Figure 1.

Cellular constituents of the blood-brain barrier (BBB). The BBB is formed by brain microvascular endothelial cells (BMECs), which are connected by tight junctions. The endothelium, together with the basal lamina, pericytes, and astrocytic end-feet forms the neurovascular unit. Some substances diffuse freely into and out of the brain parenchyma, others such as nutrients need specific transporters, while molecules such as insulin, leptin and transferrin are transported by receptor- mediated transcytosis. (Reprinted from Reference [11] in accordance with the Creative Commons Attribution).