vasoconstriction [L, vas + constrigere, to tighten] , a decrease in the diameter of a blood vessel. It plays an important role in the control of blood pressure and the distribution of blood throughout the body. Vasoconstriction is triggered by stimulation of the vasomotor constriction center in the medulla. Impulses from this center travel along sympathetic nerve fibers and cause contraction of the smooth muscle layers of arteries, arterioles, and, to a lesser extent, venules, and veins, bringing about constriction of these vessels. Vasoconstriction is also induced by vasomotor pressure reflexes, chemical reflexes, the medullary ischemic reflex, and impulses from the cerebral cortex and the hypothalamus. Compare vasodilation. −vasoconstrictive, adj.
