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.
This is because PVCs make the heart pump blood less effectively. What Causes PVCs? In some cases, no cause of PVCs is found. When a cause is found, it is either chemical or structural. Chemical. Changes in the bodyâs chemistry can prompt PVCs. For instance, raised levels of certain hormones, such as adrenaline or thyroid, can cause PVCs. Consuming substances such as alcohol and caffeine can also cause them.