Our blood-brain barrier stops bugs and toxins getting to our brain. Here’s how it works

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Our brain is an extremely complex and delicate organ. Our body fiercely protects it by holding onto things that help it and keeping harmful things out, such as bugs that can cause infection and toxins.

It does that though a protective layer called the blood-brain barrier. Here’s how it works, and what it means for drug design.

The Conversation, Rattiya Thongdumhyu/Shutterstock, Petr Ganaj/Pexels

First, let’s look at the circulatory system

Adults have roughly 30 trillion cells in their body. Every cell needs a variety of nutrients and oxygen, and they produce waste, which needs to be taken away.

Our circulatory system provides this service, delivering nutrients and removing waste.

A fenestrated capillary
Fenestrated capillaries let nutrients and waste pass through. Vectormine/Shutterstock

Where the circulatory system meets your cells, it branches down to tiny tubes called capillaries. These tiny tubes, about one-tenth the width of a human hair, are also made of cells.

But in most capillaries, there are some special features (known as fenestrations) that allow relatively free exchange of nutrients and waste between the blood and the cells of your tissues.

It’s kind of like pizza delivery

One way to think about the way the circulation works is like a pizza delivery person in a big city. On the really big roads (vessels) there are walls and you can’t walk up to the door of the house and pass someone the pizza.

But once you get down to the little suburban streets (capillaries), the design of the streets means you can stop, get off your scooter and walk up to the door to deliver the pizza (nutrients).

We often think of the brain as a spongy mass without much blood in it. In reality, the average brain has about 600 kilometres of blood vessels.

The difference between the capillaries in most of the brain and those elsewhere is that these capillaries are made of specialised cells that are very tightly joined together and limit the free exchange of anything dissolved in your blood. These are sometimes called continuous capillaries.

Continuous capillary
Continuous capillaries limit the free exchange of anything dissolved in your blood. Vectormine/Shutterstock

This is the blood brain barrier. It’s not so much a bag around your brain stopping things from getting in and out but more like walls on all the streets, even the very small ones.

The only way pizza can get in is through special slots and these are just the right shape for the pizza box.

The blood brain barrier is set up so there are specialised transporters (like pizza box slots) for all the required nutrients. So mostly, the only things that can get in are things that there are transporters for or things that look very similar (on a molecular scale).

The analogy does fall down a little bit because the pizza box slot applies to nutrients that dissolve in water. Things that are highly soluble in fat can often bypass the slots in the wall.

Why do we have a blood-brain barrier?

The blood brain barrier is thought to exist for a few reasons.

First, it protects the brain from toxins you might eat (think chemicals that plants make) and viruses that often can infect the rest of your body but usually don’t make it to your brain.

It also provides protection by tightly regulating the movement of nutrients and waste in and out, providing a more stable environment than in the rest of the body.

Lastly, it serves to regulate passage of immune cells, preventing unnecessary inflammation which could damage cells in the brain.

What it means for medicines

One consequence of this tight regulation across the blood brain barrier is that if you want a medicine that gets to the brain, you need to consider how it will get in.

There are a few approaches. Highly fat-soluble molecules can often pass into the brain, so you might design your drug so it is a bit greasy.

Person holds tablet and glass
The blood-brain barrier stops many medicines getting into the brain. Ron Lach/Pexels

Another option is to link your medicine to another molecule that is normally taken up into the brain so it can hitch a ride, or a “pro-drug”, which looks like a molecule that is normally transported.

Using it to our advantage

You can also take advantage of the blood brain barrier.

Opioids used for pain relief often cause constipation. They do this because their target (opioid receptors) are also present in the nervous system of the intestines, where they act to slow movement of the intestinal contents.

Imodium (Loperamide), which is used to treat diarrhoea, is actually an opioid, but it has been specifically designed so it can’t cross the blood brain barrier.

This design means it can act on opioid receptors in the gastrointestinal tract, slowing down the movement of contents, but does not act on brain opioid receptors.

In contrast to Imodium, Ozempic and Victoza (originally designed for type 2 diabetes, but now popular for weight-loss) both have a long fat attached, to improve the length of time they stay in the body.

A consequence of having this long fat attached is that they can cross the blood-brain barrier, where they act to suppress appetite. This is part of the reason they are so effective as weight-loss drugs.

So while the blood brain barrier is important for protecting the brain it presents both a challenge and an opportunity for development of new medicines.

Sebastian Furness, ARC Future Fellow, School of Biomedical Sciences, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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  • The Joy Of Missing Out

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    What this is not going to be: a sour grapes thing.

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    You’ve probably read before the phrase “wherever you go, there you are”, but this phrasing brings attention to the fact that you already are where you are.

    There are quite possibly aspects of your current life/situation that are not ideal, but take a moment to appreciate where you are in life. At the very least, you are probably in a safe warm dry house with plenty of food available; chances are you have plenty of luxuries too.

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    The Joy of Saying No – by Natalie Lue

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  • Your Brain on Art – by Susan Magsamen & Ivy Ross

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    The notion of art therapy is popularly considered a little wishy-washy. As it turns out, however, there are thousands of studies showing its effectiveness.

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  • How can I stop overthinking everything? A clinical psychologist offers solutions

    10almonds is reader-supported. We may, at no cost to you, receive a portion of sales if you purchase a product through a link in this article.

    As a clinical psychologist, I often have clients say they are having trouble with thoughts “on a loop” in their head, which they find difficult to manage.

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    However, because they are about things that have either already happened or might happen in the future (but are not happening now), we cannot fix the problem, so we keep going over the same thoughts.

    Who overthinks?

    Most people find themselves in situations at one time or another when they overthink.

    Some people are more likely to ruminate. People who have had prior challenges or experienced trauma may have come to expect threats and look for them more than people who have not had adversities.

    Deep thinkers, people who are prone to anxiety or low mood, and those who are sensitive or feel emotions deeply are also more likely to ruminate and overthink.

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    We all overthink from time to time, but some people are more prone to rumination.
    BĀBI/Unsplash

    Also, when we are stressed, our emotions tend to be stronger and last longer, and our thoughts can be less accurate, which means we can get stuck on thoughts more than we would usually.

    Being run down or physically unwell can also mean our thoughts are harder to tackle and manage.

    Acknowledge your feelings

    When thoughts go on repeat, it is helpful to use both emotion-focused and problem-focused strategies.

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    Acknowledging those emotions, using self-care techniques and accessing social support to talk about and manage your feelings will be helpful.

    The second part is being problem-focused. Looking at what you would do differently (if the thoughts are about something from your past) and making a plan for dealing with future possibilities your thoughts are raising.

    But it is difficult to plan for all eventualities, so this strategy has limited usefulness.

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    Think about why these thoughts are showing up

    Our feelings and experiences are information; it is important to ask what this information is telling you and why these thoughts are showing up now.

    For example, university has just started again. Parents of high school leavers might be lying awake at night (which is when rumination and overthinking is common) worrying about their young person.

    Man lays awake in bed
    Think of what the information is telling you.
    TheVisualsYouNeed/Shutterstock

    Knowing how you would respond to some more likely possibilities (such as they will need money, they might be lonely or homesick) might be helpful.

    But overthinking is also a sign of a new stage in both your lives, and needing to accept less control over your child’s choices and lives, while wanting the best for them. Recognising this means you can also talk about those feelings with others.

    Let the thoughts go

    A useful way to manage rumination or overthinking is “change, accept, and let go”.

    Challenge and change aspects of your thoughts where you can. For example, the chance that your young person will run out of money and have no food and starve (overthinking tends to lead to your brain coming up with catastrophic outcomes!) is not likely.

    You could plan to check in with your child regularly about how they are coping financially and encourage them to access budgeting support from university services.

    Your thoughts are just ideas. They are not necessarily true or accurate, but when we overthink and have them on repeat, they can start to feel true because they become familiar. Coming up with a more realistic thought can help stop the loop of the unhelpful thought.

    Accepting your emotions and finding ways to manage those (good self-care, social support, communication with those close to you) will also be helpful. As will accepting that life inevitably involves a lack of complete control over outcomes and possibilities life may throw at us. What we do have control over is our reactions and behaviours.

    Remember, you have a 100% success rate of getting through challenges up until this point. You might have wanted to do things differently (and can plan to do that) but nevertheless, you coped and got through.

    So, the last part is letting go of the need to know exactly how things will turn out, and believing in your ability (and sometimes others’) to cope.

    What else can you do?

    A stressed out and tired brain will be more likely to overthink, leading to more stress and creating a cycle that can affect your wellbeing.

    So it’s important to manage your stress levels by eating and sleeping well, moving your body, doing things you enjoy, seeing people you care about, and doing things that fuel your soul and spirit.

    Woman running
    Find ways to manage your stress levels.
    antoniodiaz/Shutterstock

    Distraction – with pleasurable activities and people who bring you joy – can also get your thoughts off repeat.

    If you do find overthinking is affecting your life, and your levels of anxiety are rising or your mood is dropping (your sleep, appetite and enjoyment of life and people is being negatively affected), it might be time to talk to someone and get some strategies to manage.

    When things become too difficult to manage yourself (or with the help of those close to you), a therapist can provide tools that have been proven to be helpful. Some helpful tools to manage worry and your thoughts can also be found here.

    When you find yourself overthinking, think about why you are having “hot thoughts”, acknowledge your feelings and do some future-focused problem solving. But also accept life can be unpredictable and focus on having faith in your ability to cope. The Conversation

    Kirsty Ross, Associate Professor and Senior Clinical Psychologist, Massey University

    This article is republished from The Conversation under a Creative Commons license. Read the original article.

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  • Apple Cider Vinegar vs Balsamic Vinegar – Which is Healthier?

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    Our Verdict

    When comparing apple cider vinegar to balsamic vinegar, we picked the apple cider vinegar.

    Why?

    It’s close! And it’s a simple one today and they’re both great. Taking either for blood-sugar-balancing benefits is fine, as it’s the acidity that has this effect. But:

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    • Of the two, apple cider vinegar is the one more likely to contain “the mother”, that is to say, the part with extra probiotic benefits (but if the vinegar has been filtered, it won’t have this—it’s just more common to be able to find unfiltered apple cider vinegar, since it has more popular attention for its health benefits than balsamic vinegar does)

    So, two wins for apple cider vinegar there.

    Want to learn more?

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    Take care!

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