Final answer:
The autonomic nervous system (ANS) regulates blood pressure by constricting smooth muscles in blood vessel walls, increasing blood pressure.
Step-by-step explanation:
The autonomic nervous system (ANS) controls the regulation of blood pressure. The sympathetic branch of the ANS adjusts blood pressure by constricting the smooth muscles in the walls of blood vessels, increasing blood pressure. This is done through the release of norepinephrine from postganglionic sympathetic fibers and the hormones epinephrine and norepinephrine released from the adrenal medulla. The parasympathetic system has no significant input to systemic blood vessels, so the sympathetic system determines their tone.