blood brain barrier

blood-brain barrier

The separation of the brain, which is bathed in a clear cerebrospinal fluid, from the bloodstream. The cells near the capillary beds external to the brain selectively filter the molecules that are allowed to enter the brain, creating a more stable, nearly pathogen-free environment.

Note: Oxygen, glucose, and white blood cells are molecules that are able to pass through this barrier. Red blood cells cannot.

Main Entry: blood–brain barrier
Function: noun
: a naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration andformation of tight cell-to-cell contacts) that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues —abbreviation BBB

blood-brain barrier n.
Abbr. BBB
A physiological mechanism that alters the permeability of brain capillaries so that some substances, such as certain drugs, are prevented from entering brain tissue, while other substances are allowed to enter freely.