[The blood-brain barrier. I. Morphologic data].

The blood-brain barrier (BBB) is situated between the blood and brain extracellular space (ECS), at the endothelial cells of the cerebral capillaries joined by tight junctions. Its characteristics allow a great selectivity in the blood-brain exchange of solutes: nearly total exclusion of some of them, enhancement of exchange for others. The choroid plexuses, situated at the blood-cerebrospinal fluid interface, play a similar role between blood and CSF. Neither interface can be studied separately.