Name: how the blood-brain barrier works
Uploaded: 2025-10-23T11:47:15.000Z
Duration: 49 s
Channel: JoVE

The human brain is isolated from the circulatory system via a protective barrier called the blood-brain barrier, which consists of endothelial cells that line the capillaries of the central nervous system.

The blood-brain barrier also consists of a basement membrane and specialized neural cells called astrocytes that are in close contact with the capillaries. These components help to prevent unwanted substances from crossing.

This barrier controls the chemical exchange between the blood and the interstitial fluid in the brain via different types of proteins that form junctional complexes. Generally, only lipid-soluble compounds can diffuse across the barrier, while water-soluble compounds cross via active or passive transport.

the blood-brain barrier

The Blood-brain Barrier

<h4>Overview</h4>

The blood-brain barrier (BBB) refers to the specialized vasculature that provides the brain with nutrients in the blood while strictly regulating the movement of ions, molecules, pathogens, and other substances. It is composed of tightly linked endothelial cells on one side and astrocyte projections on the other. Together they provide a semipermeable barrier that protects the brain and poses unique challenges to the delivery of therapeutics.

<h4>Cellular Components</h4>

The BBB is made up of a variety of cellular components, including endothelial cells and astrocytes. These cells share a common basement membrane and together regulate the passage of components between the circulation and the interstitial fluid surrounding the brain.

The first type of cellular component, specialized endothelial cells, make up the walls of the cerebral capillaries. They are connected by extremely tight and complex intercellular junctions. These junctions create a selective physical barrier, preventing simple diffusion of most substances, including average to large-sized molecules such as glucose and insulin.

A second cell type, astrocytes, are a type of glial cell of the central nervous system which influences endothelial cell function, blood flow, and ion balance in the brain through interaction and close association with cerebral vasculature. They provide a direct link between the vasculature and neurons: they extend processes&#8212;called endfeet&#8212;that wrap around blood vessels on one end while making intimate contact with neurons at synapses on the other end.

<h4>Chemical Exchange</h4>

The ability of a substance to cross the BBB and the efficiency with which this exchange occurs depends on the chemical and molecular properties of each molecule or ion. In general, small lipid-soluble components, such as oxygen and carbon dioxide, undergo rapid, simple diffusion through the endothelial layer. In contrast, larger or water-soluble components often require a more selective process that may involve passive or active transport through an endothelial cell. The exchange of these substances generally occurs more slowly or may not occur at all, depending on the relative abundance and efficiency of molecule-specific receptors and transport proteins on the surface of endothelial cells, among other factors.

<h4>The BBB Protects the Brain</h4>

The neural protection facilitated by the BBB is critical to proper brain health and function. Dysregulation of the BBB can lead to severe neurological disease including multiple sclerosis, infection, and ischemia due to an inadequate blood supply. Conversely, the activity of the BBB may be detrimental to the treatment of some neurologic diseases by preventing or substantially reducing the passage of neuroactive pharmaceutical drugs into the central nervous system. For this reason, drugs with neurological targets must be designed in a way that facilitates passage through the BBB.

Overview

The blood-brain barrier (BBB) refers to the specialized vasculature that provides the brain with nutrients in the blood while strictly ...

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how the blood-brain barrier works

The blood-brain barrier is a specialized system of blood vessels that helps control what enters the brain. It delivers nutrients from the blood while tightly regulating ions, molecules, pathogens, and other substances. This semipermeable barrier protects the brain and also makes it harder to deliver some therapies.

The blood-brain barrier includes several cellular parts, especially endothelial cells and astrocytes. These cells share a common basement membrane and regulate movement between the circulation and the fluid around the brain. Specialized endothelial cells form the walls of cerebral capillaries. They are joined by very tight intercellular junctions, which create a selective physical barrier. This barrier blocks simple diffusion of most substances, including molecules as large as glucose and insulin.

Astrocytes are glial cells in the central nervous system. They influence endothelial cell function, blood flow, and ion balance in the brain. Astrocytes connect closely with the cerebral vasculature. Their processes, called endfeet, wrap around blood vessels on one end and make contact with neurons at synapses on the other. This gives them a direct link between blood vessels and nerve cells.

What crosses the barrier depends on a molecule's chemical and molecular properties. Small lipid-soluble substances, such as oxygen and carbon dioxide, move across by rapid simple diffusion. Larger or water-soluble substances usually need a more selective process. They may move through an endothelial cell by passive or active transport. In many cases, this exchange is slower, or it may not occur at all, depending on receptors and transport proteins on the endothelial surface.

The blood-brain barrier is essential for brain health and normal function. When it does not work properly, severe neurological diseases can occur, including multiple sclerosis, infection, and ischemia from poor blood supply. The barrier can also make treatment difficult because it can reduce the passage of neuroactive drugs into the central nervous system. For that reason, medicines aimed at the brain must be designed to pass through the blood-brain barrier.

How the Blood-Brain Barrier Works

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The blood-brain barrier is a specialized system of blood vessels that helps control what enters the brain. It delivers nutrients from the blood while tightly regulating ions, molecules, pathogens, and other substances. This semipermeable barrier protects the brain and also makes it harder to deliver some therapies. The blood-brain barrier includes several cellular parts, especially endothelial cells and astrocytes. These cells share a common basement membrane and regulate movement between the...

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key terms and concepts

Learn how the blood-brain barrier protects the brain, which cells build it, what can cross it, and why it matters for disease and drug delivery.

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How the Blood-Brain Barrier Works

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