When one is cold or the external temperature is low, most venous return from the distal part of the arm travels in the deep veins where it picks up heat from the nearby brachial artery en route. However, when one is hot, and especially during exercise, venous return from the distal arm travels in the superficial veins and those vines tend to bulge superficially in a person who is working out. Explain why venous return takes a different route in the second situation.
Blood transport helps with temperature homeostasis. By using the superficial veins the body can release excess body heat.