Scientists explain the body’s mechanism for filtering which substances should reach the brain through the bloodstream.

As much as science reveals, so many more questions still remain unanswered. A website called “The Naked Scientists” answers some of these questions sent by people from across the world. The questions range from why the chameleon changes colour to the Shakespearean exclamation “What’s in a name?”. Many interesting discoveries of science can be understood from here. One among them is a comparatively less known fact that your blood does not flow into your brain. Would you have believed that the organ which gives you identity is not being fed by your blood stream? Further, that it has an intellect of its own as we shall see, and so seems to function with its own knowledge and not by yours.

Scientists say, “People talk about this blood-brain barrier. This notional structure which in some way keeps the brain isolated, cocooned inside you, biochemically and physically away from what is happening in your blood stream is absolutely true. The history of the blood brain barrier goes back a hundred and something years to a guy called Paul Ehrlich.”

Ehrlich was a German scientist. His basic interest was in dyes. He would inject dyes into the body and watch its movement and accordingly map the body. It is then that he found that most of the time the brain never got coloured! The dye never got in there. This intrigued him. Say the scientists, “…And so he realised that there must be some kind of barrier separating what goes round in the blood stream from the delicate tissue inside the brain.”

While it is clear that the tissues found in the brain are quite different from those found in the rest of the body, the talk declares unilaterally that they know little more about blood brain barriers. One clue they do have is that there are “…special junctions between cells that line the surface of the brain that separate the brain tissue from blood vessels.” Apparently “these cells make very tight junctions” — that is what the point where they are joint is called — and these tight junctions act as blockers, they do not allow the blood stream to enter.

If the answer had stopped there it would still be less fascinating. It goes on further to say the membranes of those cells separate what’s in the bloods stream from what is in the blood tissue but are not completely averse to the goodies that blood brings them. The explanation says, “…certain substances can move very easily into the brain, especially if they’re substances that can dissolve well in fat, because of course the membranes of cells are made of fat. So lipid-soluble drugs like heroin, cigarettes-nicotine, cocaine, they’re very oily molecules. They go into the brain beautifully and that’s why they tend to be addictive, because they move preferentially into fatty tissue like the ones found in the brain.”

The converse is that substances which don’t dissolve in fat very well don’t get into the brain very well.

The story does not end even here. As a rule that which does not dissolve in fats is rejected by the brain, but like there are exceptions to every rule, there are exceptions here too. If the brain requires something, it amends the rule and lets it pass into its tissues.

“So sometimes if it needs a certain chemical that wouldn’t be able to diffuse in very easily, it has special transporters which can scrutinise what is going past in the blood, grab goodies that it wants and move those into the brain. This is what people found when they were giving the drug L-Dopa for Parkinson’s Disease. L-Dopa is an amino acid. It dissolves in water. It does not dissolve in brain tissue very well, but it gets into the brain much better than it should do, and the reason is there are these special transporters that get hold of it and shove it into the brain,” say the scientists.

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