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The sympathetic nervous system (SNS) predominantly causes vasoconstriction in arterioles, which is crucial for regulating blood flow and maintaining blood pressure during times of stress or physical activity. This response occurs through the release of norepinephrine, which binds to alpha-adrenergic receptors located on vascular smooth muscle, leading to contraction and consequently narrows the lumen of the vessels.

As a result of this constriction, there's an increase in peripheral resistance which elevates blood pressure and redirects blood flow away from non-emergency organs and toward vital organs such as the heart and muscles. This physiological mechanism is particularly important during 'fight or flight' situations where immediate energy and resource mobilization are required.

Understanding that the sympathetic nervous system is responsible for the constriction of arterioles helps clarify how the body effectively manages blood distribution and pressure in response to varying physiological demands.