The critical periods of development of an embryo of
Separate fabrics and bodies are formed during various periods of growth of an embryo and fruit. At the same time body tissues at the moment of the maximum intensity of processes of a differentiation become highly sensitive to the damaging influence of external environment (the ionizing radiation, infections, chemical agents).
Such periods of which hypersensibility to influence of the damaging factors is characteristic call
“the critical periods of an embryogenesis“. The probability of formation of deviations in development during the critical periods is highest.the blastogenesis Period
According to WHO data the first critical period of development falls
on the first 2 weeks of development - the blastogenesis period. Response during this period is realized by the principle “everything or nothing“, that is the germ or perishes, or, owing to the increased stability and ability to restoration, continues to develop normally. The morphological violations arising on this term are called “blastopatiya“. Carry the anembrioniya which is formed owing to early death and a resorption of an embrioblast, an aplaziya of a zheltochny bag, etc. to them. Some researchers refer ektopichesky pregnancy and violations of depth of implantation of the developing germ to blastopatiya. The most part of the germs damaged in the period of a blastogenesis and also those which were formed of the defective gametes bearing mutations during this period eliminirutsya by spontaneous abortions. According to scientific literature the frequency of interruption of pregnancy on this term makes about 40% of all taken place pregnancies. Most often, the woman does not even manage to learn about her approach and regards an episode as a delay of a menstrual cycle.
the Embryonic period
the Second critical period of pre-natal development proceeds from 20 - go to 70 - go for later fertilization is time of the maximum vulnerability of a germ. All embryonic period - from the moment of implantation till 12th week, - is very responsible period in development of the person. This time when there is bookmark and formation of all vitals, is formed a placentary circle of blood circulation, the germ gets “human shape“.
the Fetalny (fetal) period
the Fetalny period lasts from 12th week until the birth. At this time there is a maturing of an organism - the thin differentiation of bodies and fabrics which is followed by rapid growth of a fruit. At influence of adverse factors on the developing organism during the embryonic period so-called “embriopatiya“ which are shown by malformations are formed. The same harm, influencing a fruit during the fetalny period, provoke development of fetopatiya of which morphological defects are not characteristic. Frequency of embriopatiya is rather high - in the embryonic period not less than 10% of the registered pregnancies come to an end with spontaneous abortions.
In the first 2 - 3 months of pre-natal life intensive cell fission and formation of fabrics and bodies happens. Thanks to division, growth and resettlement of cages each part of a body get certain outlines - process of a morphogenesis is carried out. Generally processes of a morphogenesis come to the end on 8 - oh to week of development. Based on knowledge of terms of formation of bodies, it is possible to do the conclusions about development of congenital defects in connection with impact on an embryo of concrete vrednost. For example, in literature many data on teratogenny action of anticonvulsive preparations, in particular, of a valproat are saved up. This preparation can induce a complex of congenital anomalies, including, a combination of spinal hernia to defect of an interventricular partition of heart. Such defects can be observed at a valproatny syndrome, however for this purpose it is necessary that the woman accepted a preparation till 8th week of pregnancy as to this term the smykaniye of an interventricular partition and formation of the vertebral channel comes to the end.calls
of Violation of development in the fetal period fetopatiya (from armor of “fetus“ - a fruit). Malformations during this period can arise only in the bodies which did not end the formation (brain tissue, teeth, genitals, lungs). Formation of so-called “secondary“ malformations - that is distortions of development of normally created bodies owing to inflammatory processes (for example, toxoplasmosis, viral infections) or the violations of maturing leading to formation of displaziya or hypoplasias of bodies and fabrics is characteristic of this period.Ability to react inflammatory processes on infectious damage at a fruit is formed by
after 5 - go month of development. Also the contribution to pathology of the fetal period is made by metabolic disorders and chronic intoxications at mother, it is possible to give a diabetic and alcoholic fetopatiya as an example. From violations of pre-natal development the congenital malformations (CM) have the greatest clinical and social value.
the Modern science considers that not less than 50% of all VPR have the complex multiple-factor nature, that is are formed under the influence of hereditary and environmental factors whereas 5% of VPR are induced by teratogenny influences. Refer any harm under the influence of which VPR can be created to teratogenny influences.to
Knows several hundreds of teratogenny factors, however practical value at the person have only a little:
- Endocrine diseases of mother (diabetes);
- Physical impacts (temperature or ionizing);
- Chemicals to which some medicines (retinoida, valproyevy acid, talidomid, etc.) and alcohol belong;
- Biological factors (infections - toxoplasmosis, a rubella, etc.)
Part of these factors are capable to induce certain teratologichesky syndromes, well-known to doctors around the world. These syndromes can be realized as embrio - or fetopatiya, depending on a concrete factor and term of pregnancy on which it influences.
Realization of teratogenny effect depends on many components, the part from which is defined by germ biology. There are most powerful components defining extent of the damaging action of a teratogen:
- nature of a teratogen;
- dose of a teratogen;
- influence duration;
- age of a germ or fruit;
- genetic predisposition of the formed organism;
- genetic features of an organism of mother, namely: functioning of system of a detoxication of xenobiotics, neutralizations of free radicals, etc.
In development of a human body by the most vulnerable are 1 - y and 2 - oh the critical period of ontogenesis is the end 1 - oh the beginning 2 - oh weeks after fertilization and 3 - 6 weeks of pregnancy. Influence of vrednost during 2 - go the period leads to formation of the greatest number of VPR.
Krom critical needs to consider the terminatsionny periods of action of a teratogen - that is a pregnancy deadline during which the adverse factor can induce anomalies of development. This period is defined by a date of completion of formation of body and differs for various bodies and fabrics, for example, the rough malformation of a brain - an anentsefaliya, can be created as a result of teratogenny influences till 8th week of pregnancy whereas defects of an interventricular partition of heart - to 10 - oh weeks.Value of a genetic component of the formed organism can be shown to
on the example of a talidomidny syndrome and an alcoholic fetopatiya. The Talidomidny syndrome was created only at 20% of children whose mothers during pregnancy on its same terms accepted identical doses of a talidomid.Influence of teratogenny factors is most often realized by
in the form of development of multiple defects and anomalies of development which formation depends on a dose of the damaging agent, duration of his influence and term of pregnancy, on which there was an adverse influence.