The body stays cool by doing what to blood vessels near the skin, and it stays warm by doing what to those blood vessels?

The function of blood vessels in temperature regulation is crucial for maintaining the body's homeostasis. When the body needs to cool down, the blood vessels near the skin dilate, allowing more blood to flow to the surface. This increased blood flow enhances heat loss through the skin because the warm blood coming from the body's core transfers its heat to the cooler external environment.

Conversely, when the body needs to conserve heat, the blood vessels constrict. This constriction reduces blood flow to the skin, which helps retain body heat by limiting heat loss to the surrounding environment.

Thus, the correct answer reflects the physiological responses of dilation and constriction of blood vessels to manage the body’s temperature effectively.