Secondary Lympoid Organs: Lymph Nodes - Video Tutorials & Practice Problems
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1
concept
Introduction to Lymph Nodes
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In this video, we're going to begin our lesson on secondary lymphoid organs with an introduction to lymph nodes. Now, lymph nodes are small bean shaped structures, which is why we're showing you some images of beings down below so that you can compare them to the typical structure of a lymph node that we have right here and notice that both of them have an indentation that you can see right here. And this indentation in the lymph node is called the hill hilum. Now, these lymph nodes are going to be found all along lymphatic vessels throughout practically the entire body from your hands and your feet up through your arms and legs into your torso region and even up into your head. However, larger and more prominent lymph nodes are strategically located in regions of the body where lymphatic vessels tend to merge to form lymphatic trunks. And those are going to be the regions that we have indicated here in this image on the right hand side, which are the cervical region or the cervical lymph nodes, which are found here in the neck region, the axillary uh lymph nodes or the axillary region, which is the armpit or under the arm. And the inguinal lymph nodes or the inguinal region, which is this region where your thighs meet the abdomen. Now, the primary function of these lymph nodes is to filter the lymph of harmful pathogens and foreign substances. And these lymph nodes are actually incredibly good at filtering the lymph. In fact, it's estimated that about 99% of all of the pathogens and foreign substances that arrive at a lymph node are trapped within the lymph node and filtered from the lymph before the lymph is returned back to the bloodstream. So that's pretty remarkable. And it goes to show how important these lymph nodes are to our immunity. Now, the amount size and shape of lymph nodes actually varies drastically from individual to individual. And so in terms of the amount, we can't quite put an exact number on it. However, typically there are hundreds of lymph nodes in a single person. In fact, it's estimated that there can be anywhere from about 400 up to about 700 lymph nodes in a single person, which makes lymph nodes the most numerous lymphoid organ. By far. Now, again, the size can also vary anywhere from about just a few millimeters in diameter, up to over an inch in diameter. And although the shape is typically being shaped, again, the shape can also vary but not only does the amount size and shape of lymph nodes vary from individual to individual but it is also dynamic within each of us. And so the amount size and shape of lymph nodes can change within each of us depending on the specific situation and specific factors such as for example, infection, inflammation and immune activity. And it's pretty well known that when you do get sick, your lymph nodes tend to swell up and enlarge and you can often feel them in your neck region when you are sick. Now, because lymph nodes are secondary lymphoid organs. It's no surprise that each lymph node contains lots of immunocompetence lymphocytes such as T and B lymphocytes or T and B cells. And although the primary function of lymph nodes is to filter the lymph and trap pathogens. Lymph nodes are also critical for immune system activation, essentially stimulating the immune system to generate a response. And really this is what makes these lymph nodes secondary lymphoid organs. Now, later in our course, we're going to talk a lot more details about immunity and a lot of these specific uh cells and uh their roles. However, recall from previous lesson, videos that dendritic cells are cells that are able to capture antigens and distant tissues. And they can actually transport those antigens to nearby lymph nodes and present those antigens to lymphocytes in order to activate the lymphocytes. And those activated lymphocytes could either carry out an immune response right then and there in that lymph node or the activated lymphocytes may actually enter into the bloodstream and migrate to that distant site of infection in order to generate the immune response in that distant site of infection. And again, these are ideas that we'll get to talk more about later in our course when we're talking about immunity. But this here concludes our brief introduction to lymph nodes. And as we move forward, we'll get to talk more about the structure of the lymph node. So I'll see you all in our next video.
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example
Secondary Lympoid Organs: Lymph Nodes Example 1
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So here we have an example problem that asks which of the following is not a function of lymph nodes. And we've got these four potential answer options down below. And option A says filtration of lymph or filtering out pathogens from the lymph or in other words, removing disease causing agents from the lymph. And of course, this is definitely a function of lymph nodes. It's probably the main function of lymph nodes if you will. And so we can eliminate answer option A because we are looking for the option that is not a function of lymph nodes. Now, option B says providing a site for lymphocytes to mature. Now, on first glance, this might seem like a function of lymph nodes. However, recall that lymphocytes mature in the primary lymphoid organs, which are the red bone marrow for B cells and the thymus for T cells. And so lymph nodes are not primary lymphoid organs, they are secondary lymphoid organs, which means that lymph nodes already have mature lymphocytes and the lymph nodes do not provide a site for lymphocytes to mature, which means that answer option B is not a function of lymph nodes. So we can indicate that answer. Option B is the correct answer that we are looking for. Now, just to be sure, let's check. Option C and D. Option C says initiating the immune response when a foreign antigen is detected. And of course, we know that this is also a function of lymph nodes. So we can cross off option C and then option D says these are all functions of lymph nodes. But again, we've already identified. Option B is not a function of lymph nodes. So we can also cross off option D. And again, option B is the correct answer to this example problem that concludes this example and I'll see you all in our next video.
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Problem
Problem
In which of the following areas are lymph nodes usually highly concentrated?
A
Feet.
B
Chest.
C
Hands.
D
Neck.
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concept
Lymph Node Structure
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10m
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In this video, we're going to talk about lymph node structure and how lymph actually flows through that structure, which are both critically important to the functions of lymph nodes. So notice down below, we've got this diagram representing the typical structure of a lymph node. And externally, these lymph nodes are surrounded by a capsule made of dense irregular connective tissue which provides structural integrity to the lymph node and protects the delicate insides of the lymph node. So notice that down below in the diagram, the capsule is being labeled right over here. But again, it is going to surround the entire exterior of the lymph node as you can see here. Now, internally lymph nodes are divided into two interior regions which are the outer cortex and the inner medulla. And to make these two regions more clearly visible, we're going to highlight them in specific colors. So the outer cortex we're going to highlight in this light blue color. So notice that down below in this diagram, everything that I'm highlighting in this light blue color represents the outer cortex of the lymph node which notice resembles the shape of the letter C. And so you can think that the letter C in outer cortex is for the shape that it resembles in many of these lymph nodes. Now, you can also see that the outer cortex makes up about 80 ish percent of the lymph node and it encircles almost the entire lymph node, all except the hellum which recall is this indentation that you can see here in the lymph node. Now, the inner medulla, we will highlight in this hot pink color. And of course, that's going to be this inner region that you can see right here. And it does lie deeper to the outer cortex, but the inner medulla does extend to the surface of the lymph node at the helm. Now, this region that you can see that I'm highlighting here in this orangish color is sometimes referred to as the per cortex since it lies in between the outer cortex and the inner medulla. Now, what's important to note is that lymphocytes such as B and T lymphocytes or B and T cells are strategically located within the lymph nodes to optimize their functions. And so what you should note is that the outer cortex of lymph nodes has lymphoid follicles, which recall from previous lesson videos are also sometimes referred to as lymphoid nodules and consist of densely packed spheres of lymphoid tissues and they often have germinal centers with populations of dividing B cells. And so the outer cortex of lymph nodes has those lymphoid follicles with mostly populations of B cells or B lymphocytes. Now, on the other hand, the inner medulla has lymphoid tissue that we refer to as medullary cords. And those medullary cords have populations of both B cells and T cells as well. So if we take a look at the diagram down below, notice on the far left, we're showing you the outer cortex which is where the lymphoid follicles or the lymphoid nodules can be found. And again, recall from previous lesson videos that these are going to be these densely packed spheres of lymphoid tissue that can have lighter staining germinal centers, which is where the populations of B cells are going to be actively divided. And you can see that uh there are plenty of these lymphoid follicles in the outer cortex of each of these lymph nodes. Now, you can also see in this diagram, the inner medulla and the medullary cords, which again are going to be the lymphoid tissues in the medulla that contain populations of both B cells and T cells as well. Now, the trabecula are going to be inward capsular extensions that partially divide the outer cortex into compartments. And it also helps to redirect and direct the flow of lymph through the lymph node, which is critically important. So if we take a look down below at the diagram, you can see that one of the trabecular are being labeled right over here. And again, it's an inward extension of the capsule. And you can see plenty of these trabecula all throughout. And again, these trabecula are breaking up the outer cortex into these compartments that we can see here. Now, the lymph nodes also contain what are known as sinuses. And these sinuses are series of lymph carrying channels or tunnels that have these branching reticular fibers and lymphoid cells as well. And so the lymph will actually flow through all of these different sinuses. And as they flow through the sinuses, they are going to be filtered of pathogens and foreign substances. So let's take a closer look at this diagram down below. And what you'll notice is that we've got these lymphatic vessels over here on the left hand side. And these lymphatic vessels are specifically referred to as a Ferran lymphatic vessel spelled with the letter A. And this is because this is how lymph is going to arrive at the lymph node. And so you can think that the letter A in a Ferran lymphatic vessels is for the letter A in arriving at the lymph node. And so notice that inside of these aer lymphatic vessels over here, we've got these black arrows representing the arrival of lymph at the lymph node. Now, on the opposite side of the lymph node over here at the hill, we've got these other lymphatic vessels which are specifically referred to as eer lymphatic vessels spelled with the letter E. And this is because this is how lymph is going to exit the lymph node. And so you can think that the letter E in E fern lymphatic vessels is for the letter E in exiting the lymph node. Now, what's really important to note is that there are more aer lymphatic vessels and fewer eer lymphatic vessels. Which means that the rate of lymph arrival is significantly greater than the rate of lymph exiting the lymph node. Which ultimately means that the rate of lymph flow through the lymph node is going to be relatively slow. And that slow rate of lymph flow is critically important because it optimizes immune interactions, which is critically important to the function of the lymph nodes. Now notice over here on the right in this box, we've got the lymph flow through the lymph node structures and it's starting here at the top and making its way downwards. And so, of course, we know already that lymph is going to arrive at the lymph node via a Ferran lymphatic vessels. And from there, the lymph is going to enter into a series of sinuses as you can see here and again, recall that these sinuses are really just a series of lymph carrying channels or tunnels. And the first sinus that the lymph will enter into is the subcapsular sinus, which we have color coded here in a yellow color. And as its name implies, the subcapsular sinus is going to be immediately beneath the capsule. And that's because the root sub means below and subcapsular means below the capsule. And so again, you can see that the sinus immediately beneath the capsule is highlighted in that yellow color or the subcapsular sinus. Then from the subcapsular sinus lymph will enter into the trabecular sinus, which we have color coded in this blue color over here. And the trabecular sinus as its name implies is going to be parallel to the trabecular and the subcapsular and trabecular sinuses are going to be found in the outer cortex of the lymph node. Now, from the trabecular sinus, the lymph is going to enter into the medullary sinus, which is going to be found in the Meola and notice that the medullary sinus is going to be this hot pink color that you can see over here. Now, from the medullary sinus, the lymph is going to enter into the efferent lymphatic vessels and exit the lymph node. And so you can see that these black arrows throughout this diagram show you the flow of lymph through the lymph node. And as lymph is flowing through the lymph node, the lymph is able to trickle and diffuse into other areas of the lymph nodes such as the lymphoid follicles and the medullary sinuses. And of course, that lymph is going to be carrying potentially pathogens and foreign substances that can ultimately activate these immune cells and those activated immune cells either carry out an immune response right then and there inside of the uh lymph node or those activated immune cells can actually enter into the bloodstream directly. So notice that we've got an artery coming in here and a pair of capillaries and a vein coming out. And so the activated lymphocytes can actually make their way directly into the bloodstream and migrate to the site of infection and carry out an immune response at that distant site of infection. Now, the last note that I'll leave you all off with is that, although in previous lesson videos, we said that all of the lymph is going to be returned to the bloodstream at the uh veins near the heart. Uh This is going to be true, but it's not all of the lymph, it's the vast majority. So there is a very, very small percentage of lymph and uh a percentage of activated lymphocytes that can actually enter the bloodstream at each lymph node. And so uh you can see here that the bloodstream is going to be closely connected with these lymph nodes. So it's an opportunity for some cleanse the lymph to enter back into the uh bloodstream. So this here concludes our brief lesson on the lymph node structure and we'll be able to get a lot of practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
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example
Secondary Lympoid Organs: Lymph Nodes Example 2
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So here we have an example problem that asks which of the following features are present in both the thymus and in lymph nodes. And we've got these four potential answer options down below which say medulla sinuses, lymphoid nodules or germinal centers. Now recall from our previous lesson videos that the thymus is somewhat unique amongst the other lymphoid organs and that it lacks lymphoid nodules or lymphoid follicles. And so option C is not going to be present in the thymus. So for that reason, we can eliminate answer option C and recall that the germinal centers are the central areas within lymphoid nodules or lymphoid follicles that have populations of B cells that are actively proliferating or dividing. And so because the lymphoid nodules are missing from the thymus, so are the germinal centers. So we can eliminate answer option D as well. So now we're between either option A or option B and recall that option B, the sinuses are present in the lymph nodes since these are going to be channels that carry lymph. However, the thymus does not have sinuses like the lymph nodes. Uh do so. For that reason, we can eliminate answer option B and of course, this leaves answer option A which is the correct answer. Recall that the thymus has an outer cortex and an inner medulla in every lobule and the lymph nodes also have an outer cortex and an inner medulla. So the medulla is found in both the thymus and the lymph nodes, although they serve different functions in these organs. Uh The mela is still a, a uh a feature in each of these organs. So option A is the correct answer to this example problem that concludes its example and I'll see you all in our next video.
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Problem
Problem
Lymph enters the convex side of a lymph node via ___________ lymphatic vessels. It moves through the _________ & then into the ____________. Lymph exits the node at its hilum, via ___________ lymphatic vessels.
A
Efferent; cortex; medulla; afferent.
B
Efferent; medulla; cortex; afferent.
C
Afferent; cortex; medulla; efferent.
D
Afferent; medulla; cortex; efferent.
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example
Secondary Lympoid Organs: Lymph Nodes Example 3
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1m
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So here we have an example problem that says to correctly label the indicated areas of the lymph node down below. Now, over here, on the left hand side, this first label is labeling this lymphatic vessel, which is an a Ferran lymphatic vessel, which recall allows for lymph to arrive to the lymph node. And so you can think that the A in a Ferran is for the A in arrive. Now, on the other side, over here, this label is labeling this lymphatic vessel, which is an E Ferran lymphatic vessel and recall that the E ferr lymphatic vessel will allow lymph to exit the lymph node. So you can think that the E and E fern is for the E and exit. And these E Ferran lymphatic vessels are present at the hellum, which is this indentation here that you can see. Now, one thing to notice here is that there are a lot more aer lymphatic vessels than there are eer lymphatic vessels. And what this means is that the flow of lymph is going to be slowed down in the lymph node, which is ideal for optimizing immune interactions. Now, the next label that you can see over here on the far left is labeling this layer of dense irregular connective tissue that is encapsulating and surrounding the lymph node. And that is going to be the capsule. Now, over here, this label is labeling one of the inward extensions of the capsule and that is going to be the trabecula. And so really this year concludes this example problem. So I'll see you all in our next video.
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Problem
Problem
Which of the following options correctly represents the flow of lymph through a lymph node?