Question

practice it
what is the blood - brain barrier?
a membrane that connects the lungs and heart.
a condition where the brain is unable to receive oxygen.
a protective mechanism that shields the brain from harmful substances.
a network of veins in the brain.
a type of medication used to treat migraines.

Explanation:

The blood - brain barrier is a protective structure. It is made up of tightly - packed cells that line the blood vessels in the brain. Its main function is to prevent harmful substances (such as toxins, certain drugs) from entering the brain while allowing essential nutrients and oxygen to pass through.

Answer:

A protective mechanism that shields the brain from harmful substances.