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.
Ventricular Arrhythmias. Premature ventricular contractions (PVCs) are the most common cause of irregular heart rhythms. The heartbeat is created by an electrical signal that originates in an area of specialized cells in the heartâs upper right chamber, the right atrium. premature ventricular contraction (PVC) is a too-early heartbeat that originates in the ventricles and disrupts the heartâs normal rhythm.