Bone Tissue Structure PDF

So, I will be describing the structure of, we have two main types of bone tissue, bone tissue. There are two main types, we have compact bone and we also have spongy bone. Alright, so for what the compact bone might look like when you look at it under the microscope, So what you will see is you will...

So, I will be describing the structure of, we have two main types of bone tissue, bone tissue. There are two main types, we have compact bone and we also have spongy bone. Alright, so for what the compact bone might look like when you look at it under the microscope, So what you will see is you will see, like, let's say this is the medullary cavity, which is the space inside of a long bone, right? The medullary cavity. But the whole, the rest of the bone, outside of it, we call it compact bone. So let's say this is the edge of the compact bone. And if you look to see, I'm just going to do this. I'll talk about this in a little bit. in a little bit. Okay, but if you look to see what most of that thick collar of compact bone looks like, you're going to see all these concentric circles, right? These are the concentric circles that you find inside, so again just want to make sure that you know that this is the medullary cavity, right? make sure that you know that this is the medullary cavity, right? I'm in the I'm in the diaphysis part of a lung bone and so I'm going to just take one of these circles that you're looking at right here and I'm just going to make it a little bit bigger because I want to show some some structure in it right so so that right there what I drew I pulled one of them out and this whole thing right here is called an osteon or same thing as saying haversion system okay and the osteon you're going to see that again kind of structure is repeated over at different levels as you're going to see okay now what you see here again is one of these little guys here I've taken one out so this middle circle is nothing don't don't confuse it with this over here this is way bigger this one is a lot smaller but what you have right at the center of that of that haversian system is what you call the central canal or just like an AMP everything has two names central canal it can also be called the Harvorsian Canal. And the Harvorsian Canal is where you're going to have your blood vessels. You're going to have arteries and veins, so I'm just going to put the arteries in here, but just remember that right in the middle of each of these, right in the middle of each of these, you're going to have blood vessels. There's blood vessels inside right in the center of those circles, so I'm just going to put a dot representing the artery that you have inside of each of these circles right so that's your blood supply so your your bones are vascular so if you break them they will ooze out blood it's not a high-pressure blood vessel but it will ooze out blood if you break a bone right and you should also have the artery I mean the vein but I'm not gonna I'm not gonna you know put the veins in all these because they're blue anyway but you have arteries and veins within them and that's the blood supply to your to your bone. So again the central canal, herversion canal is for blood supply. blood supply. Okay now if you look the osteon is made of all these concentric circles and each of these concentric circles is called a lamella, right? circles and each of these concentric circles is called a lamella, right? So these are lamella. Okay and they're actually called concentric lamella because we're going to have different types of lamella concentric lamella and when we talked about tissues if you remember bone is a type of connective tissue and remember that connective tissues are made out of cells and then they have fibers and they have ground substance right so so where are the cells the cells are going to be found between your lamella right so I can have some cells here these represent my cells my specialized cells okay so I'm not going to draw them all the way around but they're found throughout and again the specialized cells that are found in bone so for any connective tissue I will just remind you so that for connective tissue, you have cells, you have fibers, and you have ground substance. and you have ground substance. And for the connective tissue, what are the specialized cells called? specialized cells called? They are called osteocytes, right? And so each of those is an osteocyte. So these are my little osteocytes. And also remember that it is the cells that are secreting the fibers and are secreting the ground substance. So the lamella are making that extracellular matrix, the extracellular matrix that's around the cells. So that would be the lamella. So I'm just going to say this is going to be the lamella. Okay, and so later on we'll see, I'll show you diagrams of what the lamella looks like. The lamella is super organized. You have a lot of collagen fibers, so these fibers are collagen, and you have a lot of those collagen fibers, and they are super organized. So, in an osteon, I could pull out one lamella, so it might look like this when I'm pulling it out. So, here's one lamella, right? And then I can pull it out from the other lamellas, right? So, I can pull one out and pull the other one kind of like one inside the other. And in this lamella, in this first lamella, my collagen fiber is running this direction, but in the other lamella they would be running in this direction and then in this one they're again running in that direction and so on so the collagen fibers are super super organized and they will give your bone some flexibility obviously you're not going to bend it completely but it is able to absorb shock because you have these collagen fibers okay So that's what the lamella are made of, so you have the collagen, and then on top of the collagen you are putting the salts on top, and thus you're making the bone stronger, so it's got some flexibility because of the collagen, but then you're also depositing salts on top of it, yeah. And so, so you have your osteocytes and just to go back and make sure that's the same. Yeah, the osteocytes, remember that these osteocytes secreted all the collagen, secreted the ground substance. And they are completely surrounded by solid material. So again, these osteocytes are going to be enclosed in a tiny little space. So, the space is called the lacuna, right? So, osteocytes are inside a lacuna. And I think the last thing I need to talk about is notice that my blood supply is here, right in the center, right? So, again, the lamella are made of collagen, and then you have put a bunch of salt on top. So, it is super, super dense. And so if you were to try to get diffusion to supply these cells that are on the outside, right, it would never get there because that material is too dense. So what you're going to find in bone tissue is that there's a bunch of little canals and literally the word means little canal. So you're going to see a bunch of little canals that go, yeah, they go through your bone. and basically what they do is these little canals help to connect one osteocyte to another. osteocyte to another. So these are called canaliculi. Canaliculi, that means small canal, and these are what allow nutrients and oxygen to get from my central canal to the outer osteocytes, and it also allows waste from these osteocytes to go back into that vein, right? So, so canoleculi are the little connections, and of course you got, you actually have the space inside the bone, but then you got actually membrane, like extensions of these osteocytes, because these osteocytes are kind of spider-like, and they have their little spider extensions going through those canaliculi and connecting to other cells that are further away and not only do you do osteocytes connect side to side but if you were looking at it from the side of the bone they also connect up and down so these osteocytes are very well connected to each other through these canaliculae that will allow nutrients to go through, right? All right, so the last thing I'll mention about this compact bone is that there are different kinds of lamella. So we talked about the ones that form these circles around each, inside of each of these, right? circles around each, inside of each of these, right? Inside the osteon, they are right here are also lamella but these are called circumferential lamella so maybe I'll do it down here I'll point to this one right here so this one and this one these are called circumferential circumferential lamella and what these lamella do I kind of think of my osteons like pipes right and I don't want my pipes to be rolling out or getting out of order and so I put this circumferential lamella all the way around my my my bone and it's holding all the osteons in place right it adds support to my bone right so that's another type of lamella and then a third type of lamella is notice that I have right they're just kind of filling in the spaces here and so I'm going to put right here so this right here is called interstitial interstitial lamella these are the lamella that are going to be found between osteons so so as you know your bone, when you produce it, is constantly turned over. You have to replace it, the proteins get old. It is said that you replace your bone tissue every seven years. And so you're constantly remodeling different parts of the bone at any particular time. And so these interstitial lamella are kind of remnants of previous osteons that you had inside. So now you just have little parts because you tear part of it down and then start building. So again it's just remnants of what was previously there and it fills in the space between those new osteons that are produced. So that's in general the structure of compact bone. We looked at compact bone here. Now for spongy bone, spongy bone, I'm going to draw a spongy bone over here, and spongy bone looks like this. You have, we call them little bone spicules, right, in every direction, right, but these little bone spicules are called trabeculae. Trabecula for one, if you put an E, it's plural, but These are, I call them little bone spicules, right? And if I were to make a cross-section through one of these trabecula, this is what I would see. Okay, yeah, all right. So, if you look at this, right? If you look at the cross-section of a trabecula, a trabecula looks similar to an ossaloid. But there is a difference. There is a difference between this and the osteon. osteon. And the big difference is that, again, they're small. They're not going to have as many layers as you see here. There are fewer layers. But the other major difference is that there is no central canal, right? Here we have a central canal, but over here there is no central canal. All you have is your cells right you have cells here so in this case where are my osteocytes or how do my osteocytes get what they need in terms of oxygen and nutrients if you do not have blood supply right and so again if you remember where did we see spongy bone, right? Spongy bone is seen in the ends of long bones in the epiphysis if you remember. It's also seen in flat bones in the middle of a flat bone, right? And again remember that anytime you see spongy bone you think red bone marrow, right? So there's bone marrow, red bone marrow filling in all this right here. And what is red bone marrow? red bone marrow basically is what produces your blood cells so basically it is surrounded by blood cells and of course they're going to end up in the bloodstream and so the nutrients are coming in from outside of this trabecula so there's no need for a central canal because these are very small and so instead of the nutrients coming from the inside out here the nutrients are coming from the outside in but in this case of course you still do have your little canaliculi right and again you don't have too many layers of lamella around these and so again the difference between this bone that you see here this is super compact lots of osteons over here you have a lot of space between your trabecula, right? So very open kind of bone tissue, it's more delicate. But again, when you look at it under the microscope, there is a little bit of a difference because of course, the structure of it. So that's the main difference between your compact bone and your spongy bone.