What is an example of a counter current system in the body?

An example of a countercurrent system in the body is the arrangement of blood vessels in the extremities that helps conserve heat. There are two sets of blood vessels. In one set, arteries carrying warm blood to the hands or feet run side-by-side with veins carrying cool blood back from them. The warmth is transferred into the venous blood before it reaches the rest of the body. If heat loss had to wait for diffusion across tissues on the surface of veins, we would require much warmer clothes (more insulation)