What is Vasoconstriction
Vasodilation (definition) = the increase in the internal diameter of blood vessels that is caused by relaxation of smooth muscles within the wall of the vessels, thus causing an increase in blood flow. The opposite effect is vasoconstriction.
During vasodilation, when blood vessels dilate, the blood flow is increased due to a decrease in vascular resistance. However, for practical purposes, dilation of arteries and arterioles has the most significant therapeutic value since these blood vessels are the main contributors to systemic-vascular resistance and, therefore, dilation of arteries and arterioles leads to an immediate decrease in arterial blood pressure and heart rate. Hence, chemical-arterial dilators are used to treat heart failure, systemic and pulmonary hypertension, and angina. Dilation of venous-blood vessels decreases venous-blood pressure. Such agents can be used to reduce cardiac output, venous-and-arterial pressure, tissue edema (due to better capillary-fluid filtration), and myocardial oxygen demands. Let us consider practical or real-life aspects of vasodilation and vasoconstriction. These major aspects are ignored by official medical sources.