What does the blood-brain barrier let through, and which cells build it? · Grey Matter

The barrier itself is the endothelial cells of brain capillaries, sealed to one another by tight junctions built mainly of claudin-5; pericytes on the capillary wall and the end-feet of astrocytes that cover it induce and maintain those properties.

What does the blood-brain barrier let through, and which cells build it?

The barrier itself is the endothelial cells of brain capillaries, sealed to one another by tight junctions built mainly of claudin-5; pericytes on the capillary wall and the end-feet of astrocytes that cover it induce and maintain those properties. Gases and small fat-soluble molecules (oxygen, carbon dioxide, alcohol, many anaesthetics) diffuse through the cells. Nutrients cross on dedicated carriers, glucose on GLUT1 and large neutral amino acids on LAT1, while efflux pumps such as P-glycoprotein push many drugs back into the blood. Charged molecules, proteins and most medicines are kept out, which protects the neurons' environment and makes the brain hard to treat.