The blood-brain barrier (BBB) maintains brain homeostasis by regulating the movement of compounds across the endothelium of cerebral capillaries.
BBB serves to maintain brain homeostasis by regulating the influx and efflux of compounds to and from the brain. The presence of a barrier was first documented by Paul Ehrlich in the late nineteenth century. However, it was not until the advent of the electron microscope that the makeup of the BBB was begun to be understood. The brain microvascular endothelium comprises the BBB. In contrast to endothelium from other vascular beds, the morphologic features unique to the brain microvascular endothelium, such as tight junctions, increased electrical resistance, and lack of pinocytic vesicles, provide limited and selective access to this highly specialized organ. Only lipophilic molecules less than 600 Da can passively diffuse through the BBB. This protects the brain from toxins,...