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. 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.