Basic concepts of ontogenesis
The process of human individual development includes quantitative and qualitative changes. Growth represents an increase in body mass and dimensions due to cell division and enlargement, and the accumulation of non-cellular substance. It is implemented at the cellular, tissue, and organ levels.
Physical development characterizes the set of morphological and functional traits that determine the body's endurance and functional capacity. To assess these indicators, standardized tools are used, including centiles and SDS scores, separated by sex in accordance with the principle of sexual dimorphism.
Laws of child growth and development
The development of the organism from birth to maturity is subject to objective patterns:
- Uneven rate: the rate of body length increase changes in a wave-like manner. The first year of life provides the maximum gain (20–30 cm/year), in the second year the rate slows down to 10–15 cm/year, in childhood it is 4–6 cm/year, and a growth spurt occurs during puberty (from 10 cm/year).
- Heterochrony: non-simultaneous maturation of organs and tissues. For example, the head outpaces the limbs in growth at an early age.
- Sexual dimorphism: differences in the rates and final indicators of physical development between boys and girls, driven by endocrine factors.
- Biological reliability: redundancy of compensatory and regulatory mechanisms that ensure homeostasis stability.
Hormonal regulation of growth processes
The control of growth and tissue maturation varies depending on the child's age and the stage of ontogenesis:
| Age period | Main regulatory factors |
|---|---|
| Intrauterine period | Insulin, insulin-like growth factors, thyroid hormones (for differentiation) |
| Pre-puberty | Somatotropic hormone (growth hormone / GH), thyroid hormones |
| Puberty | Sex hormones, initiating the growth spurt and closure of growth plates |
Sex hormones during puberty accelerate linear growth, but simultaneously cause ossification of the epiphyseal cartilage, which completes the process of body length increase.
Four pillars of growth: Unevenness, Heterochrony, Sexual dimorphism, and Biological reliability (U-H-S-B).
Class and exam questions
What is heterochrony of growth and development?
This is a physiological pattern in which individual organs, tissues, and functional systems reach maturity at different times. This principle ensures the phased maturation of the entire organism.
How does the rate of linear growth change during childhood?
Growth rates are uneven: the maximum rate is observed in the first year of life (20–30 cm/year), followed by a slowdown in the second year (10–15 cm/year), during childhood the rate is stable (4–6 cm/year), and a sharp spurt is noted in puberty.
What hormones regulate fetal growth in utero?
Somatotropic hormone does not affect the fetus due to the absence of receptors. Insulin and insulin-like growth factors are of primary importance, while thyroid hormones are responsible for cellular differentiation.
What else to study on this topic
- Infancy and its specific pathology
- General biological properties of ontogenesis (irreversibility, specialization, cyclicity)
- Critical periods of organism development
- Influence of environmental factors, acceleration and retardation
- Classification of childhood periods according to N.P. Gundobin
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