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Duration of postembryonic development. Postembryonic period of development. Mature period in human development

Duration of postembryonic development. Postembryonic period of development. Mature period in human development

Regardless of the method of reproduction, the beginning of a new organism is given by one cell, containing hereditary inclinations and possessing all the characteristic features and properties of the whole organism.
Individual development lies in the gradual realization hereditary information received from parents.

The Beginning of Evolutionary Embryology put by Russian scientists A.O. Kovalevsky and I.I. Mechnikov. They first discovered three germ layers and established the principles of development of invertebrate and vertebrate animals. Ontogenesis, or individual development, is the entire period of an individual’s life from the formation of the zygote until the death of the organism.

Ontogenesis is divided into two periods:

- embryonic period: from the formation of the zygote to birth or exit from the egg membranes;
— postembryonic period: from exit from the egg membranes or birth to the death of the organism.

Stages embryonic development(using the example of lancelet)

Splitting up - repeated division of the zygote through mitosis. Formation of blastula - a multicellular embryo.

Gastrulation - formation of a two-layer embryo - gastrula with an outer layer of cells (ectoderm) and an inner layer lining the cavity (endoderm). In multicellular animals, often after the formation of a two-layer embryo, a third germ layer appears - the mesoderm, which is located between the ecto- and endoderm.

The embryo becomes three-layered. The essence of the gastrulation process is the movement of cell masses. The cells of the embryo practically do not divide and do not grow. The first signs of cell differentiation appear.

Organogenesis — formation of a complex of axial organs: neural tube, notochord, intestinal tube, mesodermal someites. Further differentiation of cells leads to the emergence of numerous derivatives of the germ layers - organs and tissues. From the ectoderm are formed: the nervous system, skin, organs of vision and hearing. From the endoderm the following are formed: intestines, lungs, liver, pancreas. From the mesoderm - notochord, skeleton, muscles, kidneys, circulatory and lymphatic systems.
During organogenesis, some rudiments influence the development of other rudiments (embryonic induction). The interaction of the parts of the embryo is the basis of its integrity. During embryonic development, the embryo is very sensitive to the influence of environmental factors. Such harmful effects, like alcohol, tobacco, drugs, can disrupt the course of development and lead to various deformities.

Postembryonic or postembryonic development begins from the moment of birth or exit from the egg membranes and lasts until the death of the organism. It comes in two types: direct and indirect.

With direct development the born offspring are similar in everything to adult individuals, live in the same environment and eat the same food, which exacerbates intraspecific competition (birds, reptiles, mammals, some insects, etc.).

With indirect development a new organism is born in the form of a larva, which undergoes a series of transformations in its development - metamorphoses (amphibians, many insects). Metamorphosis is associated with the destruction of larval organs and the emergence of organs characteristic of adult animals. For example, in a tadpole, during the process of metamorphosis, which occurs under the influence of thyroid hormone, the lateral line disappears, the tail resolves, limbs appear, lungs and a second circle of blood circulation develop.

Meaning of metamorphosis:

- larvae can feed independently, grow and accumulate substances to form permanent organs, living in an environment that is not typical for adults;

— larvae can play an important role in the dispersal of organisms (for example, the larvae of bivalve mollusks).

— different habitats reduce the intensity of intraspecific struggle for existence.

Indirect development of individuals is an important adaptation that arose during evolution

Embryonic and postembryonic development

Further development is associated with an increase in size and the acquisition of sexual maturity. For example: the development of reptiles, birds, mammals.

Indirect development, or development with metamorphosis - the emerging organism differs in structure from the adult organism, is usually simpler in structure, may have specific organs, such an embryo is called a larva. The larva feeds, grows, and over time the larval organs are replaced by organs characteristic of the adult organism (imago). For example: the development of a frog, some insects, various worms.
Postembryonic development is accompanied by growth.

Phylogeny (from the Greek phylos - tribe, race and geneticos - related to birth) is the historical development of organisms. In biology, phylogeny considers development biological species in time. Taxonomy, the classification of organisms by similarity, is based on phylogeny but is methodologically different from the phylogenetic representation of organisms.

Phylogeny views evolution as a process in which a genetic line—organisms from ancestor to descendant—branches over time, and its individual branches may specialize relative to a common ancestor, merge through hybridization, or disappear through extinction.

Topic 3.3 Postembryonic development

Terminology

1.Amnion- the body of the embryo, surrounded by a water membrane.

2. Metamorphosis– transformation into the period of development.

3. Definite growth- time-limited growth.

4. Growth uncertain- lasting throughout life.

5. Divergences– divergence of signs.

6. Phylogenesis– historical development of organisms.

Postembryonic period of development

At the moment of birth or the release of the organism from the egg shells, the embryonic period ends and the post-embryonic period of development begins, ending with the death of the organism.

Postembryonic development can be direct or accompanied by transformation - metamorphosis.

During direct development, an organism emerges from the egg shells or from the mother’s body, which contains all the main organs characteristic of an adult organism (reptiles, birds, mammals). Postembryonic development in these animals is reduced mainly to growth and puberty. During development with metamorphosis, a larva emerges from the egg, usually simpler in structure than an adult animal, with special larval organs that are absent in the adult state. The larva feeds, grows, and over time the larval organs are replaced by organs characteristic of adult animals.

Consequently, during metamorphosis, larval organs are destroyed and organs characteristic of adult animals appear.

For example, in ascidians (a type of chordate), a larva is formed that has all the main characteristics of chordates: notochord, neural tube, gill slits. The larva swims freely, and then attaches to a hard surface and undergoes metamorphosis: the tail disappears, the notochord and neural tube disintegrate. Ascidia leads an attached lifestyle. The structure of the larvae indicates their origin from chordates leading a free lifestyle. During the process of metamorphosis, ascidians switch to a sedentary lifestyle, and therefore their organization is simplified.

The larval form of amphibians is a tadpole, which is characterized by gill slits, a lateral line, and one circle of blood circulation. During the process of metamorphosis, which takes place under the influence of thyroid hormone, the tail disappears, limbs appear, the lateral line disappears, and lungs develop. The similarity of a number of structural features between the tadpole and fish is noteworthy.

An example of complete metamorphosis is the development of insects. Butterfly caterpillars or dragonfly larvae differ sharply in structure, lifestyle and habitat from adult animals. Thus, metamorphosis is associated with a change in lifestyle or habitat.

Development in some insects, such as the cockroach, occurs with incomplete metamorphosis.

The significance of metamorphosis is that the larvae can feed independently and grow, accumulating cellular material to form permanent organs characteristic of adult animals. In addition, free-living larvae of attached animals play an important role in the spread of the species and in the expansion of its range. A change in lifestyle or habitat during ontogenesis, due to the fact that the larval forms of some animals live in different conditions and have other food sources, reduces the intensity of the struggle for existence within the species.

In a number of cases, processes occurring in individual development indicate events that took place in phylogenesis, i.e. process historical development of this type.

The postembryonic period of development has different durations.

Ontogenesis. Embryonic and postembryonic development

For example, a mayfly lives 2-3 years in the larval state, and 2-3 hours or 2-3 days in the adult state. Adults do not feed due to the lack of mouthparts. After fertilization and egg laying, they die. In most cases, the postembryonic period is longer. In humans, it includes the stage of puberty, the stage of maturity and old age.

In mammals, there is a dependence of life expectancy on the duration of puberty and pregnancy.

Postembryonic development is accompanied by growth. A distinction is made between indefinite growth, which continues throughout life, and definite growth, limited to a certain period. Indefinite growth is observed in trees and mollusks. In many animals, growth stops shortly after reaching puberty.

Biogenetic law

All multicellular organisms develop from a single fertilized cell. The development of embryos in animals belonging to the same type is largely similar. In the early stages of development, vertebrate embryos are very similar. These facts are confirmed by the validity of the law of embryonic similarity: “Embryos exhibit, already from the early stages, a certain general similarity within the type.”

The similarity of the embryos of different systematic groups indicates their common origin. Subsequently, the structure of the embryos reveals characteristics of class, genus, species, and, finally, characteristics characteristic of a given individual. The divergence of characteristics of embryos during development is called embryonic divergence and is explained by the history of the development of a given species, reflecting the evolution of one or another systematic group animals.

All stages of development are subject to variability. Mutations affect genes that determine the structural and metabolic features of embryos at the earliest stages of development. But the structures that arise in embryos play an important role in the processes of further development. Therefore, changes in the early stages usually lead to underdevelopment and death of the organism. On the contrary, changes in later stages, affecting less significant traits, can be beneficial for the organism and in such cases are picked up by natural selection.

The appearance in the embryonic period of development of characteristics characteristic of distant ancestors reflects evolutionary transformations in the structure of organs.

Numerous examples point to the deep connection between the individual development of organisms and their historical development.

This connection is expressed in biogenetic law: Ontogenesis (individual development) of each individual is a multiple and rapid repetition of phylogeny (historical development) of the species to which this individual belongs.

The biogenetic law played an important role in the development of evolutionary ideas. In some cases, changes that distinguish the structure of adult organisms from the structure of their ancestors appear in the embryonic period.

In some cases, changes occur in the middle stages of development.

Thus, phylogeny is based on changes occurring in the ontogeny of individual individuals.

Development of organisms and the environment. An organism cannot live outside its environment. It is equally impossible for an organism to develop outside environment. For example, a chicken egg develops only at a certain temperature. No less important is the ionic composition for the development of aquatic organisms. All species are not indifferent to oxygen concentration, carbon dioxide content, etc.

There are critical periods in the development of the embryo when the embryo is more sensitive to the action of external agents. The organism develops under conditions characteristic of individuals of a given species, and outside these conditions development is disrupted.

Thus, the impact of unfavorable factors on the body in most cases necessarily affects the development of the offspring.

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At the moment of birth or the release of the organism from the egg shells, the period of postembryonic development begins. Postembryonic development of humans includes juvenile(lat. juvenilis - adolescence, childhood - not reaching puberty), pubertal

(lat. pubertas - manhood, puberty) and period aging which ends in death - the cessation of the body's vital functions. Death is necessary for the change of generations - one of the main driving forces of evolution.

Postembryonic development of animals can be direct, when an organism similar to the adult (reptiles, birds, mammals) emerges from the egg or the mother’s body, and indirect, when formed during the embryonic period larva structure is simpler than that of an adult organism, and differs from it in the ways of nutrition, movement, etc. (coelenterates, flat and annelids, crustaceans, insects, amphibians). Thanks to active feeding, the larva grows intensively, and over time, the larval organs are replaced by organs characteristic of adult animals. At incomplete metamorphosis In insects, a larva hatches from an egg. The replacement of larval organs with organs of an adult organism occurs gradually without stopping feeding and moving the body (in locusts). Complete metamorphosis In addition to the larva, it includes a non-motile stage pupae. Complex changes occur inside the pupa associated with the restructuring and formation of organs of the adult stage - imago(at butterflies).

The larval form of amphibians, the tadpole, is characterized by the presence of gill slits, a lateral line, a two-chambered heart, and one circulation. During the process of metamorphosis, the tail resolves, limbs appear, the lateral line disappears, the lungs and the second circle of blood circulation develop (Fig. 11.10). A number of structural features of tadpoles and fish (lateral line, structure of the heart and circulatory system, gill slits) are similar. After metamorphosis is completed, an organism is formed that has the features of an adult.

Postembryonic development is characterized by intensive growth, the establishment of final body proportions, and a gradual transition of organ systems to functioning in a mode characteristic of a mature organism. Postembryonic development, like embryogenesis, is accompanied by growth. There are indefinite growth, which continues throughout life, and definite growth, limited to a certain period. Indefinite growth is observed in woody forms of plants, some mollusks, and in vertebrates - fish, rats. However, their size is limited by the lifespan of organisms of a given species. In many animals, growth stops shortly after reaching puberty. In humans, growth ends at the age of 20-25. During the aging period, a slight decrease in body size occurs, the nature of the activity of the endocrine glands changes, gametogenesis stops and physiological functions weaken.

Rice. 11.10.

Human aging, like the aging of other organisms, is a biological process of a decrease in the morphofunctional capabilities of the body upon reaching a certain age. There is a gradual degradation of human body systems and the consequences of this process. Physiological changes that occur in the human body with age are primarily expressed in a decrease in biological functions and ability to adapt to stressful situations. These physiological changes are usually accompanied by psychological and behavioral changes.

Aging is accompanied by numerous molecular changes in nucleic acids and proteins, the number of structural abnormalities of chromosomes increases, and changes in mitochondria and other cell organelles are possible. During the aging process, all systems and organs undergo irreversible changes that reduce their functionality. Death, as a rule, occurs as a result of diseases of old age - strokes, heart attacks, cancer, etc. Death is a natural stage in the ontogenesis of all organisms. Without death there would be no change of generations and no biological evolution of organisms on Earth. There is a distinction between clinical and biological death.

Clinical death - reversible transition period between life and death - expressed in loss of consciousness, cessation of cardiac activity, breathing, everything disappears external signs vital activity of the body. At the same time, the onset of oxygen starvation does not yet cause irreversible changes in the organs and systems that are most sensitive to it. When cardiac and respiratory activity is restored, the body can “return” to life. This is the goal of resuscitation efforts. However, the ability to restore normal function in cells of different tissues is not the same: the cerebral cortex dies first (after 5 minutes), then the cells of the intestines, lungs, liver, muscles and heart.

Biological death is the almost complete cessation of physiological processes in cells and tissues. The time before death of the tissues that make up the human body is mainly determined by their ability to survive in conditions of low or no oxygen. This ability is different for different tissues and organs. As medicine advances, the ability to resuscitate dead patients changes. The possibility of transplantation is associated with the phenomenon of survivability of organs and tissues of the human body. The more viable organs are, the greater the likelihood of their successful further functioning in another organism.

Anchor points

Postembryonic development is mainly limited to growth, puberty and reproduction.
In many simply structured animals, the stage of active reproduction is preceded by a larval stage, culminating in metamorphosis.
Postembryonic development can be divided into three periods: pre-reproductive, reproductive and post-reproductive.
The pre-reproductive period in highly organized vertebrates is reduced to intensive growth and puberty.

Lecture 3

Fundamentals of embryology. Spermato- and oogenesis. Biological entity fertilization."

1. The role of embryology in veterinary and zootechnical practice.

2. The concept of onto-, phylogeny; anisagamous (parthenogenetic) reproduction and gametogenesis.

3. Biological essence and advantages of sexual reproduction;

4. Structure, biological properties and development of sperm:

Mechanisms of forward movement of sperm;

Duration of survival in the female reproductive tract.

5. Features of the structure and development of eggs. Their classification in connection with the level of animal organization, conditions and nature of embryogenesis.

6. Development and structure of germ cells.

The role of embryology in veterinary and zootechnical practice.

Embryology(embryon - embryo, logos - teaching) - the science of the patterns of development of the animal body from the moment of fertilization of the egg and the formation of the zygote to birth or hatching from the egg.

The development of embryology began in Greece more than 2 thousand years ago. For the first time, Hippocrates described the development of the embryo in a chicken egg and tried to understand the process of embryo development in mammals.

Later, Aristotle quite fully described the process of development of internal organs in mammals during embryogenesis. Described the functions of the placenta and umbilical cord. They were the first to discover that in initial period developments appear in the body common features, characteristic of animals in general, and later particular characteristics are formed, characteristic this type, or type of animal.

With the invention of the microscope in the 17th century, Levenchuk discovered sperm, and Graaf described the follicles in the ovary, mistaking them for the egg. And only 150 years later, eggs were discovered inside the follicles.

Subsequently, many scientists contributed to the development of embryology, including those who worked in Russia (Wolf, Pandre, Ber, Kovalevsky, Severtsov, Bogolyubsky, etc.)

Embryology has developed particularly rapidly in the last 50 years due to the use of modern methods research (electron microscopy, histochemistry, histoautoradiography, microsurgery, tissue culture, etc.

The achievements of modern embryology have found wide application in the practice of animal husbandry and veterinary medicine. These include artificial insemination of animals, stimulation of multiple births, and embryo transplantation. Genetic engineering manipulations allowed scientists to obtain an animal from a somatic cell (Dolly the Sheep in Scotland).

Knowledge of embryology allows veterinarians to find out the causes of infertility and other obstetric issues, which is necessary for the effective treatment of animals, increasing their fertility and thereby accelerating the reproduction of animals.

The concept of onto-, phylogeny; anisagamous (parthenogenetic) reproduction and gametogenesis.

The concept of ontogenesis

Ontogenesis is the individual development of an organism, during which the transformation of its morphophysiological, physiological-biochemical and cytogenetic characteristics occurs. Speaking more in simple language, ontogeny or individual development is a period of time that lasts from the moment of conception and ends at the moment of death.

Therefore, in ontogenesis there are 2 periods of development: embryonic and postembryonic.
During the embryonic period, the human embryo is located in the mother’s uterine cavity, where it receives all the necessary nutrients and oxygen, and also releases metabolic products. Such a metabolism between the maternal body and the embryo becomes possible due to the presence of a special organ - the placenta.

In most multicellular animals, regardless of the complexity of their organization, the stages of embryonic development that the embryo goes through are the same. In the embryonic period, there are three main stages: cleavage, gastrulation and primary organogenesis.

Splitting up. The development of an organism begins at the single cell stage. A fertilized egg is a cell and at the same time already an organism at its most early stage its development. As a result of multiple divisions single cell organism turns into multicellular. The diploid nucleus, which appears during fertilization through the fusion of a sperm and an egg, begins to divide within a few minutes, and the cytoplasm also divides with it. The resulting cells decrease in size with each division, so the division process is called cleavage. During the period of fragmentation, cellular material accumulates for further development. Fragmentation ends with the formation of a multicellular embryo - blastula. The blastula has a cavity filled with fluid, the so-called primary body cavity.

In cases where there is little yolk in the cytoplasm of the egg (as in the lancelet) or relatively little (as in the frog), fragmentation is complete, i.e., the egg divides entirely.

Otherwise, the period of fragmentation occurs in birds. Yolk-free cytoplasm makes up only 1% of the total volume of a chicken egg; the entire remaining cytoplasm of the egg, and therefore the zygote, is filled with a mass of yolk. If you look closely at a chicken egg, on one of its poles directly on the yolk you can see a small spot - a blastula, or germinal disk, formed as a result of crushing the yolk-free section of the cytoplasm containing the nucleus. In such cases, crushing is called incomplete. Incomplete fragmentation is also characteristic of some fish and reptiles.

In all cases - in the lancelet, and in amphibians, and in birds, as well as in other animals - the total volume of cells at the blastula stage does not exceed the volume of the zygote. In other words, the mitotic division of the zygote is not accompanied by the growth of the resulting daughter cells to the volume of the mother, and their sizes as a result of a series of successive divisions progressively decrease. This feature of mitotic cell division during cleavage is observed during the development of fertilized eggs in all animals.

Some other features of crushing are also characteristic of various animal species. For example, all cells in a blastula have a diploid set of chromosomes, are identical in structure and differ from each other mainly in the amount of yolk they contain. Such cells, devoid of signs of specialization to perform certain functions, are called unspecialized (or undifferentiated) cells. Another feature of cleavage is the extremely short mitotic cycle of blastomeres compared to the cells of an adult organism. During the very short interphase, only DNA duplication occurs.

Gastrulation. The blastula, as a rule, consisting of a large number of blastomeres (for example, in a lancelet of 3000 cells), during development passes into a new stage, which is called gastrula (from the Greek gaster - stomach). The embryo at this stage consists of clearly distinguishable layers of cells - the so-called germ layers: the outer, or ectoderm (from the Greek ectos - located outside), and the internal, or endoderm (from the Greek entos - located inside). The set of processes leading to the formation of a gastrula is called gastrulation.

In the lancelet, gastrulation is carried out by invagination of one of the poles of the blastula inward, towards the other; in other animals, either by stratification of the wall of the blastula, or by overgrowing the massive vegetative pole with small cells of the animal pole.

In multicellular animals, except coelenterates, in parallel with gastrulation or, as in the lancelet, after it, the third germ layer appears - mesoderm (from the Greek mesos - located in the middle), which is a set of cellular elements located between the ecto- and endoderm in primary body cavity - blastocele. With the appearance of mesoderm, the embryo becomes three-layered.

Thus, the essence of the gastrulation process is the movement of cell masses. The cells of the embryo practically divide and do not grow. However, at this stage the use of the genetic information of the embryonic cells begins, and the first signs of differentiation appear.

Differentiation, or differentiation, is the process of its occurrence and the increase in structural and functional differences between individual cells and parts of the embryo. From a morphological point of view, differentiation is expressed in the formation of several hundred types of cells of a specific structure that differ from each other. From unspecialized blastula cells, epithelial cells of the skin, intestinal epithelium, lungs gradually emerge, nerve and muscle cells, etc. appear. From a biochemical point of view, cell specialization lies in the ability to synthesize certain proteins that are characteristic only of a given cell type. Lymphocytes synthesize protective proteins - antibodies, muscle cells - the contractile protein myosin. Each type of cell produces its own proteins, unique to it. Biochemical specialization of cells is ensured by selective - differential activity of genes, i.e. in the cells of different germ layers - the rudiments of certain organs and systems - begin to function different groups genes.

U different types In animals, the same germ layers give rise to the same organs and tissues. This means that they are homologous. Thus, from the cells of the outer germ layer - ectoderm - in arthropods, chordates, including fish, amphibians, reptiles, birds and mammals, the skin and their derivatives, as well as the nervous system and sensory organs, are formed. The homology of the germ layers of the vast majority of animals is one of the proofs of the unity of the animal world.

Organogenesis. After completion of gastrulation, the embryo forms a complex of axial organs: neural tube, notochord, and intestinal tube. In the lancelet, the axial organs are formed as follows: the ectoderm on the dorsal side of the embryo bends along midline, turning into a groove, and the ectoderm located to the right and left of it begins to grow on its edges. The groove is the primordium nervous system- sinks under the ectoderm, and its edges close. A neural tube is formed. The rest of the ectoderm is the rudiment of the skin epithelium.

The dorsal part of the endoderm, located directly under the nerve rudiment, is separated from the rest of the endoderm and folds into a dense cord - the notochord. From the remaining part of the endoderm, mesoderm and intestinal epithelium develop. Further differentiation of the embryonic cells leads to the emergence of numerous derivatives of the germ layers - organs and tissues. In the process of specialization of the cells that make up the germ layers, the nervous system, sensory organs, skin epithelium, and tooth enamel are formed from the ectoderm; from the endoderm - intestinal epithelium, digestive glands - liver and pancreas, epithelium of gills and lungs; from the mesoderm - muscle tissue, connective tissue, including loose connective tissue, cartilage and bone tissue, blood and lymph, as well as the circulatory system, kidneys, gonads.

Postembryonic period of development

At the moment of birth or the release of the organism from the egg shells, the embryonic period ends and the postembryonic period of development begins. Postembryonic development can be direct or accompanied by transformation (metamorphosis).

During direct development (in reptiles, birds, mammals), an organism of small size emerges from the egg shells or from the mother’s body, but with all the main organs characteristic of an adult animal already formed. Postembryonic development in this case is reduced mainly to growth and puberty.

During development with metamorphosis, a larva emerges from the egg, usually simpler in structure than an adult animal, with special larval organs that are absent in the adult state. The larva feeds, grows, and over time the larval organs are replaced by organs characteristic of adult individuals. Consequently, during metamorphosis, larval organs are destroyed and organs characteristic of adult animals appear.

The postembryonic period of development has different durations. For example, mayflies in the larval state live 2-3 years, and in the mature state - from 2-3 hours to 2-3 days, depending on the species. In most cases, the postembryonic period is longer. In humans, it includes the puberty stage, the maturity stage and the old age stage.

In mammals and humans, there is a known dependence of life expectancy on the duration of puberty and pregnancy. Typically, life expectancy exceeds the pre-reproductive period of ontogenesis by 5-8 times.

Postembryonic development is accompanied by growth. A distinction is made between indefinite growth, which continues throughout life, and definite growth, limited to a certain period. Indefinite growth is observed in woody forms of plants, some mollusks, and in vertebrates - fish, rats.

In many animals, growth stops shortly after reaching sexual maturity. In humans, growth ends at the age of 20-25.

The following modified periods of ontogenesis are distinguished, which have evolutionary significance.

Diapause. In the embryonic period of a number of vertebrates, there is diapause, i.e. cessation of development for a more or less long period. It has adaptive significance. Thus, in marsupials and rodents, the development of embryos stops if the development of the new offspring coincides in time with the feeding of the previous litter by the female. This is a lactation pause, usually lasting several days. In other orders of mammals, long periods of up to 7 months are observed. obligatory diapauses. For example, in sable, fertilization occurs in July. The fertilized egg is crushed, the development process reaches the blastocyst stage and is inhibited. Implantation and further development begin only in March. The described diapause arose in the evolution of the named animal species through selection for the birth of offspring in the season most favorable for feeding.

Deembryonization. This term refers to a strong shortening of the embryonic period itself, which occurs under the shells of the egg. Deembryonization, observed in placental mammals, is combined with a sharp decrease in the yolk in their eggs and the establishment of a connection with the maternal body through the placenta.

Embryonization. The process of embryonication consists of lengthening the time of protection of the embryo from the external environment due to the embryonic membranes and the maternal body. At this time, the embryo goes through periods corresponding to the embryonic and larval periods. The developing organism is protected until the juvenile stage is formed. After birth, there is no significant restructuring of the body, and development is underway direct, i.e. without metamorphosis.

Embryonic development was especially evident in the process of evolution of terrestrial vertebrates. Already in many amphibians, for example in the horned frog of the Solomon Islands, all development occurs under the egg membranes, from which an animal that has already undergone metamorphosis hatches. Complete embryonication occurs in reptiles and birds in connection with their transition to terrestrial existence. A special change in the embryonic and larval periods occurred in placental mammals. Along with deembryonication, as mentioned above, they experienced maximum embryonication, but not under the shells of the egg, but in utero. The period of free larval development has completely disappeared.

The prefetal and fetal periods of development, which pass under the egg membranes or in utero, are together equivalent to the larval period. They immediately follow the embryonic period, include the middle and later phases of morphogenesis, are characterized by the presence of provisional organs, the transition to active nutrition, and the beginning of the functioning of the senses (hearing, taste, etc.).

Provisional organs in mammals include the embryonic membranes, some parts of the circulatory system, and temporary structures of the skin. In oviparous and marsupial mammals, the embryo in the prefetal stages already begins to feed on mother's milk, and in birds and placental mammals it swallows amniotic fluid. The beginning of the functioning of the hearing organ is described in emu embryos, which react vigorously to the cry of adult birds already in the last quarter of the incubation period.

The period of metamorphosis in terrestrial vertebrates is correspondingly simplified, since the fetus is largely similar to the adult. However, the discarding of the embryonic membranes, the opening of embryonic fusions, changes in the respiratory organs, blood circulation and in the skin at the time of birth and in the first week after birth represent rearrangements corresponding to metamorphosis.

A number of biologists, as part of the postembryonic period of ontogenesis, distinguish the postembryonic period itself (from the moment of birth to the moment of acquisition of puberty) and the period of aging (from the moment of acquisition of puberty to death). Isolating these periods is advisable in biology, since a number of organisms die immediately after reproduction. In medicine, it is not customary to distinguish these periods, since every healthy person reaches puberty and then goes through a period of aging.

A modified period of ontogenesis is neoteny. In the evolution of many vertebrate groups, there is a tendency towards earlier achievement of sexual maturity. This tendency is most pronounced in tailed amphibians. Thus, in the family Ambistomatidae, larvae (axolotls) acquired the ability to reproduce before the onset of metamorphosis and transformation into the adult stage, but they did not completely lose the ability to transform into the adult stage.

II. From the history of the formation and development of ethical standards in Russian speech culture.

II. PROBLEMS OF INTERNATIONAL COOPERATION IN THE FIELD OF ECONOMIC DEVELOPMENT

The significance of disruption of ontogenetic mechanisms in the formation of developmental defects.

Developmental defects sound conducting system middle ear can cause congenital hearing impairment along with disorders of other parts of the auditory analyzer. Congenital fixation of the stapes leads to congenital conduction deafness with otherwise normal ear development. Defects of the malleus and incus are often combined with first arch syndrome. The mechanisms of occurrence of such malformations may be disturbances in the resorption (death) of young connective tissue in the tympanic cavity and arrest of development of the entire area of the first visceral arch. Most types of congenital deafness are genetic and hereditary.

Developmental defects digestive system are expressed in underdevelopment (hypogenesis) or complete absence of development (agenesis) of sections of the intestinal tube or its derivatives, in the absence of a natural opening, narrowing of the canal, persistence of embryonic structures, incomplete rotation and heterogony of various tissues into the wall of the gastrointestinal tract.

Congenital defects of cardio-vascular system There are dozens of varieties. The incidence rate is 6-10 per 1000 newborns. Defects of the cardiovascular system can be isolated or in combination with defects of other systems, i.e. multiple defects. Isolated defects are often multifactorial, but dominant and recessive forms are also known. Among the defects included in the multiple group, damage to the cardiovascular system is often accompanied by chromosomal and gene syndromes. Defects of the cardiovascular system mainly represent either the underdevelopment of any structures in embryogenesis, or the persistence of these embryonic structures, while they should be modified and take on a definitive form. Sometimes there are gross violations of the topography of the heart and blood vessels.

The period of development of an organism from birth to death.

The postembryonic period is characterized by:

1. Intensive growth

2. Establishing the final proportions of the body

3. The gradual transition of organ systems to functioning in a mode characteristic of a mature organism.

In postembryonic ontogenesis, a distinction is made between the juvenile and pubertal periods, as well as the period of old age, ending with death.

Juvenile period. This period (from the Latin juvenilis - young) is determined by the time from the birth of the organism to puberty. It occurs differently in different organisms and depends on the type of ontogenesis of the organisms. This period is characterized by either direct or indirect development.

In the case of organisms that are characterized direct development (many invertebrates, fish, reptiles, birds, mammals, humans), hatched from egg shells or newborns are similar to adult forms, differing from the latter only in smaller size, as well as underdevelopment of individual organs and imperfect body proportions.

A characteristic feature of the growth in the juvenile period of organisms subject to direct development is that the number and size of cells increase, and the proportions of the body change. Human growth during different periods of his ontogenesis is shown in Fig. 95. The growth of different human organs is uneven. For example, head growth ends in childhood, legs reach proportional size by about 10 years. The external genitalia grow very quickly between the ages of 12 and 14 years. A distinction is made between definite and indefinite growth. A certain growth is characteristic of organisms that stop growing at a certain age, for example, insects, mammals, humans. Indefinite growth is characteristic of organisms that grow throughout their lives, for example, mollusks, fish, amphibians, reptiles, and many types of plants.

When indirect development organisms undergo transformations called metamorphoses(from lat. metamorphosis - transformation). They represent modifications of organisms during development. Metamorphoses are widely found in coelenterates (hydra, jellyfish, coral polyps), flatworms(fasciolas), roundworms (roundworms), mollusks (oysters, mussels, octopuses), arthropods (crayfish, river crabs, lobsters, shrimp, scorpions, spiders, mites, insects) and even some chordates (tunicates and amphibians). In this case, complete and incomplete metamorphoses are distinguished. The most expressive forms of metamorphosis are observed in insects that undergo both incomplete, so complete metamorphoses.

Incomplete transformation- this is a development in which an organism emerges from the egg shells, the structure of which is similar to the structure of an adult organism, but its size is much smaller. Such an organism is called a larva. During the process of growth and development, the size of the larvae increases, but the existing chitinized cover prevents a further increase in body size, which leads to molting, i.e., the shedding of the chitinized cover, under which there is a soft cuticle. The latter straightens out, and this is accompanied by an increase in the size of the animal. After several moults, the animal reaches maturity. Incomplete transformation is typical, for example, in the case of the development of bedbugs.

Complete transformation- this is a development in which a larva is released from the egg shells, significantly different in structure from adult individuals. For example, in butterflies and many insects the larvae are caterpillars. Caterpillars are subject to molting, and can molt several times, then turning into pupae. From the latter, adult forms (imago) develop, which do not differ from the original ones.

Puberty. This period is also called mature, and it is associated with the sexual maturity of organisms. The development of organisms during this period reaches its maximum.

The growth and individual development of animal organisms are subject to neurohumoral regulation by humoral and nervous regulatory mechanisms.

In vertebrates, the endocrine glands are the pituitary gland, pineal gland, thyroid, parathyroid, pancreas, adrenal glands and gonads, which are closely related to one another. The pituitary gland in vertebrates produces gonadotropic hormone, which stimulates the activity of the gonads. In humans, the pituitary hormone affects growth. With a deficiency, dwarfism develops; with an excess, gigantism develops. The pineal gland produces a hormone that affects seasonal fluctuations in the sexual activity of animals. Thyroid hormone influences the metamorphosis of insects and amphibians. In mammals, underdevelopment of the thyroid gland leads to growth retardation and underdevelopment of the genital organs. In humans, due to a defect in the thyroid gland, ossification and growth are delayed (dwarfism), puberty does not occur, and mental development stops (cretinism). The adrenal glands produce hormones that influence metabolism, growth and differentiation of cells. The gonads produce sex hormones that determine secondary sexual characteristics. Removal of the gonads leads to irreversible changes in a number of characteristics. For example, in castrated roosters, the growth of the comb stops and the sexual instinct is lost. A castrated man acquires an external resemblance to a woman (a beard and hair on the skin do not grow, fat is deposited on the chest and pelvic area, the timbre of the voice is preserved, etc.).

At all periods of ontogenesis, organisms are capable of restoring lost or damaged body parts. This property of organisms is called regeneration, which can be physiological and reparative.

Physiological regeneration- This is the replacement of lost body parts in the process of vital activity of the body. Regenerations of this type are very common in the animal world. For example, in arthropods it is represented by molting, which is associated with growth. In reptiles, regeneration is expressed in the replacement of the tail and scales, in birds - feathers, claws and spurs. In mammals, an example of physiological regeneration is the annual shedding of antlers by deer.

Reparative regeneration- this is the restoration of a body part of the body that was violently torn away. Regeneration of this type is possible in many animals, but its manifestations vary. For example, it is common in hydras and is associated with the reproduction of the latter, since the entire organism regenerates from a part. In other organisms, regeneration manifests itself in the form of the ability of individual organs to recover after the loss of any part. In humans, epithelial, connective, muscle and bone tissues have a fairly high regenerative ability.

Old age as a stage of ontogenesis. Old age is the penultimate stage of animal ontogenesis, and its duration is determined by the total lifespan, which is a species characteristic and which varies among different animals. Old age has been studied most accurately in humans.

There are a variety of definitions of human old age. In particular, one of the most popular definitions is that old age is the accumulation of successive changes that accompany an increase in the age of an organism and increase the likelihood of its illness or death. The science of human aging is called gerontology (from the Greek geron - old man, old man, logos - science). Its task is to study the patterns of age transition between maturity and death.

Scientific research in gerontology extend to various areas, starting with studies of changes in the activity of cellular enzymes and ending with elucidating the influence of psychological and sociological mitigations in environmental stress on the behavior of old people.

In the case of humans, a distinction is made between physiological old age, old age associated with calendar age, and premature aging caused by social factors and diseases.

The desire to understand the nature of aging of the body has been around for a long time. IN Ancient Greece Hippocrates believed that aging is associated with excess in food and insufficient exposure to fresh air. Aristotle believed that aging is associated with the consumption of thermal energy by the body. The importance of food as a factor in aging was also noted by Galen. But for a long time there was not enough scientific data to objectively understand this problem. Only in the 19th century. There has been some progress in the study of aging, and theories of aging have begun to be formulated.

One of the first most famous theories of aging of the human body is the theory of the German physician H. Hufeland (1762-1836), who noted the importance of longevity labor activity. We have heard his statement that not a single lazy person lived to old age. Even more famous is the endocrine theory of aging, which originates from experiments performed in the middle of the last century by Berthold (1849), who showed that the transplantation of testes from one animal to another is accompanied by the development of secondary sexual characteristics. Later, the French physiologist C. Brown Secard (1818-1894), based on the results of injecting himself with extracts from the testes, argued that these injections had a beneficial and rejuvenating effect. At the beginning of the 20th century. There is already a belief that the onset of old age is associated with the extinction of the activity of the endocrine glands, in particular the gonads. In the 20-30s. based on this belief in different countries many surgeries have been done to rejuvenate elderly or old people. For example, G. Steinach in Austria tied up the spermatic cords of men, which led to the cessation of external secretion of the gonads and, supposedly, to some rejuvenation. S.A. Voronov in France transplanted testes from young animals to old ones and from monkeys to men, and Tushnov in the USSR rejuvenated roosters by injecting them with histolysates of the gonads. All these operations led to some effects, but only temporary. After these impacts, the aging process continued, and even more intensely.

At the beginning of our century, the microbiological theory of aging arose, the creator of which was I. I. Mechnikov, who distinguished between physiological and pathological old age. He believed that human old age is pathological, that is, premature. The basis of I.I. Mechnikov’s ideas was the doctrine of orthobiosis (Orthos - correct, bios - life), according to which the main cause of aging is damage to nerve cells by intoxication products formed as a result of putrefaction in the large intestine. By developing the doctrine of a normal lifestyle (observance of hygiene rules, regular work, abstinence from bad habits), I.I. Mechnikov also proposed a method of suppressing putrefactive intestinal bacteria by consuming fermented milk products.

In the 30s. The theory about the role of the central nervous system in aging has become widespread. The creator of this theory is I.P. Pavlov, who established the integrating role of the central nervous system in the normal functioning of organisms. Followers of I.P. Pavlov showed in experiments on animals that premature aging is caused by nervous shocks and prolonged nervous overstrain.

The theory of age-related changes in connective tissue, formulated in those years by A. A. Bogomolets (1881-1946), deserves mention. He believed that the physiological activity of the body is ensured by connective tissue (bone tissue, cartilage, tendons, ligaments and fibrous connective tissue) and that changes in the colloidal state of cells, loss of their turgor, etc. determine age-related changes in organisms. Modern data indicate the importance of calcium accumulation in connective tissue, since it contributes to the loss of its elasticity, as well as the thickening of blood vessels.

There is also a known hypothesis according to which aging is the result of changes in mitochondrial metabolites with subsequent dysfunction of enzymes.

Death. Death is the final stage of ontogenesis.

Death is the cessation of the vital activity of an organism, its death as a separate living system. The science of death is called thanatology.

Distinguish natural death, which occurs as a result of a long-term gradual decline in the vital functions of the body during the aging process, and premature death caused by diseases and damage to vital organs.

Death in higher mammals includes two stages: clinical and biological death.

Signs clinical death is the cessation of the most important vital functions: loss of consciousness, cessation of heartbeat, breathing, etc. However, at this time, most cells and organs still remain alive, their metabolism remains orderly. Then biological death develops, associated with the cessation of self-renewal, loss of order in the metabolism, and the onset of self-digestion and decomposition in the cells. The cerebral cortex dies first, and after some time the cells of the epithelium of the intestines, lungs, liver, then the heart muscle and other organs die. This process takes many hours. For some time, the corpse continues to peristalsis, hair and nails grow.

Clinical death is a transitional state between life and death, when there are no signs of life, but the tissues are still alive. It is possible to return an organism from a state of clinical death - to reanimate it. Revival of a person is possible only within 6-7 minutes from the moment of clinical death, until irreversible processes begin in the cerebral cortex.

Control questions to secure:

1. The doctrine of ontogenesis.

2. Embryonic period.

2.1. Splitting up.

2.2. Gastrulation.

2.3. Formation of organs and tissues.

3. Provisional organs of vertebrate embryos.

3.1. Amnion

3.2. Chorion

3.3. Yolk sac

3.4. Allantois

4. Mechanisms of ontogeny.

4.1. Cell division

4.2. Cell migration

4.3. Cell differentiation

4.4. Embryonic induction

5. Critical periods of ontogenesis.

6. Classification of congenital malformations.

7. The significance of disruption of ontogenetic mechanisms in the formation of developmental defects.

Main:

1. Biology. In 2 books. Book 2: Textbook. for special universities/ V.N. Yarygin, V.I. Vasilyeva, I.N. Volkov, V.V. Sinelshchikova; Ed. V.N. Yarygina. - 2nd ed., revised. - M.: Higher. school, 2008.

2. Biology with general genetics. Slyusarev A.A. ed. 2-E, M.: Medicine, 2007

Postembryonic development of animals is divided into three periods:

4.1. Postembryonic period of animal development

Period of growth and formation(pre-reproductive )

This period is characterized by the continuation of organogenesis that began in embryonic life and an increase in body size. By the beginning of this period, all organs reach the degree of differentiation at which a young animal can exist and develop outside the mother’s body or outside the egg membranes. From this moment, the digestive tract, respiratory organs and sensory organs begin to function. The nervous, circulatory and excretory systems begin their function even in the embryo. During the period of growth and morphogenesis, the species and individual characteristics of the organism are finally formed, and the individual reaches the size characteristic of the species. Later than other organs, the reproductive system differentiates. When its formation ends, the second stage of postembryonic development begins.

Maturity period(reproductive).

During this period of maturity, reproduction occurs. The duration of this period is various types animals are different. In some species (mayflies, silkworms) it lasts only a few days, in others it lasts many years.

Old age period ( post-reproductive).

Characterized by a decrease in metabolic rate and involution of organs. Aging leads to natural death.

4.2. Postembryonic period of human development

Postembryonic postnatal) period of human development, otherwise called postnatal, is also divided into three periods (Fig. 5):

Juvenile (before puberty);

Mature (adults, sexually mature state);

Old age period ending in death.

In other words, we can say that for humans it is also possible to distinguish pre-reproductive, reproductive and post-reproductive periods of post-embryonic development. It should be borne in mind that any scheme is conditional, since the actual state of two people of the same age may differ significantly. Therefore, the concept of chronological (calendar) and biological age was introduced. Biological age is determined by the totality of the metabolic, structural, and functional characteristics of the organism, including its adaptive capabilities. It may not correspond to the calendar.

Scheme 5

4.2.1. Juvenile period

According to the accepted periodization, the juvenile period begins after birth and lasts for women up to 21 years, and for men up to 22 years.

The baby's first month is considered the neonatal period. The position of the child at this time resembles the position of the fetus in the uterus. The baby sleeps most of the day, waking up only at feeding time. Caring for a child requires strict adherence to feeding times and preferably with mother's milk, special purity, and a temperature not lower than 20 ◦ C.

From the first month to a year the period of time is called chest

During the first year of life, many changes occur in the child’s motor system. At the end of the first month he tries to straighten his legs, at one and a half months he lifts and holds his head, at six months he sits, and at the end of the first year of life he tries to take his first steps. The child’s psyche also develops during this period. In the 2nd month, the baby smiles when the mother appears or when shown bright pictures; By the 4th month, he takes toys into his mouth, examines them, and begins to distinguish between adults. In the second half of infancy, the child begins to understand many of the parents' phrases. The active movements of the child at this time contribute to the development of the muscular and skeletal systems, better supply of the body with nutrients and oxygen, i.e. strengthening metabolic processes in the child’s body, and most importantly, they normalize the activity of the nervous system. Water and air procedures are necessary for the child during this period.

Three rules must be followed by adults when caring for a child during this period: gradualism, repetition, systematicity. The child will develop a clear routine for his life conditioned reflexes, the education of which makes it possible for the child to develop life skills that ensure high resistance of the body to the effects of adverse factors.

Early childhood- period from one to 3 years. During this period, the child grows rapidly, eats the same food as adults, and develops a desire for independence and self-respect. He masters many new movements and imitates adults while playing.

Preschool period- period from 3 to 7 years. During this period, children show great interest in the world around them. Curiosity is so great that this period is also called the stage of questions: where? When? For what? Why? During this period, the brain continues to grow and internal speech is formed. The external manifestation of this is the child’s conversations with himself and with toys. For a child during this period, play is important. It occupies the same place as sports and work in an adult. Games develop a child and encourage him to be creative.

School period- period from 7 to 17 years. This period is divided into early(7-11 years old), average(11-15 years old for boys and 11-14 years old for girls) and senior(15-17 years old). For the early school period, the main thing is studying. This is serious, intense work in mastering written speech, in nurturing collectivism, in learning new things about the world around us, in assimilating the experience accumulated by many generations of people. All this contributes to the harmonious mental, physical and volitional development of schoolchildren.

Secondary school The period is also called adolescence. Children undergo a profound restructuring of the activity of all organs and physiological systems. This is associated with puberty, with the intensive formation of sex hormones, which entails characteristics of physical and physiological development in both boys and girls. In adolescence, speech development ends, character formation and moral formation of the individual occur.

Adolescents, as well as older schoolchildren, are characterized by an accelerated pace of physical and sexual development, called acceleration. For example, in the 20s of our century, the height of 14-year-old boys reached an average of 145.4 cm, in the 70s the height reached 162.6 cm, and body weight increased on average by 13.5 kg. The average height and body weight of girls also increased noticeably. The reasons for acceleration have not yet been fully studied, but it has been found that the physical development of modern children does not entail their moral and social maturation.

Thus, they distinguish between physiological, psychological and social maturity. Physiological maturity- This is the puberty of the body. The time it takes to reach physiological maturity varies from person to person. It depends on climatic, hereditary and other factors. Psychological maturity- this is the moral stability of girls and boys, self-control of behavior in the family and society. Social maturity- this is a person’s conscious attitude to reality, this is the completion of a person’s education, the beginning of work, economic independence, this is, if necessary, the fulfillment of a civic duty to the state.