Gross Anatomy of Bones - Structure of a Long Bone - Online Tutor, Practice Problems & Exam Prep

Long bones consist of two epiphyses (wider ends) and a diaphysis (shaft). The epiphysis contains spongy bone and is covered with articular cartilage for smooth joint movement. The diaphysis is made entirely of compact bone and houses the medullary cavity filled with yellow marrow. The metaphysis connects the epiphysis and diaphysis, featuring the epiphyseal plate, crucial for bone growth during puberty. Nutrient foramina allow blood vessels and nerves to enter the bone, ensuring its vitality and function.

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 2 ends and a shaft, that shaft connecting the two ends. We're going to 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 2 epiphyses. 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 going to 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 going to say that articular cartilage covers the epiphysis at the joint, and that's just because, cartilage is going to 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 going to call the diaphysis. So we're just going to say here, that's the tubular shaft. And importantly, that's going to be made entirely of compact bone.

That's going to 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 going to be a solid layer of compact bone. It's going to be much thicker than the compact bone on the ends or on that epiphysis of the bone. And so if we look at this, we can see this in our diagram here.

This is the shaft. You can see there's no spongy bone in that shaft, and we are going to label this the diaphysis. Now before we go on, I just want to note diaphysis, epiphysis. It can be really easy to get those confused and flip 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 epi 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 through the middle of a long bone. Alright. We said that that is compact bone, but it’s not solid compact bone. It’s going to have this space in the middle. That space, we’re going to call the medullary cavity.

That's just going to be the space inside the diaphysis. Of course, it's not completely empty. It's going to 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 marrow is not drawn in. Now 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 going to 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 don't know when, but relatively recently in human history, evolution figured out that millions of years ago. That hollow structure with nice thick compact bone making this pipe-like structure is going to give your long bones a lot of strength while making sure that they're not too heavy.

Okay. So the one part that we have not talked about yet, we're going to call the metaphysis. The metaphysis is the part where the epiphysis and the diaphysis I'm just going to say meet 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 want to 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. You've probably heard of this. You may have heard it called the growth plate. The growth plate is going to be a line of hyaline cartilage that allows for bone growth. So long bones are going to grow differently than other bones.

They're going to have this line of hyaline cartilage, and they are going to grow in length from that cartilage. They're going to grow wider in a different way, more similar to other bones, and that's something that, you'll learn later on. But for now, you really want to know the structures there that that epiphyseal plate is going to be this line of hard, hyaline cartilage, and we're just going to say that's the site of bone growth until you finish puberty. Now once you stop growing, that epiphyseal plate is going to transition into what we’re going to 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 going to be those epiphyseal plates or the growth plates. That end of the femur actually has 2 growth plates.

You'll see, 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. Okay. Again, you're going to learn 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 going to go into a little bit more detail in the structure of a long bone coming up. And after that, we're going to 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 us that forensic analyses can use bones to establish a rough age of a skeleton, and then it wants to know what specific structure in the metaphysis might a forensic scientist look at to determine age. So I'll ask you. Alright. If you want to know the age of the skeleton, roughly, you can look at the metaphysis. What are you looking for?

Well, remember, in the metaphysis, that's that widening end of a long bone, and in there, you have the epiphyseal plate or epiphyseal line. In children, that starts out as cartilage because that's where growth is occurring in the long bone, where the long bone is growing longer. And in adults, it gets converted to compact bone. And so by looking at where it is in that stage from cartilage to compact bone, you can give the rough age of a skeleton. So I'm going to write here the epiphyseal plate/line.

Alright. Now the second part here, it wants to know what would you expect this structure to be comprised of at the following ages. Alright. Well, we kind of already said that, but we also here have these x-rays of different hands. We have a child's hand, an adolescent's hand, and an adult's hand, and that's what we want to know.

What do you expect that epiphyseal plate or line to be comprised of as a child, an adolescent, or an adult? Alright. So I'll just give you one second to think of that. What do you think for each one? Well, as I look down at the images, we can see here.

So this is the child's hand right here, and we can look for that epiphyseal plate or epiphyseal line. Here, it's very clear. This is the radius. Right? That's the end of the long bone in the arm there, and you can see this epiphyseal plate right there.

And then the epiphysis is this sort of bone that's sort of sitting on the end there. This is actually one bone. The same thing in these metacarpals here. You have the metacarpals, and then you have what looks like a little space, and then the epiphysis of each one of those bones is just sort of sitting on the end there. Well, that's because that epiphyseal plate is still cartilage, and cartilage doesn't show up as well on an x-ray.

So in a child, that epiphyseal plate is cartilage. Alright. And now what about an adolescent? Well, that's our adolescent there. So in your teenage years, you're growing a lot, but then growing kind of slows down.

So we can see that in this image again. We can see there's still a very clear line separating the diaphysis from the epiphysis in that metaphysis, and that's that epiphyseal plate. So if there's a very clear line that you can see, that means that it's still cartilage. But I'm going to say here that it's thinning. Not that the cartilage is thinning, but just the size of that space is thinning.

The epiphyseal plate is not as big because growth is slowing down. And then finally, we can look at this adult's hand. And, well, if you look for that epiphyseal plate, there's no more space here. There's no more space at the end of the metacarpals there because it has grown together. It is now compact bone.

Alright. For that, remember, the epiphyseal plate starts out as cartilage because that's where the growth of the long bone happens. When you stop growing, it gets converted to compact bone. More practice problems after this. I will 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 going to 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 the bone is also all compact bone, and compact 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 going to be located in the diaphysis of bones, and it's for blood vessels and nerves 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 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 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 what we want to 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 going to give specific names. We're going to give it the nutrient artery is going to bring the blood into the medullary cavity or into the bone. The nutrient vein is going to carry the blood out of the bone, and the nerves are also going to pass through the nutrient foramen as well.

Now at the metaphysis and the epiphysis, things are going to be a little different. There isn't a single nutrient foramen. Up where the spongy bone is, you're going to have several smaller foramina. So a foramen is a hole, many small holes we're going to call foramina. So these are located in the metaphysis and also in the epiphysis.

And this is also going to be true for bones that aren't long bones. Anywhere you have that compact bone with spongy bone on the inside instead of that one hole in the shaft, you're going to have many smaller foramina. Okay. With that, like always, we have an example of 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 vocabulary 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. Our 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 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 going to be C, the diaphysis. We now have the epiphysis.

Remember, you have two epiphyses, 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 going to give that depiphysis. 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 section, here's something pointing to that empty space of the medullary cavity. So I'm pretty confident that's going to 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 going to be found in the epiphyses. Now the place that we see that zoomed in is going to be right here, and here's our spongy bone.

So that is going to be i, 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.

Here’s what students ask on this topic:

What are the main structural components of a long bone?

A long bone consists of two main parts: the epiphyses and the diaphysis. The epiphyses are the wider ends of the bone, containing spongy bone and covered with articular cartilage for smooth joint movement. The diaphysis, or shaft, is made entirely of compact bone and houses the medullary cavity filled with yellow marrow. The metaphysis connects the epiphysis and diaphysis and features the epiphyseal plate, crucial for bone growth during puberty. Nutrient foramina allow blood vessels and nerves to enter the bone, ensuring its vitality and function.

What is the function of the epiphyseal plate in long bones?

The epiphyseal plate, also known as the growth plate, is a line of hyaline cartilage located in the metaphysis of long bones. It is crucial for bone growth during puberty, allowing the bone to increase in length. As a person matures and reaches the end of puberty, the epiphyseal plate transitions into the epiphyseal line, converting to compact bone and ceasing further growth in length.

How does the structure of the diaphysis contribute to the strength of long bones?

The diaphysis, or shaft, of a long bone is made entirely of compact bone, which provides significant strength and rigidity. The compact bone forms a thick, solid outer layer, while the medullary cavity inside is hollow and filled with yellow marrow. This pipe-like structure offers an optimal strength-to-weight ratio, making the bone strong yet not overly heavy. Engineers have found that this design, similar to a hollow rod, provides excellent structural integrity.

What is the role of nutrient foramina in long bones?

Nutrient foramina are small holes located in the diaphysis of long bones, allowing blood vessels and nerves to enter the bone. These foramina are essential for supplying the bone with nutrients and oxygen, ensuring its vitality and function. The nutrient artery brings blood into the medullary cavity, while the nutrient vein carries blood out. In the metaphysis and epiphysis, several smaller foramina serve a similar purpose, facilitating the distribution of blood and nerve supply throughout the bone.

What is the difference between the epiphysis and diaphysis of a long bone?

The epiphysis and diaphysis are distinct parts of a long bone. The epiphysis is the wider end of the bone, containing spongy bone and covered with articular cartilage for smooth joint movement. In contrast, the diaphysis is the tubular shaft made entirely of compact bone, housing the medullary cavity filled with yellow marrow. The epiphysis is involved in joint articulation and growth, while the diaphysis provides structural support and strength to the bone.