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.
Premature Ventricular Contractions. Premature ventricular contractions (PVCs) are a type of arrhythmia (irregular heartbeat). They are common and can affect people of all ages. PVCs are often not dangerous. But if other heart problems are present, PVCs can cause serious health issues. This sheet tells you more about PVCs and how they are treated.