Physiol. the barrier created by the walls of the capillaries of the brain that prevents certain substances, as most proteins and drugs, from passing from the blood into the brain tissue and cerebrospinal fluid
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.
- (anatomy) A structure in the central nervous system (CNS) that keeps various substances found in the bloodstream out of the brain while allowing in the substances essential to metabolic function, e.g. oxygen.