Fig. 6

Modes of drug transport across the brain barriers. In the figure, the BBB is shown, but the modes of drug transport also apply to the other barriers. In simple passive transport, drugs cross the BBB (or the other brain barriers) passively through the cells (transcellular) or between the cells (paracellular) by diffusion. In facilitated transport, drug diffusion across the BBB is aided by helper molecules. In vesicular transport, drugs move across the BBB through vesicles that are formed within the barrier. In active transport, drugs are actively transported into the brain by specific influx transporters or out of the brain by efflux transporters. TJ tight junction