Lymphoid Cells & Tissues - Online Tutor, Practice Problems & Exam Prep

Lymphoid cells, including lymphocytes (T cells, B cells, and natural killer cells), macrophages, dendritic cells, and reticular cells, play crucial roles in the immune system. Lymphoid tissue, composed of reticular connective tissue, supports the proliferation and activation of these immune cells. It exists in two forms: diffuse lymphoid tissue, which is widely distributed, and lymphoid follicles, found in lymphoid organs, featuring germinal centers for B cell proliferation. Understanding these components is essential for grasping adaptive and innate immunity mechanisms.

Lymphoid Cells

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. In our next lesson video, we'll talk more about these lymphoid tissues, but they are going to be important for lymphoid organs, which we'll also discuss more as we move forward in our course. Really, there are four 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 it's all a review from some of our previous lesson videos, and the only new piece of information here is that this collection of cells is referred to as lymphoid cells, and that these lymphoid cells are found in lymphoid tissues.

The first type of lymphoid cell that we have listed here is lymphocytes. Recall that lymphocytes are leukocytes or white blood cells, and include T cells or T lymphocytes, as well as B cells or B lymphocytes. These T and B cells are important for adaptive immunity, which we'll discuss more about later in our course when we focus on immunity. However, 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 discuss more about later in our course.

The next type of lymphoid cell that we have listed here are macrophages, which, recall, are also leukocytes or white blood cells, but they are specialized for phagocytosis, which is the process of cellular eating, so they can basically ingest foreign material and break them down.

The next type of lymphoid cell that we have listed here are dendritic cells, which, recall, are also a type of leukocyte or white blood cell, and these cells are important for capturing antigens, foreign antigens, and presenting them on their surface to alert and activate other immune cells. We'll discuss more about the functions of all these immune cells later in our course when we focus on immunity.

Last but not least, the final type of lymphoid cell listed here are reticular cells, which we also discussed in our previous lesson videos when we talked about reticular connective tissue, a type of loose connective tissue. As its name implies, reticular cells are going to produce reticular fibers. Recall that reticular fibers are net-like or branched, and they form a supportive network in lymphoid tissues.

Let's take a look down below at this image where we can start to visualize a few things. Notice on the left over here, we are zooming into the lymph node of this person, and what you'll notice is that this lymph node has lymphoid tissue and lymphoid cells. Over here on the right, we have the lymphoid cells listed. It includes lymphocytes such as T lymphocytes and B lymphocytes, or T cells and B cells. It also can include natural killer cells, but they are not shown here in this image. Additionally, we 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 and present them on their surface to alert and activate other immune cells. And then we have reticular cells, which are going to be producing reticular fibers, and these fibers are the brown branches that you can see, forming this net-like or branched structure that forms the supportive network for all these cells, but can also act somewhat like a spider web to trap pathogens. And so, this 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. I'll see you all in our next video.

Lymphoid Cells & Tissues Example 1

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.

Which of the following is not considered a type of lymphoid cell?

• A. T cells.
• B. B cells.
• C. Platelets.
• D. Macrophages.

Lymphoid Tissue

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 refer to how densely packed the lymphoid tissue is, and the distributions refer to where the lymphoid tissue can be found in the body.

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 practically all epithelial tissue, including underneath our skin, all around our body, and underneath the mucous 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 into 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 background.

Now, the next type of arrangement and distribution are going to be the lymphoid 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 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.

Lymphoid Cells & Tissues Example 2

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 four 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.

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.

Here’s what students ask on this topic:

What are the main types of lymphoid cells and their functions?

The main types of lymphoid cells include lymphocytes (T cells, B cells, and natural killer cells), macrophages, dendritic cells, and reticular cells. T cells and B cells are crucial for adaptive immunity, with T cells attacking infected cells and B cells producing antibodies. Natural killer cells are part of innate immunity, targeting virus-infected and cancerous cells. Macrophages perform phagocytosis, ingesting and breaking down foreign material. Dendritic cells capture antigens and present them to other immune cells, activating them. Reticular cells produce reticular fibers, forming a supportive network in lymphoid tissues.

What is the difference between diffuse lymphoid tissue and lymphoid follicles?

Diffuse lymphoid tissue has a loose arrangement of lymphoid cells and is widely distributed throughout the body, often found in association with areolar connective tissue. It is present under epithelial tissues, including the skin and mucous membranes of the respiratory and digestive tracts. Lymphoid follicles, also known as lymphoid nodules, are densely packed spheres of lymphoid tissue found within lymphoid organs. They often contain germinal centers where B cells actively proliferate. Unlike diffuse lymphoid tissue, lymphoid follicles are not as widely distributed and are primarily located in lymphoid organs.

What is the role of reticular cells in lymphoid tissues?

Reticular cells play a crucial role in lymphoid tissues by producing reticular fibers, which form a supportive network. These fibers have a net-like or branched structure, providing a scaffold that supports other lymphoid cells. This network not only supports the cells but also helps trap pathogens, acting somewhat like a spider web. Reticular cells are essential for maintaining the structural integrity of lymphoid tissues and facilitating the immune response by creating an environment conducive to the proliferation and activation of immune cells.

How do lymphoid follicles contribute to the immune response?

Lymphoid follicles, or lymphoid nodules, contribute to the immune response by providing a site for the proliferation and activation of B cells. These follicles often contain germinal centers, which are areas where B cells rapidly divide and differentiate in response to antigens. This process is crucial for the production of antibodies, which are essential for targeting and neutralizing pathogens. The dense arrangement of lymphoid follicles within lymphoid organs ensures a concentrated and efficient immune response, particularly during infections.

Where can diffuse lymphoid tissue be found in the body?

Diffuse lymphoid tissue can be found throughout the body, closely associated with areolar connective tissue. It is present underneath practically all epithelial tissues, including the skin and mucous membranes lining the respiratory and digestive tracts. This widespread distribution allows diffuse lymphoid tissue to play a significant role in the initial immune response by providing a first line of defense against pathogens that enter the body through these surfaces.