Question

When we are 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 picks up heat (by countercurrent exchange) from the nearby brachial artery en route. However, when we are 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.

Answer 1

Answer:

When the body is cold, the blood inside the body travels via different route to rise the temperature of the body so that it fells hot and stable.

During the time of exercise, the blood distribution changes and hypothalamus  signals for reduced vasometer stimulates the vessels present in skin.

Blood moves through the capillary beds and radiates heat from the body to make it feel cool.

This is a short term neural control mechanism of the body to meet the specific demands.