blood-brain barrier

American  

[bluhd-brayn] / ˈblʌdˈbreɪn /

noun

Physiology.

1. a layer of tightly packed cells that make up the walls of brain capillaries and prevent substances in the blood from diffusing freely into the brain: passage across the cell membranes is determined by solubility in the lipid bilayer or recognition by a transport molecule.

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blood-brain barrier Scientific  

1. A physiological mechanism that alters the permeability of capillaries in the brain, so that some substances, such as certain drugs, are prevented from entering brain tissue, while other substances are allowed to enter freely.

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blood-brain barrier Cultural  

1. 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.

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Discover More

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

Etymology

Origin of blood-brain barrier

First recorded in 1940–45

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Example Sentences

See Examples For:

blood-brain barrier

One major obstacle is the blood-brain barrier, a protective system that limits which substances can enter the brain from the bloodstream.

From Science Daily ● Nov. 3, 2026

Such an approach could avoid one of the major difficulties in developing neurological treatments: getting drugs across the blood-brain barrier, which prevents many substances from entering brain tissue.

From Science Daily ● Oct. 20, 2026

The greater accumulation was accompanied by evidence that the blood-brain barrier had become leaky.

From Science Daily ● Oct. 19, 2026

Ninety percent of those particles were small enough to qualify as nanoplastics, which are small enough to cross the blood-brain barrier and be absorbed into human cells.

From Los Angeles Times ● Oct. 17, 2026

There are many layers of tissue, bone, and skin to keep it protected from the outside, but there's also a "blood-brain barrier" that keeps out many substances circulating in the blood.

From "Phineas Gage" by John Fleischman

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