Barrier Functions
- Protects against potentially harmful molecules from entering the brain
- Provided through 4 main mechanisms:
- Paracellular barrier: endothelial tight junction restrict free movement of water
- Transcellular barrier: Low level of inherent endocytosis and transcytosis prevents transport of substances to the cytoplasm
- Enzymatic barrier: Complex set of enzymes capable of metabolising compounds before crossing the BBB
- Efflux barrier: Large number of efflux transporters present which can remove molecules from cells of the BBB
Carrier Functions
- Transports nutrients, metabolites and essential ions to ensure the maintenance of a constant environment for the functioning of neurons
- Provided through a number of mechanisms:
- Passive and facilitated diffusion: Allows small lipid soluble molecules, water and gases to pass through the membrane
- Specific transport proteins: Provides a supply of essential nutrients such as glucose and amino acids
- Transcytosis: Ensures important metabolic molecules such as insulin can reach the brain