Asked by: Philip Boylan, by email
The blood-brain barrier (BBB) exists to protect the brain from infection and to isolate it from hormones and neurotransmitters used in the rest of the body. It prevents bacteria and large molecules from reaching brain cells, but it is by no means a complete barricade. Oxygen, CO2, water and glucose are all able to pass through the BBB. Fat-soluble drugs, like barbiturates, are also able to cross it.