diffusion barrier
impedes passage of most compounds from blood to brain

structural elements

non-fenestrated endothelial cells
- i.e. continuous lipid bilayer
with tight junctions in between
basal lamina (basement membrane)
pericytes
astrocyte foot processes - ensheaths capillaries
perivascular potential space

how does it barrier

physical barrier - because of tight junctions
transport barrier - active transport mechanisms are the gatekeepers
metabolic barrier - ??

transport function

so what kinds of drugs can cross the BBB?

easy diffusion across a lipid bilayer →
- small
- high lipid solubility
- low volume of distribution
For specifically hydrophilic drugs:
- A high concentration in the blood stream, to rely on the concentration gradient to force the drug through the paracellular route (eg. ethanol)
- Low protein binding, so that a large free fraction is available
molecular similarity with another actively transported substance
- e.g. Lithium (pretends it's sodium)

https://derangedphysiology.com/main/cicm-primary-exam/nervous-system/Chapter-111/blood-brain-barrier

Disruption can lead to cerebral oedema.