Thanks to Brilliant for supporting  this episode of SciShow.

Go to Brilliant.org/SciShow to get  started learning STEM for free, and if you’re interested in an annual premium  subscription you’ll get 20% off our link. [♪ INTRO] Bones. You know 'em, you love  'em, and you…probably have them shout out to all the crabs who watch SciShow!

And bones have a couple of  obvious roles in the body: protecting our organs and giving  muscles something to attach to. You may even know a few of their other  jobs, like producing blood cells. And last year, we dove into  bones as mineral stores.

But bones aren’t just structural body parts, and they do way more than we  tend to give them credit for. They help make your brain grow  and work, keep males fertile, and keep you from getting hungry! Recently, scientists have discovered that  bones are significant endocrine organs, meaning they produce hormones and other chemical signals  that our body uses for things like sexual function or metabolism.

And those chemicals that come from your bones  can affect a wide array of body systems. By uncovering what they do and why, we can learn how to keep people from getting sick and prevent sick people from getting even sicker. So, first off, let’s talk about  what’s actually in your bones.

Bones have a strong, calcium-rich “skeleton.” But they also contain a variety of cells. Some of them, like adipocytes,  store fat or nutrients. Others, called hematopoietic stem cells, make platelets, and both  red and white blood cells.

And other bone-specific cells create  and shape the tissue of the bone. Cells called osteoblasts help make bone,  and osteoclasts actually dissolve it, striking a careful balance, so you  don't get too much bone, or too little. And these cells are in constant communication,  not only with each other but with your body.

Bone-specific cells can react to and  make their own signals based on chemicals from the body, like the hormone adiponectin. When your body is low on incoming calories, your bone marrow fat cells sense  that and start producing adiponectin. That hormone makes your cells  more sensitive to insulin, among other things, which regulates  the amount of sugar in your blood by making cells suck more of  it out of your bloodstream.

At the same time, it also seems like the  hormone might trigger cells in places like the skeletal muscle to  use energy more efficiently. Like most studies, results  are still kind of variable and up in the air, so more  research needs to be done. But at least for some people, it appears  to be the kind of molecule that says "okay, we're not getting a lot  of food, time to get efficient." Osteoblasts cells, the bone-specific ones, can also respond to those body cues and  produce a hormone called osteocalcin.

This protein increases the amount  of sugar taken up by muscle cells, boosts insulin production, and  increases insulin sensitivity. But insulin is just one tiny  piece of your metabolism; there are also messengers that tell  you your hunger has been satiated. And, you guessed it, osteoblasts have you covered on that front, too.

They produce lipocalin-2, a protein that has the ability  to cross the blood-brain barrier, the veil that separates your  brain from the circulatory system and protects it from harmful  chemicals or pathogens. When the protein crosses the barrier, it suppresses the hunger  signal sent by your brain.. And osteocalcin has its hands in other pies,  too; it can help regulate male fertility.

The protein promotes testosterone  production in the Leydig cells located in the testes and  extends their cellular lifespan. Having more of that testosterone around  can help increase the creation of neurotransmitters, chemicals  that help neurons communicate, and encourage their  development in the hippocampus, an important brain region that plays a  part in our ability to remember things. So it looks like osteocalcin has a more  direct effect on the brain as well, though we’re still learning exactly what that is. we have mouse models that show it may  help the brain develop in the womb, too, since osteocalcin, at least from the  mouse mom, can cross the placenta and reach the growing baby. when this hormone is missing, there are  some noticeable effects in the brain.

In experiments, scientists showed that  osteocalcin-deficient mice had problems with spatial memory and anxiety. Meanwhile, giving them more of this chemical corrected age-related  cognitive decline and anxiety. Finally, because we’re still not done yet, osteocalcin also seems to be a  part of the body’s stress response.

Having osteocalcin around  seems to inhibit parts of what’s known as the  parasympathetic nervous system, which is the part of the nervous  system that calms things down. In short, it effectively takes the brakes  off of the fight or flight response. So it turns out that chemical signals from  our bones do a ton of different things!

But this also means that when these  things go wrong, it may make people sick in a lot of different ways,  or make illnesses more severe. This area is still being explored, but it’s possible that bone  diseases, like osteoporosis, may also disrupt the endocrine system. What’s worse, it might mean that, since patients  on long-term bed rest in the hospital also often   lose bone mass, there may be some knock-on  effects, like problems controlling blood sugar,   an increased risk of dementia, and can increase  in risk factors for other issues like strokes.

The good news is that knowing a problem exists  is the first step to treating the problem.   It’s possible that drugs that treat bone-related  illnesses may one day help with problems elsewhere   in the body or may help people stuck in the  hospital for a long time recover better. A trial in which people were given  bone-forming medicine for osteoporosis also saw their blood glucose  levels drop, for instance. So, bones aren’t just the scaffolding  that the good parts of the body rest on they’re an active participant  in diverse processes, from making your blood to  affecting how hungry you feel and even influencing your  recovery from a serious illness.

An impressive feat for something  we just thought of as a framework for holding up the important parts of the body! Bones aren’t the only good thing for your brain, like you could learn new STEM skills  with today’s sponsor, Brilliant. Brilliant is an online  interactive STEM-learning platform that helps you gain a deeper  understanding of concepts in math, science, and computer science by taking  you through the subjects piece by piece in visually stimulating, hands-on ways.  Brilliant is also constantly  expanding their catalog of courses, so whether you’re a beginner, an  expert, or anywhere in between, there’s an interactive course  to help you improve and learn, like their newly updated  course on Scientific Thinking, where you can use scientific principles  to understand the world around you.  To check them out you can sign up  with the link in the description or head to Brilliant.org/SciShow to get  20% off the annual Premium subscription. [♪ outro]