The individual development of organisms is a set of biological processes that determine the growth and change of cells throughout the entire period of their existence. The common scientific name is ontogenesis. Its main task is to observe, identify the main stages and features of each period, identify patterns, as well as analyze changes and identify factors that these changes can cause.
The individual development of the body is inherent not only to man, but also to all living creatures and plants. The main stages of development are:
- Pre-embryonic development (gametogenesis).
- Prenatal period of development (development of the embryo itself, embryogenesis).
- Postnatal period (development from birth: growth, mass increment,regeneration, modification).
- Gerontological period (aging).
- The death of an organism (death is not isolated as a separate stage in ontogenesis, but any individual development ends with it).
We will not consider the individual development of the plant organism in this short article, but dwell on the development of representatives of the animal world that is closer to the person. The stages of development, as already mentioned, do not change in a person and correspond to those indicated above.
Gametogenesis in humans is composed of two components: spermatogenesis (maturation of male germ cells - spermatozoa) and oogenesis (maturation of female germ cells - eggs). Fertilization is possible only under the condition of mature germ cells in the male and female. When pathologies arise in fertilization, organisms can be formed - chimeras, some of which are quite viable.
Human embryogenesis is one of the most important stages. It is divided into the initial stage (0 - 1 week after fertilization), the embryonic stage itself (2 - 8 weeks) and the fetal or fetal stage (9 weeks - birth). It is during this period that vital organs are formed, the body takes shape, genetic or other pathologies can manifest themselves.
The individual development of the body in the postnatal period consists in the further development of organs, an increase in size and mass, the acquisition of new mental functions, a change in motor activity and the development of its new species.
The postnatal period is the most important in the development of a new person. Its length is about 17 years (from newborn to adolescence). The individual development of the organism in this period is influenced not only by the features caused by heredity, but also by psychological and social factors. Consciousness, speech, thinking and other processes of
higher nervous activity are formed. By the end of this period, new individuals, as a rule, come with complete gametogenesis.
Aging of an organism is a stage of wilting, depletion of all resources of an organism. Irreversible disorders occur in nerve cells,
myelin sheaths, the quality of vision and hearing decreases, vital organs “wear out”, skin integuments change, reproduction function is lost, and tissue regeneration slows down, etc.