Vascular Control by Ions and
Other Chemical Factors
Many different ions and other chemical factors can either dilate or
constrict local blood vessels. Most of them have little function in overall regulation of the circulation,
but some specific effects are:
1. An increase in calcium ion concentration causes vasoconstriction. This results from the
generaleffect of calcium to stimulate smooth muscle contraction.
2. An increase in potassium ion concentration causes vasodilation. This results from the
ability ofpotassium ions to inhibit smooth muscle contraction.
3. An increase in magnesium ion concentration causes powerful vasodilation because magnesium
ions inhibit smooth muscle contraction.
4. An increase
in hydrogen ion concentration (decrease in pH) causes dilation of the
Conversely, slight decrease
in hydrogen ion concentration causes arteriolar constriction.
5. Anions that have significant effects on bloodvessels are acetate and citrate, both of which cause mild degrees of vasodilation.
6. An increase in carbon dioxide concentration causes moderate vasodilation
in most tissues, but marked vasodilation in the brain. Also, carbon dioxide in
the blood, acting on the brain vasomotor center, has an extremely powerful
indirect effect, transmitted through the sympathetic nervous vasoconstrictor
system, to cause widespread vasoconstriction throughout the body.