Classification of types of crushing. Splitting up

Material taken from the site www.hystology.ru

Fragmentation is a further process of development of a unicellular zygote, during which a multicellular blastula is formed, which consists of a wall - a blastoderm and a cavity - a blastocoel. In the blastoderm, the roof, the bottom and the marginal zone located between them are distinguished. In the process of mitotic division of the zygote, new cells are formed - blastomeres, which remain closely associated with each other.

At the initial stage of cleavage, a multicellular organism is similar in size to a zygote, since its blastomeres, dividing, do not reach the size of the original cell. The nature of crushing c. the evolutionary series of chordates is different, which is largely due to the number and distribution of the yolk in the oocytes.

Crushing can be complete (holoblastic) or partial (meroblastic). In holoblastic cleavage, all the material of the zygote takes part, in meroblastic cleavage, only that zone that is devoid of yolk.

Completecrushing is classified into uniform and uneven. Complete uniform cleavage (Fig. 43) is characteristic of eggs with a small amount of yolk (oligolecital) and yolk evenly distributed throughout the cytoplasm of the cell (isocytal). Lancelet, roundworm, etc. can serve as an example of such cleavage. In a fertilized egg, two poles are distinguished: the upper - animal and lower - vegetative.

After fertilization, the yolk, a small amount of which was evenly distributed to the entire cytoplasm, moves to the vegetative pole. The first cleavage furrow runs in the meridional direction and divides the zygote into two blastomeres, which correspond to the future left and right half of the embryo's body. The second cleavage groove also runs meridionally at right angles to the first, and now the embryo consists of four blastomeres. The third cleavage groove has an equatorial direction, so each blastomere is divided into two parts. Such an embryo is built of eight blastomeres, while four of them were formed from the vegetative pole of the zygote, and therefore they contain the entire yolk of the zygote and are large in size. These blastomeres correspond to the back of the body; animal - four - front.

Then two meridional grooves appear, dividing the embryo into 16 blastomeres. The fifth cleavage is two latitudinal grooves, in the embryo there are 32 blastomeres. They start

Fig. 43. Layout of crushing grooves in the lancelet (A):

I - an embryo at the stage of two blastomeres; II - an embryo at the stage of four blastomeres; III - an embryo at the stage of eight blastomeres; IV - an embryo at the stage of 16 blastomeres; V - an embryo at the stage of 32 blastomeres; VI - embryo at the stage of 64 blastomeres; VII - an embryo at the stage of 128 blastomeres. Blastula structure (B): 1 - blastoderm; 2 - blastocoel; 3 - bottom; 4 - edge zone; 5 - the roof of the blastula.

gradually move away from each other, contacting only with the side surfaces. Inside the embryo, at first a small cavity is formed - the blastocoel, which gradually increases. After the sixth cleavage, 64 cells are formed, with the cleavage furrows running meridionally. After the seventh cleavage (four latitudinal grooves appear), the embryo consists of 128 blastomeres.

Later, the synchronicity in the division of the embryo is disturbed, the blastomeres move to the periphery and are located in one layer, forming a blastoderm, and a blastocoel forms in the center of the embryo.

The crushing ends with the formation of a blastula, the shape of which resembles a ball filled with liquid. The wall of the ball is formed by the cells of the blastoderm.

Thus, with complete uniform cleavage, the material of the entire zygote participates in division and after each division (cleavage) the number of cells (blastomeres) doubles.

In the blastoderm, the following areas are differentiated: a roof built of relatively small blastomeres; the bottom is the larger blastomeres and the marginal zone lying between the bottom and the roof of the blastula.

Fig. 44. Complete irregular fragmentation of the amphibian zygote. Blastula structure:

1 - micrometers; 2 - macrocytes; 3 - blastoderm; 4 - blastocoel.

Complete irregular cleavage is characteristic of mesolecital (average amount of yolk) and telolecital (yolk is located at the vegetative pole) oocytes. An example of this type of cleavage is the cleavage of an amphibian zygote (Fig. 44).

Crushing begins with the formation of two meridional crushing grooves following each other at right angles. They quickly divide the yolkless animal pole of the zygote into two and then into four small blastomeres. The vegetative pole, which contains the entire yolk of the zygote, is cleaved much more slowly, and the blastomeres that arise here are larger in size.

The third furrow runs closer to the animal pole of the zygote and has a latitudinal direction. Latitudinal cleavage grooves are replaced by meridional ones, and very soon asynchrony and tangentiality appear (division of blastomeres into

Fig. 45. Partial (discoidal) cleavage of the chicken embryo:

A, B - crushing stages - top view (A - two meridian grooves, IN - later stage of crushing); FROM - section of the embryonic disc (a, b, c, - marginal cells located on the yolk; d, e, f, g, h - cells isolated from the yolk).

plane parallel to the surface of the zygote) in cleavage, so it ends with the formation of a multilayer blastula. The roof of the blastula is built of small blastomeres called micromeres. The bottom consists of large blastomeres - macromeres. All yolk is localized in macromeres. The blastocoel is shifted towards the animal pole and reduced in size. Blastula, formed in the process of holoblastic (complete) crushing, is called celloblastula.

Partial, or meroblastic (discoidal), crushingcommon in fish, reptiles, birds, and characteristic of polyilecital (much yolk) and telolecital eggs (Fig. 45).

Only the surface layer of the animal pole of the zygote, devoid of yolk, participates in cleavage, since the cell nucleus and cytoplasm without yolk are located here. The rest of the zygote is loaded with yolk and therefore does not split.

The first two meridional furrows pass through the animal pole at an angle to one another. They do not extend to the vegetative pole, and therefore the latter remains undivided into blastomeres. The meridional furrows are replaced by latitudinal and tangential ones. Blastomeres formed during cleavage are located on the yolk in one layer. This layer is called the embryonic disc, so the cleavage is called discoidal.

To build the body of the embryo, only its central part is used - the embryonic flap. The rest of the embryonic disc participates in the formation of temporary (provisional) organs - embryonic membranes, which create favorable conditions for the development of the embryo.

Cleavage ends with the formation of a blastula, in which the blastocoel looks like a narrow slit and is shifted to the animal pole. The roof of the blastula is built of blastomeres. The marginal zone is the intensively dividing cells (blastomeres) of the peripheral zone of the embryonic disc. The bottom is the yolk of the zygote vegetative pole, undivided into blastomeres. This type of blastula is called discoblastula.

Thus, from the material presented, it follows that in chordates there is a certain relationship between the amount of yolk in oocytes and the nature of cleavage. It changes from complete (holoblastic) to partial (meroblastic), and blastula - from celloblastula to disco blastula.

The general properties of the developing embryos of all classes of animals at the stage of cleavage are a gradual increase in the number of cells, and hence DNA, since daughter cells are always diploid; an increase in the area of \u200b\u200bcell surfaces; increasing regional differences in cell populations.

Introduction

Technological part

Selection of equipment for the 1st stage of crushing

Crushers that are suitable for installation in 1 stage of crushing are selected according to the initial data:

1. According to the ultimate strength of the material in compression σ comp\u003d 50 10 6 Pa

2. By the maximum size of a piece of source material δ n.mah\u003d 0.8m.

The choice of a crushing or impact machine can be made approximately according to Table 1.

Table 1

SchDS-12x15.

With the width of the discharge slot and\u003d 110mm capacity is equal to:

where V- the value of the crusher productivity;

K p - coefficient of grindability;

Change in the width of the discharge slot;

and - the width of the unloading slot.

- we accept 1 crusher

0 55 110 165 220 δ, mm

Fig. 2. Characteristics of the dispersion composition of the starting material

With the size of the gap and\u003d 110mm maximum particle size at the exit from the crusher, according to Fig. 2 will be equal to:

Grinding degree is equal to:

Then at Кδ \u003d 1.2 (see Fig. 3.7) and G \u003d25.79 kg / s,

crusher motor power will be:

What does not exceed the value N dvselected crusher ( N dv\u003d 160kW)

Therefore, we take 1 crusher SCHDS-12x15s N dv\u003d 160 kW (for 1 crusher 160 kW).

Comparing these data, we choose a crusher M-13-11.

Let's construct a curve of the dispersion composition of the material at the exit from the crusher To do this, we calculate the values \u200b\u200brequired for the calculation:

The peripheral speed of the rotor along the tops of the hammers

The mass of a perfect hammer

Let us calculate the final particle size for three values \u200b\u200bof δ n:

1.165 mm; 2.110mm; 3.55mm.

In the first case, δ n \u003d 165mm;

In the second case, δ n \u003d 110mm;

In the third case, δ n \u003d 55mm;

0 55 110 165 220 δ, mm

Fig. 3. Characteristics of the dispersion composition of the starting material

We select a ball mill for the final particle size after grinding. It is recommended to load material into it δ n.max ≤ 6 · 10 -3 m. From fig. 3 it follows that 20% of the material exiting the crusher is made up of particles larger than 6 · 10 -3 m, this fraction of the material must be crushed to a size of δ n.max ≤ 6 · 10 -3 m.

The coarse fraction of the material selected on the screen is returned for regrinding to a hammer mill M-13-11.

Then the total capacity of the crusher will be:

The number of crushers required to ensure the initial volumetric capacity is:

- we accept 1 crusher.

With δ k.ma x \u003d 14.6 mm, the value of α will be:

Finally, we take α \u003d 32mm.

The crusher motor power will be:

What does not exceed the value N dvselected crusher ( N dv\u003d 130kW). Therefore, we take 1 crusher M-13-11 with N dv\u003d 130 kW.

Dumping height of material into the crusher:

Environmental protection

Environmental issues in cement and lime production primarily include the following:

Air emissions

Energy and fuel consumption

Wastewater

Solid waste generation

1. Requirements for the sanitary protection of water resources.

1.Discharge of sewage and drainage (hereinafter - sewage) waters pumped out from mines and open-pit mines after use in enrichment processes at concentrating and briquette factories, as well as household wastewater into water bodies is allowed only after their effective purification and disinfection with laboratory control of suspended and substances dissolved in water. The design of treatment facilities should provide a calculation of the settling time of wastewater with a justification for the use (or refusal to use) coagulants and flocculants. It is not allowed to put into operation technological equipment before the commissioning of wastewater treatment facilities.

2. The productivity of water treatment facilities should be calculated for a possible increase in the capacity of enterprises (at least 20 years) in accordance with the requirements of SNiP "Water supply. External networks and structures. Design standards" and SNiP "Sewerage. External networks and structures. Design standards ".

3. Water supply schemes for enterprises should provide for the organization of reverse cycles of water use for technical purposes.

4. Discharge of wastewater from enterprises into water bodies must be carried out in strict compliance with the requirements for the quality of discharged water at the first point of water use downstream in accordance with SanPiN "Protection of surface waters from pollution", SanPiN "Sanitary standards for the maximum permissible content of harmful substances in water of water bodies household and drinking and cultural and household water use "and additions to it," Methodological guidelines for the sanitary protection of water bodies from wastewater pollution from coal industry enterprises ".

5. Rivers, reservoirs, lakes, streams, ponds, artificial canals, as well as underground waters used for drinking, cultural, domestic and balneological purposes are subject to sanitary protection.

6. Surface wastewater from the territory of enterprises and washings from the floors of industrial premises before being discharged into water bodies should be subjected to local treatment or sent to general treatment facilities.

7. Treatment facilities of enterprises must comply with the "Regulatory requirements for the design and construction of enterprises, buildings and structures in the northern construction and climatic zone, permafrost and negative temperatures."

2. Requirements for the sanitary protection of atmospheric air and land resources.

1. Sanitary protection of atmospheric air in areas where lime industry enterprises are located should be carried out in accordance with SanPiN "Hygienic requirements for the protection of atmospheric air in populated areas", GOST "Nature protection. Atmosphere. Rules for establishing permissible emissions of harmful substances by industrial enterprises". Operating enterprises must have maximum permissible emissions standards, agreed and approved in the prescribed manner.

2. Projects for operation, extinguishing and development of combustible raw materials should be developed in accordance with industry guidelines.

3. Raw materials warehouses should be located outside settlements and enterprises from the leeward (for prevailing winds) side to the enterprise, residential buildings, public and municipal buildings of the side.

4. To prevent air pollution by combustion products and dust, effective measures must be taken to prevent spontaneous combustion. The use of burning raw materials is prohibited and must be extinguished.

5. During firefighting, the concentration of carbon monoxide and sulfur dioxide should be measured at workplaces at the beginning of each shift. If the content of harmful gases exceeds the permissible limits, measures must be taken to ensure the safety of work.

6. The use of solid waste in industries, including the construction industry, is possible only with the permission of the State Sanitary and Epidemiological Supervision authorities.

7. When transporting lime in railway wagons and on flatcars, measures must be taken to prevent spills and dust blowing off.

8. It is prohibited to store and unload lime and rock in unspecified places during their transportation by cable cars, automobile, conveyor or rail transport.

9. In the event of liquidation of an enterprise, the Feasibility Study for its closure shall provide for measures and means to eliminate the adverse environmental consequences of the termination of activities.

Occupational Safety and Health

1.Safety

1. In accordance with the Guidelines "Hygienic criteria for assessing working conditions in terms of hazard and hazard factors of the working environment, the severity and intensity of the labor process." The head of the enterprise is obliged to provide workers employed in industries with harmful and hazardous working conditions with collective and personal protective equipment, washing and disinfecting preparations in accordance with the "Standard industry norms for free distribution of special clothing, special footwear and other personal protective equipment to workers and employees" and GOST "Personal protective equipment for workers. General requirements and classification", teach the rules of their use and control the use. The use of PPE should not replace the requirements for the development and implementation of technical measures to reduce the levels of hazardous and harmful production factors to acceptable hygienic standards.

2. To protect the respiratory system from dust, all persons engaged in work where it is possible to contain it in the air above the MPC level must be provided with respirators that meet the requirements of GOST SSBT "Personal protective equipment for respiratory organs". The modes of use of respirators should be established taking into account the concentration of dust in the air of the working area and the time spent in them by workers and agreed with the authorities of the State Sanitary and Epidemiological Supervision. Manufacturing operations that are not permissible without respirators should be identified. It is allowed to use respirators only of those types, the technical characteristics of which are agreed with the bodies of the State Sanitary and Epidemiological Supervision.

3. Workers exposed to intense noise, including in underground mine workings, must use personal protective equipment that meets the requirements of GOST "Personal protective equipment for hearing organs. General technical conditions". When choosing personal protective equipment, it is necessary to take into account the spectral characteristics of acoustic vibrations (App. 6).

4. Workers must be provided with personal protective equipment against vibration (anti-vibration gloves, shoes, etc.). Individual protection equipment against vibration must comply with GOST "Personal protection equipment for hands from vibration. General technical requirements and test methods" and GOST "Special vibration protection footwear. General technical requirements".

5. To protect the skin from the effects of harmful substances, high or low temperature of the surfaces of the controls, workers should be provided with protective equipment that meets GOST SSBT "Special protective clothing. Personal protective equipment for legs and hands. Classification". Mittens, gloves, protective ointments and pastes that meet the requirements of GOST SSBT "Dermatological protective equipment. Classification. General technical requirements" should be used as PPE for the skin of hands from dust and harmful substances.

6. Storage, use, repair, cleaning and other types of preventive treatment of special clothing, footwear and other personal protective equipment must be carried out in accordance with the requirements of the "Instruction on the procedure for providing workers and employees with special clothing, special shoes and other personal protective equipment." Removal of PPE from the facility is prohibited.

7. Waterproof overalls and wet special shoes must be dried at a temperature not exceeding 50 ° C after each shift. Leather special shoes should be lubricated with a softening ointment after drying.

8. Special footwear should be washed using 5% chloramine B solution or 1% fiton solution for 15 minutes. or other approved disinfectants. Respirators, safety helmets, braces and socks should also be sanitized with disinfectants.

9. Overalls and special footwear for patients with pustular skin diseases and fungal diseases of the feet and hands should be disinfected daily with 5% chloramine B solution or other disinfectants.

2. Safety requirements during work

1. The crusher is obliged to work in the established overalls and footwear, use personal protective equipment: respirator, anti-noise liners, protective helmet.

2. The crusher is obliged to: be attentive and comply with the requirements of the established sound and light signals; move along established walkways and walkways; keep your workplace clean, not allowing it to be cluttered with foreign objects; when handing over the shift, report to the shift foreman about malfunctions in the operation of the crusher and the measures taken to eliminate them, make an entry in the shift handover log.

3. The crusher is put into operation by the crusher in 1 - 2 minutes. after giving the installed sound or light signals. With remote centralized control of technological equipment, the crusher is started by the plant dispatcher from the control panel. Before starting the equipment, a warning light and sound signal is given. The crusher, upon receiving the signals, must move to a safe distance from the equipment. Signals for the signals supplied must be posted at the crusher workstation.

4. Start-up of the crusher and its operation are carried out in accordance with the instruction manual. If there is unusual noise or knocking when starting, indicating a malfunction of the crusher, the crusher should be turned off, reported to the master and not turned on until the malfunctions are eliminated.

5. Remove and install barriers; tighten springs, bolts; lubricate bearings by hand, put on and take off V-belts; adjust the size of the discharge slot; clean the crusher, inspect the mechanisms; it is allowed to carry out repair work only after the crusher has completely stopped, the electric motor is disconnected from the mains, the fuses have been removed. Disconnect from the network with dielectric gloves, standing on an insulating mat. Place the sign "Do not switch on! People are working!" On the starting device.

6. When the crusher is in operation, it is prohibited to: look into the mouth of the crusher; inspect mechanisms near moving parts; leave without the permission of the foreman from his workplace.

7. In the event of a power outage, the crusher is obliged to disconnect the electric motor from the mains and completely clean the crushing chamber of material.

8. The crusher must spend most of the time in a room (cabin) that provides an adequate view of the service area, equipped with a control panel and a telephone. If, according to the working conditions, the crusher is outside the cabin, then he must use personal protective equipment: a protective helmet, anti-noise liners, a respirator.

9. Large non-crushed pieces of stone must be removed from the throat using lifting means with special devices. It is forbidden to remove pieces of rock stuck in the working space of the crusher by hand and crush them with sledgehammers.

10. To prevent accidents, it is necessary not to overload the crusher, monitor the operation of the centralized lubrication of the cone crusher, monitor the condition of the pulley and flywheel of the jaw crusher.

11. When performing repair work on crushers, lowering the crusher into the working space of the crusher must be carried out using ladders and using safety belts. At the same time, a temporary platform should be arranged above the crusher's inlet to prevent various objects from falling onto people. Attach the safety belt only to permanent, securely reinforced structures. Anchoring points should be marked on structures.

12. When performing locksmith work, the crusher must use serviceable tools. Hammers, hammers must be firmly attached to wooden handles. Wrenches must match the size of the nuts and bolts. It is prohibited to extend the key with another key. If necessary, use a wrench with an extended handle.

13. At the end of the repair, the crusher must remove tools, spare parts and other items from the crusher.

14. The crusher should be put into operation after the repair under the supervision of the foreman or the foreman who performed the repair work.

Technical and economic part

When choosing preliminary equipment for the first stage of crushing, the following was taken into account:

The ultimate strength of the material in compression σ compress \u003d 50 · 10 6 Pa;

The size of the loaded piece δ n.max, mm;

Minimum width of the unloading slot α, mm, taking into account regulation Δα, mm;

Compliance with original performance;

Minimum engine power N dv .

For first stage crushing is suitable for crushers SCHDS-12x15; KKD-1000/150 and DDZ-16.

Table 8

Crusher options for 1 crushing stage

Comparing these data, we choose a crusher ShchDS-12x15, because the other 2 crushers consume power twice the selected one and the maximum particle size at the crusher outlet in relation to the others.

For second stage material crushing is suitable for KSD-1750Gr crushers; SchDS-6x9; DDZ-6 and M-13-11.

Table 9

Crusher options for stage 2 crushing

Comparing these data, we choose a crusher M-13-11. Other crushers also pass in terms of power, but the maximum chunk size at the exit of the crusher is the minimum value of the selected crusher. As a result, no additional crushing stage is required.

For second stage grinding with the required power value (1.3 ... 1.5) N shz\u003d 334 ... 385.5 kW we choose a dry ball mill ShBM-287/470 from N dv\u003d 410kW, since other crushers have a large power reserve ( ShBM-287/410 from N dv\u003d 650kW and ShBM-320/570 from N dv\u003d 700kW) or do not pass in terms of power and the mass of the loaded balls is less than the required one.

Application.

Table 1

Introduction

CRUSHING - the process of breaking up pieces of ore, coal and other solid material in order to obtain the required size (more than 5 mm), granulometric composition or degree of mineral disclosure.

Crushing is based on the action of external forces - compression, tension, bending or shear, which are manifested to the maximum extent in weakened sections of a piece, caused by defects in its structure (size, shape), layering, porosity and fracturing. For crushing processes, the most important characteristics are strength (strength) and crushing of pieces. For the energy evaluation of crushing, several hypotheses have been put forward and used in calculations: about the proportionality of the elementary work of crushing to the increment in the surface area of \u200b\u200ba piece or the square of its diameter; about the proportionality of the elementary work of deformation of a piece to a change in its initial volume or cube of its diameter; about the proportionality of the elementary work spent on crushing a piece, a change in its initial volume and an increase in the surface area of \u200b\u200bthe piece, about the relationship between the stress at the ends of the crack of the piece and the critical length of the crack; on the proportionality of the elementary work of crushing the geometric mean increment in volume and surface area.

Preferred fields of application of the hypotheses: for coarse crushing (the surface increment is small), the crushing work is determined by Kirpichev's hypothesis; with fine crushing (grinding, abrasion) - according to Rittinger's hypothesis. Bond's law is fairly accurately applicable for average fragmentation. The theory of crushing makes it possible to quantitatively describe crushing processes in machines of various types and their parameters - crushing work, engine power, productivity, greatest crushing forces, etc.

Crushing can be carried out by the following methods: crushing, which occurs as a result of exceeding the deformation stresses, the ultimate compressive strength of the material; splitting - due to wedging (stretching) and subsequent rupture of the piece; kink - due to bending; cutting off - due to shear; abrasion, manifested to a small extent - due to shear and subsequent cutting; impact - due to the action of compressive, tensile, bending and shear stresses. Crushing is used, as a rule, for large and medium crushing of hard rocks and coals, splitting or impact - mainly for brittle and viscous rocks (coal, limestone, asbestos ores, etc.). The tensile strength of the pieces is tens of times less, however, for design reasons, in modern crushing practice, crushing is the main destructive effect.

According to the type of implementation of crushing methods, it is divided into mechanical (the most common), pneumatic, or explosive, electrohydraulic, electro-pulse, electrothermal, aerodynamic, according to the method of impact on the material - into static and dynamic. Static methods of mechanical crushing - crushing, splitting, breaking. It is carried out in jaw, cone and roller crushers. Dynamic crushing methods - impact, abrasion (impact crushers), splitting, crushing (rod crushers-disintegrators). According to the size of the final product, large (100-350 mm), medium (40-100 mm), fine crushing (5-40 mm) are distinguished. By technological purpose - preparatory (for preparing the material for enrichment or other types of processing), final (when the crushing products are commercial, for example, when producing high-quality coals), selective (in which one of the components of the material, which is less durable, under the influence of the same external force is destroyed more intensively than another, more durable).

The crushing process is usually combined with preliminary screening, when all the source material first goes to the screen, and only large pieces are sent to the crusher, the undersize product of the screen goes further, bypassing the crusher. There are open and closed crushing cycles.

With an open crushing cycle, the product passes through the crusher only once. When closed, the product from the crusher goes to the screen, insufficiently crushed pieces are again sent to the crusher for additional crushing, and small pieces - for further processing. With a closed crushing cycle, the product quality is improved (the particle size distribution is uniform), the energy consumption and wear of the crusher parts are reduced. Depending on the required size of the finished product to obtain a high degree of crushing, several crushing stages are used sequentially: when crushing non-ferrous metal ores, usually 2, 3 or 4, ferrous metal ores and coal of 2 or 3 stages.

The development of the theory of crushing is associated with the clarification of the laws and the design development of wear-resistant machines and devices with minimum specific crushing energy consumption.

Technological part

Selection of equipment for stage I - crushing

The biological significance of crushing

Transition to multicellularity
Increased nuclear-cytoplasmic ratio

Crushing characteristics

Fragmentation as a special stage of animal ontogenesis has characteristic features that are characteristic of most animals, but may be absent in some groups.

Blastomeres divide very quickly (in Drosophila, once every 20 minutes) and more or less synchronously.
Interphase is reduced to S-period; in this regard, the transcription of the embryo's own genes is completely suppressed, only maternal mRNA stored in the oocyte are transcribed.
There is no growth period between divisions, so the total mass of the embryo does not grow.

For all these characteristics, the cleavage of mammals sharply deviates from the typical one. Their blastomeres divide slowly, the synchronicity is disrupted after 1-2 divisions, at the same time the embryo's own genome is activated.

Classification of crushing types

On the basis of a number of essential characteristics (the degree of determinism, completeness, uniformity and symmetry of division), a number of types of crushing... The types of cleavage are largely determined by the distribution of substances (including yolk) over the cytoplasm of the egg and the nature of intercellular contacts that are established between blastomeres.

Fragmentation can be: deterministic and regulatory; complete (holoblastic) or incomplete (meroblastic); uniform (blastomeres are more or less the same in size) and uneven (blastomeres are not the same in size, two or three size groups are distinguished, usually called macro- and micromeres); finally, according to the nature of symmetry, radial, spiral, various variants of bilaterized and anarchic fragmentation are distinguished. In each of these types, a number of options are distinguished.

By the degree of determinism

Deterministic

Non-deterministic (regulatory)

(Blastomeres are totipotent)

By the degree of completeness of divisions

Holoblastic crushing

The crushing planes separate the egg completely. Allocate full uniform cleavage, in which blastomeres do not differ in size (this type of cleavage is characteristic of homolecital and alecitic eggs), and complete uneven cleavage, in which blastomeres can vary significantly in size. This type of crushing is typical for moderate telolecital eggs.

Meroblastic crushing

Discoidal

limited to a relatively small area at the animal pole,
crushing planes do not pass through the entire egg and do not capture the yolk.

This type of crushing is typical for telolecital eggs rich in yolk (birds, reptiles). This fragmentation is also called discoidal, since as a result of cleavage at the animal pole, a small disc of cells (blastodisc) is formed.

Superficial

the nucleus of the zygote is divided in the central islet of the cytoplasm,
the resulting nuclei move to the surface of the egg, forming a superficial layer of nuclei (syncytial blastoderm) around the central yolk. Then the nuclei are separated by membranes, and the blastoderm becomes cellular.

This type of crushing is observed in arthropods.

By the type of symmetry of a crushing egg

Radial

Bilateral

There is 1 plane of symmetry. Typically for roundworm.

Anarchic

Blastomeres are weakly connected to each other, at first they form chains or a shapeless mass; often, one species has different variants of the location of blastomeres. Typically for coelenterates.

Literature

Belousov L.V. Fundamentals of General Embryology. - Moscow: Moscow University Publishing House: Science, 2005. - ISBN 5-211-04965-9
Tokin B.P. General embryology: Textbook. for biol. specialist. un-tov. - 4th ed., Rev. and add. - M .: Higher. shk., 1987 .-- 480 p.

Embryogenesis
Developmental biology
Stages	Zygote Morula Blastula (Organisms: Diploblasts Triploblasts) Blastocyst Gastrula Neirula Embryo
Processes	Egg crushing Blastulation Gastrulation (delamination, intussusception, immigration, epiboly) Neurulation Organogenesis
Germ leaves	Ectoderm Endoderm Mesoderm
Cell differentiation	Blastomere Embryoblast Trophoblast Epiblast Hypoblast

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anarchic fragmentation - ANARCHIC EMBRYOLOGY ANARCHIC CRUSHING [DISORDER, CHAOTIC] - metagenetic jellyfish eggs crushing - Oceania armata The first furrow of the cleavage is meridional, incising; it appears at the animal pole. The second furrow is also ... ... General Embryology: Glossary of Terminology

crushing hetero-square - ANIMAL EMBRYOLOGY HETEROSQUARE CRUSHING - crushing of annelids, molluscs, nemertines, planarian. Uneven spiral cleavage, when the cells of the main quartet (the first four blastomeres) are not the same in size, then their derivatives also ... ... General Embryology: Glossary of Terminology

asynchronous crushing - ANIMAL EMBRYOLOGY CRUSHING ASYNCHRONOUS - crushing telolecital eggs (amphibians). The division of vegetative blastomeres is slower in comparison with the blastomeres of the animal pole ... General Embryology: Glossary of Terminology

crushing bilateral - ANIMAL EMBRYOLOGY BILATERAL CRUSHING [BILATERAL SYMMETRIC] - eggs crushing of nematodes, rotifers, ascidians. It is characterized by the appearance of bilateral symmetry in the arrangement of blastomeres already at the early stages of cleavage. Each blastomere ... ... General Embryology: Glossary of Terminology

holoblastic crushing - ANIMAL EMBRYOLOGY GOLOBLASTIC CRUSHING [COMPLETE] - crushing of eggs of alecitic (flatworms), isocytal type (lancelet) and some egg cells of telolecitic type (amphibians). All parts of the zygote are crushed. When crushing, all ... ... General Embryology: Glossary of Terminology

Splitting up is a series of mitotic divisions of the zygote with the formation of many smaller daughter cells (blastomeres). Mitotic divisions of the zygote, and subsequently of blastomeres, occur with an increase in the number of cells, but without an increase in their mass, therefore they are called cleavage.

In man splitting up has no fundamental differences from that of other vertebrates, but proceeds much more slowly. Cleavage is complete, or holoblastic (cleavage grooves pass through the entire embryo), uneven (as a result of cleavage, daughter cells are formed - blastomeres of unequal size) and asynchronous (different blastomeres are cleaved at different rates, therefore the embryo contains an odd number of cells at separate stages of cleavage) ...

First division of crushing lasts on average about 30 hours, the subsequent ones are shorter (about 20-24 hours). In the process of cleavage, the embryo moves along the fallopian tube and, on the 6th day of development, enters the uterine cavity.

Blastomeres of the first generation in humans, like the zygote, are totipotent (each blastomere is capable of developing into a full-fledged organism). Before the stage of 8 blastomeres, the embryonic cells form a loose, unformed group, and only after the third division they establish tight contacts with each other, forming a compact cell ball of 16 blastomeres, called morula. Compaction creates conditions for the development of the outer cell mass and the inner cell mass.

The last - This is the material of the future body of the embryo (embryoblast) and extraembryonic organs. Blastomeres of the outer cell mass - small and numerous (there are about 10 times more of them than the cells of the inner cell mass), are the source of the development of trophoblast.

When morula enters the proximal part of the fallopian tube and then into the uterine cavity, through its transparent zone the fluid contained in the fallopian tube and uterus begins to penetrate. Morula cavitation occurs. First, fluid accumulates between cells and forms small gaps, which then merge into a single cavity inside the morula (blastocoel). Trophoblast cells, which secrete liquid, also participate in the formation of fluid and cavitation.

From the moment the cavity appears, the embryo is called blastocyst... The cells of the inner cell mass of the blastocyst are localized at one of the poles and face the cavity. The cells of the outer cell mass are flattened and, limiting the cavity, form the blastocyst envelope - the trophoblast. During the period of movement of the crushing embryo along the fallopian tube, the fact that the remaining transparent zone prevents the blastocyst from sticking to the walls of the tube is of great importance and the embryo enters the uterine cavity. Here he is freed from the transparent zone and begins to implant (submerge) into the lining of the uterus. Embryo implantation proceeds in parallel with gastrulation.

The essence of the crushing stage. Cleavage is a series of successive mitotic divisions of the zygote and further blastomeres, ending in the formation of a multicellular embryo - blastula. The first division of cleavage begins after the unification of the hereditary material of the pronuclei and the formation of a common metaphase plate.

The cells that arise during cleavage are called blastomeres (from the Greek. Blaste-sprout, primordium). A feature of mitotic cleavage divisions is that with each division the cells become smaller and smaller until the ratio of the volumes of the nucleus and cytoplasm, which is usual for somatic cells, is reached. In the sea urchin, for example, this requires six divisions and the embryo consists of 64 cells. Cell growth does not occur between successive divisions, but DNA is necessarily synthesized.

All DNA precursors and essential enzymes are accumulated during ovogenesis. As a result, mitotic cycles are shortened and divisions follow each other much faster than in ordinary somatic cells. At first, the blastomeres are adjacent to each other, forming a cluster of cells called morula. Then a cavity is formed between the cells - a blastocoel, filled with fluid. The cells are pushed back to the periphery, forming a blastula wall - blastoderm. The total size of the embryo by the end of cleavage at the blastula stage does not exceed the size of the zygote.

The main result of the cleavage period is the transformation of the zygote into a multicellular single-shift embryo.

Cleavage morphology. As a rule, blastomeres are located in a strict order relative to each other and to the polar axis of the egg. The order, or method, of crushing depends on the amount, density and distribution of the yolk in the egg. According to the rules of Sachs - Hertwig, the cell nucleus tends to be located in the center of the cytoplasm free of yolk, and the spindle of cell division - in the direction of the greatest extent of this zone.

In oligo- and mesolecital eggs, cleavage is complete, or holoblastic. This type of cleavage occurs in lampreys, some fish, all amphibians, as well as in marsupials and placental mammals. With full crushing, the plane of the first division corresponds to the plane of bilateral symmetry. The plane of the second division runs perpendicular to the plane of the first. Both furrows of the first two divisions are meridian, i.e. begin at the animal pole and spread to the vegetative pole. The egg cell is divided into four more or less equal in size blastomeres. The plane of the third division runs perpendicular to the first two in the latitudinal direction. After that, uneven cleavage appears in mesolecital eggs at the stage of eight blastomeres. At the animal pole there are four smaller blastomeres - micromeres, at the vegetative pole - four larger ones - macromeres. Then the division goes again in the meridian planes, and then again in the latitudinal ones.

In polycytal oocytes of teleost fishes, reptiles, birds, as well as monotremes, the cleavage is partial, or meroblastic; covers only the yolk-free cytoplasm. It is located in the form of a thin disc at the animal pole; therefore, this type of fragmentation is called discoidal.

When characterizing the type of cleavage, the relative position and rate of division of blastomeres are also taken into account.

If the blastomeres are arranged in rows above each other along the radii, the cleavage is called radial. It is typical of chordates and echinoderms. In nature, there are other variants of the spatial arrangement of blastomeres during cleavage, which determines such types of it as spiral in mollusks, bilateral in roundworms, anarchic in jellyfish.

The relationship between the yolk distribution and the degree of synchronicity of division of animal and vegetative blastomeres was noted. In oligolecital eggs of echinoderms, cleavage is almost synchronous; in mesolecital egg cells, the synchronicity is disturbed after the third division, since vegetative blastomeres divide more slowly due to the large amount of yolk. In forms with partial cleavage, divisions are asynchronous from the very beginning, and blastomeres occupying a central position divide faster.

I-two blastomeres, II-four blastomeres, III-eight blastomeres, IV-morula, V-blastula;

1-cleavage grooves, 2-blastomeres, 3- blastoderm, 4-blastoel, 5- epiblast, 6- hypoblast, 7-embryoblast, 8-trophoblast; the sizes of the embryos in the figure do not reflect the true size ratios

By the end of cleavage, blastula is formed. The type of blastula depends on the type of cleavage, and therefore on the type of egg. Some types of cleavage and blastula are shown in Fig. 7.2 and diagram 7.1. For a more detailed description of cleavage in mammals and humans, see Sec. 7.6.1.

Features of molecular genetic and biochemical processes in

crushing. As noted above, mitotic cycles during the cleavage period are greatly shortened, especially at the very beginning.

For example, the entire fission cycle in sea urchin eggs lasts 30-40 minutes, while the 8-phase lasts only 15 minutes. The 01- and 02-periods are practically absent, since the necessary supply of all substances has been created in the cytoplasm of the egg cell, and the larger, the larger it is. DNA and histones are synthesized before each division.

Partial (meroblastic)

discoidal asynchronous

discoblastula (bird)

The rate of advancement of the replication fork along the DNA during cleavage is normal. At the same time, more points of initiation are observed in blastomere DNA than in somatic cells. DNA synthesis occurs in all replicons simultaneously, synchronously. Therefore, the DNA replication time in the nucleus coincides with the doubling time of one, moreover, a shortened replicon. It was shown that when the nucleus is removed from the zygote, cleavage occurs and the embryo in its development reaches the blastula stage. Further development stops.

At the beginning of cleavage, other types of nuclear activity, for example, transcription, are practically absent. In different types of eggs, gene transcription and RNA synthesis begin at different stages. In cases where there are many different substances in the cytoplasm, as, for example, in amphibians, transcription is not activated immediately. RNA synthesis in them begins at the stage of early blastula. In contrast, in mammals, RNA synthesis already begins at the stage of two blastomeres.

In the period of cleavage, RNA and proteins are formed, similar to those synthesized in the process of oogenesis. These are mainly histones, cell membrane proteins and enzymes necessary for cell division. These proteins are used immediately along with the proteins previously stored in the cytoplasm of the oocytes. Along with this, during the cleavage period, the synthesis of proteins that did not exist before is possible. This is supported by data on the presence of regional differences in the synthesis of RNA and proteins between blastomeres. Sometimes these RNAs and proteins begin to act at a later stage.

Cytoplasmic division - cytotomy - plays an important role in cleavage. It has a special morphogenetic significance, as it determines the type of cleavage. In the process of cytotomy, a constriction is first formed with the help of a contractible ring of microfilaments. The assembly of this ring takes place under direct

the influence of the poles of the mitotic spindle. After cytotomy, the blastomeres of oligolecital eggs remain connected to each other only by thin bridges. It is at this time that they are easiest to separate. This is because cytotomy leads to a decrease in the contact area between cells due to the limited surface area of \u200b\u200bthe membranes.

Immediately after cytotomy, the synthesis of new sections of the cell surface begins, the contact zone increases and the blastomeres begin to touch tightly. Cleavage furrows run along the boundaries between individual areas of ovoplasm, reflecting the phenomenon of ovoplasmic segregation. Therefore, the cytoplasm of different blastomeres differs in chemical composition.