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.
Without qualification, trigeminy often means trigeminal PVCs, though it can occasionally also refer to trigeminal premature junctional contractions/PJCs or trigeminal premature atrial contractions/PACs. PVCs refer to early depolarizations commencing in the ventricle instead of the sinus node. Ventriculartrigeminy is defined as the occurrence of a PVC every third beat. A high frequency of trigeminy PVCs in heart disease patients has been found to cause ventricular fibrillation and unexpected death.