Now in this particular video we're going to be starting to look at a long bone and specifically the different structures that are inside of it. It's important. It's a good way of looking at different types of bone and exactly what they're made of because long bones kind of have all of it. If you look at this, remember from the previous video that all bones are made of compact bone on the outside and spongy bone on the interior. We showed you a flat bone as an example of this in the last video, but now in this video you can clearly see, and this is a real bone here, it's been sliced.
longitudinally. As you look at this you'll be able to see the compact bone on the outside and the spongy bone in the middle of that. And what we're looking at here also you may want to refer back to this picture when you take a look at this is an actual bone slice but here's a nice little sketch that kind of shows all the different things that we want to see.
When we look at a long bone this is a humerus actually the humerus. The humerus is a good example because you can clearly see the spongy bone in this end piece here. So the first structure we're going to identify in a long bone is called the diaphysis.
The diaphysis is the long shaft of a long bone. Then you have two epiphyses. You can see the spelling here. It's a tricky one. Get to know it well.
So there is a proximal epiphysis, which is closest to the attachment point. And then there's the distal epiphysis, which is further away from the attachment point. So epiphyses are either end of a long bone.
Early in development, you have a structure inside of the epiphysis, or I'm sorry, you have a structure that is basically in between the epiphysis and the diaphysis, which is called an epiphyseal plate. Early in development, the bones are actually entirely made of hyaline cartilage. This is the last part of a long bone to develop. Once it has developed, it is called an epiphyseal line.
So early in development, it's called an epiphyseal plate. And then once growth has ceased. then this is called the epiphyseal line. This is also called a growth plate.
Now, early in development, this is especially a weak spot when it's still an epiphyseal plate, and it does tend to be subject to certain particular types of fracture, which are very, very serious at times for particular reasons, which we will discuss down the line. If you look at the shaft or the diaphysis of a long bone, inside the middle of the diaphysis, you have a hollow space. This is a cavity and it is called the medullary cavity that literally means hollow space in the middle, medullary cavity.
This contains mostly yellow marrow, which is lipid or fat. This is not a site of bone cell formation. Yellow marrow is just fat.
The red marrow is going to be tending to be found in red bone marrow, which is responsible for bone cell formation, is going to be found in your spongy bone. Alright, there are two different membranes that we're going to be covering here, but they're much more than membranes. So I want to take a closer look at the shaft here so that we'll be able to see both of them.
I just want to point both of them out really quick. The first one is called periosteum, here's the word, and it's shown kind of in a light blue here. Peri, you may recall, means outer or next to. And endosteum, the word endo, means inner or inside. So there's a periosteum around the outside of the bone, and then there's an endosteum on the inside of the bone.
And you can, I don't know if you can really see it, but it's basically present in here that lines the medullary cavity. But the endosteum also lines the spongy bone. The endosteum is found lining all those little trabeculae inside of the spongy bone.
Okay. The periosteum is actually quite involved. You can see there's a lot of arrows pointing to it here and there. There's actually not everything is shown here.
The periosteum, the outer part of the periosteum is made of dense, irregular connective tissue. So it's very strong, very resistant to any kind of tearing. Inside of the periosteum, you're going to have cells called osteoblasts and osteoclasts.
There are also many nerves, lymphatic vessels, and blood vessels inside of here. One of the things that is shown in this picture are structures called sharpies fibers, also called perforating fibers. Perforating is a very good word for it because perforating means that it actually punctures into something, and that's exactly what these guys do.
These are like fibers of collagen that hold the periosteum to the bone and actually dive into or perforate the bone and really cling to it. So the periosteum cannot be peeled off easily. it's actually very, very strongly attached to the outside of the bone.
There's a very interesting case study that we're going to do about the sharpies fibers. Okay, the same thing with the endosteum. The endosteum also has the same general purpose as periosteum. It contains osteoblasts and osteoclasts, and it covers the inner part of bone, as I suggested earlier.