Leaf valves: structure and characteristics. Papillary valves and tendon muscles Functions of the papillary muscles and tendon filaments
The structure of the flap valve
Posterior interventricular sulcus.
The interventricular sulci run from the coronary sulcus towards the apex of the heart along the anterior and rear surface respectively and correspond to the interventricular septum of the heart. In the furrows are the own vessels and nerves of the heart. This sulci correspond to partitions dividing the heart into 4 sections: longitudinal interatrial and interventricular septa divide the organ into two isolated halves - right and left heart, transverse septum divides each of these halves the upper chamber is the atrium and the lower chamber is the ventricle.
The right side of the heart contains venous blood, and the left arterial.
The structure of the chambers of the heart.
Right atrium is a cavity with a volume of 100-185 ml, resembling a cube in shape, located at the base of the heart on the right and behind the aorta and pulmonary trunk. Separates from the left atrium atrial septum on which is visible oval fossa, which is a remnant of an overgrown hole that existed between the two atria in embryogenesis.
The superior and inferior vena cava, the coronary sinus and the smallest veins of the heart flow into the right atrium. top atrium is atrial appendage , on the inner surface of which longitudinal muscle ridges are visible - comb muscles.
The right atrium communicates with the right ventricle through the right atrioventricular orifice.
Between the latter and the confluence of the inferior vena cava is the opening of the coronary sinus, and next to it are the point mouths of the smallest veins of the heart.
Right ventricle . It has the shape of a pyramid with the top facing down. Occupies most of the anterior surface of the heart. Separates it from the left ventricle interventricular septum, most of which is muscular, and the smaller one, located at the very top, closer to the atria, is membranous. Top wall two holes:
1. behind - right atrioventricular
2. in front - opening of the pulmonary trunk.
The atrioventricular orifice is closed by the right atrioventricular valve (tricuspid valve),
1. sashes - there are three of them - anterior, posterior, medial, which are triangular tendon plates.
2. Tendon chords (thread)
During ventricular systole, the tricuspid valve closes, and the tension of the tendon chords prevents the leaflets from eversion towards the atrium.
Between the ventricle and the pulmonary trunk there is also a valve called crescent.
The semilunar valve is made up of
Front, left and right
Semilunar dampers,
Arranged in a circle, convex
Surface into the cavity of the right
The ventricle rather concave and free
Edge - into the lumen of the pulmonary trunk.
When the muscles of the ventricle contract, the semilunar valves are pressed against the wall of the pulmonary trunk by blood flow and do not prevent the passage of blood from the ventricle; during relaxation, when the pressure in the cavity of the ventricle drops, the return flow of blood fills the pockets between the wall of the pulmonary trunk and each of the semilunar valves and opens the valves, their edges close and do not allow blood to pass to the heart.
Left atrium . It has the shape of an irregular cube. Delimited from the right interatrial septum; also has a left ear. In the back section top wall four pulmonary veins open into it, devoid of valves, through which arterial blood flows from the lungs. It communicates with the left ventricle through the left atrioventricular orifice, only near which there are pectinate muscles, the rest of the surface is smooth.
left ventricle . Cone-shaped, its base is turned upwards. In the anterior upper section there is an opening of the aorta, through which the ventricle communicates with the aorta, and the left atrioventricular opening. At the exit of the aorta from the left ventricle, there is an aortic valve - the semilunar valve - consisting of right, left, back flaps. The aortic valves are thicker than those in the pulmonary trunk.
The left atrioventricular orifice is closed by the cuspid valve, which consists of two cusps (anterior and posterior) and is therefore also called mitral , tendon chords and two papillary muscles.
In order to diagnose cardiac diseases, a stethoscope is used auscultation (listening) heart: in this case, the mitral valve is auscultated in the region of the apex of the heart, the valves of the pulmonary trunk and aorta - in the second intercostal space, respectively, at the right and left edges of the sternum. The place of auscultation (listening) of the tricuspid valve is the point located at the base of the xiphoid process of the sternum.
STRUCTURE OF THE HEART WALL.
The wall of the heart consists of three layers: the inner - the endocardium,
Middle - myocardium, the thickest,
Outer - epicardium.
1. Endocardium - lines all the cavities of the heart, tightly fused with the underlying muscle layer. From the side of the cavities of the heart is lined with endothelium. The endocardium forms the cusp and semilunar valves.
2. Myocardium is the most powerful and thick wall of the heart. The muscular layer of the walls of the atria is thin due to a small load. Comprises surface layer, common to both atria, and deep- separate for each of them. In the walls of the ventricles, it is the most significant in thickness and consists of three layers: the outer one is longitudinal, the middle one is annular, and the inner longitudinal layers. The muscular layer of the left ventricle is more powerful than the right one.
The composition of the cardiac striated muscle tissue includes typical contractile muscle cells-cardiomyocytes and atypical - cardiac myocytes, which form the conduction system of the heart, which ensures the automaticity of heart contractions, and also coordinates the contractile function of the myocardium of the atria and ventricles of the heart.
3. epicardium - covers the outer surface of the heart and the parts of the aorta and pulmonary trunk closest to the heart, vena cava. It is part of the fibrous-serous membrane of the pericardium. In the pericardium there are two layers:
fibrous pericardium, formed by dense fibrous connective tissue, and
serous pericardium, also consisting of fibrous tissue with elastic fibers.
The serous pericardium consists of an internal visceral plate (epicardium), which directly covers the heart and is tightly connected with it, and an external parietal plate, lining the fibrous pericardium from the inside and passing into the epicardium at the place where large vessels leave the heart.
Fibrous pericardium at the base of the heart passes into the adventitia of large vessels; pleural sacs are adjacent to the pericardium on the side, from below it adheres to the tendon center of the diaphragm, and in front it is connected by connective tissue fibers to the sternum.
The pericardium isolates the heart from surrounding organs, and the serous fluid between its plates reduces friction during heart contractions.
An important role in functions of atrioventricular valves the apparatus holding the valves plays - tendon threads attached, on the one hand, to the free edge of the valve cusps, on the other, to the tops of the papillary muscles. With endocarditis and myocarditis, these formations are involved in the process, undergo pathological changes, and therefore, to a greater or lesser extent, disrupt the function of also affected valves to a certain extent.
tendon threads like valves, they consist of fibrous, cell-poor tissue covered with a very thin layer of endocardium. Passing into the tissue of the valve leaflets, the fibrous tissue of the filaments is fan-shaped distributed in the fibrous plate of the leaflet. From each papillary muscle, one or more tendon threads depart, which are attached to the free edges of the valves or, less often, to their ventricular surface.
A bunch of threads from each papillary muscle is divided in the left ventricle into two parts, of which one goes to the posterior leaflet, the other to the anterior. The distribution of filament attachment to the valves in the right ventricle is not so clearly defined. A large number of thin tendon filaments start directly from the muscles of the ventricles and go to different parts of the valves. Tendon threads of the left ventricle are thicker and more numerous than the right one.
If all threads are the same tense, then the valve flaps are evenly stretched (A. M. Eliseeva, 1948).
Naturally, when endocarditis the inflammatory process can also pass to the tendon threads; valve leaflets undergo changes with their tendon filaments. As a result of the organization of thrombotic masses and sclerosis, thickening, shortening, coarsening and compaction of the tendon filaments occur. Sometimes adjacent tendon filaments are soldered together either due to the organization of thrombotic masses enveloping them, or due to the growth of connective tissue from the side of the valves.
In these cases, they may form connecting plates like the swimming membranes of a frog's foot. The process of sclerosis can also capture the tops of the papillary muscles. With ulcerative endocarditis, the process passes to the tendon threads, leads to their destruction, ruptures. Sometimes all the tendon threads of one valve are torn.
important role in ensuring normal The function of the atrioventricular valves belongs to the papillary (papillary) muscles. These muscles in the left ventricle are relatively large, it is in the right. With tension of the papillary muscles, the adjacent edges of the valves approach each other.
With inflammation myocardium the same processes are observed in the papillary muscles. The bases of the papillary muscles are affected first and most severely. Sclerosis and death of muscle tissue are also more pronounced in papillary muscles than in the rest of the myocardium. This is also confirmed by the data of M. A. Skvortsov (1950).
Spreading ulcerative endocarditis or purulent myocarditis can lead to the destruction of the papillary muscles, to their separation. The same pathology can cause a heart attack of the ventricular wall with the capture of the papillary muscle or with its limited necrosis. Most often this happens with the posterior papillary muscle of the left ventricle. At the autopsy, a piece of muscle is found, freely hanging on the tendon threads (EM Gelstein, 1951).
break or even full detachment of the valve, tendon filaments, and papillary muscles can also be observed without destructive processes in the endocardium or myocardium - due to significant physical stress, sharp bruises and compression of the chest, falling from a height, direct injuries of the heart. These same causes can cause rupture of the walls of the heart and large vessels. Traumatic rupture of the heart occurs especially easily with pathological changes in the myocardium on the basis of myocarditis, cardiosclerosis, aneurysms (V. N. Sirotinin, 1913; A. Foght, 1920).
Pathological processes leading to sclerosis (cusps, foramens, tendon filaments and their muscles) underlie the pathology that is commonly called heart defects or, more precisely, heart valve defects. Damage to the valves leads to a greater or lesser disruption of the heart, as a result of which a more or less pronounced circulatory failure develops.
Right ventricle of the heart occupies most of the anterior surface of the organ. It has a thicker wall, because. three layers of myocardium are located here, and not two, as in the left and right atria. The cavity of this part of the heart has an interesting shape, which would be easy to study if you pour plaster into it and make an impression. It would turn out to be a kind of "cobblestone" with two spurs. Accordingly, three parts are distinguished in the ventricle (Fig. 1): entrance department(1) - has a short length, but very wide, originates from the atrioventricular opening (2), exit department(3), called in old manuals the "arterial sinus" and leading to the pulmonary trunk with its semilunar valve (4), and muscular department(5), which occupies the main volume. The inner surface of the muscular section is also smooth due to the endothelium, but not so smooth: from the side of the wall of the ventricle, fleshy crossbars protrude into the cavity (more often they are called trabeculae), from the largest of which - the transverse marginal trabeculae - the papillary muscles originate. Most often there are three of them: anterior (6), posterior (7) and septal (8), but it happens that there are more of them.
Fig.1. Scheme of the structure of the right ventricle
A very important element structures of the ventricles of the heart are chords - tendon threads(9), or in literal translation from Latin tendon strings. These are thin whitish threads originating from the tops of the papillary muscles and ending on the surfaces of the three cusps of the atrioventricular valves (also, by the way, anterior, posterior and septal). There is a kind of overlap in this. So the anterior papillary muscle “sends” the threads mainly to the anterior of the three valves and partly to the posterior, the posterior muscle mainly to the posterior valve and partly to the third, septal. Accordingly, from the septal papillary muscle, the tendon filaments approach the same leaf of the tricuspid valve and in several bundles to the anterior one. Output and input departments, divides supraventricular ridge, it flows into the cavity of the left ventricle. The exit and entrance sections are clearly distinguishable, more even from the inside, since the bulk of the trabeculae falls on the muscular section. Recall that the right ventricle has two openings: the atrioventricular and the opening of the pulmonary trunk.
The posterior section is presented left ventricle of the heart. The diaphragmatic surface, the blunt edge and the apex of the heart, as well as the left part of the coronary and both interventricular sulci, which are the outer boundaries, can serve as landmarks for the location of the left ventricle. Although left ventricle of the heart smaller than the right one, it does not differ much from it. There are also three layers of myocardium, however, the wall of the left ventricle is even thicker 1.2 cm due to the more developed muscle layer. It is worth noting that the wall of the right ventricle is 0.3 cm in size. The following departments are also distinguished in the left ventricle (Fig. 2): input(1), that is, closest to the atrioventricular opening (2), day off(3) continuing into the aorta (4), and muscular(5), but in the case of this cavity of the heart, there is no such pronounced boundary as the supraventricular crest between the inlet and outlet sections. This is another feature and difference in structure of the ventricles of the heart.
Fig.2. Scheme of the structure of the left ventricle
There is only a rather conditional delimiter between the inlet and outlet sections, and this is the anterior leaflet (6) of the mitral valve. This delimiter is conditional since it is such only during the opening of the valve (Fig. 2, a). If the valve is closed, then there is no anterior cusp in the cavity, the division of the ventricle into sections is not noticeable (Fig. 2b). go to the mitral valve tendon threads papillary muscles, two papillary muscles (or two groups of muscles) are most developed: anterior (7) and posterior (8), respectively tendon threads these muscles go to the anterior and posterior leaflets of the mitral valve. There are two holes: atrioventricular and aortic. The first with a bicuspid (mitral) valve. The second is covered with three semi-lunar wings. The left ventricle sends blood to the aorta through the aortic opening, and then the blood is distributed throughout the body.
The valves of the heart are a complex set of anatomical structures that function as a whole. Its constituent parts (fibrous rings, cusps, tendon chords and papillary muscles, and for the aortic valves and pulmonary trunk - fibrous rings, sinuses and semilunar valves) have pronounced individual features of the structure, shape, size and position.The valve apparatus, which is in anatomical and functional unity, consists in correlative relationships with other components of the heart, as a result of which, as a result of these correlations that occur both in the embryonic and postnatal periods, significant changes in its design occur with age, which deepen the created individual , typical and age differences.
Left atrioventricular valve
The mitral valve apparatus is a complex complex structure, the morphological elements of which are the connective tissue atrioventricular ring, cusps, papillary muscles and tendon chords.
Functionally, the mitral valve apparatus also includes the left atrium and the left ventricle. The normal function of the valve depends on both the anatomical and functional usefulness of all its elements.
The mitral valve consists of two main leaflets: a large anterior (aortic, or septal) and a smaller posterior (mural). The posterior leaf usually consists of three or more lobules (scallops), which are still separated by subcommissures in the fetus.
Valves and lobules develop variably in each individual. The number of valves is different: 2 valves in 62% of people, 3 in 19%, 4 in 11% and 5 in 8% of people.
The line of attachment of the anterior leaflet occupies less than half of the annulus circumference. Most of its circumference is occupied by the rear flap. The front flap is square or triangular in shape and has a larger area than the back. The wide and movable anterior leaflet plays the main role in the closing function of the mitral valve, and the posterior leaflet plays a predominantly supporting function.
Histologically, the mitral valve leaflets consist of three layers: 1) a fibrous layer, consisting of dense collagen, continuously continuing into tendon chords; 2) the spongy layer, which is located on the side of the atrial surface and forms the anterior edges of the leaflet (it consists of a small number of collagen fibers and an abundance of proteoglycans, elastin and connective tissue cells); 3) a fibroelastic layer that covers most valves. The fibroelastic layer thickens with age due to increased production of elastin and collagen; similar changes are also seen in myxomatous degeneration of the mitral valve.
The epicardial fibers in the left ventricle, emanating from the base of the heart, descend to the apex and are introduced into the cavity in the form of two papillary muscles, which have a vertical orientation of the myocardial fibers. The anterolateral papillary muscle usually has one large head (nipple) and a more developed muscle structure. The posteromedial papillary muscle may have two or more nipples. The structure of papillary muscles is diverse. Muscles may have a common base and several apices, or one apex and a divided base.
The distance from the papillary muscles to the mitral annulus averages 23.5 mm. The posterior medial papillary muscle is usually supplied by the right coronary artery (in 10% of cases by the left circumflex artery). The anterolateral papillary muscle receives its blood supply from the left descending and circumflex coronary arteries.
During diastole, papillary muscles are visible in the inflow tract of the left ventricle. During the period of systole, they are determined in the output tract. By contracting, papillary muscles increase left ventricular output. In diastole, papillary muscles make up 5-8% of the volume of the left ventricle, while in systole - 15-30%. The anterior and posterior papillary muscles contract simultaneously and are innervated by both sympathetic and parasympathetic nerves.
A dense network of tendon chords extends from the papillary muscles to both mitral valves. Chords are classified into three functional groups. The first group (primary) - chords located in close proximity to the papillary muscles. They progressively separate and attach to the main edges of the valves. Primary chords are fundamental in preventing valve prolapse in systole. The second group (second-order chords) - are reference. These chords branch out and attach to the ventricular surface of the cusps at the transition from the tuberous zone to the smooth zone and thus form the edges corresponding to the border of the cooptation of the cusps. Second-order chords play an important role in optimizing left ventricular systolic function. The third group (tertiary or basal) departs from the trabeculae of the left ventricle and has a fan-shaped shape. Additionally, there are commissural chords and split chords.
Chords contain nerve fibers and some ("immature") chordae may contain muscle fibers. The chorda apparatus consists of about 25 main (from 15 to 32) chordae branches extending from the papillary muscles, which, separating at the valves, form over 100 small chords. Chords have a differentiated microstructure depending on the type. The presence of vessels in the chords characterizes them as an integral component that coordinates the work of the subvalvular apparatus. The main chords of the anterior mitral cusp are more vascularized than the other chords. The anterior and posterior marginal chordae contain more deoxyribonucleic acid and collagen than the other chordae.
The mitral valve is a developing structure. Changes in structure and function occur according to the needs of the circulatory system. The increasing load on the body with age determines the anatomical and functional restructuring of the valve, aimed primarily at improving its obturator function.
Tricuspid valve
In children under 1 year of age, the diameter of the right atrioventricular orifice is 0.8 - 1.7 cm (usually 1.2-1.5), up to 6 years - 1.7-2.6 cm (usually 2.0-2, 3), up to 12 years - 2.3-3.1 cm (usually 2.5-2.8), up to 17 years - 2.6-3.6 cm (usually 2.7-3.0). In boys, the diameter of the hole is 0.1-0.5 cm larger than in girls.
The number of leaflets in the right atrioventricular valve in children ranges from 2 to 4. With age, the number of leaflets increases. Obviously, in the postnatal period, there is still a restructuring of the valve, and the formation of additional leaflets is an adaptive mechanism, the purpose of which is to improve the obturator function of the valve.
Usually, there are three main cusps - anterior, posterior and septal, which are observed in 55.7% of cases. In children, an additional anterior cusp occurs in 7.5% of cases, the posterior one - in 21%, and the septum - in 3% of cases.
The dimensions of the sashes are individually different. The front sash has the largest dimensions. In children, the width of the anterior sash is 0.7-4.5 cm, the height is 0.4-2.7 cm. The width of the septal sash is 0.6-3.0 cm, the height is 0.4-2.0 cm. Width rear sash - 1.6-4.5 cm, height - 1.4-3.0 cm.
Additional sashes are smaller than the main ones and, as a rule, have a triangular shape. In children, their width is 0.4-2.5 cm, height 0.4-2.2 cm.
Comparison of data on the number of leaflets and their sizes with data on the circumference of the right atrioventricular orifice found that with a larger circumference, larger leaflets and more of them are more common. With a small circumference of the right atrioventricular opening, there are usually 3 valves with a small width and height.
The papillary muscles, being a continuation of the muscles of the right ventricle, can have a variety of shapes. In the right ventricle, papillary muscles of a cylindrical, conical shape, in the form of a truncated tetrahedral pyramid, can be distinguished. The papillary muscles may have several heads (multi-headed). The number of papillary muscles in the right ventricle ranges from 2 to 11. In children, the number of anterior papillary muscles is from 1 to 3, the number of posterior papillary muscles is from 1 to 4. The number of septal papillary muscles in children and adults varies from 0 to 5. In children in In 3.5% of cases, the posterior papillary muscles are absent, in 6% - septal ones. With age, the number of papillary muscles in the right ventricle decreases, which is associated with the fusion individual muscles into compact, irregularly shaped muscles with multiple heads. Part of the muscles lags behind the growth of the heart with age, shortens and even disappears. The anterior papillary muscles are the largest, and the septal muscles are the smallest. In children, the length of the anterior papillary muscles is 0.6-2 cm, the posterior - 0.3-1.4 cm, the septal - 0.2-0.8 cm. The length of the papillary muscles of the right ventricle is associated with the length of the heart: long papillary muscles are observed on long hearts, short ones on short ones.
From the papillary muscles, tendon chords begin, which are attached to the valves along their free edge, as well as along the entire ventricular surface up to the annulus fibrosus. The number of tendinous chords extending from the anterior papillary muscles in children ranges from 5 to 16. 4 to 16 chords depart from the posterior papillary muscles, from 1 to 13 chords from the septal papillary muscles. Parietal chords were from 3 to 15 in children.
Analysis of the obtained data on the structure of the tricuspid valve allowed S.S. Mikhailov to distinguish two extreme forms of its structure. simple form the structure of the tricuspid valve is observed with a narrow and long heart in each age group. With this form of valve structure, the diameter of the fibrous ring is the smallest (in children under the age of 1 year - 0.8-1.2 cm, up to 6 years - 1.7-2.0 cm, up to 12 years - 2.3-2, 8 cm, up to 18 years - 2.6-3.0 cm, in adults - 2.7-3.0 cm), its branches are thin, more often there are 2-3 valves and 2-4 papillary muscles, from which it departs to valves 16-25 chords.
The second form of the structure of the tricuspid valve is complex. This form is noted on preparations of a wide and short heart. With this form of valve structure, the diameter of the fibrous ring is the largest (in children under the age of 1 year - 1.3-1.7 cm, up to 6 years - 2.1-2.6 cm, up to 12 years - 2.9-3, 1 cm, up to 18 years - 3.1-2.6 cm, in adults - 3.6-4.8 cm), its branches are thick, valves 4-6, papillary muscles 6-10, outgoing chords 30-40.
aortic valve
The aortic valve is located at the mouth of the aorta and consists of three semilunar cusps attached to the annulus fibrosus. The state of the latter and the structure of the initial part of the aorta have a direct impact on the function of the valves, so the fibrous ring of the aorta and the sinuses of Valsalva are usually referred to as components of the aortic valve.
Each valve has the appearance of a thin plate, the mechanical basis of which is the fibrous layer, which is a continuation of the fibrous ring of the aorta. From the side of the aorta and ventricle, the fibrous plate is covered with endothelial, subendothelial layers and a layer of elastic fibers.
There are right, left and posterior (non-coronary) leaflets of the aortic valve. The junctions of the valves with each other are called commissures. There are anterior commissure (between the right and left valves), right commissure (between the right and posterior valves), and posterior commissure (between the left and posterior valves).
The sizes of the semilunar flaps have both age and individual differences. Usually the width of the semilunar valves exceeds the width of the aortic sinuses, and their height, on the contrary, is less than the height of the aortic sinuses. The width of semilunar valves in children is: right - from 8.4?2.16 to 17.0?3.1 mm, left - from 7.2?2.2 to 16.0?3.2 mm, back - from 9.00 × 2.56 to 21.5 × 1.62 mm; in adults, the right valve - from 25.00? 3.53 to 28.0? 2.6 mm, the left - from 22.5? 3.1 to 26.0? 28.0 × 3.2 mm.
The space between the wall of the aortic sinuses and outer surface semilunar valves (facing the wall of the sinus) is called the holes of the aortic valves (lunalae valvularum semilunarium). Due to the fact that the semilunar valves are wider than the aortic sinuses, and the height of the valves is less than the height of the sinuses, blood under pressure, when it enters the aortic bulb, spreads into the holes of the semilunar valves, displaces them downward, closing the aortic valve.
The aortic crescents are supplied with blood not only due to the flowing oxygenated blood in the aorta, but also due to their own microvascular bed, the state of which plays an important role in the normal functioning of the valve and in the development of pathological processes.
Pulmonary valve
The valve of the pulmonary trunk consists of the annulus fibrosus, the wall of the trunk and three semilunar valves attached to it. In the initial part of the pulmonary trunk, as well as in the aorta, there is an extension in which there are recesses - the sinuses of the pulmonary trunk.
The fibrous ring is located in the same way as in the aorta, from the inner surface of the junction of the wall of the arterial cone with the wall of the pulmonary trunk. The semilunar cusps of the pulmonary valve originate from the medial edge of the annulus fibrosus. Fibrous rings covered with endocardium form the bottom of the sinuses of the pulmonary trunk.
The semilunar valves originate from the annulus fibrosus of the pulmonary trunk and are represented by a fold of the endocardium. There are anterior, left and right semilunar valves of the pulmonary trunk. The lower edges of the flaps are fused with the lower edges of the sinuses. There are nodules (noduli) on the upper edges of the flaps. The dampers, together with the sinuses, form holes (lunuli). The sizes of the semilunar valves are slightly larger than the sinuses of the pulmonary trunk.
In parallel with the growth of the heart, the size of the main vessels increases, but the rate of their growth is slower. So, if the volume of the heart by the age of 15 increases 7 times, then the circumference of the aorta - only 3 times. Over the years, the difference in the size of the lumen of the openings of the pulmonary trunk and aorta somewhat decreases. If by the time of birth the ratio of the lumens of the pulmonary trunk and the aorta exceeds 20-25% (aorta - 16 mm, pulmonary trunk - 21 mm), then by 10-12 years their lumen is equal, and in adults the lumen of the aorta exceeds the lumen of the pulmonary trunk (aorta - 80 mm, pulmonary trunk - 74 mm). The circumference of the pulmonary trunk in children is constantly larger than the circumference of the trunk of the ascending aorta. The lumen of the arteries as a whole narrows somewhat with age relative to the size of the heart and the increasing length of the body. Only after 16 years there is some expansion of the arterial vascular bed.
The length of the aorta before the bifurcation at the time of birth is on average 125 mm, its diameter at the exit is about 6 mm. The same width is characteristic of the descending department. The isthmus of the aorta, located 10 mm from the origin of the left subclavian artery, has an internal diameter of only about 4 mm. In the first months of life, the isthmus area expands, and after half a year, the narrowing of the lumen is no longer determined here.
The pulmonary trunk at the time of birth is relatively short and divides into two approximately equal pulmonary arteries, which in some children creates a pressure difference between the vessels, reaching up to 8-15 mm Hg, and can cause the characteristic systolic murmur of peripheral pulmonary stenosis. After birth, the lumen of the pulmonary trunk at first does not increase, and the diameter of the pulmonary arteries grows quite intensively, which leads to the disappearance of the pressure drop, usually after 5-6 months. The wall of the pulmonary trunk consists of a framework of elastic fibers alternating with smooth muscle elements. In response to hypoxia and acidosis, the lumen of the artery may decrease significantly. In a child of the first weeks and months, the muscular layer of the pulmonary vessels is less pronounced, which explains the lower response of children to hypoxia.
The left atrioventricular (mitral) valve, valva atrioventricularis sinistra (v. mitralis), is attached along the circumference of the left atrioventricular orifice; the free edges of its valves protrude into the cavity of the ventricle. Like the tricuspid valve, they are formed by duplication of the innermost layer of the heart, the endocardium. This valve, when the left ventricle contracts, prevents the passage of blood from its cavity back into the cavity of the left atrium. In the valve, an anterior cusp, cuspis anterior, and a posterior cusp, cuspis posterior, are distinguished, between which two small teeth are sometimes located. The anterior cusp, being strengthened on the anterior sections of the circumference of the left atrioventricular orifice, as well as on the connective tissue basis of the aortic orifice closest to it, is located to the right and more anteriorly than the posterior one. The free edges of the anterior leaflet are fixed by tendon chords, chordae tendineae, to the anterior papillary muscle, m.. papillaris anterior, which starts from the anterior wall of the ventricle. The anterior fold is slightly larger than the posterior one. Due to the fact that it occupies the area between the left atrioventricular orifice and the aortic orifice, its free edges are adjacent to the aortic orifice. The back leaf is attached to the back section of the circumference of the specified hole. It is smaller than the anterior one and, in relation to the opening, is located somewhat posteriorly and to the left. Through the chordae tendineae, it is fixed mainly to the posterior papillary muscle, m .. papillaris posterior, which begins on the posterior wall of the ventricle. Small teeth, lying in the intervals between large ones, are fixed with the help of tendon chords either to the papillary muscles or directly to the wall of the ventricle. In the thickness of the teeth of the mitral valve, as well as in the thickness of the teeth of the tricuspid valve, there are connective tissue, elastic fibers and a small amount muscle fibers associated with the muscle layer of the left atrium. The anterior and posterior papillary muscles can each be divided into several papillary muscles.
Answer
