Final answer:
The blood-brain barrier (BBB) is the structure that prevents certain drugs and pathogens from entering the CNS, allowing only specific molecules like glucose and amino acids. Although it serves as a protective shield for the CNS, it also poses challenges for medication delivery into the brain.
Step-by-step explanation:
The Blood-Brain Barrier (BBB)
The structure that slows the passage or prevents some drugs and disease-causing organisms from entering the CNS is known as the blood-brain barrier (BBB). The BBB is a selective permeability barrier that allows nutrients like glucose and amino acids through, but restricts most other substances, including many pathogens and pharmaceuticals. This protective mechanism ensures the CNS is shielded from potentially harmful substances circulating in the blood but also poses a significant challenge for drug delivery, as medications must be designed to penetrate this barrier effectively.
Physically, the BBB is made up of capillary endothelial cells that form tight junctions, controlling the transfer of materials from the blood to the brain. The BBB's role is essential for maintaining a stable environment for the brain and spinal cord, yet its selectivity also complicates treatment strategies for CNS infections as well as delivery of drugs targeting neural tissue.