| Brain: Circumventricular organs | ||
|---|---|---|
| Scheme showing relations of the ventricles to the surface of the brain. Circumventricular organs primarily surround the third ventricle and fourth ventricle. | ||
| Gray's | subject #189 825 | |
| NeuroNames | hier-1242 | |
Circumventricular organs (CVO) are so named because they are positioned at distinct sites around the margin of the ventricular system of the brain.
They are among the few sites in the brain which have an incomplete blood–brain barrier. As a result, neurons located in circumventricular organs can directly sense the concentrations of various compounds, particularly peptide hormones, in the bloodstream, without the need for specialized transport systems which move those compounds across the blood–brain barrier.
A useful mnemonic device for remembering this aspect of their function, though not the source of the name, is that they allow factors to 'circumvent' the blood–brain barrier.
These organs secrete[1] or are sites of action of a variety of different hormones, neurotransmitters and cytokines.
They are sometimes classified by whether they are secretory or sensory.[2]
Circumventricular organs include the following:
| Name | Secretory/sensory | Ventricle | Function |
|---|---|---|---|
| Subfornical organ | sensory | third | fluid regulation |
| Organum vasculosum of the lamina terminalis | sensory and secretory | third | detects peptides, fluid regulation |
| Median eminence | secretory | third | regulates the anterior pituitary through the release of neurohormones |
| Posterior pituitary (neurohypophysis) | secretory | third | store and secretes the hormones oxytocin and ADH into the blood, but does not synthesize either hormone |
| Subcommissural organ | secretory | third | secretes certain proteins into the Cerebrospinal fluid, its specific function is as yet unknown. |
| Pineal gland | sensory and secretory | third | stimulated by darkness to secrete melatonin and is associated with circadian rhythms |
| Area postrema | sensory | fourth | the vomiting centre of the brain (can detect noxious substances in the blood and stimulate vomiting in order to rid the body of these toxic chemicals) |
The choroid plexus is also sometimes considered a circumventricular organ.