The circumventricular organs are neuroendocrine anatomical structures localised around the ventricles of the brain. They are characterised by a rich vasculature and fenestrated (permeable) capillaries. As such, with the exception of the subcomissural organ, they are also characterised by the absence of the blood-brain barrier.
Gross anatomy
Circumventricular organs can be classified either as sensitive or secretory. The former act as chemoreceptors, monitoring hormone levels in the cerebrospinal fluid and blood, and the latter allow secretion of hormones in the peripheral blood.
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