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.
Premature ventricular contractions (PVCs, PVC) are premature heartbeats originating from the ventricles of the heart. Premature ventricular contractions are premature because they occur before the regular heartbeat. The heart has four chambers. The upper two chambers are the atria, and the lower two chambers are the ventricles.
Premature ventricular contractions (PVCs) are heartbeats that occur earlier than they should. These early beats briefly interrupt the heart 's rhythm. A PVC may feel like a skipped heartbeat or a flutter. PVCs are the most common type of change in heart rhythm. They are common in children and teens as well as in adults.