Division somatic and gametes

Mitosis –process of formation of two daughter cells identical to an initial maternal cage. It is characteristic for all types of fabrics and for all nuclear organisms. Provides renewal of cages in the course of their aging. Is the cornerstone of asexual reproduction of an organism. Value of a mitosis consists in increase in quantity of cages and uniform distribution of genetic material between two daughter cells. Process of indirect cell fission can be subdivided into some main phases: pro-phase, metaphase, anaphase, telofaza.

In a pro-phase spiralling of chromosomes leads to their shortening and a thickening, and pro-phase chromosomes come to light in the form of thin threads. The cage contains the doubled quantity of DNA after replication in the S-period. The number хроматид corresponds to quantity of DNA (4n, 4c). Parallel to condensation of chromosomes disintegration of kernels results from condensation and an inactivation of ribosomal tsistron in a zone the yadryshkovykh of organizers. Along with it destruction of a nuclear cover begins: a nuclear time disappears, the cover breaks up to fragments. The major event professional elements are a formation of a spindle of division (an akhromatinovy figure of division).

Meiosis – the wayof cell division which is the cornerstone of a reduction of number of chromosomes is characteristic for life cycle only of gametes and a sporoobrazovaniye at plants. Four gametes – cages with a haploid set of chromosomes are formed of an initial maternal cage.

Biological value of meiosis is the cornerstone of maintenance of constancy of number of chromosomes of a look from generation to generation. Besides, meiosis provides kombinativny variability as chromosomes of different couples (bivalents) disperse independently from each other, it leads to a recombination of parental sets of chromosomes. In meiosis there is also a recombination of identical sites of homologous chromosomes because of a krossingover.

In development of a metaphyte of a cage are differentiated and become fabric functioning units (spetsializatsializirovanny). Today the differentiation of cages is considered as emergence in them special proteins which or function in a cage (enzymes), or sekretirutsya by cages (ekskreta, inkreta). Emergence in cells of such special proteins is result of repression the sootkvetstvuyushchikh of genes on molecules of DNA specific to all cages of this organism. In separate types of fabrics (epitelialny, retikulyarny, blood) cellular population is presented the differony.

Any violations of a gistofiziologiya of separate cages of an organism form a basis for development of pathological processes. And it is in this regard easy to see that cages represent an initial target for any influences of factors that very often leads to development of diseases of all metaphyte.

The differentiated (mature) cages can function various time. So neurons remain during all life of an individual, and an enterotsita of a small intestine some days. The most part of cages perishes and is replaced with others. The Skokrost of replacement (proliferation) at different cages isn't identical.

The death of a cage can result from influence of negative external factors (a trauma, chemical or radiation defeat, etc.), thus, the razkrusheniye of a cage occurs chaotically, and products of its disintegration render an irritant action on an environment and provoke development of inflammatory reaction. The similar casual death of cages is called as a necrosis and serves as asubject of studying of pathological anatomy.

The majority of cages perish at realization of special natural genetic mechanisms. Genetically programmed cellular death is called apoptosis. The mechanism of emergence of apoptosis is very difficult.

At chromosomes of each cage there are genes starting synthesis of the enzymes stimulating it to division, and the genes providing synthesis of the enzymes interfering division. In the functioning cage, these sinteza are counterbalanced. For ensuring vital balance the cage has to receive signals from other cages of an organism, is more often in the form of specific molecules of oligopeptid (tsitokin). Action of tsitokin (several tens) on one types of cages stronger, on others - weak or even can not be shown. Now at the description of intercellular interactions even more often apply the term "tsitokinny network".

Fenotipichesky manifestations of such death of cages are various and known давно:пикноз (wrinkling of a kernel), хроматолизис (decrease in colourability of a kernel), кариорексис (disintegration of a kernel). Only recently it was shown that it is only private manifestations of apoptosis.

After death of a kernel also cytoplasm collapses, its remains fagotsitirutsya and processed by macrophages and can be used by other cages again. Round the cages which underwent apoptosis, inflammatory process doesn't arise, and activity of fabric proceeds without violations

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