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How does the blood-brain barrier limit the entry of chemicals into the brain?
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More than 100 species of mushrooms are known to be poisonous to humans.
The blood-brain barrier protects the brain by restricting the movement of substances from the bloodstream into brain tissue. This protection is achieved through specialized, tight capillary walls reinforced by glial cells that wrap around the capillaries. To reach nerve cells, molecules must diffuse through these two distinct layers.12
The barrier's permeability is highly selective:
- Readily Permeable: Molecules that are highly lipid-soluble, as well as oxygen, carbon dioxide, and water, can diffuse through the barrier with ease.32
- Slightly Permeable: It allows limited passage of certain electrolyte ions, such as sodium and potassium.2
- Poorly Permeable: It effectively blocks large molecules, including proteins and most water-soluble chemicals.2
This structural defense is essential for preventing the entry of many toxic substances, though its effectiveness can vary; for instance, the barrier is less developed in children, making them more susceptible to the toxicity of heavy metals like lead.2