Discovery of a New Animal Heat-Exchanger
by Phillip Eichman
Engineers often use some type of heat-exchanger to increase the efficiency of modern heating and cooling equipment. Heat is transferred from one liquid or air supply to another without any actual mixing or contact. Structures employing similar principles have been discovered in several animals, including the legs of wading birds and flukes or flippers of marine mammals.
These structures, usually called a rete or retia (plural), are examples of what are referred to as counter-current heat exchangers. They are made up of blood vessels (arteries and veins) that run parallel to each other, but the blood flows in opposite directions. Thus, warm blood in the arteries from the body passes very close to cooled blood returning in the veins to the body from the extremities. Heat is transferred from the warmer blood to the cooler as the blood flows through these vessels, thus conserving body heat. Such an arrangement can prevent hypothermia or excessive loss of body heat to the environment. Even though these animals often live in an environment that is much cooler than their body temperature, they can conserve body heat through such counter-current heat exchangers.
Whales and other marine mammals, such as seals and dolphins, also utilize a thick layer of body fat, or blubber, to help insulate the body core and conserve heat in cold ocean water. Recently, zoologists have discovered that the tongue of grey whales, and also likely other baleen whales as well, have counter-current heat exchangers to minimize heat loss from their large tongue. Because the tongue is muscular and used in feeding, it has very little fat for insulation and is a potential source for major heat loss. In the study, it was found that the tongue of these whales has an extensive counter-current exchange system, called lingual retia, used to conserve heat while feeding in cold northern waters. Like other retia that have been studied, these structures allow the cooler blood to be warmed by the heat exchange mechanism, thus reducing heat loss by the tongue and conserving internal body heat.
Perhaps most fascinating of all is the efficiency of the heat-exchange mechanism in conserving heat loss. Using special electronic sensors, the zoologists were able to determine that more heat is actually lost through the heavily insulated outer skin than through the tongue, even though the tongue has a much thinner layer of fat and is highly vascularized.
The existence of such highly efficient and complex structures such as these would certainly raise the question of how they originated. Like modern heating or cooling equipment designed by engineers, structures such as these would seem more likely to be the result of design by an intelligent Creator, than to have evolved through random chance events. Once again, the study of the creation points us back to the Creator.
Reference: J.E. Heyning and J.G. Mead, "Thermoregulation in the Mouths of Feeding Grey Whales," Science, 278:1138-1139, November 7, 1997. For additional details see: K.Schmidt-Nielsen, Animal Physiology, Cambridge University Press, 1997.
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