So now that we've covered epithelial tissue in our previous lesson videos, in this video, we're going to begin our introduction to the second primary tissue in our lesson, which is connective tissue. And so connective tissue is actually the most abundant and the most widely distributed tissue throughout the human body. We can pretty much find connective tissue in almost all areas of the human body. Connective tissue is also the most diverse tissue class among all 4 primary types of tissue. Connective tissue is the most diverse in terms of both its structure and its function. Notice down below, we're showing you these 4 micrographs that are all of connective tissues that we'll get to talk more details about as we move forward in our course. But what you'll notice is that just by looking at these 4 micrographs, you can clearly see that they are very different from one another. That goes to show how diverse of a tissue class connective tissue actually is. Notice the micrograph on the far left is actually showing us some connective tissue proper. The second micrograph is showing us some cartilage, which is also a type of connective tissue. The third micrograph is showing us some bone, again a type of connective tissue. And the fourth micrograph on the far right is showing us some blood. Again, another type of connective tissue. We already know that our bones are really hard and solid structures. Whereas we know that our blood is actually a liquid. Just this right here goes to show how diverse of a tissue class connective tissue actually is. However, despite all of the diversity of connective tissue, all connective tissues are going to have the following two things in common that we have numbered down below, number 1 and number 2. The first common feature of all connective tissues is that they are all derived from embryonic mesenchyme, which we covered briefly in some of our previous lesson videos. And the second common feature of all connective tissue is that the cells of connective tissue actually occupy far less space than their ECM or their extracellular matrix, which takes up much more space in connective tissue. Unlike the cells of epithelial tissues, which we know from our previous lesson videos are really tightly packed or really tightly pressed together with lots of tight junctions and desmosomes, and there's relatively little ECM between those cells, the cells of the connected tissue are actually not in direct contact with one another because they are spaced out or separated by the relatively large amounts of ECM or extracellular matrix. In fact, connective tissue is unique among the 4 types of primary tissue and that the extracellular matrix can actually be significantly more prominent than the cells themselves. As we move forward in our course, we're going to talk more details about connective tissue. But this here concludes our introduction to connective tissue. In our next lesson video, we'll be able to focus on the structure of connective tissue. So I'll see you all there.
Introduction to Connective Tissue - Video Tutorials & Practice Problems
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Intro to Connective Tissue
Video transcript
Structure of Connective Tissue
Video transcript
In this video, we're going to talk about the structure of connective tissue. Recall from our previous lesson videos that all tissues, including connective tissue, are made of groups of cells and their extracellular matrix, or their ECM. But recall that the extracellular matrix can be more prominent in some types of tissues versus other types of tissues. For example, recall from our previous lesson videos that epithelial tissue consists of cells that are really tightly packed together and have relatively little ECM between the cells. However, once again, when it comes to connective tissues, they actually have the most prominent ECM or extracellular matrix that can take up most of the volume of the tissue and actually separate the cells because of the relatively large amounts of ECM. And so because connective tissue has the most prominent ECM, this is why we focus on its structure in this video.
Now, recall that the extracellular matrix or the ECM is really just the material that is immediately outside of the cells. And the extracellular matrix is actually made of ground substance and protein fibers. The ground substance is really just unstructured material that's between the tissue cells and between the protein fibers in the ECM. Depending on the type of connective tissue, the ground substance can actually range in its viscosity or range in its thickness from being a rock-hard solid, like bone, for example, to being a liquid like blood, for example. The different types of protein fibers that are found in the extracellular matrix can actually contribute to the viscosity of the ground substance.
Moving forward, we'll learn that there are three different types of protein fibers and we'll talk about the differences in those three different types of protein fibers later in our course. But for now, you should note that the different types of fibers and the different amounts of each of those fibers can actually contribute to the tissue's physical properties. For example, contributing to the strength of the tissue, the flexibility of the tissue, and the ability for the tissue to recoil or spring back to its original shape.
All tissues, including connective tissues, are made of groups of cells. The cells of connective tissue can secrete and maintain the components of the extracellular matrix, including the ground substance and the protein fibers. Also, the cells will support the specialized functions of the connective tissue. In most types of connective tissue, there are two main types of cells, which are the blast cells and the site cells. The blast cells are going to end with the root "blast," which is why they're called blast cells. These blast cells are going to be immature cells that have the ability to divide, and they are more active. They actively build and actively secrete the components of the ECM, again, including the ground substance and the protein fibers. As we'll learn moving forward in our course, the blast cells of connective tissue proper are fibroblasts. Other examples of blast cells include osteoblasts, which are found in the bone, and chondroblasts, which are found in the cartilage.
The site cells are going to end in the root "site." These cells are going to be more mature cells that are a little bit less active. They don't really divide as much, and they are more about maintaining the extracellular matrix rather than actively building and secreting the components of the extracellular matrix. In terms of maintenance, it's only going to do minor repairs and just routine maintenance. As we'll learn moving forward, an example of a site cell in connective tissue proper is going to be the fibrocytes, which notice ends in the root "sites" which is why they are site cells. Other types of site cells, examples of site cells are going to be osteocytes which are found in bone and chondrocytes which are found in cartilage. If major or significant repair or major or significant growth of the tissue is needed, then sometimes these site cells can actually revert back to blast cells so that they can actively build and secrete the ECM for that significant repair and, again, that significant growth. But if it's really just maintaining the ECM, then it's just going to be minor repairs. And again, those would be the site cells.
So notice down below we have an example, and it's asking us how connective tissue is like ice cream with different toppings mixed in. Notice that we've got these two really delicious-looking ice cream cones down below. What you'll notice is that we have the major components of the tissues here in the middle. Recall that all tissues are going to be composed of, again, groups of cells, but also their extracellular matrix. We've learned that the extracellular matrix is going to be composed of ground substance and protein fibers or just fibers for short. What you can see here is that we've got this key here that is showing us how ice cream with different toppings mixed in is similar to connective tissue. Notice that the ground substance, the unstructured material between the cells and the protein fibers, is like the base of the ice cream, either a chocolate base, for example, or a vanilla base, for example. Changing the ground substance can change the tissue. Again, the ground substance can change in viscosity or its thickness. It could be a rock-hard solid, or a liquid. Just like ice cream, when you just take it out of the freezer, it's kind of more rock-hard and more solid. Or if you have ice cream that's been left out for a little bit, it's kind more liquidy. The protein fibers are going to be things such as chocolate swirls, or caramel swirls, or little candy cane swirls. Again, there are three different types of fibers, and different amounts and different types of those fibers can contribute to the viscosity of the ground substance and also contribute to the physical properties of the connective tissue. And then of course, every tissue is going to be composed of groups of cells and those cells can be of different types and the different types of cells can lead to different connective tissues. Notice we're using things like marshmallows and little chocolate chips and gummy bears and sprinkles and other candies to represent the different types of cells. Notice that this ice cream over here, which, you know, has a chocolate based ground substance and marshmallows and chocolate chips and chocolate swirls as protein fibers is going to be a different connective tissue or represent a different connective tissue than this other vanilla based ice cream here, representing the ground substance with little gummy bears and sprinkles and candies as the cells and again, little cotton candy swirls as the protein fibers. This is how connective tissue can resemble ice cream with different toppings mixed in. As we move forward in our course, we'll be able to talk more details about connective tissue. But for now, this here concludes our brief lesson on the structure of connective tissue, and we'll be able to get some practice upon these concepts moving forward. So I'll see you all in our next video.
What part of connective tissue takes up most of the volume?
Extracellular Matrix.
Cells.
Epithelium.
Glands.
Functions of Connective Tissue
Video transcript
In this video, we're going to talk about some of the functions of connective tissue. Recall from our previous lesson videos that connective tissue is the most diverse class of tissue in terms of both its structures and its functions. It actually has a lot of different functions. Rather than making an exhaustive list of all the different functions of connective tissue, in this video, we're going to talk more broadly about the functions of connective tissue. As we move forward in our course in different videos talking about specific types of connective tissue, then we can talk more details about their specific functions. But again, in this video, we're going to talk more broadly about functions of connective tissue. Once again, it's important to emphasize that connective tissue functions are very diverse. They can be grouped into these 5 main functions that you can see down below in our image. Notice that the top layer of the image is actually listing the 5 functions. The middle layer here is showing a symbol or an image to support the function. Toward the bottom, we have specific examples of the function. Notice that the very first function that we have here for connective tissue is that it can actually provide protection. Similar to how armor can provide protection to what lies underneath. For example, bones such as the rock-hard skull, for example, can actually protect the soft structures that lie underneath such as the delicate brain.
Now, the next function that we have here is connective tissue can transport materials, actually transport the materials, instead of just regulating the transport like what epithelial tissue does. When we say transport materials, we can actually think of connective tissue such as blood, for example. Notice down below we are saying that blood can actually physically transport gases, such as oxygen gas, for example, and nutrients such as glucose, for example. The blood can actually transport these gases and nutrients throughout the entire body to deliver oxygen and glucose to all tissues everywhere in the body. The blood can also transport wastes such as carbon dioxide gas from the tissues to the lungs where we can exhale that carbon dioxide gas. Transporting materials is a function of connective tissue. Just like a car can transport materials, blood can also transport materials like gases and nutrients, for example.
Now, the next function that we have here is a little bit more intuitive because connective tissue is going to be important for connecting or binding things together. It's also going to be important for support. Binding and support is a function of connective tissue. In terms of binding, structures such as tendons, which are made of connective tissue, can actually bind or connect muscles to bones. Ligaments, which are also made of connective tissue, can bind or connect bones to other bones. In terms of support, recall from our previous lesson videos that connective tissue actually supports epithelial tissue. Recall that epithelial tissue is avascular, which means that it does not have any blood vessels. It actually relies on the underlying vascular connective tissue that does have blood vessels. The vascular connective tissue with its blood vessels can supply the avascular epithelial tissue with nutrients, such as glucose for example, and also gases such as oxygen. It can also help to eliminate the waste from the epithelial tissue as well. Notice that we're saying, in this little symbol or image here, notice that we've got some epithelial tissue highlighted here in green. Notice that this muscle man down below is just a silly way for us to say, this is the connective tissue that underlies the epithelial tissue that is actually supporting the epithelial tissue. You can think that this weight here is actually the basement membrane that separates the epithelial tissue from the underlying connective tissue.
Now, the next function that we have here is that connective tissue can actually offer insulation, or it can insulate the body. Connective tissue is going to include fat. Fat, fat cells are called adipocytes. We'll talk about them later in our course. But connective tissue does include fat. Fat can really help to insulate the body and keep the body warm. Just like your winter coat can keep you warm during the winter when it's really cold outside. These fat these fat cells or adipose sites, that store lots and lots of fat can help with insulation and offer insulation to keep the body warm.
Now the 5th and final function that we have listed here is it can actually provide storage. And so, it can actually store energy. Again, the fat cells can store fat and fat can serve as long term energy storage. Notice that we have these same fat cells here, these adipose sites. Just like a battery can store energy, these fat molecules can also be storing long term energy. Another example is that bones can actually store calcium and phosphates. So, when the body needs calcium and phosphates, it can actually use bones as a reservoir for calcium and phosphates. We'll be able to talk about that later in our course. But for now, this here concludes our brief lesson covering some of the functions of connective tissue. As we move forward in our course talking about specific types of connective tissue, we'll get to talk more details about their specific functions. But for now, this here concludes this video, and I'll see you all in our next video.
Functions: Epithelial vs. Connective Tissue
Video transcript
In this video, we're going to briefly compare the functions of epithelial and connective tissues. And so we already know from our previous lesson videos that epithelial and connective tissues are both pretty diverse in terms of their functions. And so because of this, some of their functions may seem to overlap a little bit. And because of that, we're going to compare their functions so that we can clear up any potential confusion. And so, notice down below we have this 3 column table with blanks and we're going to fill out the blanks as we go through the video. And notice that the middle column has the functions of the tissues. And so once again, please remember that this is not an exhaustive list of all of the different functions of these tissues. And these are really just broader groupings of the functions of these tissues.
Now, in the column on the far left, we have examples of epithelial tissue functions. And in the column on the far right, we have examples of connective tissue functions. And so, the very first function listed here is protection. And so, recall from our previous lesson videos that epithelial tissue does function in protection. And a classic example of that is going to be the outermost layers of our skin. And of course, we know that our skin is going to protect us from the outside world. It protects us against physical trauma and chemicals and all kinds of things that we can encounter in the outside world. And so recall from our previous lesson videos, the outermost layers of our skin are made of keratinized stratified squamous epithelia, which means that it consists of multiple layers of cells where the cells on the apical surface are flat or squished in their shape. The keratinized part of that means that it's going to have the protein keratin, which is going to make the tissue tougher and help with protection even more.
Now, when it comes to connective tissue, we also said that it functions in protection. And recall that the rock hard bones, such as for example, the skull, can help to protect the delicate softer tissues that lie underneath such as the brain. The skull protects the brain. Now, in terms of transport, recall we said that epithelial tissue can actually regulate transport. And so, really when we are talking about regulating transport, we're talking about epithelial tissue serving as the boundary adjacent to open space. And it can regulate the transport of molecules across the tissue for absorption or excretion or filtration. And so, a classic example of where regulating transport can occur is in the digestive lining. Which recall from our previous lesson videos, the digestive lining contains simple columnar epithelia or one layer of these tall and narrow column shaped cells.
Now, when it comes to transport, recall we also said this was a function of connective tissue as well. More specifically, we said that blood is an example of connective tissue. And we know that the blood can transport, actually physically transport, things such as oxygen gas and nutrients such as glucose, and also waste products such as carbon dioxide gas. And so, the transport function here is different. Where again, epithelial tissue is going to be more so regulating the transport of substances across the tissue, and it's not going to be physically transporting things. Epithelial tissue won't physically transport things. Whereas with connective tissue, the blood is actually physically transporting the gases and nutrients throughout the entire body.
Now, in terms of sensations, recall from our previous lesson videos that this is a notable function of epithelial tissue. And so recall that epithelial tissue can actually work closely with nervous tissue in order to allow for sensations. And so recall that epithelial tissue is actually going to connect us to the outside world since it covers and lines things such as our skin. And so, sensations such as touch, when we go to touch things, the pressure can be detected by the epithelial tissue and then the epithelial tissue can go on to activate the nervous tissue and the nervous tissue can transmit an electrical signal for processing which allows for the full sensation. And so, sensation is a notable function of epithelial tissue. And again, recall epithelial tissue is avascular, meaning it does not have blood vessels, but it is innervated, meaning that it does have nerves and nervous tissue. And so that's how we know it works in close connection with nervous tissue.
Now, in terms of sensation being a function of connective tissue, although connective tissue can be innervated and can contain nerves and nerve endings, we don't really associate sensation as one of the primary functions of connective tissue. And the reason for that is because connective tissue has lots and lots of diverse functions. So it's even more diverse in its functions than epithelial tissue. And also, connective tissue doesn't connect us to the outside world or link us to the outside world like what epithelial tissue does. And so, for that reason, sensation is not usually going to be associated with connective tissue function. So we'll put an x for that.
Now, in terms of secretions, of course, we know from our previous lesson videos that glandular epithelial tissue is going to form glands, and glands are cellular structures that specialize in secretion or releasing products. And so for sure, with epithelial tissue, we can say that glands secrete products and, those secreted products can include secretions such as sweat or mucus or enzymes, and more things as well. Now, in terms of connective tissue functioning in secretion, yes, all tissue cells are going to be able to secrete components of their own extracellular matrix, and they all may have some function of secretion. But connective tissue is not going to specialize and form specialized secretions like what glands do. And so for that reason, in terms of secretion being a primary function that's notable of connective tissue, that's not really going to be the case. So we'll put an x through it as you see here.
Now, in terms of support, insulation, and storage, these are not really going to be functions of epithelial tissues. And so, for that reason, we'll put X's over here in these rows. But in terms of support, connective tissue does, of course, support epithelial tissue. Recall that epithelial tissue is avascular, meaning that it does not have blood vessels. But the underlying connective tissue is or can be vascular. And that means that it does have blood vessels and so the blood vessels can actually provide nutrients and support the epithelial tissue. So, in terms of support, what we can put here is that connective tissue is found underneath the epithelial tissue or and really we can say underneath the skin, because recall the outermost layers of the skin have epithelial tissue and then of course underneath the skin is going to be that connective tissue that's vascular.
Now, in terms of insulation, again, this is going to be a function of connective tissue because connective tissue is going to include the fat cells, which are called adipocytes. And they store fat and fat can help to insulate the body and keep it warm just like your winter coat can keep you warm during the winter. And so, the more fat, the better your body can be insulated and retain heat. And then, of course, we know that storage is also going to be a function of connective tissue because, again, bones can actually store calcium, but also those adipose sites, those fat cells can store fat for long term energy storage. And so, energy can be stored and also, components such as calcium can also be stored in the bone.
And so this here concludes our brief comparison of the functions of epithelial and connective tissue and hopefully this was somewhat helpful for you to compare the functions. So, that concludes this video and I'll see you all in our next video.
Introduction to Connective Tissue Example 1
Video transcript
So here we have an example problem that's asking, what type of tissue is responsible for support of the body? And we've got these 4 potential answer options down below. And so of course, we know from our previous lesson videos that connective tissue does support the body. And so, we can go ahead and indicate that answer option b, connective tissue, is the correct answer to this example problem. And so, recall from our previous lesson videos that connective tissue actually supports epithelial tissue. Because recall epithelial tissue is avascular, meaning it does not have any blood vessels. But the underlying connective tissue is vascular with blood vessels. Which means that the connective tissue can support epithelial tissue by providing nutrients and oxygen gas, for example. And of course, the connective tissue is going to support the epithelial tissue that's found throughout the body. And also, we know from our previous lesson videos that bones are a type of connective tissue. And so, the bones that make up our skeleton are going to give our body the structure and support that it needs. And so, that's another reason how we could have indicated option b, connective tissue, is correct. Now, epithelial tissue is not going to function primarily in support of the body.
Muscles tissue and nervous tissue we have not yet talked about. And so, we'll talk about muscle tissue and nervous tissue later in our course in different videos. But for now, this concludes this example and I'll see you all in our next video.
During a dissection, a student comes across a tissue they don't recognize. They note it makes the internal structure of the spleen (an organ of the immune system that filters blood) and when they examine a section under the microscope, they see long dark branched structures, small circular cells, and a significant amount of ECM. What type of tissue could this be?
Nervous Tissue.
Muscle Tissue.
Epithelial Tissue.
Connective Tissue.
Both epithelial and connective tissue are involved in transport of materials in the body. How do their functions differ?
Epithelial tissue provides a mechanism of transport while connective tissue regulates transport.
Epithelial tissue facilitates diffusion while connective tissue uses active transport.
Epithelial tissue regulates transport while connective tissue provides a mechanism for transport.
Epithelial tissue transports nutrients while connective tissue transports hormones.
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