Cerebrospinal fluid

CSF is a clear colorless fluid, formed as an ultrafiltrate of blood, forms in the ventricles of the brain and surrounds the brain and spinal cord in the subarachnoid space.  CSF provides a mechanical cushion for the brain against the skull, and also provides immunological protection to the brain.

CSF is produced in the choroid plexuses in the ventricles of the brain, and slowly flows from the ventricles into the subarachnoid space around the brain and spinal cord.  Under normal conditions only about 150 ml of CSF occupies the ventricles and subarachnoid space.  About 500 ml are made per day, so about 500 ml are returned to the venous blood per day, through the arachnoid granulations and other pathways.