Blood Flow Regulates Heat Exchange

a close up above view of an american alligator

Biological Strategy

American alligator

AskNature Team

Image: Lacey Steward / Flickr / CC BY - Creative Commons Attribution alone

Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Reptiles

Class Reptilia (“creeping”): Lizards, crocodiles, turtles, snakes

Reptiles retain some of the key characteristics that first enabled vertebrates to live permanently on land. They have dry skin covered in scales made of keratin that help prevent water loss. (Amphibians still need to stick close to water to keep their skin moist.) Many reptiles reproduce by laying eggs that are watertight and have a yolk, so eggs can develop on land while staying moist and nourished. Reptiles are also ectotherms, meaning they don’t produce their own body heat. This means they burn through energy much more slowly than “warm blooded” creatures of the same size. It also means that they need to keep warm to keep active, which is why you might see them spending a seemingly inordinate amount of time simply basking in the sun.

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Skin of alligators regulates heat exchange by increasing blood flow.

Image: Adam Fagen /

“Alligators possess several thermoregulatory abilities that may be of interest to architects. First, alligators have the ability to drop their body temperature when they are not receiving enough oxygen. This seems to offset changes that would otherwise occur in ventilation, oxygen consumption, acid-base balance, and lactate levels. Second, alligators warm their bodies much more quickly than they cool off. The ratio of rate of heating to rate of cooling is dependent on body mass, but is generally 2-3. The ratio is maximal when the alligator is 5 kg, indicating that there is an optimal size for control of heat exchange. The speedy rate of warming in alligators can be attributed to increased blood flow in the skin. During cooling, blood flow does not change. In fact, the results of one study suggest that blood flow is not at all involved in cooling. When blood flow to the appendages was occluded, the rate of warming dropped significantly, while the rate of cooling did not change. There may be an optimum body size for the control of heat exchange. The ratio of rate of heating to rate of cooling is maximum when the alligator is 5 kg. Alligators warm their bodies up to twice as fast as they cool down. There is greater blood flow in the skin during warming than during cooling.” (Courtesy of the Biomimicry Guild)