Describe the structure and function of the blood-brain barrier.

The blood–brain barrier is formed by brain endothelial cells and it allows the passage of water,  and lipid-soluble molecules by diffusion, as well as the selective transport of molecules such as glucose and amino acids that are decisive  to neural function. The another function of it is that it allows specific transport proteins that determine which substances can cross the barrier. HOPED THIS HELPS YOU :)

Active site is where they touch.