blood-brain barrier

anatomy

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June 18, 2026

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The blood-brain barrier is a specialized structure that protects the brain by controlling what substances can pass from the bloodstream into brain tissue. It is formed by modified brain capillaries that have fewer openings and tight cell-to-cell connections.1

This barrier prevents many substances from leaving the blood and entering the brain. Astrocytes, star-shaped cells in the nervous system, play a role in this process. Their processes form end feet that make contact with capillaries, contributing to the barrier's function. The blood-brain barrier was first described in 1934.12

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