Blood Brain Barrier

The blood-brain barrier (BBB) is a highly specialized barrier system that separates the blood circulating in the body from the brain and spinal cord. It is made up of endothelial cells which line the blood vessels supplying the brain, along with astrocyte foot processes and several other supporting cells.

Function

The main function of the blood-brain barrier is to protect the brain and spinal cord from harmful substances while allowing essential nutrients and molecules to pass through. It achieves this by tightly regulating the movement of substances between the blood and the brain.

Structure

The BBB is composed of several components:

• Endothelial Cells: These cells line the blood vessels of the brain and form tight junctions between each other, creating a physical barrier to prevent the passage of most substances.
• Astrocyte Foot Processes: Astrocytes are star-shaped cells that surround the blood vessels in the brain. Their foot processes extend and interact with the endothelial cells, providing additional structural support and helping to maintain the integrity of the BBB.
• Pericytes: These cells are located on the outside of the endothelial cells and play a role in maintaining the stability of the blood-brain barrier.
• Basement Membrane: A thin layer of extracellular matrix proteins that adds structural support to the barrier.

Regulation

The blood-brain barrier is highly regulated to control the transport of substances into and out of the brain. It uses various mechanisms such as:

• Transporters: Specialized proteins that actively transport essential nutrients, ions, and molecules across the barrier.
• Enzymes: Some enzymes present in the BBB metabolize certain substances, preventing them from entering the brain.
• Tight Junctions: The tight junctions between endothelial cells are impermeable to large molecules and prevent most substances from freely crossing the barrier.
• Active Efflux Pumps: These pumps actively remove potentially harmful substances that have entered the brain back into the bloodstream.

Importance

The blood-brain barrier is vital for maintaining the homeostasis and proper functioning of the brain and central nervous system. It prevents toxins, pathogens, and large molecules from reaching the delicate neural tissue, while allowing the passage of essential nutrients, oxygen, and hormones that are necessary for brain function.