Blood Brain Barrier Essay

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The brain is permeated by a vast network of tiny blood vessels called capillaries- so tiny and thin that blood cells have to pass through in single file. In the brain alone there are enough capillaries that if you laid them all out end to end they would stretch from Tucson to Tijuana.

These capillaries are surrounded by a single layer of cells.

That layer of cells forms a barrier between the capillaries and the cells and fluid of the brain.

These barrier-forming cells are called "endothelial cells". You can think of "endothelial" as a synonym for "lining" or even just "barrier".

When we use the phrase Blood Brain Barrier, (which for obvious reasons we'll refer to as BBB from here on out!), we're talking about all of these
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The BBB also incorporates mechanisms to shepherd or transport certain substances *in*:

GLUCOSE- the universal energy source, which is needed by every cell in your body...
OXYGEN- electron acceptor par excellence, do without it and die...
CERTAIN IONS- cations, anions, Chlorine, Calcium, etc.. involved in nervous system transmission...Â

Finally, the BBB also lets various substances in because it either can't pump them out or its mechanisms can't tell the difference between them and one of the substances that it naturally tranports across:

ETHANOL- enters by the same pathways that let glucose in, which is why drinking alcohol affects the brain...

Obstacles For Scientists

The BBB evolved as an extremely tight barrier to protect the brain from potentially toxic compounds. Though it is an indispensable part of the Central Nervous System, its tightness makes delivering therapeutic drugs to the brain very difficult.

Question: What makes the BBB such a tight barrier?
Answer: the three components- the phospholipid bilayer, influx pumps, and efflux pumps- discussed below.
# Phospholipid Bilayer Phospholipid bilayer

The endothelial cells of the BBB are surrounded by a phospholipid bilayer that is only permeable to very small and/or lipid soluble molecules. Lipid soluble