Blood brain barrier
The blood brain barrier (BBB) functions to protect the brain from harmful chemicals and large variations in ion concentrations. It is a semi permeable membrane formed by the tight junctions of endothelial cells in the capillaries of the brain and separates the blood from the cerebrospinal fluid. At several areas the BBB is fenestrated to allow neurosecretory products to enter the blood. These areas are known as circumventricular organs and include:-
MRCPsych questions usually focus on these aspects:-
- Pineal body
- Posterior pituitary
- Area postrema
- Subfornical organ
- Vascular organ of the lamina terminalis
- Median eminence
MRCPsych questions usually focus on these aspects:-
- Endothelial cells are joined by tight junctions
- Lipid soluble molecules pass through relatively easily whereas water soluble ones do not.
- Large molecules do not pass through the BBB easily
- Molecules that are highly charged struggle to pass through
- The permeability of the BBB increases when it is inflamed
- Nasally administered drugs can theoretically bypass the BBB
- The BBB is fenestrated at the circumventricular organs (make an effort to remember the posterior pituitary and the area postrema)
