Human Anatomy - Kotsan I. Ya. 2009
Main stages of organism development in ontogenesis
Classification of age periods in the individual development of an organism
The complete cycle of individual development (ontogeny) is divided into two periods: 1) prenatal (intrauterine); 2) postnatal (extrauterine).
The prenatal period is divided into:
1. Embryonic Stage (the first 8 weeks), during which The formation of Organs and body parts characteristic of an adult human takes place.
2. Fetal stage (from week 9 to 36), characterized by growth in size and the completion of Organogenesis.
In the postnatal period (after birth), human life is divided into the following age-related periods:
1. Neonatal period — 1–10 days
2. Infancy — 10 days — 1 year
3. Early childhood — 1–3 years
4. First childhood — 4–7 years
5. Second childhood — 8–12 (boys), 8–11 years (girls)
6. Adolescence — 13–16 (boys), 12–15 years (girls)
7. Youth — 17–21 (young men), 16–20 years (young women)
8. Adulthood:
Period I — 22–35 (men), 21–35 years (women)
Period II — 36–60 (men), 36–55 years (women)
9. Elderly age — 61–74 (men), 56–74 years (women)
10. Senile age — 75–90 years (men and women)
11. Longevity (centenarians) — 90 years and older.
Last update: 08/08/2026
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