Cerebrospinal fluid (CSF) is produced by choroid plexuses in the ventricles and circulates through the brain and spinal cord, providing nutrients and protection. It is absorbed through arachnoid villi into venous sinuses. The blood-brain barrier (BBB) protects the brain by restricting diffusion between blood vessels and brain tissue through tight junctions in brain capillaries. Disruption of CSF circulation or the BBB can lead to conditions like hydrocephalus or brain edema.