The main function of the blood–brain barrier is to protect the brain and keep it isolated from harmful toxins that are potentially in the blood stream. It accomplishes this because of its structure, as is usual in the body that structure defines its function. The tight junctions between the endothelial cells prevent large molecules as well as many ions from passing between the junction spaces. This forces molecules to go through the endothelial cells in order to enter the brain tissue, meaning that they must pass through the cell membranes of the endothelial cells.Rubin, L. L., & Staddon, J. M. (1999). The Cell Biology Of The Blood–Brain Barrier. Annual Review of Neuroscience, 22(1), 11-28.
