Similar to the blood–brain barrier, the blood–CSF barrier functions to prevent the passage of most blood-borne substances into the brain, while selectively permitting the passage specific substances into the brain and facilitating the removal of brain metabolites and metabolic waste into the blood.[10][11][12][7] Despite the similar function between the BBB and BCSFB, each facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems.[10][11] For a number of substances, the BCSFB is the primary site of entry into brain tissue.[10]