Secondary Lympoid Organs: MALT: Study with Video Lessons, Practice Problems & Examples

Mucosal-associated lymphoid tissues (MALT) are crucial for immune defense, particularly in vulnerable mucosal membranes of the respiratory, digestive, urinary, and reproductive systems. Key collections include tonsils, Peyer's patches, and the appendix. Tonsils trap pathogens via tonsillar crypts, while Peyer's patches in the ileum prevent harmful bacteria from migrating. The appendix, once deemed vestigial, aids in generating memory lymphocytes and replenishing beneficial gut bacteria, supporting long-term immunity and gut health.

Introduction to MALT

In this video, we're going to continue to talk about secondary lymphoid organs with an introduction to MALT. Now MALT is an abbreviation for mucosal associated lymphoid tissues, and as its name implies, it's going to be a collection of lymphoid tissues that line mucosal membranes. And so, the mucosal membranes throughout our body are very vulnerable areas of our body because they are exposed to a lot of pathogens from the outside world, and that's why we need these collections of MALT to provide immunity and defend our bodies from these pathogens. And so the MALT serves as a frontline defense against pathogens that are constantly trying to enter our body through mucosal surfaces. And the MALT is actually located throughout mucosal epithelia, specifically, the mucosal epithelia of the respiratory, digestive, urinary, and reproductive systems. And unlike most of the other lymphoid organs that we talked about in previous lesson videos, including the thymus, lymph nodes, and the spleen, most collections of MALT actually lack an exterior capsule made of dense irregular connective tissue. And because that's the case, often, MALTs are going to be considered secondary lymphoid structures rather than secondary lymphoid organs since organs tend to be encapsulated. However, some collections of MALT may be partially encapsulated. Now, the largest collections of MALT in the body are tonsils, Peyer's patches, and the appendix. And moving forward in our course, we're going to talk about each of these larger collections of MALT in separate videos. But down below in the image, you can see over here on the left, we're showing you some tonsils, which again are larger collections of MALT that are going to be found here in the head region. And then the Peyer's patches and the appendix are going to be collections of MALT found in the digestive system, which is why we're showing you the digestive system over here. But again, we're going to talk about these in more detail moving forward in separate videos. So, that concludes our introduction to MALT, and I'll see you all in our next video.

Secondary Lympoid Organs: MALT Example 1

So here we have a pretty straightforward example problem that asks, which of the following body areas does not typically contain MALT or mucosal associated lymphoid tissues? And we've got these 4 potential answer options down below that say respiratory tract, digestive tract, central nervous system, or urogenital tract. And, of course, recall from our last lesson video that MALT or mucosal associated lymphoid tissues are going to be found in the mucosal epithelia of the respiratory tract, the digestive tract, and the urogenital tract, but they are not going to be found in the central nervous system, such as the brain and spinal cord. So for that reason, we can indicate that answer option c is the correct answer. And that concludes this example problem, so I'll see you all in our next video.

Tonsils

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.

Secondary Lympoid Organs: MALT Example 2

So here we have an example problem that asks, what is the primary function of the tonsils? And we've got these 4 potential answer options down below. Now recall from our last lesson video that the tonsils are a collection of MALT or mucosal associated lymphoid tissues around the entrance of the pharynx or the throat. And as a collection of MALT, its primary function is going to be immunity. And so keep that in mind as we go through each of these answer options.

Now option a says, eating and digestion in the mouth by secreting enzymes that break down fats and carbohydrates. And so this is not going to be the primary function of the tonsils, so we can eliminate answer option a. Option b says, secreting mucus to prevent the mouth from drying out. And, again, this is not going to be the primary function of the tonsils, so we can eliminate option b. Option c says, producing essential hormones. Again, not going to be the primary function of tonsils, which means that answer option d, the only option, must be the correct answer. And it says initiating immune responses and trapping pathogens, And so that is going to be the primary function of the tonsils. So we can indicate that option d is correct. That concludes this example, and I'll see you all in our next video.

Which pair of tonsils trap pathogens at the posterior end of the oral cavity?

• A. Palatine tonsils.
• B. Pharyngeal tonsils.
• C. Lingual tonsils.
• D. All 3 pairs of tonsils.

Digestive System Immunity: Peyer’s Patches & Appendix

In this video, we're going to talk about digestive system immunity as we discuss the collections of malt called the Peyer's patches and the appendix. Now the Peyer's patches are lymphoid follicles that are located on the interior wall of the distal portion of the small intestine, which is called the ileum. And so if we take a look at the image down below, notice that we're focusing in on the digestive system of this person. And notice that the distal portion of the small intestine is going to be this last part of the small intestine that you can see is circled in right here. And if we zoom into that, that's what the zoom is over here, you can see that the distal portion of the small intestine is really the last part of the small intestine before it transitions into the large intestine. And in the interior wall of this distal portion of the small intestine, the ileum, is where we can find the Peyer's patches, and the Peyer's patches in this image are these yellow patches that you can see here. Now what's important to note is that the gut, or our digestive system, has lots of bacteria that we often refer to as the gut microbiome. And these gut bacteria are actually good bacteria that support our overall health. However, they're only good bacteria if they remain in their specific locations. But if they move into other locations of the body, they could potentially cause us harm and disease. And so these Peyer's patches essentially are going to be important for preventing the large intestine's bacteria from escaping backwards into the small intestine, where they could potentially cause us harm and disease.

Now, the appendix was long thought to be a vestigial structure, meaning that it may have been important to our early ancestors way back in time, but for now it seems to have no significant function. However, recent studies have shown that the appendix is more important than what we've thought it to be in the past. And so the appendix is a tubular extension or an offshoot of the first part of the large intestine, which is called the cecum. And the appendix is going to contain lymphoid follicles, which of course means it's going to play a role in immunity. In fact, the appendix is important for generating memory lymphocytes for long-term immunity. Later in our course, when we discuss immunity in more detail, we'll get to talk a lot more about these memory lymphocytes. Now, the appendix can also serve as a reservoir for the beneficial gut bacteria to repopulate the gut microbiome after disturbances. And so this helps to ensure that we are able to recover after illnesses that might perhaps flush out our gut microbiome like diarrhea or something like that. And so the appendix is going to be important for that reason, and so if we take a look at the image down below, notice that the appendix is going to be this little tiny offshoot that you can see down below right here off of the cecum, the first part of the large intestine. If we zoom in over here, again, you can see right here, this is going to be the appendix. And this zoom in over here also has the appendix that is a lot easier to see, again, right here, and so we can label it as the appendix. And so the appendix is really about the size of a pinky finger, if you will, and again, it's an offshoot off of the cecum. So this here concludes our brief lesson on digestive system immunity and the Peyer's patches in the appendix. So we'll be able to get some practice applying these concepts as we move forward, so I'll see you on our next video.

Secondary Lympoid Organs: MALT Example 3

So here we have an example problem that wants us to choose one of the 4 potential answer options down below that best fills in the blank in this sentence, which says that clusters of lymphoid nodules in the wall of the ileum of the small intestine are blank, and option a says tonsils. However, recall from our previous lesson videos that tonsils are a collection of malt around the entrance of the pharynx or the throat. So they're not in the small intestine, and for that reason, we can eliminate answer option a. Now option b says appendix. However, recall that the appendix is an offshoot of the large intestine, specifically the first part of the large intestine called the cecum. But it's not going to be part of the wall of the ileum or the small intestine. So for that reason, we can eliminate option b. So now we're between either option c, Peyer's patches, or d, lymph nodes. And, of course, recall that option c, Peyer's patches are going to be lymphoid nodules or follicles in the wall of the ileum of the small intestine. So option c is going to be the correct answer to this example problem. Now option d says lymph nodes, and lymph nodes, we know, are strategically located all throughout the body. However, they're not going to be isolated specifically to the wall of the ileum of the small intestine. So option d is not going to be the best answer. Option c is correct. That concludes this example, and I'll see you in our next video.

Which of the following is not considered to be MALT?

• A. Thymus.
• B. Tonsils.
• C. Peyer’s Patches.
• D. Appendix.

Which of the following is a function of the appendix?

• A. Production of digestive enzymes.
• B. Storage of bile.
• C. Regulation of blood sugar levels.
• D. Immune response in the gut.

Here’s what students ask on this topic:

What is MALT and what role does it play in the immune system?

Mucosal-associated lymphoid tissues (MALT) are collections of lymphoid tissues that line mucosal membranes in the body, such as those in the respiratory, digestive, urinary, and reproductive systems. These tissues are crucial for immune defense as they serve as a frontline barrier against pathogens trying to enter the body through mucosal surfaces. MALT includes structures like the tonsils, Peyer's patches, and the appendix. These tissues trap and eliminate pathogens, preventing infections and supporting overall immune function. For example, tonsils trap pathogens from inhaled air and ingested food, while Peyer's patches prevent harmful bacteria from migrating within the digestive system.

Where are Peyer's patches located and what is their function?

Peyer's patches are located on the interior wall of the distal portion of the small intestine, specifically in the ileum. These lymphoid follicles play a crucial role in the immune system by preventing bacteria from the large intestine from migrating backward into the small intestine, where they could cause harm. Peyer's patches help maintain the balance of the gut microbiome and protect against potential infections. They are essential for monitoring intestinal bacteria and generating an immune response when necessary, thus contributing to overall gut health and immunity.

What are the main types of tonsils and their functions?

The main types of tonsils are the pharyngeal tonsil, palatine tonsils, and lingual tonsil. The pharyngeal tonsil is located on the posterior wall of the nasopharynx and helps trap pathogens from inhaled air. The palatine tonsils are found at the posterior end of the oral cavity and are often the ones removed during a tonsillectomy; they trap pathogens from ingested food and inhaled air. The lingual tonsil is located at the base of the tongue and also helps in trapping pathogens. All these tonsils contain tonsillar crypts that trap pathogens for elimination by leukocytes, playing a vital role in immune defense.

What is the function of the appendix in the immune system?

The appendix, once thought to be a vestigial structure, plays a significant role in the immune system. It contains lymphoid follicles that help generate memory lymphocytes, which are crucial for long-term immunity. The appendix also serves as a reservoir for beneficial gut bacteria, helping to repopulate the gut microbiome after disturbances such as diarrhea. This function supports overall gut health and ensures a quick recovery from illnesses that might disrupt the gut microbiome. Thus, the appendix contributes to both immune defense and the maintenance of a healthy gut environment.

How do tonsillar crypts contribute to the immune function of tonsils?

Tonsillar crypts are deep pits or invaginations in the tonsils that trap pathogens and foreign substances. These crypts essentially invite pathogens to fall into these enfolds, where they are then exposed to leukocytes (white blood cells) within the mucosal-associated lymphoid tissues (MALT). The leukocytes eliminate the trapped pathogens, preventing infections. This mechanism allows the tonsils to effectively remove pathogens from the air we inhale and the food we consume, playing a crucial role in the body's immune defense, especially in areas constantly exposed to external pathogens.