The Cardiovascular Control of Heat Exchange: Consequences of Body Size

For blood flow to be an effective agent for the control of heatexchange, it must occur in a region of the body where conductionresistance in the tissues is relatively high, and in an environmentwhere external resistance to heat exchange is relatively low.If either of these conditions is not met, control of heat exchangeby blood flow is not possible. Very small reptiles should notbe able to control heat exchange by blood flow in any environment,unless they control blood flow specifically to appendages. Verylarge reptiles should be able to control heat exchange by bloodflow only under certain conditions, such as in water, very highwinds, or intense radiative heating. Otherwise, they shouldhave little control. An optimum body size should exist for areptile's ability to control heat exchange using blood flow.In air, this optimum body size for alligators appears to beabout 5 kg. Theoretically, the optimum size should be substantiallylarger than 5 kg for reptiles heating and cooling in water.