Introduction to the Lymphatic System: Study with Video Lessons, Practice Problems & Examples

The lymphatic system is essential for maintaining fluid balance, aiding immunity, and absorbing dietary fats. It consists of lymph, lymphatic vessels, and lymphoid tissues and organs, such as lymph nodes and the spleen. Lymph, a clear fluid formed from interstitial fluid, is transported through lymphatic vessels back to the cardiovascular system, addressing fluid leakage. Additionally, it supports lymphocytes, crucial for immune responses, and absorbs large macromolecules like fats via specialized structures called lacteals, ensuring efficient nutrient transport throughout the body.

Why Do We Need It?

In this video, we're going to begin our introduction to the lymphatic system, which is a system of lymphatic vessels and lymphoid organs distributed throughout our bodies. Now before we talk more about what the lymphatic system actually is, let's first talk about why do we even need it to begin with, especially knowing that we already have blood vessels of the cardiovascular system branching throughout practically our entire bodies. So why would we need a second set of lymphatic vessels? Well, it turns out that although the cardiovascular system is incredibly good at performing its functions that we talked about in previous lesson videos, it still has a few inherent limitations, which we have listed down below in these three bullet points of the text. And so to answer this original question, the reason that we need the lymphatic system is because, as we'll learn more about moving forward in our course, it functionally serves to address, accommodate, and provide a solution to each of these inherent limitations of the cardiovascular system. So that's important to keep in mind as we move forward in our course. And so what are these inherent limitations of the cardiovascular system anyways? Well, recall from previous lesson videos that the cardiovascular system is a relatively high-pressure system because of the action of the heart, which is constantly pumping blood through it. And this high pressure is a good thing because it allows for the high-speed transport and the rapid delivery of oxygen and nutrients to our tissues. However, this same high pressure and high-speed transport are also inherent limitations of the cardiovascular system, because the high pressure forces some fluids and proteins to leak out of the blood capillaries. And, of course, the leakage of its contents is not going to be a good thing. And although that high pressure allows for high-speed transport, the high-speed transport does not facilitate direct interactions between immune cells and pathogens, and so the high-speed transport does not optimize immune interactions, and again, that's a limitation. And then last but not least, for the most part, the cardiovascular system is not effective at absorbing relatively large macromolecules and substances, such as fats, for example. And so again, the lymphatic system is going to be needed because it is going to function to address many of these limitations. And so notice over here, we're showing you a person, and we're showing you these greenish, lymphatic vessels branching throughout, you know, practically this person's entire body, and there's also lymphoid organs that you can see that we'll talk more about moving forward, such as the thymus, the spleen, and tonsils, for example. Now over here on the left, what we're showing you is a typical capillary bed of the cardiovascular system, just like what you've seen before in some of our previous lesson videos. But what you'll notice is different here is that we're showing you these yellow cells here, which represent tissue cells, and, of course, we know that the capillaries is where exchanges occur between the blood and the tissues. But what you'll notice is really different about this image is that we're showing you all of these blue arrows, and some of the blue arrows are outward pointing and other blue arrows are inward pointing. Now the blue arrows that are outward pointing represent the leakage of fluids and proteins from the cardiovascular system, and what you'll notice is that these outward going arrows are broader and thicker than the inward going arrows, which represent the reabsorption of those leaked fluids and proteins. And so what this means is that over time, the cardiovascular system is leaking more of its contents than it is reabsorbing it back in. And so, again, the leakage is going to be something that is a limitation. But what you'll notice is that branching in over here is a little green vessel, which is a lymphatic vessel, and it is going to serve to accommodate that limitation. And so, again, that is why we need the lymphatic system. So as we move forward in our course, we'll get to talk more about what the lymphatic system is and its function. So that concludes our brief introduction of why we need it, and I'll see you on our next video.

What Is It?

So now that we've talked about why we need the lymphatic system in our last lesson video, in this video, we're going to talk about what it is exactly. The lymphatic system is a network that primarily maintains fluid balance in the body, and it also aids immunity. These are the two primary functions of the lymphatic system. However, the lymphatic system also has additional functions that include absorbing dietary fats. As we move forward in our course, we'll get to talk more about these additional functions. The lymphatic system includes the following three components, which are lymph, lymphatic vessels, and lymphoid tissues and organs. Lymph is the clear and colorless fluid that's formed when interstitial fluid enters lymphatic vessels. Notice down below, we have a silly cartoon that helps us differentiate interstitial fluid from lymph. In this silly cartoon, the green structure that you see here represents a lymphatic vessel. The circles at the bottom represent tissue cells, and the yellow fluid immediately outside the tissue cells represents the interstitial fluid, which I will abbreviate as IF. When the interstitial fluid makes its way into this lymphatic vessel, it's now referred to as lymph. The biggest difference between lymph and interstitial fluid is its location because in terms of its contents, it's essentially the same.

The next component of the lymphatic system are the lymphatic vessels, which are tube-like structures similar to how blood vessels are tube-like structures, but instead of carrying blood, the lymphatic vessels carry lymph to veins near the heart. Ultimately, it returns leaked fluids and proteins back to the blood, and this is a function that we'll get to talk more about in our next lesson video. The last component of the lymphatic system are lymphoid tissues and organs, which include structures such as lymph nodes, the bone marrow, the thymus, the spleen, tonsils, and MALT, which stands for mucosal-associated lymphoid tissues. As we move forward in our course, we'll be able to talk a lot more about all of these different lymphoid tissues and organs. If we take a look at this image down below on the right-hand side, notice that all these green vessels that are projecting throughout practically this entire body here represent the lymphatic vessels. You can see that we're labeling the red bone marrow at the end of this long bone here, the thymus is also being labeled right here in this location, lymph nodes are going to be these bean-shaped structures that are found all along the lymphatic vessels, and the spleen is labeled right over here. Up here in the head region, we're labeling the tonsils. Again, as we move forward in our course, we'll talk more about all of these different organs and tissues, so don't worry about that. This here concludes our brief lesson on what the lymphatic system is. As we move forward in our course, we'll be able to apply these concepts and then talk more about the functions of the lymphatic system. So I'll see you all in our next video.

Introduction to the Lymphatic System Example 1

So here we have an example problem that asks, which of the following is a limitation of the cardiovascular system that is solved by the lymphatic system? And we've got these 4 potential answer options down below. Now, option A says that the cardiovascular system cannot pump enough blood to skeletal muscle during intense exercise. However, recall from our previous lesson videos that the cardiovascular system is incredibly good at performing its primary functions. And one of its primary functions is to deliver, or pump enough blood to our tissues, especially to our skeletal muscle tissues during intense exercise. And so to say that this is something that our cardiovascular system cannot do is not going to be correct. For that reason, we can eliminate answer option A. Pumping blood to the tissues is something that our cardiovascular system excels at, so it's not a limitation of the cardiovascular system. Also, the lymphatic system does not pump blood to our tissues. So that's another way we could have eliminated answer option A. Now moving on, option B says the cardiovascular system cannot absorb extremely small molecules. However, recall from our last lesson video that it's not the small molecules that the cardiovascular system has a problem absorbing, it's the larger molecules such as proteins and macromolecules that the cardiovascular system has a problem absorbing. And so for that reason, we can eliminate answer option B because extremely small molecules such as carbon dioxide gas and water, for example, can be absorbed by the cardiovascular system. So now we're between either option C or option D, and notice, option C says that erythrocytes leak out of capillaries to deliver oxygen gas (O₂) to tissues and not all of them reenter. So recall that erythrocytes are red blood cells, and also recall that erythrocytes or red blood cells do not need to leave the capillaries or leak out of the capillaries in order to deliver the oxygen gas. Instead, the oxygen gas can actually diffuse out of the erythrocytes, diffuse out of the capillaries, and diffuse into the tissue cells. And so, erythrocytes leaking out of the capillaries is not something that we would expect to normally happen. For that reason, we can eliminate answer option C. Also, the lymphatic system is not involved in delivering oxygen to the tissues. And so, of course, this leaves answer option D as the only option, and it is the correct answer, which says that plasma leaks out of capillaries and not all of it reenters. So recall that a major limitation of the cardiovascular system is that plasma, one of the major components of blood, happens to leak out of the capillaries. And, although most of the plasma is going to be reabsorbed back into the capillaries, some of the plasma is not going to be reabsorbed. So not all of the plasma reenters. And this is exactly how the lymphatic system comes into play to solve this issue because the lymphatic system will absorb all of the plasma that was not reabsorbed by the cardiovascular system, and the lymphatic system will return that leaked plasma back to the cardiovascular system. And so answer option D is the correct answer to this example problem. That concludes this problem, so I'll see you all in our next video.

Which of the following is the difference between interstitial fluid and lymph?

• A. Lymph originates in lymphatic vessels, while interstitial fluid originates in arterioles.
• B. Lymph is the term given to interstitial fluid once it has entered the lymphatic vessels.
• C. Lymph contains erythrocytes, while interstitial fluid does not contain erythrocytes.
• D. Lymph contains leukocytes, while interstitial fluid does not contain leukocytes.

One of the major functions of the lymphatic system is:

• A. Elimination of carbon dioxide gas & nitrogenous wastes.
• B. Hemostasis.
• C. Maintaining fluid balance in the body by returning lost fluid back to the cardiovascular system.
• D. Aiding in the delivery of $O_2$ to the tissues.

Functions of the Lymphatic System

In this video, we're going to talk briefly about the functions of the lymphatic system. Now when you consider the lymphatic system as a whole, including all of the different lymphoid organs, such as red bone marrow, the thymus, and the spleen, for example, then the lymphatic system has a lot of different specialized functions, and we'll get to talk more about those specialized functions as we move forward in our course and talk more about those lymphoid organs. However, for the most part, those specialized functions roll up into the 3 primary functions of the lymphatic system that we focus on in this video. Now, the first primary function of the lymphatic system is that it maintains fluid balance by returning lost or leaked fluids and proteins back to the cardiovascular system to maintain the fluids within the cardiovascular system. And so, notice down below on the left-hand side over here, it's focusing on maintaining fluid balance, and the cartoon in the bottom left is the same cartoon that we showed you in one of our previous lesson videos, and this interstitial fluid is going to result from leaked fluids from the cardiovascular system. And when the interstitial fluid is absorbed by the lymphatic vessels, that interstitial fluid is going to be referred to as lymph, and the lymph is going to make its way through the lymphatic system, through these lymphatic vessels, back to veins near the heart. And notice here that you can see the fluids are being emptied into these veins near the heart, and that's going to help maintain the fluids within the cardiovascular system. Now the next function that we have of the lymphatic system is that it produces, maintains, distributes, and supports lymphocytes, which we know are important for aiding immunity. And recall that lymphocytes are a class of white blood cells that includes B cells and T cells. And so, down below in the image in the middle section here, it's focusing on aiding immune function. And so, this is a silly cartoon where this security checkpoint here represents the lymph node, and you can see that a pathogen is making its way through this lymph node, and it's encountering these lymphocytes, the T cells and the B cells, which we know again are going to aid in immunity and help to eliminate the pathogens to prevent them from causing an infection and causing us harm. Now last but not least, the third primary function of the lymphatic system is that it actually absorbs relatively large substances that usually cannot enter into most blood capillaries. And a classic example of this are what are known as lacteals. Lacteals are specialized lymphatic capillaries of the small intestine, and what they do is they absorb dietary fats and lipid-soluble vitamins that otherwise would not be absorbed by the cardiovascular system. And so, these lacteals will ultimately drain those fats and lipid-soluble vitamins back into the cardiovascular system, which can transport those materials throughout the body where they are needed. And so, notice that down below here in this cartoon, notice that we have this molecule representing a dietary fat, and notice that it's saying that I can't pass that membrane, and that membrane would be the membrane of the cardiovascular system, but it says I can pass this one in green, the membrane of lacteals. And so what we're going to do is label this lymphatic vessel as the lacteal. And so, this here concludes our brief lesson on the functions of the lymph system, and as we move forward in our course, we'll get to continue to learn more about the lymph system and apply these concepts in the problem.

Introduction to the Lymphatic System Example 2

So here we have an example problem that wants you to imagine that you are a doctor and a patient comes to your office complaining of persistent and excessive swelling in their ankles. And then it asks, which of the following is the most likely reason that they're experiencing this? And we've got these four potential answer options down below. Now after reading through each of these four potential answer options, there are three of them that we would not expect to lead to excessive swelling in their ankles, and those three options are options b, c, and d.

Now option b says excessive production of red blood cells, which we would expect to increase blood volume, and that can lead to several different signs and symptoms. However, excessive production of red blood cells, we would expect to lead to an increase of blood volume throughout practically the entire body, and we wouldn't expect this to lead to isolated signs and symptoms in the lower extremities, such as the ankles, for example. And so we wouldn't expect answer option b to lead to excessive swelling in their ankles, and for that reason, we can eliminate answer option b.

Now option c says, respiratory tract infection, such as, for example, bronchitis, which can affect the lungs. And so, of course, this can lead to several different signs and symptoms such as coughing and congestion and fever. However, we would not expect a respiratory tract infection to lead to isolated signs and symptoms in the lower extremities such as the ankles. And so for that reason, we can eliminate answer option c.

Now option d says, lacteals not absorbing fat. Now recall from our last lesson video that lacteals are specialized lymphatic capillaries in the small intestine that play a major role in absorbing dietary fats and lipid-soluble vitamins. And so if these lacteals are not absorbing fat, then we're not going to be able to obtain the critical nutrients from our diets. And that can lead to malnutrition, which can lead to several different signs and symptoms. However, we would not expect this to lead to isolated signs and symptoms in the lower extremities, such as the ankles. And so, again, for that reason, we can eliminate answer option d.

Now, of course, this leaves answer option a as the only option which is the correct answer, which says, impaired lymphatic drainage in their legs. And, of course, we already know from our previous lesson videos that the lymphatic system will drain lymph or drain interstitial fluid from the tissues, and it will return lost fluid from the cardiovascular system back to the cardiovascular system. And so if the lymphatic drainage is impaired, that means that it will not be able to drain interstitial fluid from the tissues. That means that there will be a buildup of interstitial fluid, and that certainly can lead to swelling. And if this is occurring in the legs, then certainly this can lead to swelling in the ankles. So answer option a is the correct answer. We can go ahead and indicate that. And it turns out that this buildup, this impaired lymphatic drainage is actually a condition known as lymphedema, which is characterized by the buildup of interstitial fluid and swelling. And lymphedema is often going to occur in the lower extremities, such as the ankles. And so, again, answer option a is correct. That concludes this example, and I'll see you all in our next video.

The lymphatic ___________ return fluid to the cardiovascular system, the lymphoid organs primarily aid __________ function, and ___________ absorb fats that are too large to fit into capillaries.

• A. Organs; immune; lacteals.
• B. Vessels; immune; lymphatic vessels.
• C. Vessels; fluid balance; lymphatic organs.
• D. Vessels; immune; lacteals.

Here’s what students ask on this topic:

Why do we need the lymphatic system if we already have the cardiovascular system?

The lymphatic system is essential because it addresses the inherent limitations of the cardiovascular system. The cardiovascular system operates under high pressure, which causes fluids and proteins to leak out of blood capillaries. The lymphatic system collects and returns these leaked fluids and proteins to the bloodstream, maintaining fluid balance. Additionally, the high-speed transport in the cardiovascular system does not facilitate optimal immune interactions, whereas the lymphatic system supports immune functions by housing lymphocytes. Lastly, the lymphatic system absorbs large macromolecules like dietary fats, which the cardiovascular system cannot efficiently absorb.

What are the primary functions of the lymphatic system?

The lymphatic system has three primary functions: maintaining fluid balance, aiding immunity, and absorbing dietary fats. It returns leaked fluids and proteins to the cardiovascular system, ensuring fluid balance. It supports immune function by producing, maintaining, and distributing lymphocytes, which are crucial for fighting infections. Additionally, specialized lymphatic capillaries called lacteals in the small intestine absorb dietary fats and lipid-soluble vitamins, which are then transported throughout the body.

What are the main components of the lymphatic system?

The lymphatic system consists of three main components: lymph, lymphatic vessels, and lymphoid tissues and organs. Lymph is a clear fluid formed from interstitial fluid that enters lymphatic vessels. Lymphatic vessels are tube-like structures that transport lymph back to the cardiovascular system. Lymphoid tissues and organs include lymph nodes, bone marrow, the thymus, the spleen, tonsils, and mucosal-associated lymphoid tissues (MALT). These components work together to maintain fluid balance, support immunity, and absorb dietary fats.

How does the lymphatic system aid in immunity?

The lymphatic system aids in immunity by producing, maintaining, and distributing lymphocytes, which are a type of white blood cell. Lymphocytes include B cells and T cells, which are crucial for immune responses. Lymphoid organs such as lymph nodes act as checkpoints where pathogens are filtered and encountered by lymphocytes. This interaction helps to eliminate pathogens and prevent infections. The lymphatic system thus plays a vital role in supporting the body's immune defenses.

What is the difference between lymph and interstitial fluid?

The primary difference between lymph and interstitial fluid is their location. Interstitial fluid is the fluid that surrounds tissue cells, while lymph is the fluid that enters the lymphatic vessels. In terms of content, they are essentially the same, but once interstitial fluid enters the lymphatic vessels, it is referred to as lymph. This transition is crucial for the lymphatic system's role in maintaining fluid balance and supporting immune functions.