The choroid plexus produces most of the cerebrospinal fluid surrounding the human brain and spinal cord.
Choroid plexuses are specialized, highly vascular tissues found within the ventricles of the brain. Their epithelial cells filter and secrete components from blood to form cerebrospinal fluid, commonly called CSF. The fluid circulates through the ventricles and around the brain and spinal cord in the subarachnoid space.
CSF cushions the central nervous system, helps maintain a stable chemical environment, and assists with removal of some metabolic waste. It is continuously produced and reabsorbed, with much of the reabsorption occurring through arachnoid granulations into the venous system. Disruption of this balance can contribute to hydrocephalus.
The choroid plexus is not the same as the choroid layer of the eye. It is also different from the meninges, the protective membranes around the central nervous system. The blood–CSF barrier formed by choroid-plexus tissue helps regulate which substances enter the fluid.