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.
Most PVCs occur infrequently and are benign. Frequent PVCs may increase the risk of developing other, more serious cardiac arrhythmias. Individuals with frequent PVCs who have underlying heart disease, structural abnormalities in the heart or have had a previous heart attack have a higher risk of death. premature ventricular contraction (PVC) is a too-early heartbeat that originates in the ventricles and disrupts the heartâs normal rhythm.