Introduction to the Lymphatic System

Chapter 22, Lecture 1 is an introduction, lymphatic system functions, and gross anatomy. The ability to ward off pathogens is called resistance, and if you don't have that, you're said to be susceptible. We can look at resistance to disease in two broad areas. First is nonspecific resistance, and this is something we're all born with. We have defense mechanisms that are innate. that means that we're born with them, that provide protection against a wide range of different types of pathogens. Immunity involves activation of specific lymphocytes that are going to combat specific pathogens or other substances, and the body carries out these responses through the lymphatic system. The lymphatic system consists of lymph as well as lymphatic vessels, and lymphatic tissues, and lymphatic organs. The fluid that's called lymph is very, very similar to interstitial fluid. If you remember from the last section on blood vessels, capillary exchange, bulk flow, the excess fluid that leaves because of net filtration pressure, not all of it comes back. to the capillary and the remainder is taken up by the lymphatic capillaries. So lymph and interstitial fluid are very, very similar. The major difference between them is location. Lymph is found within lymphatic vessels and interstitial fluid is found between the cells. The lymphatic system has three functions. It returns... It drains the interstitial fluid and returns any plasma proteins to the blood. In the digestive system, it helps to transport dietary fats through specialized lymphatic capillaries called lacteals. And the third thing is it protects against invasion by nonspecific defenses and specific immune responses. This is a drawing of the different types of tissues found in lymphatic. system. We've got lymphatic organs that include the red bone marrow and the spleen seen over here, thymus in the middle of the chest, and then we also have lymph nodes, these little circular structures, and they're found throughout the body. And then we also have diffuse lymphatic tissue that would include the tonsils and the adenoids. and the Peyer's patches, those are found in the small intestine. You can see how the lymphatic vessels travel throughout the body. They tend to go closely along with the veins and arteries to the different sections of the body. Now one thing that this picture shows that we'll talk about a little bit later, is the drainage of the lymph. Remember that the lymph, the interstitial fluid that's taken up by lymphatic capillaries, is returned to the cardiovascular system at the level of the subclavian vein. The right side of the body, only a small portion of the right side of the body here in tan or peach color, and the head goes to the right lymphatic, through the right lymphatic duct to the right subclavian vein. The rest goes to the left subclavian vein. So it's not an equal right side goes here, left side goes there. The majority is going to travel in the left side. So as I said, there's three different functions, draining interstitial fluid and returning plasma proteins, transporting dietary lipids. Also fat-soluble vitamins like vitamin A, E, and K from the GI tract to the blood and facilitating immune responses. These are those lymphatic capillaries we looked at in the last section, and they're situated near capillary beds. And they have, they consist of... Endothelial cells and the interstitial fluid when the pressure here gets too high It's going to cause these cells to separate slightly and the interstitial fluid will drain into these lymphatic capillaries until the pressure is equalized on both sides and then the cells come back together again. This then drains into larger lymphatics. So the lymph capillaries merge together to form larger vessels called lymphatic vessels and they convey lymph into and out of structures called lymph nodes. Again, these capillaries, lymphatic capillaries, are blind-ended, unlike blood capillaries that are continuous. They're blind-ended, and they're more like veins because they have very thin walls. And lymphatic vessels also have valves, a lot more valves than veins do. So the same things like the skeletal muscle pump and the respiratory pump that help to send venous blood back to the heart also help to move lymph through the lymphatic vessels. The lymphatic capillaries have a slightly larger diameter than blood capillaries and again they have those overlapping endothelial cells that act as one-way valves for fluid to enter the capillary. There are, because of differences in pressure, there are filaments that anchor these cells to the tissue around them so that they don't all come apart. It keeps them in place. In the small intestine we have lacteals found in these specialized structures called villi and they transport digested fats. Here you can see the anchoring filaments around these endothelial cells that help hold them in place so the whole structure doesn't come apart when the pressure changes. So it acts as a one-way valve, the separation between these overlapping endothelial cells to allow fluid to come in when pressure is higher here than it is in there. Here you can see the lymphatic vessels and just a cross-section. Remember arteries have very thick walls, veins have thin walls, and lymphatic vessels have even thinner walls. They also have lots and lots of valves. We have two sets of lymphatic vessels. We have superficial ones and deep ones. The superficials travel with the superficial veins and the deep ones accompany the deep arteries and the deeper veins. Here you can see the drainage system. So we have the right lymphatic duct. And on the left side, where it drains into the left subclavian vein, it's not called the lymphatic duct, it's called the thoracic duct. So there are trunks that lead to these drainage ducts, and they're formed from exiting vessels of lymph nodes. And the principal lymph trunks are the lumbar, the intestinal, the bronchial mediastinal, the subclavian, and the jugular. The thoracic duct begins, and you can see the thoracic duct over here, it begins as a dilation called the cisterna chilae and it's the main collecting duct of the lymphatic system. It's going to drain up in here at the level of the left subclavian vein and it's going to receive lymph from the entire left side of the head. left side of the upper body and the entire lower extremities and abdomen. So it's going to drain lymph into the venous blood through the left subclavian vein. Okay, so the thoracic duct is going to drain over in here at the left subclavian vein. The right subclavian vein over here. is going to be where the and here you can see a close-up where the right lymphatic duct is going to drain and so lymph is dumped directly into the left and right subclavian veins and then it becomes part of the blood goes back to the heart heart pumps it to the arteries arterials and capillaries and then fluid leaves again during a bulk flow So... The lymph is going to move because milking action, skeletal muscle contraction, respiratory movements, it's aided by valves that prevent the back flow. If you have too much fluid being filtered at the level of the capillaries and not enough being reabsorbed, the lymphatic system may become overwhelmed and not be able to reabsorb all that fluid. So if you have an extensive accumulation of interstitial fluid, it could be because there's an obstruction to the lymph flow. There could be because you're filtering too much or you're not reabsorbing enough. And in either case, you'd end up with edema. So this is showing here we have blood going through the artery arterioles. And then into the capillary beds, some fluid leaves is picked up by the lymphatic capillaries, goes through the lymph nodes, lymphatic vessel, and then either goes through the right or left lymphatic duct, the right lymphatic duct or the thoracic duct, that's the one on the left, into the venous system, and then back into the heart, and then all over again. Goals for Lecture 1 are to define resistance, susceptibility, non-specific resistance, specific immunity, lacteals, and chyle. Describe the composition of lymph. What are the three functions of the immune system? Lymphatic system consists of organs and tissues, vessels, and a fluid called lymph. List the organs and tissues in the lymphatic system. Describe lymphatic capillary structure and function. Describe the formation of lymph at lymphatic capillaries and trace the flow to the subclavian veins. How does drainage into the left subclavian vein differ from that on the right side? Which areas drain into each?

We have defense mechanisms that are innate. that means that we're born with them, that provide protection against a wide range of different types of pathogens. Immunity involves activation of specific lymphocytes that are going to combat specific pathogens or other substances, and the body carries out these responses through the lymphatic system. The lymphatic system consists of lymph as well as lymphatic vessels, and lymphatic tissues, and lymphatic organs.

The fluid that's called lymph is very, very similar to interstitial fluid. If you remember from the last section on blood vessels, capillary exchange, bulk flow, the excess fluid that leaves because of net filtration pressure, not all of it comes back. to the capillary and the remainder is taken up by the lymphatic capillaries.

So lymph and interstitial fluid are very, very similar. The major difference between them is location. Lymph is found within lymphatic vessels and interstitial fluid is found between the cells.

The lymphatic system has three functions. It returns... It drains the interstitial fluid and returns any plasma proteins to the blood. In the digestive system, it helps to transport dietary fats through specialized lymphatic capillaries called lacteals. And the third thing is it protects against invasion by nonspecific defenses and specific immune responses.

This is a drawing of the different types of tissues found in lymphatic. system. We've got lymphatic organs that include the red bone marrow and the spleen seen over here, thymus in the middle of the chest, and then we also have lymph nodes, these little circular structures, and they're found throughout the body.

And then we also have diffuse lymphatic tissue that would include the tonsils and the adenoids. and the Peyer's patches, those are found in the small intestine. You can see how the lymphatic vessels travel throughout the body. They tend to go closely along with the veins and arteries to the different sections of the body.

Now one thing that this picture shows that we'll talk about a little bit later, is the drainage of the lymph. Remember that the lymph, the interstitial fluid that's taken up by lymphatic capillaries, is returned to the cardiovascular system at the level of the subclavian vein. The right side of the body, only a small portion of the right side of the body here in tan or peach color, and the head goes to the right lymphatic, through the right lymphatic duct to the right subclavian vein.

The rest goes to the left subclavian vein. So it's not an equal right side goes here, left side goes there. The majority is going to travel in the left side. So as I said, there's three different functions, draining interstitial fluid and returning plasma proteins, transporting dietary lipids.

Also fat-soluble vitamins like vitamin A, E, and K from the GI tract to the blood and facilitating immune responses. These are those lymphatic capillaries we looked at in the last section, and they're situated near capillary beds. And they have, they consist of... Endothelial cells and the interstitial fluid when the pressure here gets too high It's going to cause these cells to separate slightly and the interstitial fluid will drain into these lymphatic capillaries until the pressure is equalized on both sides and then the cells come back together again.

This then drains into larger lymphatics. So the lymph capillaries merge together to form larger vessels called lymphatic vessels and they convey lymph into and out of structures called lymph nodes. Again, these capillaries, lymphatic capillaries, are blind-ended, unlike blood capillaries that are continuous.

They're blind-ended, and they're more like veins because they have very thin walls. And lymphatic vessels also have valves, a lot more valves than veins do. So the same things like the skeletal muscle pump and the respiratory pump that help to send venous blood back to the heart also help to move lymph through the lymphatic vessels. The lymphatic capillaries have a slightly larger diameter than blood capillaries and again they have those overlapping endothelial cells that act as one-way valves for fluid to enter the capillary. There are, because of differences in pressure, there are filaments that anchor these cells to the tissue around them so that they don't all come apart.

It keeps them in place. In the small intestine we have lacteals found in these specialized structures called villi and they transport digested fats. Here you can see the anchoring filaments around these endothelial cells that help hold them in place so the whole structure doesn't come apart when the pressure changes.

So it acts as a one-way valve, the separation between these overlapping endothelial cells to allow fluid to come in when pressure is higher here than it is in there. Here you can see the lymphatic vessels and just a cross-section. Remember arteries have very thick walls, veins have thin walls, and lymphatic vessels have even thinner walls. They also have lots and lots of valves. We have two sets of lymphatic vessels.

We have superficial ones and deep ones. The superficials travel with the superficial veins and the deep ones accompany the deep arteries and the deeper veins. Here you can see the drainage system.

So we have the right lymphatic duct. And on the left side, where it drains into the left subclavian vein, it's not called the lymphatic duct, it's called the thoracic duct. So there are trunks that lead to these drainage ducts, and they're formed from exiting vessels of lymph nodes. And the principal lymph trunks are the lumbar, the intestinal, the bronchial mediastinal, the subclavian, and the jugular. The thoracic duct begins, and you can see the thoracic duct over here, it begins as a dilation called the cisterna chilae and it's the main collecting duct of the lymphatic system.

It's going to drain up in here at the level of the left subclavian vein and it's going to receive lymph from the entire left side of the head. left side of the upper body and the entire lower extremities and abdomen. So it's going to drain lymph into the venous blood through the left subclavian vein.

Okay, so the thoracic duct is going to drain over in here at the left subclavian vein. The right subclavian vein over here. is going to be where the and here you can see a close-up where the right lymphatic duct is going to drain and so lymph is dumped directly into the left and right subclavian veins and then it becomes part of the blood goes back to the heart heart pumps it to the arteries arterials and capillaries and then fluid leaves again during a bulk flow So...

The lymph is going to move because milking action, skeletal muscle contraction, respiratory movements, it's aided by valves that prevent the back flow. If you have too much fluid being filtered at the level of the capillaries and not enough being reabsorbed, the lymphatic system may become overwhelmed and not be able to reabsorb all that fluid. So if you have an extensive accumulation of interstitial fluid, it could be because there's an obstruction to the lymph flow. There could be because you're filtering too much or you're not reabsorbing enough.

And in either case, you'd end up with edema. So this is showing here we have blood going through the artery arterioles. And then into the capillary beds, some fluid leaves is picked up by the lymphatic capillaries, goes through the lymph nodes, lymphatic vessel, and then either goes through the right or left lymphatic duct, the right lymphatic duct or the thoracic duct, that's the one on the left, into the venous system, and then back into the heart, and then all over again.

Goals for Lecture 1 are to define resistance, susceptibility, non-specific resistance, specific immunity, lacteals, and chyle. Describe the composition of lymph. What are the three functions of the immune system? Lymphatic system consists of organs and tissues, vessels, and a fluid called lymph. List the organs and tissues in the lymphatic system.

Describe lymphatic capillary structure and function. Describe the formation of lymph at lymphatic capillaries and trace the flow to the subclavian veins. How does drainage into the left subclavian vein differ from that on the right side? Which areas drain into each?

Transcript for:Introduction to the Lymphatic System

Transcript for:
Introduction to the Lymphatic System