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:
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:
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 dioxide, anaesthetics, 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.
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.
Based on researches, it's known that the BBB can be weaken by[3,7]: