Final answer:
The drainage of CSF into the blood is a function of the arachnoid granulations, where the CSF is reabsorbed into the bloodstream after circulating through the CNS.
Step-by-step explanation:
The drainage of cerebrospinal fluid (CSF) into the blood is a function of the arachnoid granulations. These are outpocketings of the arachnoid membrane that protrude into the dural sinuses, acting as sites where CSF can be reabsorbed into the bloodstream. The choroid plexus, found in all four ventricles of the brain, consists of ependymal cells that filter blood to produce CSF. Once CSF has circulated through the ventricular system and the subarachnoid space, fulfilling its role of removing metabolic wastes and providing cushioning for the CNS, it is reabsorbed through the arachnoid granulations.