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Vasodilation
increase in the internal diameter of blood vessels due to relaxation of smooth muscle cells / From Wikipedia, the free encyclopedia
Vasodilation is where blood vessels widen.[1] It results from relaxation of muscle cells within blood vessel walls. The process is essentially the opposite of vasoconstriction, which is the narrowing of blood vessels.
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When vessels widen, blood flow is increased. This in turn decreases blood pressure. Drugs that cause vasodilation are called vasodilators.