What Passes the Blood Brain Barrier?
The blood brain barrier (BBB) carries out three vital functions and these are;
- Protect the brain from foreign substances that might damage it
- Maintain a constant environment for the brain
- Protect the brain from the harmful effects of some hormones
The BBB carries out its functions by preventing the passage of large molecules, and it expresses high numbers of proteins which can drive these molecules away. The structure can also slow down molecules that have a high electrical charge.
Substances that do pass through the blood brain barrier include molecules that readily dissolve in lipids. This is because the cells of the blood brain barrier have a phospholipid bilayer. Nicotine and alcohol easily dissolve in lipids and their effects can be felt very soon after they've entered the bloodstream. Other substances to be able to make it through include glucose and insulin, amino acids, oxygen, and anaesthetic drugs (lipid soluble).
The blood brain barrier provides an excellent block to bacteria, and so infections of the brain are rare. But they can occur, and are difficult to treat as antibodies cannot get across the barrier. However, some do find a way because inflammation increases blood brain barrier permeability.
The blood brain barrier does its job so well that it can make some diseases of the brain, such as cancers, very difficult to treat. This presents a huge challenge to researchers who have to work out how to design delivery methods that can get drugs through without damaging the brain or its environment.