Type O negative blood (red cells) can be transfused to patients of all blood types. It is always in great demand and often in short supply. Type AB positive plasma can be transfused to patients of all other blood types. AB plasma is also usually in short supply.
Blood-brain barrier. A blockade of cells separating the circulating blood from elements of the central nervous system (CNS); it acts as a filter, preventing many substances from entering the central nervous system.
First of all as I am sure you know the brain is protected by what is known as the Blood Brain Barrier (BBB) and what this BBB does is help protect the brain from foreign substances that may be harmful to it such as low lipid fat soluble molecules. But glycogen is allowed to pass through the BBB to help fuel the brain.