A renal countercurrent system in marine elasmobranch fish: a computer-assisted reconstruction

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Science  15 Mar 1985:
Vol. 227, Issue 4692, pp. 1351-1354
DOI: 10.1126/science.3975620


Computer-aided techniques were used to reconstruct the complex renal tubular system in the dorsal kidney region of a marine elasmobranch fish, the little skate (Raja erinacea), from a series of light micrographs of serial sections. It was established that five individual segments of one nephron, consisting of two loops and a distal tubule, are arranged in parallel within an elongated closed tissue sac. Capillaries, which form a network around these nephron segments, enter and exit this sac at the same end. This anatomical arrangement suggests that a complex renal countercurrent multiplier system may be important in fluid regulation in these fish.