Vascular activity consists of constriction of muscles within the walls of the blood vessels in response to vascular damage. This vasoconstriction narrows the path through which the blood flows and may sometimes entirely halt blood flow. The vascular phase of hemostasis affects only arterioles and their dependent capillaries; large vessels cannot constrict sufficiently to prevent blood loss. Even in small vessels, vasoconstriction provides only a brief hemostasis.