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Bones are some of the coolest structures in the human body.
They provide structure, support, and protect your vital organs, but even despite all of
that, bones still don't get the credit that they deserve and that's because bones provide
even more functions that are essential for your health, wellness, and frankly, for you
to stay alive.
Now, these functions can't actually be seen on the outside of the skeleton.
We're going to have to go to the inside of bone to discuss this further and that's exactly
what we're going to do in this video - look at the inside of real human bone tissue where
we're going to see structure and architecture that rivals anything us humans have ever created
as well as see a tissue inside that is essential for you to stay alive.
So, let's do this.
[Intro]
So, as you can see, I have two skeletons behind me, Jeffrey the skeleton as well as Cornelius
the skeleton.
Now, each of these guys wanted me to be extremely clear about how they were introduced.
Geoffrey wants all of you to know that he is an all-natural, real human skeleton as
opposed to his sibling here that's a fake plastic skeleton.
Now, to be fair to Cornelius, he doesn't describe himself that way.
He wants all of you to know that he is a perfect synthetic replica of a human skeleton.
The sibling rivalry never ends.
Unfortunately, for Cornelius, we gotta use a skeleton because we're going inside the
bone, so time for the role of shame.
Don't worry, your time will come.
All skeletal sibling rivalry and joking aside, we're extremely lucky to have a real human
skeleton in our lab.
So, let's use Geoffrey and his bones to talk about a few key points as we move to the inside
of bone tissue.
So, if we were to look at the outside surface of all of Geoffrey's bones, of my bones and
your bones and if I zoom in so I can actually touch the outside surface of the bone, the
outside surface is referred to as "compact bone" and if you were to look at like a textbook
definition of compact bone, it would say something like the dense outer portion of all of your
bones.
Now, we refer to density because there's another type of bone tissue deep or underneath compact
bone which is less dense and we'll talk about that bone tissue soon enough but compact bone
even though it's the more dense version of bone tissue, it's thickness can still vary
dramatically throughout the skeleton, especially when we talk about the long bones of the skeleton
which make up the majority of your limb bones like your humerus or where we've zoomed in
to the femur down here.
Now, the end of a long bone is referred to as the epiphysis.
Now, the reason I brought up that fancy pants name, the epiphysis or the end of the long
bone is because at the ends or at the epiphysis, the compact bone is paper thin.
So, not very thick but when we compare that to the shaft of a long bone which is referred
to as "the diaphysis", the compact bone gets much much thicker which makes sense so it
can deal with the forces throughout the shaft of that bone, but I can't show you the thickness
on Geoffrey because we haven't cut into that bone but we have another dissection here that
I want to show you.
So, this is a lower leg dissection and this is your shin bone that we truly refer to as
the tibia and I'm touching the compact bone again that outside surface of the bone.
Now, a quick little reference here, you can see a difference from here to there.
This tissue is called "periosteum" and I had to remove it from the compact bone.
Periosteum is a dense irregular connective tissue that wraps the outside of your compact
bone.
It's a really cool tissue.
It has blood vessels, nerve endings, and even bone cells in there that can help maintain
the outside surface of the bone just for regular maintenance or even if there's damage like
a fracture.
Now, speaking of a fracture, if any of you have ever had a fracture or a bone break,
you'll tear and damage the periosteum and remember, just kind of a cool FYI, the periosteum
had nerve end or even pain receptors in there.
So when you break that bone and also tear the periosteum, that periosteum is responsible
for a lot of that pain you feel with bone damage.
So, if you've ever broken a bone, throw that in the comments.
Let us know what type of bone break you've had because I'm sure some of you had some
crazy ones.
But back to the compact bone here.
What you can see right here is we cut a hole inside there.
And if I roll it towards the camera there, you might get an idea that is definitely thicker
than just the paper thin compact that we found at the ends of the bones and I'll show you
another dissection in a second that will show that even better, but this dissection shows
you how cool the long bone shaft is because it's actually even though the - even though
the outside of it is thicker, the whole shaft is still hollow and that hollow tube that
I'm sticking the probe in there that you can see is called the medullary cavity.
Now, the medullary cavity, we kind of refer to it as doing two things - one, it helps
reduce the weight of the bone.
You don't need to have compact bone just fully - full thickness throughout the whole length
of the shaft so it does reduce the weight, but also you see something inside called yellow
bone marrow.
Now, this particular dissection of the lower leg doesn't have any yellow bone marrow in
it because we removed it from the tibia, but when I first did make this hole, there was
definitely yellow bone marrow that came out but I do have another dissection that we'll
take a look at - a cut through the upper limb and we're going to look down into the humerus
to take a look at this yellow bone marrow.
So let's trade the sections here, and if you take a look here, we've got a cross section
through the upper limb here.
Now, as you can see, the compact bone, you can definitely see the thickness of that shaft
but that soft yellowy tissue inside that I've got the probe in here is the actual yellow
bone marrow.
Now, yellow bone marrow is just another form of adipose tissue.
Adipose just meaning fat.
So, energy storage and we have a lot of different places for energy storage.
Now, some of you may have even eaten yellow bone marrow.
Well, not on humans because that would be wierd, but from other animals and I've never
had it but I've heard some people really like it and you can throw that in the comments
below if you like it and tell us what it taste like, but as far as this essential function
- yes we need energy storage, but is that what I was referring to at the beginning of
the video when I was talking about some of these functions that are essential for life
and for you to stay alive?
No, that we're going to have to take a look at another portion of the inside of bone and
we're going to use Geoffrey's femur here to zoom in and take a look at that.
So, in order for us to go deeper to the inside of bone tissue, we're going to take a look
at the backs of Geoffrey's thigh bone or for you anatomy geeks, that be the posterior aspect
of the head of the femur.
Now, this isn't going to take very much for us to get to the deeper bone layer or the
deeper bone tissue because remember, the ends or the epithesis of long bones, that compact
bone was only paper thin and if you look right above my finger there, you can see some of
that compact bone is missing.
Now, even this zoomed in angle that we have here still doesn't do the inside of your bones
justice.
So, we're going to zoom in even further right to this spot.
Look at amazing this deeper bone tissue is.
Obviously, this is going to be deep to the compact bone and this deeper bone tissue is
referred to as "spongy bone".
Now, it kind of make sense if you look at it, more porous and kind of resembles a sponge.
Now, those little beams of bone that are making up the spongy bone, they would continue deeper
into the bone tissue.
It's just we're so zoomed in right now that it's hard to bring those into focus but if
I adjust the camera settings and you kind of look in the background there, you should
see those other little beams coming to focus and that's pretty amazing to see that and
let me come back into the original picture here.
Now, you've heard me mention the phrase "little beams" a few times.
So, you should probably talk about these little structures in some more detail.
So, these little beams of bone are actually referred to as trabeculae.
Trabeculae translates to weird, little beams.
Now, at first glance, the trabeculae might look like they're oriented in all sorts of
random directions but remember at the beginning of the video, I said we're going to look at
some amazing structures in architecture... the trabeculae are not oriented randomly.
They are actually precisely oriented in the direct lines of stress that your bones experience
on a day-to-day basis and they can even build up in change throughout life based on activity
and even disease states.
Like for example, when you go from a little tiny baby, not moving, to crawling, up to
walking and running, the trabeculae will build up and change based on the forces that the
body experiences based on those different movement patterns of no movement to crawling
to walking and running like a little crazy toddler.
But, we also need to talk about the spaces in between the trabeculae.
Found in the spaces between your trabeculae is something extremely important to multiple
body functions and that is red bone marrow.
That's a bit different from the yellow bone marrow that we talked about earlier which
is another form of adipose tissue but your red bone marrow produces your blood cells.
Now, we say that the red bone marrow produces three different lines or three different types
of blood cells - let's start with the first being the red blood cells, also known as erythrocytes.
Eryth just means red, cyte means cell.
We also have the white blood cells or the leukocytes produced in the red bone marrow.
Leuk just means white, again, cyte meaning cell and the third would be the platelets
which are also known as thrombocytes.
Throm just means clot.
And if we look at the functions of these cells, we can see how vitally important red bone
marrow is.
Erythrocytes or red blood cells, they're designed to carry oxygen to all the tissues throughout
the body and every about these cells is designed to carry oxygen, the shape, the hemoglobin
inside - these are actually have some few cells in the human body that actually even
get rid of the nucleus because they want more room to carry as much oxygen as possible.
The white blood cells, we can all agree are pretty important because they are involved
in immunity for things like fighting off infections, tissue repair.
So, again, vitally important to our health and well being.
The third cell line we mentioned were platelets or thrombocytes.
Thromb again meant clot.
So, these are going to get involved in clotting your blood.
So, say like you get a cut on your arm, these are the cells that get in, form the clot,
and stop the bleeding.
So, again, bone marrow being so vitally important because of the production of these different
cell types.
Now, one thing we have to mention about this is... kind of want people to think about bone
tissue sometimes gets thought of as dead tissue.
I don't know why I just have noticed that amongst my students.
It's probably because the bones tend to remain long after somebody passes away.
We use it in Halloween but bone tissues are very much alive and as we mentioned, are constantly
changing and modifying throughout life.
So this spongy bone has an extremely important function, not only to deal with stresses and
strains that our bones experience but also to protect that red bone marrow.
And one thing we also have to think about - where do we want all these blood cells?
All of these blood cells have to circulate throughout the bloodstream throughout the
entire body.
So it's kind of cool to think about is that the bones have to have little holes or passageways
for blood vessels to pass in, run through those spaces of the red bone marrow, pick
up those blood cells, and then take them out of the bone so they can distribute throughout
the whole body.
Now, just keep in mind, as the blood does go into the bone, it'll also distribute nutrients
so the bone can stay alive as well as pick up all of those different blood cells.
And one last thing I want to mention, you actually will not find red bone marrow in
the spongy bone throughout the entire skeleton.
You'll actually only find it in the spongy bone of specific bones in the adult.
Those would be the sternum in the rib cage.
You also find red bone marrow in the spine or what we also refer to as the vertebral
column.
Also, it's in the hip bones and the proximal ends of the humerus and the femur.
So, what's filling the spongy bone in all of the other regions?
Well, that would be some more yellow bone marrow because who doesn't love to store a
little bit of extra fat?
So, there was our deep dive into the depths of your bones and hopefully you guys learned
something new and interesting and speaking of learning, if haven't noticed, we, at the
Institute of Human Anatomy might be what you would call a little bit "geeky" because we
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