What do the blood vessels do when they receive the message and why?

Explanation:

These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from the tissues. Blood vessels are needed to sustain life, because all of the body's tissues rely on their functionality.

i think it's the first one because doctors aren't the ones who get rid of the old needles. most of them time it's not even doctors who give you shots, it's nurses.