What Does Crossing The Blood-Brain Barrier (BBB) Mean?

The term “blood-brain barrier” (BBB) was coined more than a century ago. At this time, scientists discovered that injectable dye was capable of permeating tissues throughout the bodies of animals. But when the dye got to the brain, it was unable to pass. The scientists deduced that some type of barrier was preventing the dye from entering the brain area.
The scientists were on to something, and today much more has been learned about how the blood-brain barrier works. Scientists now understand that this barrier is selectively permeable, which means it will permit some substances to pass through but not others.In this article, learn what it means when a substance is able to cross through the blood-brain barrier, or BBB for short. 

Blood-Brain Barrier Structure


The human body includes 10 organ systems and 5 essential major organs. But out of all of these systems, there is only one organ system that can selectively choose which substances to keep in or out. This system is the brain and spinal cord.

The 1960’s was an era of some exciting medical breakthroughs. One of these breakthroughs was the chance to view the blood-brain barrier itself for the first time. The microscope was essential in this breakthrough, which revealed that the barrier is actually an unusually tightly interwoven conglomeration of blood vessels, each lined with its own delicate insulation of endothelial cells, which regulated what gets to pass through into the interior of the vessels and what gets stopped at the gate.

Some scientists liken this to a “security system” of sorts that the brain can activate its own defenses to keep potentially unsafe materials from reaching it.

However, the presence of this security system is not always beneficial, especially when it activates to prevent beneficial medications and supplements from passing through the barrier. For this reason, researchers are continually working on new ways to convince the brain to open up its gates and let helpful substances come through.

Function of the Blood-Brain Barrier

The core function of the blood-brain barrier is to keep harmful substances from gaining access to the sensitive, delicate matter of the brain and spinal cord. Examples of toxins include bacteria, parasites, poisons and similar others.

But the blood-brain barrier is also responsible for choosing which substances to let into the inner sanctum of the brain and spinal cord interior. These approved elements include hormones, amino acids, key nutrients and similar others.

Under ideal conditions, the blood-brain barrier will accurately identify each visitor, permitting entry only to those substances that are wanted and needed. Some substances may be granted automatic entry while others may need to be transported via hitching a ride with incoming proteins. The barrier can even control how quickly various visitors are allowed inside, as well as how quickly they reach their destination.

The blood-brain barrier is what is called “dynamic,” which means it is always on the job. The interior cells are continually communicating with cells on the periphery that receive and respond to different incoming and outgoing signals. There are three main ways that visitors are restricted from crossing the barrier: size, polarity or fat (lipid) insolubility.

Sometimes, the security system of the blood-brain barrier will fail to function effectively. This can happen because the cells have become compromised due to infection or disease. It can also happen when the blood vessels responsible for guarding the gate rupture. Cancer is another reason why the blood-brain barrier sometimes isn’t able to do its job well. In some cases, such as Multiple Sclerosis (MS), it is even thought that the inadequacies of the blood-brain barrier can cause the disease to worsen.

What Does It Mean to Cross the Blood-Brain Barrier (BBB)?

Once a substance, whether toxic or beneficial, has crossed through the blood-brain barrier, it has access to the delicate cells and tissues of the brain and spinal cord. Researchers now know that certain substances with particular types of compositions are better able to cross over the barrier than others.

For example, many lipid soluble substances or substances with a very tiny molecular structure can move across the barrier with ease, sometimes by altering its function. Examples include anti-depressants, anti-anxiety drugs, hormones, cocaine, nicotine (tobacco), methamphetamines, alcohol, ecstasy (MDMA) and similar others.

Why Does It Matter Whether It Crosses the BBB?

The effectiveness of the blood-brain barrier is directly correlated with the health of the brain and central nervous system (CNS) as it operates through the spinal cord. So long as the barrier is doing an effective job at permitting entry only to beneficial molecules and sending all others away, the brain and nervous system can remain healthy and fully functional.

But when the blood-brain barrier breaks down, which can happen for a number of reasons as noted here, this can lead to functional impairment, the onset or worsening of disease, infection or inflammation, addiction to substances and other undesirable health consequences.

Conversely, when the blood-brain barrier is functioning properly, it may turn away molecules that actually have a beneficial purpose, including such goals as easing disease symptoms, providing nutritional supplementation, introducing necessary amino acids and more.

What is most interesting here is that the blood-brain barrier is not operational in equal strength across all areas and systems of the brain. In fact, certain areas of the brain don’t get any protection from the barrier at all. The pituitary gland, pineal gland, median eminence, area postrema, pre-optic recess, paraphysis and endothelium of choroid plexus get no protection from the barrier.

In these areas, which together have been dubbed the “circumventricular organs,” or CVOs for short, molecules both beneficial and toxic can cross at will. But this is only helpful when the medications or supplements being sent are targeting these structures.


Research has proven that the blood-brain barrier system has many useful applications and protects the brain and central nervous system/spinal cord from many potentially dangerous or toxic molecules. However, there are times when the barrier can also prevent entry of beneficial and needed substances.

Researchers are steadily working to find creative new ways to arrange for transport of such beneficial molecules across the blood-brain barrier. From the use of nanoparticles as transporters to finding creative disguises that trick the barrier into thinking the substance is a permitted molecule, new breakthroughs are steadily being made. In particular, a new processthat uses ultrasound to intravenously inject anti-cancer drugs along with air bubbles has shown great potential.

In the meantime, it is important to know the reasons why the blood-brain barrier exists, how it can help keep the brain and central nervous system healthy and which beneficial medications and supplements are naturally able to cross the barrier. This can make the process of choosing which supplements to take easier and also more effective.

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