- Minimize the risk of irreplaceable brain damage
- keep out most viruses, bacteria, and harmful
chemicals
However!
¥ Some viruses do cross the Blood-brain
barrier
What Happen then?
- Rabies virus invades the barrier -> infection -> death
- Syphilis-> long lasting consequence
What can Microglia do ?
- It is effective against certain other viruses. - Increase inflammatory
responses -> fight a virus w/o killing the neuron.
However!
This response may control the virus without eliminating it.
Chicken pox virus enters spinal cored -> remain there long after
they have been destroyed -> the virus may emerge decades later
-> shingles.
How does it work?
Depends on Endothelial Cells
outside the brain: separated by small gaps
in the brain: joined so tightly that they block
viruses, bacteria and other harmful chemicals
Why we don't have similar walls around all other organs?
- the barrier block useful chemical as well
as harmful ones. - useful chemical include
all fuels and normal flora, amino acids, the
building blocks for proteins
How the useful chemical enters the brain?
protein channels for H2O crossing
small, uncharged molecules
cross freely (O2, Co2)
Active transport: a protein-mediated process that
use up energy to pump chemicals from the blood
into the brain (e.g. Glucose, amino acids, purines,
choline, a few vitamins, irons, and certain
hormones
Dissolvant molecules in the fats of the membrane
cross easily, (e.g. Vitamins A and D, all drugs that
effect the brain.