The blood-brain barrier transports nutrients into the brain and prevents harmful molecules from entering.

“the blood-brain barrier serves a couple of functions I mean one is it is providing it's it's there's a combination of different cell types that make up the blood-brain barrier and a lot of vasculature right and so — blood flow you know things things are brought to the blood-brain barrier and oxygen glucose other nutrients and they are you know transported across the blood-brain barrier but it also as the word implies barrier provides a barrier to things that you don't want to get into your brain”