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 The process of individual development is a programmed sequence of functioning of individual parts of the genome and is expressed by a change in protein synthesis, the ratio of the number of individual enzymes.
At the same time, this process is determined not only by genetic prerequisites, but also significantly modulated by the influence of environmental factors on the genome realization. In turn, the fertilized egg, being a foreign organism, also actively affects the mother's immune system. On the other hand, the study of the factors ensuring the normal development of the fetus made it possible to identify a number of critical periods, which are especially sensitive to adverse influences from the maternal organism.
In connection with the above, it can be seen that the further development of modern methods for monitoring the state of the fetus is of great practical importance, since it is aimed at reducing non-fatal morbidity, in the structure of which intrauterine growth retardation, hypoxic syndrome and asphyxia of newborns occupy a leading place.
Currently, new knowledge has been obtained about the mechanism of fetal hypoxia, about changes in hemodynamics and microcirculation in the fetus with insufficient oxygen supply, about compensatory and adaptive reactions in the mother-placenta-fetus system that ensure the survival of the fetus. At the same time, shifts in metabolism in the named system during fetal hypoxia and delayed intrauterine development require further study and, especially, the need to identify possible metabolic disorders even in the premorbid stage before the clinical manifestations of the disease.
All of the above indicates that fundamental studies of relationships in the "mother-placenta-fetus" system in the process of intrauterine development of the fetus in normal or pathological conditions have not only theoretical but also great practical importance.
The relevance of the study of the functions of the fetoplacental-maternal complex - one of the main mechanisms responsible for the formation of conditions adequate for the normal intrauterine development of the fetus, is currently beyond doubt. Starting from the moment of fertilization, the interaction of the embryo and the maternal organism, and after implantation - the functioning of the "mother-placenta-fetus" system, integrate the fetal-maternal relationship. Moreover, any changes in homeostasis in the mother's body are reflected in the development of the fetus. In turn, metabolic disorders in the fetus affect the life of a pregnant woman. That is why various adverse effects on the maternal organism significantly affect the rates of embryonic and fetal development and the nature of maturation of the functional systems of the pod.
 Numerous studies of domestic and foreign scientists are devoted to the study of the patterns of functioning of the "mother-placenta-fetus" system. It has been proven that in this functional system, the placenta and amniotic fluid are the most important connecting links and are available for many types of research. The humoral connection between the maternal organism and the developing fetus is most important, since thanks to it, the mother has great opportunities to influence the functional state of the fetus and intrauterine ontogenesis, using quantitative and qualitative changes in the transplacental circulation. At the same time, a significant part of the information from the developing fetus comes to the mother also through the humoral route.
Morphological characteristics of the human placenta
In the works of a number of authors, the main stages of the evolution of the placenta are investigated, its endocrine, trophic, barrier and other important functions are reflected, the concepts of the feto-placental system, enzymatic and compensatory processes occurring in it during physiological or complicated pregnancy are presented. The human placenta is of the hemochorial type. In the process of development of this organ, the stages of differentiation, growth, maturity and aging are distinguished.
In the first half of pregnancy, placenta growth processes prevail. From the 22nd to the 36th week of intrauterine ontogenesis, an increase in the mass of the placenta and the fetus occurs evenly. By the 36th week, the placenta reaches functional and morphological maturity. Subsequently, fetal growth occurs without a pronounced increase in the functionally active components of the placenta. It was also found that an intensive increase in fetal body weight begins only after the completion of the development of the uteroplacental blood circulation system and the cessation of neoplasm and vascular growth of the microcirculatory bed.
The bulk of the placenta is represented by chorionic villi. In the early stages of pregnancy, 3 layers are distinguished in them: capillary endothelium, chorionic mesoderm and trophoblast. With the help of an electron microscope it was found that the trophoblast is heterogeneous and consists of syncytiotrophoblast, "intermediate" trophoblast and cytotrophoblast. The main functions of trophoblast are blastocyst implantation, development of uteroplacental arteries, synthesis of hormones and specific proteins of pregnancy. It should be emphasized that in this layer of villi the closest contact of the maternal and fetal blood flows takes place, and the main processes of metabolism and gas exchange occur in small resorption villi located mainly in the basal parts of the fetal part of the placenta. Under physiological conditions during full-term pregnancy, the surface area of the villi is 12.5 - 14 square meters.
After childbirth, the fetal part of the placenta is represented by a smooth amnion, the chorionic plate and the villous part of the chorion.
The amnion (fetal membrane) consists of the following layers: endothelial, basement membrane, a compact layer of fibroblasts and cancellous. The chorionic plate is covered from above with amnion, and from the side of the intervillous space it is lined with syncytiotrophoblast or fibrinoid layer of Langans. The umbilical veins and arteries pass through the connective tissue of the chorionic plate.
The cytotrophoblast of the smooth chorion grows together with the decidual tissue, linking the fetal bladder with maternal tissues. The villous part of the chorion is represented by villi, which in a full-term newborn are covered from the outside with a layer of syncytiotrophoblast. In some villi, a cytotrophoblast is visible located under the syncytiotrophoblast within the common baval membrane. In the form of a continuous layer, the cytotrophoblast is presented only in the early stages of pregnancy. As the placenta matures, the number of cytotrophoblasts decreases, the integumentary layer of the syncytiotrophoblast flattens, the capillaries approach the basement membrane of the syncytium, forming a zone of the placental-uterine barrier. There is an opinion that these are passive transport of substances with low molecular weight and that their presence in the villi zone is a sign of maturity of the placenta.
The syncytiotrophoblast has no cellular boundaries, forming a continuous layer, and is characterized by a basophilic vacuolated cytoplasm with a large number of free ribosomes and a well-developed endoplasmic reticulum. The syncytiotrophoblast thickness varies from 3 to 20 microns. The nuclei of the syncytiotrophoblast are unevenly distributed; non-nuclear areas and foci of proliferation - syncytial nodes, which are determined in 10-30% of the villi, are revealed in it. Some of these nodes bulge into the lumen, split off and form layers that are carried into the mother's bloodstream, settling in the pulmonary capillaries.The formation of syncytial nodes in the mature placenta is associated with the reduction of the capillary bed of the villi and the development, as a result, of compensatory processes on the part of the trophoblast elements. Under the syncytiotrophoblast is the stroma of the villi with the fetal capillaries passing through them.
It has been established that the most important role in the metabolic functions of the placenta is played by the syncytiotrophoblast, which is in direct contact with the maternal blood.
In the placenta, a fibrinoid is constantly found, which first appears on the surface of the basal plate and from the inside of the chorionic plate. The main purpose of a fibrinoid is a barrier function aimed at preventing an immune conflict due to a violation of the integrity of the syncytiotrophoblast and the contact of maternal and fetal tissues. Fibrinoid is often seen on terminal villi, usually in areas where there was previously damage to the syncytiotrophoblast layer. It contains immunoglobulins, fibrin, plasma. All of these types of fibrinoid are formed from the elements of maternal blood and are called maternal fibrinoid. Excessive accumulation of such fibrinoid in combination with the accumulation of lime in the chorionic plate and stroma of large villi are considered signs of aging of the placenta. Fibrinoid degeneration is especially distinguished, up to necrosis in the stroma of the villi, the so-called fetal fibrinoid, the accumulation of which is evidence of aging of the placenta or a reflection of feto-placental insufficiency. On the other hand, it is known that one of the reasons for the onset of labor is a decrease in the area of metabolism between the body of the mother and the fetus, due to the aging of the trophoblast.
RNA, protein and active protein groups are found in the chorionic epithelium. Glycogen is detected in the cytotrophoblast and stroma of villi, glycoproteins - in syncytium, basement membranes of the chorionic epithelium and capillaries of villi, glycosaminoglycans - in the stroma of villi, RNA - in syncytiotrophoblast.
Thus, the intravillous system is associated with fetal-maternal metabolism, and the paravascular network serves as a kind of shunt when the capillary system of the terminal villi is overloaded. The tone of the placental vessels depends on the gas composition of the blood flowing through the intervillous spaces.
Uteroplacental blood circulation maximally increases by 37-38 weeks of pregnancy, then the placental blood flow decreases slightly. The uteroplacental circulation reaches its highest tension by the beginning of labor.
Thus, the morphofunctional features of the fetal-placental system indicate the complex and diverse processes occurring in it and ensuring the normal development of the fetus under conditions of physiological pregnancy.
Gavrilova N.V.
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