Final answer:
Some animals have a countercurrent heat exchange system to conserve heat or cool vital parts, balancing temperatures between arteries and veins and protecting the internal organs from extreme temperatures.
Step-by-step explanation:
To conserve heat in a cold environment and to cool vital parts of the body under heat stress, some animals have a countercurrent heat exchange system. This biological adaptation allows endotherms to efficiently maintain their body temperature by transferring heat between arteries and veins that are in close proximity. The countercurrent heat exchange system is especially beneficial in preventing the cold venous blood from cooling the heart and other internal organs, and it helps maintain homeostasis within the organism's body.
Various animals possess this adaptation, including those living in aquatic environments like dolphins and sharks, as well as others such as bees and hummingbirds. In addition to maintaining warmth in colder environments, similar adaptations can also assist in cooling endotherms when necessary, such as with the large ears of elephants or the flukes of dolphins.