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Blood Brain Barrier (BBB) Print E-mail

Dr. Kennedy The mechanism and cellular structures for protecting the brain from unwanted compounds is called the blood brain barrier or BBB. T

The notion of a blood brain barrier was first introduced by Paul Ehrlich, the great German medical physiologist in the late 19th century. He found that intravenous injection of dyes into the bloodstream stained all the tissues in most organs except the brain. Using electron microscopy and electron dense tracers such as horseradish peroxidase (HRP) a group of scientists later demonstrated that the blood brain barrier is located in endothelial cells of capillaries in the brain. These endothelial cells of capillaries in the brain are different from those found in peripheral tissues in various ways:

  • Brain endothelial cells are joined by tight junctions of high electrical resistance providing an effective barrier against molecules.
  • In peripheral endothelial cells there is good transcellular movement of molecules. There is no such movement in brain endothelial cells.
  • Brain capillaries are in contact with foot processes of astrocytes which essentially separate the capillaries from the neurones.

The levels of nutritional elements actually needed by the brain may go up and down in the blood too rapidly for the brain to deal with and the blood brain barrier protects the brain against these surging fluctuations in concentrations. The blood brain barrier is both a physical barrier and a system of cellular transport mechanisms. It maintains homeostasis by restricting the entrances of potentially harmful chemicals from the blood, and by allowing the entrance of essential nutrients. Lipid soluble molecules, such as ethanol and caffeine are able to penetrate through the barrier relatively easily via the lipid membranes of the cells. However, water soluble molecules such as sodium and potassium ions are unable to transverse the barrier without the use of special transport mechanisms. To make this all more confusing, there are some areas of the brain which do not have a blood brain barrier such as the area postrema and the posterior pituitary area. Here the capillaries are fenestrated like those in peripheral tissues.



The information in this article is not meant to be medical advice.�Treatment for a medical condition should come at the recommendation of your personal physician.

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