blood-brain barrier (BBB)


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blood-brain barrier (BBB)

the barrier separating the blood from the brain parenchyma everywhere except in the hypothalamus. It is permeable to water, oxygen, carbon dioxide and nonionic solutes, such as glucose, alcohol and general anesthetics, and is only slightly permeable to electrolytes and other ionic substances. Some small molecules, e.g. amino acids, are taken up across the barrier by specific transport mechanisms.