Gross Anatomy of Bone: Periosteum and Endosteum - Video Tutorials & Practice Problems
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concept
Periosteum and Endosteum
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Bone is a type of connective tissue, but it's also wrapped by other connective tissue. Specifically, it's gonna be wrapped by the periosteum and the endosteum. These connective tissues provide bone with the blood, the nerves, the attachment points for tendons and ligaments and also the bone stem cells. So we're gonna go over these. Now, we're gonna start with the periosteum, the periosteum. Well, peri means around and ostium means bone. So literally, that means the connective tissue that is around the bone. And so we're gonna say this covers the out side of the bone and it's a covering on the bone that's really on their type. But it is something that you can see in bones. If you cut up a chicken bone, for example, it's easier to see on a raw chicken bone. You can get a sharp knife and you can get in there and start to peel that periosteum away and you can see a very thin layer of connective tissue around it. Now that periosteum, we can break it down further into two smaller layers. Though those two smaller layers you can't really see without a microscope. The first layer, the fibrous layer that's gonna be the superficial layer of the layer on the outside. And that's gonna be dense, irregular connective tissue, remember, dense irregular connective tissue is mostly collagen just running in all sorts of different directions. So this fibrous layer is the part that's gonna be vascular. It has blood vessels and it's also gonna be innervated. It has nerves. So that means that if you break the periosteum, it bleeds and it hurts. No, this is also gonna serve a bit as an attachment point for tendons and ligaments. Remember, tendons are the connections between muscles and bones and ligaments are the connections between bones and bones and those connections are mostly collagen. So we're gonna say here that the collagen from tendons and ligaments actually comes down and it weaves into the periosteum. So a lot of times you might think of the connection with a tendon on a bone sort of like it's super glued on the bone. But that's not the way it works that collagen actually weaves well, it weaves into the bone itself, but it also weaves into the periosteum. So when a muscle pulls on the bone, it doesn't just pull on the bone, it pulls on the connective tissue that's surrounding the bone as well. Now, keeping this connective tissue on really really tightly are these things called perforating fibers, perforating fibers are collagen fibers from this fibrous layer that actually weave down through and enter the bone matrix. So, remember collagen is a really, really strong rope like protein. So it's woven into the bone. So it's not just that this is wrapped on, it's woven into the bone, it's on there really tightly. So if you look over here on our image, we can see a cross section of a long bone and we have a section of the shaft of the bone, the compact bone on the outside taken out. And we can see up here it's zoomed in and we can see this tissue being pulled off the outside, that tissue because it's being pulled off the outside of the bone would be the perry ostium. And you can see here that you have some of that collagen there. That's that white. Those are those perforating fibers. The other thing that you see here that you wouldn't see that well in an actual tissue. But you can see these cells, those cells are part of the osteogenic layer. The osteogenic layer is a layer of osteo progenitor cells. These are the bone stem cells and they are gonna be closer to the bone. And it's gonna be a real thin layer, these wine the bone surface and they're gonna go on to become the different types of bone cells. And we'll learn about that more in detail in a future video. OK. Our second type of tissue though is going to be the endosteum, endosteum. Well, endo means within and again, ostium means bone. So this literally means the connective tissue that's within the bone. All the inside surfaces are gonna be lined with endosteum. So we're gonna say here it lines the inner surfaces of bones. Now, that's gonna be especially true. For example, in the spongy bone where you have all that space and all the tubi, all those different struts, all of that is going to be wrapped by this endosteum. But it's also going to be in the shaft of a long bone in that medullary cavity. In that hollow part of the long bone, there will be a endosteum lining that as well. This is gonna really just be the same composition as that osteogenic layer. So it's not gonna have all the collagen and that toughness that the periosteum has. It's just a real thin really membrane of these osteopro git or bone stem cells. And if we look over here in our image again, we see the cross section of the bone. Now we're taking a little zoom in on the inside of that bone. And since it's the inside, we can see a layer that's the end ostium. And you can see just the little cells that are lining that bone, those are the gonna be those bone stem cells. So periosteum really tough, lots of collagen on the outside endosteum, just those bone stem cells on the inside of bone with that example and practice questions to follow. I'll see you there
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example
Gross Anatomy of Bone: Periosteum and Endosteum Example 1
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2m
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This example tells us that it's important that muscles and bone maintain extremely strong connections. And I agree with that statement. It's gonna ask us though, what material is most responsible for the strength of this connection? All right. So remember, a tendon connects a muscle to a bone and a tendon is largely comprised of collagen fibers. And collagen is a protein and a fiber that we've been talking about. And we're gonna talk about a lot in this chapter. Collagen is strong like a rope, it's really flexible. But if you pull it, it has really high tensile strength, it's very difficult to break. So now it's gonna ask us what structural features aid in it performing this function. And here I want to focus on the structural features of bone because that's the chapter we're in. And to help us out here though, we have this little cutaway of bone, this picture over here. And the main thing that you see here is this bit of tissue that's coming off the bone, this covering on the bone that's being peeled away. And you can see these collagen fibers on the inside there. So the first thing that I just wanna note in the structural features are the collagen fibers themselves. As we said, the collagen fibers are extremely strong, you can pull on them and they, it's just really hard to break them even though they're very flexible. Now where the, where the tendon attaches the bone, there's usually sort of a rough spot there to give lots of surface area because those collagen fibers come in and it's not just like they're glued on, they actually get woven into everything around them. One of the things that they get woven into that we've been talking about here is gonna be that periosteum. And that's the thing that we can see sort of pulled away from the bone right there that periosteum is also largely collagen fibers and it is wrapped around the bone really tightly. So as those collagen fibers from the tight from the tendon are woven into the periosteum. When the tendon pulls, it's not just pulling on the bone, it's pulling on the periosteum that surrounds the bone. Another structural feature here that we can sort of see in these collagen fibers here is going to be the perforating fibers. Remember the perforating fibers, those are the collagen fibers of the periosteum that are actually woven down into the bone itself. Now, that's also gonna be true of the collagen fibers. At least some of the collagen fibers in the tendon, they get woven into the bone too. So it's kind of wrong to think about a tendon sort of just being super glued onto a bone. A tendon is collagen and that collagen gets woven into the bone itself. It gets woven into the periosteum. The collagen, the periosteum is woven into the bone. There's no real place where you can say the collagen of one ends and the collagen of the next one begins. That means when you pull on a tendon, it's attached really strongly to the bone. In fact, if you're likely to damage something by pulling too hard, you're more likely to damage the muscle than you are the tendon. So with that collagen is gonna be really important feature and bone going forward and I'll see you there.
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Problem
Problem
True or False; if false, select the answer that best corrects the statement.
Endosteum is most similar to the fibrous layer of the periosteum.
A
True, endosteum and fibrous layer have the same composition.
B
False, the endosteum is most similar to the osteogenic layer of the periosteum.
C
False, the endosteum contains thicker and more numerous collagen fibers than the fibrous layer.
D
False, the endosteum is connective tissue while the periosteum is cartilage.
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Problem
Problem
True or False; if false, select the answer that best corrects the statement.
A function of the fibrous layer of the periosteum is to house osteogenic cells.
A
True, the osteogenic cells reside in the fibrous layer of the periosteum.
B
False, a function of the fibrous layer is to provide attachment sites for ligaments.
C
False, a function of the fibrous layer is to provide a site for hematopoiesis.
D
False, a function of the fibrous layer is to house osteocytes.
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