Postnatal period

Extrauterine period (postnatal) - the period of individual development is significantly different from the intrauterine one. If in the first period the development of the organism occurs under more or less constant environmental conditions, then after birth the external environment has a direct and strong influence on the human body. A growing organism begins to adapt to it and a complex transformation takes place in it, while the newly acquired features join the structural features inherited.

Age Periodization

In the postnatal development of the human body, mildly defined periods with their specific characteristics of the growth, development and formation of organs are conditionally distinguished. This division is called age periodization . There are several classifications of this period. The most common is proposed by the Research Institute of Physiology of Children and Adolescents of the Russian Academy of Medical Sciences:

1. Newborns - from birth to 10 days
2. Breast age - from 10 days to 1 year
3. Earlier childhood - from 1 year to 3 years
4. First childhood - from 4 to 7 years
5. Second childhood - 8-12 years old (boys), 8-11 years old (girls)
6. Adolescence - 13-16 years (boys), 12-15 years (girls)
7. Youthful age - 17-18 years (boys), 16-18 (girls)
8. Mature age - 1st period 19–35 years
9. Mature age - 2nd period 36-60 (men), 36-55 (women)
10. The advanced age is 61–74 (men), 56–74 (women)
11. Senile age - 75—90
12. Centenarians - 90 and older

For infancy, a small growth rate is characteristic. So the body length at this time increases by 1.5 times, body weight - by 3 times. The age from 1 year to 7 years is also called the period of neutral childhood, since boys and girls almost do not differ in shape and body size from each other. In the period from 8 to 12 years in the size and proportions of the body, sexual differences appear, growth processes are accelerated, puberty in girls begins.

Adolescence is also called puberty or puberty: at this time puberty begins in boys, secondary sexual characteristics appear (voice mutation, hair growth on the pubis, axillary hollows, and then on the upper lip and chin). There is an increase in growth in length, mainly due to the lower extremities. In adolescence, the processes of growth and formation of the body basically ends, puberty sets in.

In adulthood, the shape and structure of the human body changes little, and only after 60 years the aging processes begin, which in some organs occur earlier, in others later ^[1]