Human development after birth

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

Human growth continues during the first 20-22 years of life. Then, up to 60-65 years, body length remains almost unchanged. However, in old and senile age (after 70 years), due to changes in body posture, thinning of the intervertebral discs, and flattening of the arches of the feet, body length decreases by 1.0-1.5 cm annually.

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

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

The human body weight doubles by the 5th-6th month, triples by the end of the 1st year and increases approximately 4 times by the 2nd year after birth. The increase in length and body weight occurs at approximately the same rate. The maximum annual increase in body weight is observed in adolescents: in girls - at the 13th year, and in boys - at the 15th year of life. Body weight increases until 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 limits of the 19-20-year-old age.

Over the past 100-150 years, there has been an acceleration of the morphofunctional development and maturation of the entire organism in children and adolescents (acceleration). This acceleration is more pronounced in economically developed countries. Thus, the body weight of newborns has increased by an average of 100-300 g over a century, and that of one-year-olds by 1,500-2,000 g. Body length has increased by 5 cm. The body length of children during the second childhood and adolescent periods increases by 10-15 cm, and that of adult men by 6-8 cm. The time during which a person's body length increases has decreased. At the end of the 19th century, growth continued until the age of 23-26, while at the end of the 20th century, body length growth in men occurs until the age of 20-22, and in women until the age of 18-20. The eruption of primary and permanent teeth has accelerated. Mental development and puberty occur more quickly. At the end of the 20th century, compared to its onset, the average age of menarche has decreased from 16.5 years to 12-13 years, and the onset of menopause occurs not at 43-45 years, but at 48-50 years.

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

The newborn has a round, large head, short neck and chest - long abdomen; short legs - long arms. The head circumference is 1-2 cm larger than the chest circumference, the brain section of the skull is relatively larger than the facial section. The rib cage is barrel-shaped. The spine is devoid of curves, only a slightly pronounced promontory. The bones that form the pelvic bone are not yet fused together. The internal organs are larger than in an adult. The length of the intestine in a newborn is 2 times greater than the body length, in an adult - 4-4.5 times. The brain mass in a newborn is 13-14%, and in an adult - about 2% of the body weight. The adrenal glands and thymus are larger in a newborn.

In infancy (10 days-1 year), the child's body grows most rapidly. Around the 6th month, baby teeth begin to erupt. During the first years of life, the musculoskeletal, digestive, and respiratory systems grow and develop rapidly.

In early childhood (1-3 years), all baby teeth erupt and the first “rounding” occurs: the increase in body weight outpaces the growth in length. The child’s mental development, speech, and memory progress rapidly. The child begins to navigate in space. During the 2nd-3rd year of life, growth in length prevails over the increase in body weight. Due to the rapid development of the brain, the mass of which reaches 1100-1200 g by the end of this period, mental abilities and causal thinking develop rapidly, and the ability to recognize and orientate oneself in time and days of the week is preserved for a long time. In early and first childhood (4-7 years), sexual differences (except for primary sexual characteristics) are almost not expressed. From the age of 6-7, permanent teeth begin to erupt.

During the second childhood (8-12 years), the body growth in width again predominates. By the end of this period, the body growth in length increases, the rate of which is higher in girls. Mental development progresses. Orientation in relation to months and calendar days develops. Puberty begins, earlier in girls, which is associated with increased secretion of female sex hormones. In girls, at 8-9 years old, the pelvis begins to widen and the hips to round out, the secretion of the sebaceous glands increases, and pubic hair growth occurs. In boys, at 10-11 years old, the larynx, testicles and penis begin to grow, which by the age of 12 increases by 0.5-0.7 cm.

During adolescence (12-16 years), the genitals grow and develop rapidly, and secondary sexual characteristics become stronger. Girls experience an increase in the amount of hair on the skin of the pubic area, and hair appears in the armpits. The size of the genitals and mammary glands increases, the alkaline reaction of the vaginal secretion becomes acidic, menstruation appears, and the size of the pelvis increases. In boys, the testicles and penis quickly increase in size. At first, pubic hair develops according to the female type, and the mammary glands swell. By the end of adolescence (15-16 years), hair begins to grow on the face, body, in the armpits, and on the pubis - according to the male type. The skin of the scrotum becomes pigmented, the genitals increase in size even more, and the first ejaculations (involuntary ejaculation) occur.

During adolescence, mechanical and verbal-logical memory develops.

Adolescence (16-21 years) coincides with the period of maturation of the organism. At this age, the growth and development of the organism is basically completed, all apparatuses and organ systems practically reach morphofunctional maturity.

The body structure in mature age (22 - 60 years) changes little, and in old age (61-74 years) and senile age (75-90 years) a restructuring characteristic of these age periods can be traced, which is studied by a special science called gerontology (from the Greek gerontos - old man). The time limits of aging have wide limits in different individuals. In old age, there is a decrease in the adaptive capabilities of the body, a change in the morphofunctional indicators of all apparatuses and organ systems, among which the most important role belongs to the immune, nervous and circulatory systems.

An active lifestyle and regular physical exercise slow down the aging process, but this is possible within the limits determined by hereditary factors.

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

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