Nucleoside Adenosine 7. In addition to protecting the brain from toxic substances, it controls the neuronal environment by regulating the movement of biologically important molecules in and out of the cerebral extracellular space across the capillaries. Two basic mechanisms are available to control the extracellular environment. Sodium transport system controls the concentration of NACL2 in the extracellular fluid and also induces small volume of fluid to enter the brain . The choroidal ependyma and cerebral capillary endothelium also act as miniature kidneys as they have transport systems capable of moving substances out of the ventricular fluid and cerebral extra cellular fluid respectively back into blood.
Carbohydrates is the primary fuel for brain.
Hexose transport system is at its highest capacity at the BBB and recognizes only the Dform, can easily supply the glucose requirements. Insulin is not required Two transport systems operate across BB for neutral amino acids. In addition there are separate carriers for choline, adenosine and adenine. There exists a competition for carrier sites by the transported amino acids. When the plasma concentration of one of the competing aminocids increases, its movement across enhances.