進化における両生類の陸生適応と腎臓の多様性

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  • Terrestrial adaptation and diversity of the kidney functions in the evolution of amphibia

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The amphibia bridge the phyletic gap between the aquatic fishes and the terrestrial vertebrates. This transition has involved many interesting changes of metabolism. In this short review, we have attempted to summarize the kidney structure and functions of osmoregulation in the amphibia. Amphibians excrete the water absorbed through their skin as a dilute urine. The pronephros of tadpoles may start to work in the hatching stages, and the metanephros of tadpoles is well developed and functioning. The glomerular filtration rate is relatively large and glomerular intermittency is important for regulating urine production. The proximal tubule reabsorbs approximately 20-45% of filtered water and sodium. Absorption is driven by the basolateral Na^+, K^+-ATPase common to all tubular cells. The diluting segment, an early part of the distal nephron, highly develops basolateral interdigitation and reabsorbs approximately 40% offiltered Na^+, K^+, and Cl^-, but is impermeable to water; thus, this part results in the formation of hypo-osmotic tubular fluid. In the late distal tubule, the primary mechanism of reabsorption may be via a luminal NaCl synporter, driven by the ubiquitous Na^+, K^+-ATPase on the basolateral membrane. In collecting tubules, there are two types of cells, the principal cells and the intercalated cells. Many hormonal and nervous regulations are involved in the glomerular filtration rate and reabsorptions in the amphibian nephrons.

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  • 松本歯学

    松本歯学 30 (1), 1-8, 2004-04-30

    松本歯科大学学会

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