Final answer:
The statement is true; the blood-brain barrier prevents many substances in circulating blood from reaching the CNS, thus protecting the brain from bacteria, drugs, and other potentially harmful materials.
Step-by-step explanation:
The statement is True. The blood-brain barrier (BBB) is a selectively permeable physical and chemical defense that prevents many circulating blood substances, including bacteria and many drugs, from reaching the cerebrospinal fluid (CSF) and central nervous system (CNS). While this barrier allows essential nutrients such as glucose and amino acids, as well as water and some gases to pass through, it effectively excludes many larger or non-lipid soluble molecules, protecting the brain from potential toxins and pathogens. As a result, there is no normal microbiota in the CSF, and treatments for CNS infections must consider the challenge of drug delivery across the BBB.
The blood-brain barrier comprises endothelial cells with tight junctions, a thick basement membrane, and astrocytic end-feet that all work together to restrict substance exchange between the bloodstream and CNS. This creates a unique environment for the nervous system, both protected and isolated, which makes the development of pharmaceuticals that can cross this barrier quite challenging.