What is the role of blood vessels in the dermis related to thermoregulation?
Blood vessels being capable to expand and contract play quite important role in thermoregulation.
Dermis has rich blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction.
When the temperature is high, dilated blood vessels(vasodilation) increase perfusion and heat loss while in case of low temperature constricted blood vessels(vasoconstriction) greatly reduce cutaneous blood flow and conserve heat.
That's just quite simple approach to the concept: blood vessels in dermis play a salient role in thermoregulation.
Hope it helps...