Circumventricular organs

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]

Examples

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.^{[citation needed]}

References

1. ^ Ganong WF (2000). "Circumventricular organs: definition and role in the regulation of endocrine and autonomic function". Clin. Exp. Pharmacol. Physiol. 27 (5-6): 422–7. PMID 10831247. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0305-1870&date=2000&volume=27&issue=5-6&spage=422. 
2. ^ Duvernoy HM, Risold PY (November 2007). "The circumventricular organs: an atlas of comparative anatomy and vascularization". Brain Res Rev 56 (1): 119–47. doi:10.1016/j.brainresrev.2007.06.002. PMID 17659349. http://linkinghub.elsevier.com/retrieve/pii/S0165-0173(07)00107-5. 

External links

• http://www.meddean.luc.edu/lumen/MedEd/Neuro/Circumventricular.html