[The sequence of nephron tubule differentiation in the definitive human kidney during the fetal period].

The regularities of the formation of the undifferentiated renal tubules in the definitive kidney were studied in 174 human embryos and fetuses at 4.5 to 40 gestational weeks. On the basis of the study of morphological and morphometrical parameters of these tubules, it was shown that the increase of the average tubular crossectional area was associated with the consecutive formation of the nephrons of the definitive kidney and the differentiation of the segments of their tubular portions.

[The assessment of the regularity of the nephron anlage tubule formation on the basis of provisionality principle].

The study of the definitive kidneys of 94 human embryos and fetuses at 4.5 to 12 weeks of gestation, has demonstrated that the formation of the proximal nephron tubules resulted from the cellular proliferation in the area of transition of the capsule of the renal corpuscle into the tubular part of the nephron that occurs only after the completion of the segregation of the renal corpuscle and the distal tubule within the nephron anlage. The formation of the renal tubules in the nephron anlage seems to be determined phylogenetically, while the initial differentiation of the distal tubule is a provisional feature.

[Provisionality phenomenon in the histo- organo- and systemogenesis].

This review summarizes the results of the study of the provisionality phenomenon in the development of the organs of the urinary system (mesonephros, metanephros) in viviparous (human, rat) and oviparous (bird) amniotes, human organs of mixed origin (pituitary, ovary, stomodeum) reparative regeneration of supporting tissues (in humans and Syrian hamster), morphogenesis of primary hepatic cancer developing against the background of superinvasive opisthorchiasis. It is shown that during the development of tissues and organs, the stages of provisional and definitive histo- and organogenesis could be determined; saltatory mechanism is typical for embryonic organogenesis (formation of cartilaginous skeletal primordia, meso- and metanephrons) and foci of oncogenesis. Transformation zones of the type of tissue organization in the epithelium are located in the areas of contacts of the derivatives of different embryonic primordia.

[Role of provisionality principle in realization of phylembryogeneses].

The analysis of histogenesis of skeletogenic tissues and of organogenesis of the mesonephros and metanephros in higher mammalian animals and man, is presented. The new conception of provisionality is formulated, according to which embryonic primordium and/or its derivatives possess a determined capacity to form, on its course to definitive state, temporary structures (tissues or organs), which fulfil the vital functions in the developing organism and modeling the mechanisms of development and formation of structural and functional units or the whole organ at the level of definitive morphological substrate. Provisionality is regarded as the universal principle in realization of of phylembryogeneses.