How is peripheral resistance primarily regulated in the systemic circulation?

How is peripheral resistance primarily regulated in the systemic circulation?

• A. By capillary flow
• B. By arteriolar diameter via vasoconstriction and vasodilation
• C. By venous return
• D. By lymphatic drainage

Answer: (B)

Peripheral resistance in the systemic circulation is controlled mainly by the diameter of the small arteries and arterioles, where smooth muscle can constrict or relax to change vessel radius. Because resistance changes with the radius to the fourth power, even small shifts in arteriolar diameter produce large changes in overall resistance. When arterioles constrict (vasoconstriction), resistance rises and blood pressure increases; when they dilate (vasodilation), resistance falls and pressure drops. This tone is actively regulated by the autonomic nervous system, circulating hormones, and local metabolic factors, allowing rapid adjustments to meet the body's needs. Capillary flow is a downstream effect of upstream arteriolar resistance and the capillary network’s large total cross-sectional area means capillaries themselves contribute less to the dynamic regulation of systemic resistance. Venous return influences preload and cardiac output rather than acting as the primary regulator of peripheral resistance. Lymphatic drainage does not directly modulate vascular tone or resistance.

Peripheral resistance in the systemic circulation is controlled mainly by the diameter of the small arteries and arterioles, where smooth muscle can constrict or relax to change vessel radius. Because resistance changes with the radius to the fourth power, even small shifts in arteriolar diameter produce large changes in overall resistance. When arterioles constrict (vasoconstriction), resistance rises and blood pressure increases; when they dilate (vasodilation), resistance falls and pressure drops. This tone is actively regulated by the autonomic nervous system, circulating hormones, and local metabolic factors, allowing rapid adjustments to meet the body's needs.

Capillary flow is a downstream effect of upstream arteriolar resistance and the capillary network’s large total cross-sectional area means capillaries themselves contribute less to the dynamic regulation of systemic resistance. Venous return influences preload and cardiac output rather than acting as the primary regulator of peripheral resistance. Lymphatic drainage does not directly modulate vascular tone or resistance.