Some science behind the scenes

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 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.


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