What term describes the body's mechanism to decrease the radius of a blood vessel?

What term describes the body's mechanism to decrease the radius of a blood vessel?

• A. Vasodilation
• B. Vasoconstriction
• C. Hemoconcentration
• D. Angiogenesis

Answer: (B)

Vasoconstriction is the body's mechanism to decrease the radius of a blood vessel. It occurs when the smooth muscle in the vessel wall, especially in arterioles, contracts in response to sympathetic nerve activity or certain chemical signals. As the radius narrows, the resistance to blood flow increases dramatically (resistance is highly sensitive to radius, by the fourth power), so blood flow to that region is reduced and systemic blood pressure can rise if needed. This tightening helps regulate how much blood reaches specific tissues and maintains overall hemodynamic stability. By contrast, vasodilation would widen the vessel and increase flow; hemoconcentration refers to a higher concentration of blood components due to fluid shifts, not changes in vessel size; angiogenesis means the growth of new vessels over time, not immediate radius changes.

Vasoconstriction is the body's mechanism to decrease the radius of a blood vessel. It occurs when the smooth muscle in the vessel wall, especially in arterioles, contracts in response to sympathetic nerve activity or certain chemical signals. As the radius narrows, the resistance to blood flow increases dramatically (resistance is highly sensitive to radius, by the fourth power), so blood flow to that region is reduced and systemic blood pressure can rise if needed. This tightening helps regulate how much blood reaches specific tissues and maintains overall hemodynamic stability. By contrast, vasodilation would widen the vessel and increase flow; hemoconcentration refers to a higher concentration of blood components due to fluid shifts, not changes in vessel size; angiogenesis means the growth of new vessels over time, not immediate radius changes.