Connective Tissue Proper: Dense Connective Tissue - Online Tutor, Practice Problems & Exam Prep

Dense connective tissue is categorized into three types: dense regular, dense irregular, and elastic connective tissue. Dense regular connective tissue features parallel collagen fibers, providing strength in one direction, found in tendons and ligaments. Dense irregular connective tissue has randomly arranged fibers, allowing strength in multiple directions, and is located in the dermis of the skin. Elastic connective tissue, dominated by elastic fibers, enables structures like arteries and lungs to stretch and recoil, essential for maintaining blood pressure and respiratory function.

Dense Connective Tissue

In this video, we're going to continue to talk about connective tissue proper as we begin our lesson on dense connective tissue. And so dense connective tissue, as its name implies, is going to be named for the dense arrangement of protein fibers in the extracellular matrix. Now, dense connective tissues are often going to be poorly vascularized, which means that they often are going to have very few blood vessels, especially in comparison to loose connective tissues, which recall from our previous lesson videos are very well vascularized, meaning they have lots of blood vessels. And so, because dense connective tissues are poorly vascularized with few blood vessels, this means that they receive relatively little nutrients from blood vessels. And that means that they are going to heal relatively slowly upon being damaged or injured.

In comparison to other types of tissues that are very highly vascularized and receive lots of nutrients from blood vessels. And those highly vascularized tissues tend to heal a lot more quickly because they receive the nutrients that they need in order to heal. Now the high and dense fiber content of dense connective tissue, again, the high amounts of protein fibers and the dense arrangement of the protein fibers in the extracellular matrix actually increases the strength of dense connective tissues. Now, really there are 3 different types of dense connective tissue, and those are dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue. And so, moving forward in our course, we're going to talk about each of these 3 dense connective tissues in their own separate videos.

But it is worthy of noting that these 3 different types of dense connective tissues are going to differ slightly in their fiber arrangements. But again, we'll get to talk more about that as we move forward in our course. And so, notice down below what we have is an image of our map of the lesson once again on connective tissue. And recall that connective tissues can be grouped into 2 major classes, connective tissue proper or general or fibrous connective tissue, and specialized connective tissue. Now, we'll talk about the specialized connective tissues later in our course.

Right now, we're focused on connective tissue proper. And we've already covered loose connective tissues, including areolar, reticular, and adipose tissues in our previous lesson videos. And so here in this video we're focused on dense connective tissue. And again, there are 3 types of dense connective tissues including regular, dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue. And so again, moving forward in our course, we're going to talk about each of these 3 different types of dense connective tissues in their own separate videos, starting with dense regular connective tissue.

And so this here concludes our brief lesson on dense connective tissues and I'll see you all in our next video to talk more details about dense regular connective tissue.

Dense Regular Connective Tissue

In this video, we're going to talk about the first type of dense connective tissue in our lesson, which is dense regular connective tissue. And so, of course, the word dense clearly indicates this is a type of dense connective tissue where the protein fibers in the extracellular matrix are going to be really densely arranged where they're packed really closely together. And the term regular indicates that the protein fibers create a regular pattern due to the parallel arrangement of the protein fibers. In terms of the characteristics, we can say that dense regular connective tissue is going to have a regular or a parallel fiber arrangement, which you can actually see in this little image here where you can see the fibers are, again, really densely packed together, but arranged in a regular pattern with a parallel fiber arrangement. Now, in terms of the composition, it's mostly going to be collagen fibers that are found in the extracellular matrix.

However, in some cases, there can be a smaller amount of elastic fibers. But again, it's mostly going to be collagen fibers. Recall from our previous lesson videos that collagen fibers are going to be made from smaller collagen proteins, which are non-elastic proteins that provide strength. These collagen fibers are going to be long and thick, unbranched or straight fibers, and that unbranched or straight fiber is going to allow collagen fibers to provide a lot of strength. And because dense regular connective tissues have mostly collagen fibers that provide a lot of strength, dense regular connective tissue is also known for its strength.

Now, in terms of collagen fibers, it is worthy of noting that they are not completely stiff structures and they do provide a little bit of flexibility. This is because collagen fibers are actually slightly wavy. If we take a look at this micrograph of dense regular connective tissue down below, notice the fibroblasts are going to be the darker spots that you see, and the collagen fibers are going to be really, really densely packed together. And again, collagen fibers are going to be slightly wavy. And so you'll notice that this micrograph has a little bit of a wavy pattern to it.

Because collagen fibers are slightly wavy, it gives them a little bit of flexibility when they are pulled upon and when they have tension. Those wavy collagen fibers can actually straighten out. And again, that gives it a little bit of flexibility. However, once those collagen fibers have been completely straightened out, that is when the strength of the collagen fibers really shows. Because once those collagen fibers are straightened out, those collagen fibers do not have a lot of give to them, and so they provide a lot of strength.

Now, unlike loose connective tissues, which tend to have a variety of different cell types, dense regular connective tissue primarily is going to have fibroblasts that actively secrete and build components of the extracellular matrix. And so it tends to lack a variety of other cell types, including adipocytes or fat cells, and migratory immune cells that defend against infection. And also, unlike loose connective tissues which are very well vascularized with lots of blood vessels, dense regular connective tissue is actually pretty poorly vascularized, which means that it's going to have very few blood vessels and ultimately that means dense regular connective tissues have a tendency to heal slowly. Since they are poorly vascularized, they receive relatively little nutrients from the few blood vessels that it does have. And receiving relatively little nutrients ultimately leads to slow healing upon being damaged and injured.

Now, in terms of the function, again, because it's made of mostly collagen fibers, it's no surprise that it's going to be specialized for strength. However, because these fibers are arranged in a parallel fashion, where they're all going to be parallel to one another forming that regular pattern, it's actually only going to provide strength mainly in one direction, where the forces of the pulling forces and tension are actually going to be parallel to the axis of those parallel fibers. And so, that means that really it only provides strength in one particular direction either, you know, one particular plane, either to the left or to the right, but not multiple directions. Now, in terms of the locations where we can find dense regular connective tissue, it's important to note that they can be found in ligaments, tendons, or fascia. Now, ligaments are going to be structures that connect bone to bone, tendons are going to be structures that connect muscles to bone, and then fascia is going to wrap muscle.

Notice over here in this image, we're showing you some bones being connected to other bones through ligaments. And again, those ligaments are made of dense regular connective tissue. And then in this little image, we're showing you muscles being connected to bone through tendons. And again, tendons are going to be formed through dense regular connective tissue. And then notice here we're showing you fascia, which is going to wrap around muscles, and again, that is going to be made in some cases by dense regular connective tissue.

And so it's really important for structures such as ligaments and tendons to have a lot of strength because when muscles contract, they're going to be connected to bones through tendons. And so the tendons need to have a lot of strength because they need to be able to pull the bones in a particular direction in order to move those bones. The same goes for ligaments, ligaments need to be really strong because again, when they move, they need to be able to hold the bones together for proper movements. And so, this here concludes our lesson on dense regular connective tissue, and as we move forward in our course, we'll be able to apply these concepts and learn more about other types of dense connective tissue. I'll see you all in our next video.

Connective Tissue Proper: Dense Connective Tissue Example 1

So here we have an example problem that asks what type of connective tissue is shown in the image below? And we've got these 4 potential answer options. And so when we take a closer look at this micrograph of the tissue, notice we're focusing on the pink colored tissue. And notice that the darker spots that you can see throughout this tissue represent the nuclei of the fibroblasts. And also notice that the protein fibers in the extracellular matrix are really very densely packed together.

And notice that the protein fibers form a regular pattern because those protein fibers are arranged in a parallel fashion. And so, what this means is that we are going to have dense regular connective tissue here. And so notice answer option C suggests dense regular connective tissue. And so, option C is going to be the correct answer for this example problem. Now, option A says areolar connective tissue, but recall that it is a type of loose connective tissue that has very loosely arranged protein fibers in a random direction and creates those pores or small open spaces.

And again, we don't really see that in this really densely packed region of the tissue, so we can eliminate option A. Option B says dense irregular connective tissue, which we have not yet covered in our previous lesson videos, but we will cover in our next lesson video. So we should have been able to eliminate option B. And then option D is dense elastic connective tissue, which, again, we have not yet covered in our previous lesson videos and we'll cover moving forward in our course. So again, we could have eliminated option D for those reasons.

And so this is option C is the correct answer to this example, and that concludes this example. So I'll see you all in our next video.

What feature about dense regular connective tissue makes them well suited for tendons?

• A. The uniform direction of fibers make it extremely strong.
• B. The multidirectional fibers withstand forces from different directions.
• C. The elastic fibers optimize for recoil.
• D. The high adipocyte content cushions joints.

Dense Irregular Connective Tissue

In this video, we're going to talk about the second type of dense connective tissue in our lesson, which is dense irregular connective tissue, which is pretty much made of the same structural components as dense regular connective tissue. And the biggest difference is that the protein fibers in the extracellular matrix are going to form an irregular or a random protein fiber arrangement. And so we can say that dense irregular connective tissue is going to have really densely packed protein fibers in the extracellular matrix that form an irregular or a random protein fiber arrangement instead of being in a parallel arrangement like dense regular connective tissue. Now, in terms of the composition, again, it's mostly going to be collagen protein fibers that make up the fibers in the extracellular matrix. However, there can be a smaller amount of elastic protein fibers as well.

But, again, it's mostly collagen fibers. And so recall that the collagen fibers are made up of smaller collagen proteins, which are non-elastic proteins that are designed for strength. And so recall that these collagen fibers are going to be relatively long, thick, unbranched, and straight protein fibers, which give them a lot of strength. However, the collagen fibers are not completely stiff, and they have a little bit of a wave to them, which gives them a little bit of flexibility. But, again, once those fibers have been straightened out, that is when their strength truly shows because they are going to, again, resist pulling forces and tension.

Now in terms of the function, because the collagen fibers are randomly arranged in all kinds of directions, this means that dense irregular connective tissue is going to be specialized for strength, but actually in multiple different directions, unlike being specialized for strength in just one particular direction along the axis of the parallel fibers in dense regular connective tissue. And so because these fibers are, again, randomly arranged in dense irregular connective tissue, that means that all of the fibers are not going to be working together in the same direction. And so that means that it's not going to be quite as strong as dense regular connective tissue, which has parallel arranged collagen fibers that are all working in the same direction. And so in terms of its functions, it is going to provide structural strength and protection, again, because it can resist forces in multiple directions. And so we can expect to find it in locations of the body where they need to be able to resist forces in multiple directions.

For example, dense irregular connective tissue is actually going to be found beneath the areolar loose connective tissue in our skin. And so, dense irregular connective tissue actually makes up the larger portion of the dermis, which is part of our skin. And there, it's going to help prevent the tearing of the skin, again, because it can resist forces in multiple directions. Dense irregular connective tissue can also be found wrapping joints, organs, such as the heart, for example. It makes up the pericardium around the heart or part of it, and it can be found wrapping around bones as well.

Notice here we have an image showing a diagram of the skin. Recall from our previous lesson videos that the outermost layers of the skin are made of an epithelial tissue known as stratified squamous epithelia, which is this outer layer that you can see highlighted right there. And then beneath that, this light blue layer that's very thin represents the areolar connective tissue, a type of loose connective tissue that we talked about in our previous lesson videos. And then beneath the areolar connective tissue, as we indicated over here in the text, is going to be where the dense irregular connective tissue can be found in the skin. And so that's going to be represented by this darker, larger blue region that you can see indicated here.

The dense irregular connective tissue makes up the vast majority of the layer of the skin known as the dermis. And there, it's going to provide, again, resistance to forces in multiple directions, which are really important for the skin to have. In fact, an interesting note is that the product leather is made from the dermis of animal skins. And in the dermis, again, it's made of mostly dense irregular connective tissue. And the ability for dense irregular connective tissue to resist forces in multiple directions is what gives the product leather its durability.

Now, beneath the dense irregular connective tissue is a layer known as the subcutaneous layer, which is mostly made of adipose tissue. Later in our course, in a different chapter when we're talking about the integumentary system, we're going to talk a lot more details about the skin and so we'll revisit all of this again. Dense irregular connective tissue, again, can also be found wrapping joints. Notice here, we can see the dense irregular connective tissue wrapping the joints, again, allowing it to resist forces in multiple directions, which are important for joints. Notice here, we have a micrograph of the dense irregular connective tissue.

What you'll notice is that the fibers are going to be very thick fibers. And the darker spots that you can see in a purplish or bluish color, those are the fibroblasts. And so notice that, again, the fibers are going to be made of mostly collagen fibers. And you can see that they have some regions here that are kind of longitudinal, you know, collagen fibers. But then there are other regions that you can clearly see are more dense and irregularly shaped, collagen fibers.

These irregularly shaped collagen fibers that have this random arrangement allow this entire dense irregular connective tissue to resist forces again in multiple different directions. And so this here concludes our lesson on dense irregular connective tissue. Moving forward, we'll be able to apply these concepts and talk about the last type of dense connective tissue. I'll see you all in our next video.

Putting It Together: What is Under Your Skin?

So now that we've covered loose connective tissues and some types of dense connective tissues, in this video, we're going to be putting it all together and briefly talking about what's under your skin. Now, it's important to note that later in our course in a different chapter when we're talking about the integumentary system, we'll talk a lot more details about the skin. But here in this video, we're only briefly going to talk about what's under your skin. And so there are actually many layers of connective tissue and epithelial tissue that come together to create the skin. And so notice down below we have a diagram showing you what's under our skin.

And notice on the left, we are focusing on the layers, whereas on the right, we have the functions for each of those layers. And so recall from our previous lesson videos that the outermost layers of our skin are made of epithelial tissue. And so notice that the outermost layer here, again, is made of epithelial tissue. More specifically, stratified squamous epithelium, which recall means that it's going to have multiple layers of these flat or squished cells on the apical surface. And the stratified squamous epithelium actually has multiple functions, but its primary function is protection.

It does protect, and it protects by preventing chemicals and microbes from penetrating through the skin into deeper tissues. Now, beneath the stratified squamous epithelium is areolar connective tissue, which recall is a type of loose connective tissue. And it is going to be highly vascular, meaning it has lots and lots of blood vessels, which is going to allow it to support the epithelial tissue which is avascular. Now, notice beneath the areolar connective tissue here in this darker blue region, we have the dense irregular connective tissue where the collagen fibers in the extracellular matrix take on an irregular or random fiber arrangement, which allows it to resist multidirectional forces, which is important for the skin to be able to do. And so notice that the dense irregular connective tissue here is making up a pretty large portion of the skin.

Now deeper to the dense irregular connective tissue is the subcutaneous layer, which contains adipose connective tissue. And adipose connective tissue has multiple functions including providing insulation, helping to keep the body warm. And so once again, later in our course, we'll talk a lot more details about the skin, but hopefully, this little diagram here putting it all together was helpful to show you how the skin comes together with these multiple layers of connective tissue and epithelial tissue. So, that concludes this video and I'll see you all in our next video.

Connective Tissue Proper: Dense Connective Tissue Example 2

So here we have an example problem that asks what property of dense irregular connective tissue makes it well suited to withstand the wear and tear experienced by the skin. And we've got these 4 potential answer options down below. And so recall from our previous lesson videos that dense irregular connective tissue does not have a uniform direction of fibers because those fibers are irregularly or randomly arranged. And it's actually dense regular connective tissue that has the uniform direction of fibers since those fibers are arranged in a parallel fashion. And so because of this, we can actually eliminate answer option a.

Now notice option b says, the multidirectional collagen fibers resist force from multiple different directions. And so this is actually going to be the correct answer. Again, recall that the collagen fibers in dense irregular connective tissue are irregularly or randomly arranged, and that random arrangement allows those collagen fibers to provide strength and resist forces from different or multiple directions. And so answer option b is going to be the correct answer for this example problem. Now notice option c says the elastic fibers optimize for recoil.

Now recall that there can be elastic fibers in the extracellular matrix, but they're going to be in much smaller amounts than the collagen fibers. So for that reason, we can eliminate answer option c. And also those elastic fibers are not going to help with the wear and tear, if you will, because they don't necessarily provide strength. They provide a little bit of flexibility, which can also be important for wear and tear. But again, it's more the multidirectional collagen fibers that are going to make the skin well suited for wear and tear.

Now answer option d says the high adipocyte content cushions the skin. But recall from our previous lesson videos that dense irregular connective tissue, like dense regular connective tissue, does not have a variety of cell types like loose connective tissue does. And so it actually does not have a high adipocyte content. And so for that reason, we can eliminate option d. So again, option b here is the correct answer to this example.

So I'll see you all in our next video.

Elastic Connective Tissue

In this video, we're going to talk about the 3rd and final type of dense connective tissue in our lesson which is elastic connective tissue. And so elastic connective tissue is sometimes considered a subtype of dense regular connective tissue because they both have really densely arranged protein fibers that form a regular or a parallel protein fiber arrangement. And so notice here in this little image, you can see the densely packed and parallel arranged protein fibers in the extracellular matrix of elastic connective tissue, which we saw was also the case for dense regular connective tissue. And so really the way that dense regular connective tissue differs from elastic connective tissue is as its name implies with the term elastic, elastic connective tissue has an extracellular matrix dominated by elastic protein fibers. And so the elastic protein fibers are going to outnumber the collagen fibers, which recall was the opposite for dense regular connective tissue, which had mostly collagen fibers and smaller amounts of elastic fibers.

And so recall from our previous lesson videos that elastic protein fibers are made of the smaller protein elastin, which is going to 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, again, because elastic connective tissue has an extracellular matrix dominated by elastic protein fibers, that's going to contribute directly to its function, which, elastic connective tissue is actually specialized for elasticity. Again, which refers to its ability to stretch and, again, return back to its original shape after stretching. And so, elastic connective tissue is going to be really important for body structures that need to rely on the elastic ability, so that they can bend, expand, and contract. And so for example, we can expect to find elastic connective tissue and body locations such as the walls of arteries including the aorta, which is the artery highlighted here coming out of the heart, which need to be able to expand when larger volumes of blood are coming through, but then recoil back to its original shape in order to maintain blood pressure.

We can also find elastic connective tissue in the respiratory passageways including the trachea, the bronchial tubes, and other lung tissue as well, which need to be able to expand when we inhale and then recoil back to its original shape when we exhale. And we can also find elastic connective tissue in the ligaments of the spine, for example, which allows our spine to have some flexibility and allows us to be able to bend, for example. And so notice over here, we have a micrograph of elastic connective tissue. And what you can clearly see is that it is going to be it's going to have these really densely arranged elastic fibers in a regular or parallel fashion. And so you can see here, I'll use a different color, green so that you can see better, that these elastic fibers are very wavy and they can also be branched.

And what you'll notice is that they're really densely packed together. And because of these elastic fibers, this is what really gives elastic connective tissue its elastic ability. And so this here concludes our lesson on elastic connective tissue. And as we move forward, we'll be able to apply these concepts. So I'll see you all in our next video.

Connective Tissue Proper: Dense Connective Tissue Example 3

So here we have a true or false example problem that says, elastic connective tissue is high in adipocytes. And so we've got 2 potential answer options down below. Option A says, true elastic connective tissue has high quantities of adipocytes to assist in recoil. And then option B says false, elastic connective tissues has high quantities of elastic fibers to assist in recoil. And so recall from our previous lesson videos that adipocytes are fat cells, and so they store fats or triglycerides as these relatively large lipid droplets within the cell.

And so these adipocytes can be found in loose connective tissues, including adipose connective tissue and areolar connective tissue. But these adipocytes are not found in dense connective tissues, including elastic connective tissue, which is a type of dense connective tissue. And so these adipocytes are not going to play a role in recoil. And so, that's another way we could have eliminated this option. And so, option A is not going to be correct.

It's option B that is the correct answer to this example, which says false, elastic connective tissue has high quantities of elastic fibers to assist in recoil. And so we can go ahead and indicate that option B here is the correct answer to this example. That concludes this example, so I'll see you all in our next video.

Marfan syndrome is a genetic condition that affects production and maintenance of elastic fibers in the ECM. Based on this information, what may be a regular serious complication of Marfan syndrome?

• A. An inability to store nutrients as production of adipose tissue is inhibited significantly.
  
• B. Regular rupture of ligaments as the fibers in dense regular connective tissue would not be produced properly.
  
• C. Hyper elasticity of skin as dense irregular connective tissue of the dermis would stretch more.
  
• D. Rupture of the aorta, as elastic connective tissue in large blood vessels allows for stretching and recoil.

During a dissection, you are asked to identify a tough connective tissue that connects 2 of the bones of the arm. What type of connective tissue makes up that structure?

• A. Dense Regular Connective Tissue.
• B. Dense Irregular Connective Tissue.
• C. Dense Elastic Connective Tissue.
• D. Cartilage.

Review of Dense Connective Tissues

In this video, we're going to review the three different types of dense connective tissues. Since this video serves as a review, there's no new information covered that we haven't already discussed in our previous lessons. Therefore, if you're already confident about dense connective tissues, you can skip this video. However, if you need a refresher, stick around as this video could be beneficial for you. Below, we have a table listing the different types of dense connective tissues.

Notice the first column lists the particular type, the second column covers some key characteristics, the third column describes important functions, and the fourth column provides example locations where these tissues can be found in the body. It's key to remember that all dense connective tissues will have densely packed protein fibers in their extracellular matrix. We initially discussed the first type, dense regular connective tissue, which is characterized by a regular or parallel arrangement of the collagen fibers in the extracellular matrix, predominated by collagen fibers. Despite having a few elastic fibers, collagen is the main component. These fibers are designed to be strong, yet they offer some flexibility as well. Dense regular connective tissue lacks adipocytes or fat cells and migratory immune cells and is poorly vascularized, meaning it has few blood vessels. This trait is common to all dense connective tissues, contributing to their slow healing process.

The provided micrograph shows the densely packed collagen fibers in a parallel or regular arrangement, with a slight waviness that allows for some flexibility. However, once these fibers straighten, their strength is pronounced, as they offer little stretch once aligned. Functionally, because the parallel collagen fibers work together in one direction, they provide significant strength but specifically in the direction of the fibers' alignment, either from right to left or left to right. Example locations for dense regular connective tissue include forming ligaments, connecting bones to bones; tendons, connecting muscles to bones; and fascia, wrapping around muscles.

The next type we covered is dense irregular connective tissue, structurally similar to dense regular connective tissue but with protein fibers in an irregular or random arrangement. Like its counterpart, it is predominantly made of collagen fibers that provide strength. However, the random arrangement allows for strength in multiple directions, enhancing its ability to resist forces from various angles. Dense irregular connective tissue can be found beneath areolar tissue in the skin, wrapping joints, organs, and bones, helping to prevent tearing by resisting multidirectional forces. This tissue type's random fiber arrangement is what allows products like leather, derived from the dermis of animal skins, to be so durable.

Lastly, we reiterate our discussion on elastic connective tissue, sometimes categorized as a subtype of dense regular connective tissue due to its regular or parallel fiber arrangement. The primary difference is that elastic connective tissue contains a high proportion of elastic fibers, which outnumber the collagen fibers. Elastic fibers provide the ability for tissues to stretch extensively and then return to their original shape. This quality is essential for body structures requiring flexibility to bend, expand, and retract. Elastic connective tissue is found in the walls of arteries, such as the aorta, respiratory passageways including the trachea and bronchial tubes, and in the ligaments of our spine, accommodating movement and flexibility.

This concludes our review of dense connective tissues. Moving forward, we will apply these concepts and then explore specialized connective tissues. I'll see you all in our next video.

An anterior cruciate ligament (ACL) tear is a common knee injury among athletes. The function of ligaments is to attach bones to each other and keep them stable. Given what you know about connective tissue, what type of tissue do you expect would be involved?

• A. Loose Connective Tissue Proper. 
• B. Dense Regular Connective Tissue.
• C. Areolar Connective Tissue. 
• D. Dense Irregular Connective Tissue.