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When one is cold or the external temperature is low, most venous blood returning from the distal part of the arm travels in the deep veins where it is picks up heat (by countercurrent exchange) 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 veins tend to bulge superficially in a person who is working out. Explain why venous return takes a different route in the second situation. (4 points). Answer: