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.
Peripheral vascular disease (PVD) can occur when a disease or disorder causes a reduction in blood flow to any part of the circulatory system - outside of the brain or heart. Frequently caused by fatty deposits in arteries, or artheroschlerosis, this is one of the leading causes of disability in adults over 50.