Overview of the Lymphatic System Functions

When I first learned about the immune system, I remember being really confused. I couldn't visualize where it was and what it did and how it related to other parts of the body. So what I'm going to do in this video is we're going to take a look at a series of diagrams and reveal it piece by piece so that you understand by the end of this exactly what the lymphatic system does, how it's organized, and where it is in the body. So let's jump to the whiteboard and get started. So let's start with the three main functions of the lymphatic system. The first thing is it's going to prevent swelling or edema. by returning fluid to the bloodstream. So there's gonna be a buildup of fluid and tissues throughout our body. The lymphatic system is gonna take that fluid and return it to our blood circulation so they won't have swelling throughout our body. The second thing is it's gonna scan for pathogens and initiate an immune response if it finds them. So it's gonna take some of this fluid from the tissue in our body. It's gonna run it through lymph nodes. The lymph nodes will be full of B cells and T cells, all these immune system cells that are gonna detect if there's a pathogen. If there is, It's going to fight that pathogen off and start this immune response so that we can get our body back to being healthy. And that's why the lymphatic and the immune systems are often lumped together kind of as one system. Finally, the third thing it's going to do is it's going to absorb fat from our digestive tract, from the intestines, and bring that fat into blood circulation. So it turns out that fats that we eat can't go from our intestines directly into our bloodstream. It's got to take a detour through the lymphatic system in order to get to the bloodstream. We'll talk about why that is later on. So those are the three primary lymphatic system functions and throughout the video we're going to be looking at those and seeing how the lymphatic system is set up in order to accomplish those three functions. First we're going to take a look at the fluid management part of this, the part where I talked about it reducing swelling or edema in the body. So we're going to zoom in on some tissue in the body here. Here we've got an arteriole which is going to be bringing blood into this tissue area and we've got a venule which is going to be bringing blood out of that tissue area. And this arteriole is bringing blood from the heart that's oxygen rich. The venule is returning blood back to the heart that's oxygen poor. In other words, it's given off its oxygen. It's returning back to the heart. Now let's draw some tissue cells in here. And so I've got a bunch of cells here. It kind of looks like a skull. That was unintentional. There's a lot of epithelial cells and there's going to be spaces in between some of those epithelial cells. The spaces between cells are going to be filled with fluid. Now to deliver the fluid and the oxygen and all the stuff that these cells need, we're going to need capillaries. So we have a capillary that's connecting in the arterial over to the venule. In the diagram, you see a color change from red to blue, meaning that it's going to be giving off oxygen. I feel like I say this in every video I make, but the blood never actually turns to blue. It's always red, just a slightly different shade of red. But in diagrams, we use red and blue for oxygen, poor and oxygen-rich blood. Now it's not just one capillary, we've got a whole bed of capillaries. So we see this bed of capillaries with all these branches. and that's so that it can give off the oxygen and fluid and everything to all the different cells here all right let's remove a few cells so we have room to write some stuff here and like i said it's going to be giving off oxygen to these cells it's also going to be distributing water or fluid these capillaries are leaky so the water the oxygen is going to be coming out of there it's also going to have other things coming out such as proteins hormones nutrients all these different things that the cells need to survive all of that is leaking out of the capillary into the space between the cells The main two we're concerned about here are water and oxygen though. And of course, there's other stuff that needs to go back into bloodstream circulation, waste products that we don't need, such as carbon dioxide that the cells produce during cellular respiration, as well as a lot of that fluid that leaks out is going to be pulled back in to the capillaries. So we have water coming out and we have water coming back in to return to circulation. Now there's various forces that are causing the fluid to move in and out. We've got hydrostatic pressure, which is kind of just the fluid pressure of something moving through a tube. and that's going to be forcing a lot of this water out. We also have osmotic pressure, which is going to be pulling a lot of the water back in. But also, like I said, there's proteins and other stuff that are leaking out. So we've got proteins floating around in this interstitial space between the cells, and that's going to be pulling on the water and keeping some of that water outside of the blood vessels because of osmotic pressure. Hydrostatic and osmotic pressure are a little bit confusing. That's probably a topic for another video, but the main thing to know here is that water's coming out and water's coming back in, but there's more water leaving the capillaries than there is water coming back in. into the capillaries. And so that's going to lead to a buildup of fluid in this tissue over time, leading to swelling. So we need something else in this tissue that's going to remove that excess water. And so that's where the lymphatic capillaries come in. The lymphatic capillaries are these series of tubes that extend up into the capillary bed. We always use green and diagrams to represent the lymphatic system. And they branch in and out here, but they're not a continuous stream like the blood vessels are. The cardiovascular system is a closed system, meaning that the fluid could stay in the cardiovascular system and completing the circuit from the heart to the lungs, back to the heart, to the tissues of the rest of the body, and then back to the heart, and so on. The lymphatic system is an open system. It's not a continuous system that's going to go throughout the whole body and return back to its original location. So it's going to be absorbing some of this interstitial fluid, and it's going to travel through here, and that's eventually going to work its way back to the veins, returning all the excess fluid that it picks up back in. to venous circulation. But again, the thing we're focused on right here is preventing swelling. So like I said, there's water leaving, there's some water coming back in, but not enough water coming back in. So a lot of that buildup of fluid is going to enter into the lymphatic capillaries and travel down here so it can be returned back to circulation. Now let's zoom in on the end of one of these little lymphatic capillaries. So we've got our main capillary right here, the end of the lymphatic capillary. and we've got all the tissue cells that are there. Now, if you notice and look closely, there's these spaces that are between the cells and the capillary. That's where the fluid is gonna be leaving, as well as proteins and other things, how they leave the capillary through those little spaces right there. The lymphatic capillaries have spaces as well. Can't really tell in the diagram, but those spaces in the lymphatic capillaries are a little bit bigger, and that's gonna be important later on. And of course, we have red blood cells that are traveling through the capillary. Those are carrying oxygen in. carbon dioxide out now we've got a lot of fluid in this diagram there's fluid here in the blood capillary there's fluid in the lymphatic capillary there's fluid between the cells and they all have different names so blood plasma is what we call the fluid in the blood capillary we have lymphatic fluid or lymph which is the fluid that's in the lymphatic capillary. And then we have interstitial fluid, which is the fluid between the cells and the tissue. Interstitial just means between things. Now, most of this is all the same stuff. It's mostly water. There's other stuff dissolved in it, and it's flowing in and out between all these areas. We just give it different names depending on where it's located. Now let's break down all the movement happening in this diagram. First of all, we've got the blood that's coming in. So that's going to be blood plasma or fluid in the red blood cells, also white blood cells coming through there. That's coming from the heart. And then we have fluid flowing out of this area, traveling back to the heart. Of course, those capillaries are leaky. So we've got fluid that's traveling out of the capillary, which we see right here. And a lot of that fluid that leaves is going to go back into the capillary, which we see right here. Of course, not as much fluid is traveling back into the capillary. So we have a buildup of fluid in the tissue space or a buildup of interstitial fluid. So. So a lot of that fluid is going to travel into the lymphatic capillaries, becoming lymph, which is then going to travel through the rest of the lymphatic system and then back. to a vein to the subclavian vein where it's back into circulation and again the fluid in here we call blood plasma once it leaves the capillary we call interstitial fluid and once it moves from the interstitial fluid to the lymphatic capillary we call it lymph so this diagram is showing what's happening in the lymphatic system at the tissue level how these lymphatic capillaries are going to be pulling fluid this excess fluid from the interstitial space and bringing it out of that tissue so that we don't have swelling or edema throughout the tissues in her body. Next, we're going to zoom out and look kind of at the whole body level. So I've got a diagram of a person here. We're going to start here with the hands, just because it's a distal end of the arm here. And you can see all these little lymphatic capillaries that are extended out into all parts of the hand. Basically, almost anywhere in your body where there's blood or blood capillaries, there's going to be lymphatic capillaries that are there to remove that fluid. So those lymphatic capillaries are going to be picking up fluid, which came from the bloodstream, which then became interstitial fluid, and now is in the lymph vessels. So it's going to be bringing that lymph fluid up the arm closer to the middle part of the body. And if you notice right here, we've got some spots in those lymph vessels and those are going to be lymph nodes. And this is where we're getting into that second function of the lymphatic system, where we're scanning for pathogens and initiating an immune response. The lymph nodes are where a lot of that is taking place. So let's zoom in on one of those lymph nodes and take a look at the structure of the lymph node and how it does this. All right. So there's a cute little lymph node, and we're going to have first some vessels that are bringing the lymph. into the lymph node. We call these afferent vessels. Afferent just means toward, and I have the A capitalized there because in a second we're gonna see an efferent vessel. So these vessels, like this one right here, that's gonna be an afferent vessel that's bringing lymph into the lymph node. Now notice on these vessels, there are these little valves which are gonna make sure that the lymph is only flowing in one direction. And if lymph tries to flow. backward those are going to snap shut and prevent the lymph from backflowing. Since we don't have a lymphatic equivalent of a heart to push or pump the lymph fluid through the lymph vessels we've got these one-way valves. so that that lymph fluid is only traveling in the correct direction. So lymph is coming in through multiple afferent vessels here, and then the lymph is going to travel out of the lymph node through an efferent vessel. And there's only ever going to be one efferent vessel leaving a lymph node. All right, now let's take a look at a couple regions of the lymph node here. First, we've got the medulla, which is going to be kind of in the center of the lymph node right there, where the lymph is passing through to get to the efferent vessel. And then we've got the cortex, which is going to be the outer part of the lymph node. So all these sections right in here are part of the cortex. Now for this to scan for pathogen, we have to have white blood cells present or lymphocytes present Those lymphocytes are going to be B cells and T cells and macrophages and a few others, but they've got to get there somehow. Now, they're white blood cells. They need to come through the bloodstream. So we're going to have some blood vessels coming into each of the lymph nodes. Those blood vessels are going to enter in right by the efferent vessel right in here. It's going to be bringing blood in, including white blood cells. And then, of course, you've got to have a vein, which is going to be traveling out of that area. And so we've got a little capillary bed, and that's how the white blood cells are going to make it to the lymph node. So we're going to have B cells all throughout this. outer part of the cortex we're gonna have T cells kind of mainly clustered in the inner part of the cortex. So any pathogens that get into your bloodstream, some of those are gonna end up in the lymph fluid where they're gonna pass through here and they're gonna have to pass by these B cells and these T cells, which are gonna be on the lookout for antigens on those pathogens that they recognize so they can start attacking them and initiate this immune response by the body. So the lymph fluid is gonna pass by there. It's gonna fill in this medulla and then come out through the efferent vessel where it's gonna continue on its path. And we're gonna see where that path goes to next. So again, how does the lymphatic system scan for pathogens and initiate the immune response? Well, lymph is going to be traveling through these afferent vessels through the cortex where it passes by B cells and T cells. Those are going to be trying to detect and see if there's a pathogen present, and they'll start that immune cascade if there is. And if not, that lymph fluid is going to pass by out the afferent vessel where it can continue on its path. All right, let's see where all of this goes next. But first I want to point out, if you notice that the lymph nodes aren't just throughout Every part of these lymph vessels, they're kind of clustered in certain regions. Throughout this next part of our diagram here, I'm going to be pointing out lymph node regions in green and this first section here that you see is the epitrochlear section of lymph nodes. Those are gonna be located kind of on the medial side of the elbow right in there. Now all of this lymph fluid that's traveled up from the hand, it's gonna be traveling up here through this axillary or armpit region. And we're actually going to have a lot of lymph nodes in that axillary region. So you've got a lot of lymph nodes in your armpit kind of extending up here toward the neck region. Notice that almost all of those vessels are starting to converge into one bigger vessel right there. This is where the lymph fluid is about to drain back into the veins so it can return to our blood circulation. So here in our diagram, we have the right subclavian vein. and the left subclavian vein. The subclavian veins connect together to form the superior vena cava and the superior vena cava is going to bring the blood back into the heart, the right atrium, right ventricle. It can pump it to the lungs, but all of the lymph fluid that we gather is going to drain back into either the right subclavian vein or the left subclavian vein through two different ducts. The first of those is the right lymphatic duct and then the second is going to be the thoracic duct. The thoracic duct is going to extend down into your chest and down toward the abdomen. And the thoracic duct is going to get most of the lymph drainage. And the right lymphatic duct is going to get just a smaller fraction of it. We'll see more of this in a second, but the right lymphatic duct is going to get lymph from the right arm, the right side of the face, and a little bit in this region right here. Whereas the thoracic duct is going to drain all of the lymph from the left arm, the left side of the face. as well as like the whole lower half of the body. So right lymphatic duct is getting just lymph from this region right here. Thoracic duct is getting lymph from this region down here and the whole lower half of the body. The chest is also gonna have a lot of lymphatics. And so we see a lot of lymphatic vessels right here that are gonna be collecting fluid and bringing up into that axillary region. Up next is the region where we actually have the most lymph nodes and that's gonna be in the cervical region. So there's gonna be a lot of lymph nodes in our neck. There's gonna be a lot kind of in the side of our face right in here. And oftentimes that's broken up not just into cervical, but other names of regions as well. But in this video, I'm just giving kind of an overview of the location of the lymph nodes. So we've got all those lymph nodes in the cervical region. In the left side of the face, they're draining into the thoracic duct. And then in the right side of the face, all of those are going to be draining into the right lymphatic duct. So if you were to trace the path here, from the hand, the lymph is traveling up this way into the right lymphatic duct. From the face, it's traveling down to the right lymphatic duct. Or from here, it's traveling up the arm to the thoracic duct. Or from the face, down to the thoracic duct. Now let's move on to the lower half of the body. We're going to start down at the very bottom or inferior part. We're going to have some lymph nodes in the knees, and those are going to be the popliteal lymph nodes. Popliteal is just referring to the knee. That lymph fluid is going to be draining upward. It's going to head toward the inguinal lymph nodes. The inguinal lymph nodes are found right in here. And then from there, lymph fluid is going to travel up. into the abdominal lymph nodes right in through here. So if you'll notice, you don't have a lot of lymph nodes in the leg. You don't really have any below the knee. You've got a few in the knee. You've got a lot in the inguinal area right here. You've got a lot in the abdominal area right here. Now, almost all of the lymph fluid that's coming from the lower half of the body is going to be right in here where it's going to enter into something called the cisterna chyli. The cisterna chyli is just this big collecting duct for lymphatic fluid. It's going to connect all these lower lymphatic vessels up to the thoracic duct. and all that lymphatic fluid is going to drain into the left subclavian vein via the thoracic duct. A couple more branches here that I need to draw in. The next one is going to be the thoracic lymph node. So it's kind of a more lateral branch that's going to come up here. That's going to have some thoracic lymph nodes. We're going to have those on the other side as well. From what I can tell on most diagrams that I've seen, there is a lymph connection from the cisterna chyli right here up to the right lymphatic duct. So I'd imagine there is a little bit of drainage. from this lower part of the body up into the right lymphatic duct, but the vast majority of lymphatic fluid from the lower half of the body is going to travel up through the thoracic duct into the left subclavian vein. So all of these lymphatic vessels that are in almost all parts of the body, they're pulling fluid in to scan for pathogens and initiate an immune response. So if there is an invader in the body, the lymph nodes are going to find it. But don't forget about our first function of the lymphatic system, which is preventing swelling. And so they're pulling this fluid from all these different body regions where that fluid may be building up more than it should. So they're pulling that fluid out. All that fluid is going to travel toward those subclavian veins, either via the right lymphatic duct or the thoracic duct to get all that excess fluid back into the bloodstream where it belongs. So we don't have swelling throughout the body. All right, next, let's talk about that third function, the absorbing fat from intestines and delivering it to the bloodstream. So let's draw in a little boom. branch of the small intestine right here and we've got a lymphatic vessel that's going to be pulling fluid from that intestine and connecting it to the cisterna chyli right in here where it can drain it back into the thoracic duct. I just have a small section of intestine drawn but that's so that my diagram doesn't get a little bit out of hand but really these lymphatic vessels are going to be connecting all throughout the small intestine to pull that fluid out. So really this whole area right here would be full of these lymphatic vessels pulling fluid out of the intestines and into the cisterna chyli. Now, when I first learned about all this stuff, I learned that the fats and sugars and proteins and all the nutrients that we eat are going to go from the digestive system straight to the bloodstream. All those things get absorbed from the small intestine into the bloodstream. But it turns out that's not quite the whole truth. Take a look at this diagram. There's a lot going on here, but let's break it down. We've got a section of the small intestine. Inside that small intestine, if we cut it open, we'll see there's these villi or these tiny little kind of squiggly looking surface membranes that are on the surface of the small intestine. All the food that we eat after it's been broken down is traveling through this tube of the small intestine. Now we've got to get those nutrients from the lumen of the small intestine into the bloodstream. So let's zoom in on one of these villi or an anvilis. Here are the absorptive cells or enterocytes. The nutrients that we've digested are going to pass through there. And most of those are going to pass into the capillaries right here. And they're going to be traveling through the capillary, through the venule. and then back into circulation as it goes directly into the bloodstream. That's going to be true for proteins and sugars because they're soluble in water, and they're pretty small. They can pass through the membranes. Fats or lipids are a different story. Lipids are not water-soluble, so they can't just go directly into the water. They've got to be packaged. So in these absorptive cells, they're going to be packaged into something called a chylomicron. A chylomicron is a long, fancy name for basically a little water-soluble package that the lipids will get packaged into so they can enter it. into the fluid. So they get packaged into a chylomicron, but unfortunately the chylomicron, it's a little bit bulky. It's not going to fit into the capillaries to make it into the bloodstream. There's just not enough space between the cells and the capillaries. However, the lymphatic capillaries actually have more space between the cells. and the chylomicrons can fit into there. So with the lipids, which are in the chylomicrons, what they're gonna do is they're gonna travel through the lymphatic vessel right here, and they're gonna travel out, then they're gonna travel through here, up through the cisterna chyli, and the thoracic duct, and then boom, they're back into. to blood circulation, but they never had to travel directly through a blood capillary. They entered the lymphatic capillaries instead. So that's the third function, absorbing fats from the intestines, delivering those to the bloodstream through the lymphatic system. All right, next, let's go back to that path. pathogen and immune response thing again. These other organs we're about to talk about are included in the lymphatic system because they help with this immune response. The first one is going to be the thymus. The thymus is located sort of anterior to your heart. It's actually bigger when you're a kid and then it shrinks over time. By the time you're an adult, it's like a tenth of its normal size usually. But what the thymus does is it's going to produce T lymphocytes. Those T lymphocytes first grew in the bone marrow. That's where your white blood cells and red blood cells are mainly produced. They'll travel from there to the thymus, and the thymus is gonna have them develop and mature into T cells. Why do we call them T cells? Well, because they're made in the thymus, which starts with T. From the diagram, I just realized it looks like the thoracic duct is gonna be connected to the thymus. It's not. A thymus has blood vessels that are connected to it, and that's how it's getting these T cells and then sending these T cells out. And of course, a lot of these T cells are gonna end up in the lymph nodes. throughout the body. So the thymus is considered a lymphatic organ because of that. Next we have bone marrow. And so the bone marrow is going to be in bones throughout the body. I just drew kind of the head of the femur down here to represent the bone marrow. The bone marrow is going to be where all these white blood cells are created. And specifically, it's going to be where the B lymphocytes or B cells are developing and maturing. Why are they called B cells? Well, because they're made in the bone marrow, which starts with B. Of course, a lot of those B lymphocytes are going to travel through the bloodstream and they're going to make it to the lymph nodes throughout the body so they can hang out and look for pathogens in their lymph fluid. The thymus and the bone marrow are considered primary lymphatic organs because they're actually producing the cells of the lymphatic system. Another organ to talk about here is the spleen, which is considered a secondary lymphatic organ. It does a couple things. One thing it does is it kind of acts like a lymph node for your bloodstream. There aren't lymphatic vessels going to it, but there are. blood vessels going to it. And it's going to have a lot of these B cells and T cells that are going to kind of hang out and fight pathogens. If there's any that come into the spleen through the blood vessels right there. But another big thing that it does is it breaks down old red blood cells. So red blood cells have a very limited lifespan. And at the end of their lifespan, they're going to get broken down by the spleen so that we can then get rid of them. One more thing I don't have that diagram is our tonsils. Our tonsils kind of work like the spleen does. They contain lymphocytes to fight off pathogens, but they're up in the face in some of the cavities up there. All right, that was a lot of information. Now I'm going to give you a chance to practice some of that information and see if you can recall it. Here's a blank graphic of the lymphatic system functions. Pause the video, see if you can name the three functions of the lymphatic system. And those functions are one, it prevents swelling or edema by returning interstitial fluid to the bloodstream. Second, it's going to scan for pathogens and initiate an immune response if it finds pathogens. And third, it's going to absorb fats from intestines and deliver those to the bloodstream. Up next, we have this diagram of the tissue capillaries and lymphatic capillaries. Take a minute, pause the video, see if you can describe everything that's in this diagram, as well as describe what's happening in all the different parts of the diagram. All right, and here's a completed version of that diagram. As a quick overview, we've got blood coming in, traveling through here. It's gonna be dropping off water and oxygen and proteins and other nutrients to the tissue cells. Water and carbon dioxide is gonna be traveling back into the tissue capillaries so that we can get rid of it. However, we've got a lot of water leaving and only about 90% of that water is coming back. So we've got an extra 10% that we've gotta get back into blood circulation. That's where these lymphatic capillaries are gonna come in. So a lot of fluid is gonna travel back into the lymphatic capillary and it's gonna take it out of this tissue and get it back into blood circulation. We've got a zoomed in version of that, which includes blood plasma, interstitial fluid, and then lymph or lymphatic fluid. Fluid from the blood plasma is gonna travel out into the interstitial space. About 90% is gonna travel. back into the blood capillary. That other 10%, we need to get it back into blood circulation. So it's going to travel through the lymphatic vessel and then back into that subclavian vein later on. Another thing that we talked about is the lymph node. So here's a blank diagram of the lymph node. Again, pause the video. See if you can identify all the parts of the lymph node, as well as the direction that fluid travels and what all it does. All right, here's that completed diagram. Now we've got lymphatic fluid that's coming into the afferent vessels. We've got the lymphatic fluid coming out through the efferent vessel. That fluid has to travel past B cells and T cells, which are scanning that fluid, looking for any pathogens to fight off. If it finds them, it'll initiate the immune response. If not, that fluid will travel out through that efferent vessel. And we have the medulla here and the cortex is the outer part where the B cells and T cells are found. And then finally, here's our picture of the whole person. Pause the video. See if you can name all of the lymph nodes. regions as well as the other lymphatic organs and what all those lymphatic organs do. And there's all those terms again. The lymphatic fluid from the hand and the arm is going to travel up through this region, past the epitrochlear lymph nodes, through the axillary lymph nodes, and then into the thoracic duct or on this side up through the right lymphatic duct. Majority of our lymph nodes are here in the cervical region. Those are going to drain down into the thoracic. and right lymphatic duct. Fluid from the lower leg is going to travel up through the popliteal lymph nodes, up through the inguinal lymph nodes, abdominal lymph nodes, into the cisternic hyaline, which is going to travel through the thoracic duct. All of that lymph fluid is going to make it back into the left subclavian vein or the right subclavian vein. We have lymph vessels that are taking fluid from the small intestine. That's where fats are going to get absorbed into the lymphatic system so they can return to venous circulation. And finally, we have these other lymphatic organs, the thymus, where T cells develop and mature, the bone marrow, where B cells develop and mature. And we have the spleen, which contains a lot of lymphocytes, which will fight off pathogens, as well as being a site where red blood cells are broken down. All right, so that was a lot of information. It turns out the lymphatic system has a lot of parts. There's a lot of complexity to it. I didn't get into how the B cells and T cells actually do the immune response. If you're interested in that, I've got a video on that. So check that video out. It should be linked right here. Special shout out to my patrons on Patreon who helped make this video possible. If you're looking for the diagrams from this video, both the blank and completed diagrams, those are available on my Patreon. So check that out. There's a link below. And good luck learning anatomy. Hope to see you in the next video. I'll see you then.

The first thing is it's going to prevent swelling or edema. by returning fluid to the bloodstream. So there's gonna be a buildup of fluid and tissues throughout our body.

The lymphatic system is gonna take that fluid and return it to our blood circulation so they won't have swelling throughout our body. The second thing is it's gonna scan for pathogens and initiate an immune response if it finds them. So it's gonna take some of this fluid from the tissue in our body.

It's gonna run it through lymph nodes. The lymph nodes will be full of B cells and T cells, all these immune system cells that are gonna detect if there's a pathogen. If there is, It's going to fight that pathogen off and start this immune response so that we can get our body back to being healthy. And that's why the lymphatic and the immune systems are often lumped together kind of as one system. Finally, the third thing it's going to do is it's going to absorb fat from our digestive tract, from the intestines, and bring that fat into blood circulation.

So it turns out that fats that we eat can't go from our intestines directly into our bloodstream. It's got to take a detour through the lymphatic system in order to get to the bloodstream. We'll talk about why that is later on. So those are the three primary lymphatic system functions and throughout the video we're going to be looking at those and seeing how the lymphatic system is set up in order to accomplish those three functions. First we're going to take a look at the fluid management part of this, the part where I talked about it reducing swelling or edema in the body.

So we're going to zoom in on some tissue in the body here. Here we've got an arteriole which is going to be bringing blood into this tissue area and we've got a venule which is going to be bringing blood out of that tissue area. And this arteriole is bringing blood from the heart that's oxygen rich. The venule is returning blood back to the heart that's oxygen poor.

In other words, it's given off its oxygen. It's returning back to the heart. Now let's draw some tissue cells in here. And so I've got a bunch of cells here. It kind of looks like a skull.

That was unintentional. There's a lot of epithelial cells and there's going to be spaces in between some of those epithelial cells. The spaces between cells are going to be filled with fluid.

Now to deliver the fluid and the oxygen and all the stuff that these cells need, we're going to need capillaries. So we have a capillary that's connecting in the arterial over to the venule. In the diagram, you see a color change from red to blue, meaning that it's going to be giving off oxygen.

I feel like I say this in every video I make, but the blood never actually turns to blue. It's always red, just a slightly different shade of red. But in diagrams, we use red and blue for oxygen, poor and oxygen-rich blood. Now it's not just one capillary, we've got a whole bed of capillaries.

So we see this bed of capillaries with all these branches. and that's so that it can give off the oxygen and fluid and everything to all the different cells here all right let's remove a few cells so we have room to write some stuff here and like i said it's going to be giving off oxygen to these cells it's also going to be distributing water or fluid these capillaries are leaky so the water the oxygen is going to be coming out of there it's also going to have other things coming out such as proteins hormones nutrients all these different things that the cells need to survive all of that is leaking out of the capillary into the space between the cells The main two we're concerned about here are water and oxygen though. And of course, there's other stuff that needs to go back into bloodstream circulation, waste products that we don't need, such as carbon dioxide that the cells produce during cellular respiration, as well as a lot of that fluid that leaks out is going to be pulled back in to the capillaries.

So we have water coming out and we have water coming back in to return to circulation. Now there's various forces that are causing the fluid to move in and out. We've got hydrostatic pressure, which is kind of just the fluid pressure of something moving through a tube. and that's going to be forcing a lot of this water out. We also have osmotic pressure, which is going to be pulling a lot of the water back in.

But also, like I said, there's proteins and other stuff that are leaking out. So we've got proteins floating around in this interstitial space between the cells, and that's going to be pulling on the water and keeping some of that water outside of the blood vessels because of osmotic pressure. Hydrostatic and osmotic pressure are a little bit confusing. That's probably a topic for another video, but the main thing to know here is that water's coming out and water's coming back in, but there's more water leaving the capillaries than there is water coming back in.

into the capillaries. And so that's going to lead to a buildup of fluid in this tissue over time, leading to swelling. So we need something else in this tissue that's going to remove that excess water. And so that's where the lymphatic capillaries come in.

The lymphatic capillaries are these series of tubes that extend up into the capillary bed. We always use green and diagrams to represent the lymphatic system. And they branch in and out here, but they're not a continuous stream like the blood vessels are.

The cardiovascular system is a closed system, meaning that the fluid could stay in the cardiovascular system and completing the circuit from the heart to the lungs, back to the heart, to the tissues of the rest of the body, and then back to the heart, and so on. The lymphatic system is an open system. It's not a continuous system that's going to go throughout the whole body and return back to its original location.

So it's going to be absorbing some of this interstitial fluid, and it's going to travel through here, and that's eventually going to work its way back to the veins, returning all the excess fluid that it picks up back in. to venous circulation. But again, the thing we're focused on right here is preventing swelling.

So like I said, there's water leaving, there's some water coming back in, but not enough water coming back in. So a lot of that buildup of fluid is going to enter into the lymphatic capillaries and travel down here so it can be returned back to circulation. Now let's zoom in on the end of one of these little lymphatic capillaries. So we've got our main capillary right here, the end of the lymphatic capillary. and we've got all the tissue cells that are there.

Now, if you notice and look closely, there's these spaces that are between the cells and the capillary. That's where the fluid is gonna be leaving, as well as proteins and other things, how they leave the capillary through those little spaces right there. The lymphatic capillaries have spaces as well.

Can't really tell in the diagram, but those spaces in the lymphatic capillaries are a little bit bigger, and that's gonna be important later on. And of course, we have red blood cells that are traveling through the capillary. Those are carrying oxygen in.

carbon dioxide out now we've got a lot of fluid in this diagram there's fluid here in the blood capillary there's fluid in the lymphatic capillary there's fluid between the cells and they all have different names so blood plasma is what we call the fluid in the blood capillary we have lymphatic fluid or lymph which is the fluid that's in the lymphatic capillary. And then we have interstitial fluid, which is the fluid between the cells and the tissue. Interstitial just means between things.

Now, most of this is all the same stuff. It's mostly water. There's other stuff dissolved in it, and it's flowing in and out between all these areas.

We just give it different names depending on where it's located. Now let's break down all the movement happening in this diagram. First of all, we've got the blood that's coming in. So that's going to be blood plasma or fluid in the red blood cells, also white blood cells coming through there.

That's coming from the heart. And then we have fluid flowing out of this area, traveling back to the heart. Of course, those capillaries are leaky. So we've got fluid that's traveling out of the capillary, which we see right here.

And a lot of that fluid that leaves is going to go back into the capillary, which we see right here. Of course, not as much fluid is traveling back into the capillary. So we have a buildup of fluid in the tissue space or a buildup of interstitial fluid. So. So a lot of that fluid is going to travel into the lymphatic capillaries, becoming lymph, which is then going to travel through the rest of the lymphatic system and then back.

to a vein to the subclavian vein where it's back into circulation and again the fluid in here we call blood plasma once it leaves the capillary we call interstitial fluid and once it moves from the interstitial fluid to the lymphatic capillary we call it lymph so this diagram is showing what's happening in the lymphatic system at the tissue level how these lymphatic capillaries are going to be pulling fluid this excess fluid from the interstitial space and bringing it out of that tissue so that we don't have swelling or edema throughout the tissues in her body. Next, we're going to zoom out and look kind of at the whole body level. So I've got a diagram of a person here. We're going to start here with the hands, just because it's a distal end of the arm here.

And you can see all these little lymphatic capillaries that are extended out into all parts of the hand. Basically, almost anywhere in your body where there's blood or blood capillaries, there's going to be lymphatic capillaries that are there to remove that fluid. So those lymphatic capillaries are going to be picking up fluid, which came from the bloodstream, which then became interstitial fluid, and now is in the lymph vessels. So it's going to be bringing that lymph fluid up the arm closer to the middle part of the body. And if you notice right here, we've got some spots in those lymph vessels and those are going to be lymph nodes.

And this is where we're getting into that second function of the lymphatic system, where we're scanning for pathogens and initiating an immune response. The lymph nodes are where a lot of that is taking place. So let's zoom in on one of those lymph nodes and take a look at the structure of the lymph node and how it does this. All right.

So there's a cute little lymph node, and we're going to have first some vessels that are bringing the lymph. into the lymph node. We call these afferent vessels. Afferent just means toward, and I have the A capitalized there because in a second we're gonna see an efferent vessel.

So these vessels, like this one right here, that's gonna be an afferent vessel that's bringing lymph into the lymph node. Now notice on these vessels, there are these little valves which are gonna make sure that the lymph is only flowing in one direction. And if lymph tries to flow.

backward those are going to snap shut and prevent the lymph from backflowing. Since we don't have a lymphatic equivalent of a heart to push or pump the lymph fluid through the lymph vessels we've got these one-way valves. so that that lymph fluid is only traveling in the correct direction. So lymph is coming in through multiple afferent vessels here, and then the lymph is going to travel out of the lymph node through an efferent vessel. And there's only ever going to be one efferent vessel leaving a lymph node.

All right, now let's take a look at a couple regions of the lymph node here. First, we've got the medulla, which is going to be kind of in the center of the lymph node right there, where the lymph is passing through to get to the efferent vessel. And then we've got the cortex, which is going to be the outer part of the lymph node. So all these sections right in here are part of the cortex.

Now for this to scan for pathogen, we have to have white blood cells present or lymphocytes present Those lymphocytes are going to be B cells and T cells and macrophages and a few others, but they've got to get there somehow. Now, they're white blood cells. They need to come through the bloodstream. So we're going to have some blood vessels coming into each of the lymph nodes. Those blood vessels are going to enter in right by the efferent vessel right in here.

It's going to be bringing blood in, including white blood cells. And then, of course, you've got to have a vein, which is going to be traveling out of that area. And so we've got a little capillary bed, and that's how the white blood cells are going to make it to the lymph node.

So we're going to have B cells all throughout this. outer part of the cortex we're gonna have T cells kind of mainly clustered in the inner part of the cortex. So any pathogens that get into your bloodstream, some of those are gonna end up in the lymph fluid where they're gonna pass through here and they're gonna have to pass by these B cells and these T cells, which are gonna be on the lookout for antigens on those pathogens that they recognize so they can start attacking them and initiate this immune response by the body.

So the lymph fluid is gonna pass by there. It's gonna fill in this medulla and then come out through the efferent vessel where it's gonna continue on its path. And we're gonna see where that path goes to next.

So again, how does the lymphatic system scan for pathogens and initiate the immune response? Well, lymph is going to be traveling through these afferent vessels through the cortex where it passes by B cells and T cells. Those are going to be trying to detect and see if there's a pathogen present, and they'll start that immune cascade if there is. And if not, that lymph fluid is going to pass by out the afferent vessel where it can continue on its path.

All right, let's see where all of this goes next. But first I want to point out, if you notice that the lymph nodes aren't just throughout Every part of these lymph vessels, they're kind of clustered in certain regions. Throughout this next part of our diagram here, I'm going to be pointing out lymph node regions in green and this first section here that you see is the epitrochlear section of lymph nodes. Those are gonna be located kind of on the medial side of the elbow right in there.

Now all of this lymph fluid that's traveled up from the hand, it's gonna be traveling up here through this axillary or armpit region. And we're actually going to have a lot of lymph nodes in that axillary region. So you've got a lot of lymph nodes in your armpit kind of extending up here toward the neck region.

Notice that almost all of those vessels are starting to converge into one bigger vessel right there. This is where the lymph fluid is about to drain back into the veins so it can return to our blood circulation. So here in our diagram, we have the right subclavian vein. and the left subclavian vein. The subclavian veins connect together to form the superior vena cava and the superior vena cava is going to bring the blood back into the heart, the right atrium, right ventricle.

It can pump it to the lungs, but all of the lymph fluid that we gather is going to drain back into either the right subclavian vein or the left subclavian vein through two different ducts. The first of those is the right lymphatic duct and then the second is going to be the thoracic duct. The thoracic duct is going to extend down into your chest and down toward the abdomen. And the thoracic duct is going to get most of the lymph drainage. And the right lymphatic duct is going to get just a smaller fraction of it.

We'll see more of this in a second, but the right lymphatic duct is going to get lymph from the right arm, the right side of the face, and a little bit in this region right here. Whereas the thoracic duct is going to drain all of the lymph from the left arm, the left side of the face. as well as like the whole lower half of the body.

So right lymphatic duct is getting just lymph from this region right here. Thoracic duct is getting lymph from this region down here and the whole lower half of the body. The chest is also gonna have a lot of lymphatics. And so we see a lot of lymphatic vessels right here that are gonna be collecting fluid and bringing up into that axillary region. Up next is the region where we actually have the most lymph nodes and that's gonna be in the cervical region.

So there's gonna be a lot of lymph nodes in our neck. There's gonna be a lot kind of in the side of our face right in here. And oftentimes that's broken up not just into cervical, but other names of regions as well. But in this video, I'm just giving kind of an overview of the location of the lymph nodes. So we've got all those lymph nodes in the cervical region.

In the left side of the face, they're draining into the thoracic duct. And then in the right side of the face, all of those are going to be draining into the right lymphatic duct. So if you were to trace the path here, from the hand, the lymph is traveling up this way into the right lymphatic duct. From the face, it's traveling down to the right lymphatic duct.

Or from here, it's traveling up the arm to the thoracic duct. Or from the face, down to the thoracic duct. Now let's move on to the lower half of the body. We're going to start down at the very bottom or inferior part.

We're going to have some lymph nodes in the knees, and those are going to be the popliteal lymph nodes. Popliteal is just referring to the knee. That lymph fluid is going to be draining upward.

It's going to head toward the inguinal lymph nodes. The inguinal lymph nodes are found right in here. And then from there, lymph fluid is going to travel up.

into the abdominal lymph nodes right in through here. So if you'll notice, you don't have a lot of lymph nodes in the leg. You don't really have any below the knee. You've got a few in the knee. You've got a lot in the inguinal area right here.

You've got a lot in the abdominal area right here. Now, almost all of the lymph fluid that's coming from the lower half of the body is going to be right in here where it's going to enter into something called the cisterna chyli. The cisterna chyli is just this big collecting duct for lymphatic fluid. It's going to connect all these lower lymphatic vessels up to the thoracic duct. and all that lymphatic fluid is going to drain into the left subclavian vein via the thoracic duct.

A couple more branches here that I need to draw in. The next one is going to be the thoracic lymph node. So it's kind of a more lateral branch that's going to come up here.

That's going to have some thoracic lymph nodes. We're going to have those on the other side as well. From what I can tell on most diagrams that I've seen, there is a lymph connection from the cisterna chyli right here up to the right lymphatic duct. So I'd imagine there is a little bit of drainage. from this lower part of the body up into the right lymphatic duct, but the vast majority of lymphatic fluid from the lower half of the body is going to travel up through the thoracic duct into the left subclavian vein.

So all of these lymphatic vessels that are in almost all parts of the body, they're pulling fluid in to scan for pathogens and initiate an immune response. So if there is an invader in the body, the lymph nodes are going to find it. But don't forget about our first function of the lymphatic system, which is preventing swelling.

And so they're pulling this fluid from all these different body regions where that fluid may be building up more than it should. So they're pulling that fluid out. All that fluid is going to travel toward those subclavian veins, either via the right lymphatic duct or the thoracic duct to get all that excess fluid back into the bloodstream where it belongs. So we don't have swelling throughout the body. All right, next, let's talk about that third function, the absorbing fat from intestines and delivering it to the bloodstream.

So let's draw in a little boom. branch of the small intestine right here and we've got a lymphatic vessel that's going to be pulling fluid from that intestine and connecting it to the cisterna chyli right in here where it can drain it back into the thoracic duct. I just have a small section of intestine drawn but that's so that my diagram doesn't get a little bit out of hand but really these lymphatic vessels are going to be connecting all throughout the small intestine to pull that fluid out.

So really this whole area right here would be full of these lymphatic vessels pulling fluid out of the intestines and into the cisterna chyli. Now, when I first learned about all this stuff, I learned that the fats and sugars and proteins and all the nutrients that we eat are going to go from the digestive system straight to the bloodstream. All those things get absorbed from the small intestine into the bloodstream. But it turns out that's not quite the whole truth.

Take a look at this diagram. There's a lot going on here, but let's break it down. We've got a section of the small intestine. Inside that small intestine, if we cut it open, we'll see there's these villi or these tiny little kind of squiggly looking surface membranes that are on the surface of the small intestine. All the food that we eat after it's been broken down is traveling through this tube of the small intestine.

Now we've got to get those nutrients from the lumen of the small intestine into the bloodstream. So let's zoom in on one of these villi or an anvilis. Here are the absorptive cells or enterocytes. The nutrients that we've digested are going to pass through there.

And most of those are going to pass into the capillaries right here. And they're going to be traveling through the capillary, through the venule. and then back into circulation as it goes directly into the bloodstream. That's going to be true for proteins and sugars because they're soluble in water, and they're pretty small.

They can pass through the membranes. Fats or lipids are a different story. Lipids are not water-soluble, so they can't just go directly into the water. They've got to be packaged. So in these absorptive cells, they're going to be packaged into something called a chylomicron.

A chylomicron is a long, fancy name for basically a little water-soluble package that the lipids will get packaged into so they can enter it. into the fluid. So they get packaged into a chylomicron, but unfortunately the chylomicron, it's a little bit bulky. It's not going to fit into the capillaries to make it into the bloodstream.

There's just not enough space between the cells and the capillaries. However, the lymphatic capillaries actually have more space between the cells. and the chylomicrons can fit into there.

So with the lipids, which are in the chylomicrons, what they're gonna do is they're gonna travel through the lymphatic vessel right here, and they're gonna travel out, then they're gonna travel through here, up through the cisterna chyli, and the thoracic duct, and then boom, they're back into. to blood circulation, but they never had to travel directly through a blood capillary. They entered the lymphatic capillaries instead.

So that's the third function, absorbing fats from the intestines, delivering those to the bloodstream through the lymphatic system. All right, next, let's go back to that path. pathogen and immune response thing again. These other organs we're about to talk about are included in the lymphatic system because they help with this immune response.

The first one is going to be the thymus. The thymus is located sort of anterior to your heart. It's actually bigger when you're a kid and then it shrinks over time. By the time you're an adult, it's like a tenth of its normal size usually.

But what the thymus does is it's going to produce T lymphocytes. Those T lymphocytes first grew in the bone marrow. That's where your white blood cells and red blood cells are mainly produced.

They'll travel from there to the thymus, and the thymus is gonna have them develop and mature into T cells. Why do we call them T cells? Well, because they're made in the thymus, which starts with T.

From the diagram, I just realized it looks like the thoracic duct is gonna be connected to the thymus. It's not. A thymus has blood vessels that are connected to it, and that's how it's getting these T cells and then sending these T cells out.

And of course, a lot of these T cells are gonna end up in the lymph nodes. throughout the body. So the thymus is considered a lymphatic organ because of that. Next we have bone marrow. And so the bone marrow is going to be in bones throughout the body.

I just drew kind of the head of the femur down here to represent the bone marrow. The bone marrow is going to be where all these white blood cells are created. And specifically, it's going to be where the B lymphocytes or B cells are developing and maturing.

Why are they called B cells? Well, because they're made in the bone marrow, which starts with B. Of course, a lot of those B lymphocytes are going to travel through the bloodstream and they're going to make it to the lymph nodes throughout the body so they can hang out and look for pathogens in their lymph fluid.

The thymus and the bone marrow are considered primary lymphatic organs because they're actually producing the cells of the lymphatic system. Another organ to talk about here is the spleen, which is considered a secondary lymphatic organ. It does a couple things.

One thing it does is it kind of acts like a lymph node for your bloodstream. There aren't lymphatic vessels going to it, but there are. blood vessels going to it. And it's going to have a lot of these B cells and T cells that are going to kind of hang out and fight pathogens.

If there's any that come into the spleen through the blood vessels right there. But another big thing that it does is it breaks down old red blood cells. So red blood cells have a very limited lifespan. And at the end of their lifespan, they're going to get broken down by the spleen so that we can then get rid of them. One more thing I don't have that diagram is our tonsils.

Our tonsils kind of work like the spleen does. They contain lymphocytes to fight off pathogens, but they're up in the face in some of the cavities up there. All right, that was a lot of information.

Now I'm going to give you a chance to practice some of that information and see if you can recall it. Here's a blank graphic of the lymphatic system functions. Pause the video, see if you can name the three functions of the lymphatic system.

And those functions are one, it prevents swelling or edema by returning interstitial fluid to the bloodstream. Second, it's going to scan for pathogens and initiate an immune response if it finds pathogens. And third, it's going to absorb fats from intestines and deliver those to the bloodstream. Up next, we have this diagram of the tissue capillaries and lymphatic capillaries. Take a minute, pause the video, see if you can describe everything that's in this diagram, as well as describe what's happening in all the different parts of the diagram.

All right, and here's a completed version of that diagram. As a quick overview, we've got blood coming in, traveling through here. It's gonna be dropping off water and oxygen and proteins and other nutrients to the tissue cells. Water and carbon dioxide is gonna be traveling back into the tissue capillaries so that we can get rid of it. However, we've got a lot of water leaving and only about 90% of that water is coming back.

So we've got an extra 10% that we've gotta get back into blood circulation. That's where these lymphatic capillaries are gonna come in. So a lot of fluid is gonna travel back into the lymphatic capillary and it's gonna take it out of this tissue and get it back into blood circulation. We've got a zoomed in version of that, which includes blood plasma, interstitial fluid, and then lymph or lymphatic fluid.

Fluid from the blood plasma is gonna travel out into the interstitial space. About 90% is gonna travel. back into the blood capillary. That other 10%, we need to get it back into blood circulation. So it's going to travel through the lymphatic vessel and then back into that subclavian vein later on.

Another thing that we talked about is the lymph node. So here's a blank diagram of the lymph node. Again, pause the video. See if you can identify all the parts of the lymph node, as well as the direction that fluid travels and what all it does. All right, here's that completed diagram.

Now we've got lymphatic fluid that's coming into the afferent vessels. We've got the lymphatic fluid coming out through the efferent vessel. That fluid has to travel past B cells and T cells, which are scanning that fluid, looking for any pathogens to fight off. If it finds them, it'll initiate the immune response.

If not, that fluid will travel out through that efferent vessel. And we have the medulla here and the cortex is the outer part where the B cells and T cells are found. And then finally, here's our picture of the whole person.

Pause the video. See if you can name all of the lymph nodes. regions as well as the other lymphatic organs and what all those lymphatic organs do.

And there's all those terms again. The lymphatic fluid from the hand and the arm is going to travel up through this region, past the epitrochlear lymph nodes, through the axillary lymph nodes, and then into the thoracic duct or on this side up through the right lymphatic duct. Majority of our lymph nodes are here in the cervical region.

Those are going to drain down into the thoracic. and right lymphatic duct. Fluid from the lower leg is going to travel up through the popliteal lymph nodes, up through the inguinal lymph nodes, abdominal lymph nodes, into the cisternic hyaline, which is going to travel through the thoracic duct.

All of that lymph fluid is going to make it back into the left subclavian vein or the right subclavian vein. We have lymph vessels that are taking fluid from the small intestine. That's where fats are going to get absorbed into the lymphatic system so they can return to venous circulation.

And finally, we have these other lymphatic organs, the thymus, where T cells develop and mature, the bone marrow, where B cells develop and mature. And we have the spleen, which contains a lot of lymphocytes, which will fight off pathogens, as well as being a site where red blood cells are broken down. All right, so that was a lot of information.

It turns out the lymphatic system has a lot of parts. There's a lot of complexity to it. I didn't get into how the B cells and T cells actually do the immune response.

If you're interested in that, I've got a video on that. So check that video out. It should be linked right here.

Special shout out to my patrons on Patreon who helped make this video possible. If you're looking for the diagrams from this video, both the blank and completed diagrams, those are available on my Patreon. So check that out.

There's a link below. And good luck learning anatomy. Hope to see you in the next video. I'll see you then.

Transcript for:Overview of the Lymphatic System Functions

Transcript for:
Overview of the Lymphatic System Functions