Blood brain barrier

The blood-brain barrier (BBB) is a semipermeable membrane that regulates what enters and leaves the brain, in order to protect it from harmful substances. The BBB is composed of endothelial cells that line the vasculature of the brain and are connected by tight junctions, which prevent compounds from passing freely between them. The BBB selectively allows molecules such as oxygen and glucose to cross into the brain, while preventing toxins and other foreign substances from entering. Damage or dysfunction of the BBB can allow harmful substances to enter the brain and lead to inflammation and neurological damage.