What is the Blood Brain Barrier?
The blood-brain barrier (BBB) is a highly selective semipermeable barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). Composed of endothelial cells that line the blood vessels, tight junctions, and astrocyte end-feet, the BBB serves to protect the brain from toxins, pathogens, and other harmful substances while allowing the passage of essential nutrients, oxygen, and some small molecules. The BBB plays a crucial role in maintaining the brain’s homeostasis and protecting it from fluctuations in the blood composition. However, the same protective properties that shield the brain from potentially harmful substances can also pose challenges for the delivery of therapeutic drugs to the CNS.
Examples of the Blood Brain Barrier in neuroscience
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Permeability of Small Molecules
Small, lipid-soluble molecules such as oxygen and carbon dioxide can freely cross the blood-brain barrier, allowing for the exchange of essential gases between the blood and the brain. This ensures proper oxygen supply to the brain and the removal of waste products, maintaining overall brain health.
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Transport of Glucose
Glucose is the primary source of energy for the brain. The blood-brain barrier facilitates the transport of glucose from the blood into the brain using specialized glucose transporter proteins, ensuring that the brain has a constant supply of energy to function efficiently.
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Protection Against Toxins and Pathogens
The blood-brain barrier plays a crucial role in protecting the brain from harmful substances, such as toxins and pathogens, that may be present in the blood. Due to the selective nature of the BBB, most bacteria, viruses, and toxic substances are prevented from entering the brain, reducing the risk of infection and damage to the delicate neural tissue.
