Blood-brain barrier

: A protective network of blood vessels and cells that filters blood flowing to the brain.

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blood-brain barrier n a naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration and formation of tight cell-to-cell contacts) that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues abbr. BBB

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the mechanism that controls the passage of molecules from the blood into the cerebrospinal fluid and the tissue spaces surrounding the cells of the brain. The endothelial cells lining the walls of the brain capillaries are more tightly joined together at their edges than those lining capillaries supplying other parts of the body. This allows the passage of solutions and fat-soluble compounds but excludes particles and large molecules. The importance of the blood-brain barrier is that it protects the brain from the effect of many substances harmful to it. A disadvantage, however, is that many useful drugs pass only in small amounts into the brain, and much larger doses may have to be given than normal. Brain cancer, for example, is relatively insensitive to chemotherapy, although drugs such as diazapam, alcohol, and fat-soluble general anaesthetics pass readily and quickly to the brain cells.

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blood-cerebral barrier the barrier system separating the blood from the parenchyma of the central nervous system. Its anatomical component consists of unique endothelial cells in the brain capillaries, having tight junctions without fenestrations and with few microvilli and few vesicles for fluid transport. Its physiologic component in part consists of enzymes unique to the brain endothelia and of active transport via carrier proteins.