The adrenal medulla develops from neural tissue and secretes two hormones, epinephrine and norepinephrine. These two hormones are secreted in response to stimulation by sympathetic nerve, particularly during stressful situations. A lack of hormones from the adrenal medulla produces no significant effects.
While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and thus triggers a premature heartbeat.
The brain is the exclusive target of PACNS, a rare condition resulting in strokes, headache, confusion, and fever. Other forms of vasculitis, however, can also involve the brain, including PAN and CSS, and these. conditions can also cause damage to major nerves, as is also seen in small vessel vasculitis.