What is the role of the blood-brain barrier in protecting the brain?

The blood-brain barrier protects the brain by acting as a filter between brain tissue and blood-borne substances, preventing harmful toxins and metabolites from entering the brain.

The blood-brain barrier is an impermeable network of brain capillaries that maintains a stable environment for the brain, which is sensitive to changes in circulating nutrients, hormones, and ions. It selectively allows certain substances to cross while blocking others, thus providing protection against potentially harmful agents. However, it is less effective against fat-soluble molecules and gases, allowing some substances like nicotine and alcohol to affect the brain.