The blood-brain barrier (also called BBB) is a kind of “border” of closely spaced cells within fine blood vessels of the brain. The blood-brain barrier is semipermeable, which means it lets some substances, such as water, oxygen, carbon dioxide to pass into the brain. So nutrients required by the brain are supplied and the metabolic products that are created are removed. Another important task of the BBB is protects the brain from pathogens, toxins and certain messenger substances which are circulating in the blood.
