Blood–brain barrier
Say it: BLUD BRAYN BAIR-ee-ur
The blood–brain barrier is the tightly sealed lining of the brain's capillaries that controls which substances can pass from the blood into brain tissue.
Definition
What is the blood–brain barrier?
The blood–brain barrier separates circulating blood from the fluid that bathes neurons in the brain and spinal cord. Its core is the endothelial cells lining the capillaries, which, unlike those in most organs, are sealed to one another by tight junctions, have no pores and move very little material across in vesicles. Pericytes on the outer surface of the capillaries and the end feet of astrocytes wrapped around them help create and maintain these features; together with nearby neurons they form what is called the neurovascular unit.
Water, oxygen, carbon dioxide and small fat-soluble molecules diffuse through, but glucose, amino acids and other nutrients enter only on dedicated carrier proteins, and pumps in the endothelial membrane push many unwanted molecules back into the blood. This shields the brain from toxins, microbes and swings in blood chemistry. A few small sites next to the ventricles, the circumventricular organs, lack a full barrier so that they can sense the blood or release hormones into it.
The barrier is a major hurdle in pharmacology, because most drugs cannot cross it. In Parkinson's disease, for example, giving dopamine is useless because it cannot cross, so patients receive its precursor levodopa, which an amino acid transporter carries into the brain. Bacterial meningitis and multiple sclerosis are among the conditions that make the barrier leaky.
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- Glial cellA glial cell is a non-neuronal cell of the nervous system that supports, insulates, feeds and protects neurons and helps regulate their signaling.
- Central nervous systemThe central nervous system is the brain and spinal cord, the part of the nervous system that takes in sensory input, integrates it and sends out commands.
- PharmacokineticsPharmacokinetics is the study of how the body absorbs, distributes, metabolizes and excretes a drug, and how drug levels change over time.
- BioavailabilityBioavailability is the fraction of a drug dose that reaches the general circulation unchanged, along with how quickly it gets there.
- Parkinson's diseaseParkinson's disease is a progressive brain disorder in which dopamine-producing neurons die, causing tremor, stiffness, slow movement and poor balance.
- DopamineDopamine is a catecholamine neurotransmitter made from tyrosine that helps control movement, motivation and learning from reward.
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Written for biofideX in plain words, after checking these references:
- Daneman and Prat, The Blood–Brain Barrier, Cold Spring Harbor Perspectives in Biology (PMC)
- Queensland Brain Institute: What is the blood–brain barrier?
- NCI Dictionary of Cancer Terms: blood-brain barrier
- NCBI MeSH: Blood-Brain Barrier
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