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

"Glioblastoma is metabolically reprogrammed and expresses GLUT1 at three times the levels of normal brain tissue, so the particles preferentially accumulate in tumor tissue after crossing the blood-brain barrier," Olena Taratula said.

From Science Daily ● Jul. 17, 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 researchers propose that aging or injury can weaken the blood-brain barrier, allowing immune cells from the bloodstream to enter the brain.

From Science Daily ● Jun. 12, 2026

The blood-brain barrier blocks 99% of Alzheimer’s drug doses, but new “brain-shuttling” technologies aim to overcome this.

From Barron's ● Jun. 3, 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