Title

A Corrosion Casting Study of the Structure of Cetacean Kidneys

Event Name/Location

16th Biennial Conference on the Biology of Marine Mammals, San Diego, CA, December 12-16, 2005

Document Type

Conference Proceeding

Publication Date

12-2005

Abstract

Using a corrosion casting technique the precise vascular, tubular and collecting duct anatomy of cetacean kidneys was investigated. Kidneys were obtained from two stranded Kogia sp., two stranded Tursiops truncatus, and one stranded Steno bredanensis. After removal from the carcass, the kidneys were perfused with physiological saline. Mercox resin (Ladd Research, Williston VT, USA) was then perfused into the kidneys until the plastic emerged from the vein draining the organ. The kidneys were placed into a jar of hot (~50°C) water for 30-60 minutes until resin polymerization was complete. Once the resin was fully polymerized, the kidney tissues were digested in a sodium hydroxide solution, leaving a plastic cast of the perfused part of the kidney. The casts were examined and photographed under light microscopy. In the Kogia kidneys, within each reniculus the afferent arterioles, glomeruli, and efferent arterioles were found to be surrounded by a fine spherical network of the vasa recta. All kidneys strongly resembled a bunch of grapes, with the reniculi arranged in groups arising from separate branches of the renal artery, and drained by separate branches of the renal vein and collecting duct, consistent with published literature. In contrast to statements that each reniculus acts as an independent kidney, our results indicate that the cetacean kidney is actually composed of several lobes with each lobe consisting of multiple reniculi all fed by a single branch of the renal artery and all drained by a single branch of the renal vein and a single branch of the ureter. The renicular structure of cetacean kidneys may be an adaptation to diving, facilitating reperfusion after peripheral vasoconstriction during diving, or allowing parts of the kidney to be shut down or diminished in use to conserve energy, conserve water, or maintain electrolyte balance.

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