[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 increase of the proportion of the epithelium in the structure of undifferentiated tubule is determined by the segregation of the proximal and distal tubules within the forming nephrons. The sequence of the initial stages of the renal tubule differentiation is dictated by the ergontic correlations; it developes from the proximal tubule to the distal one and is different from the succession of their formation in the process of the early nephronogenesis.