The term secretory circumventricular organs refers to circumventricular organs classified on the basis of function; they discharge neurohormones into the blood stream or ventricles in response to neural input from other structures. The neurohypophysis, the subcommissural organ and, perhaps, the organum vasculosum belong to this group ( Duvernoy-2007 ). The other circumventricular organs belong to the humerosensory system.