The Blood Brain Barrier
Keeping The Bad Stuff Out
Have you ever wondered what it is that protects our brains? Many people would assume that it is only our skull that protects our brains, but there is also something inside our body which plays a big part in our brain's health and that is the blood brain barrier. It's not often talked about but it helps keep our brains clear of unwanted chemicals and compounds, but in doing so, it makes certain treatments difficult.
The blood brain barrier was discovered in the 1900's when dyes were put into the body and they stained every organ except the brain. This showed to scientists that there was some kind of a barrier or filter stopping the dye in the blood from getting to the brain. Basically, what they had found was a membranic structure which is there to protect our brains from chemicals within our blood. It does this whilst still ensuring that vital metabolic function occurs. Generally the barrier is made up of endothelial cells which are contained within the brain capillaries. These cells are packed together so tightly that no chemicals can get passed them. They are supported by astrocyte cell projections and it is similar to the Blood-Cerebrospinal fluid barrier.
Endothelial cells are found in other parts of the body too. One organ that is also covered by the blood brain barrier is the eye. The retinas in our eyes are protected by the barrier with and extension known as the blood retinal barrier. The only difference between endothelial cells in the brain and endothelial cells in the rest of the body is that within the brain they are packed closer together. In the rest of the body they do not need to filter out any chemicals and so that is why they are more spaced out.
In and Out
The reason why the brain does not get any infections is thanks to efficacy of the barrier. The thing that you need to remember though is that antibodies cannot pass through the barrier. So if you ever were to get an infection of the brain, it would be extremely difficult to treat.
There are some things that need to get through the barrier however and these include hormones. Hormones are needed by the brain as they control our bodily functions. However, they cannot pass through the blood directly into the brain; otherwise the brain cannot control them. For this reason a system has been set up within the body to deal with the various hormones. They are sent to various sites where neurons sample the composition of the blood. It is at these sites where the barrier is known to be 'leaky'.
Since the blood brain barrier is designed to not let anything through which has is bigger than 500 Daltons, medications often cannot bypass the barrier. This means that conditions such as Parkinson's disease, Meningitis and HIV are incredibly difficult to treat.
Currently research is being carried out to determine new ways of getting medication into the brain without the need to go through the bloodstream. Research is also being carried out to see if important molecules can be disguised in order to get them through the barrier. The only molecules that can really pass through the barrier include oxygen and various nutrients.
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