In this video, we're going to talk about the tonsils. Now, the tonsils are collections of MALT or mucosal associated lymphoid tissues that are found around the entrance of the pharynx or the throat, which is a region of the body that's constantly being bombarded by pathogens from the foods that we consume on a regular basis and the air that we're constantly inhaling all of the time. And so, the tonsils, as a collection of MALT, play an important role in immunity, essentially removing pathogens from the foods we consume and the air we inhale. And because the tonsils are located in a region of the body constantly bombarded by pathogens, the tonsils are often going to become inflamed.
Now, recall from our last lesson, that most collections of MALT do not have a capsule and are not fully encapsulated. And this applies to the tonsils as well. They are not fully encapsulated. And recall, this means that the tonsils are often going to be considered secondary lymphoid structures rather than secondary lymphoid organs since most organs tend to be encapsulated. And tonsils have epithelium that invaginates anteriorly or folds in on itself to form what are known as tonsillar crypts. And these tonsillar crypts are really deep pits or folds that are going to trap pathogens and foreign substances for their ultimate elimination by the leukocytes that are found within the malt.
Now, really, there are three main sets of tonsils that are actually named according to their location, and that's what we're going to focus on in this image down below. And so, the first main type of tonsil that you should be aware of is the pharyngeal tonsil, which as you can see over here in this image, is found on the posterior wall of the nasopharynx, or in other words, on the back wall of the nasal cavity. And the pharyngeal tonsil over here in this image, with the person with their open mouth, notice that this dotted white line that I'm tracing over here represents the removal of the palate, and that allows us to be able to see the pharyngeal tonsil here in this person's mouth. Now, the next set of main tonsils that you should be familiar with are the palatine tonsils, which as you can see over here in this image, are found on the posterior end of the oral cavity, or in other words, on the back end of the mouth. And these palatine tonsils are actually a pair of tonsils, meaning that there are two palatine tonsils, one on either side of the mouth, as you can see here. And often, these palatine tonsils are the ones that may need to be surgically removed in a tonsillectomy. Now, the last main type of tonsil that you should be familiar with is the lingual tonsil, which as its name implies with the term lingual, which means tongue, is going to be found at the base of the tongue as you can see over here. And in this image, you can see the lingual tonsil right there.
Now, notice that in this dotted box here, we're zooming in to one of the palatine tonsils, and that's what we can see over here in this micrograph. And what you'll notice is that one of the tonsillar crypts is being labeled right here. Again, this invagination or this fold or this deep pit that, again, will trap pathogens, essentially inviting pathogens and foreign substances to fall into this crack, where, ultimately, those pathogens and foreign substances will be eliminated by leukocytes found within the MALT. And also, notice that we're labeling the germinal center of one of the lymphoid follicles here. And so, recall from previous lesson videos that lymphoid follicles are also sometimes referred to as lymphoid nodules, and they are going to be these really densely packed spheres of lymphoid tissues that often have these lighter staining germinal centers that have populations of dividing B cells. And so, you can see several of these lymphoid follicles here, throughout this micrograph.
This here concludes our lesson on tonsils, and as we move forward, we'll be able to apply these concepts. So, I'll see you all in our next video.