In its protective role, the blood-brain barrier becomes an obstacle in delivering therapeutic drugs to specific regions of the brain in the treatment of a variety of brain disorders
Describe what the blood-brain barrier is made of, and how different compounds are capable of crossing it.
Answer: The blood brain barrier is formed by tight junctions between the endothelial cells lining the brain capillaries. It prevents materials from leaking out of the bloodstream and into the central nervous system. These cells do not perform pinocytosis. Despite the tight junctions, there are still ways that compounds can cross the blood-brain barrier including:
1. Dissolving in the membrane. Small lipid-soluble molecules such as ethanol and some barbiturate drugs can cross directly into the central nervous system.
2. Catalyzed transport mechanisms (protein exchanger, channel, pump) allow the brain to take up circulating nutrients such as glucose and amino acids.
3. In some areas of the brain, the blood-brain barrier is more permeable. In particular, the regions around the pineal gland, the pituitary gland, and parts of the hypothalamus are quite permeable, allowing secreted molecules such as hormones to leave the brain and enter the circulatory system.
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