Microscopic Anatomy of Bones - Bone Cells - Video Tutorials & Practice Problems
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1
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Introduction to Bone Cells
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Microscopic Anatomy of Bones - Bone Cells Example 1
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This example tells me that calcium homeostasis is important for muscle contraction and nerve functioning. Bone cells help maintain blood calcium levels between 8.6 and 10.3 mg per deciliter. If the blood calcium level drops to 8 mg per deciliter, which type of bone cell would become more active and which type of bone cell would become less active? All right, then it shows me a picture of four different bone cells. So I just wanna identify these real quickly. First up, we have this sort of flattened bone cell. Those flattened bone bone cells are the bone stem cells. We call those osteo progenitor cells. Next, we have this sort of cube shaped one here, an osteopor cell that bone stem cell may go on to become an osteoblast. And remember that BB stands for build osteoblasts, build new bone, some osteoblasts once they've built, built new bone will go on to become this sort of spidey shaped bone cell here. This is a mature bone cell. The mature bone cells are osteocytes. And then finally, we have this giant bone cell down here. In reality, it'd be much bigger than these other ones that has this real ruffled border and multiple nuclei. This is going to be the osteoclast. And remember clast C is for cut osteoclasts, cut into the bone and they remove bone when that's necessary. So, in this case, our blood calcium levels have dropped and we need to raise blood calcium levels to do that. We need to remove some bone to remove bone. What type of bone cell do you wanna use? An osteoclast? Osteoclasts? That ruffle border are gonna uh let out uh acids and enzymes that are gonna break down the bone. They're gonna take that calcium. It's gonna go into the blood and raise that blood calcium level. So what's gonna become more active? The osteoclast? Now, what's gonna become less active? Well, if you're trying to take calcium out of the bone, you don't wanna be building new bone blast B stands for build osteoblasts will become less active. All right, with that. Remember that bone is not just there for structure also for calcium homeostasis. And I'll see you in the next video.
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concept
Osteoblasts
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4
concept
Osteocytes
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Now it's time to talk about the osteocytes. I remember these by saying the osteocytes, the sites are the mature bone cells. So these are the mature bone cells that maintain the matrix. Remember, osteocytes come from osteoblasts. Osteoblasts build new bone, sometimes they build themselves into the matrix and then they become the osteocytes. So I think of it as a trapped osteoblast that becomes an osteocyte. But they're not just like in the matrix, they built themselves a little room or a little chamber in which to live in. And that little rooms called a lacuna or the plural is the lacuna. These lacuna are the rooms that osteocytes are housed within. Now, they're there for a reason though they are there to monitor bone stress and also to contribute some to calcium homeostasis. But let's talk about the stress. First, your bone is always being replaced, you're always removing some bone and building it new. Again, one of the ways your body knows where to do that is from the osteocytes. They're monitoring the bone around them. And if it's showing signs of stress, they'll send out a little message and it will say, hey, replace this bone, the osteoclasts will come in. Remove this, the bone osteoblasts will come in and build new bone and some of those osteoblasts will get stuck in the matrix and become the new osteocytes. Now, for calcium homeostasis, you have a ton of calcium in your bones, but you also need calcium in other parts of your body. So it's really easy for your ca for your blood to stash a little calcium in your bones or just to take a little bit out. Most of that job is done by the osteoclasts and the osteoblast, but the osteocytes contribute to it as well. All right. Finally, I want you to think if you're living in bone, if you're living in this chamber inside bone, well, you still need to get the nutrients, you still need to get rid of waste, you need to communicate. So these cells can't be completely trapped in the bone. They're not, they have small projections that reach out and allow them to communicate and diff and diffusion with other cells by gap junctions. So these cells have these projections that reach out to the smallest cracks in the bones called canoli, which we'll talk about in a later video and they sort of hold hands with the cells around them. And these gap junctions remember gap junctions are ways that diffusion can happen between cells really easily. So that's the way that they can get the nutrients they need, they can get rid of waste and they can communicate as long as some of those cells are in contact with the, with the capillaries and where the blood is gonna be. So to illustrate all this, we have this uh illustration of a brick structure down here and we have six osteocytes living in their Lani. But uh what I want you to see here is these projections that are reaching out and connecting with all the cells around them, almost like these sort of spider webby, almost octopus, like arms reaching out and touching the cells around them. So they can exchange materials and also communicate. So they're not completely stuck in that bone matrix. All right. Finally, I just want to remind you osteocytes start out as osteopor cells, they become osteoblasts. Some of those then become osteocytes. That's the end of that cell line. So when these sites are done well, they're just gonna die, but they can live a long time. Some of them live for decades until that bone is replaced. All right, with that, our final bone cell type is gonna be the osteoclasts. We'll do that next.
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concept
Osteoclasts
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example
Microscopic Anatomy of Bones - Bone Cells Example 2
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This question tells me that osteoporosis is a common condition in older adults, especially women, bones become weak due to an imbalance between osteoblast and osteoclast activity. Then it wants to know which type of cell would be more active and which type of cell would be less active in an individual with osteoporosis and explain your reasoning. It also gives us a little picture here. It's the epiphysis of the femur and on the left, we can see that the spongy bone is, well, it looks normal. There's all these really small holes between the struts of the spongy bone. And on the right, this is an image of what it might look like for someone with osteoporosis. That spongy bone seems to be hollowed out as there's fewer struts connecting the spongy bone. So what would be more active to produce something like this? So remember, osteoblasts blasts build, they lay down new bone matrix. Well, osteoclasts clasts cut, they remove the bone matrix. So if the bones getting hollowed out like this, it sounds to me that the osteoclast is gonna be relatively more active. And my reasoning, osteoclasts remove bone matrix. Well, in contrast, what's gonna be less active. Well, if it's building less bones blast build, so osteoblasts will be less active. The reason lasts, produce B matrix and you don't need a big imbalance for this to add up over time. Right? Osteoporosis isn't something that just happens overnight. It's years of a slight imbalance and over those years, this bone just becomes more and more hollowed out. The spongy bone gets fewer struts connecting it and because there's less matrix, the bone becomes more fragile. All right, with that, more questions to follow and I'll see you there.
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Problem
Problem
How does the structure of an osteocyte allow communication with adjacent cells?
A
Osteocytes have cellular projections that meet and form gap junctions with adjacent osteocytes.
B
Osteocytes have ruffled borders to release signaling molecules that communicate with adjacent osteocytes.
C
Osteocytes have significant surface area to allow for rapid diffusion across the cell membrane.
D
Osteocytes are multinucleated allowing them to make more protein rapidly and pass information quickly.
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Problem
Problem
A central theme in anatomy is the relationship between structure and function. What structural feature of osteoclasts aids in their function of osteolysis?
A
Their multiple nuclei allow for more rapid production and deposition of collagen.
B
Their cellular projections allow cell to cell communication.
C
Their flattened shape allows them to move through the bone more easily.
D
Their ruffles border increases surface area between the osteoclasts and the matrix.
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Problem
Problem
Which pathway correctly identifies the relationship between bone cells?
A
Osteoprogenitor → osteoblast → osteoclast
B
Osteoprogenitor → osteoblast → osteocyte
C
Osteoclast → osteocyte → osteoblast
D
Osteoclast → osteoprogenitor → osteoblast
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Problem
Problem
What is the major function of bone cells found in lacunae?
A
Bone reabsorption.
B
Bone deposition.
C
Monitoring bone stress.
D
Laying down new organic matrix.
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