What is the significance of the blood-brain barrier?

• A. To stabilize blood sugar levels
• B. To protect the brain from harmful substances
• C. To regulate brain temperature
• D. To facilitate neurotransmission

Answer: (B)

The blood-brain barrier is crucial for the protection of the brain by selectively allowing substances to pass from the bloodstream into the brain while blocking potential harmful agents. This barrier consists of tightly packed endothelial cells lining the brain's blood vessels, which limit permeability to larger molecules and most pathogens. By preventing toxins, pathogens, and certain drugs from entering the brain tissue, the blood-brain barrier helps maintain the delicate environment necessary for optimal neuronal function and overall brain health.

While the other options deal with important physiological processes, they do not accurately reflect the primary role of the blood-brain barrier. Stabilizing blood sugar levels pertains more to the regulation of glucose metabolism rather than the protective function of the barrier. Regulating brain temperature is managed by other mechanisms, such as blood flow and physiological responses to heat. Facilitating neurotransmission relates to the processes of signaling between neurons, which occurs once substances are already in the brain, but does not pertain to the protective role of the blood-brain barrier.