Stroke volume is intrinsically increased by larger preload. So venous vasoconstriction leads to increased cardiac output by increased stroke volume (increased venous return). This can be stimulated by the sympathetic nervous system. Venous vasodilation would have the opposite effect..
Also to know is, why does vasoconstriction cause an increase in blood pressure?
Vasodilation caused by relaxation of smooth muscle cells in arteries causes an increase in blood flow. When blood vessels dilate, the blood flow is increased due to a decrease in vascular resistance. Therefore, dilation of arteries and arterioles leads to an immediate decrease in arterial blood pressure and heart rate.
What does vasoconstriction do to blood flow?
Blood flow to individual organs, or throughout the entire circulatory system, can be regulated by changing the diameter of the arterioles. Vasodilation of the arterioles decreases resistance and increases blood flow. Vasoconstriction of the arterioles increases resistance and decreases blood flow.
Why does constriction of arterioles increase blood pressure?
So in brief, regional vasoconstriction, within physiological limits, will increase blood pressure, but conversely decrease flow because blood is shunted to other lower resistance areas.