Which of the following is true of the blood-brain barrier? a. the barrier is formed by cells that line the capillaries of the brain. b. the barrier is uniform, protecting all brain structures. c. the barrier functions to regulate the chemical composition of the extracellular fluid surrounding the brain cells. d. the barrier pumps glucose out of the brain into the bloodstream.

The barrier functions to regulate the chemical composition of the extracellular fluid surrounding the brain cells.

Explanation:

Blood-brain barrier

It is a very selective semipermeable membrane , hence allow some specific substance to pass via it . This barrier separates the  extracellular fluid in the central nervous system  and the circulating blood from the brain .

The barrier is composed of the endothelial cells .

Passive diffusion is shown in this system , and allows molecules like the water , glucose , amino acid to pass .

It regulates the chemical composition of the fluid of brain cell .

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