Microscopic Anatomy of Bones - The Osteon - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
1
concept
Osteon
Video duration:
5m
Play a video:
So far, we've talked about the different components of the bone matrix and we talked about the different bone cells. But now we want to put it all together and think how is bone really structured at the microscopic level? We're gonna start doing that by talking about the osteon, the osteon. Well, it's sometimes called the Hirsen system, but you're more likely to know it as the osteon, you might see hiver system. So you should be familiar with that word, at least this is gonna be the structural unit of compact bone and compact bone has a very regular structure to it. And we can look at that here. So we're gonna look over here at our diagram to start, you're very likely to see a diagram at least very similar to this. And here we see a, a section of bone and on the inside, we see some spongy bone. But we're looking at the compact bone here and what you can see it where it's cut and cross section. You can see all these circles that are sort of packed in tight to each other. Each one of those circles is an osteon. And the way I think of it when you look at an osteon, it's almost look like, looks like you're looking at a cross section of a tree trunk, right? You see the the rings of the tree trunk in a circle and to make compact bone, you take all these tree trunks and you just sort of push them up tightly together. So you can also see it here in this zoomed in section, we see one osteon uh with those different rings around the center. So now let's identify those specific parts of the osteon. First, up, we have the central canal, the central canal contains the blood vessels and nerves and we can see that labeled in a down here and we can see these blood vessels and nerves running through the central canal through the center of the osteon. Remember bone is living dy dynamic tissue. So it needs a blood supply. This is how the blood gets to the bone. Now, we also said that that these uh central canals are surrounded by these rings. These rings are going to be the lamelle or singular one lamella. And so these are gonna be the concentric rings of matrix. And you can see that a little bit more clearly. In b here, we've pulled out the concentric lamelle there to see the different rings surrounding the central canal. Now, finally, we talked about this a little bit in a previous video. We have the Lacue or the singular Lacuna these are the chambers that contain the osteo sites. And remember the osteocytes are the mature bone cells that live in the bone. And so you can see these lacuna, it's most clearly in. See here we're zoomed in, they're run along the lamella sort of in these rings. You see these darker spots where the bone cells live. Those are the chambers that are holding the osteocytes. But remember this is living dynamic bone. We need to get blood supply into it and we need to get nutrients to the cells. So we have all these little canals and canaliculi that are running through this bone to do that. So we're gonna go through each one of those. Now. Well, first off, we have the central canals and we already talked about that. We said that's a, they're running through the center of the osteon. But importantly, they are running parallel to the length of the bone, at least through the diaphysis, the shaft of the long bone and in the, around the spongy bone, around the ends of bones or other bones, they're at least running parallel to each other. These are going to supply uh blood and house those nerve fibers and they're gonna be relatively large. Now, they're still microscopic, but they're big enough to hold blood vessels. Now, the next one we wanna talk about though is the perforating canals and the perforating canals you can see in d here and the way I think of the perforating canals, the perforating canals run perpendicular, perforating perpendicular to the central canals. And they are there to connect the central canals to other blood vessels and nerves, right. If you have central canals that are all running in parallel, they can't run in parallel forever, they need to connect to each other. These perforating canals connect the different central canals to each other. And they also, as you can see here, connect them to the spongy bone or to the medullary cavity where the blood supply for the bone is. These are also gonna be relatively large. Well, because again, microscopic, but they're big enough to hold those blood vessels. Now, finally, we have these smallest little spaces in the bone. These are gonna be the canaliculi and the canaliculi are labeled e here and they're kind of hard to see because they are so small. These are connecting all the different Launi and I'm sort of just drawing them in here so that you can see them in a little bit more detail. Uh They are connecting the different lacuna to each other and also to the central canal because Launi remember there are these chambers that the osteocytes live in, but those osteocytes need nutrients. And so the canaliculi are the way that nutrients and waste and messages can diffuse through that bone. So these are therefore gonna run in all directions connecting those different lacuna with each other and they're there for communication and transport between osteocytes and these are going to be very small, right? They just hold these little extensions from the cells reaching out and connecting with each other. OK, a picture like this or an actual microscopic image of this is something you are very likely to see, very likely to need to label or at least identify labels on. So we're gonna practice that more coming up and I'll see you there.
2
example
Microscopic Anatomy of Bones - The Osteon Example 1
Video duration:
2m
Play a video:
In this example, we want to label this image and this image is quite clearly a cross section of bone at the microscopic level. So let's go ahead and get labeling first off, we wanna circle one osteon. Remember the osteon we said is the functional unit of bone. And when I look at an osteon or when I look at a cross section of bone, what I see often are these sort of like all these different tree trunks that are kind of packed together each individual tree trunk in cross section is gonna be the osteon. So in this image, we see two of them, we can see one here that I just circled and says to only circle one, but I'll just point out the other one here is is the other one that we can see at least most of. All right. So I've circled my one osteon. Now we want to draw arrows pointing to at least three lacuna. Now remember the lacuna, that's where the osteocytes, the mature bone cells live. The bone matrix is this solid matrix. So you need this little chamber in which the cells can live. And in a cross section like this. It looks like these sort of flattened black dots. There's probably 100 of them in this picture. I only need to label three. Well, there's one, there's one, there's one says at least three. Here's another one, right? We could do that all day. OK. Next up, we're going to label two lamelle. The lamelle. If you think of this Asian as a tree trunk, the lamelle are the different rings of the trees. And you can see that these lacuna are in those rings. So I just need to put a dotted line on two of them. That's kind of about where one is hard to hit it. Exactly. But you get the idea. OK. And that leaves us with draw a star on the central canal. The central canal is the middle of the osteon. It's in the center and it's the canal that holds the blood vessels and the nerves and we can see it as this black circle right there. All right. Labeling a picture like this is something that in my experience that does come up on tests relatively often. So you probably want to be able to do it that see you in the next video.
3
Problem
Problem
Choose the words that best complete the follow statement: The structural unit of compact bone is the ___________ which is comprised of concentric __________.
A
Lacuna: Osteons
B
Osteon: Lamellae
C
Lamella: Lacunae
D
Osteon: Lacunae
4
Problem
Problem
What would be one possible result if bone developed without canaliculi?
A
Bones would lose their strength; they would remain rigid, but would become brittle.
B
Blood vessels could not pass through the bone, meaning bone cells would not receive nutrients.
C
Bone could not be remodeled as osteoblasts and osteoclasts could no longer travel through the bone tissue.
D
Osteocytes could not receive nutrients or send signals as they would not be in contact with other cells.
5
Problem
Problem
Which statement about central canals and perforating canals is correct?
A
The central canal runs through the center of the osteon, while perforating canals allow nutrients to diffuse from the central canal to the osteocytes in lacunae.
B
Because the blood vessels in central canals all run parallel, perforating canals are necessary to connect them.
C
Perforating canals carry the nerve supply for the bone, while central canals carry the blood supply.
D
Perforating canals run parallel to the osteon, while the central canals connect perforating canals to the medullary cavity in the center of the bone.
6
concept
Structure of Lamellae
Video duration:
2m
Play a video:
We now just want to spend a little bit of time talking about the structure of lamella. And remember the lamellae are these layers of bone matrix and in the osteon, they're in concentric circles. And so we're talking about the bone matrix here and that bone matrix is made of collagen which gives bone its strength, it's strong but flexible like a rope. And also the hydroxy appetite crystals which give bone its hardness and the hydroxy appetite crystals. That's where the calcium is in your bone, it's very hard, but it's also very fragile. So here we're gonna say that the arrangement of the lamella give bones strength in multiple directions. And if we're talking about strength, we're talking about the collagen. So let's look at our diagram here real quick. We have uh an osteon here, but we have the different lamelle pulled away so that we can see see each concentric lamella. So we have 123 lamella. And if we just look at this first one, all the way on the left, we see these, we have these lines on it that are sort of spiraling around in parallel, that's gonna be the direction of the collagen in the lamella, the collagen is all running in parallel with those hydroxy appetite crystals sort of lined up between it and it's lined up spiraling around the lamella. Now, this we're gonna say means the collagen is all running in the same direction within one Lamela when it's built that way, that's gonna really increase strength. So I'm gonna indicate that just by drawing an up arrow, it's gonna increase strength, but only in that one direction, right? If you apply stress from a different direction, it's not gonna be as strong. So when you look at uh between lamella or between adjacent lamella, here we look at our two lamella over here on the right and we can see that we have the spiral going in one direction in the first one, but then the next lamella, the spiral is going in the opposite direction or the alternate direction, I'll say here. So that means that in one Lamela, all these collagen fibers are running parallel, but in the next one, it's layered over in an alternate direction that is gonna give strength in multiple directions. And because it's in a spiral and they're spiraling in opposite directions, that means that these are gonna be really good. I'm gonna say here at resisting the twist, we're gonna resist the twist one way to break things to break something like the rodlike shape like a bone, right is to twist it. Well, these collagen fibers running in spirals in opposite directions is gonna be really good at resisting twisting. All right. So remember collagen gives it strength, but the arrangement of the collagen in the melle gives its strength in multiple directions with that practice problems that follow, give them a try.
7
Problem
Problem
Collagen fibers run in alternate directions between lamellae. What would the effect on bone be if all of the collagen fibers were oriented in the same direction?
A
The bone would lose its hardness and would bend easily.
B
The bone would break more easily if stress were applied from a different direction.
C
The structure of the osteon could not form; lamellae arise naturally from the alternating directions of collagen.
D
The periosteum could not attach properly as the perforating fibers rely on the alternating pattern of collagen.
Do you want more practice?
We have more practice problems on Microscopic Anatomy of Bones - The Osteon