EMBRYOLOGY(Greek embryon uterine fetus, embryo + logos doctrine) - the science of the patterns of embryonic development of the body. Embryology of humans and viviparous animals studies the period of intrauterine development of the organism. Embryology of oviparous - the period of development before hatching from the egg; Embryology of amphibians is a period of development ending with metamorphosis (see). Plant embryology is also distinguished. Currently, human and animal embryology studies not only the period of intrauterine development, but also the period of postnatal development, in which the processes of histogenesis, organogenesis and morphogenesis (for example, the formation of the reproductive system) continue.
Instead of the term “embryology”, the names “ontogenetics”, “mechanics of development”, “dynamics of development”, “physiology of development”, etc. were proposed as if they were more consistent with the content of science. However, the term “embryology” is still used to this day.
The subject of animal and human embryology is actually the study of all processes occurring in the body during its development, including the periods of progenesis, fertilization (see), embryonic development (see), fetal development (see Fetus), as well as the postnatal period.
Embryology studies both the general patterns of phylogenesis, manifested in the development of all multicellular animals (from sponges and coelenterates to vertebrates and humans), and the features of the ontogenetic development of humans and representatives of individual types, classes and species of animals. The study of the development of a whole organism is carried out by analyzing the development process (both the whole organism and its parts) on different levels; at the same time, the formation of organs and systems, changes in tissue, cellular and subcellular structures can be traced. The main theoretical basis of E. is the biogenetic law (see).
The process of individual human development is considered as a historically (phylogenetically) determined process. A certain sequence of the main stages of embryonic development is repeated in all multicellular animals. Thus, the formation of the axial complex of primordia, notochord, neural tube, and the formation of gill pouches indicate the common origin of humans and chordates; segmentation and differentiation of the mesoderm, the formation of an initially cartilaginous and then a bone skeleton in the human embryo reflect evolutionary changes in the skeleton among vertebrates; the yolk sac, amnion, allantois are inherited by humans from reptiles; the formation of the placenta is characteristic of humans and placental mammals; powerful development of the trophoblast and early separation of the extraembryonic mesoderm are observed in human and ape embryos. However, especially early development and specialization of the extraembryonic mesoderm, the latest closure of the anterior end of the neural tube, and a number of other features of embryogenesis are observed only in humans.
The founders of embryology are considered to be Hippocrates and Aristotle (4th century BC). Hippocrates and his followers argued for the pre-existence of all parts of the future fetus in the paternal and maternal “seed” (see Preformism), that is, the development process was reduced only to quantitative changes (growth without differentiation). This view was opposed by the more progressive teaching of Aristotle about the sequential formation of organs in the process of embryogenesis (see Epigenesis). In 1600-1604, Fabricius gave a detailed description for his time of the development of the human and chicken embryo. The foundation for the identification of eggs as a science was the work of W. Harvey, “Research on the Origin of Animals” (1651), in which the egg was first considered as the source of the development of all animals. At the same time, W. Harvey, like Aristotle, believed that the development of vertebrates occurs mainly through epigenesis, arguing that not a single part of the future fetus “exists in the egg actually, but all parts are in it potentially.” M. Malpighi (1672), who discovered the organs of a chicken embryo using a microscope early stages its development, joined the preformist ideas that dominated science almost until the middle of the 18th century. K. F. Wolf in his works “The Theory of Generation” (1759) and “On the formation of the intestines in the chicken” (1768-1769) convincingly proved that the growth of the embryo is a development process. Refuting preformationist ideas, he laid the foundations of embryology as a science of development. In 1827, K. M. Baer discovered and described the eggs of mammals and humans. In his classic work “On the History of the Development of Animals” (1828-1837), he for the first time traced the main features of the embryogenesis of a number of vertebrates, clarified the concept of germ layers introduced by X. I. Tsander as the main embryonic organs and traced their development. He proved that human development occurs in the same sequence as the development of other vertebrates. K. M. Baer's law (see Embryo) on the similarity of development of different classes of vertebrates had great value for the progress of embryology as a science, in this regard, he is rightfully considered the founder of modern embryology.
In the creation of evolutionary comparative embryology, based on the theory of Charles Darwin, which, in turn, had great importance for the approval and further substantiation of the doctrine of evolution (see), an exceptional role belongs to domestic researchers I. I. Mechnikov and A. O. Kovalevsky. They found that the development of all types of invertebrates passes through the stage of separation of germ layers, homologous to the germ layers of vertebrates, and this indicates the unity of origin of all types of multicellular animals. A great contribution to the development of evolutionary embryology was made by Russian scientists A. N. Severtsov, who created the theory of phylembryogenesis, and P. G. Svetlov, who developed the theory of critical periods of ontogenesis and metamerism of chordates (see Embryo). The end of the 19th - beginning of the 20th century was marked by the active development of experimental methods, much of the credit for the development of which belongs to the German scientists E. Pflueger, Ru, domestic scientists D. P. Filatov, M. M. Zavadovsky, P. Ivanov, N. V. Nasonov and others. A great contribution to the development of science was made by A. A. Zavarzin, N. G. Khlopin, P. K. Anokhin, B. L. Astaurov, G. A. Shmidt, B. P. Tokin, A. G. Knorre, D. M. Golub, A. N. Studitsky, L. I. Falin and others.
Depending on the objectives and methods of research, general, comparative, ecological and experimental embryology are distinguished (see Experimental Embryology).
At first, embryology developed mainly as a morphological science and was of a descriptive nature (descriptive embryology). The method of observation and description made it possible to establish that development proceeds from simple to complex, from general to specific, from homogeneous to heterogeneous. Based on descriptive works on various biological species and classes, comparative embryology arose, which made it possible to identify certain similarities between the development of animals and humans. Subsequently, embryologists began to study not only the development of shape and structure, but also the formation of the functions of organs and tissues. Ecological embryology studies the factors that ensure the existence of the embryo, that is, the features of its development in certain conditions environment and the ability to adapt if they change.
Modern embryology is characterized by a comprehensive morphophysiological approach to the study and interpretation of the development process. Along with methods of observation and description, complex research methods are widely used in crust and time: microscopic, microsurgical, biochemical, immunological, radiological, etc. Their diversity is due to the close connection of embryology with other sciences. Embryology is inseparable from genetics (see Human Genetics, Medical Genetics), since ontogenesis (see) essentially reflects the implementation of the mechanism of heredity; is closely related to cytology (see) and histology (see), because the holistic process of development of the organism is based on a set of processes of reproduction, migration, differentiation, cell death, interaction between cells. One of the main problems of histology - the doctrine of histogenesis - is at the same time part of embryology. Embryology studies the process of morphological differentiation (formation of specialized cells) and chemical. differentiation (chemical organization) of pecks, patterns of metabolic processes in the development of the body. Based on the close relationship with cytology, molecular biology and genetics, a new complex branch of biology arose - developmental biology. The successes of embryology were of great importance for the development of anatomy (see) and histology. Embryology, studying changes in the chemical composition and metabolic processes of developing structures (chemical embryology), as well as the formation of functions (embryophysiology), uses data from biochemistry (see) and physiology (see).
The tasks of embryology are not only to explain phenomena and identify their patterns, but also to be able to control the development of the organism. Thus, the knowledge and methods of embryology have direct application in the national economy, in particular animal husbandry, fish farming, sericulture, are used to study the influence of the environment on the development of the organism, serve as the basis for work on introduction, restructuring of biocenoses, etc. The most important for humans is the application achievements of embryology in medicine. Medical embryology is increasingly becoming an independent science and is one of the theoretical foundations of preventive medicine. The development of medical aspects of modern embryology plays an important role in solving problems such as birth control, infertility, organ and tissue transplantation, tumor growth, immune reactions of the body, physiological and reparative regeneration, reactivity of cells and tissues, etc. Research in the field of embryology is of great importance in revealing the pathogenesis of various malformations (see). Such important problems of embryology as cell growth and differentiation are closely related to issues of regeneration, oncogenesis, inflammation, and aging. The fight against antenatal and child mortality largely depends on solving the fundamental problems of embryology.
In modern embryology, great importance is attached to the study of progenesis processes, as well as the search for ways to control progenesis and embryogenesis, which is only possible by deciphering the mechanisms that control reproductive function and ensure homeostasis of human and mammalian embryos. These mechanisms represent a complex interaction of genetic, epigenomic, internal and external factors, which determine the temporal and spatial sequence of gene expression and, accordingly, cytodifferentiation and morphogenesis; an important role in the process of embryogenesis is assigned to the neuroendocrine and immune systems, biologically active substances etc. The study of the mechanisms of regulation of normal and pathological embryogenesis at various levels of organization (organ, tissue, cellular, chromosomal) can help in finding ways to control the individual development of animals and humans, as well as in developing effective methods for the prevention of congenital malformations and pathological conditions. Much attention is paid to the study of the mother - extra-embryonic organs - fetus system. The genetic characteristics of the human placenta and its specific changes in hereditary diseases are studied; Amniotic fluid is examined to diagnose diseases in the prenatal and postnatal periods. Work on in vitro cultivation of eggs and embryos and transplantation of early embryos to an “adoptive mother” opens up prospects for restoring reproductive function in tubal infertility. These studies make it possible to understand the mechanisms of fertilization and development in the preimplantation period, analyze developmental pathology, and evaluate the direct effect on the embryo various factors, including medicines, and also allow us to get closer to solving such a general biological problem as cytodifferentiation. Research is being conducted to test drugs, chemical substances, polluting the environment, in order to identify their possible embryotoxic and teratogenic effects. A search is underway for drugs (vitamins, antitoxins, etc.) that stop the teratogenic effect of a particular substance. Research in the field of genetic engineering (see), aimed at interfering with the structure and function of the genome of germ cells, makes it possible to cause changes in the genome (see) of mammalian embryos, which in the future will make it possible to obtain animals that are devoid of undesirable characteristics and have specified properties. Thanks to the development of these methods, it will be possible to create organisms that are producers used in medicine. biological substances, such as human hormones, antisera, etc., as well as model some hereditary human diseases.
Problems of embryology in the USSR are being developed at the Institute of Developmental Biology named after. N.K. Koltsov Academy of Sciences of the USSR, Institute of Evolutionary Morphology and Animal Ecology named after. A. N. Severtsova of the USSR Academy of Sciences, Institute of Experimental Medicine of the USSR Academy of Medical Sciences. Institute of Human Morphology of the USSR Academy of Medical Sciences, as well as at the departments of histology and embryology of high fur boots and honey. institutes of Moscow, Leningrad, Novosibirsk, Simferopol, Minsk, Tashkent, etc.
In many countries there are scientific societies of anatomists, which include embryologists. In the USSR there is the All-Union Society of Anatomists, Histologists and Embryologists.
In our country, journals are published that reflect the problems of embryology: since 1916 - “Archive of Anatomy, Histology and Embryology”, since 1932 - “Advances in Modern Biology”, since 1970 - “Ontogenesis”, etc. (for details, see Anatomy). The following main journals devoted to the problems of embryology are published abroad: “Archiv fur Entwicklungsmechanik der Organismen”, founded by V. Py, “Biological Bulletin”, “Journal of Experimental Zoology”, “Journal of Embryology and Experimental Morphology”, “Developmental Biology” and etc.
Since 1949, international congresses and conferences on embryology have been regularly convened. On XI International Congress anatomists in Mexico City in 1980 was adopted new edition embryological nomenclature (see), the Russian version of which was prepared by Soviet morphologists.
Teaching of embryology in the USSR is carried out in the departments of histology and embryology of medical and veterinary institutes, in the biological faculties of universities, in the departments of anatomy and physiology of pedagogical institutes.
Bibliography:
Story- Blyakher L. Ya. History of embryology in Russia (from the mid-18th to the mid-19th century), M., 1955; Ginzburg V.V., Knorre A.G. and Kupriyanov V.V. Anatomy, histology and embryology in St. Petersburg - Petrograd - Leningrad, Brief essay, L., 1957, bibliogr.; Needham D. History of embryology, trans. from English, M., 1947.
Textbooks, manuals, major works- Bodemer W. Modern embryology, trans. from English, M., 1971, bibliogr.; Brache J. Biochemical embryology, trans. from English, M., 1961, bibliogr. ; Volkova O. V. and Pekarsky M. I. Embryogenesis and age-related histology of human internal organs, M., 1976; Vyazov O. E. Immunology of embryogenesis, M., 1962, bibliogr.; Dyban A.P. Essays on pathological human embryology. L., 1959; 3ussman M. Biology of development, trans. from English, M., 1977; Ivanov P. P. Guide to general and comparative embryology, L., 1945; Carlson B. Fundamentals of embryology according to Patten, trans. from English, vol. 1-2, M., 1983; Knorre A. G. Brief outline of human embryology, L., 1959; aka, Embryonic histogenesis. L., 1971; Pathophysiology of intrauterine development, ed. N. L. Garmasheva, Leningrad, 1959; Patten B. M. Human embryology, trans. from English, M., 1959; Stanek I. Human Embryology, trans. from Slovak, Bratislava, 1977; Tokin B. P. General embryology, M. 1977; Falin L.I. Human embryology, Atlas, M., 1976; An analysis of development, ed. by V. H. Williera. o., Philadelphia - L., 1955; Are in L. B. Developmental anatomy, Philadelphia, 1965; Hamburger V. A manual of experimental embryology, Chicago, 1960; Langman J. Medizinische Embry ologie, Stuttgart, 1976; Nelsen O. E. Comparative embryology of the vertebrates, N. Y., 1953; Patten V. M. a. Carlson V. M. Foundations of embryology, N. Y., 1974; Pflugfelder O. Lehrbuch der Ent-wicklungsgeschichte und Entwicklungsphy-siologie der Tiere, Jena, 1962; Toivonen S. Primary embryonic Induction, L., 1962; Schumacher G.-H. Embryonale Entwicklung des Menschen, Stuttgart, 1974; Snell R. S-Clinical embryology for medical students, Boston - Toronto, 1983; ThomasJ. B. Introduction to human embryology, Philadelphia, 1968.
Periodicals- Archive of anatomy, histology and embryology, L.-M., since 1931 (1917-1930 - Russian archive of anatomy, histology and embryology); Acta embryologiae et morphologiae experimentalis. Palermo, since 1957; Archives diatomic, d*hist ologie et d'embryologie, Strasbourg, since 1922; Developmental Biology, N. Y., since 1959; Excerpta medica. Sect. 1. Anatomy, Anthropology, Embryology and Histology, Amsterdam, since 1947; Journal of Embryology and Experimental Morphology, L., since 1953.
O. V. Volkova.
Embryology studies the features of embryo development from the moment of conception to the birth of a child. Embryogenesis process, which is the main subject of scientific research, can be divided into several stages:
- the formation of a zygote, which occurs at the moment of fertilization of an egg by a sperm;
- formation of blastula due to active cell fragmentation;
- gastrulation, which implies the appearance of the main germ layers and organs;
- histogenesis and organogenesis of organs and tissues of the fetus, placenta;
- systemogenesis, meaning the formation of all the main systems of the child’s body.
In addition, thanks to embryology, the most dangerous periods intrauterine development that can negatively affect the fetus under the influence of certain factors. So, The following moments of ontogenesis are considered critical:
- fertilization itself;
- implantation of the embryo into the wall of the uterus, occurring on the 7th day;
- formation of the rudiments of the main tissues, lasting from 3 to 8 weeks;
- brain formation occurring from 15 to 20 weeks;
- development of all organs and systems of the fetus (from 20 to 24 weeks);
- birth.
During these periods, the influence of various internal and external processes can lead to slow, abnormal development or even death of the child. Therefore, at this stage of pregnancy it is worth paying special attention to the health of the woman and the fetus.
Clinical embryology studies problems and deviations from the norm in ontogenesis, looks for ways to solve them and helps to avoid any violations. Moreover, this science seeks probable reasons various developmental pathologies (including the occurrence of deformities), factors acting on the course of embryogenesis, as well as ways to influence it at all possible stages. Subjects of study also include asexual reproduction, regeneration and pathological development of tissues and organs. There are schools that study the problems of oncological tumors, their patterns and causes of occurrence.
History of embryology
Even in ancient times, scientists were interested in the mysteries of the emergence and development of a child in the womb. Hippocrates and Aristotle were the founders of the most famous theories of embryogenesis, competing with each other almost until the 19th century: performism and epigenesis.
Representatives of the idea of performism believed that the new organism is present in the “egg” already in a ready-made state, only very reduced in size, and over time it only increases in size. However, theorists did not know exactly whether the embryos were contained in the mother’s body or the father’s body and how the properties of the second parent were transmitted to them.
One of the adherents of performism was the mathematician G. Leibniz, who put forward the assumption that if there are embryos in the egg, then in its ovaries there should be the eggs themselves with the next generation of embryos, and so on. Another example of similar views is the Swammerdam theory, which states that in the egg of a butterfly there is a caterpillar, in the caterpillar itself there is a pupa, and in it there is a butterfly.
Scientists who adhered to epigenesis, of which W. Harvey was a prominent representative, believed that the “egg” contained a structureless substance that had the potential for the formation of future organs and tissues. In the 18th century, K. F. Wolf, during his studies of chicken embryos, made the discovery of primary layers, which then form organs. In the early 19th century, this observation was confirmed and became generally accepted among scientists.
At the same time big discovery was made by K. Baer. Studying vertebrate embryos, he came to the conclusion that they are all similar to each other at the earliest stages of development. Moreover, over time they become more and more different. That is, embryogenesis occurs from the general to the specific, first forming the characteristics of the type, then the class, and so on. Thus, the concept of phylogenesis, or the repetition of evolutionary processes during human ontogenesis, arose. Later, on the basis of this theory, a biogenetic law was formed, described in the works of Charles Darwin.
The doctrine of recapitulation—the repetition by higher organisms of the stages of development of lower ones—has also become famous. In addition, A. Kovalevsky and I. Mechnikov made a great contribution to the development of embryology, proving that the embryogenesis of all mammals passes through the formation of three germ layers. In addition, the merits of P. Svetlov, who is the founder of the theory of critical moments of embryogenesis, are invaluable.
Experimental embryology, as a science, began to develop thanks to V. Roux, who, by isolating blastomeres, revealed some patterns in embryogenesis and pathology under the influence of certain factors. In the 20th century, a new direction in science appeared - microsurgery on embryos. As a result, new techniques were invented: removing the shells from the egg, transplanting parts of the embryo and preparing a nutrient medium for the development of the embryo.
Embryology in our time
The science studying embryogenesis has currently achieved great results. There are several areas of embryology:
- general embryology;
- comparative;
- environmental;
- experimental;
- ontogenetic.
All of them are closely related to cytology, histology, medicine, biochemistry, biology, genetics and physiology.
There are several methods for studying embryogenesis and embryos as such. These include:
- examination of fixed sections using various techniques (light microscopy, immunocytochemistry and others);
- a method for marking embryonic cells to monitor their changes;
- explantation, the essence of which is the transfer of a separate part of the embryo onto a nutrient medium for cultivation and study;
- nuclear transplantation, which made cloning possible.
Thanks to advances and research in embryology, it has become possible not only to monitor the stages of fetal development, but also to manage them, to prevent the occurrence of defects and deformities. In addition, women with a history of recurrent miscarriages or infertility were given the chance to become mothers.
The methods of artificial insemination and surrogacy came into existence only with the help of advances and techniques of embryology. Now the formation of an embryo and its growth can be carried out in artificial conditions, on a specially prepared nutrient medium. In addition, by examining embryos, embryologists can select more viable embryos from pathological and weak ones, and thereby prevent cases of frozen pregnancies or the birth of a child with developmental defects.
In IVF clinics and research institutes there are specialists who deal with the problems of fertilization and intrauterine development. It is worth noting that this area of medicine has reached significant heights and continues to develop, opening up new horizons and opportunities for people. Her role in modern world is becoming more and more significant.
EMBRYOLOGY
the science that studies the development of an organism in its earliest stages before metamorphosis, hatching, or birth. The fusion of gametes - an egg (ovum) and a sperm - with the formation of a zygote gives rise to a new individual, but before becoming the same creature as its parents, it has to go through certain stages of development: cell division, the formation of primary germ layers and cavities, the emergence of embryonic axes and axes of symmetry, the development of coelomic cavities and their derivatives, the formation of extraembryonic membranes and, finally, the emergence of organ systems that are functionally integrated and form one or another recognizable organism. All this constitutes the subject of the study of embryology. Development is preceded by gametogenesis, i.e. formation and maturation of sperm and egg. The development process of all eggs of a given species proceeds generally the same.
Gametogenesis. Mature sperm and egg differ in their structure, only their nuclei are similar; however, both gametes are formed from identical-looking primary germ cells. In all organisms that reproduce sexually, these primary germ cells are separated in the early stages of development from other cells and develop in a special way, preparing to perform their function - the production of sex, or germ cells. Therefore, they are called germ plasm - in contrast to all other cells that make up the somatoplasm. It is quite obvious, however, that both germ plasm and somatoplasm come from a fertilized egg - the zygote, which gave rise to a new organism. So basically they are the same. The factors that determine which cells become reproductive and which somatic cells have not yet been established. However, eventually the germ cells acquire quite clear differences. These differences arise during the process of gametogenesis. In all vertebrates and some invertebrates, primary germ cells arise away from the gonads and migrate to the gonads of the embryo - the ovary or testis - with the bloodstream, with layers of developing tissues, or through amoeboid movements. In the gonads, mature germ cells are formed from them. By the time the gonads develop, the soma and the germ plasm are already functionally separated from one another, and, from this time on, throughout the life of the organism, the germ cells are completely independent of any influences of the soma. That is why the characteristics acquired by an individual throughout his life do not affect his reproductive cells. Primary germ cells, while in the gonads, divide to form small cells - spermatogonia in the testes and oogonium in the ovaries. Spermatogonia and oogonia continue to divide repeatedly, forming cells of the same size, indicating compensatory growth of both the cytoplasm and nucleus. Spermatogonia and oogonia divide mitotically, and, therefore, they retain the original diploid number of chromosomes. After some time, these cells stop dividing and enter a period of growth, during which very important changes occur in their nuclei. Chromosomes, originally received from two parents, are connected in pairs (conjugated), coming into very close contact. This makes subsequent crossing over possible, during which homologous chromosomes are broken and joined in a new order, exchanging equivalent sections; as a result of crossing over, new combinations of genes arise in the chromosomes of oogonia and spermatogonia. It is assumed that the sterility of mules is due to the incompatibility of chromosomes obtained from their parents - a horse and a donkey, due to which the chromosomes are not able to survive when closely connected to each other. As a result, the maturation of germ cells in the ovaries or testes of a mule stops at the conjugation stage. When the nucleus has been rebuilt and a sufficient amount of cytoplasm has accumulated in the cell, the division process resumes; the entire cell and nucleus undergo two different types of divisions, which determine the actual process of maturation of germ cells. One of them - mitosis - leads to the formation of cells similar to the original one; as a result of another - meiosis, or reduction division, during which cells divide twice - cells are formed, each of which contains only half (haploid) number of chromosomes compared to the original, namely one from each pair (see also CELL) . In some species, these cell divisions occur in the reverse order. After the growth and reorganization of nuclei in oogonia and spermatogonia and immediately before the first meiotic division, these cells are called first-order oocytes and spermatocytes, and after the first meiotic division - second-order oocytes and spermatocytes. Finally, after the second meiotic division, the cells in the ovary are called eggs (ovules), and those in the testis are called spermatids. Now the egg has finally matured, but the spermatid still has to undergo metamorphosis and turn into a sperm. One important difference between oogenesis and spermatogenesis needs to be emphasized here. From one first-order oocyte, maturation results in only one mature egg; the other three cores and not a large number of cytoplasms turn into polar bodies, which do not function as germ cells and subsequently degenerate. All the cytoplasm and yolk, which could be distributed among four cells, are concentrated in one - in the mature egg. In contrast, one first-order spermatocyte gives rise to four spermatids and the same number of mature sperm without losing a single nucleus. Upon fertilization, the diploid, or normal, number of chromosomes is restored.
Egg. The egg is inert and usually larger than somatic cells of a given organism. The mouse egg is approximately 0.06 mm in diameter, while the diameter of the ostrich egg can be more than 15 cm. The eggs are usually spherical or oval, but can also be oblong, like those of insects, hagfish or mud fish. The size and other characteristics of the egg depend on the quantity and distribution of the nutritious yolk in it, which accumulates in the form of granules or, less commonly, in the form of a solid mass. Therefore, eggs are divided into different types depending on their yolk content. Homolecithal eggs (from the Greek homs - equal, homogeneous, lkithos - yolk). In homolecithal eggs, also called isolecithal or oligolecithal, there is very little yolk and it is evenly distributed in the cytoplasm. Such eggs are typical of sponges, coelenterates, echinoderms, scallops, nematodes, tunicates and most mammals. Telolecithal eggs (from the Greek tlos - end) contain a significant amount of yolk, and their cytoplasm is concentrated at one end, usually designated as the animal pole. The opposite pole, on which the yolk is concentrated, is called the vegetative pole. Such eggs are typical of annelids, cephalopods, lancelets, fish, amphibians, reptiles, birds and monotremes. They have a well-defined animal-vegetative axis, determined by the gradient of yolk distribution; the core is usually located eccentrically; in eggs containing pigment, it is also distributed along a gradient, but, unlike the yolk, it is more abundant at the animal pole.
Centrolecithal eggs. In them, the yolk is located in the center, so that the cytoplasm is shifted to the periphery and the fragmentation is superficial. Such eggs are typical of some coelenterates and arthropods.
Sperm. Unlike the large and inert egg, sperm are small, from 0.02 to 2.0 mm in length, they are active and are able to swim a long distance to get to the egg. There is little cytoplasm in them, and there is no yolk at all. The shape of spermatozoa is varied, but among them two main types can be distinguished - flagellated and non-flagellated. Flagellate-free forms are relatively rare. In most animals, the sperm plays an active role in fertilization. See also SPERM.
Fertilization. Fertilization is a complex process during which a sperm penetrates an egg and their nuclei fuse. As a result of the fusion of gametes, a zygote is formed - essentially a new individual, capable of developing in the presence of the necessary conditions for this. Fertilization causes the activation of the egg, stimulating it to successive changes leading to the development of a formed organism. During fertilization, amphimixis also occurs, i.e. a mixture of hereditary factors as a result of the fusion of the nuclei of an egg and a sperm. The egg provides half of the necessary chromosomes and usually all the nutrients needed for the early stages of development. When the sperm comes into contact with the surface of the egg, the vitelline membrane of the egg changes, turning into the fertilization membrane. This change is considered evidence that the egg has been activated. At the same time, on the surface of eggs containing little or no yolk, the so-called. a cortical reaction that prevents other sperm from entering the egg. In eggs that contain a lot of yolk, the cortical reaction occurs later, so that several sperm usually penetrate into them. But even in such cases, fertilization is performed by only one sperm, the first to reach the nucleus of the egg. In some eggs, at the point of contact of the sperm with the plasma membrane of the egg, a protrusion of the membrane is formed - the so-called. fertilization tubercle; it facilitates sperm penetration. Typically, the head of the sperm and the centrioles located in its middle part penetrate the egg, while the tail remains outside. Centrioles contribute to the formation of the spindle during the first division of a fertilized egg. The fertilization process can be considered complete when the two haploid nuclei - the egg and the sperm - fuse and their chromosomes conjugate, preparing for the first fragmentation of the fertilized egg.
See also EGG.
Splitting up. If the appearance of the fertilization membrane is considered an indicator of egg activation, then division (crushing) serves as the first sign of the actual activity of the fertilized egg. The nature of crushing depends on the quantity and distribution of yolk in the egg, as well as on the hereditary properties of the zygote nucleus and the characteristics of the egg cytoplasm (the latter are entirely determined by the genotype of the maternal organism). There are three types of fragmentation of a fertilized egg. Holoblastic cleavage is characteristic of homolecithal eggs. The crushing planes separate the egg completely. They can divide it into equal parts, like a starfish or sea urchin, or into unequal parts, as in the gastropod Crepidula. The fragmentation of the moderately telolecithal egg of the lancelet occurs according to the holoblastic type, however, the unevenness of division appears only after the stage of four blastomeres. In some cells, after this stage, cleavage becomes extremely uneven; the resulting small cells are called micromeres, and large cells containing the yolk are called macromeres. In mollusks, the cleavage planes run in such a way that, starting from the eight-cell stage, the blastomeres are arranged in a spiral; this process is regulated by the nucleus. Meroblastic cleavage is typical of telolecithal eggs, which are rich in yolk; it is limited to a relatively small area at the animal pole. The cleavage planes do not pass through the entire egg and do not include the yolk, so that as a result of division, a small disk of cells (blastodisc) is formed at the animal pole. This fragmentation, also called discoidal, is characteristic of reptiles and birds. Superficial crushing is typical for centrolecithal eggs. The zygote nucleus divides in the central island of cytoplasm, and the resulting cells move to the surface of the egg, forming a superficial layer of cells around the central yolk. This type of cleavage is observed in arthropods.
Crushing rules. It has been established that fragmentation obeys certain rules, named after the researchers who first formulated them. Pflueger's Rule: The spindle always pulls in the direction of least resistance. Balfour's rule: the rate of holoblastic cleavage is inversely proportional to the amount of yolk (yolk makes it difficult to divide both the nucleus and the cytoplasm). Sachs' rule: cells are usually divided into equal parts, and the plane of each new division intersects the plane of the previous division at a right angle. Hertwig's rule: The nucleus and spindle are usually located in the center of active protoplasm. The axis of each fission spindle is located along the long axis of the protoplasmic mass. The division planes usually intersect the mass of protoplasm at right angles to its axes. As a result of the crushing of fertilized eggs of any type, cells called blastomeres are formed. When there are many blastomeres (in amphibians, for example, from 16 to 64 cells), they form a structure resembling a raspberry and called a morula.
A - Stage of two blastomeres. B - Stage of four blastomeres. B - Morula, consisting of approximately 16 blastomeres (age of the embryo is approximately 84 hours). G - Blastula; the lighter central area indicates the formation of the blastocoel (age of the embryo is approximately 100 hours). 1 - Polar bodies.
Blastula. As fragmentation continues, the blastomeres become smaller and more closely adjacent to each other, acquiring a hexagonal shape. This shape increases the structural rigidity of the cells and the density of the layer. Continuing to divide, the cells push each other apart and eventually, when their number reaches several hundreds or thousands, they form a closed cavity - the blastocoel, into which fluid flows from the surrounding cells. In general, this formation is called a blastula. Its formation (in which cellular movements do not participate) ends the period of egg fragmentation. In homolecithal eggs, the blastocoel can be located in the center, but in telolecithal eggs it is usually shifted by the yolk and is located eccentrically, closer to the animal pole and directly below the blastodisc. So, the blastula is usually a hollow ball, the cavity of which (blastocoel) is filled with fluid, but in telolecithal eggs with discoidal cleavage, the blastula is represented by a flattened structure. With holoblastic cleavage, the blastula stage is considered complete when, as a result of cell division, the ratio between the volumes of their cytoplasm and nucleus becomes the same as in somatic cells. In a fertilized egg, the volumes of yolk and cytoplasm do not correspond at all to the size of the nucleus. However, during the process of cleavage, the amount of nuclear material increases slightly, while the cytoplasm and yolk only divide. In some eggs, the ratio of nuclear volume to cytoplasmic volume at the time of fertilization is approximately 1:400, and at the end of the blastula stage it is approximately 1:7. The latter is close to the ratio characteristic of both the primary germ and somatic cells. The late blastula surfaces of tunicates and amphibians can be mapped; To do this, intravital dyes (that do not harm the cells) are applied to different parts of it - the color marks made are preserved during further development and make it possible to determine which organs arise from each area. These areas are called presumptive, i.e. those whose fate under normal development conditions can be predicted. If, however, at the stage of late blastula or early gastrula these areas are moved or swapped, their fate will change. Such experiments show that, up to a certain stage of development, each blastomere is capable of turning into any of the many different cells that make up the body.
Gastrula. Gastrula is the stage of embryonic development at which the embryo consists of two layers: the outer - ectoderm, and the inner - endoderm. In different animals this two-layer stage is reached different ways, since eggs of different species contain different quantities yolk. However, in any case main role Cell movements, not cell divisions, play a role in this.
Intussusception. In homolecithal eggs, which are characterized by holoblastic cleavage, gastrulation usually occurs by invagination of the cells of the vegetal pole, which leads to the formation of a two-layered, cup-shaped embryo. The original blastocoel contracts, but a new cavity is formed - the gastrocoel. The opening leading into this new gastrocoel is called the blastopore (an unfortunate name, since it opens not into the blastocoel, but into the gastrocoel). The blastopore is located in the area of the future anus, at the posterior end of the embryo, and develops in this area most of mesoderm - third, or middle, germ layer. The gastrocoel is also called the archenteron, or primary gut, and it serves as the rudiment of the digestive system.
Involution. In reptiles and birds, whose telolecithal eggs contain a large amount of yolk and are crushed meroblastically, the blastula cells in a very small area rise above the yolk and then begin to curl inward, under the cells of the upper layer, forming the second (lower) layer. This process of rolling up the cell layer is called involution. The upper layer of cells becomes the outer germ layer, or ectoderm, and the lower layer becomes the inner layer, or endoderm. These layers merge into each other, and the place where the transition occurs is known as the blastopore lip. The roof of the primary intestine in the embryos of these animals consists of fully formed endodermal cells, and the bottom is made of yolk; the bottom of the cells is formed later.
Delamination. In higher mammals, including humans, gastrulation occurs somewhat differently, namely through delamination, but leads to the same result - the formation of a two-layer embryo. Delamination is the separation of the original outer layer of cells, leading to the appearance of an inner layer of cells, i.e. endoderm.
Auxiliary processes. There are also additional processes that accompany gastrulation. The simple process described above is the exception, not the rule. Auxiliary processes include epiboly (fouling), i.e. movement of cell layers along the surface of the vegetative hemisphere of the egg, and concrescence—the union of cells over large areas. One or both of these processes may accompany both intussusception and involution.
Gastrulation results. Final result gastrulation involves the formation of a two-layer embryo. Outer layer the embryo (ectoderm) is formed by small, often pigmented cells that do not contain yolk; From the ectoderm, tissues such as, for example, the nervous and upper layers of the skin subsequently develop. Inner layer(endoderm) consists of almost unpigmented cells that retain a certain amount of yolk; they give rise mainly to the tissues lining the digestive tract and its derivatives. It should, however, be emphasized that there are no deep differences between these two germ layers. The ectoderm gives rise to the endoderm, and if in some forms the boundary between them in the region of the blastopore lip can be determined, then in others it is practically indistinguishable. In transplantation experiments it was shown that the difference between these tissues is determined only by their location. If areas that would normally remain ectodermal and give rise to skin derivatives are transplanted onto the lip of the blastopore, they fold inward and become endoderm, which can become the lining of the digestive tract, the lungs, or the thyroid gland. Often, with the appearance of the primary intestine, the center of gravity of the embryo shifts, it begins to rotate in its shells, and the anterior-posterior (head - tail) and dorso-ventral (back - abdomen) axes of symmetry of the future organism are established for the first time.
Germ layers. Ectoderm, endoderm and mesoderm are distinguished based on two criteria. Firstly, by their location in the embryo in the early stages of its development: during this period, the ectoderm is always located outside, the endoderm is inside, and the mesoderm, which appears last, is between them. Secondly, by their future role: each of these leaves gives rise to certain organs and tissues, and they are often identified by their further fate in the development process. However, let us recall that during the period when these leaves appeared, no fundamental differences existed between them. In experiments on the transplantation of germ layers, it was shown that initially each of them has the potency of either of the other two. Thus, their distinction is artificial, but it is very convenient to use when studying embryonic development. Mesoderm, i.e. the middle germ layer is formed in several ways. It may arise directly from the endoderm by the formation of coelomic sacs, as in the lancelet; simultaneously with the endoderm, like in a frog; or by delamination, from the ectoderm, as in some mammals. In any case, at first the mesoderm is a layer of cells lying in the space that was originally occupied by the blastocoel, i.e. between the ectoderm with outer and endoderm with inside. The mesoderm soon splits into two cell layers, between which a cavity called the coelom is formed. From this cavity the pericardial cavity surrounding the heart is subsequently formed. pleural cavity, surrounding the lungs, and abdomen, in which the digestive organs lie. The outer layer of mesoderm - somatic mesoderm - forms, together with the ectoderm, the so-called. somatopleura. From the outer mesoderm, striated muscles of the trunk and limbs, connective tissue and vascular elements of the skin develop. The inner layer of mesodermal cells is called splanchnic mesoderm and, together with the endoderm, forms the splanchnopleura. From this layer of mesoderm, smooth muscles and vascular elements of the digestive tract and its derivatives develop. In the developing embryo there is a lot of loose mesenchyme (embryonic mesoderm), filling the space between the ectoderm and endoderm. In chordates, during development, a longitudinal column of flat cells is formed - the notochord, the main hallmark this type. Notochord cells originate from the ectoderm in some animals, from the endoderm in others, and from the mesoderm in others. In any case, these cells can already be distinguished from the rest at a very early stage of development, and they are located in the form of a longitudinal column above the primary gut. In vertebrate embryos, the notochord serves as the central axis around which the axial skeleton develops, and above it the central nervous system. In most chordates this is a purely embryonic structure, and only in lancelets, cyclostomes and elasmobranchs does it persist throughout life. In almost all other vertebrates, the cells of the notochord are replaced by bone cells that form the body of the developing vertebrae; It follows from this that the presence of a notochord facilitates the formation of the spinal column.
Derivatives of germ layers. Further fate three germ layers are different. From the ectoderm develop: all nervous tissue; outer layers of skin and its derivatives (hair, nails, tooth enamel) and partially the mucous membrane of the oral cavity, nasal cavities and anus. The endoderm gives rise to the lining of the entire digestive tract - from the oral cavity to the anus - and all its derivatives, i.e. thymus, thyroid gland, parathyroid glands, trachea, lungs, liver and pancreas. From the mesoderm are formed: all types connective tissue, bone and cartilage tissue, blood and vascular system; all types of muscle tissue; excretory and reproductive systems, dermal layer of skin. In an adult animal there are very few organs of endodermal origin that do not contain nerve cells originating from the ectoderm. In every important body Mesoderm derivatives are also contained - blood vessels, blood, and often muscles, so that the structural isolation of the germ layers is preserved only at the stage of their formation. Already at the very beginning of their development, all organs acquire a complex structure, and they include derivatives of all germ layers.
GENERAL PLAN OF BODY STRUCTURE
Symmetry. In the early stages of development, the organism acquires a certain type of symmetry characteristic of a given species. One of the representatives of colonial protists, Volvox, has central symmetry: any plane passing through the center of Volvox divides it into two equal halves. Among multicellular animals, there is not a single animal that has this type of symmetry. Coelenterates and echinoderms are characterized by radial symmetry, i.e. parts of their body are located around the main axis, forming a kind of cylinder. Some, but not all, planes passing through this axis divide such an animal into two equal halves. All echinoderms at the larval stage have bilateral symmetry, but during development they acquire radial symmetry, characteristic of the adult stage. For all highly organized animals, bilateral symmetry is typical, i.e. they can be divided into two symmetrical halves in only one plane. Since this arrangement of organs is observed in most animals, it is considered optimal for survival. A plane running along the longitudinal axis from the ventral (ventral) to the dorsal (dorsal) surface divides the animal into two halves, right and left, which are mirror images of each other. Almost all unfertilized eggs have radial symmetry, but some lose it at the time of fertilization. For example, in a frog egg, the place of sperm penetration is always shifted to the anterior, or head, end of the future embryo. This symmetry is determined by only one factor - the gradient of yolk distribution in the cytoplasm. Bilateral symmetry becomes apparent as soon as organ formation begins during embryonic development. In higher animals, almost all organs are formed in pairs. This applies to the eyes, ears, nostrils, lungs, limbs, most muscles, skeletal parts, blood vessels and nerves. Even the heart is laid down as a paired structure, and then its parts merge to form one tubular organ, which subsequently twists, turning into the adult heart with its complex structure. Incomplete fusion of the right and left halves of the organs manifests itself, for example, in cases of cleft palate or cleft lip, which are rarely found in humans.
Metamerism(dismemberment of the body into similar segments). The greatest success in the long process of evolution was achieved by animals with segmented bodies. The metameric structure of annelids and arthropods is clearly visible throughout their lives. In most vertebrates, the initially segmented structure later becomes barely distinguishable, but at the embryonic stages their metamerism is clearly expressed. In the lancelet, metamerism is manifested in the structure of the coelom, muscles and gonads. Vertebrates are characterized by a segmental arrangement of some parts of the nervous, excretory, vascular and support systems; however, already in the early stages of embryonic development, this metamerism is superimposed by the accelerated development of the anterior end of the body - the so-called. cephalization. If we examine a 48-hour chick embryo grown in an incubator, we can identify both bilateral symmetry and metamerism, most clearly expressed at the anterior end of the body. For example, muscle groups, or somites, first appear in the head region and are formed sequentially, so that the least developed segmented somites are the posterior ones.
Organogenesis. In most animals, one of the first to differentiate is alimentary canal. In essence, the embryos of most animals are a tube inserted into another tube; the inner tube is the intestine, from the mouth to the anus. Other organs included in the digestive system and the respiratory organs are formed in the form of outgrowths of this primary intestine. The presence of the roof of the archenteron, or primary gut, under the dorsal ectoderm causes (induces), possibly together with the notochord, the formation on the dorsal side of the embryo of the second most important system of the body, namely the central nervous system. This occurs as follows: first, the dorsal ectoderm thickens and forms the neural plate; then the edges of the neural plate rise, forming neural folds, which grow towards each other and ultimately close - as a result, the neural tube, the rudiment of the central nervous system, appears. The brain develops from the front part of the neural tube, and the rest of it develops into the spinal cord. As the neural tissue grows, the cavity of the neural tube almost disappears - only a narrow central canal remains. The brain is formed as a result of protrusions, invaginations, thickening and thinning of the anterior part of the neural tube of the embryo. From the formed head and spinal cord Paired nerves originate - cranial, spinal and sympathetic. The mesoderm also undergoes changes immediately after its emergence. It forms paired and metameric somites (muscle blocks), vertebrae, nephrotomes (rudiments of excretory organs) and parts reproductive system. Thus, the development of organ systems begins immediately after the formation of the germ layers. All development processes (under normal conditions) occur with the precision of the most advanced technical devices.
FETAL METABOLISM
Embryos developing in an aquatic environment do not require any integument other than the gelatinous membranes covering the egg. These eggs contain enough yolk to provide nutrition to the embryo; the shells protect it to some extent and help maintain metabolic heat and, at the same time, are sufficiently permeable so as not to interfere with free gas exchange (i.e., the entry of oxygen and the exit of carbon dioxide) between the embryo and the environment.
Extraembryonic membranes. In animals that lay eggs on land or are viviparous, the embryo needs additional membranes that protect it from dehydration (if eggs are laid on land) and provide nutrition, removal of metabolic end products and gas exchange. These functions are performed by extraembryonic membranes - amnion, chorion, yolk sac and allantois, which are formed during development in all reptiles, birds and mammals. The chorion and amnion are closely related in origin; they develop from somatic mesoderm and ectoderm. The chorion is the outermost membrane surrounding the embryo and three other membranes; this shell is permeable to gases and gas exchange occurs through it. The amnion protects the embryonic cells from drying out thanks to the amniotic fluid secreted by its cells. The yolk sac, filled with yolk, together with the yolk stalk, supplies the embryo with digestible nutrients; this membrane contains a dense network of blood vessels and cells that produce digestive enzymes. The yolk sac, like the allantois, is formed from splanchnic mesoderm and endoderm: endoderm and mesoderm spread over the entire surface of the yolk, overgrowing it, so that eventually the entire yolk ends up in the yolk sac. In reptiles and birds, the allantois serves as a reservoir for the final metabolic products coming from the kidneys of the embryo, and also ensures gas exchange. In mammals, these important functions are performed by the placenta - a complex organ formed by chorionic villi, which, growing, enter the recesses (crypts) of the uterine mucosa, where they come into close contact with its blood vessels and glands. In humans, the placenta completely provides the embryo with respiration, nutrition, and the release of metabolic products into the mother’s bloodstream. Extraembryonic membranes are not preserved in the postembryonic period. In reptiles and birds, upon hatching, the dried membranes remain in the egg shell. In mammals, the placenta and other extraembryonic membranes are expelled from the uterus (rejected) after the birth of the fetus. These shells provided higher vertebrates with independence from the aquatic environment and undoubtedly played an important role in the evolution of vertebrates, especially in the emergence of mammals.
BIOGENETIC LAW
In 1828, K. von Baer formulated the following principles: 1) the most general characteristics of any large group of animals appear in the embryo earlier than less general characteristics; 2) after the formation of the most common features less common ones appear and so on until the appearance of special characteristics characteristic of a given group; 3) the embryo of any animal species, as it develops, becomes less and less similar to the embryos of other species and does not go through the later stages of their development; 4) the embryo of a highly organized species may resemble the embryo of a more primitive species, but is never similar to the adult form of this species. The biogenetic law formulated in these four provisions is often misinterpreted. This law simply states that some stages of development of highly organized forms have a clear similarity with some stages of development of forms lower on the evolutionary ladder. It is assumed that this similarity can be explained by descent from a common ancestor. Nothing is said about the adult stages of the lower forms. In this article, similarities between germinal stages are implied; otherwise the development of each species would have to be described separately. Apparently, in the long history of life on Earth, the environment played a major role in the selection of embryos and adult organisms best suited for survival. The narrow limits created by the environment in relation to possible fluctuations in temperature, humidity and oxygen supply reduced the diversity of forms, leading them to relatively general type. As a result, the similarity in structure arose that underlies the biogenetic law when it comes to embryonic stages. Of course, in existing forms, during the process of embryonic development, features appear that correspond to the time, place and methods of reproduction of a given species. Ontogenesis, i.e. the development of an individual precedes phylogeny, i.e. group development because mutations usually occur in germ cells before fertilization. Changes in the embryo naturally precede, and often cause, changes in the adult that have evolutionary significance. A new individual is “laid” at the moment of fertilization, and embryonic development only prepares it for the vicissitudes of adult existence and the creation of future embryos.
see also
CYTOLOGY;
HEREDITARY ;
SYSTEMATICS OF ANIMALS.
LITERATURE
Carlson B. Fundamentals of embryology according to Patten, vol. 1. M., 1983 Gilbert S. Developmental biology, vol. 1. M., 1993
Collier's Encyclopedia. - Open Society. 2000 .
EMBRYOLOGY EMBRYOLOGY
(from embryo and...logy), in a narrow sense - the science of embryonic development, in a broad sense - the science of the individual development of organisms (ontogenesis). E. animals and humans studies pre-embryonic development (oogenesis and spermatogenesis), fertilization, embryonic development, larval and post-embryonic (or postnatal) periods of individual development. Embryol. research in India, China, Egypt, and Greece is known before the 5th century. BC e. Hippocrates (with his followers) and Aristotle studied the development of embryos. animals, especially chickens, as well as humans. A significant shift in the development of E. occurred in the middle. 17th century with the advent of W. Harvey’s work “Research on the Origin of Animals” (1651). Of great importance for the development of E. was the work of K. F. Wolff “The Theory of Generation” (1759), the ideas of which were developed in the works of X. I. Pander (the idea of germ layers), K. M. Baer (discovery and description eggs of humans and mammals, a detailed description of the main stages of embryogenesis of a number of vertebrates, clarification of the subsequent fate of the germ layers, etc.), etc. The foundation of evolution. compare E., based on the theory of Charles Darwin and which, in turn, substantiates the relationship of animals of different taxa, was founded by A. O. Kovalevsky and I. I. Mechnikov. Let's experiment. E. (originally the mechanics of development) owes its development to the works of V. Ru, X. Driesch, X. Spemann, D. P. Filatov. In the history of E. for a long time The struggle lasted between supporters of epigenesis (W. Harvey, K. F. Wolf, X. Driesch, etc.) and preformationism (M. Malpighi, A. Leeuwenhoek, C. Bonnet, etc.). Depending on the objectives and methods of research, they distinguish between general, comparative, experimental, population and ecological E. Compare data. E. means that degrees are built by natures. animal system, especially in its higher sections. Let's experiment. E., using the removal, transplantation, and cultivation outside the body of the rudiments of organs and tissues, studies the causal mechanisms of their origin and development in ontogenesis. E.'s data are of great importance for medicine and agriculture. x-va. In recent decades, at the intersection of E. with cytology, genetics and mol. Developmental biology arose from biology. E. plants(E.r.), phytoembryology is a private discipline within the framework of plant morphology that studies the formation and patterns of development of the plant embryo. In the E. of holo- and angiosperms, the ontogenetic processes occurring in the ovule or branch are considered, and the structure and development of gametophytes, germ cells, and zygotes are also studied. Accumulation of information on E. r. began in ancient times. In the 16th-18th centuries. The main focus was on establishing sex in flowering plants, which began with experiments on hybridization (J. Kölreuther) and cross-pollination (K. Sprengel) and completed with the discovery of the meaning of cross-pollination (C. Darwin). The first is microscopic. the description of the egg and embryo sac in flowering plants was undertaken by M. Malpighi (1675), and the discovery of the endosperm in the seed belongs to N. Grew (1672). How to be independent, discipline E. r. began to form only in the middle. 19th century, which means it was largely associated with the development cell theory, Darwin's evolutionary theory and the improvement of microscopy. technology. To the beginning 20th century fundamental discoveries were made about the patterns of development of the male gametophyte in holo- and angiosperms (V. Hoffmeister, V.I. Belyaev) and the development of the pollen tube (J. Amici); V.I. Belyaev described the main meiotic units in sporogenic cells. Controversial issues of macrosporogenesis and double fertilization in angiosperms were resolved by the works of E. Strasburger, I. N. Gorozhankin and S. G. Navashin. As a result, the classic research, modern problems in economics have developed, including important stages ontogenesis - anther development, micro-sporogenesis, formation of a male hematophyte (pollen grain) from microspores, formation of a pollen tube, macro-sporogenesis and formation of an embryo sac from a macrospore - a female hematophyte, double fertilization, development of the endosperm and embryo. In addition to these issues, the study of the causes of sterility of gametes and zygotes, apomixis, polyembryony, and parthenocarpy is of great importance for genetic selection work. Questions of the development of generative organs and their functions in lower groups (algae, lichens, fungi) that do not have an embryo were not considered for a long time in E. r. However, in recent decades there has been great interest in the study of these groups from the standpoint of phytoembryology. Comparative E. R. deals with both the study and comparison of the developmental features of embryonic characters in representatives of various taxa, and the comparison of the nature of the alternation of generations in the plant development cycle. The results of these works play a huge role in resolving controversial issues of plant taxonomy and in constructing phylogenetics. systems
.(Source: “Biological Encyclopedic Dictionary.” Editor-in-chief M. S. Gilyarov; Editorial Board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected - M.: Sov. Encyclopedia, 1986.)
embryologyThe science of the embryonic development of humans, animals, and plants. There are general, comparative, experimental and ecological embryology. One of the founders of comparative animal embryology was A.O. Kovalevsky. In modern embryology of humans and animals, experimental embryology has acquired particular importance, making it possible to solve the problems of artificial insemination and cloning, as well as environmental embryology, which studies the impact of various environmental factors on the development of the human and animal fetus.
.(Source: “Biology. Modern illustrated encyclopedia.” Chief editor A. P. Gorkin; M.: Rosman, 2006.)
Synonyms:
See what "EMBRYOLOGY" is in other dictionaries:
Embryology… Spelling dictionary-reference book
- (from Ancient Greek ἔμβρυον, germ, “embryo”; and λογία, logia) is the science that studies the development of the embryo. An embryo is any organism in the early stages of development before birth or hatching, or, in the case of plants, before germination.... ... Wikipedia
Greek, from embryon, fetus, and lego, I say. The doctrine of embryos. Explanation of 25,000 foreign words that have come into use in the Russian language, with the meaning of their roots. Mikhelson A.D., 1865. EMBRYOLOGY, the study of the development of animals and plants... ... Dictionary of foreign words of the Russian language
embryology- ANIMAL EMBRYOLOGY – the science of the structure and patterns of development of the embryo. PLANT EMBRYOLOGY EMBRYOLOGY is a branch of science that studies the emergence and development of male and female gametophytes, the processes of fertilization, embryo development and... ... General embryology: Terminological dictionary
Modern encyclopedia
embryology- and, f. embriologie f. A department of biology that studies the development of animal embryos, including humans. Ush. 1940. || outdated, translated The embryonic state of something. ALS 1. Without knowing the embryology of science, without knowing its fate, it is difficult to understand its modern... ... Historical Dictionary Gallicisms of the Russian language
Embryology- (from embryo and...logy), a science that studies pre-embryonic development (formation of germ cells), fertilization and embryonic development of the body. The first knowledge in the field of embryology is associated with the names of Hippocrates and Aristotle. Creator... ... Illustrated Encyclopedic Dictionary
- (from embryo and...logy) the science of pre-embryonic development (formation of germ cells), fertilization, embryonic and larval development of the body. There are animal and human embryology and plant embryology. There are general, comparative,... Big Encyclopedic Dictionary
EMBRYOLOGY, a biological discipline that studies the origin, development and functioning of embryos, both animal and plant. This discipline traces all stages of the process from fertilization of the ovum (EGG) to birth (hatching,... ... Scientific and technical encyclopedic dictionary
EMBRYOLOGY, embryology, many. no, female Department of biology that studies the development of animal embryos, including humans. Dictionary Ushakova. D.N. Ushakov. 1935 1940 ... Ushakov's Explanatory Dictionary
Books
- Histology and embryology of the oral cavity and teeth. Study guide, Gemonov Vladimir Vladimirovich, Lavrova Emilia Nikolaevna, Falin L.I., Study guide includes a theoretical part on embryology and histology of the oral cavity and teeth, an atlas, a workshop, test and educational materials (examples) with control questions, ... Category: Anatomy and physiology Publisher:
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