Answer and explanation:
Arteries are the blood vessels that take blood from the heart to the tissues where it's needed. For this task to be achieved, arteries have different structures and properties in each of their layers.
Arteries have 3 layers, also called tunicas: the intima (in contact with the blood), the media, and the adventitia (the most external layer).
The media -or middle layer- is composed of smooth muscle tissue and elastic connective tissue. This tunica is usually the thickest of the three and has a hugely important role in blood flow and blood pressure regulation.
Blood pressure (BP) is a variable that the body needs to maintain in a range for everything to work effectively. When blood pressure falls, the middle layer of the artery contracts (both in response to the change in blood flow and thanks to the action of specific hormones) so blood can flow somewhat faster and compensate for the disturbance in BP. On the other hand, when blood pressure rises, the middle layer of the artery dilates, to make the blood flow slower.
Smooth muscle tissue is fundamental for contraction, while elastic connective tissue is needed for dilatation.