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

Loose connective tissue includes three main types: areolar, reticular, and adipose connective tissue. Areolar connective tissue, known as the universal packing material, supports and binds organs, while reticular connective tissue forms internal scaffolding for soft organs like lymph nodes and the spleen. Adipose connective tissue, primarily composed of adipocytes, stores energy as triglycerides, provides insulation, and cushions organs. Each type plays a crucial role in maintaining structural integrity and supporting various bodily functions, highlighting the importance of connective tissues in overall health.

Loose Connective Tissue

In this video, we're going to continue to talk about connective tissue proper as we begin our lesson on loose connective tissue. And so loose connective tissue, as its name implies, is going to be a connective tissue named for its loose arrangement of protein fibers found in the extracellular matrix. Now, loose connective tissues are often going to be vascular, which means that often loose connective tissues are going to have blood vessels in them. Now, loose connective tissue is commonly known as the packing material of the human body. And this is because loose connective tissues are found all throughout the body in various locations, including in the spaces in between organs as well as underneath the epithelia throughout pretty much the entire body, and it can form the internal structural framework inside of some organs.

Now, really there are 3 different types of loose connective tissue. And so those 3 different types of loose connective tissue are areolar connective tissue, reticular connective tissue, and adipose connective tissue. And so moving forward in our course in different videos, we're going to talk a lot more about details concerning each of these 3 different types of loose connective tissue. Now, it is worth noting that these three types of loose connective tissue actually differ from each other in terms of their protein fiber arrangement in their extracellular matrix, in terms of the amount and the types, and they also differ from each other in terms of the cell types. And we'll be able to talk more about that as we move forward talking about each of these 3 types in their own separate videos.

And so notice down below, what we have is the map of our lesson, which we've seen before in some of our previous lesson videos. And so again, we know that connective tissue 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 in different videos. Right now, we're focused on connective tissue proper, more specifically, on loose connective tissues. And, of course, we've introduced here that there are 3 different types of loose connective tissues, including areolar connective tissue, reticular connective tissue, and adipose connective tissue.

And so once again, we'll talk about each of those 3 different types of loose connective tissues moving forward in our course, but for now, this here concludes our brief introduction to loose connective tissues, and so I'll see you all in our next video to talk more details about areolar connective tissue.

Areolar Connective Tissue

In this video, we're going to talk about the first type of loose connective tissue in our lesson, which is areolar connective tissue. And so, the word areolar is actually a Latin term that means small open spaces. And so what you'll notice is down below in the micrograph of areolar connective tissue, there appear to be all of these small open spaces or pores throughout the entire tissue. And so this is a direct result of the loosely arranged protein fibers in the extracellular matrix. And so notice that all of these lines that are striking through this micrograph here are all of the protein fibers in the extracellular matrix.

And notice that these protein fibers are all loosely arranged in areolar connective tissue in such a way that it appears to create all of these small open spaces. And so, hopefully, all of this is a helpful reminder for you that areolar connective tissue is a type of loose connective tissue with these loosely arranged fibers that seem to create all of these small open spaces in areolar connective tissue. Now, areolar connective tissue is actually the most widely distributed connective tissue in the human body. And so it can actually be found in pretty much all areas of the human body. Now, areolar connective tissue is commonly referred to as the universal packing material of the human body.

Again, because it's so widely distributed and can be found in areas such as the spaces in between organs, and so it can wrap those organs and cushion and bind those organs together. It can be found around blood vessels and nerves and muscles, and areolar connective tissue is also found supporting the epithelial tissue throughout pretty much the entire body. And so notice over here on the right, we have a diagram that is showing you the epithelial tissue here. And notice that immediately beneath the epithelial tissue, we have the basement membrane. And notice that immediately beneath the basement membrane is areolar connective tissue, a type of loose connective tissue.

And recall from our previous lesson videos that often loose connective tissues are vascular, and that does apply to areolar connective tissue. It is vascular, which means that it contains blood vessels. And those blood vessels in the areolar connective tissue can support the avascular epithelium by providing nutrients and helping to eliminate waste. Now, in terms of the composition, areolar connective tissue actually has all three types of protein fibers, including collagen fibers, reticular fibers, and elastic fibers, and that's going to contribute to its diverse functions. Now, also, because areolar connective tissue is a type of loose connective tissue and loose connective tissue is a type of connective tissue proper, recall from our previous lesson videos that connective tissue proper tend to have a gelatinous ground substance that is a semi-fluid, something in between a solid and a liquid.

And so that means that the ground substance is going to be somewhat viscous or thick and that's going to create a somewhat thick matrix. Now, in terms of the composition of cells, areolar connective tissues can have a bunch of different types of cells, including the fixed and resident cells associated with connective tissue proper, including fibroblasts, which again are blast cells that are going to actively secrete and build components of the extracellular matrix, including the ground substance and the protein fibers. And it's also going to include fibrocytes, which are going to be less active and are going to more maintain the extracellular matrix with minor repairs and routine maintenance. Now, areolar connective tissue is also going to have migratory immune cells, including mast cells, which are going to release the chemical histamine that is important for inflammation. And also, it includes the migratory macrophages, which are going to be important for phagocytosis, which is essentially engulfing pathogens for elimination.

Also, areolar connective tissue has adipocytes, which are fat cells, and these adipocytes are going to be considered a fixed or resident cell that is found in areolar connective tissue. Now, these adipocytes, which are fat cells, again, they store fat molecules, which can actually be used as a nutrient for long-term energy storage. And also, those fat cells or adipocytes with all of that fat can provide insulation as well. Now, in terms of the functions, areolar connective tissues have many different functions. But here in this video, we're going to focus on 3 main functions that they have.

And so, the first is supporting and binding. Again, we know that areolar connective tissue is going to support the epithelial tissue cells. Again, areolar connective tissue is vascular, and so it can support the epithelial tissue since, again, areolar connective tissue is usually found immediately underneath the epithelial cells, right underneath the basement membrane. And in terms of binding, again, areolar connective tissue can be found in it's it basically serves as the universal packing material. And so, it can be found in the spaces in between organs and help to provide cushioning and bind those organs together.

And also, it can help to essentially bind the epithelial tissue, the areolar connective tissue can bind the epithelial tissue to any underlying tissues that are beneath. Now, because areolar connective tissue has these migratory immune cells, including mast cells and macrophages, it can actually be really important for protecting, and protecting against infection and invaders. And so this is also a really intuitive way to understand why areolar connective tissue is found throughout the entire body. Because at any point in time, any location of our body can become infected. For, for example, if we get a cut in any region of our body, it can get infected.

And so, we need to be able to have areolar connective tissue in many regions of our body in order to help protect us against infection. And also, areolar connective tissue because it does have these small spaces and pores, it can actually serve as a reservoir for water and fluids and nutrients. And so actually storing nutrients is a function of areolar connective tissue. So it can store nutrients and fluids. And again, areolar connective tissue is vascular, meaning it has blood vessels.

And so those blood vessels deliver the nutrients to the areolar connective tissue where those nutrients and fluids can be stored and the areolar connective tissue can supply nutrients and fluids to the epithelia, for example, and other surrounding tissues. Now, in terms of the locations, again, areolar connective tissue, the universal packing material of the body is found all throughout the body in various locations, including underneath the epithelia pretty much throughout the entire body. And so, again, over here, you can see in the micrograph that these darker red spots are actually the nuclei of the cells, likely the fibroblasts or the fibrocytes. And, again, the fibers are going to be all of these lines that you can see striking through the extracellular matrix. And so this here concludes our lesson on areolar connective tissue.

And as we move forward in our course, we'll be able to apply these concepts and problems and also learn more about other types of loose connective tissue. So I'll see you all in our next video.

Connective Tissue Proper: Loose Connective Tissue Example 1

So here we have an example problem that asks, how does the structure of areolar connective tissue help it act as packing material? And we've got these 4 potential answer options down below. Now option a says that the ground substance holds fluid. And so recall from our previous lesson videos that areolar is actually a term for small open spaces, which you can actually see under the light microscope is due to the loose arrangement of protein fibers in the extracellular matrix. And so because areolar connective tissue has those small open spaces or that porous look to it, it's actually able to serve as a reservoir for nutrients and fluids.

And also recall that areolar connective tissue is a type of loose connective tissue, which is a type of connective tissue proper. And recall from our previous lesson videos that connective tissue proper tends to have a gelatinous ground substance that is somewhat of a semi-fluid in between a solid and a liquid. And so because it does have this semi-fluid ground substance, it does allow the ground substance to store some fluid. And so option a is actually going to be true. Now notice option b says a combination of branched and straight fibers create strength.

Now recall from our previous lesson video that areolar connective tissue actually has all three of the protein fibers in its extracellular matrix, including collagen fibers, reticular fibers, and elastic fibers. And recall that the term reticular in reticular fibers is a term that means netlike. And so that reminds us that reticular fibers have collagen proteins arranged in a net-like or a branched fashion. And so for sure, we know it's going to have branched fibers. And also elastic fibers can also be branched and wavy.

Now we know that collagen fibers are actually going to have their collagen proteins arranged in an unbranched or straight pattern. And so, of course, this means that a combination of branched and straight fibers are going to be present, and that's going to help create strength because having straight fibers like collagen fibers creates strength in one particular direction in terms of how it's arranged, and branched fibers can actually create resistance to forces in multiple directions. And so that's going to give it a lot of strength and a lot of versatility. And so option b is also going to be true. And so notice option c says the presence of adipocytes acts as cushions and recall that adipocytes are fat cells that store lipids and so those lipids can actually serve as long term energy storage and they can help provide a cushion and insulation.

And so these adipocytes are found in areolar connective tissue. And so also option C is correct as well. And so this means that answer option D, all of the above is going to be the correct answer for this example problem. And so all of these are going to help areolar connective tissue have the properties that it needs to serve as the universal packing material in the human body. So that concludes this example, and I'll see you all in our next video.

Reticular Connective Tissue

In this video, we're going to talk about the second type of loose connective tissue in our lesson, which is reticular connective tissue. And so recall from our previous lesson videos that one of the 3 protein fibers that can be found in the extracellular matrix are reticular protein fibers. And so it's no surprise that reticular connective tissue is only going to have those reticular protein fibers in its extracellular matrix, which is why reticular connective tissue is called reticular. And, also, this is why the fibroblasts of reticular connective tissue are actually called reticular cells. Because, again, these reticular cells only produce those reticular protein fibers in the extracellular matrix.

Now because there are only reticular fibers in the extracellular matrix of reticular connective tissue, what this means is that the other two types of protein fibers, including collagen fibers and elastic fibers, are not found in their extracellular matrix, which means that the extracellular matrix of reticular connective tissue is going to have a lack of structural diversity. And that lack of structural diversity is going to lead to a lack of functional diversity in reticular connective tissue as well. Now recall that the term reticular is actually a term that means netlike. And so this reminds us that those reticular protein fibers are going to have those collagen proteins arranged in a netlike or a branched structure. And that branch structure actually allows it to resist forces in multiple directions, which is really important for being able to provide structural support.

And so reticular connective tissue is going to be important for providing structural support by, again, using its branched reticular protein fibers in its extracellular matrix. Now, in addition to the reticular cells and reticular connective tissue, there can also be a host of other migratory immune cells in reticular connective tissue as well. Now, in terms of the functions of reticular connective tissue, here in this video, we're only going to focus on one main function of reticular connective tissue, and that is going to be that reticular connective tissue forms the internal scaffolding for soft organs, such as, for example, the lymph nodes, the spleen, the liver, the kidneys, the thymus, and the bone marrow, for example. And so because reticular connective tissue does form the internal scaffolding providing structural support in these soft organs, it means that reticular connective tissue is going to support the functions of each of these soft organs. For example, reticular connective tissue with its branched reticular fibers can actually be used to filter dead blood cells in the spleen, and it can also be used to filter microbes in the lymph nodes, for example.

And in the bone marrow, reticular connective tissue is going to provide the structural framework for hematopoiesis to occur, which is actually the process of blood formation, which again occurs in the bone marrow. And so, again, what we're saying here is that reticular connective tissue, because it provides that structural support and that internal scaffolding framework inside of these soft organs, it's going to support the functions of each of these organs. And so notice over here on the right, we're showing you an image of a person and you can see the lymphatic vessels going through this person here. And each of these bulges that you can see throughout the lymphatic vessels represent lymph nodes. And again, we know that reticular connective tissue is going to form the internal structural framework of these lymph nodes as well as the bone marrow, and the bone marrow is found inside of the bones as you can see in this little image.

It's also going to form the internal structural framework of the kidneys, of the spleen, the liver, and the thymus as well. And so notice here we have a micrograph that's showing you reticular connective tissue where you can see all of these reticular cells. And in some micrographs, you're actually able to see the reticular fibers that are branching through the extracellular matrix. With the proper staining for a certain, you can see them. And in this particular micrograph, they're a little bit harder to see, but they can be seen.

And so this here concludes our lesson on reticular 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 loose connective tissue. So I'll see you all in our next video.

Adipose Connective Tissue

In this video, we're going to talk about the 3rd loose connective tissue in our lesson, which is adipose connective tissue. And so as its name implies, what the term adipose, adipose connective tissue is going to be composed mostly of adipocytes, which, recall from our previous lesson videos, are fat cells that store fats or triglycerides as these relatively large lipid droplets that take up most of the volume of the adipocyte and push off its cytoplasm and organelles, including its nucleus off to the periphery or the perimeter of the adipocyte. And so notice if we take a look at this micrograph of adipose connective tissue, that the adipocytes or fat cells are being indicated as these circular white cells that you can see throughout the tissue. And so the white component of these cells is actually that relatively large lipid droplet made of fats or triglycerides that, again, takes up most of the volume of the adipocyte and pushes off its cytoplasm and organelles, including the nucleus off to the periphery or the perimeter of the cell. And although that's the case, these adipocytes are still functional cells, and so they can still secrete components, including components of the extracellular matrix, such as ground substance and protein fibers.

However, the extracellular matrix in adipose connective tissue is going to be sparse. And so it does have a sparse matrix, which means that it has relatively little extracellular matrix. And so that's why these adipocytes in the adipose connective tissue appear to be really tightly packed together as you can see in the micrograph. However, although they appear to be really tightly packed together, these cells are still very loosely arranged, which is why this is a loose connective tissue. And so each of these adipocytes, although they appear to be tightly packed together, they can actually enlarge in their size as their lipid droplet enlarges when they store more lipids or more fats.

And they can also decrease in their size as they release fats to the body, which can be used as energy in other locations of the body. And so it's important to note that adipose connective tissue is actually a highly vascularized tissue, which means that it's going to have many, many blood vessels, which is really important for the adipose connective tissue to receive nutrients that it can ultimately store as fats or lipids in the lipid droplet. And it's also important for the adipose connective tissue to release lipids or fats into the bloodstream, which again can be transported to other areas of the body and utilized as energy. And so, really, one of the most important characteristics to note about adipose connective tissue is that it is able to store energy by storing these lipid or fat or triglyceride molecules. And also, those lipids can serve to insulate the body to keep it warm due to its high adipocyte content.

Again, lots and lots of adipocyte storing lots of fat. And so it can also provide a cushion in order to serve some protective features as well. And so in terms of the functions, adipose tissue can have many different functions, but here we are highlighting 3 main functions of adipose tissue. The first is going to be to store nutrients and energy. Again, we know that these adipocytes have a relatively large lipid droplet that is storing fats or triglycerides, and so it can actually store those molecules for a long period of time, and then it can release components of fats into the bloodstream where, again, they can be transported to other areas of the body and utilized as energy when the body needs it.

Now another function of adipose tissue is that it is going to protect by absorbing shock. Again, it can provide some cushioning and that cushioning can help to provide a little bit of protection. And then the third function is that adipose connective tissue can serve to insulate the body and keep the body warm. And so we'll find that adipose connective tissue is actually found in the deep or deep to the layers of the skin. And so you can see it's, deep, it's gonna be found deep to the layers of the skin in the, what's known as the subcutaneous layer.

And so there it is actually going to help insulate the body and keep the body warm, preventing the body from losing too much heat. Now, the adipocytes or adipose tissue can actually be found in several different areas of the body. It cannot actually be found anywhere where areolar connective tissue is found. And so we know areolar connective tissue can be found all throughout the body. And so, adipose tissue can also be found all throughout the body, including the abdomen or the stomach area, if you will, around the eyes to provide cushioning and protection around the eyes and also around organs such as the kidneys and the heart, for example, which may need additional, you know, fat molecules for energy and even in the breasts, for example.

And so notice over here in our diagram, we are showing you how, in the top left, this is representing the skin and what you'll notice is that the outermost layers of the skin are made of epithelial tissue. Immediately beneath that, we talked about how areolar connective tissue is supporting the epithelial tissue, that's a type of loose connective tissue. Then this darker blue area that you can see here, that's actually representing dense irregular connective tissue, which we have not yet talked about. We'll talk about that later in our course, but you'll notice that this is really the skin, that layer there, and then notice that immediately beneath the skin, this yellow layer here, this is the adipose connective tissue, which is found in the subcutaneous layer. Again, deep to the outermost layers of the skin here or deep to these particular layers that I indicated of the skin.

Now you can also find adipose tissue all throughout the body, including around the eyes here. As you can see, these yellow areas represent adipose tissue, again, providing cushioning and protection for the eyes. And it can also be found in the abdomen and it's found in all people and it can also be found in regions of the body that are genetically controlled. And so, some people can accumulate fat in areas such as underneath their chin or in their back or, in their hips and their thighs and things like that. So it can have a genetic component to it in terms of where the adipose tissue tends to accumulate.

And so this year concludes our lesson on adipose connective tissue and we'll be able to get some practice applying these concepts and learn about 2 different types of adipose connective tissue as we move forward in our course. So I'll see you all in our next video.

Types of Adipose Tissue

In this video, we're going to talk about 2 different types of adipose tissue. The first being white adipose tissue or white fat, and the second being brown adipose tissue or brown fat. The color of these tissues does not play a significant role in skin pigmentation or skin color. Instead, the color of these tissues indicates what they appear to look like under a light microscope. White adipose tissue or white fat is going to appear white under a light microscope.

Whereas brown adipose tissue or brown fat is going to have a more pigmented, darker brownish color to it under a light microscope. In our last lesson video, the adipose connective tissue that we mostly referred to was white adipose tissue or white fat since it is the most abundant adipose tissue in adults. It's important for storing energy, as adipocytes or fat cells can store fats or triglycerides as these relatively large lipid droplets. They can break down those lipids and release them into the bloodstream where they can be transported throughout the body and utilized as an energy source.

White adipose tissue can be found below the skin all throughout the body in regions known as the subcutaneous layer, which we'll talk more about later in our course. It can also be found in the visceral layer around some organs, such as the kidney and the heart. It's important to note that adipocytes do not grow through traditional cell division. Instead, adipocytes grow in size, but not via cell division. There are precursor cells that can differentiate into adipocytes to create more adipocytes.

Mature adipocytes do not go through cell division in the traditional way to create more adipocytes. Instead, they grow in size and allow the lipid droplet to also grow. When a surgery such as liposuction occurs, where it essentially sucks out most of the adipose tissue in regions of the body, the remaining adipose tissue and adipocytes are still able to enlarge in size. It is still possible for people to gain weight even after a surgery such as liposuction that removes a lot of the adipose tissue.

Now, when it comes to brown adipose tissue or brown fat, it can still be found in limited amounts in specific regions of adults. However, brown adipose tissue or brown fat is much more common in infants or babies. The brownish coloration of brown adipose tissue is because it is more highly vascularized than white adipose tissue, and the mitochondria in brown adipose tissue are pigmented, generating lots of heat. This heat generation by the mitochondria keeps infants and babies warm because infants do not really have the shivering reflex to generate heat. They rely more on the brown adipose tissue to keep them warm.

In brown fat, the lipid droplets tend to be smaller and more numerous, and they are used to provide energy to the mitochondria. Notice that there are a lot more mitochondria in the brown fat than in the white fat. These mitochondria generate lots of heat to keep infants warm. Below we have a micrograph where you can see that the cells appearing whiter are the white fat, and the darker, more pigmented fat is the brown fat.

This concludes our lesson on these 2 different types of adipose tissue, and moving forward, we'll be able to apply these concepts in some problems. I'll see you all in our next video.

Connective Tissue Proper: Loose Connective Tissue Example 2

In this video, we have an example problem that says, if liposuction procedures remove adipose tissue, then why do patients report gaining weight back? We've got these four potential answer options down below. And so it is true that liposuction surgery or procedures remove adipose tissue. However, they do not remove all of the adipose tissue because some adipose tissue is critical for the healthy functioning of the body. And so the adipose tissue that remains is still capable of growing even after a liposuction procedure.

But recall that the adipocytes or fat cells do not grow in the traditional sense through cell division like most other cells do. Instead, mature adipocytes grow in terms of their size rather than growing through cell division. And so after a liposuction surgery or procedure, if the patient doesn't maintain a healthy lifestyle, including a healthy diet and regular exercise, it is possible for the adipocytes and the remaining adipose tissue to grow in their size. Notice answer option a says, because adipocytes undergo cell division. And again, mature adipocytes don't really grow via cell division like other cells typically do.

For that reason, we can eliminate answer option a. Option b says that because adipose tissue is avascular, but recall that adipose tissue is actually highly vascularized, which means that it has a lot of blood vessels. To say that it is avascular is incorrect. Then notice that answer option d says because adipose tissue holds more water, but we know adipose tissue has mostly adipocytes which have lots of lipid droplets and lipids are hydrophobic or water fearing. And so that is not going to be a feature that allows this tissue to hold more water.

For that reason, we can eliminate option d. And so, of course, answer option c here is going to be the correct answer which says that because adipocytes can increase in their size. And again, that is going to be the correct answer here, so c here is correct and that concludes this example. So, I'll see you all in our next video.

Review of Loose Connective Tissues

In this video, we're going to do a review of the 3 different types of loose connective tissues. And so because this video is a review, what that means is that 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 loose connective tissues, then you could 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 that being said, notice down below we have a table of the 3 different types of loose connective tissue where in the far left column we have the type of loose connective tissue, the next column has some key characteristics of the tissue, the following column has some important functions of the connective tissue.

And then the last column has some example locations of where the connective tissue can be found in the human body. And so recall from our previous lesson videos that the first type of loose connective tissue that we covered in our lesson was areolar connective tissue. And recall that the term areolar is actually a Latin term that means small open spaces. And so when you look at the micrograph of areolar connective tissue, you can see that the protein fibers are loosely arranged creating those small open spaces or that porous look to this areolar connective tissue. Now recall that areolar connective tissue is actually the most widely distributed connective tissue throughout the entire human body and can be practically found in all areas of the body.

And so this is why areolar connective tissue is known as the human body's universal packing material. Now in terms of its characteristics, areolar connective tissue is going to have a viscous or a gelatinous extracellular matrix that is going to be a semi-fluid, something in between a solid and a liquid. And areolar connective tissue is going to have all three of the protein fibers in its extracellular matrix, including collagen fibers, reticular fibers, and elastic fibers. And because it has so much structural diversity in its extracellular matrix, that's also going to contribute to its functional diversity as well. And so it has a lot of different functions.

Now, in terms of its cell types, mostly, areolar connective tissue is going to have fibroblasts, which recall are the cells that actively build and secrete components of the extracellular matrix. However, it can also have fibrocytes, which can maintain the extracellular matrix through minor repairs and routine maintenance. And they can also have these migratory immune cells such as macrophages, which perform phagocytosis or engulfing of invaders for elimination. And also, they can contain those mast cells, which are going to release the chemical histamine, which can cause inflammation and again help to eliminate invaders. Now, areolar connective tissue can also have adipocytes.

Wherever areolar connective tissue is found, adipocytes can also be found. And recall adipocytes are fat cells that can actually store fats or triglycerides. And so in terms of the function, notice that it can have many different functions, but we focus on these 3 specific ones. The first being support and binding. We know that areolar connective tissue can actually be found underneath the epithelia throughout the entire body.

And so notice here we have a diagram where we have the epithelial tissue and of course, we have the basement membrane immediately beneath, But then notice that below that, we have the areolar connective tissue, which tends to be vascular or has lots of blood vessels, which allows it to support the avascular epithelia throughout the entire body. And also, it can be found in the spaces between organs, which is why, again, it's known as the universal packing material, where it can help to bind those organs together. Now, because areolar connective tissue has these migratory immune cells, like micro macrophages and mast cells, it can also help to defend against infection. And that is also a key reason why areolar connective tissue is found all throughout the body. Because at any point in time, any region of our body can become infected if it gets cut, for example.

And so it's important to have areolar connective tissue to help defend against infection throughout the entire body. And then again, because areolar connective tissue has those small spaces and that porous look to it, it can actually serve as a reservoir for storing nutrients and fluids. And so it can actually provide nutrients and fluids to the surrounding tissues. And again, because areolar connective tissue is vascular, it can receive nutrients from the blood, store those nutrients and fluids, and then deliver those nutrients and fluids to the surrounding tissues, such as the epithelia, for example. Now, the next type of connective loose connective tissue that we covered in our lesson was reticular connective tissue.

And recall, reticular connective tissue is only going to have those reticular protein fibers in the extracellular matrix, which is why it's called reticular connective tissue and why the fibroblasts of reticular connective tissue are called reticular cells. Because, again, they only produce the reticular fibers. And that means that the collagen fibers and elastic fibers are not found in the extracellular matrix of reticular connective tissue. And so it has a lack of structural diversity in the extracellular matrix and that lack of structural diversity is also going to roll into a lack of functional diversity as well. Now, reticular connective tissue is going to have a viscous gelatinous or gel like matrix that is a semi fluid, something in between a solid and a liquid.

And in terms of its functions, we focus on the main function here, which is that it can serve as the internal scaffolding for many soft organs, including the lymph nodes, the spleen, the liver, the kidneys, the thymus, and the bone marrow. And so because it forms the internal scaffolding providing structural support in these organs, it can actually help to support the functions of each of these organs. Now, the next or the last type of loose connective tissue that we talked about in our lesson was adipose connective tissue, which recall adipose connective tissue is going to be mostly made of adipocytes or fat cells that store fats or triglycerides as these relatively large lipid droplets within the cell that can take up the vast majority of the volume of the cell. And so, the adipose connective tissue tends to have a sparse, a sparse viscous matrix, so it has relatively little extracellular matrix, which is what makes these adipose sites appear to be really tightly packed together. But again, these adipose sites are very loosely arranged, which is why it is a loose connective tissue.

And so these cells, although they appear to be really tightly packed together, they can easily enlarge in their size and they can also release lipids and decrease in size. And when they release those broken down lipids, those lipids can be essentially, absorbed into the bloodstream and transported throughout the bloodstream to other areas of the body where those lipid components can serve as energy sources. And so, adipose connective tissue is going to be highly vascularized, meaning it has lots and lots of blood vessels and that allows the blood vessels to bring nutrients to the adipose tissue where it can essentially store those nutrients in the form of lipids. And, again, it allows the adipose sites to break down their lipids and transport those broken down lipids in the blood to other areas of the body where those lipids can serve as an energy source. And so in terms of the functions, again, it's going to be able to store nutrients and energy in the form of lipids.

It's able to absorb shock since it can act as a cushion and help to protect, and it can also insulate by keeping the body warm, since it's found in the layers underneath the skin. And so again, it can be found deep to the layers of the skin, it can be found in areas of the body such as the abdomen or the stomach area, as you can see here in this little image. It can also be found around the eyes where it can provide cushioning and protection, and around organs such as the kidneys and the heart, and it can also be found in the breasts. And so, adipose connective tissue is also going to have a genetic component to it that is going to determine where it can be found in the body. And so in some people, you can find that adipose connective tissue tends to accumulate under the chin or in the back or in areas such as the hips or the thighs, for example.

And so this here concludes our brief review of the 3 different types of loose connective tissue. And as we move forward in our course, we'll be able to get some practice applying these concepts. So I'll see you all in our next video.

What part of areolar tissue allows it to protect against infection?

• A. Fibroblasts. 
• B. Fibrocytes.
• C. Adipocytes.
• D. Macrophages.

During a dissection, you are asked to identify a connective tissue with a gel like matrix that forms the inside structure of the spleen. What is the type of connective tissue?

• A. Areolar Connective Tissue. 
• B. Reticular Connective Tissue.
• C. Adipose Connective Tissue. 
• D. Cartilage.

How does areolar tissue and epithelial tissue work together to prevent infection?

• A. Both areolar tissue and epithelial tissue are richly supplied with blood, mast cells, and macrophages, providing defense against microbes. 
• B. Areolar tissue provides both the collagen that creates a barrier in epithelial tissue and the macrophage that travel through epithelial tissue defending against microbes.
• C. Epithelial tissue provides a tight barrier that microbes cannot pass. Areolar tissue contains immune cells for when that barrier is compromised. 
• D. Areolar tissue provides a tight barrier that microbes cannot pass and epithelial tissue sends signals directing the immune system where white blood cells are needed.

Max hears that wrinkles are formed because the dense irregular connective tissue under the skin produces less collagen as we age. To counteract this, they go out and buy a skin cream that claims to contain collagen fibers. Based on what you know about connective tissue and epithelial tissue, do you expect the collagen fibers in this hypothetical skin cream to affect the underlying connective tissue?

• A. Yes, because the collagen allows connective tissue to stretch, so supplementing with collagen fibers will allow the skin to stretch & tighten to remove wrinkles. 
• B. Yes, because epithelial tissue is specialized for absorption, so biological molecules like collagen fibers will be quickly integrated into areolar tissue.
• C. No, because areolar tissue mostly produces elastin, so the difference in collagen production is unlikely to affect wrinkles. 
• D. No, because stratified squamous epithelial tissue prevents the passage of most molecules, so the large collagen fibers will not reach the underlying areolar and dense irregular connective tissues.