Vasoconstriction and vasodilation are the two processes in which blood vessels are involved. Vasoconstriction is when the blood vessels narrow because of the contraction of the muscular walls of vessels. Vasodilation is the opposite of vasoconstriction, meaning the widening of blood vessels due to the relaxation of muscular walls. On a cellular level, both changes are dependent on the quality of work of vascular smooth muscle cells in a vascular wall. However, smooth muscles cannot be voluntarily controlled; thus, they are automatically regulated by chemical signals in the body. Such mediators and hormones as epinephrine, endothelin, and vasopressin may regulate vasoconstriction. During vasodilation, relaxation occurs by removing contractile stimuli like acetylcholine, bradykinin, or histamine that form nitric oxide.
Vasoconstriction and vasodilation can be advantageous and disadvantageous to the human body. For example, when a person feels cold, vasoconstriction is effective in keeping the body warm. This process allows for maintaining a healthy blood flow, which helps control the body temperature and raise blood pressure if necessary. Vasodilation is also characterized by certain benefits like increasing blood flow, enhancing healthy muscles, and improving circulation. When a person is injured, removing as much metabolic waste as possible from the injury site is necessary. The vasodilation process widens blood vessels, fills them with oxygen and essential nutrients, and repairs the area.