Blood brain barrier

The blood–brain barrier (BBB) is the mechanism by which circulating blood is ‘filtered’ in such a way that unwanted molecules, pathogens or other substances in the blood are unable to enter the brain.

Cells at three key interfaces form barriers between the blood and the CNS. 

• the blood-brain barrier itself 
• blood-CSF barrier  - see the craniosacral system and cerebrospinal fluid
• and the arachnoid barrier - see the craniosacral system.

The barrier is actually not a gate as such but a rather complex set of mechanisms all of which have a filtering function  - BBB-endothelial cells, astrocyte end-feet, and pericytes (PCs).  

Endothelial cells, for example,  restrict the diffusion of both microscopic objects (e.g., bacteria) and large or hydrophilic molecules from getting into the cerebrospinal fluid (CSF), while allowing the diffusion of small hydrophobic molecules (O₂, CO₂, hormones).

Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins.  But the blood brain barrier can be disrupted via

• Osmosis 
• Biochemically by the use of vasoactive substances such as bradykinin
• Blockage

It can also be by passed if any of the substances tags a ride using an endogenous substance such as glucose.  If it is an endogenous substance it will get through.

Observations

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• Blood-brain barrier flux of aluminum, manganese, iron and other metals suspected to contribute to metal-induced neurodegeneration
• CNS Diseases and Uveitis
• Effect of low-frequency but high-intensity noise exposure on swine brain blood barrier permeability and its mechanism of injury
• Effects of GSM modulated radio-frequency electromagnetic radiation on permeability of blood-brain barrier in male & female rats
• Influence of nanoparticles on blood-brain barrier permeability and brain edema formation in rats
• Magnevist
• Mercury in foods and fish and selenium as a chelation agent
• Metal transporters in intestine and brain: their involvement in metal-associated neurotoxicities
• Oliver Sacks - L-DOPA, Parkinson's, Tourette's and mania