Human development after birth

After birth, the child grows rapidly, the mass and length, the surface area of the body increase.

Human growth lasts for the first 20-22 years of his life. Then, up to 60-65 years, the body length hardly changes. However, in the elderly and senile age (after 70 years) due to changes in body posture, thinning of the intervertebral discs, flattening of the arches of the feet, the body length is reduced by 1.0-1.5 cm per year.

By the end of the first year of the child's life, the length of the body increases by 21-25 cm. The periods of early and first childhood (1 year - 7 years) are characterized by a rapid decrease in the growth rate.

At the beginning of the second childhood (8-12 years), the growth rate is 4.5-5.5 cm per year, and then increases. In adolescence (12-16 years), the annual increment in body length in boys is 5.8 cm on average, in girls - about 5.7 cm. Girls have the most intensive growth at the age of 10 to 13 years, and in boys - in 13-16 years, then growth slows down.

The body weight of a person doubles by the 5th-6th month, triples by the end of the first year and increases about 4 times to 2 years after birth. The increase in length and body weight occurs at approximately the same speed. The maximum annual increase in body weight is observed in adolescents: girls - on the 13th, and in boys - at the age of 15. Body weight increases to 20-25 years, and then stabilizes and usually does not change until 40-46 years. It is considered important and physically justified to maintain body weight within the figures of 19-20 years of age.

For the last 100-150 years there is an acceleration of morphofunctional development and maturation of the whole organism in children and adolescents (acceleration). This acceleration is more evident in economically developed countries. Thus, the body weight of newborns for the century increased by an average of 100-300 grams, the year-olds by 1500-2000 g. The body length increased by 5 cm. The length of the body of children in the periods of the second childhood and in adolescents increases by 10-15 cm, and in adult men by 6-8 cm. The time has decreased for the length of the human body to grow. At the end of XIX century. Growth continued to 23-26 years, at the end of the XX century. In men, the body length increases to 20-22 years, and in women - up to 18-20 years. Erection of dairy and permanent teeth was accelerated. Mentally there is a mental development, puberty. At the end of XX century. Compared with its beginning, the average age of menarche decreased from 16.5 years to 12-13 years, and the onset of menopause occurs not in 43 years - 45 years, but in 48-50 years.

After birth, during the period of continuing human growth, morphofunctional features are noted in each age period.

The newborn's head is rounded, large, the neck and chest are short - The abdomen is long; legs short - arms long. Circumference of the head 1-2 cm more than the circumference of the chest, the brain area of the skull is relatively larger than the facial. Chest barrel shaped. The spine is devoid of bends, only a slight prominence of the cape. The bones that form the pelvic bone are not yet fused together. Internal organs are larger than in adults. The length of the intestine in a newborn is 2 times the length of the body, in an adult - 4-4.5 times. The mass of the brain in a newborn is 13-14%, and in an adult - about 2% of the body weight. Adrenal glands and thymus differ in large sizes in a newborn.

In infancy (10 days-1 year) the body of the child grows most quickly. Approximately from the 6th month, teething begins. During the first years of life, the musculoskeletal system, digestive and respiratory systems are rapidly growing and developing.

During the early childhood (1-3 years), all milk teeth erupt and the first "rounding" occurs: the increase in body weight outruns the growth of the body in length. The child's mental development, speech, and memory progress rapidly. The child begins to navigate in space. During the 2-3rd year of life, growth in length predominates over weight gain. In connection with the rapid development of the brain, whose mass reaches 1100-1200 g by the end of this period, mental abilities develop rapidly, causal thinking, the ability to recognize, orientate in time, and days of the week persists for a long time. In early and in the first childhood (4-7 years), sex differences (except for primary sexual characteristics) are almost not expressed. From 6-7 years begins eruption of permanent teeth.

In the period of the second childhood (8-12 years), the body's growth in width again prevails. By the end of this period, the body is growing in length, the rate of which is greater in girls. Progression of mental development. An orientation towards months and calendar days is developing. Begins puberty, earlier in girls, which is associated with increased secretion of female sex hormones. In girls at the age of 8-9, the pelvis begins to expand and the thighs round, the secretion of the sebaceous glands increases, and the pubis embryos develop. In boys in 10-11 years, the growth of the larynx, testicles and penis begins, which by 12 years increases by 0.5-0.7 cm.

In adolescence (12-16 years), sexual organs rapidly grow and develop, secondary sexual characteristics are amplified. Girls increase the amount of hair on the skin of the pubic region, hair appears in the armpits. The sizes of genital organs, mammary glands increase, the alkaline reaction of the vaginal secretion becomes acidic, menstruation appear, and the pelvic size increases. In boys, the testicles and penis rapidly increase. In the beginning, the pubic hair spread develops according to the female type, the mammary glands swell. By the end of the adolescent period (15-16 years), hair growth begins on the face, body, in the armpits, on the pubis - according to the male type. The skin of the scrotum is pigmented, the genital organs are even more enlarged, the first ejaculations occur (involuntary ejaculation).

In adolescence, mechanical and verbal-logical memory develops.

The youthful age (16-21 years) coincides with the period of maturation of the organism. At this age, the growth and development of the body is basically complete, all apparatuses and systems of organs practically reach morphofunctional maturity.

The structure of the body in adulthood (22 years - 60 years) varies little, and in the elderly (61-74 years) and senile (75-90 years), the perestroika characteristic of these age periods is traced, which is studied by the special science of gerontology (from the Greek gerontos - the old man). The time boundaries of aging have wide limits for different individuals. In the old age, the adaptive capabilities of the organism decrease, the morphofunctional indices of all apparatuses and systems of organs change, among which the immune, nervous and circulatory systems play an important role.

Active lifestyle, regular physical training slows down the aging process, but this is possible within the limits determined by hereditary factors.

A man from a woman is distinguished by sexual characteristics. They are divided into primary (genitals) and secondary (development of pubic hair, mammary glands, change of voice, etc.).

[1], [2], [3]