Which of the following statements is true regarding the blood-brain barrier?

Answer

The correct statement regarding the blood-brain barrier is: "The blood-brain barrier restricts the movement of certain substances from the bloodstream into the brain while allowing others to pass freely." ### Detailed Explanation: The blood-brain barrier (BBB) is a selective permeability barrier that protects the brain from potentially harmful substances while still allowing essential nutrients to pass through. Made up of tightly packed endothelial cells lining brain capillaries, the BBB prevents large or polar molecules from entering the brain, such as many drugs and toxins. However, the barrier facilitates the transport of necessary substances like oxygen, glucose, and other vital nutrients. Certain lipophilic (fat-loving) molecules can also pass through more easily. Understanding the function of the BBB is crucial in pharmacology, especially in developing treatments for brain and central nervous system disorders. Therefore, the statement emphasizing the selective nature of the BBB accurately describes its role in protecting the brain.