(physiology) Constriction or narrowing of a blood vessel.
Dilation or widening of the blood vessels.
decrease in the diameter of blood vessels
dilation of blood vessels (especially the arteries)
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels.
Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles.