Defending the Fortress
(Workbook Page 31)
Molecules in the bloodstream pass through the circulatory system directly into the brain via the Blood Brain Barrier (BBB). The BBB is a highly selective network of specialized capillaries, astrocytes and microglia. It functions to keep out destructive substances and mounts the first response aimed at destroying invaders. There are three layers of the BBB. Layer one is composed of capillaries and lets only the smallest substances pass in and out of the brain. Capillaries are only one cell thick. In the peripheral body, about every third or fourth cell in a capillary has a loose junction. This is a larger space between individual cells that allows larger substances to leave the capillary for the tissue or enter it from the tissue. In the brain there are no loose junctions. Because of this, viruses, bacteria, toxins and large molecules have a hard time crossing through the capillaries into the brain, preventing them from doing harm.
Astrocytes comprise layer two. Astrocytic projections or “feet” wrap around the capillaries and strengthen the barrier. They respond to unknown substances with a massive release of inflammatory cytokines that attack the substances and call forth other glia.
The microglia are the third layer of the BBB. They attack anything suspicious with a pinpoint barrage of inflammatory chemicals aimed at destroying the substances.
During sleep, the astrocytic feet pull back from the capillaries in the brain by 30%. This allows the Cerebrospinal Fluid to rush across brain capillary surfaces at 16 times normal speed, creating a downward pressure and forcing waste material through tight junctions between capillary cells. Thus the brain deep cleans itself while we sleep, removing waste and sending it to the general circulation where it will be detoxified and eliminated by liver, gastrointestinal tract and kidneys.
Look at the graphic on page 31 of the Neuroplastic Transformation workbook. It shows a capillary in the brain running through an astrocyte. Every nerve cell, capillary, microglial cell and oligodendrocyte are contained within astrocytes. Look at the graphic on page 30 of the workbook.