Structures that affect circulation - arterioles and vasomotor responses

■ Small arteries and arterioles determine SVR. ■ Blood pressure drops significantly as blood passes through arterioles. ■ Decreasing arteriole radius and decreased wall elasticity are the main reasons for increased SVR. ■ Small changes in arteriole radius can cause large changes in resistance and blood flow. ■ Smooth muscle in the wall of an arteriole controls its radius. ■ Vasoconstriction: Smooth muscle in arteriole wall contracts, reducing vessel radius. ■ Vasoconstriction increases SVR and decreases local blood flow. ■ Vasodilation: Smooth muscle in arteriole wall relaxes, increasing vessel radius. ■ Vasodilation decreases SVR and increases local blood flow.

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