The walls of blood vessels in the brain have a special property that prevents large molecules from moving out of the bloodstream and into the brain. This property, called the blood-brain barrier, serves to protect the brain by keeping potentially harmful substances from entering the brain.
A breakdown in the blood-brain barrier commonly occurs at the site of tumor growth. Acquired immunodeficiency syndrome (AIDS) has also been linked to a breakdown in the blood-brain barrier.
by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain