At the interface between blood and the brain, endothelial cells are stitched together by these tight junctions, which are composed of smaller subunits, frequently biochemical dimers, that are transmembrane proteins such as occludin, claudins, junctional adhesion molecule (JAM), or ESAM, for example.> Each of these transmembrane proteins is anchored into the endothelial cells by another protein complex that includes zo-1 and associated proteins.> Blood-brain barrier is composed of high-density cells restricting passage of substances from the bloodstream much more than endothelial cells in capillaries elsewhere in the body.> Astrocyte cell projections called astrocytic feet ("glia limitans") surround the endothelial cells of the BBB, providing biochemical support to those cells.> BBB is distinct from the quite similar blood-cerebrospinal-fluid barrier, which is a function of the choroidal cells of the choroid plexus, and from the blood-retinal barrier, which can be considered a part of the whole realm of such barriers.">