Hopkins Marine Station Student Paper

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Title: Cranial, orbital rete, and red muscle vein anatomy indicate a high degree of endothermy in the brain and eye of the salmon shark, Lamna ditropis
Student Author(s): Tubbesing, Victor
Faculty Advisor(s): Block, Barbara
Pages: 21
Location: Final Papers Biology 175H
Date: June 1997
Abstract: Geographic range, extent of red muscle, supra-hepatic rete size, and limited temperature measurements have placed the salmon shark, Lamna ditropis, as the warmest of the lamnid sharks. Yet its anatomy has remained largely undescribed, and measurements of brain or eye temperatures in particular have not been taken. In this study, three specimens were examined to determine if the morphological requirements for a warm brain and eyes are present. In addition to local heat-producing red muscle of the eye and jaw, other notable features were found. A well-developed orbital rete lies within a venous sinus on both sides of the cranium. Cool, oxygenated blood from the gills can pass through the dividing vessels of this exchanger before reaching the brain or eyes. Since venous blood in the sinus flows opposite the arterial blood, counter-current heat exchange can occur. A vein originating in the red swimming muscle potentially contributes to the warmth of the venous sinus by supplying blood directly from the warmest part of the shark. Before collecting in the orbital sinus, this red muscle vein bathes the brain in warm blood. These morphological data suggest the salmon shark has a significant capacity to warm the brain and eyes.