Gross Anatomy of Bones - Structure of a Long Bone - Video Tutorials & Practice Problems

Overview of Long Bones

When talking about the gross anatomy of bone, we said that long bones are unique and they're unique because they consist of two ends and a shaft that shaft connecting the two ends. We're gonna talk about the details of those structures. Now, so we'll start with what we call the epiphysis. The epiphysis is the wider end of a long bone. So there's a wider end on each end of the bone. So there's that epiphysis at each end together, a long bone has two epiphysis. And if we look at our diagram over here, we have an image of a femur, that's the longest long bone in the body, a frontal view of the femur and a lot of it's in cross section. So you can see the inside of the bone and you'll just notice that each end of the bone gets wider. And so each end is an epiphysis. And down here at the bottom, we have it labeled. So I'm just gonna fill this in the epiphysis. Now, the structure of the epiphysis is pretty much like all other bone. We've talked about spongy bone on the inside with a layer of compact bone on the outside where the epiphysis enters a joint, it's going to be covered with articular cartilage. So we're gonna say that articular cartilage covers the epiphysis at the joint. And that's just because uh cartilage is gonna be smoother and softer than bone. And if you talk to any old basketball player who says they have no more cartilage in their knees, they'll tell you it's really painful if you have just bone on bone, rubbing up against each other. That hyaline cartilage nice, soft and smooth, it makes it so your bones glide over each other nice and easily in joints. Now, that brings us to the shaft of the long bone, the shaft of the long bone, we're gonna call the diaphysis. So we're just gonna say here that's the tubular shaft. And importantly, that's gonna be made entirely of compact bone that's gonna be different than all the other bone. We've talked about all the other bone we've talked about. Remember has spongy bone on the inside the shaft or diaphysis of a long bone is gonna be a solid layer of compact bone. It's gonna be much thicker than the compact bone on the ends or on the epiphysis of the bone. And so if we look at this, we can see this uh in our diagram here, this is the shaft. You can see there's no spongy bone in that shaft and we are gonna label this the diaphysis. Now, before we go on, I just wanna know diaphysis epiphysis. It can be really easy to get those confused and flip in your, in your head. So let's just talk about how we keep them straight. Well, by this point, you should really just know what epi means that prefix epi, epi means on top of or at the end of something on the surface of something. So epi epiphysis, it's at the end of the long bone. The way I actually think of it is that I remember really well, that my epidermis is my outer layer of skin. And that always reminds me what that pi prefix means. Now, in contrast, the diaphysis, the way I remember that dia I think of the diameter of a circle and the diameter of a circle is the line through the middle of a circle. The diaphysis is the line or the shaft to the middle of a long bone, right? We said that that is compact bone, but it's not solid compact bone. It's gonna have this space in the middle, that space we're gonna call the medullary cabinet. That's just gonna be the space inside the diaphysis. But of course, it's not completely empty, it's gonna be filled with something, it's filled with marrow and specifically yellow marrow in adults. In our diagram, you can see this, we have medullary cavity labeled here and it's just showing the empty section of the middle of that bone just because the, the um the marrow is not drawn in. No. Why is it built this way? Well, any engineer will tell you that if you're making a rod like structure and you want the best strength to weight ratio, you're gonna build something like this, something like a pipe that has a nice thick solid outer structure in a ring with a hollow inside. So engineers have figured out that well, I I don't know when, but relatively recently in human history evolution figured out that hundreds of millions of years ago, that hollow structure with nice thick compact bone making this pipeline like structure is gonna give your long bones a lot of strength while making sure that they're not too, too heavy. Ok. So the one part that we have not talked about yet, we're gonna call the metaphysis. The metaphysis is the part where the epiphysis and the diaphysis, I'm just gonna say meat or join. And so you can just see it's this region right here where the spongy bone starts, where the bone is getting wider, where the medullary cavity ends. And we wanna call this out because there's a really important thing that goes on in there in the metaphysis is going to be the epiphyseal plate and you've probably heard of this, you may have heard it called the growth plate. The growth plate is gonna be a line of hyaline cartilage that allows for bone growth. So long bones are gonna grow differently than other bones. They're gonna have this line of hyaline cartilage and they are gonna grow in length from that cartilage. They're gonna grow wider in a different way, more similar to other bones. And that's something that uh you'll learn later on. But for now, you really want to know the structure is there that, that epiphyseal plate is gonna be this line of heart uh hyaline cartilage. And we're just gonna say that it's the site of bone growth until you finish puberty. Now, once you stop growing, uh that epiphyseal plate is going to transition into what we're gonna call the epiphyseal line. This plate will convert to compact bone and we can see both these structures over here. We are zoomed in on this metaphysis and epiphysis. And we have two images of it. This lower image here is showing a juvenile or an adolescent bone. And you can see that in the spongy bone, you have this little blue line here and this blue line here of cartilage. And that's gonna be those epiphyseal plates or the growth plates that end of the femur actually has two growth plates. You'll see. Uh Here is somebody who has finished puberty who has stopped growing that cartilage isn't there anymore. Now, you just see this thin line of compact bone with spongy bone on either side of it. OK. Again, you're gonna uh learn the, the details about bone growth later on right. Now, you just need to be able to identify those things in the structure of the bone. We're gonna go into a little bit more detail in the structure of a long bone coming up. And after that, we're gonna get into the microscopic anatomy of bones. I'm excited to do it with you.

Gross Anatomy of Bones - Structure of a Long Bone Example 1

This example tells me that forensic analysis can use bones to establish the rough age of a skeleton. And then it asks what specific structure in the metaphysis might a forensic scientist look at to determine age? All right, remember the metaphysis is the part where the diaphysis, the shaft of the long bone meets the epiphysis that widened end of a long bone. So it's the part of the bone where it's getting wider. And in the metaphysis, we said is the epiphyseal plate or epiphyseal line. The epiphyseal plate is where growth happens in a long bone where long bones grow longer. And we said that in Children through adolescence that's comprised of cartilage and that's where growth happens. But as growth ends that cartilage becomes compact bone. So what can you look at? You can look at the ep physio plate and I'm gonna say slash line. And then it asks, what would you expect this structure to be comprised of at the following ages and asks about a child, an adolescent and adult. But it also gives me this image for reference and we see an X ray of three different hands. And I can tell that. It's a child's hand on the left and adolescents hand in the middle and adult hand on the right. We'll see why I can say that in a second. Uh, but we can see the ends of the long bones of the arm here. We can see the wrist bones, we can see the hand bones and we can see the finger bones there. All right. In a child. What would you expect to see? Well, the ep physio plate in a child, the child is growing a lot. So you would expect to see a lot of cartilage. And we can see that in the picture if we look at the end of it, what is the ulna right here? Right. You can see the bone ends, there's a space and then there's another piece of bone. That's all the ulna, this little end piece of bone here. That's the epiphysis of the ulna. And that space is the epiphyseal plate. We can also see it very clearly on the metacarpals bones. And, and then there's another little piece of bone. The epiphysis, that little space is the epiphyseal plate where growth is happening next up. We have an adolescent and an adolescent. Well, you're going adolescence, you know, early teenage years, you're going through a lot of growth. But as you go through puberty growth slows and as you become an adult, you're gonna stop growing. So, from adolescence, it's definitely gonna start as cartilage. But I'm just gonna say that it's gonna be um thinning because over time, as an adolescent, you slow your growth and growth eventually stops. And again, we can see that on this image here in the middle, we have a hand of an adolescence and we can see that, you know, on the ulna, this epiphysis is definitely larger. You can still clearly see the growth plate there, the ep physio plate, but it's thinner than it is in the child. The same thing with these meta uh metacarpals here, you can see the epiphysis, but the ep physio plate that space looks a little bit thinner. So finally, we have an adult, an adult, we said that is gonna be converted to compact bone and growth of a long bone is no longer possible. And we can see that again. In this X ray, we look at the end of the ulna. Well, there's no space there anymore. If we look at the end of the metacarpals here, we can still see the epiphysis there clearly, but there's no space because the X ray just sees bone, there's no more cartilage. All right, with that practice problems to follow. And I'll see you there.

During a skiing accident, Jean-Luc breaks the shaft of his humerus. What is the anatomically correct term for the portion of the bone that he broke?

• A. Metaphysis
• B. Epiphysis
• C. Diaphysis
• D. Articular Cartilage

Osgood-Schlatter disease is a painful condition that affects the proximal end of the tibia (a long bone) just distal to the knee. It primarily affects athletically active children between the ages of 10 and 14. The condition develops when the patellar tendon places strain on this area of the tibia as the area is not as stable as other regions of the bone in children this age. Why would this region not be as stable as other regions of the tibia?

• A. The medullary cavity does not fully develop until adulthood, meaning the yellow marrow would not provide shock absorption.
• B. The spongy bone of the epiphysis would not have fully calcified so the bone in that area would not be as hard.
• C. Articular cartilage is not fully formed until adulthood meaning there would be more stress in the joint.
• D. Children in this age are going through a growth spurt meaning there is a significant amount of cartilage in the epiphyseal plate.

Nerves and Blood Supply

To wrap up the gross anatomy of bone and specifically the structure of a long bone, we're now gonna talk about nerves and blood supply. So remember, bone is living dynamic tissue and as such, it contains blood vessels and nerves. But the outside of bone is also all compact bone and compact. The bone is well, it's pretty solid stuff. It's pretty Impenetrable. So for blood vessels and nerves to get into the bone, well, it needs a way in the way in is through the nutrient foramen. The nutrient foramen is just a small hole and it's gonna be located in the diaphysis of bones and it's for blood vessels to nourish to go through. Now, for the most part, a diaphysis has a single nutrient foramen. Sometimes there's more than one but usually just one. And I say it's a small hole, but it's macroscopic, it's big enough blood uh blood vessel to supply the blood supply for the entire diaphysis of the bone. And if we look over here, we have a diagram showing a section of diaphysis or a section of that uh shaft of bone and part of it's cut away. So we can see the medullary cavity and the yellow marrow on the inside. But we wanna look at are these blood vessels and these nerves going around the outside here. And you can see they come up and then they go in this single hole there. That single hole is our nutrient foramen. Now, once inside those blood vessels can spread out through the medullary cavity and they can give blood supply to all of the bone and the marrow that's in that shaft of bone. So what goes in? We're gonna give specific names. We're gonna give it, the nutrient artery is gonna bring the blood into the medullary cavity or into the bone. The nutrient vein is gonna carry blood out of the bone and the nerves are also gonna pass through the nutrient frame in as well. Now, at the metaphysis and the epiphysis, things are gonna be a little different. There isn't a single nutrient foramen up where the spongy bone is, you're gonna have several smaller foramina. So a foramen is a hole, many small holes we're gonna call foramina. So these are located in the metaphysis and also in the epiphysis. And this is also gonna be true for bones that aren't long bones anywhere. You have that um compact bone with spongy bone on the inside instead of that one hole in the shaft, you're gonna have many smaller foramina. Ok? With that like always, we have an example, practice problems to follow. Give them a whirl.

Gross Anatomy of Bones - Structure of a Long Bone Example 2

This problem wants us to label this diagram and it gives us most of the vocab words from this section to do that. So let's get going. We have a articular cartilage, articular cartilage is that cartilage that covers the epiphysis in the joint. And so we can see a little bit right here. We can also see it down here, but here there's an arrow pointing to it. So I'm pretty confident that that is a the articular cartilage. Next, we have b compact bone or compact bone is the dense bone that's on the outside of the epiphysis or the entire shaft of the long bone. Now, there's nothing pointing to the bone in the epiphysis. But I see right here in this uh part showing me the shaft here. It's showing me some compact bone. So I am confident that that is b compact bone. Here. Next, we have the diaphysis, the diaphysis was the shaft of the long bone. And we see this bracket here showing me the entire shaft. So that's gonna be c the diaphysis. We now have the epiphysis. Remember you have two epiphysis, the widened ends of each long bone. So we have epiphysis here and here. But this one down here is the bracket. So I'm gonna give that d epiphysis. Next, we have the medullary cavity. The medullary cavity is the hollow part of the shaft of the long bone, the center of that long bone. And so you can see it here. Now, there's nothing pointing to it there though. So when we looked at the zoom in the section, here is something pointing to that empty space of the medullary cavity. So I'm pretty confident that's gonna be my answer. E on this line right here that brings us to the nutrient foramen. Remember the nutrient foramen is the hole in the shaft of the long bone that blood vessels and nerves can enter into the medullary cavity. So I see a hole right here that is going to be f nutrient foramen. Next, we have the nutrient artery. The nutrient artery is the blood vessel that enters the nutrient foramen. So here's our nutrient foramen, here's our blood vessel that's entering it. So that means that this line here is going to be g the nutrient artery. Next, the periosteum periosteum is the covering of the bone that connective tissue. We can see it getting peeled off the bone right there. That means that that line is going to be h the periosteum leaves us with finally spongy bone in a long bone spongy bone is gonna be found in the epiphysis. Now, the place that we see that zoomed in is gonna be right here and here's our spongy bone. So that is going to be a spongy bone. And with that, we've labeled a diagram.

What problems would arise if a bone lacked a nutrient foramen?

• A. Bones would lose their tensile strength.
• B. The periosteum would not adhere to the bone properly.
• C. The articular cartilage would not form.
• D. Bones would lose blood supply and nerves.

Which bone structure is most closely associated with the perforating fibers?

• A. Nutrient Foramen.
• B. Periosteum.
• C. Medullary Cavity.
• D. Epiphyseal Plate.

Achondroplasia is the most common form of dwarfism. A person with this condition will have short arms and legs but a normal sized head and trunk. Achondroplasia literally means 'without cartilage formation'. Why would a disorder that affects cartilage formation lead to dwarfism?

• A. Cartilage is more prevalent in the limbs as there are more articulating joints in the arms and legs.
• B. Long bones grow in length at the epiphyseal plate, which is composed of cartilage until puberty.
• C. Long bones are covered with articular cartilage at joints. A lack of cartilage at the joint would inhibit growth.
• D. Without cartilage, the medullary cavity would not form properly shortening the diaphysis.

Where would you be more likely to find red marrow and why?

• A. The nutrient foramen, red marrow produces blood cells, and the nutrient foramen contains blood vessels.
• B. The endosteum, red marrow produces blood cells, and the endosteum contains progenitor bone cells.
• C. The epiphysis, red marrow is found in spongy bone, and spongy bone is found in the epiphysis.
• D. The diaphysis, the medullary cavity of the diaphysis is filled with marrow.