Answer to Question #99439 in Zoology for Helen Najera

Question

What arctic animals use countercurrent circulation? Where in those animals is it most conspicuous?

Answer 1

The arctic animals that use countercurrent circulation are arctic fox, polar bears and penguin to keep their body warm without losing heat of the body, so that they can survive in the snow.

This type of circulation is found in the legs of an Arctic fox treading on snow. The paws are necessarily cold, but blood can circulate to bring nutrients to the paws without losing much heat from the body. Proximity of arteries and veins in the leg results in heat exchange, so that as the blood flows down it becomes cooler, and doesn't lose much heat to the snow. As the (cold) blood flows back up from the paws through the veins, it picks up heat from the blood flowing in the opposite direction, so that it returns to the torso in a warm state, allowing the fox to maintain a comfortable temperature, without losing it to the snow. This system is so efficient that the Arctic fox does not begin to shiver until the temperature drops to −70 °C (−94 °F).

The most conspicuous evidence of these arctic animal is what they leave behind on the ice—their poop. The brown stains stand out really well on the fresh snow.