Blood flow and heat exchange in reptiles

Reptiles are popularly deisgnated "cold-blooded", when in fact they can sustain high and steady bpdy temperatures just as mammals and birds do. Reptiles accomplish this not through high rates of internal heat production, as do mammals and birds. Rather, they engage in quite sophisticated exploitation of heat exchange between their bodies and their environment.

This is sometimes called behavioral thermoregulation, although this is only a partial description. Lizards, for example, will often shuttle between locations where they can absorb heat from the sun, or warm ground, and then venture into cooler spots to forage and do other things lizards do. This is called shuttling thermoregulation. By shuttling between locations where they absorb heat and locations where they lose it, a lizard's body temperature will oscillate within a narrow range, which can be impressively warm.

This means of temperature regulation can only be partially behavoral. Heat flows into or out of a lizard's body at the skin. Inside the skin, heat flows into and out of the body by conduction and by transport in blood flowing between the body and skin. This is what our own bodies do, when our skin flushes in the heat and blanches in the cold. When the body is too warm, increasing blood flow to the skin helps dump excess heat to the environment. When the environment is cold, blood flow to the skin is restricted so that heat may be retained in the body.

In shuttling thermoregulation, similar patterns of blood flow can alter the course of body temperature. Specifically, blood flow to the skin is elevated when the lizard is warming, so that the body heats rapidly. When the lizard is moving about in cool environments, blood flow to the skin is restricted, so that the body cools slowly.

In this way, the lizard can maximize the time it spends foraging and attending to other important duties, and minimize the time it must devote to warming.

This is the phenomenon I wanted to study.

Further reading

Cowles, R. B. and C. M. Bogert (1944). A preliminary study of the thermal requirements of desert reptiles. Bulletin of the American Museum of Natural History 83(5): 261-296.

Dreisig, H. (1984). Control of body temperature in shuttling ectotherms. Journal of Thermal Biology 9: 229-234.

Judd, F. W. (1975). Activity and thermal ecology of the keeled earless lizard Holbrookia propinqua. Herpetologica 31(2): 137-150.

Blood flow pages

Heat exchange

Why alligators?

What we did

What we found