Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2002

General Part
Human Development and Body Structure
Developmental Stages of the Human Organism

The Development of the human Organism (ontogeny) is divided into two main periods: intrauterine (prenatal) and extrauterine (postnatal). The intrauterine period spans from Fertilization to birth and consists of two phases: embryonic (the first 2 months) and fetal (months 3–9). The extrauterine period extends from birth until the individual's death.

The Embryonic period of development is characterized by Organogenesis and histological differentiation, whereas the fetal period involves further tissue differentiation, overall body growth, and the completion of organ formation. Accordingly, based on the recommendations of the International Symposium on Age Periodization (Moscow, 1965), the age periods of Human Development are classified as follows:

Newborns

1–10 days

Infancy

10 days – 1 year

Early childhood

1–3 years

First childhood

4–7 years

Second childhood

8–12 years (boys)

8–11 years (girls)

Adolescence

13–16 years (boys)

12–15 years (girls)

Youth

17–21 years (young men)

16–20 years (young women)

Adulthood

Period I – 22–35 years (men)

– 21–35 years (women)

Period II – 36–60 years (men)

– 36–55 years (women)

Elderly age

Ages 61–74 (men)

Ages 56–74 (women)

Senile age

Ages 75–90 (men and women)

Centenarians aged 90 and over



Last update: 08/08/2026

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