Counter-current heat exchangers

Counter-current heat exchange is an highly efficient means of minimizing heat loss through the skin's surface because heat is recycled instead of being dissipated. This way, the heart does not have to pump blood as rapidly in order to maintain a constant body core temperature and thus, metabolic rate.

When animals like the leatherback turtleand dolphinsare in colder water in which they are not acclimatized to, they use this CCHE mechanism. Counter current heat exchangers are made up of a complex network of peri-arterial venous plexuses that run from central cardiovascular system(heart) and through the blubber to peripheral sites (i.e. the tail flukes, dorsal finand pectoral fins)[1]. Each plexus consists of a singular artery containing warm blood from the heart surrounded by a bundle of veins containing cool blood from the body surface. As these fluids run past each other they create a heat gradient in which heat is transferred. The warm arterial blood transfers most of its heat to the cool venous blood in order to conserve heat by recirculating it back to the body core. Since the arteries are losing a good deal of their heat, by the time they reach the periphery surface, there will not be as much heat lost through convection[1].

References

[1]Meagher, E. M. "The relationship between heat flow and vasculature in the dorsal fin of wild bottlenose dolphins Tursiops truncatus." The Journal of Experimental Biology 2002: 3475-3486.

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It uses material from the http://en.wikipedia.org/wiki/Counter-current+heat+exchangers Wikipedia article Counter-current heat exchangers.