The Marvels of the Blood-Brain Barrier

Have you survived, or are you presently suffering from the “three week” head cold that is currently spreading like wild fire? This writer had it and even in a fevered state, like any good scientist, continued to ask questions. The “cold” related questions: why, with the sinus headache, constantly draining phlegm cough - things directly associated with the head - did the effects not spread to the brain tissue, mere millimetres away from all this infected goop? The answer, found after a minute of searching the web, is the Blood-Brain Barrier or BBB.


The human brain, like those of most animals with a spinal cord (which is essentially an extension of the brain) requires a stable environment, lots of oxygen and protection from the chemical chaos going on in the blood flowing through the circulatory system. It can’t function effectively when assaulted by hormone messages, changes in ion concentration, vibration, etc. So, the brain and spinal column, supported within the boney confines of the skull and spine, float in cerebral spinal fluid more commonly described as CSF. This straw colored fluid, very similar in composition to plasma, serves as shock absorber, nutrition highway, waste removal system and a pretty fine barrier to the rest of the body.


In fact, CSF effectively isolates the brain and spinal cord from the rest of the body, including systemic blood flow. It might seem impossible to believe that very little of the blood circulating around your body actually comes in direct contact with your brain. So, how then could all the blood rushing past fingers pressed to your carotid artery on the side of your neck not flow directly to the brain? Welcome to the marvels of the BBB.

Just above your jaw line leading up to the base of the skull, the carotid artery funnels down into an intricate network of smaller vessels and in a distance of less than a centimeter is fed through a maze of capillaries, the smallest blood vessel. Just outside the capillary wall, specialized endothelial and glial cells are aggregated so tightly that only the smallest things can get through: oxygen, carbon dioxide, glucose and substances like nicotine and alcohol, but not much else. That pesky cold virus can’t get through, neither can most bacteria and parasites. Opiates can get through but 95 % of prescription drugs cannot, including cancer fighting molecules used to fight brain tumors.

To put things in perspective about how truly effective the BBB really is, consider the approximately 5.5 litres of blood that fill our circulatory system. Each minute this amount is pumped throughout the body carrying oxygen and nutrients. Of the oxygen present in blood hemoglobin, 20 % goes to the brain, an organ that makes up less than 2% of body mass. And all of this blood and oxygen - that we may have envisioned flowing directly to the brain - is actually all diffused and filtered through the BBB. Quickly and most effectively. A natural engineering marvel.


For the most part the BBB functions effectively throughout our lives, however, there are things that can cause short and perhaps even long term disruptions. Exposure to microwaves, radiation, chronic high blood pressure, strokes and, yes, Alzheimer’s disease have been shown to have adverse effects on the filtration capabilities of the BBB.


As always, where we provide a suggestion or two for readers to further research the topics discussed in this column, this week proved difficult to find one that was not all scientific gobbledygook and the best we could find on the Blood-Brain Barrier is:

Differentiation of blood-brain barrier endothelial cells

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