Osteon Anatomy & Compact Bone Structure (Skeletal System)

0:00We're covering the skeletal system, but

0:01our goal is to focus on just an osteon.

0:05And what is an osteon? We have two types

0:08of tissue when we look at bone. We have

0:11osseous tissue in the form of spongy

0:13bone, and then compact bone. The

0:16functional unit or smallest piece of

0:19compact bone is an osteon. I'm going to

0:22show you a model for us to focus on the

0:24components or structures of an osteon,

0:27but just for review when we look at the

0:29two types of tissue, spongy bone, we

0:33tend to see more towards the ends of

0:34bone or what we call the epiphysis or

0:36the epiphyses. If we went on a high

0:38magnification or looked at other models

0:40that we see it's made up of these little

0:42porous structures called spicules or

0:44trabeculae that give us that porous

0:47nature that makes it look sponge-like.

0:50But when we look at compact bone, just

0:53by definition, it's more compact tissue.

0:56And so it gives us more of that strength

0:58that we tend to see more in the shaft of

1:00the diaphysis. Let's focus just on the

1:03structural piece of an osteon. As I look

1:06at an osteon, there's thousands and

1:09thousands and it depends on the bone,

1:11but how they're uniform and structured

1:14is in a circular pattern. Depending on

1:16your size, your age, and then when we

1:19look at the type of bone, is it a femur

1:21or is it a smaller bone like a carpal,

1:24we have less osteons, but there can be

1:25thousands of these and how they're

1:27organized is from a circular pattern. It

1:30gives us structural strength based on

1:32how it's all connected with the blood

1:34supply within it. Remember, one of our

1:36primary functions of bone is blood

1:39formation, which the bone is heavily

1:41active or moving material throughout it.

1:44And because of that, we replace our

1:46skeleton within just a few years. After

1:4910, 12 years, you're already reforming a

1:51lot of this tissue that helps create the

1:54bones that you have in your skeletal

1:55system.

1:56The way we primarily do that when we

1:59look at the center of an osteon, we call

2:02that an aversion canal or central canal.

2:05This is the point where we have blood

2:07supply, we have nerve supply, we have

2:09lymphatic supply. We're using these

2:12blood vessels, our arteries and veins

2:14and these smaller vessels that we look

2:16capillaries and venules that are

2:18bringing in the supplies we need to

2:20maintain this tissue and then also to

2:23bring out the waste it goes back into

2:25the cardiovascular system. We use this

2:28as a way as an aversion system to move

2:31around materials. How we organize it

2:34though is in circles. So it's circles

2:37within circles within circles within

2:39circles. As I look at this, it's just

2:42looking like a tree trunk or a dartboard

2:44or a bull's-eye to where I just have

2:46circles within circles. The way this

2:48forms is as I form one osteon and then

2:51another, it's perforating and creating

2:54this deposition to where I'm changing

2:56the shape around these blood supplies

2:58and I keep circling around it to form

3:01new osteons. We have different circles

3:04and we refer to these as lamellae.

3:06There's different types. What we're

3:08focusing on is we call concentric

3:10lamellae. Concentric meaning it's the

3:13primary circle within a circle within a

3:16circle that gives up the osteon. You

3:19might also see interstitial lamellae and

3:22that's from the remnants of making the

3:24osteon that go more vertical. Then you

3:27see circumferential to where that's

3:29towards the periphery of the tissue. Our

3:31focus is looking at what we call

3:33concentric referring to these lamellae

3:36or these circles that just keep circling

3:38through kind of like a tree trunk. Then

3:40as I look at this, what's maintaining

3:42the tissue are my cells, the osteocytes.

3:45Remember bone only has like 2 to 3%

3:48cells. The rest is what it makes,

3:50whereas other types of tissue like

3:52epithelial tissue, it's a bunch of cells

3:54that are stacked together. We have our

3:56primary cells that we've learned,

3:58osteoblasts. Osteoblasts are the younger

4:01cells that are secreting the matrix that

4:03give me that bony formation that gives

4:06us the hard mass of the compact bone.

4:09What we see is a lot of calcium

4:11compounds, calcium carbonate, calcium

4:13phosphate, that gives us the strength of

4:15the bone to allow for that compression

4:17non-stop. What we have is showing here

4:20an osteocyte. Remember things

4:22differentiate or change. So, an

4:24osteoblast

4:26differentiates into an osteocyte. The

4:29osteocyte's now the older cell that

4:31helps maintain the tissue. And what it

4:34sits in is a lacunae or a lacuna, and

4:37this is a fluid-filled space that allows

4:40for maintaining those cells and then

4:43allowing the movement of materials,

4:45things like nutrients, waste, and gases.

4:48How do we do that? With these little

4:50structures called canaliculi. Canaliculi

4:53are little canals. When you look under a

4:55microscope, they tend to look like

4:57lashes, like eyelashes or sun rays, but

5:00these are little microscopic canals that

5:03are connected from the lacunae to help

5:05those osteocytes move materials in and

5:08out. And again, things like nutrients,

5:10waste, gases, whatever the cells need at

5:13their particular point to maintain the

5:15tissue. We'll see lacunae and osteocytes

5:18throughout the model of the osteon. It's

5:21just highlighting this section. There's

5:22multiple cells throughout the actual

5:25osteon, and we refer to those

5:26osteocytes. As we look this, we're using

5:29this system of this blood supply to

5:32connect from cell to cell with these

5:34canaliculi, with all these circles,

5:36lamellae, as part of this whole aversion

5:39system through this central canal. And

5:42this is just one osteon. Remember

5:44there's thousands and thousands of them,

5:47depending on the bone that are all

5:48compact together to give me compact

5:51bone. This is describing one of our

5:53osseous tissues, compact bone versus

5:56spongy bone. This is an osteon.