 Here, everybody, Dr. O here. In this video, we're going to talk about the basic structure of bone and some of the terminology we're going to use. Let's go ahead and take a look at this picture here first. On the two ends, you see the proximal and distal epiphysis. So proximal means closer to the origin of the body, distal further away, but the epiphyses are going to be the ends of your long bones. These are primarily going to be spongy or cancerless bone, and they're still going to have red marrow even into adulthood. So the ends of your bones are called the epiphyses. We'll cover them more in our next unit, because that's where our joints or articulations are going to be. Then the shaft of a long bone is going to be called the diaphysis. So the diaphysis is primarily going to be compact bone, very strong and dense. Inside the diaphysis, you're going to see the medullary, or what I like to call the marrow cavity, which is going to be full of marrow. When you're young, this would be red marrow. As you get older, more and more transitions into yellow marrow. So the two ends of your bones are called the epiphyses, and the shaft itself is called the diaphysis. Where the shaft and the two ends come together is called the metaphysis. So when you're young, this is going to be where the epiphyseal plate or your growth plate is, and then as you get older and bone lengthening has ceased, then you'll now see what's called the epiphyseal line. It actually becomes a bony fusion or a synostosis. So that's going to be the shaft of the bone, the two ends, and then the place where they come together. So the metaphysis is very important when you're young, though, because of that growth plate. So most bones are going to be a combination of the compact bone we talked about and spongy bone. So a bone needs to be strong and dense. It's going to have more compact bone if it needs to transfer weight and maybe be lighter and withstand some of the compressive forces. You're going to see compact bone for that, but if it needs to transfer weight, if it needs to be a little bit flexible and light, then it's going to have more spongy bone. Here you see what a typical flat bone would look like. This is the parietal bone of the skull. So you have two layers of compact bone, sandwiched between them. You have what's called a dip blow of spongy bone between the two. So we don't talk about them very much. When we're talking about a typical bone, let's think of a typical long bone. I like this because it shows that when we think of bones, we generally do think of the minerals, especially think of calcium. And we think about our bones being strong and dense, and that's great. But our bones have to be dense, but they also have to be flexible. So that's why about 2 thirds of your bone is going to be mineral. And that's what your bones are calcified, ossified. And that's what makes them really strong and dense. That's great. But if a bone is too dense and not flexible, it'll shatter. It'll actually be quite weak. So the other third of your bone is going to be protein, primarily collagen. And collagen is going to allow the bone to have some, to tolerate compression and tension. I always think of a bone lab experiment that I have students do where if you put a bone in vinegar, it will remove some of the minerals and it'll make it really flexible. So you see the minerals are there to make your bones dense and rigid and hard. But if you take that same bone, or one that you haven't put in vinegar, and you put it in the oven and you cook the collagen, if you denature the protein in that bone, it'll be brittle and fall into pieces. So bones have to be the perfect combination of strength yet flexibility. I always like to say that bones that don't bend will break. So here we see just how the collagen, how the spongy bone is actually arranged, collagen is the protein, and then how the spongy bone is arranged is to allow one side of a bone to tolerate compression because this is the head of your femur. It has to withstand your body weight. Imagine you running and jumping. It has to take that compression. The other side has to be able to handle the tensile forces as well, though. And the other cool thing about the bones, especially having the spongy bone at the ends, is it allows us to transfer weight. This is how the weight would be transferred from your pelvis down to your legs, down to the ground. So all right, so that's the basics of bone shape. Primarily know the terminology though, diaphysis, epiphysis, those are very important. And then know the difference between compact bone and spongy bone. I hope this helps. Have a wonderful day. Be blessed.