The blood brain barrier or BBB is border that separates extracellular fluid in the central nervous system (CNS) and the blood that is circulating from the brain.
This barrier is allows the passage by facilitate diffusion (passive diffusion) and through the selective proteins of molecules such as glucose, amino acids that are essential for the neural function.
BBB stands for the blood brain barrier. The proper functioning of the brain is meant by the amino acids. Amino acids are most necessary for production of proteins which are essential for the working of any cell.
In general antibodies and large polysaccharides like starch are too large and are not able to cross the blood-brain barrier. Whereas urea does not have specialized proteins and therefore they cannot enter the brain.
