Final answer:
CSF is produced by the choroid plexus and circulated through the ventricular system and subarachnoid space of the brain. It is reabsorbed into the blood at arachnoid granulations that connect with the venous system, helping remove metabolic wastes and acting as a cushion for the CNS.
Step-by-step explanation:
The cerebrospinal fluid (CSF) enters the circulation via a process that involves its flow through the ventricular system of the brain and the reabsorption into the blood. The choroid plexus in the four ventricles produces CSF, which circulates through the ventricular system. From there, it moves into the subarachnoid space through the median and lateral apertures. The function of the CSF is to remove metabolic wastes from the nervous tissue and act as a cushion for the brain and spinal cord.
Once the CSF is in the subarachnoid space, it flows around the central nervous system (CNS) and is then absorbed back into the blood at arachnoid granulations. These are outpocketings of the arachnoid membrane into the dural sinuses that allow for the transfer of CSF into the venous system. From the dural sinuses, blood drains out of the head and neck through the jugular veins, carrying the reoxygenated blood and filtered waste away from the brain.