blood-brain barrier

Definition of blood-brain barrier
National Cancer Institute

blood-brain barrier

(blud-brayn BAYR-ee-er)
A network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain. The blood-brain barrier lets some substances, such as water, oxygen, carbon dioxide, and general anesthetics, pass into the brain. It also keeps out bacteria and other substances, such as many anticancer drugs. Also called BBB.

Source: NCI Dictionary of Cancer Terms