Human Anatomy - Kotsan I. Y. 2009

Cardiovascular System
Circulatory System
Age, sex, and individual characteristics of the heart

The newborn's Heart is rounded in shape and relatively large in size. Its transverse diameter is 2.7–3.9 cm, length is 3.0–3.5 cm, and anteroposterior dimension is 1.7–2.6 cm. During the first 15 days of life, There is a slight decrease in heart volume, after which it begins to grow again, doubling its initial size by the end of the first year of life. Individual PARTS OF THE heart change unevenly across different age periods: during the 1st year of life, the atria grow faster than the ventricles. Between the ages of 2 and 5 years, and especially at 6 years, the growth of both atria and ventricles occurs with equal intensity. After 10 years, the ventricles increase in size faster than the atria. The total heart mass in a newborn is 24.0 g, doubling by the end of the 1st year of life, tripling by 4–5 years, increasing fivefold by 9–10 years, and tenfold by 15–16 years. There are two periods of active heart growth: the first occurs during the first year of life, and the second during Puberty. A gradual, slow increase in heart size continues even after 30 years of age. In women, given the same height and body mass, The Heart dimensions are smaller than in men.

In newborns and infants, the heart is positioned higher than in adults and lies almost horizontally. Only by the end of the first year of life, due to the child adopting an upright posture and the descent of the Diaphragm, does the heart assume an oblique position. The lower border of the heart in children under one year old is located one intercostal space higher than in adults; the upper border is at the level of the second intercostal space; the right border most frequently lies along the right sternal margin, or 0.5–1.0 cm to the right of it; and the apex of the heart projects into the fourth left intercostal space (lateral to the midclavicular line). With age, the apex shifts, and by 6–12 years it corresponds to the lower border of the fifth rib.

THE POSITION OF the diaphragm, which changes depending on the respiratory phase, is of great importance in determining the position of the heart in a living person. During inspiration, the heart descends; during expiration, it is elevated by the diaphragm. In overweight and elderly individuals, the heart is positioned higher. The Location OF THE heart also depends on the body type (somatotype). In individuals with a brachyorphic body type, the heart appears to be elevated by the diaphragm and rests upon it, assuming a horizontal position. In individuals with a dolichomorphic body type, the heart is lowered, acquiring a vertical position. In mesomorphic individuals, an oblique position of the heart is observed.

At the age of 30–40 years, a certain increase in the Connective Tissue stroma is observed in the myocardium. As a person ages, adipose tissue accumulates beneath the epicardium, and thickening of the endocardium occurs. These changes can be significantly slowed down or even prevented through regular physical activity. In individuals engaged in physical labor and in athletes, the size and mass of the heart are greater than in those engaged in sedentary or intellectual work. Furthermore, sports that involve prolonged endurance training (such as rowing or marathon running) lead to myocardial hypertrophy and an increase in overall heart dimensions. Swimming, short-distance running, boxing, football, and other sports result in less pronounced cardiac hypertrophy.