blood-brain barrier

noun

ˈbləd-ˈbrān- 

: a naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration and formation of tight cell-to-cell contacts) that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues

Examples of blood-brain barrier in a Sentence

Recent Examples on the Web

The virus will break through his underdeveloped blood-brain barrier and begin attacking his brain matter directly, leading to primary measles encephalitis. —Elizabeth Bruenig, The Atlantic, 12 Feb. 2026

The vessels also showed genetic activity and physical properties similar to those seen in the developing human brain, including features of the blood-brain barrier, which regulates what enters and exits brain tissue. —The Week Us, TheWeek, 10 Feb. 2026

This tipped the scientists off that there must be some molecule from the cancerous cells that can cross the blood-brain barrier and inflict good, not harm. —New Atlas, 29 Jan. 2026

Instead, within about 40 minutes of taking it, L-theanine crosses the blood-brain barrier and can help calm the nervous system, lowering heart rate and blood pressure. —Allison Forsyth, Health, 28 Jan. 2026

Word History

First Known Use

1934, in the meaning defined above

Rhymes for blood-brain barrier

• noncarrier
• carrier

Medical Definition

blood-brain barrier

noun

: a naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration and formation 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