Final answer:
The muscles and blood vessels act as d. effectors in the negative feedback loop of thermoregulation. They help restore normal body temperature by dilating or constricting blood vessels, depending on whether body temperature is too high or too low.
Step-by-step explanation:
The muscles and blood vessels play the role of effectors in the negative feedback loop of thermoregulation. In this process, the stimulus is a change in body temperature. When the body temperature deviates from the set point, the muscles and blood vessels respond to restore normal body temperature. For example, when body temperature is too high, the blood vessels dilate (vasodilation) to allow more blood flow near the skin surface, promoting heat loss through radiation and sweating.
When body temperature is too low, the blood vessels constrict (vasoconstriction) to reduce blood flow near the skin surface, conserving heat. In both cases, the actions of the muscles and blood vessels are controlled by the integration center, which is the hypothalamus in the brain.