Lymphatic Vasculature: Study with Video Lessons, Practice Problems & Examples

The lymphatic system consists of various vessels, including lymphatic capillaries, vessels, trunks, and ducts, which transport lymph—a clear fluid—toward the cardiovascular system. Unlike the cardiovascular system, which circulates blood in a loop, the lymphatic system is linear, beginning at capillaries and ending at ducts. Key mechanisms for lymph propulsion include skeletal muscle contractions, smooth muscle contractions in larger vessels, pulsation of nearby arteries, and the respiratory pump. Lymphatic capillaries are highly permeable, allowing larger substances like proteins and pathogens to enter, aiding in immune response and fluid balance.

Types of Lymphatic Vessels

In this video, we're going to begin our lesson on lymphatic vasculature as we introduce the types of lymphatic vessels. So as lymph moves through the lymphatic system, it travels through the following 4 types of lymphatic vessels that we have numbered down below in the text, 1 through 4, and these are lymphatic capillaries, lymphatic vessels, lymphatic trunks, and lymphatic ducts. They're organized from the smallest and the most numerous lymphatic vessels, which are the lymphatic capillaries, down to the largest and the least numerous lymphatic vessels, which are the lymphatic ducts.

Now unlike the vasculature of the cardiovascular system, which we know carries blood in two directions, arteries carry blood away from the heart and veins carry blood back towards the heart vasculature of the lymphatic system only carries lymph in one direction, and that's going to be towards veins that are near the heart. This is important to keep in mind as we move forward in our course.

Now the very first type of lymphatic vessel that we have here in our lesson are the lymphatic capillaries, which again are the smallest of these lymphatic vessels. They have the smallest wall structure and the smallest lumens, and they're also the most numerous of the lymphatic vessels. They're going to represent the start of the lymphatic vessels. This is because the lymphatic capillaries will collect interstitial fluid in order to initially form the lymph, just as what we discussed in some of our previous lesson videos.

Then, of course, that lymph that is initially formed in the lymphatic capillaries will make its way through all of these other lymphatic vessels until it gets to these lymphatic ducts. If we take a look at our diagram down below, notice the lymphatic capillaries are being labeled down below right here, and they are very closely associated with blood capillaries of the cardiovascular system. This is because recall that the blood capillaries will actually leak fluids and some proteins into the interstitial spaces. And because these lymphatic capillaries are so closely associated, they can absorb those leaked fluids and proteins, and those absorbed leaked fluids and proteins can make their way through the lymphatic vasculature back to the veins near the heart where they are returned back to the cardiovascular system.

Now notice that these lymphatic capillaries are actually merging to form larger and larger lymphatic vessels, and that is going to be the second type of lymphatic vessel that we have here. They are also sometimes referred to as collecting lymphatic vessels. This is because they collect lymph from these merging lymphatic capillaries. These lymphatic vessels are going to be less numerous than the lymphatic capillaries, but they're going to be larger in terms of their wall structure and their lumens.

In fact, these lymphatic vessels can have all 3 tunics or all 3 layers that we talked about in some of our previous lesson videos, with the wall structure of blood vessels. These lymphatic vessels may actually have some smooth muscle in their walls that can contract in order to propel some lymph through the lymphatic vessels. You can see these lymphatic vessels being labeled down below in our diagram.

Another thing that you'll notice down below in our diagram is these little bulges that you see here represent valves that are going to be very similar to the venous valves that we talked about in previous lesson videos and veins. However, what you'll notice about these valves that we can label here is that they're going to be significantly more abundant in the lymphatic system than they are in the veins of the cardiovascular system. These valves, they are going to allow for lymph to flow in one direction. So lymph will be able to flow past the valve, but it will prevent the backflow of lymph. Once lymph passes through these valves, it's almost like a checkpoint to ensure that the lymph will not move backwards. The lymph is always going to be flowing, again, from these lymphatic capillaries towards the veins near the heart.

Another thing that you'll notice labeled in these diagrams are these large bean shaped structures, which are lymph nodes. We can go ahead and label them as so. These lymph nodes are going to be strategically positioned throughout the lymphatic vasculature, and they are going to play a large role in immunity, essentially detecting and eliminating pathogens that arrive at the lymph nodes, and it can also activate the immune system to essentially target pathogens in other areas of the body as well. We'll get to talk more about these lymph nodes as we move forward in our course, but it is important to note that the lymph nodes are going to be strategically positioned throughout the lymphatic vasculature, and there are hundreds of lymph nodes scattered throughout different regions of our body.

Now, these lymphatic vessels are going to continuously merge to form lymphatic trunks. These lymphatic trunks collect lymph from merging lymphatic vessels. They are going to be less numerous than the lymphatic vessels, but then, again, they're going to be larger in terms of their wall structure and their diameter. These lymphatic trunks are often going to be named based on the regions of the body that they drain lymph from. You can see them down below in the image here, they're going to be larger and thicker than the previous lymphatic vessels that we talked about.

Of course, these lymphatic trunks are going to merge to form these lymphatic ducts, which are the last type of lymphatic vessel. These are going to be the largest of all of the lymphatic vessels, but also the least numerous. In fact, there are really only 2 lymphatic ducts that you should be aware of, and those are going to be the right lymphatic duct and the left lymphatic duct, which is also sometimes referred to as the thoracic duct. We'll get to talk more about these lymphatic ducts as we move forward in our course. But what's important to note about these ducts is that they are going to empty the lymph into the veins at the end of the lymphatic vessels. So whereas the lymphatic capillaries represent the start of the lymphatic vessels, the lymphatic ducts represent the end of the lymphatic vessels since this is where the lymph is actually being returned back to the cardiovascular system.

So this here concludes our lesson on the types of lymphatic vessels, and as we move forward, we'll be able to continue to learn more about lymphatic vessels and apply these concepts in problems as well. So I'll see you in our next video.

Lymphatic Vasculature Example 1

So, here we have an example problem that asks, which part of the lymphatic system is most closely associated with cardiovascular capillary beds? We've got these 4 potential answer options down below, which are lymphatic capillaries, lymphatic trunks, lymph nodes, and thymus. Now, the first option that we can eliminate right off the bat is answer option d, which says thymus. This is because the thymus is a lymphatic organ, or a lymphoid organ that we'll talk more about moving forward in our course. Although it does have its own blood supply and its own capillaries, it is a single organ that is located in a single region of the body, and it's not associated with practically all the capillary beds throughout the body. For that reason, we can eliminate answer option d.

The next option we can eliminate is answer option c, which says lymph nodes. Lymph nodes are strategically located throughout the body, and we'll talk more about lymph nodes moving forward in our course. Although these lymph nodes can have a blood supply and capillary beds, lymph nodes are not going to be associated with practically every capillary bed throughout the body, and so for that reason, we can eliminate answer option c.

Now we're between either option a or option b, and recall from our last lesson video that it's the lymphatic capillaries that are going to be most closely associated with cardiovascular capillary beds because recall that the cardiovascular capillary beds have a limitation in that they lose fluids to the tissues, and when they lose fluids, those fluids need to be returned back to the cardiovascular system. These lymphatic capillaries are associated with practically every cardiovascular capillary bed to help reabsorb those lost fluids and return those lost fluids back to the cardiovascular system. So, option a is going to be the correct answer to this example problem, and option b says lymphatic trunks, but these lymphatic trunks are going to be larger lymphatic vasculature, or larger lymphatic vessels that are not going to be as closely associated with capillary beds. So, a here is the correct answer. That concludes this example, and I'll see you all in our next video.

At the end of the lymphatic system, lymph is returned to the _________; specifically to the ___________.

• A. Bloodstream; subclavian arteries.
• B. Lymphoid organs; subclavian arteries.
• C. Lymphoid organs; subclavian veins.
• D. Bloodstream; subclavian veins.

Cardiovascular System vs. Lymphatic System

In this video, we're going to compare the cardiovascular system to the lymphatic system as we complete this table behind me. And so notice that the left hand side of the table is all about the cardiovascular system, which we covered in great detail in previous lesson videos. So this is mostly review, and the right hand side of the table is all about the lymphatic system, which is the main focus of these videos. Now recall from previous lesson videos that the cardiovascular system vasculature forms a circulatory network or a loop since arteries carry blood away from the heart, and veins carry blood back towards the heart. However, the lymphatic system vasculature is not a circulatory network or a loop. Instead, it is going to be more linear or blind-ended with a definitive beginning at the lymphatic capillaries and a definitive end at the lymphatic ducts. And so if we take a look at our images down below, we can actually see this and notice that on the left hand side, we've got the same image that we've seen many times before showing the circulatory network or the loop of the cardiovascular system, and the right hand side is showing the linear or blind-ended vasculature of the lymphatic system that, again, has a definitive beginning at the lymphatic capillaries and a definitive end at the lymphatic ducts.

Now the cardiovascular system, of course, is going to transport blood, which is a red and viscous or thick fluid, whereas the lymphatic system is going to transport lymph, which is a clear and colorless fluid. Now the cardiovascular system is going to be functionally optimized for nutrient and gas exchanges, such as oxygen and carbon dioxide gas exchanges, whereas the lymphatic system is going to be functionally optimized for returning lost or leaked fluids and proteins from the cardiovascular system back to the cardiovascular system to maintain fluid balance. And the lymphatic system is also functionally optimized for immune surveillance and response.

Now the cardiovascular system is going to have the heart, which we know acts as a pump to propel blood throughout the entire cardiovascular system. And the heart, which serves as a pump, creates a relatively high pressure system throughout the cardiovascular system, which keeps the blood flow pretty high and moving the blood quickly, which allows for the rapid transport and delivery of nutrients and gases. However, the high pressure and the high-speed transport does not optimize immune interactions. Now the lymphatic system, on the other hand, lacks an organ that serves as a pump, and so it relies on other means to propel lymph throughout the lymphatic system that we'll get to talk more about moving forward in our course. However, the lack of an organ that serves as a pump creates a relatively low pressure system that keeps the lymph flowing slowly. And this slow flow of lymph and low pressure optimizes immune activity, which allows the lymphatic system to perform immune surveillance and response.

Now, the cardiovascular system is going to have less variation in terms of the vessel locations across different individuals, which usually means that there are more vessels that need to be memorized when it comes to the cardiovascular system. However, the lymphatic system has more variation when it comes to vessel locations across different individuals. And because there's so much more variation, that means, usually, there's less to memorize when it comes to vessel locations. Now, the cardiovascular system has larger vessels that have a wall made up of 3 tunics or 3 layers that we talked about in previous lesson videos, and includes the tunica intima, the tunica media, and the tunica externa. And the lymphatic system also has larger vessels that can also have a wall made up of 3 tunics, which are going to be very similar to the tunics of the cardiovascular system.

Now the cardiovascular system has, some veins, especially the veins of the limbs, the arms and legs, that have valves, venous valves, that prevent blood backflow. And the reason that it doesn't need as many valves is because it's a relatively high pressure system. Now because the lymphatic system is a low pressure system, it is actually going to have significantly more valves than the cardiovascular system. So lymphatic vessels have even more valves than the cardiovascular system. Now the blood capillaries of the cardiovascular system are usually not permeable to relatively large substances, such as cellular debris and larger macromolecules, like larger proteins and fat molecules. Whereas the lymphatic system capillaries are going to be more permeable, to larger substances. And so the lymphatic capillaries are able to absorb those larger substances that most blood capillaries are not able to absorb. And so down below in this image, you'll notice that we've also included an image of the thymus and an image of the spleen, which are lymphoid organs that we'll get to talk more about moving forward in our course. But for now, this here concludes our video on the cardiovascular system and lymphatic system comparisons, and we'll be able to learn more as we move forward in our course and apply these concepts and problems as well. So I'll see you all in our next video.

Lymphatic Vasculature Example 2

So here we have an example problem that asks, which of the following is not common to both lymphatic trunks and cardiovascular veins? And we've got these 4 potential answer options down below. Now option a says, a wall consisting of three tunics or layers. And, of course, recall from our last lesson video that this is something that actually is common to both lymphatic trunks and cardiovascular veins. Because recall that the larger vessels of both the lymphatic system and the cardiovascular system can have three tunics or three layers in their walls.

And so because we're looking for what is not common to both of these, we can eliminate answer option a. Now, option b says transport of erythrocytes, which recall erythrocytes are red blood cells. And these erythrocytes, or red blood cells, are really maintained within the traditional vasculature of the cardiovascular system, including cardiovascular veins. But these erythrocytes or red blood cells are not transported by the lymphatic system, including lymphatic trunks, which means that option b is something that is not common to both lymphatic trunks and cardiovascular veins, meaning that option b is the correct answer to this example problem. But let's check option c and d just to be sure.

Option c says, valves to prevent backflow. Now recall that cardiovascular veins, especially the veins of the limbs, such as the arms and legs, can have valves in them to prevent the backflow of blood. And recall that lymphatic trunks and valves of the lymphatic system can have even more valves than cardiovascular veins, and so both of them can have valves to prevent backflow. And so for that reason, we can eliminate answer option c, and then option d says anatomical variations among the population of the exact locations of vessels. And, of course, there is going to be variations across different individuals for both cardiovascular veins and lymphatic trunks.

And so, because this is something that is common to both of these, we can eliminate answer option d. And, of course, this means option b is the correct answer. That concludes this example, so I'll see you all in our next video.

Which of the following is NOT a function of lymphatic vessels?

• A. Return of leaked proteins to the blood.
• B. Transportation of fat from the intestine to the blood.
• C. Delivery of nutrients to tissues.
• D. All of the above are functions of lymphatic vessels.

Lymphatic Capillaries

In this video, we're going to talk more about lymphatic capillaries, which we already know from previous lesson videos are the smallest of the lymphatic vessels and the most numerous as well. And as you can see in this image down below, the lymphatic capillaries, which are shown in green, are often closely associated with blood capillaries of the cardiovascular system. Because, again, recall from previous videos that blood capillaries often leak fluids and some proteins, and those leaked fluids and proteins can be absorbed by the lymphatic capillaries and propelled through the lymphatic vessels to be ultimately returned back to the cardiovascular system to maintain fluid balance. Now these lymphatic capillaries are significantly more permeable than most blood capillaries of the cardiovascular system, and this has to do with the unique structure of the lymphatic capillaries. In fact, these lymphatic capillaries are so permeable that it was once incorrectly thought in the past that they were open-ended like a straw. But again, today, we know that this is not the case, and the lymphatic capillary permeability has to do with the unique structure. And so the adjacent endothelial cells that make up the walls of the lymphatic capillaries overlap with each other in such a way to form one-way valves or one-way flaps. And these one-way valves or one-way flaps will actually open up in order to allow interstitial fluid to enter into the lymphatic capillary as lymph. However, when pressure inside the lymphatic capillary builds up, those one-way flaps or valves will close-up so that the lymph cannot leak out of the lymphatic capillary and back into the interstitial space. And the open flaps of the lymphatic capillaries will actually allow relatively large substances to enter into the lymphatic capillaries, And these large substances include large macromolecules, like larger proteins and fat molecules, but also cellular debris, and even pathogens are able to enter as well. And usually, these larger substances are too large to enter into most blood capillaries. So if we take a look at the image down below on the right-hand side, notice that it's zooming into one of these lymphatic capillaries. And what you'll notice is that these endothelial cells that make up the walls of these lymphatic capillaries overlap with each other to create these one-way flaps or valves that, again, can open up. So here we're showing you an open flap. And when these flaps are open, they allow interstitial fluid to enter into the lymphatic capillary as lymph. However, when, again, when pressure builds up inside of the lymphatic capillaries, these one-way valves will actually close up to prevent the lymph from leaving the capillary. And so this ensures that the lymph is going to remain within the capillary and be propelled forward throughout the lymphatic system. Now, what's important to note here is that we have these little brown structures shown, and these brown structures are anchoring proteins to help ensure that these lymphatic capillaries remain in place even when their valves are opening and closing. And so, really, this is the unique structure that allows these lymphatic capillaries to be significantly more permeable than most blood capillaries. So this here concludes our brief video on lymphatic capillaries, and we'll be able to apply these concepts and learn more as we move forward in our course. So I'll see you all in our next video.

Lymphatic Vasculature Example 3

So here we have an example problem that says, lymphatic capillaries are so permeable that it was once thought that they were open-ended like a straw. However, an issue with this exact design is that it would also allow lymph to easily leak out of lymphatic capillaries. And then it asks, how does the overlapping endothelial structure overcome this issue? And we've got these four potential answer options down below. And so, of course, recall from our last lesson video that lymphatic capillaries are not actually open-ended like a straw. Instead, they are closed-ended. But recall that the lymphatic capillaries have a unique structure where their endothelial cells overlap with each other to create these one-way flaps or these one-way valves that allow interstitial fluid to enter into the lymphatic capillary as lymph, but those flaps or valves will close to prevent the escape of that fluid. And so, notice that answer option A says, overlapping cells form a one-way valve that allows fluid to enter but not escape. And so, answer option A is the correct answer to this example problem, so we can go ahead and indicate that. But just to be sure, let's check these other options. Option B says the pressure in the lymphatic capillary is never higher than in the surrounding tissue, so fluid can't escape. Now this is actually not the case. It is possible for the pressure inside the lymphatic capillary to be greater or higher than the pressure in the surrounding tissue. However, when this is the case, those valves or flaps will be closed to prevent the escape of the fluid, and so option B is not going to be the correct answer. Option C says it forms a tight seal that prevents fluid from entering or leaving. However, recall that the endothelial cells, again, they are not forming a tight seal. Instead, they are loosely overlapping each other in order to create these flaps that can open and close. And so, they are not quite creating a tight seal. A tight seal would prevent fluids from entering into the lymphatic capillary. But, of course, that is not going to be the case, so we can eliminate answer option C. Option D says that it forms a semipermeable membrane so that substances can enter via active transport or facilitated diffusion, but that's not how interstitial fluid enters into lymphatic capillaries. It does not require energy in the form of active transport, and it does not require facilitated diffusion. The fluids will enter through the open flaps or open valves, and so that's why we can eliminate answer option D. Again, option A is the correct answer. So that concludes this example, and I'll see you all in our next video.

Why is it important for lymphatic capillaries to be closely associated with cardiovascular capillaries?

• A. They take up the erythrocytes that leak out of the cardiovascular capillaries.
• B. They need to deliver oxygen and nutrients to the cardiovascular capillaries.
• C. They take up some fluid that has leaked out of cardiovascular capillaries.
• D. They need to receive $CO_2$, which is released by the cardiovascular capillaries.

Lymphatic Ducts

In this video, we're going to talk more about lymphatic ducts, and recall from our previous lesson videos that lymphatic ducts are the largest of the lymphatic vessels, and they empty their lymph into veins that are near the heart in order to return the leaked fluids and proteins back to the cardiovascular system to maintain fluid balance. And these lymphatic ducts are the least numerous of the lymphatic vessels. In fact, there are only 2 major lymphatic ducts, and those are the right lymphatic duct and the thoracic duct, which is also sometimes referred to as the left lymphatic duct. Now the right lymphatic duct is a very short duct, much shorter than the thoracic duct. And as its name implies with the term "right," the right lymphatic duct is going to be draining lymph from the upper right side of the body, including the right side of the head and thorax and the right arm. And the thoracic duct is a much longer duct, and it's going to be draining lymph from the rest of the body that isn't already drained by the right lymphatic duct.

And so let's take a look at the image down below on the left-hand side. Notice that here we are labeling the right lymphatic duct, which is on the right side of this person's body, and notice that it is a very short duct, only about an inch long or so, and it is going to be draining lymph into the veins that are near the heart. And so what you'll notice is that it is specifically draining lymph into the junction of the right subclavian vein and the right internal jugular vein. And again, it drains the lymph into the cardiovascular system right here at this region, returning those leaked fluids and proteins back to the cardiovascular system. And again, the right lymphatic duct is going to be draining lymph from the upper right side of the body. As you can see over here in this other image, this entire region that is colored in orange is going to be drained by the right lymphatic duct.

Now the thoracic duct, once again, is a much longer duct. In fact, it originates down here in the abdomen at this region called the cisterna chyli, which is a sac that stores lymph from the lower body. And the thoracic duct originates here at the cisterna chyli and it extends upwards as you see here much, much longer. And again, it's going to be draining lymph into the veins that are near the heart, specifically, the left subclavian vein and the left internal jugular vein junction. And so, again, the lymph will be drained right here into these veins, returning the leaked fluids and proteins back to the cardiovascular system. And the thoracic duct is going to be draining lymph from the rest of the body that isn't drained by the right lymphatic duct. And so as you can see over here in this image, the regions that are colored in blue, including the entire lower body and the upper left side of the body, are going to be drained by the thoracic duct.

And so moving forward in our course, we're going to be able to apply these concepts and problems, and we'll also continue to learn more about the lymphatic system. So I'll see you all in our next video.

Lymphatic Vasculature Example 4

So here we have an example problem that asks, which of the following correctly describes the path of lymph originating in the right foot? And we've got these four potential answer options below that all start with lymphatic capillaries, but then from that point on differ in the paths that they take. In order to remind you of what we learned in our last lesson video, I've gone ahead and drawn a little sketch. I'm not the best artist, so bear with me here. But here you can see the sketch that I've drawn. And in this sketch, you can see that lymph from the upper right side of the body, colored here in orange, is going to be drained by the right lymphatic duct, whereas lymph from the rest of the body, colored here in blue, is going to be drained by the thoracic duct. Recall that in this problem, we're looking at the path of lymph originating in the right foot, and notice that all of the lower body, including the right foot, is going to be drained by the thoracic duct. We can eliminate any answer option that does not suggest the lymph will be drained by the thoracic duct. For example, we can eliminate answer options A and answer option C, which both suggest that the lymph is being drained by the right lymphatic duct, but, again, that's not going to be the case. Now we're between either answer option B or answer option D, and notice that they only differ in that option B suggests lymph going from the lymphatic capillary into lymphatic vessels and then into the lymphatic trunk before the thoracic duct, and then option D suggests lymphatic capillaries, but then it suggests the lymphatic trunk comes before the lymphatic vessels, and recall from previous lesson videos that this is not going to be correct. The lymph is going to start with the smallest lymphatic vessels and make its way into larger and larger lymphatic vessels. Recall that the lymphatic trunk is larger than the lymphatic vessels, and so the correct path is going to be answer option B. So we can indicate that B here is the correct answer to this example problem, and option D is not correct since it has the lymphatic trunk coming before the lymphatic vessel. That concludes this example problem, and I'll see you all in our next video.

True or False: Lymph originating from your head is always drained through the thoracic duct.

• A. True.
• B. False; it is always drained through the right lymphatic duct.
• C. False; the left side is drained by the thoracic duct while the right side is drained by the right lymphatic duct.
• D. False; the right side is drained by the thoracic duct while the left side is drained by the right lymphatic duct.
• E. False; there are no lymphatic capillaries in your head.

Transport of Lymph

In this video, we're going to talk about the transport or the propulsion of lymph through the lymphatic vasculature. And so unlike the cardiovascular system, which we know has the heart that serves as a pump to propel blood through the blood vessels, the lymphatic system actually lacks a direct pump like the heart to keep the fluid moving. And so the question becomes, well, how is the lymph transported or propelled through the lymphatic vasculature? And the answer is that a multitude of mechanisms contribute to lymph flow. And so notice that down below in the image, we've got these 4 boxes, each with a mechanism that contributes to lymph flow. And so in the box on the far left, we have one of the greatest contributors to lymph flow, and that is going to be skeletal muscle contractions. So recall that skeletal muscles are muscles that we have voluntary control over their contractions. And so whenever you extend, bend, flex, or move a muscle, the shape of those muscles changes in such a way that it can compress nearby lymphatic vessels and propel the lymph through them. And so that's exactly what we're showing you down below in this image. Notice that the skeletal muscle is contracting and changing its shape in such a way that it's actually compressing this nearby lymphatic vessel, and that is propelling the lymph through the lymphatic vessel.

And another thing that you'll notice is that these lymphatic vessels have lots of valves in them that you can see here, and these valves ensure the one way flow of the lymph. So lymph is able to flow past the valves, but the valves prevent the backflow of lymph, and so it keeps the lymph flowing in one direction, the correct direction, which is towards the veins that are near the heart. In fact, it's well known that physical exercise, which requires skeletal muscle contractions, greatly increases the rate of lymph return back to the cardiovascular system. Now the next box that we have here refers to smooth muscle contractions, and recall that smooth muscles are muscles that we do not have voluntary control over their contractions. And so especially for the larger lymphatic vessels, they can actually have some smooth muscle in their walls. And so notice that the pink that you can see down below in this image around the larger lymphatic vessels represents the smooth muscle in the walls. And so when these larger lymphatic vessels stretch from having a large amount of lymph in them, the smooth muscles can detect that stretching and contract, and the contraction can narrow down the lumens of these lymphatic vessels and that can propel the lymph through them. And, again, the valves are going to be there to ensure that there is no backflow of the lymph. Now these smooth muscles, again, are really only found in the larger lymphatic vessels, so the smaller lymphatic capillaries do not have smooth muscle in them. Now the next box that we have here are the pulsation of nearby arteries. Now recall that pulsation refers to the rhythmic contraction and dilation of the arteries, And so it turns out that these lymphatic vessels are often nearby arteries, and these arteries, because they can pulsate, again, contract and dilate in a rhythmic fashion, the movement of the arteries can actually compress some nearby lymphatic vessels, and that can propel the lymphatic or the lymph through the lymphatic vessels.

Now last but not least, over here on the far right, what we have is the respiratory pump, and this is referring to our breathing. And so we are constantly breathing, inhaling and exhaling. And whenever we inhale, take a deep breath, the pressure in our abdomen changes where there's increased pressure, and that increased pressure changes the microenvironment around the lymphatic vessels that are in our abdomen, and that can actually compress those lymphatic vessels that are in the abdomen, and that can propel the lymph through the, the lymphatic vessels that are in our, abdomen. And then, of course, when we exhale, the pressure in the abdomen is going to decrease. However, the valves that are present all throughout the lymphatic vessels are going to prevent the backflow of lymph. And so the inhale is really going to change the pressure and help to propel the lymph through the lymphatic vessels that are in our abdomen and thoracic regions. So really, this here concludes our lesson on the transport and the propulsion of lymph, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Lymphatic Vasculature Example 5

So here we have an example problem that asks, which of the following is not a mechanism used by the lymphatic system to propel lymph. And we've got these 4 potential answer options down below. Now, option A says, pulsation of nearby arteries, and the pulsation refers to the rhythmic contraction and dilation of these arteries. And recall from our last lesson video that this was one of the mechanisms that we listed that can help propel lymph through the body. And so for that reason, we can eliminate answer option A, since, again, we're looking for the option that is not a mechanism that propels lymph. Now moving on, option B says contraction of nearby skeletal muscle, and this is probably the most effective means of propelling lymph through the lymphatic system. And so option B certainly is a mechanism that propels lymph, so for that reason we can eliminate answer option B.

Now, option C says, contraction of cardiac muscle allows the heart to serve as a pump for lymph. However, recall from our last lesson video that unlike the cardiovascular system, the lymphatic system does not have a pump that propels the fluid. And so, although the heart does serve as a pump to propel blood through the cardiovascular system, the heart does not serve as a pump to propel lymph through the lymphatic system. So for that reason, we can indicate that answer option C is the option that is not a mechanism used to propel lymph through the lymphatic system. So option C is the answer that we are looking for, so we can indicate C here is the correct answer.

Now option D says contraction of smooth muscle, and we can eliminate this one as well because recall that the larger lymphatic vessels can have smooth muscle in their walls that can contract to help propel lymph, and so, we can eliminate option D. Again, C is the correct answer. That concludes this example, and I'll see you all in our next video.

After sitting for hours on a long flight where movement is limited, people may experience some swelling in their legs and feet. Which of the following explains this phenomenon?

• A. Smooth muscle is not active, so lymph is not circulated effectively.
• B. Skeletal muscles in the legs and feet are inactive, reducing the rate of lymph flow.
• C. The respiratory “pump” from breathing is not as effective.
• D. The change in air pressure at high altitude significantly disrupts lymph flow, particularly in the lower body.

Here’s what students ask on this topic:

What are the main types of lymphatic vessels and their functions?

The lymphatic system consists of four main types of vessels: lymphatic capillaries, lymphatic vessels, lymphatic trunks, and lymphatic ducts. Lymphatic capillaries are the smallest and most numerous, collecting interstitial fluid to form lymph. Lymphatic vessels, also known as collecting vessels, transport lymph from the capillaries and have valves to prevent backflow. Lymphatic trunks are larger vessels that drain lymph from specific body regions. Finally, lymphatic ducts, the largest and least numerous, return lymph to the cardiovascular system by emptying into veins near the heart. These vessels work together to maintain fluid balance and support immune function.

How does the lymphatic system differ from the cardiovascular system?

The lymphatic system and cardiovascular system have several key differences. The cardiovascular system forms a circulatory loop, with arteries carrying blood away from the heart and veins returning it. In contrast, the lymphatic system is linear, starting at lymphatic capillaries and ending at lymphatic ducts. The cardiovascular system transports blood, a red and viscous fluid, while the lymphatic system transports lymph, a clear and colorless fluid. The cardiovascular system is optimized for nutrient and gas exchange, whereas the lymphatic system focuses on returning leaked fluids and proteins to maintain fluid balance and performing immune surveillance. Additionally, the cardiovascular system has the heart as a pump, creating high pressure, while the lymphatic system relies on mechanisms like skeletal muscle contractions and lacks a central pump, resulting in lower pressure and slower flow.

What mechanisms propel lymph through the lymphatic system?

Several mechanisms contribute to the propulsion of lymph through the lymphatic system. Skeletal muscle contractions compress nearby lymphatic vessels, propelling lymph forward. Smooth muscle contractions in the walls of larger lymphatic vessels also help move lymph. The pulsation of nearby arteries can compress lymphatic vessels, aiding lymph flow. Additionally, the respiratory pump, which involves changes in abdominal pressure during breathing, helps propel lymph through vessels in the abdomen and thoracic regions. Valves within lymphatic vessels ensure one-way flow, preventing backflow and maintaining the correct direction of lymph movement towards the cardiovascular system.

What is the role of lymphatic capillaries in the lymphatic system?

Lymphatic capillaries play a crucial role in the lymphatic system as they are the starting point for lymph formation. These capillaries are highly permeable, allowing them to absorb interstitial fluid, proteins, and larger substances like cellular debris and pathogens. The unique structure of lymphatic capillaries, with overlapping endothelial cells forming one-way valves, ensures that interstitial fluid enters the capillaries as lymph but cannot leak back out. This permeability and structure enable lymphatic capillaries to collect and transport lymph, which is then propelled through the lymphatic vessels, trunks, and ducts, ultimately returning to the cardiovascular system to maintain fluid balance and support immune function.

What are the major lymphatic ducts and their functions?

The lymphatic system has two major ducts: the right lymphatic duct and the thoracic duct. The right lymphatic duct is short and drains lymph from the upper right side of the body, including the right side of the head, thorax, and right arm. It empties lymph into the junction of the right subclavian vein and the right internal jugular vein. The thoracic duct is much longer, originating in the abdomen at the cisterna chyli and draining lymph from the rest of the body. It empties into the junction of the left subclavian vein and the left internal jugular vein. Both ducts return lymph to the cardiovascular system, maintaining fluid balance and returning leaked proteins and fluids.