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.
If you have a known heart problem, such as heart failure or heart disease, PVCs may be a sign that a dangerous heart rhythm could occur. So if you have a heart problem, talk to your doctor if you feel any change in your heartbeat. The cause of PVCs usually isn't known. But the chance of having PVCs can be increased by: 1  Having too much or too little of certain minerals (electrolytes) in your body. 2  Having too little oxygen in your blood, which could happen if you have COPD or pneumonia. 3  Using some medicines, such as albuterol.