vasoconstriction is a physiological mechanism that reduces the diameter of the blood vessels.
Vasoconstrictors (adrenalin) are substances that narrow the blood-vessels. The clinical use of vasoconstrictors is to increase blood pressure or to locally reduce blood flow.
increases the diameter of the vessels (vaso) through dilatation. This dilatation is possible through relaxation of the muscles from the vessels walls (arteries and veins).
the upper part of the skull.