blood-brain barrier

American  

[bluhd-breyn] / 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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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

Example Sentences

See Examples For:

blood-brain barrier

The researchers also detected a substantial decline in cell populations that help maintain the blood-brain barrier.

From Science Daily ● Sep. 15, 2026

The brain has its own specialized immune cells, along with the blood-brain barrier, which restricts many substances and cells from entering brain tissue.

From Science Daily ● Aug. 14, 2026

GLUT1 can also recognize mannose, allowing the coated nanoparticles to use the same pathway to cross the blood-brain barrier.

From Science Daily ● Jul. 17, 2026

The biggest concern is fine particulate matter, he explained -- particles 2.5 micrometers or smaller that can penetrate deep into the lungs, enter the bloodstream and even cross the blood-brain barrier.

From Barron's ● Jul. 2, 2026

Oxygen and nutrients can cross the blood-brain barrier, but many dangerous substances like bacteria cannot.

From "Phineas Gage" by John Fleischman