A protective complex surrounding most blood vessels in the brain.
Acts as a barrier between the bloodstream and the brain's extracellular space.
Allows selective substances like water, oxygen, and small lipid-soluble substances to cross easily.
Prevents toxins, pathogens, and harmful substances from entering the brain from the circulatory system.
Structure
Tight Junctions:
Central components of the blood-brain barrier structure.
Formed by endothelial cells that make up the interior lining of blood vessels.
In the rest of the body, small spaces between endothelial cells allow substances to pass through; however, in the brain, cells are fused tightly to restrict diffusion.
Astrocytes:
Glial cells with extensions known as astrocytic end-feet.
These end-feet surround blood vessels.
Play crucial roles in forming and maintaining the blood-brain barrier.
Involved in signaling that prompts the formation of tight junctions.
May have additional roles in regulation and maintenance.
Exceptions
Not all brain vessels have a blood-brain barrier.
Circumventricular Organs:
Lack a blood-brain barrier.
Located around the brain's ventricles.
Require access to the bloodstream for their functions.
Example: The posterior pituitary gland, which releases hormones directly into the bloodstream.
Significance
Protects the brain from harmful substances while allowing necessary nutrients and gases to pass through.
Essential for maintaining the brain’s internal environment.