Specialized Connective Tissue: Cartilage - Online Tutor, Practice Problems & Exam Prep

Specialized connective tissues, including cartilage, bone, and blood, serve unique functions. Cartilage, which is avascular, consists of chondroblasts and chondrocytes within lacunae, and has a firm yet flexible extracellular matrix. There are three types of cartilage: hyaline, fibrocartilage, and elastic cartilage. Hyaline cartilage, the most abundant, reduces friction and serves as a precursor to bone. Fibrocartilage, the strongest, withstands compression and tension, found in intervertebral discs. Elastic cartilage provides flexibility, located in the external ear and epiglottis, allowing structures to maintain shape while being stretchable.

Specialized Connective Tissues

So now that we've covered connective tissue proper, including loose and dense connective tissues, in our previous lesson videos, in this video we're going to begin our lesson on the second major class of connective tissues, which are the specialized connective tissues with a focus on cartilage for the next few videos. Recall from our previous lesson videos that specialized connective tissues, as their name implies with the term specialized, are going to be optimized for very specific roles that are unique to the tissue. This is different than connective tissue proper, which tends to have more generalized functions and roles. Also, recall that specialized connective tissues tend to have a ground substance in the extracellular matrix that is either a solid or a liquid, rather than being a gelatinous semi-fluid like the ground substance of connective tissue proper. Recall from our previous lesson videos that there are three different types of specialized connective tissue: cartilage, bone, and blood and lymph.

Moving forward in our course in separate videos, we're going to talk more about each of these three different types of specialized connective tissue. Notice down below, we have our map of the lesson on connective tissue. We know that connective tissues can be grouped into two major classes. The first major class is connective tissue proper, or general or fibrous connective tissues, which includes loose connective tissues such as areolar, reticular, and adipose tissues, and dense connective tissues such as dense regular, dense irregular, and elastic connective tissues. We've already covered connective tissue proper in our previous lesson videos, and so here in this video, we're focusing our attention on the second major class of connective tissues, which are the specialized connective tissues, which once again includes cartilage, bones, and blood and lymph.

Now, what you'll notice is that there are three different types of cartilage, including hyaline cartilage, fibrocartilage, and elastic cartilage. Moving forward in our course, we're going to talk about all of these different types of specialized connective tissues in their own separate videos in more detail, starting with cartilage. This concludes our introduction to our lesson on specialized connective tissue, and I'll see you all in our next video to learn more about cartilage.

Overview of Cartilage

In this video, we're going to do an overview of cartilage, which is the first type of specialized connective tissue in our lesson. And so, recall from our last lesson video that there are 3 different types of cartilages. Those are hyaline cartilage, fibrocartilage, and elastic cartilage. Moving forward in our course, we'll talk about each of these 3 different types of cartilages in their own separate videos. But in this video, we're going to do an overview of all of these cartilages.

In terms of their characteristics and their properties, cartilage is actually somewhat in between that of bones and dense connective tissues. We know that bones are rock-hard structures that are very well designed for withstanding compression forces from load-bearing, heavy weights of the body. Whereas dense connective tissues, such as those found in tendons and ligaments, for example, are more so designed for withstanding tension forces from being pulled rather than withstanding compression forces from load-bearing, heavy weights of the body. Cartilage is somewhat in between these because it is a very tough connective tissue, yet it is more flexible than bones and less flexible than dense connective tissues. It is able to resist both tension forces from being pulled and compression forces from load-bearing heavy weights of the body.

As we'll learn moving forward in our course, bones are very well vascularized with lots of blood vessels. Recall from our previous lesson videos that dense connective tissues are very poorly vascularized with few blood vessels. Cartilage is somewhat in between the two because it is avascular, meaning that it has no blood vessels. This is going to cause very slow healing of cartilages upon being damaged or injured.

Cartilage is a very tough yet flexible connective tissue. It has a very firm but flexible and rubbery extracellular matrix. In terms of its cell types, there are 2 main cell types in cartilages. It's helpful to note that the root chondro is a root that means cartilage. You can find this root chondro in the two main cell types, chondroblasts and chondrocytes.

Chondroblasts are blast cells, as it ends with the root 'blast'. Recall from our previous lesson videos that blast cells are immature cells that are more active. They more actively divide and build and secrete components of the extracellular matrix, including the ground substance and protein fibers. The second main cell type are the chondrocytes, which are site cells, as it ends with the root 'sites'. Recall that site cells are mature cells that are less active. They less actively divide, and they are more so about maintaining the extracellular matrix through minor repairs and routine maintenance.

These chondrocytes are mature and are actually derived from the chondroblasts, which are immature. Chondroblasts that are actively secreting and building components of the extracellular matrix, upon actively doing that and maturing into chondrocytes, can actually become trapped in spaces within the extracellular matrix known as lacunae. These lacunae are chambers that house chondrocytes.

The perichondrium is going to be a tissue that supports most cartilages. It's helpful to know that the root peri is actually a root that means around. Perichondrium is going to be around the cartilage. It is dense irregular connective tissue, which we talked about in our previous lesson videos and we know is poorly vascularized with few blood vessels, but it still does have some blood vessels which allows it to provide blood flow to the cartilages and nutrients to the avascular cartilages.

Now, this perichondrium is found around most cartilages, including most hyaline cartilages and elastic cartilages. As we'll learn moving forward in our course, it's actually not supporting or found around fibrocartilage. We'll talk more about this as we move forward in our course. As you can see in our image, cartilages can be found all throughout the body in various structures, including our nose, where it can provide the shape of our nose.

It can also be found in our trachea. It connects the bones of our ribs to the sternum, which is our chest bone. It can also be found in between the vertebrae in our spine where it can absorb shock and provide cushioning. It's also found in between the joints in our legs and the joints in our arms, where again, it can provide cushioning and shock absorption. It can also make up structures in our ears as well.

And what you'll notice is that we have a little sketch of some cartilage. What you'll notice is that it is going to have the 2 main cell types, chondroblasts and chondrocytes. Again, these chondrocytes are going to be found in spaces, which you can see here, called lacunae. And again, the singular is actually lacuna. In a single lacunae, the space that you can kind of see going around these chondrocytes, you can either find pairs of chondrocytes as you see here, or you could find single chondrocytes.

Most cartilages, including most hyaline cartilages and elastic cartilages, are going to have a perichondrium. Again, this dense, irregular connective tissue surrounds most of the cartilages and is going to provide blood flow and nutrients. So, this here concludes our overview of cartilage. As we move forward in our course, we'll be able to talk more details about each of the 3 different types of cartilages. I'll see you all in our next video.

Specialized Connective Tissue: Cartilage Example 1

So here we have a pretty straightforward example problem that wants us to select one of these four potential answer options down below that best fills in the blank to complete the sentence. And so it says that the primary cells of cartilage reside in blank. Option a says lacunae, option b says gap junctions, option c says osteons, and option d says that options a through c are all correct. And so, recall from our last lesson video that cartilage has two primary types of cells, Chondroblasts and chondrocytes. And the chondrocytes are the ones that are going to reside in chambers within the extracellular matrix called lacunae.

And so, option a, lacunae is going to be the correct answer to this example problem. Now, option b which says gap junctions, those are going to be junctions that connect the cytoplasm of 2 neighboring cells. But gap junctions are not really going to be a defining feature of connective tissues where the cells are usually spaced apart and not in direct contact with one another. So we can eliminate option b. Option c says osteons, which are actually structural units of bones that we'll get to talk more about later in our course.

But again, these osteons are not part of cartilage. So, for that reason, we can eliminate option c and then of course, we can eliminate option d as well. And so a, lacunae is the correct answer here and I'll see you all in our next video.

Hyaline Cartilage

In this video, we're going to talk about the first type of cartilage in our lesson, which is hyaline cartilage. Hyaline cartilage is actually the most abundant cartilage throughout the entire human body and is also the weakest form of cartilage among the 3 different types of cartilage. Now hyaline cartilage is actually named for its appearance in the human body, appearing as bluish white color with a very smooth, glassy type of appearance that can actually have some shine to it.

The root "hyal" in hyaline cartilage is a root that means glass. Hopefully, this can remind you of hyaline cartilage's very smooth and glassy type of appearance. In terms of its composition, hyaline cartilage has very small, fine, or thin bundles of collagen fibers in its extracellular matrix. We know that these collagen fibers are long, unbranched, and straight fibers that give the tissues lots of strength and a little bit of flexibility, making hyaline cartilage a very tough connective tissue.

However, because these collagen fibers are arranged in very small, fine, or thin bundles, this is what makes hyaline cartilage the weakest form of cartilage among the 3 different types of cartilages. In terms of its function, because hyaline cartilage has this smooth, glassy type of appearance, that smooth nature actually helps to reduce friction between bones. Like all cartilages, which are very tough connective tissues with some flexibility as well, hyaline cartilage serves as a very strong and flexible structural support. Notably, hyaline cartilage serves as the precursor to bone in the fetus, and human embryos have skeletons made almost entirely of hyaline cartilage initially.

As the human develops, that hyaline cartilage is slowly replaced with bone. In terms of the body locations where we can expect to find hyaline cartilage, it serves as a strong and flexible structural support in body locations such as the nose, the larynx or the voice box, and the trachea or the windpipe. It is also found at the ends of long bones where it helps to reduce friction between the bones. This can be found in areas such as our knee, elbow, and shoulder.

Hyaline cartilage is also associated with developing bones as well because it is the precursor to bone in the fetus. It makes up most of the skeleton of the human embryo and is slowly replaced with bone as the human develops. Hyaline cartilage is found in the nose, helping to give our nose its structure and shape. It is found in the larynx and the windpipe where it helps to prevent the collapse of the windpipe and still allows for some flexibility for the expansion and contraction as we breathe.

It is also found connecting the bones of our ribs to the sternum or our chest bone, where it can give our ribs some flexibility as it expands and contracts during breathing. It can also be found in joints at the ends of long bones where it reduces friction between bones. We have a micrograph of hyaline cartilage, highlighting a chondrocyte within the lacunae. Recall that the lacunae are chambers in the extracellular matrix that house the chondrocytes, which are the mature cells of cartilage.

The matrix is a firm yet flexible and rubbery extracellular matrix, and most types of hyaline cartilage are surrounded by the perichondrium, a layer of dense irregular connective tissue that is vascular and can help to support the hyaline cartilage by providing nutrients through its blood vessels. Like all cartilages, hyaline cartilage is avascular, and not all hyaline cartilage has the perichondrium. For example, the cartilage at the ends of long bones, sometimes referred to as articular cartilage, does not have a perichondrium mainly because it needs the cartilage to be available to reduce the friction between bones. This here concludes our lesson on hyaline cartilage, and we'll be able to apply these concepts and learn about other types of cartilages as we move forward in our course. So I'll see you all in our next video.

Specialized Connective Tissue: Cartilage Example 2

So here we have an example problem that asks, how does the appearance of hyaline cartilage help you remember its function? And we've got these 4 potential answer options down below. Recall from our previous lesson videos that hyaline cartilage is actually named for its appearance. Recall that the root hyal in hyaline cartilage is a root that means glass. Hopefully, this can remind you that hyaline cartilage has a very smooth, glassy type of appearance to it.

It actually does not have a webbed appearance. For that reason, we can eliminate answer option b, which says webbed appearance insulates the body. That's not going to be true. We can also eliminate answer option d, which also says webbed appearance resists compression. Now hyaline cartilage does resist compression, but it's not going to have a webbed appearance.

That's why we can eliminate option d. Now we're between either option a or option c. Notice option a says smooth appearance transports nutrients. But we never said that hyaline cartilage is important for transporting nutrients. In fact, it's not important for transporting nutrients.

For that reason, we can eliminate answer option a. Thus, option c must be the correct answer, which says smooth appearance reduces friction. Recall that hyaline cartilage does have a smooth glassy appearance to it and can be found at the ends of bones where it can reduce friction between the bones. For this reason, we can indicate that answer option C is the correct answer to this example, and that concludes this example. I'll see you all in our next video.

Fibrocartilage

In this video, we're going to talk about the second type of cartilage in our lesson which is fibrocartilage. And so, in terms of its characteristics, fibrocartilage is actually a little bit of a blend between hyaline cartilage and dense regular connective tissue which recall is a type of connective tissue proper. And also recall that connective tissue proper is sometimes referred to as fibrous connective tissue. And so the root fibro in fibrocartilage can remind you that fibrocartilage is a blend between fibrous connective tissue or connective tissue proper, mainly dense regular connective tissue, and a blend between cartilage or hyaline cartilage. Now, like all cartilages, fibrocartilage is avascular.

Meaning that it does not have any blood vessels. But unlike most cartilages in the body, fibrocartilage does not have a perichondrium or a layer of dense irregular connective tissue that surrounds the cartilage and usually has a blood supply that is able to support the avascular cartilage. But again, because fibrocartilage does not have a perichondrium, it does not have that supporting dense irregular connective tissue. And that means that fibrocartilage is going to rely even more on the diffusion of nutrients from surrounding tissues that may be vascular. And so, what that means is that fibrocartilage is going to have a tendency to heal slowly, very slowly.

And so, damages and injuries to fibrocartilage can really be detrimental to the health. Now, fibrocartilage is also going to be unique in that in addition to its chondroblasts and chondrocytes, it's also going to have some fibroblasts. Which recall, fibroblasts are cells of fibrous connective tissue or connective tissue proper. Again, another reminder that can be the root fibro in fibrocartilage, has some fibroblasts. Now, these fibroblasts recall, are going to be really important for producing the fibrous proteins in the extracellular matrix.

And in fact, fibrocartilage is known for having very very dense bundles of collagen fibers in the extracellular matrix. And because it has such dense bundles of collagen fibers, this actually makes fibrocartilage the strongest cartilage amongst the three different types of cartilage. And fibrocartilage, because it has so many dense bundles of collagen fibers, it's actually going to have relatively little ground substance in its extracellular matrix. Especially in comparison to hyaline cartilage. Now, in terms of its functions, again, because it has such dense bundles of collagen fibers, it's going to have quite a lot of strength.

And so, in terms of its function, it will be able to resist both compression forces that come with the bearing of weight from the body and it's also able to withstand tension forces from stretching as well. And so, in terms of body locations, we can expect to find fibrocartilage in areas of the body that need to be able to withstand lots of compression and tension. And so, they actually can be found making up the intervertebral discs, which is the fibrocartilage found in between the vertebrae of our spine. Which you can see over here in this image. Notice that we're zooming in on the spine of this woman here.

And notice that in between the vertebrae of the spine right here in blue is where the fibrocartilage can be found. And again, it's very very strong and so it can actually allow for shock absorption and cushioning. Now, it can also, fibrocartilage can also be found in the menisci of the knees. And the menisci is really just the meniscus of the knee. It's the plural version of the meniscus of the knee.

And so, in the knee, of course, that's in the lower part of our body. And it needs to be able to withstand lots of compression forces, since it's bearing the weight of our entire upper body, pretty much. And so, it's really important to have really really strong fibrocartilage in the menisci of the knee. And so notice down here we have a micrograph showing you some fibrocartilage and what you'll notice is that again, we're highlighting the chondrocytes within the lacunae, which again are those chambers that house the chondrocytes. There are also going to be chondroblasts and some fibroblasts in fibrous connect cartilage as well.

Fibrous cartilage has some fibroblasts. And the extracellular matrix, which you'll notice has really, really dense bundles of collagen fibers that are more regularly arranged, which is why it's more of a blend between dense regular connective tissue and not so much dense irregular connective tissue since the bundles of fibers are not totally randomly arranged in fibrocartilage. And so, this here concludes our lesson on fibrocartilage and moving forward, we'll be able to apply these concepts and talk about the last type of cartilage in our lesson as well. So, I'll see you all in our next video.

Elastic Cartilage

In this video, we're going to talk about the 3rd and final type of cartilage in our lesson, which is elastic cartilage. Elastic cartilage is actually quite similar to hyaline cartilage except for the fact that, as its name implies with the term "elastic," elastic cartilage is going to have significantly more elastic protein fibers in its extracellular matrix. In terms of its composition, once again, the ECM or the extracellular matrix is going to be filled with lots and lots of elastic protein fibers. Recall from our previous lesson videos that elastic protein fibers are made from smaller proteins called elastin, which is an elastic protein that allows for elasticity. This recalls the ability to stretch significantly, but then, equally as importantly, return back to its original shape after being stretched. Elastic cartilage certainly is going to have elasticity.

In terms of its functions, it's going to be able to help maintain the shape of structures while still providing great flexibility and elasticity. In terms of locations, example locations where elastic cartilage can be found include the external ear, which is quite flexible and stretchy and has that elastic ability, where it returns to its original shape after stretching. It can also be found in the epiglottis, which is a structure found in our throat area. Notice here in this little image, we're zooming into the throat area, and you can see the epiglottis is this structure here. The epiglottis acts as a flap to cover up our windpipe, our trachea, as we're swallowing foods and drinks, so that those foods and drinks are directed down our esophagus and into our digestive system, instead of being directed down into our trachea and into our respiratory system. The epiglottis needs to have that elastic ability to be able to bend and stretch, but then again, return back to its original shape after bending and stretching. Elastic cartilage can also be found in the external ear as well.

Notice below, we have a micrograph showing you elastic cartilage. The main cell types are going to be chondroblasts and chondrocytes. We're indicating a chondrocyte within a lacuna, which recall that the lacunae are going to be these chambers within the extracellular matrix that house chondrocytes. The extracellular matrix is going to be tough yet flexible, especially in elastic cartilage, which has lots and lots of elastic protein fibers allowing for elasticity. Like most cartilages in the body, elastic cartilage is going to be surrounded by a perichondrium, a layer of dense irregular connective tissue that is vascular and has blood. This is going to be able to support the avascular nature of the elastic cartilage. But again, because elastic cartilage is avascular itself, that is going to lead to slow healing.

This here concludes our lesson on elastic cartilage and moving forward, we'll be able to apply these concepts and talk about other types of specialized connective tissues. So, I'll see you all in our next video.

Specialized Connective Tissue: Cartilage Example 3

So here we have an example problem that asks, how does the structure of fibrocartilage benefit its function in intervertebral discs? And we've got these 4 potential answer options down below. So, option a says that large amounts of collagen bundles resist compression but allow flexibility. Now, this option seems reasonable, but let's skip it for now and check the other options.

So option b says, large amounts of elastic fibers resist compression but allow flexibility. Now recall from our previous lesson videos that fibrocartilage has an extracellular matrix made of really dense and thick bundles of collagen fibers. Elastic fibers are not predominant in large amounts in the extracellular matrix. Elastic fibers are more important for elasticity and they don't really allow for the resistance of compression forces like collagen fibers do. For those reasons, we can eliminate answer option b.

Now option c says adipocytes provide shock absorption. Recall that adipocytes are fat cells that store fats or triglycerides as these relatively large lipid droplets within the adipocytes. Adipocytes are mainly found in loose connective tissues such as adipose connective tissue and areolar connective tissue. But these adipocytes are not going to be found in fibrocartilage. So, for that reason, we can eliminate answer option c. Although fibrocartilage does have chondroblasts and chondrocytes, do recall that they also have some fibroblasts. But again, they don't have any adipocytes or fat cells.

Now, option d says, chondrocytes provide shock absorption. This is an interesting answer option, but it's important to note that it's not the cells that provide shock absorption; the chondrocytes are the cells. It's mainly going to be the extracellular matrix that's produced by the cells that provides the shock absorption in the tissue. So, option d can be eliminated for that reason. Of course, this means option a is the correct answer. Fibrocartilage is going to have large amounts of collagen bundles in its extracellular matrix, which allows it to resist compression forces, but also allows it to have a little bit of flexibility since collagen fibers have a little bit of flexibility as well.

And so, option A here is the correct answer to this problem. And again, those intervertebral discs are in between the vertebrae or the bones within the spine.

This here concludes this example, and I'll see you all in our next video.

Review of Types of Cartilage

In this video, we're going to do a review of the 3 different types of cartilages. And so because this video is a review, really there's no new information covered in this video that we haven't already covered in our previous lesson videos. And so if you're already feeling really good about the 3 different types of cartilages, then you can feel free to skip this video if you'd like. But if you're looking for a little bit of review, then stick around because this video could be really helpful for you. And so notice down below what we have is a table of the 3 different types of cartilages.

Where in the first column, we indicate the particular type of cartilage. The second column has some key characteristics. The third column has some key functions. And the fourth column has some example locations of where these cartilages can be found in the body. And so recall that the first type of cartilage that we covered in our lesson was hyaline cartilage.

And so, recall that hyaline cartilage is actually the most abundant cartilage throughout the entire human body. And it's also the weakest cartilage amongst the 3 different types of cartilages. Now, also recall that hyaline cartilage is named for its appearance. And the root hyal in hyaline cartilage is a root that means glass, which can be helpful to remind us that hyaline cartilage is going to have a very smooth and glassy appearance to it. Now, in terms of its extracellular matrix, it's going to have these very small or thin or fine bundles of collagen fibers.

Now, of course, the collagen fibers are going to allow hyaline cartilage to be a very strong yet flexible tissue. However, because again, these are very small or thin or fine bundles of collagen fibers, really this is what makes hyaline cartilage the weakest of the 3 different types of cartilages. And also, because they are small and fine and thin, that also makes them harder to see under the light microscope under regular staining techniques. And so, if we take a look at this micrograph, you can see the cells within hyaline cartilage including the chondroblasts and the chondrocytes. And recall, the chondrocytes are going to lie within these chambers called lacunae.

And so, you can see here, throughout this tissue these different chondrocytes lying within the lacunae chambers. Now, in terms of its functions, hyaline cartilage is again, because of its smooth glassy appearance, it can actually reduce friction between bones as those bones are moving because of the muscles. And also, because hyaline cartilage again does have lots of collagen fibers, it is going to be a strong and flexible tissue. So, it is going to allow for it to serve as a strong and flexible structural support. And also, very notably of hyaline cartilage, it's actually a precursor to bone in the fetus.

And so, recall that the human fetus and human embryo actually have skeletons that are made almost entirely of hyaline cartilage initially. And then as the human develops, the hyaline cartilage in the skeleton is slowly replaced with bone over time. Now, in terms of the body locations where hyaline cartilage can be found, It can be found at the ends of bones where, again, it can help to reduce the friction between bones. Again, it can serve as a strong and flexible structural support in areas such as the nose and the larynx or the voice box and the trachea or the windpipe. And again, it's associated with developing bones as well because, again, hyaline cartilage makes up the vast majority of the fetus, the fetal skeleton and the human embryo skeleton.

And again, it's slowly going to be replaced with bone over time. And so notice that in these images, you can see that hyaline cartilage is indeed found at the ends of bones where it helps to reduce friction between bones. It's found in the larynx and the trachea. It's also found giving structural support to our nose, and it can also connect the bones of our ribs to the sternum, which is our chest bone.

Now, the second type of cartilage that we covered in our lesson, recall was fibrocartilage. And recall that fibrocartilage was actually an intermediate blend between hyaline cartilage and dense regular connective tissue. And recall that the root fibro can actually remind us of that because the root fibro can remind us of fibrous connective tissue, which is really connective tissue proper, more specifically dense regular connective tissue. And again, the cartilage part here reminds us that it's an intermediate blend between dense regular connective tissue and hyaline cartilage. Now, recall that fibrocartilage is unique in that it does not have a perichondrium around the cartilage and recall the perichondrium is a layer of dense irregular connective tissue that is poorly vascularized but still supplies some blood vessels to support the avascular cartilage.

Recall that all of these cartilages are avascular. Now, most hyaline cartilages are going to have a perichondrium, but not all of them will. But fibrocartilages do not have any perichondrium. Also, fibrocartilage, it because it is this mixture between dense regular connective tissue and hyaline cartilage, it's actually going to have chondroblast, chondrocytes, and some fibroblasts as well. And so those fibroblasts will help to create dense and thick bundles of collagen fibers, which really gives fibrocartilage its strength.

And so, fibrocartilage is actually the strongest cartilage amongst these 3 different types of cartilage. Now, it also is going to have very minimal or little ground substance in comparison to hyaline cartilage, for example. And so notice over here we're showing you this micrograph of fibrocartilage and in this micrograph what you'll notice is that there are very dense bundles of collagen fibers in its extracellular matrix, and they're more regularly arranged than irregularly arranged in a random pattern, which again helps to give fibrocartilage its strength. Now, in terms of its functions, it is going to be able to resist both compression forces from weight bearing, from load bearing weights of the body and it's also going to be able to resist tension forces from being pulled as well. And so, we can find fibrocartilage in areas of the body such as forming the intervertebral discs between the vertebrae of our spine, which is what this image here is showing.

You can see we're zooming into this woman's spine here and you'll notice that in between the vertebrae, this little blue layer that you see between them, that is going to be the intervertebral disc, which again is made mostly of fibrocartilage. And it can also be found in the menisci of the knee, which is really just the plural form of the meniscus of the knee. And again, that helps it to withstand the compression forces, since our knees need to be able to basically bear the load of the weight of most of our upper body. Now, the third and final type of cartilage that we covered in our lesson was elastic cartilage. And so, as its name implies, elastic cartilage is going to be very similar to hyaline cartilage, except it's going to have a lot more elastic protein fibers in its extracellular matrix.

And so, the ECM or the extracellular matrix is going to be filled with lots and lots of elastic fibers. And recall that those elastic fibers are going to be made of smaller elastin proteins, which allow for elasticity or the ability to stretch significantly. But then equally as importantly, return back to its original shape after being stretched. And so that's going to in terms of its function, elastic cartilage will help to maintain the shape while still providing great elasticity or flexibility. And so, we can find elastic cartilages in areas of our body such as the external ear which our ears are pretty flexible and have that elasticity.

And we can also find it in the epiglottis for example, which is the structure here in our throat that actually can move to block the passage of foods and drinks when we're swallowing. So, that those foods and drinks are directed to our esophagus to go into our digestive system instead of going down into our trachea and into our respiratory system. And so, this here concludes our review of the 3 different types of cartilages and as we move forward in our course, we'll be able to get a little bit of practice and we'll also be able to talk about other types of specialized connective tissues as well. So, I'll see you all in our next video.

True or False: The nose and the ear are made of the same type of cartilage.

• A. True: they are both hyaline cartilage. 
• B. True: they are both elastic cartilage.
• C. False: the nose is elastic cartilage and the ear is hyaline cartilage.
• D. False: the nose is hyaline cartilage and the ear is elastic cartilage.

Janine fell off her bike, cutting her knee and tearing the hyaline cartilage of her knee joint. At the doctor's office, she is told the cuts will heal in a few weeks, but the cartilage will take months. Using what you know about tissues, why does the cartilage take longer to heal?

• A. Cartilage is unable to regenerate because it lacks -blasts cells but epithelial tissue can regenerate. 
• B. Cartilage has limited blood supply while areolar tissue below the skin is vascular.  
• C. Cartilage has a more complex structure than epithelial or connective tissue proper, so it takes longer to heal. 
• D. The lacunae in cartilage make the healing process slower because the chondroblasts can't move.