Development and age specific features of the heart
Last reviewed: 23.04.2024
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In human ontogenesis, the heart develops from the mesoderm in the form of a paired bookmark at the stage of 1-3 somites (approximately on the 17th day of development of the embryo). This simple bookmark forms a simple tubular heart, which is located in the neck. Ahead it passes into a primitive bulb of the heart, and posteriorly into an enlarged venous sinus. The anterior (cephalic) end of a simple tubular heart is arterial, and the posterior one is venous. The middle section of the tubular heart intensively grows in length, therefore it bends in the form of an arc in the ventral direction (in the sagittal plane). The top of this arc is the future top of the heart. The lower (caudal) section of the arc is the venous part of the heart, the upper (cranial) part is arterial.
Then a simple tubular heart, which looked like an arc, bends counter-clockwise S-shaped and turns into a sigmoid heart. On the external surface of the sigmoid heart appear the atrioventricular groove (future coronal sulcus).
The general atrium grows rapidly, embracing the arterial trunk from the rear, two protuberances (front) of the right and left ears visible on the sides (front). The atrium communicates with the ventricle with a narrow atrioventricular canal. In the canal walls, ventral and dorsal thickenings occur - atrioventricular endocardial ridges, of which then the valves - two- and three-leafed - develop on the border of the heart chambers.
At the mouth of the arterial trunk, four endocardial ridges are formed, which later turn into semilunar valves (valves) of the beginning of the aorta and pulmonary trunk.
At the 4th week, the primary (interatrial) septum appears on the inner surface of the common atrium. It grows in the direction of the atrioventricular canal and divides the common atrium into the right and left. From the upper-posterior wall of the atrium, a secondary (interatrial) septum grows, which fuses with the primary and completely separates the right atrium from the left.
At the beginning of the 8th week of development, a fold appears in the posterior part of the ventricle. It grows upward and upwards towards the endocardial ridges of the atrioventricular canal, forming an interventricular septum that completely separates the right ventricle from the left. Simultaneously, two longitudinal folds appear in the arterial trunk, growing in the sagittal plane towards each other, and also downwards towards the interventricular septum. Connecting together, these folds form a septum that separates the ascending part of the aorta from the pulmonary trunk.
After the occurrence of interventricular and aortolulent septa, a four-chambered heart is formed in the human embryo. A small oval aperture (the former interatrial opening), through which the right atrium communicates with the left, closes only after birth, i.e. When the small (pulmonary) circulatory system begins to function. Venous sinus of the heart narrows, turning together with the reduced left common cardinal vein into the coronary sinus of the heart, which flows into the right atrium.
In connection with the complexity of the development of the heart, congenital malformations of its development arise. The most common incomplete infection (defect) between the atrial (rarely interventricular) septum; incomplete separation of the arterial trunk into the ascending part of the aorta and the pulmonary trunk, and sometimes the narrowing or complete closure (atresia) of the pulmonary trunk; nezaraschenie arterial (botallova) duct between the aorta and the pulmonary trunk. At the same individual, sometimes 3 or even 4 defects are observed simultaneously in a certain combination (the so-called triad or tetrad of Fallot). For example, the narrowing (stenosis) of the pulmonary trunk, the formation of the right aortic arch instead of the left (dextralization of the aorta), incomplete infection of the interventricular septum and a significant increase (hypertrophy) of the right ventricle. There are also possible developmental defects of bicuspid, tricuspid and semilunar valves due to abnormal development of endocardial ridges. First of all, the harmful factors affecting the organism of parents and especially the mother's organism in the early stages of pregnancy (alcohol, nicotine, drugs, some infectious diseases) are the causes of heart defects (as well as of other organs).
The newborn has a rounded heart. Its transverse dimension is 2.7-3.9 cm, the average length is 3.0-3.5 cm. The atria are large compared to the ventricles, the right is much larger than the left. The heart grows particularly quickly during the first year of the child's life, and its length increases more than the width. Individual parts of the heart vary in different age periods unequally. In the first year of life, the atria grow faster than the ventricles. At the age of 2 to 5 years and especially at 6 years, the growth of the atria and ventricles occurs equally intensively. After 10 years, the ventricles increase faster. The total mass of the heart in a newborn is 24 g. At the end of the first year of life, it increases approximately 2-fold, to 4-5 years-3-fold, at 9-10 years-5-fold and to 15-16 -10-fold. The heart weight is 5-6 years more in boys than in girls; in 9-13 years, on the contrary, it is more in girls. At 15 years old, the heart mass is again higher in boys than in girls.
The volume of the heart from the period of newborn to 16 years of age increases by 3-3.5 times, with the most intensively increasing from 1 year to 5 years and during puberty.
Myocardium of the left ventricle grows faster than myocardium of the right ventricle. By the end of the second year of life, its mass is twice the mass of the right ventricle. At the age of 16 these ratios persist. In children of the first year of life fleshy trabeculae cover almost the entire inner surface of both ventricles. The most strongly developed trabeculae in adolescence (17-20 years). After 60-75 years, the trabecular network is flattened, its mesh character is preserved only in the region of the apex of the heart.
In newborns and children of all age groups, pre-ventricular valves are elastic, the valves are shiny. In the 20-25 years, the valves of these valves become denser, their edges become uneven. In the old age there is a partial atrophy of the papillary muscles, in connection with which the function of the valves may suffer.
In newborns and infants, the heart is high and lies transversely. The transition of the heart from the transverse position to the oblique begins at the end of the first year of life. 2-3 years old children have an oblique position of the heart. The lower border of the heart in children under 1 year is located on one intercostal gap higher than in adults. The upper border is at the level of the second intercostal space, the apex of the heart is projected in the fourth left intercostal space (outside the mid-inclusive line). The right border of the heart is most often located respectively to the right edge of the sternum, 0.5-1.0 cm to the right of it. As the child's age increases, the ratio of the sternal-rib (anterior) surface of the heart to the chest wall changes. In newborns, this surface of the heart is formed by the right atrium, the right ventricle and most of the left ventricle. With the front chest wall, mainly the ventricles touch. Children older than 2 years, in addition, to the chest wall is still part of the right atrium.
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