Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Key stages of human ontogeny

When studying Human Development and its individual and age-related characteristics in anatomy and other disciplines, researchers rely on scientifically grounded data on age periodicity. The scheme of human age periodicity, which accounts for anatomical, physiological, and social factors, was adopted at the 7th Conference on Problems of Age Morphology, Physiology, and Biochemistry (1965). It distinguishes twelve age periods (Table 1).

Class="center">Table 1 Human Age Periods

Period

Age

1. Intrauterine

embryonic

0—8 wks

fetal

9 wks — 9 mos

2. Newborn

1 — 10 days

3. Infancy

10 days — 1 yr

4. Toddlerhood

1—3 yrs

5. First childhood

4—7 yrs

6. Second childhood

8—12 yrs (boys) 8—11 yrs (girls)

7. Adolescence

13—16 yrs (boys) 12—15 yrs (girls)

8. Youth

17—21 yrs (young men) 16—20 yrs (young women)

9. Adulthood

1st period

2nd period

22—35 (men)

21—35 (women)

36—60 (men)

36—55 (women)

10. Elderly age

61—74 yrs (men) 56—74 yrs (women)

11. Senile age

75—90 yrs (men and women)

12. Longevity

90 yrs and older

Individual development, or ontogeny, takes place across all periods of life—from conception to death. Human ontogeny comprises two main periods: pre-birth (intrauterine, prenatal—from the Greek natos, meaning born) and post-birth (extrauterine, postnatal).



Last update: 10/08/2026

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