Human Anatomy Part 1 - K. A. Dubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

General Part
Human Development and Body Structure
Concept of Critical Periods in Embryonic Development

Critical Periods of individual embryonic development refer to those stages characterized by an increased sensitivity of the Organism, or parts of it, to adverse environmental and internal factors that can lead to structural anomalies, congenital diseases, impaired growth and differentiation, embryonic death, and more. In addition to critical periods common to the embryo as a whole, there are specific sequential periods when various Organs are laid down. According to P. G. Svetlov, during critical periods the regulatory capacities of the developing organism decrease, thereby reducing its resistance to negative influences.

The critical periods of embryonic development include progenesis and Meiosis (the stage of germ Cell maturation), Fertilization, implantation (days 6–8), which coincides in time with The first phase of Gastrulation, placentation (weeks 3–8), occurring during the second phase of gastrulation, neurulation and the Initial Stages of Organogenesis, periods of intensive Brain development (weeks 15–20), The formation of major functional systems (weeks 20–24), and the course of childbirth. In the Postnatal period of ontogenesis, critical periods include the newborn period (the first year of life) and Puberty (ages 11–16). Knowledge of the critical periods of embryonic development is of great importance for developing Methods to protect Pregnancy and safeguard health during corresponding childhood periods.