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Blood-Brain Barrier


BBB we talk about here is not Better Business Bureau, but Blood-Brain Barrier.  Better Business Bureau, a consumer watchdog, is meant to provide protection for consumers.  Similarly, blood-brain barriers (BBB) in human body is meant to provide protection for our brain.


The Importance of Blood-Brain Barrier


The BBB is one of the human body's many barriers which include the gut, the airways, the skin, the oral cavity, the vagina, the placenta, etc.  It is arguably the most important one because it:

  • Protects the brain from "foreign substances" in the blood that may injure the brain.
  • Protects the brain from hormones and neurotransmitters in the rest of the body.
  • Maintains a constant environment for the brain.
What's Blood-Brain Barrier?

Blood-brain barrier (BBB) is a physiological mechanism existing in brain to prevent harmful substances such as certain drugs from entering brain while other substances are allowed to enter freely.  In other words, the BBB is semi-permeable: it allows some materials to cross, but prevents others from crossing.


The barrier is located at the brain blood capillaries, which are unusual in two ways:

  1. The cells which make up the walls of these vessels (the endothelium) are sealed together at their edges by tight junctions that form a key component of the barrier. 
  2. These capillaries are enclosed by the flattened ‘end-feet’ of astrocytic cells (one type of glia), which also act as a partial, active, barrier. 

These sealing junctions prevent water-soluble substances in the blood from passing between the cells and therefore from freely entering the fluid environment of the brain cells.  Thus the only way for water-soluble substances to cross the BBB is by passing directly through the walls of the cerebral capillaries, and because their cell membranes are made up of a lipid/protein bilayer, they also act as a major part of the BBB.  In contrast, fat-soluble molecules, including those of oxygen and carbon dioxideanaesthetics, and alcohol can pass straight through the lipids in the capillary walls and so gain access to all parts of the brain.


Apart from these passive elements of the BBB there are also enzymes on the lining of the cerebral capillaries that destroy unwanted peptides and other small molecules in the blood as it flows through the brain.


Finally, there is another barrier process that acts against lipid-soluble molecules, which may be toxic and can diffuse straight through capillary walls into the brain. In the capillary wall there are three classes of specialized ‘efflux pumps’ which bind to three broad classes of molecules and transport them back into the blood out of the brain.


Breakdown of Barriers


Once the 
blood-brain barrier is broken down, it can harm our body in many ways.  For example, in some patients, Alzheimer's disease may be caused (or more likely, aggravated) by a breakdown in the blood–brain barrier[5].

Based on researches, it's known that the BBB can be weaken by[3,7]:
  • Hypertension (high blood pressure)
  • Development
    • The BBB is not fully formed at birth.
  • Hyperosmolitity
    • A high concentration of a substance in the blood can open the BBB.
  • Microwaves
    • Researches have found that there is possible modification of blood-brain-barrier permeability by mobile phone and other microwave fields[4].
  • Radiation
  • Infection
    • Exposure to infectious agents can open the BBB.
  • Trauma, Ischemia, Inflammation, Pressure
    • Injury to the brain can open the BBB.
  • Lifestyles and Diets
    • The over-comsumption of insulinogenic foods and proteotoxins, such as advanced glycation and lipoxidation molecules, gluten and zein, and a reduced intake of fruit and vegetables, are key factors behind the commonly observed elevated inflammation and the endemic of obesity and chronic diseases, factors which cause most barriers including BBB increasingly permeable[1,7].

References

  1. Gut microbiota, immune development and function
  2. Blood-brain barrier (answers.com)
  3. The Blood Brain Barrier (http://faculty.washington.edu/)
  4. Brain interactions with RF/microwave fields generated by mobile phones (Center for Research on Globalization)
  5. Nagele, Robert G. (2006). "Alzheimer's disease: new mechanisms for an old problem"
  6. Symptoms of Brain Tumor (Travel and Health)
  7. Aspartame
    • BBB was discussed from 23:45 to 25:12 in the video.
  8. Feeding the Diabetic Brain

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