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. And so 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. And so 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. And so these collagen fibers are going to be long and thick, unb branched or straight fibers. And that unb branched 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. And this is because collagen fibers are actually slightly wavy. And so if we take a look at this micrograph of dense regular connective tissue down below, notice the fiber blasts 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. And so because collagen fibers are slightly wavy, it gives them a little bit of flexibility when they are pulled upon and when they have tension. And so 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 adipocyte 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 flu few blood vessels that it does have and receiving relatively little nutrients ultimately leads to slow healing upon being damaged and uh 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, intention 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, uh 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 connected tissue, it's important to note that they can be found in ligaments, tendons or FASA. Now, ligaments are going to be 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. And so 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 again, 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 and the same goes with ligaments, ligaments need to be really, really strong because again, when they move, they need to be able to hold the bones together for proper movements. And so this year 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. So I'll see you all in our next video.