Biology of individual development (ontogenesis). What is ontogenesis: stages of development of organisms

ONTOGENESIS (ontogenesis; Greek on, ontos being + genesis origin, origin) - the process of individual development of an organism, which is a set of regular, interconnected, characterized by a certain time sequence of morphological, physiological and metabolic transformations in the body from the moment of its isolation as an individual until death or cessation of existence in its previous capacity ( for example, as a result of division of a single-celled organism).

The term “ontogenesis” was introduced in 1866 by German. zoologist E. Haeckel in connection with the formulation of the basic biogenetic law (see), according to which ontogenesis is a short and condensed repetition of phylogeny - the process historical development individual types, classes, orders, families, genera, species of living organisms. In accordance with modern views, O. is not only the result of phylogeny (see), but also its basis, and phylogeny itself appears as a historical series of ontogenies.

O. is usually divided into embryonic (embryonic, prenatal) and postembryonic (post-embryonic, postnatal) periods. The first covers the period of time from fertilization to birth (or until exit from the egg membranes), the second - from birth to death.

The duration of each period of oxygen is determined by the characteristics of organisms of a given species, as well as by the action of environmental factors. Amount of nutrients, cut this type animals can be used to ensure the initial stages of development, depends on the duration of the embryonic period.

Based on the totality of the properties of an organism at relatively early stages of individual development, ensuring its adaptive relationships with the environment, free larval, secondary larval and non-larval types of development are distinguished.

The free larval type of development - development with metamorphosis (see), or indirect development - is characterized by the presence in its life cycle special intercalary stage - larval, during which the organism differs from the mature individual and has necessary equipment for an independent lifestyle (see Larvae). The transition from the larval to the mature form is called metamorphosis. The larval type of development is characteristic of animals that lay eggs with a relatively small amount of nutritional material.

In the non-larval type of development, also called direct, the embryos long time develop under the cover of the egg membranes, and the young organism leaves them, being capable of independently obtaining food. In some species, after hatching, the young individual receives food from its parents (for example, oviparous mammals). With a non-larval type of development, the organism, by the time it emerges from the egg shells, corresponds in its basic structural plan, set of organs and systems to the sexually mature form, differing from it only in smaller body sizes, underdevelopment (mainly in quantitative terms) of certain systems, including reproductive, etc.

This type of development is typical for animals that lay eggs with a significant amount of yolk, enclosed in special shells (shell, cocoon, etc.).

O. of placental mammals (including humans) has a number of features. The early stages of O. proceed according to the type of intrauterine development, in which the fertilized egg (embryo) develops inside the mother’s body and nutrients throughout embryogenesis, they enter the embryo first directly from the uterus and then through the placenta.

This type of development is phylogenetically the youngest and best ensures the survival of the individual.

The intrauterine period of human development is usually divided into the actual embryonic and fetal periods. The first of these takes place during the first 7 weeks of development. From the 8th week, the fetal period begins, characterized by growth, further differentiation of organs, the formation of their functions and ending with birth.

The problem of animal health in the post-embryonic period is reflected in theories of growth and maturation of the organism from the moment of birth to the onset of puberty. In particular, M. M. Zavadovsky proposed a theory indicating the importance of the interaction of organs in postnatal development and the role of the endocrine glands in this process. Theories of aging have also been proposed, emphasizing the role of genetic factors or indicating a predominant role in determining the rate of aging of factors environment(see Gerontology).

The theory of O., which, based on the concepts of thermodynamics, links together the processes of oogenesis, embryonic and postnatal development, aging, regeneration, and malignant growth, was proposed by A. I. Zotin. In accordance with this theory, O. of a living organism, which is open system, is generally considered as a process of approaching the energy level of an organism to a more probable final stationary state, corresponding to the transition of living to nonliving and characterized by the lowest rates of energy dissipation. This process begins from the moment of fertilization and is possible thanks to the process of oogenesis that precedes it, when future organism in the form of an egg formed by the maternal organism, due to its vital activity it acquires an energetically less probable, but such a state, which makes the development of a new individual possible. We can say that during oogenesis, the egg acquires the ability to provide the O. process as a whole.

According to the ideas under consideration, initial stages processes of regeneration, wound healing, and malignant growth are provided by the internal resources of the body, the transition of the latter to an energetically less probable state, but characterized by increased plastic capabilities.

Division of postnatal O. into age periods reflects changes in the morphofunctional parameters of the body over time after its birth. Existing options such divisions are aimed at providing a solution specific tasks age physiology and medicine. The most detailed division of the O. segment from the moment of birth to the achievement of puberty has been developed. The periods of neonatality, infancy, childhood and school age, puberty and adulthood (see Age), as well as periods of presenile and senile changes (see Old age, aging).

Bibliography: Zavarzin A. A. DNA synthesis and kinetics of cell populations in the ontogenesis of mammals, D., 1967, bibliogr.; Zotin A.I. Thermodynamic approach to the problems of development, growth and aging, M., 1974; Knorre A. G. Embryonic histogenesis, JI., 1971; Koltsov N.K. Cell organization, M.-JI., 1936; Patten B. M. Human embryology, trans. from English, M., 1959; Svetlov P. G. Physiology (mechanics) of development, vol. 1-2, JI., 1978; T about k and N B. P. General embryology, M., 1977; WaddingtonK. Morphogenesis and genetics, trans. from English, M., 1964; aka, Basic biological concepts, in the book: On the way to theory. biol., trans. from English, ed. B.JI. Astaurova, t. 1, p. 11, M., 1970; Shmalgauzen I.I. The problem of Darwinism, JI., 1969; Schmidt G. A. Types of embryogenesis and their adaptive significance, M., 1968; Yablokov A.V. and Yusufov A.G. Evolutionary doctrine, M., 1976.

V. N. Yarygin, S. B. Tarabrin.

from Greek ontos - existing and genes - giving birth, born) - process of development individual organism, in contrast to phylogeny as the process of species formation. The term was introduced by the German biologist Haeckel (in 1866).

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ONTOGENESIS

Greek birth, origin), the process of development of an individual organism, in contrast to phylogenesis as the process of formation of systematic. groups. The term "O." introduced in 1866 by E. Haeckel, who proceeded from his concept of individual development as a brief reproduction of phylogeny. O. distinguishes quantitative (increase in the size and live weight of the organism, life expectancy) and qualitative (differentiation, the emergence of new functions and structures) aspects. In the course of O. in higher animals and humans, relatively clearly demarcated phases alternate: embryogenesis, maturation, adulthood, and aging. In invertebrates and lower vertebrates, various types of oxygen are observed, often accompanied by a restructuring of the entire structure of the body (metamorphosis).

The directed, coordinated nature of changes under O. already in antiquity (Aristotle) ​​and in Wed. century was put forward as an argument in favor of the presence in the body of a certain “ vitality" During the Renaissance, the doctrine of preformation spread, i.e., the presence inside the embryo of all parts of the body in an implicit “preformed” (preformed) form (see Preformationism). In the 18th century The concept of preformation was replaced by the doctrine of epigenesis (J. Buffon, K. F. Wolf, P. L. Maupertuis), whose supporters considered O. as a series of qualities. neoplasms.

According to modern ideas, new formations that continuously occur in the course of O. under the influence of the environment appear in unity with the moment of preformationism, since they are realized in the adult organism of inheritances. the characteristics are already recorded in the original zygote on the molecules of the DNA substance structured in genes. Contradiction between conservative inheritances. side of the development of the organism and individual variability, directly or indirectly related to the environment and adaptation, is removed in phylogenesis, leading to the fixation of useful changes in the course of oxygen through nature. selection in the new and also relates. the constancy of a more perfect (or more adequate to a given environment) genotype, which also determines a new type of oxygen. In the interpretation of the functional side of oxygen in biology of the 20th century. two methodologically different approaches predominate: “from the whole to the particular” (J. Coghill) and “from the particular to the whole,” or the theory of local integration (A. A. Volokhov, J. Barcroft, M. Malcolm). According to the first approach, in O. they are first formed nonspecifically. reactions, from which specialists are then isolated. acts; according to the second, primary local forms activities, which then develop into an integral system of functions. In addition to O. of the body as a whole, they also talk about O. department. organs, functions, O. behavior and psyche. Identification of patterns of O. human. consciousness in its connection with biology. And social factors education and personality formation contributes to the study of the entire mental complex. phenomenon as an integral developing system.

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Ontogenesis is the individual development of an organism from its birth to death. The period of ontogenesis from the fertilized egg to the release of the young individual from the egg shells or the mother’s body is called embryonic (embryonic) development (embryogenesis). After birth or hatching from an egg, the postembryonic period begins.

In the animal world, the most common three types of ontogenesis are larval, non-larval and intrauterine. With the first of them, the development of the organism occurs with metamorphosis, with the second, formation occurs in the egg, with the last - inside the mother's body.

Human embryogenesis is divided into periods, each of which is characterized by structural features, type of nutrition, respiration and excretion. In medical practice, two concepts are usually used: for 8 weeks developing organism called embryo (see); starting from the 9th week, i.e. from the moment of formation of the rudiments of organs, by the fetus. The postembryonic period of a person is divided into age periods. See also Organogenesis, .

Ontogenesis (from the Greek ontos - existing and genesis - development) is the history of individual development.

Charles Darwin gave an evolutionary interpretation of ontogeny. Similarity of embryos different types he explained the related relationships existing between species. Subsequently, ontogenesis was studied in various directions. The doctrine of germ layers as a natural stage in the development of all multicellular animals was created. The creation of experimental embryology made it possible to study embryonic development experimentally. IN last years Physiological and biochemical embryology is developing successfully. In the USSR, the ecological direction in embryology began to develop.

The type of embryogenesis in many cases reveals a characteristic alternation during evolution: from the original, primary free larval to non-larval and then to one of the forms of secondary larval embryogenesis.

The type of embryogenesis is associated with its periodization. The largest unit of periodization is the link. In most animals, ontogeny consists of three parts. Each link is divided into several periods. Thus, the embryonic link in lower vertebrates is divided into two periods - embryonic and larval, in higher vertebrates into three - embryonic, pre-fetal and fetal. There are also transitional states - hatching from egg shells in reptiles and birds; birth in mammals; metamorphosis (see) in many animals.

The initial stages of ontogenesis in humans are characterized by a faster pace of development than in related species (for example, chimpanzees). Next comes a slowdown in both antenatal and postnatal development. This slowdown is due to intensive brain growth both during intrauterine development (the brain of a newborn weighs on average 340 g) and in the first years after birth (the brain of a 2-year-old child weighs over 1 kg). The growth of the brain is associated with a slowdown in ossification, which partly depends on the size of the pelvic ring.

As a rule (when two species of placentals are closely related), smaller animals have a shorter pregnancy.

Postnatal human ontogenesis is divided into four periods (ages): childhood, adolescence, adolescence and adulthood.

ONTOGENESIS- the process of individual development of an organism (from its birth to death). The period of ontogenesis from fertilization of the egg to the release of the young individual from the egg shells or the mother’s body is called germinal, or embryonic, development (embryogenesis); After birth, the postembryonic period begins.

The study of heredity and variability has shown that the sequential development of the characteristics of an organism in ontogenesis occurs under the control of the genetic apparatus. On different stages During ontogenesis, coordinated regulation of the activity of various genes occurs. The mechanisms of this regulation and the specific sequence of deployment of the genetic program in the ontogenesis of various species of organisms are being intensively studied. It has been proven that although all cells of one organism potentially carry the same genetic program, but, firstly, as the organism develops, its different cells use different parts of this program, and secondly, the nature of the work of genes is greatly influenced by external conditions , in relation to the cell and to the given organism, environment.

Detailed information about how gene activity is regulated has so far been obtained from microorganisms. This process has yet to be studied in higher organisms. However, it is clear that the regulation of gene activity in higher organisms, including humans, is carried out continuously throughout ontogenesis. Much data has been accumulated on how certain genes are “turned on” at different stages of development of a given organism and in its different organs. For example, during the course of a person’s life, the type of hemoglobin molecules synthesized changes three times. In the early stages of embryo development, the so-called embryonic hemoglobin. Then, after a certain time, the gene that controls the synthesis of these molecules “falls silent” (suppressed) and another gene encoding the so-called begins to work instead. fetal hemoglobin.

Later, another change occurs, the synthesis of the third type of hemoglobin begins - adult type hemoglobin.

The need to replace one type of hemoglobin with another is due to the different needs of organisms. Thus, during intrauterine development, the body is supplied with oxygen from the mother’s blood, and since the first two types of hemoglobin (embryonic hemoglobin and fetal hemoglobin) bind oxygen better than adult-type hemoglobin, it is clear why, during evolutionary development, such an important adaptation as the change types of hemoglobin at different stages of ontogenesis. The sometimes observed delay in the change from early types of hemoglobin to the adult type or their incomplete change leads to the disease - thalassemia.

Stopping genes from working does not mean destroying them. Experiments on plants have shown that isolated cells from almost all parts of the plant (leaves, roots and stems) are capable, under appropriate conditions, of beginning to divide and give rise to a mature normal organism. Similar experiments were carried out on animals.

Along with the changes programmed in the organism itself in the work of different genes, the activity of genes is influenced in many ways by the environment. It has been established that the development of any trait is a consequence not only of the genetic program that is already laid down in the fertilized egg and then unfolds during ontogenesis, but is also determined by the action of the environment. Observations of identical twins have proven this point. In these twins, the genetic program at the initial moments of development was the same, but subsequent differences in living conditions lead to certain differences in their physical appearance. and mental development.

At the same time, it should be emphasized that there is a complex relationship between the development of certain characteristics in humans (as in any other representatives of higher organisms) and individual genes. Certain signs are formed under the control large number genes and it has not yet been clarified how many, which and how genes connected to each other control the formation of individual organs (for example, the eye or even parts of the eye). Clarifying these questions is a matter for the future, and such work is being carried out by biologists. Little is known, for example, how eye color is inherited, as well as some other characteristics.

The study of the genetic development program is of great practical importance. significance, especially in relation to genes that determine susceptibility to various diseases. A large number of inherited diseases have been discovered (many diseases of the nervous system, metabolism, etc.), which are detected only at certain stages of ontogenesis. Knowledge of the characteristics of such diseases is extremely important for their early detection and treatment. The same information is essential for medical genetic counseling, since early detection of carriage of genes that determine the development of a particular disease allows specialists in medical genetics to make recommendations about the degree of risk of transmitting such genes to offspring.

Types and periodization of ontogenesis:

Direct (no transformation)

1. Non-larval (oviparous)

eggs are rich in nutrients, a significant part of ontogenesis in the egg in the external environment

Intrauterine

provision of vital functions and development of the embryo by the maternal body through the placenta, the role of provisional organs

Indirect (with transformation)

1. Complete: egg – larva – pupa – adult

   Not complete: egg – larva – adult