Why don't penguins' feet freeze

01:00 Mon 26th Mar 2001 |

This is an intriguing question posed by Henryn. Read The Answerbank's in depth discussion below or click here to see Homer's answer.

Q. What adaptations have penguins made to keep their feet from freezing

A. The system that stops a penguin's foot from freezing is very elaborate and sophisticated and employs two mechanisms.

The first one allows the penguin to control the rate of blood flowing to its feet by varying the diameter of arterial vessels supplying the blood. In cold conditions the flow is reduced, when it is warm the flow increases.

The second mechanism takes the form of 'counter current heat exchangers' at the top of the legs. The arteries, which supply warm blood and oxygen to the penguin's feet break up into many small vessels which are closely linked to similar numbers of venous vessels bringing cold blood back from the feet. So, when heat is lost from the arterial vessels, the venous vessels running in the opposite direction pick it up and carry it back through the body, rather than out through the feet. This means that in the very remote regions of the skin, cells get oxygen but heat isn't lost through this skin.

Q. Why are the feet the main problem

A. The feet pose particular problems since they cannot be covered with insulation in the form of feathers or blubber, yet have a big surface area.

Q. So, what temperature are penguin's feet, normal body temperature

A. No, in the winter, penguins' feet are held a degree or two above freezing, this minimises taking heat away from the rest of the body, whilst avoiding frostbite.

Q. Are penguins the only animals that can change the flow of blood through their arteries

A. No, humans can do this too, only on a simpler level, which is why our hands and feet become white when we are cold and pink when warm.

Are there any other amazing animal adaptations you'd like explained Just click here to post a question.

by Lisa Cardy

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