Final answer:
The blood-brain barrier (BBB) is a protective structure that prevents or slows the passage of drugs and disease-causing organisms into the Central Nervous System (CNS). It is formed by endothelial cells and selectively allows certain molecules to pass through while restricting others. This barrier presents challenges for drug delivery to the CNS.
Step-by-step explanation:
The structure that prevents or slows the passage of some drugs and disease-causing organisms from entering the Central Nervous System (CNS) is called the blood-brain barrier (BBB).
The BBB is a highly selective membrane formed of endothelial cells that separates circulating blood from the extracellular fluid in the CNS. It allows essential molecules like glucose and amino acids to pass through, but restricts the entry of most other substances, including drugs and pathogens.
This protective barrier poses challenges for drug delivery to the CNS, as pharmaceutical companies need to design drugs that can effectively cross the BBB to have a desired effect on the nervous system.