Why penguins feet do not freeze’?

Penguin feet on ice.

Penguin feet

They are constantly on snow or ice or in ice water.

Their feet get close to freezing without freezing.

If warm blood was pumped into them, it would return to the body chilled.

Soon the heat loss through the feet would be so great that not only the feet but the whole penguin would freeze.

So an ingenious heat-exchange mechanism solves the problem.

The arteries entering the feet are surrounded by veins leaving the feet.

Thus the cold blood leaving the feet via these veins takes up heat from the warm blood descending in the arteries.

The arterial blood thus cooled is adequate for feet that have lots of tendons but few muscles—cold tendons can function adequately whereas chilled muscles cannot.

By means of this ingenious heat exchange, the penguin’s body is kept warm and its feet do not freeze.