Question

practice it what substances are blocked by the blood - brain barrier? only medicines and drugs are blocked by the blood brain barrier. antibodies and other immune system molecules. harmful substances like bacteria, viruses, and toxins. harmless substances like water and glucose. all substances are allowed through the blood - brain barrier.

Explanation:

The blood - brain barrier is a protective mechanism. It blocks large molecules like antibodies and most immune system molecules to prevent immune responses in the brain which could be harmful. It also blocks harmful substances such as bacteria, viruses, and toxins. It does not block harmless substances like water and glucose which are needed by the brain, and not all medicines and drugs are blocked.

Answer:

B. Antibodies and other immune system molecules; C. Harmful substances like bacteria, viruses, and toxins