Hello everyone! Welcome to the first content video of week number six. In this video we're going to be talking about the very basic introduction to the skeletal system.
Now hopefully before you access this video you went through and did the smart book assignment so you basically know what tissues make up the skeletal system, it's not just bone, and the basic functions of the skeletal system as well. So from that, you should have gleaned that it's not all we always thought the skeletal system was supposed to be about. It's not just about protection, although that's a big part of it.
It's not just about support, although that's also a big part of it. It's not just about movement, although that's a pretty big part of it. It also makes our blood. It helps to keep our blood calcium at a level that it should be.
It also helps us regulate our triglycerides in our body. All of those things are so important to our overall health and well-being. And by extension, it's super important for the maintenance of our whole body homeostasis.
But we'll get into all of that in a later video. This video is just the surface. So let's start by talking about how we as anatomists will classify bones.
And we're not even talking about like compact versus spongy. We'll get into that later. No, this is literally just what does it look like. The first kind of bone and the bone that we're going to be spending the most time in this video talking about is the long bone.
A long bone is exactly what it sounds like. It is a bone that is long. Our example of a long bone is actually the longest and strongest bone of the body and that's over here and that's the femur. The femur is what you would consider your thigh bone.
Now if we have long bones, we're bound to have some short bones too. That's going to be our next category. Short bones are going to be bones that are nearly the same length and width. So they're going to look roughly square or maybe a slightly elongated rectangle, maybe a circle.
That's generally what short bones are going to look like. Our example bone for short bones are the carpals and tarsals. The carpal bones are our wrist bones.
And so those are going to be contained within our wrist or the butt of the hand. As far as the tarsal bones, those are going to be the bones that make up the heel or the ankle part of your foot. Our next category are flat bones.
There are a couple of different kinds of flat bones that we'll talk about, but a really good couple of examples of a flat bone would be the flattened part of the scapula as well as the bones of the skull. You can see. it's quite thin. So that is going to be the example of a flat bone, or the bones of the skull and the scapula. This leads in nicely to the next category of bones, and that is the irregular bones.
Irregular bones are going to be irregularly shaped. Once again, anatomists are not that clever when we're naming stuff. Our example of an irregular bone can be the parts of the scapula that are not flat, or a more common example would be the vertebra.
The vertebra are the bits and pieces that make up our spinal column. The last shape of bone that we're going to talk about is the sesamoid bone. A sesamoid bone is kind of interesting because it is a bone that's not really attached to any other bone. It's kind of floating between two bones. The most notable example of a sesamoid bone would be the patella, which is our kneecap.
And what you're going to see when we look at the dissection of the knee, which is later on, I think next week in our APR lab, you're going to see that the kneecap is actually going to be embedded within the patellar tendon, which is a tendon that's going to extend from the femur, the thigh bone, all the way onto the tibia or the shin bone. Okay, so the next part of this lecture, we're going to be talking about the regional anatomy of a long bone. The reason why we're doing this is so that when we do start to get into calcium homeostasis and bone marrow and that kind of thing, it's not going to be that big of a challenge for you to envision it because we're going over it now. If you've ever seen a cartoon of a bone, you'll remember that on one side of the bone is kind of those two knobby bits and then you have the long shaft in the middle and then another two knobby bits.
And that's not too far off. from the general anatomy and vocabulary that we're going to be using. So in the diagram below I have the femur.
It has been sectioned coronally, so what we're seeing is the entirety of the interior part of the long bone. That's going to be important because we're going to be able to see a very important feature. of the long bone, which is here.
This is called the medullary cavity. The medullary cavity is one of the reasons why our bones are not heavy. They're not, I mean, they are heavy because they're filled with stuff, but the reason why they can be filled with stuff is because of the medullary cavity.
It's going to be filled with bone marrow and some fat, but we're going to talk about that in a second. That medullary cavity is going to be sitting in an area of the bone that is called the diaphysis. The diaphysis is what we would consider to be the shaft. There is only one diaphysis in a long bone, it's just one shaft, but on either side of the shaft we have the epiphyses.
The epiphysis, epi remember means on the surrounding or on top or something like that, and that should give you an idea that it's on either side of the diaphysis. The epiphyses are going to be the places of joint articulation. So that's going to be where, for example, the ball of the ball and socket joint that is the femur is going to attach to the hip. The distal epiphysis, which you're going to see down here, that is going to be where our tibia and fibula articulate at the knee.
Okay, so we've got the ends of the bones and we have the middle of the bone, but there is a very... critical area on this image that I want to draw your attention to because when we start talking about interstitial lengthening and elongation and growth, it's going to be a very important vocabulary term for you to understand. This particular structure is called the metaphysis or the metaphyses in plural.
You can actually see where the diaphysis and epiphyses are going to meet the metathesis because you can see a line that is literally where those two things have met. So this line that I'm outlining here is the metathesis. You can remember this term as metaph or middle, meta, middle.
I mean, I would just say that any M would stand for middle. So if we scroll down we're gonna be able to see a zoomed in version of live bone. the one that hasn't been stripped of all of the living tissue.
In this particular diagram, I'm going to talk to you about the surface tissues that make up the long bone. But first, I want to remind you of a couple of different prefixes that we may have kind of talked about in previous lectures, but I want to make sure that we address it again. The first is endo, and remember endo means inside, and then peri going to mean outside.
So if we put this together with the word ostium which refers to bone then we're going to have endosteum and periosteum. So the first thing that I want you to see is the endosteum which is going to be the inner part of the bone and it's going to be the inner surface where the medullary cavity is. It's not going to encompass the medullary cavity.
It's kind of that hollowed out bit of the bone that is in contact with the medullary cavity. The periosteum is going to have perforating fibers called Sharpe fibers. Again, there's a whole thing with eponyms that we're not going to get into, but these perforating fibers of bone tissue are going to be penetrating into the bone matrix itself. In the next lecture, we are going to talk about what bone matrix is and what we mean by that.
Just understand that the periosteum is going to be that outer layer that is perforating into that bone matrix. And so it is impossible to separate periosteum. It's realistically impossible to separate out periosteum from the bone matrix itself because of those penetrating fibers.
There's one other thing that I have labeled on here and one other thing that I'm going to label on here. The thing that's labeled already is articular cartilage and that's going to be down here. I'm going to outline that in blue. The articular cartilage is going to be very important. It's made out of hyaline cartilage.
Remember that from back in unit two. Articular cartilage made out of hyaline cartilage. It's going to be very important for shock absorption.
And this particular surface, which is the distal epiphysis of the femur, which is the place of articulation at the knee joint, is going to be the part of the body that needs the most articular cartilage at this particular surface because it's going to bear all of our weight at one point or another. When we're walking, we're walking on one foot at a time. You're going to bear all of your weight on a single knee on any given step.
One thing that I want to talk about is how both the endosteum and the periosteum have within them bone building and remodeling cells. We're going to talk about what those are in the next video, but I want you to understand that both endosteum and periosteum while they have very different functions, have the same group of cells within them. I mentioned one thing that I was going to label that's not already labeled on here and it's this little blood vessel that's coming in. I don't really want to label the blood vessel itself, I want to label the hole into which it is perforating.
This hole is called the nutrient foramen and every long bone is going to have one because without one it literally cannot survive. And there is real living tissue in bone. Your bone can die.
It may just seem like ceramic, but it's not. It is a real living, breathing organ. The last thing we're going to talk about is the idea of bone marrow. Bone marrow in and of itself is just a really generic term.
It refers to any kind of soft tissue that's going to occupy that medullary cavity. Bone marrow can occupy the medullary cavity of a long bone but can also occupy the spaces between trabeculae which are kind of cross beams in spongy bone. We'll talk about that in a future video. But that bone marrow can occupy all of those different spaces and bone marrow can be separated into two different kinds of marrow. The first kind of marrow is called red marrow and red bone marrow is derived from myeloid tissue.
Red marrow is going to occur in pretty much every single bone in a child. Red marrow is composed entirely of hematopoietic tissue and what hematopoietic tissue means is that it's going to be the source of pretty much every kind of blood cell that we have. In and of itself bone marrow could be considered its own organ. And that's because it is composed of several different kinds of tissue arranged very delicately and intentionally.
And its real job is to create and build and sustain red and white blood cells. In adults, it's only found in a limited number of places. It's found in the skull, vertebrae, the ribs, the sternum, part of the pelvic girdle, which is going to be the hips and the head of the femur. But the proximal heads of both the humerus, which is going to be our arm bone, and then the femur, which is our thigh bone, only the proximal head, so the big parts, are going to have red marrow. So the reason why adults don't have as much is because as we age, red marrow turns into yellow marrow.
So that's what we're going to talk about next. Yellow marrow is almost exclusively found in adults. Most of our red marrow is going to turn into this fatty yellow marrow substance. It no longer produces blood, instead it produces triglycerides.
So that's one of the main reasons why kids don't have issues with triglycerides, but adults do. The other crappy thing about this is that yellow marrow doesn't really produce blood anymore. It's because we're not growing, or at least not vertically we're not growing. With kids, they need all of that extra blood.
They need their blood production to be in hyperdrive because they are growing all the time. For those of us who haven't grown in 15 years, we do not have a whole lot of red marrow. Instead, we have almost exclusively yellow marrow.
So I think that is enough to be getting on with for our introductory video for this particular unit. In the next video we're going to be talking about the cells and tissues that make up our bones and We're going to start off by talking about the matrix associated with the bones So if you haven't go ahead and review the concept of ground substance and matrix And that way we can hit the ground running in our next video. I'll see you then