How do bones make blood?

by / Jun 01, 2022


This post is edited from an episode of the Is That True? Podcast, where host Arionne fact-checks different kid questions. Today’s episode looks at the question How do bones make blood?, submitted by Roxy. 

Arionne: The fact we’ll be investigating today is really interesting. It has a lot to do with people and how our bodies work.


Roxy: My name is Roxy. I’m 5 years old. And I live in Portland. And how do bones make blood? 


Arionne: Roxy! Wow! When I was 5, I didn’t know much about how our bodies work. Like at all! That’s such a cool fact. And I think I’ve heard something like that, but I think we need to investigate it. 


So first, let’s make sure we all get on the same page. Basically, let’s make sure we all know a few basic things about your fact. We MIGHT mostly know what blood and bones do in our bodies, but let’s just make sure.


We kind of learn about blood early. If you’re like me, I fell a lot as a kid. I still do! I like to be active and run and dance and do things, but that also means I trip and fall sometimes and might scrape a knee or elbow. Has that ever happened to you?


Well, when that happens, we might see blood. And that’s OK! Blood helps our bodies a whole lot. It carries the things we need to different parts of our bodies. That’s why we see it if we get a scrape.


And bones we might learn about a little later. I think I learned about it from a song! You know the one: 


Knee bone connected to the thigh bone

Thigh bone connected to the hip bone

Hip bone connected to the back bone


Ha! I love it! It’s so good.


But back to our investigation. I have a BEST friend who knows a lot about blood. And she was the first person to come to mind when I heard Roxy’s question. Her name is Maisha Ferguson and she’s literally one of my favorite people in the whole world! (You probably feel that way about your best friends.)


So I called up Maisha. That was it! I just called her up to ask. And I realized that I’m lucky enough to have a friend who has a super cool job and who can answer these types of questions. She’s a pathologists’ assistant.




Maisha: Hi, my name is Maisha Ferguson. I am a pathologists’ assistant, which most people don't know about and rarely ever hear about let alone pathology. 


Arionne: Maisha has been a pathologists’ assistant since we graduated from college together. That was a LONG time ago. But I realized, I still didn’t know what a pathologists’ assistant does every day. So she explained it to me.


Maisha: Um,I work in the lab and surgical pathology. So usually anything that comes out of surgery, uh, most people are familiar with getting their appendix removed or tonsils removed gallbladders, things like that, that the surgeon removes during a surgery comes to me in a lab. It is my job to examine these specimen macroscopically, which means I will give measurements, weights, [and] section the specimen.

Describe what I see. And then the sections that I take of this get processed. They go to the pathologist who will examine it microscopically, which is under the microscope. And they're looking at the smaller cells. 


Arionne: Got it. So basically pathology has a lot to do with kind of, the parts of our bodies that we put in, take out, all that good stuff. Right. 


Maisha: Pathology is, um, the study of disease. 


Arionne: Oh, perfect. Okay. So you are the perfect person for us to talk to about this fact. So we got a fact that says, is it true that our bones can make blood? So Maisha is that true? 


Maisha: It is true and very true.


And interesting too. Um, so in pathology, the pathologist [looks] at everything. Like I said, at the cellular level, I usually work with tissues. So skin. Liver, like I said, gallbladders heart, any organs in your body, but there is a cytopathology that deals with bodily fluids. So blood, urine, saliva, um, any other fluids that your body may make, if you're sick.


So your blood is also something that they look at at the cellular level and your bone, as well as something that we can look at at the cellular level and what I love so much about pathology and other specialties that have to do with pathology. Um, your body works at this tiny, like—these different cells, all do different things.


And I think that that is so interesting. So yes, your bones make blood. 


Arionne: Amazing! Friends! Roxy was right. But HOW do our bones make blood?


Maisha: Okay. So in your long bones, like your arms [or] your legs, they have a hard outside and then a core in the sensor. Which you see if you're eating chicken and if you break like the chicken leg, you can see that the inside of it is red and mushy.


The outside is white and hard. The sensor part of those bones is the marrow and it's usually spongy bone. It's soft. Um, Inside of this marrow are specific cells called STEM cells, which are found in other parts of the body too. But these STEM cells are able to differentiate or evolve into a more mature cell that your body may need in this situation.


And you're in your marrow. You have blood STEM cells. So let's say somebody might've gotten a cut and they're bleeding a lot. Your body is like, we are losing blood. We need to make more red blood cells. So there are signals that go to these STEM cells. Hey, we need red blood cells in your marrow. The signals go to these STEM cells.  


The STEM cells then begin to evolve into red blood cells. Once they finally formed the red blood cells, they enter your bloodstream through tiny, tiny vessels that are in your marrow that go out of the bone and then they turn into larger veins arteries. And then that way the red blood cells go into the vessel, travel through your body, get oxygen from your lungs, and then go to the rest of your body.



Arionne: Wow. Okay. And so that is really cool. So really it's our bone marrow that is making the blood. Why would we need to use bone marrow to make blood?


Maisha: Well, I think that's kind of like the interesting thing about the body is everything has its own structure and function. Why, we’re made to have our marrow, make the blood.


You know other things like when people say, well, why do we even have tonsils? If you can take them out, you don't need them. Why can you take out our appendix? What is our appendix good for most of the time, we don't really have a reason for it. Why [do] our bones make the marrow? I mean, why [does] our marrow [make] blood?


Maybe it's because you have the safety of the hard outside of the bone to protect all of these specialized cells that we need to make the bone, the blood. That would be my first guess and really the only guess, but that I don't have the actual answer for.


Arionne: Got it. Got it. Do you know why we might use some of this blood, like, when we use the, make, use the bone marrow to make the blood, like, what are some of the common uses for that? 


Maisha: So the main use for when your body is making blood is really just so that you have the red blood cells to continue to circulate throughout your body. The red blood cells carry oxygen and other nutrients to different organs tissues in your body.


And actually you. Red blood cells don't last your entire lifetime. So just like your body continues to make skin cells. You also have to keep making red blood cells because you lose them for whatever reason, like I said before, if you're bleeding or they just age out and die. So that's the main reason why we need the blood to get oxygen to all of the rest of our body.


Arionne: And there’s something really interesting I learned from Maisha about how making blood can also help us. It can help people feel better who are sick with certain diseases that affect our blood, like types of cancers. Cancer is a really scary thing because it can make us really sick. And it can sometimes be hard to heal from it. BUT, people who are healthy can donate a part of their bone—the bone MARROW—to help people who are sick make blood that can help them feel better.


Maisha: So I work in pathology in this, the study of disease. Um, so I tend to see a lot of things, um, mostly with different cancers.


Um, and a lot of times you'll see things where people want to get people to donate to bone marrow registries. There are people that have different issues with their blood and might be a genetic issue with your blood, like sickle cell or just other diseases like leukemias and lymphomas, things like that, that originate from these, um, cells that just might not be doing what they need to do.

So with that, patients can get bone marrow transplants where my bone marrow isn't creating the type of blood that my body needs and it's making me sick, but there's a healthy person that matches with me. I can get their bone marrow and to replace what I have.


And then hopefully that helps me to get better because now the types of cells that it should make to help keep me healthy. 


Arionne: Ah, that's so good to know. Thank you so much Maisha. I appreciate it. 


Maisha: You're welcome. This is all so interesting of how the body works. These little tiny cells and so much every day.