Circumventricular organs are small specialised areas around the third and fourth ventricles where the blood brain barrier is absent. This lets the brain sample the blood directly or release hormones into it.
| Location | Around the walls of the third and fourth ventricles |
|---|---|
| Parts |
|
| Connections |
|
| Blood Supply | Fenestrated capillaries from local branches of the circle of Willis and vertebrobasilar system |
Sense blood levels of salt, hormones and toxins, and release hormones into the bloodstream.
They explain how circulating substances trigger thirst, fever and vomiting. The area postrema is the vomiting trigger zone targeted by anti-sickness drugs. These areas can enhance on contrast scans normally, which should not be mistaken for disease.
Stimulation of the area postrema by drugs in the blood.
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