Cerebrospinal fluid clears byproducts like A-beta proteins from interstitial fluid into the blood for excretion.

“cerebral spinal fluid is in a simplistic way the sewage system of the brain when the brain receives its metabolites its nutrients from the circulation it crosses the blood-brain barrier through the junction of the endothelial cells into brain cells that is a fluid surrounding brain cells that we call the interstitial fluid brain cells will take up whatever they need whether it's an astrocyte a microglia or a neuron and produce some byproducts one of the commonly studied byproducts are a beta proteins which are accumulating in diseases like alzheimer's those byproducts will then get cleared into the csf the csf or cerebrospinal fluid as i mentioned before is a form of a system that allows drainage from the brain cells from the interstitial fluid”