2. Regulate body temperature.
When the outside temperature is high, the skin capillary network opens largely, the blood flow of the body surface increases, the skin heat dissipation increases, so that the body temperature is not too high. When the temperature is low, the skin capillary network is partially closed, and part of the blood flow goes directly into the vein through the arteriovenous anastomotic branch, which reduces the blood flow on the body surface, reduces heat dissipation and maintains the body temperature. When the temperature is high, the body sweats a lot, sweat evaporation process can take away part of the body's heat, play a role in reducing body temperature.