart consists of three layers: the outer - the epicardium, the middle - the myocardium, and the inner - the endocardium.
The outer shell of the heart. Epicard
The epicardium is a smooth, thin and transparent membrane. It is the inner plate of the pericardium (pericardium). The connective tissue base of the epicardium in various parts of the heart, especially in the furrows and in the apex, includes adipose tissue. With the help of the specified connective tissue, the epicardium is fused with the myocardium most tightly in the places of the least accumulation or absence of adipose tissue.
The muscular layer of the heart, or myocardium
The middle, muscular layer of the heart (myocardium), or cardiac muscle, is a powerful and significant part of the thickness of the heart wall.
A dense fibrous tissue lies between the muscle layer of the atria and the muscle layer of the ventricles, due to which fibrous rings are formed, right and left. From the side of the outer surface of the heart, their location corresponds to the area of \u200b\u200bthe coronary groove.
The right fibrous ring that surrounds the right atrioventricular opening is oval in shape. The left fibrous ring does not completely surround the left atrioventricular foramen: on the right, left and behind, and has a horseshoe shape.
With its anterior sections, the left fibrous ring attaches to the root of the aorta, forming triangular connective tissue plates around its posterior periphery - right and left fibrous triangles.
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 rings there is a hole through which the atrial musculature is connected to the ventricular musculature by means of the neuromuscular atrioventricular bundle conducting impulses.
In the circumference of the openings of the aorta and pulmonary trunk are also interconnected fibrous rings; the aortic ring is connected to the fibrous rings of the atrioventricular openings.
The muscular layer of the atria
In the walls of the atria, two muscle layers are distinguished: superficial and deep.
The superficial layer is common to both atria and represents muscle bundles that run mainly in the transverse direction; they are more pronounced on the anterior surface of the atria, forming here a relatively wide muscle layer in the form of a horizontally located inter-auricular bundle, passing to the inner surface of both ears.
On the posterior surface of the atria, the muscle bundles of the superficial layer are partially woven into the posterior sections of the septum.
On the posterior surface of the heart, in the gap formed by the convergence of the boundaries of the inferior vena cava, the left atrium and the venous sinus, between the bundles of the superficial layer of muscles there is a depression covered with an epicardium - the nerve 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 atrial musculature with the ventricular musculature - 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 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 neck 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 cusps of the mitral and tricuspid valves.
The comb muscles are also formed by the bundles of the deep layer. They are most developed on the inner surface of the antero-right wall of the right atrium, 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 very short and thin bundles, the so-called fleshy crossbars. Crossed in different directions, they form a very thin loop-like network.
The muscular membrane of the ventricles
In the muscular membrane (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 with two other, outer and deep, layers, but surrounds each ventricle separately.
The outer, relatively thin, layer consists of oblique, partly rounded, partly flattened bundles. The bundles of the outer layer begin at the base of the heart from the fibrous rings of both ventricles and partly from the roots of the pulmonary trunk and aorta. On the front surface of the heart, the outer bundles go from right to left, and along the back - from left to right. At the apex of the left ventricle, those and other bundles of the outer layer form the so-called vortex of the heart and penetrate into the depths of the walls of the heart, passing into the deep muscle layer.
The deep layer consists of bundles that rise from the apex of the heart to its base. They have a cylindrical, partly oval shape, they are repeatedly split and reconnected, forming loops of various sizes. The shorter of these bundles do not reach the base of the heart, are directed obliquely from one wall of the heart to another, in the form of fleshy crossbars. The beams are located in large numbers along the entire inner surface of both ventricles and have different sizes in different areas. Only the inner wall (septum) of the ventricles immediately under the arterial openings is devoid of these crossbars.
A number of such short, but more powerful muscle bundles, partially associated with both the middle and the outer layers, protrude freely into the cavity of the ventricles, forming papillary muscles of various sizes cone-shaped.
There are three papillary muscles in the cavity of the right ventricle, and two in the cavity of the left. From the apex of each of the papillary muscles, tendon strings begin, through which the papillary muscles are connected to the free edge and partly to the lower surface of the cusps of the tricuspid or mitral valves.
However, not all tendon strings are associated with the papillary muscles. A number of them begin directly from the fleshy crossbeams formed by the deep muscle layer and are most often attached to the lower, ventricular, valve surface.
The papillary muscles with tendinous strings hold the leaflet valves closed when they are slammed by the blood flow from the contracted ventricles (systole) to the relaxed atria (diastole). However, meeting 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 series 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 right one. The bundles of the middle muscle layer of the right ventricle are flattened and have an almost transverse and somewhat oblique direction from the base of the heart to the apex.
In the left ventricle, among the bundles of the middle layer, one can distinguish bundles lying closer to the outer layer and located closer to the deep layer.
The interventricular septum is formed by all three muscle layers of both ventricles. However, the muscle layers of the left ventricle take a large part in its formation. Its thickness is almost equal to the thickness of the wall of the left ventricle. It projects towards the right ventricular cavity. 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 called the membranous part. The septal flap of the tricuspid valve is attached to the membranous part.
The atrial musculature is isolated from the ventricular musculature. An exception is a bundle of fibers that begins in the atrial septum in the coronary sinus. 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, an initial, thickened, part is distinguished, 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 is divided into the right and left legs in the upper-posterior part of the muscular part of the septum ...
The right leg, short and thinner, follows the septum from the side of the right ventricular cavity to the base of the anterior papillary muscle and spreads in the muscle layer of the ventricle in the form of a network of fine fibers (Purkinje).
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 disintegrates into a thin network of fibers that form the anterior, middle and posterior bundles that propagate in the myocardium of the left ventricle.
At the confluence of the superior vena cava in the right atrium, between the vein and the right ear is the sinus-atrial node.
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.
From the side of the cavities of the heart, the endocardium is covered with endothelium.
The endocardium lines all the cavities of the heart, is tightly adhered to the underlying muscle layer, follows all its irregularities formed by the fleshy crossbars, comb and papillary muscles, as well as their tendon outgrowths.
The endocardium passes without sharp boundaries onto the inner membrane of the vessels extending from the heart and flowing into it - the hollow and pulmonary veins, the aorta and the pulmonary trunk. In the atria, the endocardium is thicker than in the ventricles, while it is more thickened in the left atrium, less where it covers the papillary muscles with tendon strings and fleshy crossbars.
In the most thinned sections of the atrial walls, where gaps are formed in the muscle layer, the endocardium is in close contact and even fuses with the epicardium. In the area of \u200b\u200bfibrous rings, atrioventricular openings, as well as openings of the aorta and pulmonary trunk, the endocardium, by doubling its leaf, endocardial duplication, forms the cusps of the mitral and tricuspid valves and semilunar valves of the pulmonary trunk and aorta. The fibrous connective tissue between both sheets of each of the cusps and semilunar valves is connected to 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 apex reaching almost the level of the angle of the sternum. In width, it spreads more to the left than to the right.
In the pericardial sac, there are: the anterior (sternocostal) part, the posterior lower (diaphragmatic) part, and two lateral - right and left - mediastinal parts.
The sternocostal part of the pericardial sac faces the anterior chest wall and is located respectively on the body of the sternum, V-VI costal cartilages, intercostal spaces and the left part of the xiphoid process.
The lateral parts of the sternocostal part of the pericardial sac are covered by the right and left leaves of the mediastinal pleura, separating it in the anterior regions from the anterior chest wall. The areas of the mediastinal pleura that cover the pericardium are called the pericardial part of the mediastinal pleura.
The middle of the sternocostal part of the bag, the so-called free part, is open in the form of two triangular-shaped intervals: the upper, smaller, corresponding to the thymus gland, and the lower, larger, corresponding to the pericardium, facing their bases upward (to the sternum notch) and downward (to the diaphragm ).
In the area of \u200b\u200bthe upper triangle, the sternocostal part of the pericardium is separated from the sternum by loose connective and adipose tissue, in which the thymus gland is laid in children. The compacted part of this fiber forms the so-called superior sterno-pericardial ligament, which fixes the anterior wall of the pericardium to the handle of the sternum.
In the area of \u200b\u200bthe lower triangle, the pericardium is also separated from the sternum by loose tissue, in which the compacted part is isolated, the lower sterno-pericardial ligament, which fixes the lower pericardium to the sternum.
In the diaphragmatic part of the pericardial sac, the upper section is distinguished, which is involved in the formation of the anterior border of the posterior mediastinum, and the lower section, which covers the diaphragm.
The upper section is adjacent to the esophagus, thoracic aorta and azygos vein, from which this part of the pericardium is separated by a layer of loose connective tissue and a thin fascial sheet.
The lower part of the same part of the pericardium, which is its base, grows tightly with the tendon center of the diaphragm; slightly spreading to the anterolateral areas of its muscle part, it is connected to them by loose fiber.
The right and left mediastinal parts of the pericardium are adjacent to the mediastinal pleura; the latter is connected to the pericardium by means of loose connective tissue and can be separated by careful preparation. In the thickness of this loose tissue, which connects the mediastinal pleura with the pericardium, passes the phrenic nerve and the accompanying pericardial-umbilical-phrenic vessels.
The pericardium consists of two parts - the inner, serous (serous sac) and the outer, fibrous (fibrous, pericardial sac).
The serous pericardial sac consists of two serous sacs, as it were, nested one into the other - the outer, freely surrounding the heart (the serous sac of the pericardium proper), and the inner - 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 internal 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 the ligaments, to the inner surface of the sternum.
The epicardium passes into the pericardium at the base of the heart, in the region of the confluence of large vessels: the hollow and pulmonary veins and the exit of the aorta and pulmonary trunk.
Between the epicardium and the pericardium there is a slit-shaped space (cavity of the pericardial sac) containing a small amount of fluid from the pericardium, which wets the serous surfaces of the pericardium, causing this to slide one serous plate over the other during heartbeats.
As indicated, the parietal plate of the serous pericardial sac passes into the visceral plate (epicardium) at the site of the confluence and exit of the heart of large blood vessels.
If, after removing the heart, the pericardial sac is viewed from the inside, then the large vessels in relation to the pericardium are located along its posterior wall along approximately two lines - the right, more vertical, and the left, somewhat inclined to it. On the right line, the superior vena cava, two right pulmonary veins and the inferior vena cava lie from top to bottom, on the left line - the aorta, pulmonary trunk and two left pulmonary veins.
At the site of the transition of the epicardium into the parietal plate, several different shapes and sizes of sinuses are formed. 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 leaf; posterior to them are the atria and next to the right - the superior vena cava. The epicardium from the side of the posterior wall of the initial sections of the aorta and the pulmonary trunk goes up and back to the atria located behind them, and from the latter - down and forward again to the base of the ventricles and the root of these vessels. Thus, between the aortic root and the pulmonary trunk in front and the atria in the back, a passage forms - a sinus, clearly visible when the aorta and pulmonary trunk are pulled anteriorly, and the superior vena cava - posteriorly. This sinus is bounded from above by the pericardium, from behind by the superior vena cava and the anterior surface of the atria, in front by the aorta and the pulmonary trunk; the right and left transverse sinus is open.
Oblique sinus of the pericardial sac... It is located below and behind the heart and represents the space bounded in front by the posterior surface of the left atrium covered by the epicardium, behind by the posterior, mediastinal, part of the pericardium, on the right by the inferior vena cava, on the left by the pulmonary veins, also covered by the epicardium. In the upper blind pocket of this sinus, there is a large number of nerve nodes and trunks of the heart plexus.
Between the epicardium covering the initial part of the aorta (up to the level of the brachiocephalic trunk from it), and the parietal plate extending from it in this place, a small pocket is formed - the aortic protrusion. On the pulmonary trunk, the transition of the epicardium to the specified parietal plate occurs at the level (sometimes below) the arterial ligament. On the superior vena cava, this transition is carried out below the place where the azygos vein flows into it. On the pulmonary veins, the junction almost reaches the gate 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 is a fold of the pericardial sac, the so-called fold of the superior left vena cava, in the thickness of which lies the oblique vein of the left atrium and the nerve plexus.
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Myocardium (myocardium) -the most powerful shell, 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 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.
Figure: 2.4. "Skeleton" of the heart from above (diagram): Figure: 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 supports the valve apparatus.
Figure: 2.5. Heart muscle (left) Figure: 2.5. Heart muscle (left):
1
- right atrium;
2
- the 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
- 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 enter 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 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).
Figure: 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.
Figure: 2.6. Conductive system of the heart:
1
- sinus-atrial and
2
- atrioventricular nodes;
3
- bundle of His;
4
- legs of the bundle of His;
5
- Purkinje fibers
Sinoatrial node
The sinus-atrial 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 belonging to both parts of the autonomic nervous system penetrate into the node. The cells of the node are capable of generating pulses 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 with 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.
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.
Surgery after a heart attack
