[Development of various nephron populations in birds during ontogenesis]

Microanatomy of nephrons during ontogenesis has been studied in domestic hens. In the bird kidneys, as well as in mammalian kidneys, three populations of nephrons can be detected: juxtamedullary, or deep nephrons, superficial and situating between them intracortical nephrons. In formation of the bird renal medulla only loops of the juxtamedullary nephrons participate. During ontogenesis in the kidneys of birds, like in mammalians, juxtamedullary nephrons are the first to be formed; they can be obtained from kidneys of 14-day-old chicken embryos, however, a complete formation of the nephron structure is terminated after hatching. During development the length of the juxtamedullary nephrons increases nearly by one order, while the length of the superficial and intracortical nephrons increases no more than twice. The diameter of the glomeruli in the juxtamedullary nephrons during development increases nearly twice, in the superficial and intracortical nephrons only a slight increase is noted. A relative length of the proximal canaliculus of the intracortical and superficial nephrons gradually increases during ontogenesis and practically does not change in the juxtamedullary nephrons, in them the nephron loop becomes longer. The developmental pattern in various parts of the superficial, intracortical and juxtamedullary nephrons in general features is similar in mammalians and birds.