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.
Other potential causes of elevated BNP levels include diastolic dysfunction, acute coronary syndromes (very sensitive but not specific), hypertension with LVH, valvular heart disease, atrial fibrillation, and pulmonary embolism, pulmonary hypertension, sepsis, COPD, or hyperthyroidism.