BBB & CSF Flashcards
How is the composition of ECF regulated
CSF made by choroid plexus
BBB protests from fluctuations
Glial cells (astrocytes) condition/buffer
What are the FIVE functions of CSF
1) Fills ventricles (30mL) and forms thin layer in subarachnoid space (120mL)
2) Acts as a cushion/shock absorber makes brain buoyant
3) Appropriate environment for neurones and glia
4) Medium of exchange
5) Removal of waste
CSF movement
1) Lateral Ventricles (cortex)
2) Foramina of Monroe
3) Third Ventricle (thalamus)
4) Cerebral aqueduct of sylvius
5) Fourth Ventricle (Brain stem)
6) Two foramina of luschka and magendie
7) Subarachnoid space
Where are the ventricles derived?
What sort of circulation does CSF have?
What permits this circulation?
What are problems with this?
Ventricles derived from centre of neural tube
Rostral - caudal CSF circulation
3 foramina projecting into SAS permit CSF circulation
aqueduct and foramina can become blocked causing hydrocephalus
How is CSF secreted?
Ultra-filtration of plasma across fenestrated capillary wall into ECF beneath basolateral membranee of choroid epithelial cell
These secrete fluid into ventricles.
Difference of secretion from 1)basolateral and 2)apical membranes
1) Faces plasma, uses transporters
Na+ gradient used to promote accumulation of HCO3-
Important for neutralising acids
2) Ventricle
Na+K+ ATPase pumps - Na+ efflux
HCO3- and Cl- leave following electrochemical gradient
Aquaporins (AQP1) facilitate movement of water
What are the properties of endothelium cells?
What do these limit molecules to
TIGHT JUNCTIONS not fenestrations
can’t have higher MW than 2000
What factors regulate passage across BBB
1) Lipid solubility - High solubility = greater access
2) Degree of ionisation - if ionised at pH 7.4 won’t cross
3) Protein binding - If bound too large to pass
Why can’t you use dopamine to treat parkinson’s
Ionised at 7.4
Metabolised by MAO
Use precursor L-DOPA + peripheral DOPA decarboxylase inhibitor. Inhibitor prevents L-DOPA being metabolised to dopamine outside the brain.
Name the THREE main BBB disorders
Tumours - Leaky BBB, increased nutrients/growth
Infiltration - Increased antibiotic permeability
Ischaemia - Cellular damage, water and oedema
What are Non Barrier regions.
What are the structural differences
Circumventricular organs, tight junctions replaced by normal fenestrated endothelia.
Hormones released here have direct access to general circulation
