title: Topsy-turvy: turning the counter-current heat exchange of leatherback turtles upside down.
abstract: Counter-current heat exchangers associated with appendages of endotherms feature bundles of closely applied arteriovenous vessels. The accepted paradigm is that heat from warm arterial blood travelling into the appendage crosses into cool venous blood returning to the body. High core temperature is maintained, but the appendage functions at low temperature. Leatherback turtles have elevated core temperatures in cold seawater and arteriovenous plexuses at the roots of all four limbs. We demonstrate that plexuses of the hindlimbs are situated wholly within the hip musculature, and that, at the distal ends of the plexuses, most blood vessels supply or drain the hip muscles, with little distal vascular supply to, or drainage from the limb blades. Venous blood entering a plexus will therefore be drained from active locomotory muscles that are overlaid by thick blubber when the adults are foraging in cold temperate waters. Plexuses maintain high limb muscle temperature and avoid excessive loss of heat to the core, the reverse of the accepted paradigm. Plexuses protect the core from overheating generated by muscular thermogenesis during nesting.
authors.affiliation: School of Biological, Earth and Environmental Sciences, University College Cork, North Mall Campus, Distillery Fields, Cork, Ireland j.davenport@ucc.ie.
authors.forename: John
authors.initials: J
authors.lastname: Davenport
authors.affiliation: NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, HI 96818, USA.
authors.forename: T Todd
authors.initials: TT
authors.lastname: Jones
authors.affiliation: US Geological Survey, National Wildlife Health Center, Honolulu Field Station, Honolulu, HI 96850, USA.
authors.forename: Thierry M
authors.initials: TM
authors.lastname: Work
authors.affiliation: NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, HI 96818, USA.
authors.forename: George H
authors.initials: GH
authors.lastname: Balazs
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001833:Body Temperature Regulation; D004242:Diving / Q000502:physiology; D035002:Lower Extremity / Q000033:anatomy & histology / Q000098:blood supply / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply*; D012039:Regional Blood Flow; D013696:Temperature; D014426:Turtles / Q000502:physiology*
keywords: counter-current; heat exchange; leatherback turtle; locomotory muscles