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. Author manuscript; available in PMC: 2014 Aug 1.
Published in final edited form as: Drug Deliv Transl Res. 2013 Feb 16;3(4):336–351. doi: 10.1007/s13346-013-0133-3

Figure 1-1.

Figure 1-1

Transport pathways across the blood–brain barrier [112]

A schematic of the blood–brain barrier (BBB) highlighting the proximity of the endothelial cells with the astrocyte foot processes. The major known pathways for transport across the BBB are: a | Paracellular- tight junctions restrict penetration of water-soluble agents. b | Transcellular- lipid bilayer membrane of the endothelium provides diffusive route for lipid-soluble agents. c | Transport proteins- The endothelium contains transport carriers for glucose, amino acids, and other substances. Also, are present the energy-dependent efflux transporters. d | Receptor- mediated-Certain proteins, such as insulin and transferrin, are taken up by specific receptor-mediated endocytosis and transcytosis. e | Adsorptive transcytosis- Uptake of native plasma proteins such as albumin. Pathways b–e are prominent in drug delivery across the BBB; most CNS drugs enter via route b.