Answer
The blood brain barrier (BBB) protects the brain from potentially harmful blood contents--antibodies, bacterial toxins, and macrophages. It exercises this protection by controlling what gets from the blood to brain tissue through the capillaries of the brain tissue, and capillaries of the choroid plexuses.
The major features of the BBB are the tight junctions between the endothelial cells of capillary walls. Because of these tight junctions, anything leaving these capillaries must pass through the endothelial cells. The selectivity of the endothelial membranes allows necessary substances to go through the cells, but inhibits the passage of potentially dangerous molecules, and organisms.
Work Step by Step
The blood cerebrospinal barrier (BCB) protects the brain in areas where there are choroid plexuses. This barrier is formed by tight junctions between ependymal cells in these areas. In other areas of the brain tight junctions are absent from ependymal cells to allow exchange of substances between the brain and the CSF.
The brain barrier system (BBS) is selectively permeable ; it is very permeable to water, glucose, lipid soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics. It is less permeable to sodium, potassium, chlorides, and the metabolic wastes, urea and creatinine. Unfortunately the BBS forms an obstacle to the penetration of antibiotics, and some cancer drugs into the brain.