The choroid plexus

The choroid plexus (from Greek khorion "membrane enclosing the fetus, afterbirth"; plexus: Mod.L., lit. "braid, network") is a structure in the ventricles of the brain where cerebrospinal fluid (CSF) is produced. The choroid plexus consists of modified ependymal cells. CSF is recycled (flushed) 4 times per day in order to clean out metabolites and toxins like beta amyloid. Hence the choroid plexus must produce about 500 milliliters of CSF daily (or 20.83 ml per hour).