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.
Causes of superior vena cava syndrome. SVCS is more common for people who have lung cancer, non-Hodgkin lymphoma, or cancers that spread to the chest. But cancer can cause SVCS in other ways: A tumor in the chest may press on the superior vena cava. A tumor may grow into the superior vena cava, causing a blockage.