- Components
- Tight junctions (Zonula occludens) between non-fenestrated endothelial cells.
- Astrocyte foot processes (induce barrier).
- Basement membrane.
- Permeability Rules
- Crosses: Lipid-soluble/nonpolar (O₂, CO₂, EtOH, anesthetics).
- Carrier Transport: Glucose (GLUT-1), Amino acids.
- Blocked: Polar/water-soluble (Dopamine), large molecules, bacteria.
- Key “Windows” (No BBB)
- Area Postrema (Medulla): Chemotactic trigger zone → Vomiting.
- OVLT: Senses osmolarity → ADH/Thirst.
- Neurohypophysis: ADH/Oxytocin release.
- Clinical Associations
- Vasogenic Edema: BBB breakdown (tumor/infarct) → fluid leak.
- Parkinson’s: L-DOPA crosses BBB (lipid-soluble precursor); Dopamine does not.
- Kernicterus: Immature BBB in neonates allows unconjugated bilirubin entry.