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.
This rate of production means that all of the CSF is replaced every few hours. A protective blood-brain barrier separates the brain from the bloodstream and regulates the distribution of substances between the blood and the CSF. It helps keep large molecules, toxins, and most blood cells away from the brain.