(full paper is archived in the Miller Library)
Title: Anatomical adaptations for endothermy: retia mirabilia in the salmon shark, Lamna ditropis
Student Author(s): Condie, Jana Elizabeth
Faculty Advisor(s): Block, Barbara
Location: Final Papers Biology 175H
Date: June 1997
Abstract: The Pacific salmon shark, Lamna ditropis (Hubbs & Follett, 1947), can maintain core body temperatures 7-11 degrees C above ambient waters--the highest body-temperature elevation of any shark measured to date. Gross anatomical studies of three subjects revealed that the mechanism for such endothermy is facilitated by counter-current heat exchangers common in other lamnids and scombrids. In these fish, retia mirabilia--"wonderful nets" of interwoven vessels and/or sinuses-act as metabolic heat recyclers. L. ditropis possesses four retial systems, three of which serve the viscera and muscle, much like the retia of its Atlantic cousin, the porbeagle shark, Lamna nasus. The lateral cutaneous rete begins laterally in the white muscle and serves the well-insulated internal red muscle. This tubular rete, composed of bundles of arteries and veins, is small in area near the skin, but divides and widens as it nears the internal red muscle. The viscera is warmed by the supra-hepatic rete, a two-lobed tissue lying posterier to the heart and dorsal to the liver lobes. Minute arteries repeatedly converge and coalesce in this rete in a honeycomb pattern, and the entire arterial mass is contained in a large venous sinus. The sub-renal rete consists of a small anterior retial lobe plus its lateral extension, which runs the length of the kidney, conserving metabolic heat created there. We propose that the combined efficiency of these retial systems allows L. ditropis to occupy its icy niche, the most polar of any shark.