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.
PVCs are also called premature ventricular complexes, ventricular premature beats and extrasystoles. Symptoms, Causes and Diagnosis of PVCs Symptoms of PVCs include a fluttering or flip-flop feeling in the chest, pounding or jumping heart rate, skipped beats and palpitations, or an increased awareness of your heartbeat.