Lymphoid Cells & Tissues - Video Tutorials & Practice Problems
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1
concept
Lymphoid Cells
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Video transcript
In this video, we're going to begin our lesson on lymphoid cells and tissues, but first focusing on lymphoid cells. Now lymphoid cells are cells that are found within and supporting lymphoid tissues. And in our next lesson video, we'll get to talk more about these lymphoid tissues, but they are going to be important for lymphoid organs, which we'll also get to talk more about moving forward in our course. Now, really, there are 4 types of lymphoid cells that we have numbered down below in the text, 1 through 4. And, of course, the numbers in the text correspond with the numbers you'll see down below in the image as well. Now, the good thing about these lymphoid cells is that, really, it's all review from some of our previous lesson videos, and so really the only new piece of information here in this video is that these collection of cells are referred to as lymphoid cells, and that these lymphoid cells are found in lymphoid tissues. So the first type of lymphoid cell that we have listed here are lymphocytes. And recall that lymphocytes are leukocytes or white blood cells, and it includes T cells or T lymphocytes, as well as B cells or B lymphocytes. And these T and B cells are important for adaptive immunity, which we'll get to talk more about later in our course when we focus on immunity. But the lymphocytes also include natural killer cells, or NK cells, which are going to be important for innate immunity, another type of immunity that we'll also talk more about later in our course. Now, the next type of lymphoid cell that we have here are the macrophages, which recall are also leukocytes or white blood cells, but they're going to be specialized for phagocytosis, which recall is a process of cellular eating, so they can basically ingest foreign material and break them down. Now, the next type of lymphoid cell that we have listed here are the dendritic cells, which recall are also a type of leukocyte or white blood cell, and these are going to be important for capturing antigens, foreign antigens, and presenting them on their surface in order to alert and activate other immune cells. And we'll get to talk more about the functions of all of these immune cells later in our course when we focus on immunity. Now, last but not least, the last type of lymphoid cell are reticular cells, which we also talked about in our previous lesson videos when we talked about reticular connective tissue, a type of loose connective tissue. And so, as its name implies with reticular, reticular cells are going to produce reticular fibers. And recall that reticular fibers are going to be net like or branched like, and so they're going to have lots of branches. And the reticular fibers are going to form a supportive network in lymphoid tissues. So, let's take a look down below at this image where we can start to visualize a few things. So notice on the left over here, we're zooming into the lymph node of this person right here, and what you'll notice is that this lymph node is going to have lymphoid tissue and lymphoid cells. And so over here on the right, we have the lymphoid cells listed. So again, it includes lymphocytes such as T lymphocytes and B lymphocytes, or T cells and B cells, it also can include natural killer cells as well, but they're not on here in this image. Then we also have macrophages, which, again, are going to be important for phagocytosis and ingesting, foreign material. We have dendritic cells, which are going to capture antigens, present them on their surface in order to alert and activate other immune cells. And then we have reticular cells, which are going to be producing the reticular fibers, and the reticular fibers are all of these brown branches that you can see, forming this net like or branched structure that is going to form the supportive network for all of these cells, but it can also act somewhat like a spider web in order to trap pathogens as well. And so this here concludes our brief lesson on lymphoid cells, and as we move forward in our course, we'll be able to apply these concepts and learn more about lymphoid cells and lymphoid tissues. So I'll see you all in our next video.
2
example
Lymphoid Cells & Tissues Example 1
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1m
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Video transcript
So here we have a pretty straightforward example problem that asks, what is the primary function of reticular fibers in lymphoid tissues? And we've got these 4 potential answer options down below. Now option a says to produce antibodies, which are y shaped proteins that provide immune functions, and we'll get to talk a lot more about antibodies later in our course when we're focusing on immunity. But these antibodies are not produced by reticular fibers. Instead, it's B cells or B lymphocytes that develop into antibody producing plasma cells. But, again, these reticular fibers don't produce these antibodies, so we can eliminate answer option a. Now, option b says, to engulf pathogens. However, pathogens are going to be engulfed or phagocytosed by macrophages, not by reticular fibers. So for that reason, we can eliminate answer option b. Option c says, to present antigens to b cells. However, the antigen presentation is going to occur with dendritic cells, not through reticular fibers. And so, for that reason, we can eliminate answer option c. And, of course, this leaves answer option d as the only option which is the correct answer. And so the primary function of these reticular fibers in lymphoid tissues is to provide a supportive meshwork for lymphoid cells to proliferate and to optimize immune actions. And so answer option d is the correct answer to this example. That concludes this example, and I'll see you all on our next video.
3
Problem
Problem
Which of the following is not considered a type of lymphoid cell?
A
T cells.
B
B cells.
C
Platelets.
D
Macrophages.
4
concept
Lymphoid Tissue
Video duration:
4m
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Video transcript
In this video, we're going to talk about lymphoid tissue. Now lymphoid tissue is actually made up of reticular connective tissue, which recall from way back in our previous lesson videos is a type of loose connective tissue that has reticular protein fibers in its extracellular matrix, which have a net like or branched structure. Now lymphoid tissue is also going to be made up of the lymphoid cells that we talked about in our last lesson video. Now, the primary function of lymphoid tissue is to support the proliferation and activation of immune cells, particularly lymphocytes, such as b cells and t cells. Now lymphoid tissue can actually be found in 2 different arrangements and distributions. The arrangements refers to how densely packed the lymphoid tissue is, and the distributions refers to where the lymphoid tissue can be found in the body. Now the first is going to be diffuse lymphoid tissue, which as its name implies with the term diffuse, is going to have a diffuse arrangement or a loose arrangement of lymphoid tissue. And in terms of its distribution, it's going to be widely distributed in the body. In fact, diffuse lymphoid tissue is closely associated with areolar connective tissue, which recall from way back in our lesson videos is another type of loose connective tissue that is very widely distributed and can be found underneath of practically all epithelial tissue, including underneath of our skin, all around our body, and underneath of the mucus membranes that line our respiratory and digestive tracts. And so if we take a look at our image down below over here on the left hand side, notice that we're zooming in to regions on this person's body from their head all the way down to their feet, which goes to show how widely distributed this diffuse lymphoid tissue is. And from this micrograph here, you can see the loose arrangement of the lymphoid tissue where the protein fibers are very loosely arranged and you can see these white spaces in the back. Now, the next type of arrangement and distribution are going to be the lymphoid oid follicles, which are also sometimes referred to as lymphoid nodules. Now, be careful not to confuse lymphoid follicles or lymphoid nodules with lymph nodes, which lymph nodes, we'll get to talk more about later in our course, those are a lymphoid organ, whereas lymphoid follicles and lymphoid nodules are tissues that are found within lymphoid organs. Now in terms of their arrangements, lymphoid follicles or lymphoid nodules are going to be very densely packed and consist of densely packed spheres of lymphoid tissue. And in terms of their distribution, they are not as widely distributed as diffuse lymphoid tissue. And really, lymphoid follicles or lymphoid nodules are only really found in lymphoid organs that we'll get to talk more about moving forward in our course. Now often, these lymphoid follicles or lymphoid nodules will have what are known as germinal centers, which are the central area of a lymphoid follicle or lymphoid nodule, where b cells or b lymphocytes actively proliferate and divide. And these lymphoid follicles and lymphoid nodules are actually pretty dynamic, and they can come and go as pathogens invade the tissues and as those pathogens are eliminated. However, lymphoid follicles and lymphoid nodules are a pretty consistent feature of some lymphoid organs, including lymph nodes. And so notice down below, we're showing you a lymph node structure, and we'll get to talk more about the lymph node structure as we move forward in our course. But what I'd like you to notice here is that we're highlighting one of the lymphoid follicles found within this lymph node, and so notice that the lymphoid follicle is going to be this densely packed sphere of lymphoid tissue that you can see highlighted right there. And again, often the lymphoid follicles are going to have a lighter stained germinal center where b cells are going to actively proliferate and divide. Now it turns out that practically all lymphoid organs that we're going to talk about moving forward in our course have these lymphoid follicles or lymphoid nodules except for the thymus, which as we'll learn moving forward in our course, is an exception because they lack the lymphoid follicles and nodules, and they lack b cells. And, again, as we'll learn moving forward in our course, the thymus is almost exclusively specific to the development of T cells. And so, really, this concludes our lesson on lymphoid tissue, and we'll be able to apply these concepts and continue to learn more as we move forward in our course. So I'll see you all in our next video.
5
example
Lymphoid Cells & Tissues Example 2
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1m
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Video transcript
So here we have a true or false example problem, and the statement says, diffuse lymphoid tissue is loosely arranged and only found in lymphoid organs, while lymphoid follicles are tightly packed and widely distributed throughout the body. And we've got these 4 potential answer options down below. Now at first glance, this statement might appear to be true because diffuse lymphoid tissue is loosely arranged and lymphoid follicles are tightly packed. However, the distributions in this statement are incorrect. So although diffuse lymphoid tissue is loosely arranged, it's not only found in lymphoid organs. Diffuse lymphoid tissue is found widely distributed throughout the body. And lymphoid follicles are not widely distributed throughout the body nearly as much as lymphoid, diffuse lymphoid tissue is. Instead, these lymphoid follicles are more so found only in lymphoid organs. And so the statement as written is not true, so we can eliminate answer option A. Now, option B says, false. Diffuse lymphoid tissue is densely packed and lymphoid follicles are loosely arranged, but that's not correct, so we can eliminate answer option b. Option c says false. Diffuse lymphoid tissue is widely distributed, and lymphoid follicles are mostly found in lymphoid organs. And answer option c is going to be correct. So we can go ahead and highlight answer option c and indicate that it is the correct answer to this example problem. Now option d says false, diffuse lymphoid tissue and lymphoid follicles are always found in the same regions, and that's not always going to be true. So for that reason, we can eliminate answer option d. So c here is the correct answer. That concludes this example, and I'll see you all in our next video.
6
Problem
Problem
When are germinal centers most active?
A
During an acute bacterial infection.
B
During fetal development.
C
During REM sleep.
D
During periods of intense physical activity.
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