Canonical Question
Neuro – Cerebral Circ
Variant family: at least one exam appearance has different scope. The appearance record controls whether this master answer is safe to display on that Past Paper.
Master answer
Blood brain barrier
- Anatomical and chemical partition separating the intravascular space from CNS interstitial space
Structure
- Mechanical barrier
- Endothelial cells
- Tight junctions between cells formed by membrain proteins (e.g. occludin) prevents paracellular flow
- Lack fenestrations
- Lack transcellular pathways such as vescicles
- Selective transport proteins (e.g. GLUT, various amino acid transporters)
- Pericytes embedded in basement membrane
- Astrocyte end feet
- Supportive role for endothelium
- Aquaporin regulation
- Endothelial cells
- Physiological barrier
- Enzymatic inactivation
- Enzymtes within endothelial cells metabolise substances absorbed from capillary lumen
- Monoamine oxidase
- Cholinesterase
- Aminopeptidase and endopeptidase
- Enzymtes within endothelial cells metabolise substances absorbed from capillary lumen
- Efflux pumps
- Substances that are absorbed across the luminal capillary membrane may be pumped back into capillary lumen by efflux pumps
- P-Glycoprotein
- ABC-Transporter
- Substances that are absorbed across the luminal capillary membrane may be pumped back into capillary lumen by efflux pumps
- Enzymatic inactivation
- Areas of brain outside BBB
- Subfornical organ
- Organum Vasculosum Lamina Terminalis
- Pituitary
- Area postrema
Function
- Regulate uptake of nutrients and electrolytes into brain
- Regulate migration of leukocytes and inflammatory responses in the brain
- Buffer brain parenchyma and interstitium from fluctuations in blood
- Prevent toxins and pathogens entering brain
- Some substances (such as water) pass BBB readily. These are characterised by:
- Small molecular weight
- Lipophilic (thiopentone)
- Uncharged (e.g. atropine vs. glycopyrollate)
- Poorly protein bound
Sakurai 2016
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2009B Q08 | Describe the blood brain barrier. (50% of marks) What characteristics does a drug need to effectively penetrate into the central nervous system? (50% of marks) | historical_member | — |
| 2012B Q12 | Describe the blood brain barrier (50% of marks). What characteristics does a drug need to effectively penetrate the blood brain barrier? (50% of marks) | historical_member | — |
| 2015A Q03 | Describe the structure and function of the blood brain barrier | historical_member | — |
| 2025A Q05 | With respect to the blood brain barrier (BBB), outline the following: (a) the structure (15% of marks). (b) its function (25% of marks). (c) the mechanisms by which substances, including drugs move across the BBB and explain how this is determined or regulated (45% of marks). (d) the regions that lie outside the BBB and their purpose (15% of marks). | variant | 24.00% |