METAMORPHOSES

From Big Medical Encyclopedia

METAMORPHOSES (grech, metamorphosis transformation, transformation; synonym: indirect development, full transformation) — sharp, spasmodic changes in a structure, a way of life, and it is frequent also to the habitat, occurring in development of many animals in the course of achievement of a puberal state by them; at plants metamorphosis call changes of a structure of nek-ry bodies (leaves, a stalk).

The m is characteristic of development of amphibians, insects, mollusks, Crustacea, aktsidy, etc. Biol, value M. consists in a possibility of division of a life cycle of animals on two markedly the stages differing on a way of life — larval, characterized by intensive food (see. Larvae ) and the accelerated growth, and imaginal (adult), in time the cut occurs resettlement and reproduction. At the same time the larval form living in water, the soil or on the earth, often is replaced by the flying form (mosquitoes, flies, bugs, etc.). The larva of tailless amphibians (tadpole) living in water in the course of M. turns into the frog capable to live on the land. Thus, M. promotes fuller use of the environment for the benefit of this species of an animal.

The m at insects is prepared still in the period of late embryonal — early larval development and expressed in laying of special imaginal disks — groups of the low-differentiated cells, from to-rykh during M. the main bodies of an adult organism (imago) are formed. At pupation of the grown larva there is a dissolution (histolysis) of the most part of larval bodies and education from imaginal disks of bodies of a mature animal. A part of bodies of a larva (intestines, a nervous system) remains, but undergoes considerable structural changes. The doll leaves an imaginal form, usually at once capable to a syngenesis. Larval development often continues months and even years, and life of an imago lasts only days or weeks. The m at insects is regulated by steroid hormone — ekdizony (ekdisterony), to-ry is produced by parathoracic bodies of a larva. Under the influence of hormone there is a switching off of one genes and activation of others controlling protein synthesis,

tailless amphibians of M., necessary for M. U implementation, consists in consecutive emergence in a tadpole of back and front extremities, lungs, reduction of length of intestines, a resorption of gills and a tail, change of a structure of skin, the oral device and all skull. The phenomenon of a neoteniya when the larva (axolotl) reaches the big sizes is characteristic of nek-ry amphibians having a tail (ambist), becomes puberal and breeds. However at change of environmental conditions (drying of reservoirs, decrease in the water line) the neotenichesky larva passes M. in an aquarium and turns in ambisty, capable to live out of water.

At M.'s amphibians it is controlled by hormone of a thyroid gland — thyroxine. Coordination of various processes of M. is reached by various sensitivity of various bodies of a tadpole to this or that concentration of hormone. In process of growth of a tadpole function of a thyroid gland amplifies, concentration of thyroid hormones increases in blood and new systems of bodies in that sequence are involved in M., edges are provided by natural passing of M. As well as at insects, the hormone causing M. activates certain groups of genes that leads to synthesis of the new enzymes and other proteins necessary for implementation of processes of M.

Studying of the phenomenon of M. and processes proceeding at it has great applied value. In particular, knowledge of patterns of change of forms at harmful insects (parasites and carriers of infections) promotes development of the corresponding methods of controlling with them, napr, extermination of insects at the time of an otkladka them eggs, use of chemicals and biol, means of fight against larvae in the environment of their dwelling, extermination of adult insects. The new methods based on processing of larvae by synthetic analogs of hormones M., overwhelming or, on the contrary, causing their premature M.

See also are developed Life cycle .



Bibliography: Hedgehogs I. I. Metamorfoz of insects, M., 1929; Ivanov P. P. Guide to the general and comparative embryology, L., 1945; H e y f and x A. A. and T and m about f e e in and M. Ya. Problems of regulation in molecular biology of development, M., 1978; Sabinyan D. A. Physiology of development of plants, M., 1963; N ovakY.J. Insect hormones, L., 1975; Tata J. R. Cell structure and biosynthesis during hormone-mediated growth and development, in book: Hormones in development, ed. by M. Hamburgh a. E. J. Barrington, p. 19, N. Y., 1971.


A. A. Neyfakh.

Яндекс.Метрика