Q: Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.
Question: Does blood flow increase or decrease when blood vessels constrict? Answer: decrease
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
When a blood vessel constricts, less blood can flow through it.