With no CC exchange (left), the foot stays warm and loses heat to the ice.
countercurrent exchange-figure
Back Yard Biology
Back Yard Biology 
what is exactly is the countercurrent system. why is it important to animal living in polar regions?. Is also important for humans
Counter-current systems are useful for preserving very steep gradients between two ends of a set of parallel pipes. It is of course, vital that the two pipes are running in opposite directions and are able to exchange material (e.g., oxygen, heat, etc) along their length, or the system doesn’t work. For example, in the legs of deer, or arctic foxes, or ducks standing on ice or whales and dolphins swimming in extremely cold water, warm arterial blood coming from the core of the body gives up its heat to the cooler blood returning from the feet or fins so that venous blood is warmed before returning to the core and arterial blood is cooled before reaching the periphery where it would simply be lost to the environment. In this way, animals in polar regions conserve their heat and stay warmer without excessive loss of body fat in the process.