What is the Blood-Brain Barrier?

Mary McMahon
Mary McMahon

The blood-brain barrier (BBB) is a protective barrier which is designed to keep the environment in the brain as stable as possible. It prevents many dangerous substances from entering the brain, protecting the brain from an assortment of potential risks, ranging from infection to elevated levels of hormones in the body. Of course, the BBB also hinders some helpful things, making the administration of some medications to treat brain and central nervous conditions rather challenging.

Substances can pass through the blood-brain barrier when the body experiences head trauma.
Substances can pass through the blood-brain barrier when the body experiences head trauma.

In a sense, the blood-brain barrier is like a protective moat with the drawbridge left permanently up. It is found in the capillaries which lead to the brain. Normally, the walls of the capillaries are highly permeable, allowing a variety of water-soluble components of blood to pass through them and into the body. In the brain, the capillary walls are very compact and dense, allowing few substances through to the brain.

The blood-brain barrier guards the brain from the intrusion of dangerous substances.
The blood-brain barrier guards the brain from the intrusion of dangerous substances.

This means that when toxins and infectious materials are floating around in the blood, they cannot reach the brain. For the brain, this is very good news, because the brain is a very fragile organ, and damage from an infection could be devastating. However, some harmful substances can still get through: viruses, for example, can hitch a ride right through the BBB. Substances can also pass through the blood-brain barrier when the brain's host body experiences head trauma in the form of invasive surgery or a severe fall.

Substances may cross the blood-brain barrier during invasive surgery.
Substances may cross the blood-brain barrier during invasive surgery.

Discovery of the BBB is usually credited to Edwin Goldmann, a researcher in 1913 who was trying to understand why the brain failed to change color when dye was injected into the bloodstream. He seized upon the idea of injecting dye directly into the brain, and he realized that the dye failed to spread, suggesting that some sort of barrier was keeping it in. With the development of advanced medical imaging equipment in the 1960s, researchers learned a lot more about how the blood-brain barrier worked.

This protective barrier goes both ways: harmful material cannot get into the brain, but it also cannot get out if it manages to get into the brain. This makes infections of the brain extremely difficult to treat, because the infection can be trapped in the brain, and the medications used to treat such infections elsewhere in the body may not be able to cross the blood-brain barrier. This requires the formulation of drugs which can cross this barrier, or the delivery of drugs directly into the brain.

Researchers have learned more about the blood-brain barrier from studying advanced imaging.
Researchers have learned more about the blood-brain barrier from studying advanced imaging.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments

anon1003536

Does the covid19 test compromise blood brain barrier? Is that even a possibility?

anon327388

How does the consumption of alcohol affect someone with a compromised BBB from surgery?

anon168757

It all makes sense now.

anon131282

very helpful, so easy to understand and straight to the point.

anon91971

I couldn't find a better article than this one. It's easy to understand the vocabulary is used in this article. I appreciated because I don't have a medical background.

anon69484

i had no idea there was a blood brain barrier before this point in time. uber cool

anon69395

I had a devastating fall ten years ago which fractured my skull! This piece explains my oft-times kookiness to the present day. I am 79 years old.

anon69238

interesting article. very helpful in understanding the function of blood brain barrier.

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