Final answer:
When caffeine is absent, peripheral blood vessels dilate while cerebral blood vessels constrict.
Step-by-step explanation:
When caffeine is absent, blood vessels in the body undergo changes that result in selective vasodilation in certain areas, while vasoconstriction occurs in others. Specifically, peripheral blood vessels, such as those in the skeletal muscles, heart, lungs, liver, and integument, will dilate. On the other hand, blood vessels leading to the kidneys, digestive system, and reproductive organs will constrict.