Structurally, the blood-brain barrier exists because
A)the endothelial cells lining the CNS are extensively interconnected by tight junctions.
B)normal blood flow is at a pressure too high for the delicate brain tissue.
C)only water-soluble compounds are permitted to enter by passive diffusion.
D)the hypothalamus regulates the permeability of the blood vessels.
E)None of the answers are correct.

Question

Quizplus · Accepted Answer

The blood-brain barrier is a selectively permeable membrane created by the tight junctions between the endothelial cells that line the blood vessels within the CNS. These tight junctions prevent most substances from entering the brain tissue and protect it from potentially harmful pathogens and toxins found in the blood. Therefore, choice A correctly explains why the blood-brain barrier exists. Choice B is incorrect because normal blood flow to the brain is necessary for its function, and high blood pressure does not prevent substances from entering the brain. Choice C is incorrect because lipids and gases (such as oxygen and carbon dioxide) can pass through the blood-brain barrier. Choice D is also incorrect because the blood-brain barrier is primarily regulated by the tight junctions rather than the hypothalamus.

Structurally, the Blood-Brain Barrier Exists Because