CELL DIVISION

From Big Medical Encyclopedia

CELL DIVISION — process of a reproduction of cells, as a result to-rogo new, daughter cells are formed of a stem mother cell. At metaphytes of D. to. is the cornerstone of growth and development, and also an angenesis and bodies; at unicells of D. to. — in essence process of reproduction of the organism (see. Asexual reproduction ). Thanks to D. to. the continuity of existence of consecutive generations of cells and the whole organisms is provided.

At primitive organisms (so-called prokariot, hl. obr. bacteria) which cells do not contain morphologically isolated kernel, D. to. occurs by formation of a longitudinal or cross banner, budding or multiple fission. In all cases of D. to. replication of genetic material precedes. At organisms (eukaryotes) which cells have kernels, D. to. always begins with nuclear fission (kariotomiya), after the Crimea there is a division of a cellular body into two parts — a tsitotomiya.

At the cells having a kernel distinguish two types D. to.: mitosis (see), inherent in all somatic cells of animal and vegetable organisms, and meiosis (see), characteristic of sex cells of animals, and also the plants breeding sexually. The mitosis provides education genetically equivalent (among generations) cells with a diploid (double) set of chromosomes. Meiosis represents two cell fissions following one after another, the Crimea precedes one act of chromosome replication therefore there are sex cells with a haploid (unary) set of chromosomes.

The reasons inducing cells to division are not studied yet, and connect them more often with replication of genetic material, with the changes in a metabolism occurring in the course of life activity of cells.

Cells of the embryonal period of development have the greatest mitotic activity. In an adult organism of a cell of various fabrics and bodies have various ability to division. Intensively cells of the hemopoietic bodies, male gonads, crypts of intestines whereas nervous and muscle cells in the post-natal period lose ability to division share. However the majority of the cells which are usually not sharing is under certain conditions capable to division. The injury or removal of body owing to what the phenomenon of reparative is observed can become such conditions regenerations (see), and also cultivation of highly specialized cells out of an organism. Pathology of cell fission is very various. It can be connected with damage of chromosomes, with changes in the mitotic device, with disturbances of a tsitotomiya. So, during the formation in a cell of a multipole spindle of division there comes multiple fission — on number of poles. At the same time uneven distribution of chromosomes between daughter cells, i.e. an aneuploidy takes place (see. Chromosomal complement ). Patol, mitoses often meet in tumor cells, at a radial illness, viral infections etc.

For direct division, or amitotic division (see), lack of formation of chromosomes and a spindle of division is characteristic, often there is no tsitotomiya. Amitotichesky division usually arises as reaction of fabric to the changed conditions, and the term in his understanding as way of reproduction of cells, apparently, lost the value.

See also Cell .


Bibliography: Alov I. A. Cytophysiology and pathology of a mitosis, M., 1972, bibliogr.; Alov I. A., Braude A. I. and Aspiz M. E. Fundamentals of functional morphology of a cell, M., 1969; Afanasyev Yu. I., Korolev V. V. and Kotovsk E. F. Yadro of a cell and some questions of cytogenetics, M., 1970, bibliogr.; Introduction to cytology, under the editorship of V. P. Mikhaylov, M., 1968, bibliogr.; M e z and I am D. Mitoz and physiology of cellular division, the lane with English, M., 1963, bibliogr.; Robertis E., Novinsky V. and Saes F. Cytobiology, the lane with English, M., 1973; Tsanev R. G. and Markov G. G. Biochemistry of cellular division, the lane with bolg., M., 1964, bibliogr.

E. F. Kotovsky.

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