The tissue in the walls of blood vessels that allows for regulation of vessel diameter is the smooth muscle.
The smooth muscles found in blood vessels are called vascular smooth muscles. It takes up a majority of the walls of blood vessels. It regulates the diameter or the blood vessel by contracting or relaxing.
The vascular smooth muscle also plays a role in regulating blood pressure. When it relaxes, the blood vessel dilates, which lowers blood pressure, and when it contracts, the blood vessels become constricted which increases blood pressure.
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