The blood-brain barrier (BBB) is a highly selective, semi-permeable barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). It is composed of endothelial cells, astrocyte end-feet, and pericytes that work together to regulate the movement of ions, molecules, and cells between the blood and the brain. The primary function of the BBB is to protect the brain from harmful substances and pathogens while allowing essential nutrients to pass through.
