Figure 32.16: Countercurrent Heat Exchange Here we look at blood flow and heat flow within a leg of a mammal standing in a cold environment. (A) Two different arrangements of arteries and veins are possible in the leg. In the countercurrent arrangement, the arteries and veins—carrying blood in opposite directions—are closely juxtaposed. (B) During countercurrent heat exchange, blood flows all the way to the outer end of an appendage and back, but heat does not. Heat takes a shortcut, enabling it to move back into the body core before it can be readily lost to the environment at the exposed outer end of the appendage.