| Abstract: | By microdissection method, single nephrons have been isolated from the river lamprey Lampetra fluviatilis, teleost fish Myoxocephalus scorpius (White sea), frog Rana temporaria, lizard Agama caucasica, hen Gallus domesticus and albino rat Rattus norvegicus (Wistar strain). Tubular reabsorptive capacity was measured in kidneys of lampreys and rats by the split oil droplet method. In the animals studied, each of the nephrons consists of the glomerulus, proximal, thin and distal segments. Relative length of the proximal segment does not depend on phylogenetic position of a species. Transtubular isotonic water reabsorption from the proximal tubule in rats is significantly higher than in lampreys. The level of proximal reabsorption is not related to the length of the proximal tubule in the Verterbrates studied but depends on the intensity of tubular transport. The structure which is similar to Henle's loop is present already in Cyclostomes 12]. Further stage of the progressive development of the uriniferous tubules is presented by uneven localization of nephron populations within the kideney in Reptiles. These data suggest that the effective system of osmotic concentration appeared in evolution not as the result of Henle's loop formation, but on the basis of the development of the medullar substance formed mainly by intercortical and juxtamedullar nephron populations. |
