The biological significance of the crushing stage. Splitting up

Splitting up I. Splitting up

in the technique, the process of destruction of solid material slices to reduce their size. Slices are destroyed by external forces overcoming the forces of the clutch between the particles of the material. D. is not fundamentally different from grinding (see grinding). It is conventionally believed that when D. produces products larger, and when grinding smaller 5 mM.. Methods D. ( fig. one ): crushing, splitting, abrasion and blow. Durable and abrasive materials are crushed predominantly crushing, durable and viscous - crushing with abrasion, soft and fragile - splitting and impact. Work D. is spent on the deformation of a piece and on the formation of a new surface of small pieces. Most of the energy spent dissipated in the form of heat, and only a small proportion is converted into free surface energy. solid body. Full work D. is equal to the sum of work on deformation and on the formation of new surfaces. This generalized formula was proposed by P. A. Reobener OM (1944). For approximated calculations, it is assumed that the work on D. Squa size D. with a given degree, D. is directly proportional D 2,5. D. characterize the degree of D., i.e. the ratio of the size of the greatest pieces in the material before and after D. dr. Indicator - specific energy consumption, i.e. kw· c. on 1. t. crushed material. D. combine, as a rule, with the screamer of m. Distinguish D. in the open ( fig. 2. , a) and closed ( fig. 2. , b) cycle. In the 1st case, the product is finished on the size of the product on the screens of the crusher, and also get after d.; In the 2nd - the material after the crusher is sieved on the screens of large and small (ready); Large material is returned to doggle into the same crusher. To obtain high degrees of D., sequentially several techniques (stages) D. D. When enriching the ore is crushed in 2, 3 or 4 stages, the specific energy consumption on D. from pieces with dimensions 900-1200 mM. to pieces 25. mM. - 1,5-3 kw· c. on 1. t. ore.

D. Manual and fire was known for 3000 years BC. e. The simplest machines are falling pebbles (roller), driven by water wheels, have been used already in the Middle Ages and are described by G. Agrikola. Machine d. develops from early 19 V. (See crusher).

From the 50s. In the USSR and other countries, the countries explore the hydraulic, thermal, electrothermal and other methods of D., but for the coming decades the main technologies described will remain the main.

D. is used in the mining, metallurgical, chemical, food industry, in construction and agriculture.

LIT: Levison L. B., Klyuev G. M., Production of rubble, M., 1959; Andreev S. E., Zverevich V. V., Perov V. A., Crushing, grinding and screening of minerals, 2 ed., M., 1966; Proceedings of the European Communication Meeting, Per. with him., M., 1966; Arsh E. I., Vistort G. K., Cherkasy F. B., New methods of crushing strong mountain breeds, K., 1966; Ponomarev I.V., Crushing and gripping of coal, M., 1970.

V. A. Perov.

Big soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

Antonyms:

Watch what is "crushing" in other dictionaries:

See the separation ... Dictionary of Russian Synonyms and Similar expressions in the meaningful. under. ed. N. Abramova, M.: Russian Dictionaries, 1999. Crushing partitioning, separation, section, division, membership, dismemberment; Sewing, lithotripsy, imbusion, ... ... Synonym dictionary

- (a. Breaking, crushing; N. Brechen, Zerkleinerung, QUETSCHEN; F. Broyage, Concassage; and. Molienda) The process of destruction of ore, coal and other solid material in order to obtain the required size (more than 5 mm), granulometric. ... ... Geological Encyclopedia

Crushing: crushing (technology) Grinding solid body to a certain size; Crushing (printing) Play on the prints of the same printing element twice, with displacement; Crushing (embryology) row ... ... Wikipedia

Crushing, crushing, mn. No, cf. (Book.). 1. Action on ch. crush and crush. Crushing stone. Crushing the theme. 2. The process of dividing the fertilized egg to individual cells (biol.). Dictionary Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary Ushakov

Splitting up - (grinding, grinding) - (Caras.) Reducing the size of materials depending on their hardness. [GOST R 54868 2011] Crushing of refractory raw materials [unformed refractory] - grinding pieces of refractory raw materials [unformed ... ... Encyclopedia Terms, Definitions and Explanations of Building Materials

In the technique, the process of destruction of pieces of solid material into smaller. Depending on the size of the source material, it is distinguished: large (from 1000 to 100 mm), mean (from 100 to 40 mm), small (30 5 mm) crushing ... Big Encyclopedic Dictionary

Eggs, a series of consecutive mitotic. The divisions of the fertilized egg, as a result of which it, without increasing in size, is divided into all the smallest cells of blastomeres. D. The indispensable period of ontogenesis of all multicellular animals. Usually ... ... Biological Encyclopedic Dictionary

Based on a number of essential characteristics (completeness, uniformity and symmetry of division) allocate a number types of crushing. Types of crushing are largely determined by the distribution of substances (including yolk.) by cytoplasm eggs and the nature of the intercellular contacts that are installed between blastomers.

Crushing can be

full (hurried) or incomplete (meroblastic),

uniform (Blastomers are more or less the same in magnitude) and

uneven (Blastomers are not the same in magnitude, two - three dimensional groups are distinguished, commonly referred to as macro- and micrometers), finally via the character of symmetry differ radial, spiral, various variants of bilateral and anarchic crushing. Each of these types allocate a number of options.

According to the degree of submission:

Hollow crushing

Planes of crushing separated egg completely. Highlight full uniform crushing blastomeres do not differ in size (this type of crushing is characteristic gomolecital eggs) and full uneven Crushing in which blastomers can differ significantly in size. This type of crushing is characteristic of moderately telolemic Eggs.

Meroblastic crushing discoodal

limited to a relatively small area at the animal pole,

the plane of crushing does not pass through everything egg And do not capture yolk.

This type of crushing is typical fortelolecital eggs Yellow rich (birds, reptile). Such fraction is also called discomal, as a result of crushing on the animal pole, a small disk is formed cells (blastodysk).

Discount crushing (from Greek. dískos - disk and éidos - view), one of the types crushing Eggs in animals with teloleutive eggs (scorpions, cephalopod mollusks, cartilage and bony fish, reptiles and birds). For Discount shot Only a small disk is relatively free from yolk and containing cytoplasm kernel.

Surface

core zygotes divided in the central island cytoplasm,

treatable cells move to the surface eggsforming a surface layer cells (blastoderm) Around the underlying yolk.

This type of crushing is observed. w.clavistonogich .

According to the type of symmetry of a crushing egg

Radial

Axis eggs It is the axis of radial symmetry. Typically forlanctress , sturgeon , amphibians , sharkinskiy , circulation chapter.

Spiral

IN anafhase Blastomers unfold. It is characterized by the left-right dicimmetry (enantiomorphism) already at the stage of four (sometimes two) blastomers. Typically for somemollusks , rocky andcrystal worms .

Bilateral

There are 1 plane of symmetry. Typically foraskarida .

Anarchical

Blastomers are poorly interconnected, first form chains. Typically forintestinal .

Enucleation - In histology, removal of the cell nucleus.

Epiblast= Ectoderma Otherwise ectoblast Otherwise epiblast - Outdoor reservoir of the embryo Metazoa, as well as the outer layer of the body wall of the lower Metazoa (multicellular).

Didactic unit number 3 - genetics laws

Allopoliploidy (from hello... and polyploidy) - hereditary change in plants cells, less often animals, consisting in a multiple increase numbers sets of chromosomes during interspecies or Interhown crossings. It is found in nature and can be obtained purposefully (rye-wheat, cabbage-ransic hybrids). It has important value In the processes of speciation in plants.

Anemia Fanfoni.

(G. Fanconi, born in 1892, Swiss. pediatrician; syn. Fanconi Syndrome.) Hereditary diseasecharacterized by bone marrow hypoplasia, pancytopenia, as well as skin development anomalies ( hyperpigmentation), the bone system (underdevelopment of 1 mill-or radial bone) and (or) internal organs (kidneys, spleen); It is inherited by autosomal-recessive type.

DNA giraza When it brings, she shifts on the border of the replicon and the superspio is formed, an unusually cool promotion. To eliminate it appear swimulate which are capable of cutting in the tops of the supercount in the phosphate bridge area. Cool hinge is formed and the superspio is reset through it. Enzyme appears heliaza (SSB), which stabilizes it, the biosynthesis itself begins with the synthesis of primer (seed), and the seed consists of RNA. A special multimenza complex appears - Priamos. In it 3 enzymes: 1). Praimaza (Synthesizes RNA seed) 2). DNA protein (DNA dependent ribonucleoside 3 phosphatase) 3). N "-belok (DNA dependent omefase) DNA protein and N" - CELL defines the beginning of replication with which the seed begins. This is usually a piece of 6 nucleotides. Next, Prahymos moves to the adjacent point of Ori. The first thread 3 "5" is the leading, and the second 5 "3" is delayed. After that, DNA polymerase-3 is attached to the primer. The growth of the DNA chain is the elongation chain, which goes to the terminal codons located at the point of the neighboring replicon. After that, the enzyme of RNase appears, which removes the primer, and the emptiness is formed, the DNA polymerase-1 enzyme enters it. After biosynthesis, neighboring replications are formed fragments of the providence, merging together at the expense of DNA ligase. After that, in this section of DNA, the restoration of spirality occurs. This is due to topoisomerase-3, which represents a mixture of gyrase and W-protein. Thus, there is a complete synthesis of DNA. As a result, DNA replication is as follows: 1). DNA giraza Splits the DNA Reconduct, starting with the point of Ori. 2). The border creates a superspio. 3). DNA-Swivelzacreates a cerns hinge and superspio is reset. four). Heliaza(SSB) Stabilizes single-stranded threads without giving merge. five). Priosima. Mobile replication promoter due to the bottom-protein facility creates a RNA seed at the ORI point. 6). DNA polymerase-3 Synthesizes the DNA molecule - a fragment of the provision. 7). RNAZA removes primer seed. eight). DNA polymerase-1 Building 9). DNA - Ligase Shears fragments of the provision 10). Topoisomerase-3 forms a spiral.

The content of the article

EMBRYOLOGY,science learning the development of the body on the most early stagespreceding metamorphosis, hatching or birth. Merge Games - Eggs (egg) and spermatozoa - with the formation of zygota gives the beginning of a new individual, but before becoming the same creature, as parents, it will have to undergo certain stages of development: cell division, the formation of primary germinal leaves and cavities, the emergence of the axes of the embryo and The axes of symmetry, the development of the nuclear cavities and their derivatives, the formation of extraordinary shells and, finally, the emergence of systems of organs, functionally integrated and forming one or another recognizable organism. All this is the subject of study of embryology.

Development is preceded by Gametogenesis, i.e. Education and ripening sperm and eggs. The process of the development of all eggs of this species flows in general equally.

Gametogenesis.

Mature spermatozoa and egg differ in their structure, only the kernels are similar; However, both gametes are formed from the same primary genital cells. In all organisms that breed sexually, these primary sex cells are isolated in the early stages of development from other cells and are developing in a special way, preparing to perform their function - the production of genital, or germs, cells. Therefore, they are called germinal plasma - in contrast to all other cells constituting a somatoplasm. It is clear that however, that the germ plasma and somatoplasm occurs from a fertilized egg - zygotes, which has given the beginning of a new organism. Thus, as their basis, they are the same. Factors defining which cells will become sexually, and which are somatic, still not installed. However, ultimately, sex cells acquire quite clear differences. These differences occur in the process of gametogenesis.

All vertebrates and some invertebrates primary sex cells arise away from the gonad and migrate to the gonads of the embryo - ovaries or a seed - with a blood current, with the formation of developing tissues or by amoeboid movements. In gonads, mature genital cells are formed. By the time of the development of the gonad of the catfish and the germ plasma is functionally already separately separated from one another, and, starting from this time, the body's sexual cells are completely independent of any influences of the Soma throughout the body. That is why the signs acquired by the Individual throughout his life do not affect its sex cells.

Primary sex cells, being in gonads, are divided into the formation of small cells - spermatogonius in the sementes and oogoniyev in the ovaries. Spermatogonia and Oogonia continue to be repeatedly sharing, forming cells of the same size, which indicates compensatory growth of both cytoplasm and nuclei. Spermatogonia and Oogonia are divided mitotically, and therefore they maintain the original diploid number chromosomes.

After some time, these cells stop sharing and enter in the period of growth during which very important changes occur in their nuclei. Chromosomes obtained initially from two parents are connected in pairs (conjugate), entering into very close contact. This makes it possible to follow the subsequent crosslinker (cross), during which homologous chromosomes are broken and connected in a new order by exchanging equivalent sites; As a result of crosslinker in the chromosomes of Oogoniyev and Spermatogoniyev, new combinations of genes arise. It is assumed that the sterility of mules is due to the incompatibility of chromosomes received from parents - horses and donkey, due to which chromosomes are not able to survive with a close connection with each other. As a result, the ripening of genital cells in the ovaries or the seeds of the mulet is terminated at the conjugation stage.

When the core was rebuilt and a sufficient amount of cytoplasm was accumulated in the cage, the division process resumes; The entire cell and the kernel are subjected to two different types of divisions that determine the actual ripening process of genital cells. One of them - mitosis - leads to the formation of cells similar to the initial; As a result of the other - meiosis, or the reduction division, during which the cells are divided twice, cells are formed, each of which contains only half (haploid) the number of chromosomes compared to the initial one, namely one of each pair. In some species, these cell divisions occur in the reverse order. After the growth and reorganization of the nuclei in oogonios and sperm and immediately before the first division of MEIOS, these cells receive the names of oocytes and first-order spermatocytes, and after the first division of MEIOSE - oocytes and second-order sperm. Finally, after the second division of MEIOS, the cells in the ovary are called eggs (egg cells), and in the semenist - sperm. Now the egg is completely ripe, and there will still be metamorphosis from sperm and turn into a sperm.

Here it is necessary to emphasize one important difference between oogenesis and spermatogenesis. Of one oocyte of the first order, only one mature egg is obtained as a result of maturation; the remaining three cores and not a large number of The cytoplasms are converted to polar calves that do not function as sex cells and are degenerated hereinafter. All cytoplasm and yolks that could host the four cells are concentrated in one - in a ripe egg. In contrast, one first-order spermatocyte gives the beginning of four sperm and the same number of mature spermatozoa, without losing a single nucleus. In fertilization, the diploid, or normal, number chromosome is restored.

Egg.

Inert's egg and usually larger than somatic cells of this body. The mouse egg generation is about 0.06 mm in diameter, while the diameter of the ostrich egg is more than 15 cm. Eggs usually have a spheroid or oval shape, but they are also obliged, like insects, mixins or a lot of fish. Dimensions and other signs of eggs depend on the amount and distribution in it of a nutrient yolk accumulating in the form of granules or less often, in the form of a solid mass. Therefore, eggs are divided into different types, depending on the content of the yolk.

Homolecital eggs

(from Greek. Homós - equal, homogeneous, Lékithos - yolk) . In homolecital eggs, also called isoletive or oligolecital, yolk is very small and it is evenly distributed in the cytoplasm. Such eggs are typical for sponges, shepherd, hawk, sea scallops, nematodes, shells and most mammals.

Telolecital eggs

(from the Greek. Télos - the end) contain a significant amount of yolk, and the cytoplasm is concentrated in them at one end, indicated usually as an animal pole. The opposite pole, on which the yolk concentrated is called vegetative. Such eggs are typical for ring worms, challenges of mollusks, non-examined (lancing), fish, amphibious, reptiles, birds and single-pass mammals. They are well expressed an animal-vegetative axis, determined by the gradient of the distribution of the yolk; The kernel is usually located eccentric; In the eggs containing pigment, it is also distributed over a gradient, but, unlike yolk, it is more on the animal pole.

Stolecital eggs.

In them, the yolk is located in the center, so that the cytoplasm is shifted to the periphery and crushing surface. Such eggs are typical for some shepherd and arthropods.

Sperm.

Unlike a large and inert egg cell, spermatozoa small, from 0.02 to 2.0 mm in length, they are active and able to sail a long distance to get to the egg. There are few cytoplasm in them, but the yolk is not at all.

The sperm shape is diverse, but two main types can be distinguished among them - flagella and flavored. Burnless forms are relatively rare. Most animals have an active role in fertilization belongs to a spermatozoa.

Fertilization.

Fertilization is a complex process, during which the spermatozoic penetrates the egg and their kernels merge. As a result of the merge, the zygote is formed - essentially a new part that can develop in the presence of the conditions necessary for this. Fertilization causes an activation of the egg, stimulating it to consistent changes leading to the development of the formed organism. In fertilization, amphimixis is also occurred, i.e. The mixing of hereditary factors as a result of the merger of the nuclei of the egg and sperm. The egg provides half the necessary chromosomes and usually all nutrients needed for early development stages.

When contacting the sperm with the surface of the egg, the yolk sheath of the egg changes, turning into the shell of fertilization. This change is considered evidence that the activation of the egg has occurred. At the same time on the surface of eggs containing little yolk or not containing it at all, the so-called occurs. Cortical reaction that does not allow other spermatozoa to penetrate into the egg. Eggs containing a lot of yolk, the cortical reaction appears later, so that several spermatozoa usually penetrate them. But even in such cases, fertilization makes only one spermatozoa, the first reached the egg.

In some eggs, in the place of contact of the sperm with the plasma membrane, the egg is formed to protrude membrane - so-called. Budrock fertilization; It makes it easier to penetrate the sperm. Usually, the spermatozoa head and centrioles are penetrated into the egg, which are in its middle part, and the tail remains outside. Centrioles contribute to the formation of spindles at the first division of the fertilized egg. The process of fertilization can be considered complete when two haploid kernels - egg cells and spermatozoa are merged and their chromosomes are conjugated by preparing for the first crushing of the fertilized egg.

Splitting up.

If the occurrence of the fertilization shell is considered an indicator of the activation of the egg, then division (crushing) serves as the first sign of the actual activity of the fertilized egg. The nature of crushing depends on the amount and distribution of the yolk in the egg, as well as from the hereditary properties of the zigota kernel and the characteristics of the eggs of the egg (the last entirely determined by the genotype of the parent organism). Three types of crushing of the fertilized egg are distinguished.

Hollow crushing

characteristic for gomolecital eggs. Planes of crushing separated egg completely. They can share it on equal parts like a starfish or sea hedgehog, or on unequal parts, like a brochonog mollusk Crepidula.. The crushing of the moderately telolecital eggs of the lancing occurs on the hoody type, but the uneven division is manifested only after stage of four blastomers. In some cells, after this stage, crushing becomes extremely uneven; The small cells formed are called micrometers, and large cells containing yolks - macromers. In mollusks, the plane of crushing are tested in such a way that since the stage of eight cells, blastomeres are located on the helix; This process is regulated by the kernel.

Meroblastic crushing

typically for telolecital eggs rich in yolk; It is limited to a relatively small area at the animal pole. The crushing planes do not pass through all the egg and the yolk is not captured, so that as a result of dividing on the animal pole, a small cell disc is formed (blastodisk). Such a crushing, also called discoomal, is characteristic of reptiles and birds.

Surface crushing

typically for centolecital eggs. The zygote core is divided in the central island of cytoplasm, and the cells resulting in the same time move to the surface of the egg, forming a surface layer of cells around the underlying yolk. This type of crushing is observed in arthropods.

Rules of crushing.

It has been established that crushing is subject to certain rules called the names of researchers who first formulated them. PFLUGER rule: spine always stretches towards the smallest resistance. Balfura rule: the rate of hollow crushing is inversely proportional to the number of yolk (yolk makes it difficult to divide both the core and the cytoplasm). Sax Rule: Cells are usually divided into equal parts, and the plane of each new division crosses the plane of the preceding division at right angles. Gertiga rule: the kernel and spindlers are usually located in the center of the active protoplasm. The axis of each separation of the division is located along the long axis of the protoplasm mass. The division planes usually intersect the mass of protoplasm at the right angle to its axes.

As a result of crushing of fertilized eggs of any type, cells called blastomers are formed. When blastomers become a lot (in amphibians, for example, from 16 to 64 cells), they form a structure resembling the raspberry berry and called Morula.

Blastula.

As the crushing continued, the blastomeres are becoming smaller and more densely fit to each other, acquiring a hexagonal form. Such a form increases the structural rigidity of the cells and the layer density. Continuing to divide, cells push each other and as a result, when their number reaches several hundred or thousands, form a closed cavity - blastocel, which flows fluid from surrounding cells. In general, this formation is called Blastuly. Its formation (in which cell movements are not involved) the period of crushing eggs is completed.

In the homolecital eggs, the blastocel can be located in the center, but in the telolecital eggs, it is usually shifted with a yolk and is located eccentrically, closer to the animal pole and right under Blastodi. So, Blastuly usually represents a hollow ball, the cavity of which (blastocel) is filled with liquid, but in telolecital eggs with discoomal crushing of Blastuly is represented by a flattened structure.

Upon hidden crushing, the blastuly stage is considered complete when, as a result of cell division, the ratio between the volumes of their cytoplasm and the kernel becomes the same as in somatic cells. In the fertilized egg, the volumes of yolk and cytoplasm at all do not correspond to the sizes of the kernel. However, in the process of crushing, the amount of nuclear material increases slightly, while cytoplasma and yolk are only divided. In some eggs, the ratio of the volume of the nucleus to the volume of the cytoplasm at the time of the fertilization is approximately 1: 400, and by the end of the blastuly stage - approximately 1: 7. The latter close to the ratio characteristic and for the primary sexual and for the somatic cell.

The surface of the late Blastuly shells and amphibians can be capacious; To do this, at different parts of its sections are applied (non-harm cells) dyes - made colored labels are preserved during further development And allow you to establish which organs arise from each site. These sites are called presumbitative, i.e. Such, the fate of which can be predicted under normal development conditions. If, however, at the stage of Late Blastuly or Early Gastrul, move these sites or change places, their fate will change. Such experiments show that to some specific stage of development, each blastomer is capable of becoming any of the many variety of cells constituting the body.

Gastrol.

Gastrol is called the stage of embryonic development, on which the embryo consists of two layers: outdoor - ectoderma, and internal - Entoderma. In different animals, this two-layer stage is achieved in different ways, since eggs different species Contain a different amount of yolk. However, in any case, the main role in this is played by the movement of cells, and not cell divisions.

Intussusception.

In homolecital eggs, for which typically, ripastic crushing, gastruption usually occurs by invagination (pensions) of a vegetative pole cells, which leads to the formation of a two-layer embryo having a shape of the bowl. The initial blastocel is reduced, but at the same time a new cavity is formed - Gastrozel. A hole leading to this new gastrochel is called Blastopor (the name is unsuccessful because it opens not in Blossocel, but in Gastrozel). Blastopor is located in the field of the future anal hole, at the rear end of the embryo, and in this area most of the mesoderma develops - the third, or medium, germs. Gastrozel is also called the Archentheron, or the primary intestine, and it serves as a germit of the digestive system.

Involution.

In reptiles and birds, the telolecital eggs of which contain a large amount of yolks and are crushed by murdes, blastuly cells on a very small area are lifted over the yolk and then begin to turn inside, under the cells of the upper layer, forming the second (lower) layer. This process of nutrition of the cellular reservoir is called involution. The top layer of cells becomes an outer germing leaflet, or ectoderm, and the lower - internal, or entoderma. These layers go one into another, and the place where the transition occurs, is known as the lip of Blastopore. The roof of the primary intestine in the embryos of these animals consists of quite formed entodermal cells, and the bottom - from the yolk; The bottom of the cells are formed later.

Decoration.

At the highest mammals, including a person, gastrulation takes place somewhat differently, namely, by adminolation, but leads to the same result - the formation of a two-layer embryo. Demonmission is a bundle of the initial outer layer of cells, leading to the occurrence of the inner layer of cells, i.e. Entoderm.

Auxiliary processes.

There are also additional processes accompanying gastroaction. The simple process described above is an exception, and not a rule. The auxiliary processes include epibolia (faming), i.e. The movement of the cellular layers along the surface of the vegetative hemisphere of the egg, and the CONCRESSMENTATION - the change of cells on the extensive areas. One of these processes or they both can accompany both invagination and involution.

Gastralization results.

The final result of gastruption is to form a two-layer embryo. Outer layer The embryo (ectoderma) is formed by small, often pigmented cells that do not contain yolks; Further, such fabrics are developing from Etoderma as, for example, nervous, and upper skin layers. Inner layer (Entoderma) consists of almost non-pigmented cells that retain some yolk; They start mainly tissues, lining the digestive tract and its derivatives. However, it should be emphasized that there are no deep differences between these two germs. Etoderma gives the beginning of the Entoderma, and if some forms have a border between them in the area of \u200b\u200bBlastopore's lip, it is practically indistinguishable. In transplant experiments, it was shown that the difference between these tissues is determined only by their location. If the plots that normally remain ectodermal and gave the start of the derivative of the skin, to transplant the blastopore on the lip, they turn inside and become an entoderma that can turn into the digestive tract, light or thyroid gland.

Often with the advent of the primary intestine, the severity of the embryo is shifted, he begins to turn in his shells, and in it for the first time anterior-rear (head - tail) and Dorso-Ventral (spin - belly) of the axis of symmetry of the future organism.

Germinal sheets.

Etoderma, Entoderma and Mesoderm are distinguished on the basis of two criteria. First, by their location in the embryo in the early stages of its development: during this period, Ektoderma is always located outside, Entoderma - inside, and the Mesoderma appearing in the latter - between them. Secondly, according to their future role: each of these sheets gives rise to certain organs and tissues, and they are often identified by their further fate in the development process. However, we recall that during the occurrence of these sheets, no fundamental differences between them exist. In the experiments in transplanting germinal leaves, it was shown that initially each of them possesses the potency of any of the other two. Thus, their distinction is artificially, but they are very convenient to use when studying embryonic development.

Mesoderma, i.e. The medium germinal sheet is formed in several ways. It can occur directly from the Entoderma by the formation of nominal bags, like the lancing; Simultaneously with Entoderma, like a frog; Or by procempling, from ectoderma, like some mammals. In any case, at the beginning of the Mesoderma is a layer of cells lying in the space that originally occupied Blossocel, i.e. Between the ectoderma with the outer and entoderma from the inside.

Mesoderma is soon cleaved by two cell layers, between which the cavity called the whole is formed. From this cavity, the pericardial cavity, the surrounding heart, the pleural cavity surrounding the lungs, and the abdominal cavity, in which the digestion organs lie. The outer layer of mesoderm - somatic mesoderma - forms together with the ectoderma of the so-called. Somatoople. From the outer mesoderma develops cross-ripped muscles of the body and limbs, connecting tissue and vascular skin elements. The inner layer of mesodermal cells is called a splash mezoderma and, together with the Entoderma, it forms a gllankoplav. From this layer of mesoderm, smooth muscles and vascular elements of the digestive tract and its derivatives are developing. In a developing embryo, a lot of loose mesenchym (embryonic mesoderm), filling the space between the ectoderma and an entoderma.

At the chordovy, a longitudinal column of flat cells is formed - chord, main distinctive feature of this type. Cells of chords occur from the ectoderma in some animals, from the Entoderma from others and from the Mesoderm to third. In any case, these cells already at a very early stage of development can be distinguished from the rest, and they are located in the form of a longitudinal column over the primary intestine. The embryos of vertebrate chord serves as a central axis, around which the axial skeleton develops, and above it is the central nervous system. Most of the chords have a pure embryonic structure, and only at the lancing, the head chapter and plate, it remains throughout life. Almost all other vertebrates of chords are replaced by bone cells forming the body of developing vertebrae; It follows from this that the presence of chord facilitates the formation of a spinal column.

Derivatives of embryonic leaves.

The further fate of three germinal leaves is different.

Etoderma is developing: all nervous fabric; Outdoor layers of skin and its derivatives (hair, nails, dental enamel) and partially mucous oral cavity, nose cavities and anal hole.

Entoderma gives the beginning of the tip of the entire digestive tract - from the oral cavity to the anal opening - and all its derivatives, i.e. Timus, thyroid gland, parachite glands, trachea, light, liver and pancreas.

Mesoderm are formed: all types of connective tissue, bone and cartilage fabrics, blood and vascular system; all types of muscle tissue; Selective and reproductive systems, dermal skin layer.

An adult animal has very few such organs of entodermal origin, which would not contain nerve cells originating from Etoderma. In each important organ, derivatives of mesoderms are the blood vessels, blood, often muscles, so that the structural separation of germinal leaves is maintained only at the stage of their formation. Already at the very beginning of its development, all bodies acquire a complex structure, and they include derivatives of all germinal leaves.

Common body structure

Symmetry.

In the early stages of development, the body acquires a certain type of symmetry characteristic of this species. One of the representatives of the colonial rubs, Volvox, has a central symmetry: any plane passing through the center of Volvox, divides it into two equal halves. Among the multicellular, there is not a single animal with symmetry of this type. For intestinal and hashkin, radial symmetry is characterized, i.e. Parts of their bodies are located around the main axis, forming a cylinder as it were. Some, but not all planes passing through this axis divide such an animal into two equivalent halves. All iglozze at the distortion stage have double-sided symmetry, but in the process of development, radial symmetry is acquired, characteristic of an adult stage.

For all high-organized animals, bilateral symmetry is typical, i.e. They can be divided into two symmetric half only in the same plane. Since such arrangements of organs are observed in most animals, it is considered optimal for survival. The plane passing along the longitudinal axis from the ventral (abdominal) to the dorsal (spinal) surface divides the animal into two halves, the right and left, which are mirror mappings of each other.

Almost all non-advocated eggs have radial symmetry, but some lose it at the time of fertilization. For example, a spermatozoic penetration site is always shifted to the front, or head, the end of the future embryo. This symmetry is determined by only one factor - the gradient of the distribution of the yolk in the cytoplasm.

Bilateral symmetry becomes apparent as soon as the formation of organs begins during embryonic development. At the highest animals, almost all organs are laid in pairs. This refers to the eyes, ears, nostrils, light, limbs, most muscles, parts of the skeleton, blood vessels and nerves. Even the heart is laid in the form of a pair structure, and then its parts merge, forming one tubular organ, which subsequently twisted, turning into the heart of an adult individual with its complex structure. The incomplete merge of the right and left half of the organs is manifested, for example, in cases of debris or hare lips, occasionally found in humans.

Metamer (dismemberment of the body into similar segments).

The greatest success in the long-term evolution process was reached by animals with a segmented body. The metairic structure of ringed worms and arthropods clearly seen throughout their lives. In most vertebrates, the originally segmented structure in the future becomes little distinguishable, but they are clearly expressed in the embryonic stages of metamerh.

The lancing metamer is manifested in the structure of the agencies, muscles and gonad. For the vertebrate, the segmental arrangement of some parts of the nervous, excretory, vascular and support systems is characterized; However, in the early stages of embryonic development on this metamer, the leading development of the front end of the body is superimposed - so-called. Cefalization. If you consider a 48-hour chicken embryo grown in the incubator, then it can be revealed to him at the same time and double-sample symmetry and meta merit, most distinctly expressed at the front end of the body. For example, muscle groups, or somites, first appear in the head area and are formed sequentially, so rear is the least developed segmented comment.

Organogenesis.

In most animals one of the first differentiates the digestive channel. 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 anal hole. Other bodies that are included in the digestive system and respiratory organs are laid in the form of increased this primary intestine. The presence of the roof of the Archentheron, or the primary intestine, under the dorsal ectoderma causes (induces), possibly in conjunction with the chord, education on the dorsal side of the nucleation of the second most important system of the body, namely the Central nervous system. This happens as follows: first thickens the dorsal ectoderma and a nervous plate is formed; Then the edges of the nervous plate are raised, forming nervous rollers, which grow towards each other and ultimately closed, - as a result, a nervous tube occurs, the main nervous system. From the front of the nervous tube develops a brain, and the rest of it turns into a spinal cord. The cavity of the nervous tube as the nervous tissue is growing almost disappears - only a narrow central channel remains from it. The brain is formed as a result of protrusion, phenomena, thickens and the front of the front of the neural tube of the embryo. From the resulting head and spinal cord, paired nerves - skull, spinal and sympathetic are originated.

Mesoderma also undergoes changes immediately after its occurrence. It forms pair and metairene somites (muscle blocks), vertebrae, nephrotoma (primitive separation organs) and parts of the reproductive system.

Thus, the development of organ systems begins immediately after the formation of germinal leaves. All development processes (under normal conditions) occur with the accuracy of the most advanced technical devices.

Metabolism of germs

Embeds developing in aquatic environment are not required other covers, except for adolescent shells covering the egg. These eggs contain enough yolk to ensure germ nutrition; Shells to some extent protect it and help preserve metabolic heat and, at the same time, it is enough perverse, so as not to prevent free gas exchange (that is, the flow of oxygen and the output of carbon dioxide) between the embryo and the medium.

Offshire shells.

In animals, laying eggs on land or viviorbing, the germ is needed additional shells that protect it from dehydration (if the eggs are deposited on land) and supplying food, removal of finite exchange and gas exchange products.

These functions perform extragravating shells - amnion, chorion, a gusty bag and allantois, which are generated during the development process in all reptiles, birds and mammals. Chorion and Amnion are closely related by origin; They develop from somatic mesoderm and ectoderma. Chorion is the most outdoor sheath surrounding the embryo and three other shells; This shell permeates for gases and gas exchange occurs through it. Amnion protects the cells of the embryo from drying due to the amniotic fluid secreted by its cells. Yellow bag filled with a yolk, together with the yolk stem supplies a germ-digestiform nutrients; This shell contains a thick network of blood vessels and cells that produce digestive enzymes. The gusty bag, like allantois, is formed from a splashful mesoderm and entoderma: entoderma and mesoderma spread over the entire surface of the yolk, fading it, so that in the end the whole yolk is in the yolk bag. In reptiles and birds, Allantois serves as a reservoir for the end products of the exchange coming from the bud of the embryo, and also provides gas exchange. In mammals, these important functions perform a placenta - a complex organ formed by chorion vessels, which, raging, is included in the recesses (crypts) of the mucous membrane of the uterus, where they come into close contact with its blood vessels and glands.

At the man of the placenta fully ensures the breath of the embryo, food and allocating the exchange products in the blood flow of the mother.

Exodustemic shells are not saved in posthamsbrion period. In reptiles and birds, during hatching, dried shells remain in the egg shell. The mammal placenta and the rest of the extraordinary shells are thrown out of the uterus (rejected) after the birth of the fetus. These shells provided the highest vertebral independence from the aquatic environment and, of course, played an important role in the evolution of vertebrates, especially in the occurrence of mammals.

Biogenetic law

In 1828, K.Font Baer formulated the following provisions: 1) the most common signs of any large group of animals appear in the embryo earlier than less general features; 2) after the formation of the most common features, less common and so before the emergence of special features inherent in this group; 3) the embryo of any type of animal as it becomes becoming less like embryos of other species and does not pass through the late stages of their development; 4) A germ of a highly organized species may have similarity with a germing of a more primitive species, but never looks like an adult form of this species.

The biogenetic law formulated in these four positions is often interpreted incorrectly. This law simply claims that some stages of the development of highly organized forms have obvious similarities with some stages of the development of the subordinates on the evolutionary ladder of forms. It is assumed that this similarity can be explained by the origin of the general ancestor. About adult stages of lower forms say nothing. In this article, the similarity between the germ stages is implied; Otherwise, the development of each species would have to be described separately.

Apparently, in long history Life on Earth Wednesday played a major role in the selection of embryos and adult organisms, most adapted for survival. The narrow frames created by the medium in relation to possible fluctuations in temperature, humidity and supply of oxygen, reduced the variety of forms, leading them to relatively shared type. As a result, the similarity of the structure occurred, which underlies the biogenetic law, if we are talking about germinal stages. Of course, now existing forms in the process of germinal development are manifested by features, corresponding time, place and methods of reproduction of this species.

Literature:

Carlson B. Basics of Patten Embryology, t. 1. M., 1983
Gilbert S. Biology of development, t. 1. M., 1993

Splitting up - This is a sequential division of the zygotes without the growth of the generated cells - Blastomers

Cells resulting from crushing zigotes are called blastomeriaand halters separating them from each other are called furrows of crushing.

Crushing always passes according to certain rules:

The first rule reflect location spine crushingin Blastomere, namely:
- spindle crushing is located towards the highest length of the cytoplasm, free from inclusion.

Second rulereflect direction of furrow crushing:
- The furrows of crushing are always perpendicular to the spindle of the division.

Third Rule reflect the speed of passage of grooves Crushing:
- The speed of passing the furrow of crushing is inversely proportional to the number of yolk in the egg, i.e. In that part of the cell, where the yolk is not enough, the furrows will pass with a greater speed, and in the part where the yolk is greater, the speed of passage of crushing slows down.

Crushing depends OT the number and location of the yolk In the egg.

With a small content of the yolk, all the zygotes are crushed, only a part of the zygota free from the yolk is crushed with a significant amount.

In connection with this, the eggs are divided into horbitated (crushing completely) and meroblastic (with partial crushing).

Consequently, crushing depends on the amount of yolk and taking into account a number of signs divided:

By full of coverage process material zygotes on full and incomplete;

In relation to the size of the generated blastomer on the uniform and uneven

By consistency of divisions Blastomer - synchronous and asynchronous.

Full crushing may be uniform and uneven.

Full uniform Crushing is characteristic of eggs with small amount of yolk and its more or less uniform arrangement In a fertilized egg. Such a type is crushed by the lancing egg. In this case, the first furrow passes from an animal to the vegetative pole, two blastomer is formed; The second groove is also meridional, but passes perpendicular to the first, four blastomer are formed. The third is Equatorial, eight blastomers are formed. After that, there is an alternation of meridional and latitudinal furrow crushing. The amount of blastomers after each division increases to two (2; 4; 16; 32, etc.).

As a result of such a crushing, a spherical embryo is formed, which is called blastula. Cellswhich form the wall of Blastuly, called blastodermaand cavity inside blastocel. An animal part of Blastuly is called a roof, and the vegetative part is the bottom of Blastuly.

Full uneven Crushing is characteristic of eggs with average yolk contentlocated in the vegetative part. Such eggs are characteristic of the head chapter and amphibians. In this case, the type of crushing is formed blastomers of unequal sizes. In the animal pole, small blastomeres are formed, which are called micrometers, and in vegetative - large - macrors. The first two furrows, like the lancing, pass meridionally; The third groove corresponds to the Equatorial Barrout, but shifted from the equator to the animal pole. Since in the animal pole is free from the yolk of cytoplasm, then the crushing is faster and small blastomers are formed. The vegetative pole contains the bulk of the yolk, so the crushing furrows take place slower and large blastomeres are formed.

Incomplete crushing Characteristic for telolecital and centolecital eggs. In crushing takes part only part of the egg, free from yolk. Incomplete crushing is divided into discoidal (bony fish, reptiles, birds) and surface (arthropod).

Incomplete discoomal fraction telolecital eggs are divided, which large yolk Concentrated B. vegetative part. These eggs have a rudeness of the cytoplasm in the form of an embryonic disk of the splash on the yolk in the animal pole. Crushing occurs only in the region of the germ disk. The vegetative part of the egg filled with a yolk, participation in crushing does not accept. The thickness of the embryonic disk is insignificant, therefore spindlers are spinning at the first four divisions, they are horizontally, and crushing grooves pass vertically. One series of cells is formed. After several divisions, the cells become high and spindlers are located in them in the vertical direction, and crushing grooves pass parallel to the surface of the egg. As a result, the embryonic disk turns into a plate consisting of several cell rows. There is a small cavity in the form of a gap, which is similar to Blustocels between the embryonic disk and the yolk.

Incomplete surface crushing observed in centolecital eggs from large yolk in his middle. The cytoplasm in such egg cells is located along the periphery and a slight part of it in the center near the nucleus. The rest of the cell is filled with a yolk. Through the mass of yolk pass thin cytoplasmic chipconnecting peripheral cytoplasm with nearordide. Crushing begins S. core divisions As a result, the number of nuclei increases. They are surrounded by a thin rim of the cytoplasm, move to the periphery and are located in the cytoplasm free from the yolk. As soon as the nuclei fall into surface layerHe is divided according to their number to blastomeres. As a result of such crushing, the entire central part of the cytoplasm moves to the surface and merges with peripheral. Outside is formed solid Blastodermafrom which the embryo develops, and inside located yolk. Surface crushing peculiar eggs segmental articles.

On the nature of crushing the influence and properties of the cytoplasm that define mutual location Blastomer . This feature is distinguished radial, spiral and bilateral crushing.

With radial fraction Each top blastomer is located exactly under the bottom (shepherd, iglobler, lancing, etc.).

Under spiral crushing Each top blastomer is shifted relative to the lower half, i.e. Each top blastomer is located between two lower. In this case, blastomers are located like a spiral (worms, mollusks).

With bilateral fraction Through the zygot, you can spend only one plane, on both sides of which the same blastomeres will be observed ( round worms, ascidics).

Biological importance of crushing

• Transition to multicellularity
• Increase nuclear-cytoplasmic relationship

Characteristic features of crushing

Crushing as a special stage of animal ontogenesis has specific traitswhich are peculiar to most animals, but may not be absent in some groups.

1. Blastomers are divided very quickly (drosophila - every 20 minutes) and more or less synchronously.
2. Interfac is reduced to the S-period; In this regard, the transcription of its own genes of the embryo is completely suppressed, only maternal MRNAs stored in the egg cell are transcribed.
3. There is no growth period between divisions, so the total weight of the embryo does not grow.

For all these characteristics, the crushing of mammals is dramatically deviated from the typical one. Blastomers are divided from them slowly, synchronicity is broken after 1-2 divisions, at the same time its own genome of the embryo is activated.

Classification of fragmentation types

Based on a number of essential characteristics (determinism, completeness, uniformity and symmetry of division) allocate a number types of crushing. The types of crushing are largely determined by the distribution of substances (including yolk) along the cytoplasm of the egg and the nature of the intercellular contacts, which are set between blastomers.

Crushing can be: deterministic and regulatory; full (housing) or incomplete (meroblastic); uniform (blastomers are more or less the same in size) and uneven (blastomers are not the same in size, two - three dimensional groups are distinguished, commonly referred to as macro and micrometers); Finally, the character of symmetry distinguishes radial, spiral, various variants of bilateral and anarchic crushing. Each of these types allocate a number of options.

According to the degree of determinism

Determined

Non-deterministic (regulatory)

According to the degree of completeness

Hollow crushing

Planes of crushing separated egg completely. Highlight full uniform Crushing in which blastomers do not differ in size (this type of crushing is characteristic of gomolecital and alecital eggs) and full uneven Crushing in which blastomers can differ significantly in size. This type of crushing is characteristic of moderately telolemic Eggs.

Meroblastic crushing

• Discoidal

1. limited to a relatively small area at the animal pole,
2. the plane of crushing does not pass through the whole egg and do not capture the yolks.

This type of crushing is typical for telolecital eggs rich in yolk (birds, reptiles). Such fraction is also called discomalSince as a result of crushing on the animal pole, a small cell disc is formed (blastodisk).

• Surface

1. zigota core is divided in the central island of cytoplasm,
2. the resulting nuclei move to the surface of the egg, forming a surface layer of the nuclei (sycitial blastoderma) around the underlying yolk. Then the nuclei are separated by membranes, and blastoderma becomes cell.

This type of crushing is observed. in arthropods.

According to the type of symmetry of a crushing egg

Radial

Bilateral

There are 1 plane of symmetry. Typically for Askarida.

Anarchical

Blastomers are poorly interconnected, first form chains or shapeless mass; often one species meet different variants The location of blastomer. Typically for intestinal.

Literature

• Belousov L.V. Basics of general embryology. - Moscow: Moscow University Publishing House: Science, 2005. - ISBN 5-211-04965-9
• Tokin bp General embryology: studies. For biol. specialist. University. - 4th ed., Pererab. and add. - M.: Higher. Shk., 1987. - 480 p.

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