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.
There are a variety of triggers that can cause leukocytoclastic vasculitis, though in many cases, the problem arises spontaneously with no identifiable cause. Often it appears to be caused by a misguided immune response, where the body mistakenly sees its own blood vessels as an intruder and attacks them.