Gross Anatomy of Bone: Periosteum and Endosteum - Video Tutorials & Practice Problems
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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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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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