<P> Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels , including many of those in the skin , the digestive tract , and the kidneys . This occurs as a result of activation of alpha - 1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons . These receptors exist throughout the vasculature of the body but are inhibited and counterbalanced by beta - 2 adrenergic receptors ( stimulated by epinephrine release from the adrenal glands ) in the skeletal muscles , the heart , the lungs , and the brain during a sympathoadrenal response . The net effect of this is a shunting of blood away from the organs not necessary to the immediate survival of the organism and an increase in blood flow to those organs involved in intense physical activity . </P>
what does the adrenal gland produce that is necessary for the sympathetic nervous system to function
epinephrine