An Introduction to Bone and Skeletal Tissue - Online Tutor, Practice Problems & Exam Prep

What is Bone?

Hello, and welcome to our unit on bone and skeletal tissue. Now before we dive in, before we learn any new material, I just always like to remind people and orient people to the fact that bone is living dynamic tissue. And I say this because so often when we think of bones, we think of a skeleton, something that's been dead, something that may have been dead for 100 or even 1000 years, or a Halloween skeleton or something. It's not something that we associate with life, but bone is living tissue. It has blood in it. If you break it, it's going to bleed. It has living cells in it. Those cells reproduce and replace themselves. The skeleton that you have now is different than the one you had 10 years ago. Bone responds to its environment. How you use bone is going to affect its structure. All right. So with that in mind, what we're talking about is the skeletal system, and the skeletal system comprises approximately 206 bones or about 206 bones. There's a little bit of variation from person to person. And also the associated cartilage. And to illustrate that, we have a person here and he's showing us his bones. We can see the skeleton. We can see the 206 bones of the body. Now I've told you there are 206 bones of the body, but we are not learning the 206 bones of the body in this unit. You are going to learn them later. We'll go over that later in another unit. Right now, we're talking about bone generally. What is bone? What are the types of bone? How is bone built? What does bone do? So to start with that, let's talk about the major functions of bone. Here we have 5 major functions. It's always difficult to put a number on it because someone may count something a little differently, but this is the way I like to think of it.

First up, bone supports the body, and to illustrate that we have a flying buttress on a cathedral here. Bone is the hard thing in your body that holds you up and gives you its shape. And for some things, they only will work with that structure. Your lungs, for example, need the structure of the ribs to work.

Second, bone is going to protect soft organs. And to illustrate this, we have a knight in armor here. That armor protects his body. Well, your body has things like your rib cage or your skull to protect the soft organs inside, and they do a pretty good job of it. Right? You can take a punch to the head. Now you don't want to. It may hurt you, but for the most part, in the end, you'll be okay because you have a cranium and that bone is going to protect that soft, really delicate brain inside.

Another thing bone is doing is it's going to produce blood cells, and that's going to happen in the bone marrow. And we can illustrate that here. We show a factory, and a factory is producing these blood cells coming out from that bone marrow, which is located on the inside of bones.

Bone is also going to store things. Specifically, it's going to store fat or triglycerides and also minerals, specifically calcium, which I'll write here as Ca+2. Now to illustrate that, we have a refrigerator filled with food, and the fat that it's going to store in your body, that's going to be in the form of another type of marrow. And that calcium, well, that's just in the matrix of the bone. You have a ton of calcium, and your body can use it.

Finally, bone is going to act as levers for muscles. And to illustrate this, we have a little guy here and he's lifting up something with the help of a lever. Now bones work with muscles. Muscles do one thing they can pull. What do they pull on? They pull on your bones, and when they do that as a lever, well, your arm bends. We're not going to talk about that in as much detail in this unit. In this unit, we're really going to talk about that structure of bone, how bones are built, and what bones do physiologically. I'm looking forward to it. So let's get to it.

An Introduction to Bone and Skeletal Tissue Example 1

This example says for each bone below, state whether you think the primary function is support, protection, or acting as a lever. You may choose more than one function if necessary. Alright. Quick note. In this chapter, you do not need to know the specific function of each individual bone. You will learn that later. But for now, we just want to think about this stuff a little bit generally. So let's go through our options and see what we got. First up, we have the phalanges. The phalanges are your finger bones. Well, what do you think? Support, protection, or acting as a lever? Well, your fingers do lots of movement, and when the body moves, it's because muscles are pulling on bones acting as lever. So the fingers, I'm definitely going to put an L for lever. Not really doing a lot of support or protection.

Next up, we have the vertebrae or the bones of your back. What do you think? Support, protection, or acting as a lever? Well, definitely some support. Right? That sort of is what keeps your body upright, so I'm going to put an S for support. I'm also going to put a P for protection. Your spinal cord goes down the middle of your vertebrae, and that bony protection is one of the things that protects it. And you probably know if you break your back, that compromises that protection and it can have some serious consequences. Now acting as a lever, there are muscle attachments on the vertebrae, and they do help you bend and stand up straight. So there is a little bit of lever action, but I'm not really thinking that that's a primary function, so I'm going to leave it off.

Next up, we have the parietal bones. These are the bones on the side of your cranium. So what do you think? Support, protection, or acting as a lever? Well, not really many muscle attachments there, so I'm not going to say acting as a lever. Support, I mean, it does give you the shape of your head, but really what it's doing is protecting the brain inside. So I'm going to put a P for protection.

Next up, we have the mandible or your jawbone. What do you think? Support, protection, or acting as lever? Not really a lot of support going on there, unless you consider supporting the teeth, and for protection, unless you're getting punched in the face a lot, not a lot of protection going on. What it's definitely doing is acting as a lever when you chew your food.

We have ribs. Ribs, support, protection, or acting as a lever. Well, definitely some support. Right? The ribs give you the shape of the thoracic cavity, the shape of your chest. We'll learn in the respiratory system, your lungs don't work unless you have rigid ribs giving them shape. Also protection. Right? I've stated before, pound on my chest, my heart is just fine because those ribs, the sternum are giving protection. So I'm going to put a P as well. Now acting as a lever, again, there are some muscle attachments on there. They, sort of base some muscles, but not a lot going on there in terms of levers for the ribs. So I'm going to leave that off as a primary function.

Our final bone here is going to be the humerus. That's your upper arm bone. What do you think? Support, protection, or acting as a lever? Alright. Well, really, those bones of the limbs, arms, and legs are definitely just mostly acting as levers. The more movement a bone has, the more it's acting as a lever. Not a lot of protection, not a lot of support going on there.

Alright. With that, we've run through these bones. Again, you don't need to know the specifics of every bone, but you do want to be thinking about bone functions in general. And we have more questions to follow. I'll see you there.

Which substances are stored in bones?

• A. Blood and Sodium
• B. Triglycerides and Calcium
• C. Sodium and Calcium
• D. Triglycerides and Sodium

Types of Bones

We're now going to learn how to identify different types of bones, and we're going to start by just saying that bones are characterized based on their shape. Now eventually, you're going to learn how to identify all the different bones in the body individually. We're not there yet. Right now, we just want to be able to pick up a bone and put it into one of these 5 categories based on shape. So let's take a look. We have this anatomical model. We can see the skeleton, and then we have 5 bones pulled out as an example. Let's go through each one.

First up, we have a long bone. And as our example bone here, we can see the humerus. The humerus is your upper arm bone. A long bone is going to be shaped much like a rod. And by that, I mean, it has a shaft and then it also has these expanded ends. So when you look at the humerus, you can see the shaft and the 2 expanded ends on each end. Now this is often like the type of bone that a kid will draw. It's sort of the classic bone shape is a long bone, shaft with expanded ends. Now importantly, not all long bones are long. The bones of your fingers and toes, those are long bones, even though the bones are quite short. They're called long bones because of their shape. They have a shaft and widened ends. Long bones you're going to find in your arms and your legs.

Okay. That brings us to the short bones. The short bones also based on shape. They are going to be roughly we're going to say cube shaped here. You might say sphere shaped. Sometimes I just sort of say lump shaped. Now, of course, every short bone is very specifically shaped based on what bone it is, where it is, and what it does. But because they're all sort of just these small sort of lump shaped bones, they tend to be the hardest bones to identify individually one from another in a disarticulated skeleton. Short bones, you're going to find in the wrists and the ankles, the carpals and the tarsals.

Okay. That brings us over to our flat bones. Well, flat bones, just like they sound, they are going to be thin. They're going to be pretty flat though they will be slightly curved. Our example here, we have the sternum pulled out. The sternum is like your breastplate, that bone in the middle of your chest. So flat bones though also are going to include the ribs and cranial bones. Ribs are quite long, but they're thin all the way along. They're slightly curved, and they don't have those widened ends that true long bones have. Cranial bones are going to be almost like plates, these curved plates that protect your brain inside.

That brings us to number 4 here. Number 4 is going to be irregular bones, and those I'm just going to say have an irregular shape. That's going to be your pelvis, the bones of your spine, facial bones. Irregular bones, it's really hard to describe what they look like because each one is so different from each other. The specific thing though, they're not flat. So if you see something that's kind of, you know, oddly shaped, but the entire thing is very thin, that'll be a flat bone. If it has some real thick parts on it, that's going to be an irregular bone.

Our final type of bone is going to be a sesamoid bone. Sesamoid bones develop inside a tendon. And the name sesamoid comes from the fact that some of these are really small and they kind of resemble a sesame seed. And because some of them are so small, some of them sometimes the amount that people have actually varies in number. Some sesamoid bones vary in some, I'm sorry, form in some people and don't form in others. One sesamoid bone that all people have that's quite large, that's relatively easy to identify, that's our example bone here, is the patella or your kneecap. The patella is located inside the patellar tendon. Now importantly, sesamoid bones have a lot in common with short bones. They have a lot of structural similarities, and sometimes they're grouped together. Sometimes they're grouped separately because sesamoid bones do have this unique feature that they form inside of tendons, which brings along some other peculiarities with them. So just know in your course whether sesamoid bones are considered part of short bones or whether you need to learn them independently.

Alright. With that, I'll see you in the next video.

An Introduction to Bone and Skeletal Tissue Example 2

In this example, we're going to identify whether bones are long, short, flat, or irregular. And as we look, we have an anatomical model where we can see the skeleton, and we have 4 bones pulled out. So let's go through those bones one by one. First up, we have the scapula. The scapula is also just called your shoulder blade. So I happen to have a model of the scapula here, so we can take a look. Take a look at this bone, and what kind of bone do you think it is? Well, when I look at it, pretty much every way I look at it, this bone is really thin. There really isn't a fat place on it. It does have this kind of crazy spine here, but even that is thin in at least one dimension. So when I see a bone like this where every area is pretty thin, is slightly curved, it's pretty flat, well, that's a flat bone. So I'm going to mark it with an f. The scapula is an excellent example of a flat bone.

Moving on, we have the sacrum, and I have a model of the sacrum here. What type of bone do you think this is? Well, the sacrum is the bottom of your spine, also the back of the pelvis. It's actually made by five vertebrae fusing to form one bone. And when I look at it, it's this kind of crazy shape. Sometimes I think it reminds me of a dragon's head or something like that. It would be really hard to describe this shape in any kind of detail at least quickly. And when you see something like this that is definitely not flat and it's just well, it's a really irregular shape, that's an irregular bone. So I'm going to mark it with an I. The sacrum, vertebrae, facial bones, and the hips, those are the irregular bones in the body.

As we go over, we have the femur. The femur is the largest bone in the body. It's your thigh bone. So what type of bone do you think this is? Well, when I look at it, I see that it has a shaft with two widened ends. When you have a bone with a shaft and widened ends, that's going to be a long bone. Now that may be kind of obvious for the femur because it is the longest bone in your body, but long bones don't have to be long. Right? The tip of your pinky, the bone in there, that's a long bone and it's really short. The thing that makes it a long bone, like the femur, it has a shaft with two wide ends. So the femur, a long bone.

That brings us to our last one here. These are the tarsals. So, if we look at this model of a foot here, the tarsals are the bones at the back end here. And as I look at these bones, well, I'll ask you first. What do you think they are? As I look at them, they don't really have any kind of distinct shape. They're kind of lump-like. I believe above, we described them as cube-like. You could also sort of say they're sphere-shaped. They have very specific shapes, but it's nothing to write home about. It's nothing too complex when you look at it. When you see a bone like that, relatively small, kind of lump-like, that is a short bone. The short bones are the bones of your wrists and your ankles.

Okay. With that, we've identified some bones. We have some practice problems to follow, and I'll see you there.

Where would you be most likely to find an irregular bone?

• A. Wrist or ankle.
• B. Spine.
• C. Ribs.
• D. Arm or leg.

Which of the following statements is true?

• A. Sesamoid bones are found in all joints in the body.
• B. Bones of your skull and ribs are both examples of flat bones.
• C. Your arms and legs contain mostly flat bones.
• D. Short and long bones have the same basic shape but differ in scale.