Which of the following best describes the role of the blood-brain barrier?

• A. It regulates the passage of substances from the bloodstream into the brain.
• B. It facilitates the exchange of oxygen and carbon dioxide in the lungs.
• C. It is responsible for the production of red blood cells.
• D. It aids in the digestion and absorption of nutrients in the small intestine.

Answer: (A)

Verified step by step guidance

1. Identify the primary function of the blood-brain barrier, which is to protect the brain by regulating the passage of substances from the bloodstream into the brain.
2. Understand that the blood-brain barrier is a selective permeability barrier that allows essential nutrients to pass while blocking potentially harmful substances.
3. Recognize that the blood-brain barrier is not involved in the exchange of gases like oxygen and carbon dioxide, which occurs in the lungs.
4. Acknowledge that the production of red blood cells is a function of the bone marrow, not the blood-brain barrier.
5. Clarify that digestion and absorption of nutrients occur in the small intestine, a process unrelated to the blood-brain barrier.