Basic laws of growth and development
The concept of growth implies an increase in total body mass and body dimensions due to an increase in the number and size of cells, as well as the accumulation of non-cellular substance and waste products. Growth can be limited or unlimited.
In turn, physical development combines morphological and functional indicators that determine a person's strength, endurance, and working capacity. An age period is understood as a time interval during which developmental processes and physiological characteristics are identical, and reactions to stimuli are unambiguous.
Stages of prenatal and postnatal ontogenesis
The human life cycle is divided into several global stages:
- Progenezis is the period of formation of germ cells (gametes) with a haploid set of chromosomes and their subsequent fusion during fertilization to form a diploid zygote.
- Embryonic (prenatal) period is intrauterine development lasting about 270 days. It includes the embryonic period (up to 8 weeks, when all organ systems are laid down) and the fetal period (from the 9th week until birth).
- Postembryonic (postnatal) period begins at birth and continues until the end of life, being subdivided into pre-reproductive, reproductive, and post-reproductive stages.
Table of key stages of postnatal development:
| Period | Age | Characteristic |
|---|---|---|
| Newborn period | First 10 days | Sleeping most of the time |
| Infancy | From 11 days to 1 year | Active development, first attempts to sit and walk |
| Early childhood | 1–3 years | Confident walking, mastery of speech |
| Adolescence | Boys 13–16, girls 12–15 years old | Puberty, restructuring of the neurohumoral system |
| Youth | Young men 17–21, young women 16–20 years old | Onset of physiological maturity, completion of growth |
Anatomical and physiological characteristics of the respiratory system in children
A child's respiratory organs have a number of important differences from the adult body:
- Upper respiratory tract: narrow and short nasal passages create a risk of rapid impairment of nasal breathing with minimal rhinitis, which interferes with sucking and sleeping.
- Lower respiratory tract: bronchioles have a small lumen, so mucosal edema easily leads to bronchoobstruction and atelectasis. Due to the physiological narrowing of the bronchioles upon exhalation, there is a risk of air trapping (hyperinflation).
- Biomechanics: horizontal arrangement of the ribs and weak respiratory muscles limit the depth of inspiration. Compensation for respiratory failure in infants occurs due to an increased respiratory rate.
- RR and auscultation: the frequency of respiratory movements in newborns is about 40 per minute with a pulse ratio of 1:4. Normally, puerile breathing is auscultated — enhanced vesicular breathing due to a thin chest wall.
The rule of "four eights": 8 weeks is the most vulnerable embryonic period, and the respiration-to-pulse ratio in infants is 1:4 (like 4 to 16).
Class and exam questions
What is physical development and how does it differ from growth?
Growth is an increase in body mass and dimensions due to cellular and non-cellular structures. Physical development is broader: it is a set of not only morphological but also functional indicators that determine the endurance and working capacity of the organism.
Why can a mild runny nose cause severe respiratory impairment in young children?
In young children, the nasal passages are anatomically very narrow and short. Even minimal mucosal edema during rhinitis significantly hinders nasal breathing, which disrupts the process of sucking and sleeping in infants.
What is the essence of the critical periods of intrauterine development?
These are phases of greatest vulnerability of the embryo and fetus to the action of damaging factors. The first 8 weeks of embryonic development, when active laying down of all organ systems occurs, are recognized as the main critical stage.
What else to study on this topic
- Morphological stages of embryogenesis: cleavage, gastrulation, and neurulation
- Structural features of the mature follicle and oocyte membranes (zona pellucida and corona radiata)
- Dynamics of changes in intrapleural pressure and elastic recoil of the lungs with age
- Perinatal period: antenatal, intranatal, and postnatal stages
- Particular periodization of sexual development in girls ("neutral" period and menarche)
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