Blood-Brain Barrier (BBB)

What Is The Blood-Brain Barrier (BBB)? The blood-brain barrier (BBB) is a specialized network of cells and blood vessels that protect the brain from harmful substances in the blood while allowing essential nutrients to pass through.

The cells within the blood-brain barrier include:

  • Endothelial cells
  • Pericytes
  • Astrocytes
  • Microglia
  • Capillary basement membrane


What Does The Blood-Brain Barrier (BBB) Do?

  • Maintains the homeostasis of the brain microenvironment
  • Prevents the entry of toxic substances, pathogens, and immune cells into the brain
  • Regulates the transport of nutrients and metabolic waste products


How Is The Blood-Brain Barrier Regulated?

The structure of the endothelial cells lining the capillaries is largely responsible for the degree of impermeability of the blood-brain barrier through:

  • Stronger tight junctions seal the passage of substances between adjacent cells.
  • Lack of fenestrations.
  • Active transport mechanisms instead of passive uptake, such as pinocytic activity.  
  • Use of efflux transporters, such as P-glycoprotein, BRCP, and OATP, which actively remove compounds from the endothelial cells back into the peripheral circulation, thereby reducing CNS exposure.
  • Metabolism of drugs and other endogenous substances by leveraging the actions of CYP 450 enzymes in the endothelium.

Source:  Abbott NJ, Patabendige AAK, Dolman DEM, Yusof SR, Begley DJ. Structure and function of the blood-brain barrier. Neurobiol Dis. 2010;37(1):13-25. doi: 10.1016/j.nbd.2009.07.030.