Anthropology. Stages of ontogenetic development (most important)

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Anthropology. Stages of ontogenetic development (most important)

Lecture notes, cheat sheets

Directory / Lecture notes, cheat sheets

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16. STAGES OF ONTOGENETIC DEVELOPMENT

The process of ontogenetic development can be logically divided into two stages:

▪ period of prenatal development - the intrauterine stage, lasting from the moment of formation of the zygote as a result of fertilization until the moment of birth;

▪ postnatal development - a person’s earthly life from birth to death.

The maximum activation of body length growth in the postnatal period is observed in the first months of life (approximately 21-25 cm per year). In the period from 1 year to 4-5 years, the increase in body length gradually decreases (from 10 to 5,5 cm per year). From 5-8 years, a weak half-height jump is sometimes noted. At the age of 1013-13 years in girls and 15-8 years old in boys, there is a distinct acceleration of growth - a growth spurt: the growth rate of body length is about 10-7 cm per year for boys and 9-XNUMX cm per year for girls. Between these periods, a decrease in growth rates is recorded.

The maximum growth rate of the fetus is typical for the first four months of intrauterine development; body weight changes in the same way, with the difference that the maximum speed is noted more often at the 34th week.

The first two months of intrauterine development is the stage of embryogenesis, characterized by the processes of "regionalization" and histogenesis (differentiation of cells with the formation of specialized tissues). At the same time, due to the differential growth of cells and cellular migrations, parts of the body acquire a certain outline, structure and shape. This process - morphogenesis - actively goes up to the adult state and continues until old age. But its main results are already visible at the 8th week of intrauterine development. By this time, the embryo acquires the main characteristic features of a person.

By the time of birth (between 36 and 40 weeks), the growth rate of the fetus slows down, since by this time the uterine cavity is already completely filled. It is noteworthy that the growth of twins slows down even earlier - during the period when their total weight becomes equal to the weight of a single 36-week-old fetus. It is believed that if a genetically large child develops in the uterus of a woman of small stature, growth retardation mechanisms contribute to successful childbirth, but this does not always happen. The weight and dimensions of the body of a newborn are largely determined by the external environment, which in this case is the mother's body.

Body length at birth averages about 50,0-53,3 cm in boys and 49,7-52,2 in girls. Immediately after birth, the growth rate of body length increases again, especially in a genetically large child.

Currently, body length growth slows down significantly in girls aged 16-17 years and in boys aged 18-19 years, and up to 60 years, body length remains relatively stable. After about 60 years, there is a decrease in body length.

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