Which of the following is NOT a characteristic of the blood-brain barrier?

The characteristic of the blood-brain barrier that is not true is that it prevents the passage of oxygen into the brain. This is incorrect because the blood-brain barrier is selectively permeable, meaning it regulates the movement of substances between the bloodstream and the central nervous system. However, it does allow essential molecules such as oxygen and glucose to pass through, as these are vital for brain function and metabolism.

Oxygen is necessary for cellular respiration and energy production in brain cells, so it must be able to enter the brain without restriction. The blood-brain barrier effectively prevents harmful substances and pathogens from entering the brain while still ensuring that essential nutrients and gases can reach brain tissue. This selective permeability is crucial for maintaining a stable environment for neuronal function and protecting the brain from potentially harmful agents.

In contrast, the other options accurately describe the blood-brain barrier's functions: it selectively allows specific substances, limits drug entry, and acts as a protective barrier against pathogens.