In which direction is the smooth muscle oriented: longitudinally (down the length of the blood vessels) or circumferentially (around the circumference of the blood vessel)? explain how this orientation allows for blood vessels to contract and expand.

It is known that the smooth muscles are present along the blood vessel's circumference. Thus, because of this alignment when the contraction of smooth muscles takes place, the diameter of the blood vessels also constricts. As a consequence, less concentration of blood will move inward. This is called vasoconstriction of blood vessel. On the other hand, the relaxed state of muscle leads to dilation of blood vessel. This is known as vasodilation and due to this more blood will flow in the blood vessel.

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.