Circumventricular Organs

The circumventricular organs (CVOs) of the human brain comprises of the subfornical organ (SFO), vascular organ of the lamina terminalis (OVLT), median eminence, neurohypophysis, pineal gland, subcommissural organ, area postrema, and choroid plexus. They are a group of specialized structures within the brain, so named because they occupy strategic positions along the surface of the brain ventricles. In lower vertebrates, a number of other structures, including the saccus vasculosus, paraventricular organ, and paraphysis, have also been classified in this grouping of CVOs, but are not found in adult mammalian brain. The mammalian CVOs are subdivided into two groups-namely, paraependymal CVOs and ependymal CVOs. The paraependymal CVOs are the subfornical organ, OVLT, neurohypophysis, median eminence, pineal gland, and area postrema. They are characterized in regard to their neuroectodermal component by subependymal elements that differ considerably from the ependymal cells. The paraependymal CVOs have been further categorized into sensory and secretory circumventricular organs.