circumventricular organs
several small structures located around the edges of the third and fourth ventricles, lacking the regular blood-brain barrier and thus serving as significant sites for neural-endocrine interaction. They include the area postrema, median eminence, subcommissural organ, subfornical organ, and vascular organ of lamina terminalis. Sometimes also included are the funiculus separans, neurohypophysis, and pineal body.
Medical dictionary.
2011.