Transcription
Hello people, it's Medicosis Perfectionist, where medicine makes perfect sense. Let's resume our biology playlist.
In previous videos, we talked about the innate immunity and the adaptive immunity. Today, we'll talk about the lymphatic system, which includes lymph vessels known as lymphatics and lymph nodes. If lymphocytes are the police officers, lymph nodes are police stations. This is my biology playlist, please watch these videos in order.
The lymphatic system. In order for you to understand the lymphatic system, you have to first understand the blood circulatory system. Here's your heart. The left ventricle pumps the blood into the aorta. Aorta is a huge artery. After this, we have muscular arteries, and then arterioles, and then capillaries. And then after the capillaries, we have venules, and then veins, and you go back to the right side of the heart. Okay, why do you have capillaries? Because capillaries will provide the cells with oxygen and nutrients and take away from the cells carbon dioxide and waste. Help the cell perform metabolism and get rid of the waste products of metabolism.
Suppose that 100% of blood is here, okay? You might assume that 100% is going to leave in the venous end. That's not true. About 90%. Well, how about the remaining 10%? They will be collected by lymphatic vessels, first lymphatic capillaries, and then afferent lymphatic vessels. The word afferent means to towards something, towards what? The lymph node. Oh, the police station. That's right. After this, I have efferent lymphatic vessel, which means from the lymph node, and we go back to the heart. Lymphatic vessels, and then lymphatic trunks, lymphatic ducts, whatever. We go back to veins, and I will return the 10% that I took from the venous side back to the venous side. Amazing.
Why did I do all of this? Why did I take from the veins in order to give it back to the veins? Because here we have police stations, we have police officers, we have the lymphocytes. The lymphocytes are going to destroy the bacteria by some sophisticated interrogation methods. Horrible analogy. Please understand something. The blood circulatory system is a closed system. Why? It started in the heart, it's gonna end up back in the heart. However, the lymphatic system is not a closed system. It's an open system. Why? Because I started in the interstitial fluid, and I ended up in veins. The starting point is not the same as the termination point. Oh, that's why lymphatic system is an open system, but the blood circulatory system is a closed system.
What's in the lymph? Normally, there's the fluid loss from the capillaries, that's the 10%. Some pathogens, cells of the lymphatic system such as lymph nodes, cell products such as hormones, cell debris, and chylomicrons. I'll tell you about this very soon. This is coming from the gut after you eat the cheeseburger, which is full of fat. All of this was normal. Pathologically, if there was cancer, especially if it's a carcinoma, it might get drained with lymphatics, which will give it to lymph nodes. That's why we see lymph node swellings in patients with many cancers. What else? I can see lymph node swelling in patients with bacterial or viral infections.
Now, let's talk about the food you ate. This double cheeseburger, which is absolutely delicious but contains lots of fat. Where do I digest? You digest in the stomach and the intestine. What do I absorb? In the small intestine or small bowel. Now, we will be absorbed from the gut to the blood. Okay, can I zoom in here? Yeah, let's zoom in. What do we see here? We see villi lining the wall of the intestine, and those villi look like this. Inside them, there is a lymph vessel extending, a lacteal within the villus. Here is the food that you ate. It was here in the lumen of your gut. This is your gut right here. After this, it will be transported towards the villus that lines your gut wall, and then the lacteal is gonna take this fat. And then we will package the fat. Package it in what? Mortgage-backed securities? Shut up. We package them in chylomicrons. These are your Amazon packages. And then what? Give it to lymph capillaries, and then larger lymph vessels. And lymph vessels will return them back to big veins, as you know.
Why do we do all of this? Because you ate lots of toxins. Your body will help you detoxify. You should thank your lymph nodes for that. Before the lymph node, we had efferent lymphatic vessel. After it, had efferent lymphatic vessel. That's the purpose of the lymphatic system, to clean your blood, to cleanse your system.
"Hey Medicosis, I am a healthy 21-year-old person. Should I take this natural juice cleanser that is sold online?" Shut up. "Why do you want to take it?" "Well, to cleanse my system." Your lymphatic system already does that for you for free. Your liver does that for you for free. There is no need to take a detox. There is no need to listen to snake oil salesmen. And if your mechanic tells you that you better put nitrogen into the tires of your car, run for your life because the atmospheric air already has 78% nitrogen. It's not gonna matter. Most of the air is already nitrogen. Think, people.
Lymph versus chyle. Lymph is in lymphatic vessels. Chyle is in the lacteals only in the gut. Lymph is clear. Chyle is a pig. Yeah, we just ate the stinking cheeseburger, of course it's gonna be opaque. Lymph is colorless. Chyle is milky because lacteals literally mean milk, like in lactose, galactose, lactiferous duct, lactation, etc.
Lymphatics are all over your body with many exceptions. Your brain does not have lymphatics. Why not? Your brain has its own cerebral fluid, which is basically has a similar function.
What are lymph organs? Lymph organs are organs that contain lymphocytes. Oh, such as thymus, spleen, red bone marrow, tonsils, lymph nodules, gut MALT, which is mucosa-associated lymphatic tissue.
How does lymph move inside my vessel? Well, by skeletal muscle contractions. Your muscles are contracting, they are squeezing the lymph vessels into oblivion, forcing the lymph upwards until you go back to big veins. Also, the artery pulse, which is just next to the lymphatic vessels, is gonna help the propulsion. We have two types of lymphatic vessels: superficial and deep. Superficial are in the subcutaneous tissue, but deep is way deeper. Since superficial are superficial, they will move with the superficial vessels known as veins. But deep will move with the deep arteries. Superficial drain your superficial structures. Deep will drain your internal organs.
Let's talk about lymph. Came from the Greek word Lympha, which is the goddess of fresh water. What a lovely name for my future daughter. Imagine that this is a lymph vessel, and the hydrostatic pressure, i.e., the pushing pressure, increased inside that lymph vessel. What do you think is going to happen to the fluid inside? It will start to leak to the outside. What's the outside called? The interstitial space between cells. Oh, is this called edema? Yes, indeed. And the edema is made of lymph. We call it lymphedema.
Let's talk about the anatomy of the lymph node and the spleen. Lymph nodes are kidney-shaped structures. Please try to remember this because later when we discuss kidney together, I'll tell you that the kidney is also a kidney-shaped organ. Man, stop it with these dad jokes. What do lymph nodes contain? Police officers, lymphocytes, and macrophages. And the lymph node is made of an outer part named as the cortex. This is the crust. How about the pudding? The pudding is in the core, that's the medulla. Cortex has follicles. These are follicles. What do they have? They have B lymphocytes, as we'll discuss soon. But medulla does not have follicles. Medulla has sinuses, and these sinuses will collect together and they will coalesce to form the hilum, which is the exit of the lymph node. And then we exit to the efferent vessels. So the entry is the afferent, the exit is the efferent, and we are moving in this direction. "Give me your dirty lymph, I'll clean it for you. I'll return for you clean lymph so that we can go back to big veins to return it to the blood." Now we have clean blood. The royal family might misunderstand my last sentence.
Some clinical correlations. Cancer metastasis can cause enlargement of the lymph node. Moreover, infection can also cause enlargement of the lymph node. But there is a difference. Cancer gives you a painless lymphadenopathy, but infection gives you a painful one.
Why do we need lymph nodes? They are the centers for police officers. What do you mean, Medicosis? Antigen presentation. Oh, when the antigen-presenting cells presented the antigen to the lymphocyte. Yeah, so that the lymphocyte can recognize the antigen and mature and stop being so naive. Yes, it's also room for lymphocyte activation, differentiation, and proliferation. And you will find B and T lymphocytes in your lymph nodes.
Each lymph node is made of a stroma and parenchyma. What's the stroma? It's like the chassis of the car. It's like a frame, a bed, a meshwork on top of which we will lay the actual car. Oh, now I see. So the stroma is just connective tissue matrix. On top of the matrix, I'll put the actual bulk of the substance. The bulk of the lymph node will be here. That's right. In other words, stroma provides structure, parenchyma provides function.
Let's review what we have said in the previous video. Here is a cortex, and the core is the medulla. In that outer cortex, what do we see? We see follicles. All right. What's in the follicles? B lymphocytes. And then after the cortex ends, what do we see? Paracortex. What's in the paracortex? T lymphocytes. Thank you so much. Then we have medullary cords where you find plasma cells, followed by medullary sinuses near the hilum where you find macrophages. When the follicle was made of immature B lymphocyte, it was called primary follicle. But then when the B lymphocytes matured and grew up and recognized the antigen, this became a secondary, more differentiated follicle. Here's the lymph node. This is secondary follicle containing mature B lymphocytes. The follicle is made of a germinal center, and then a mantle, and then a. All of this is in the cortex. Balance height land. Then I have paracortex, T lymphocyte land. Then medullary cords, plasma cell land, followed by medullary sinuses, which has macrophages.
If I have breast cancer, which one of these groups of lymph nodes will be swollen? The answer is the axillary lymph nodes because breast cancer and breast in general drains to the axillary nodes. Since it's cancer, do you think the lymph node enlargement will be painful or painless? The answer is painless.
The lymphatics on most of your body will end up in a humongous lymphatic duct known as the thoracic duct, with the exception of the upper right quadrant of your body. This quarter is gonna drain to the right lymphatic duct. Whether you go to the right lymphatic duct or to the thoracic duct, eventually you'll end up in big veins, which will take you to the superior vena cava, which will take you to the right atrium of the heart. Cancer, especially carcinomas, love to go to lymph. However, sarcomas, which are cancers made of connective tissue, will drain to the blood. Carcinoma is cancer made of epithelial cells. Sarcoma made of connective tissue. Carcinomas go to the lymph. Sarcomas go to the blood.
Who made the lymphocytes? The bone marrow. Who matured them? Well, it depends. If you are B lymphocyte, you mature in the bone marrow. If you are T lymphocyte, mature in the thymus. And then where do they train and linger? In the lymph node. The police officers are the lymphocytes. The police academy is the bone marrow for B lymphocytes and the thymus for T lymphocytes. The police stations are lymph nodes and other lymphatic organs.
Causes of enlarged lymph nodes are many. Here is just a sample. You will see infections, cancers, all kinds of things.
Next, the spleen. Another lymphatic organ. The spleen is made of a red pulp containing blood and a white pulp containing cells such as what? Such as my white blood cells? You mean your lymphocytes? Yeah. B lymphocytes are always in follicles. Oh, yeah, that's true. Always in the cortex, always in follicles. All right. How about the T lymphocytes? Now, the T is always in the P. In the lymph nodes, they were in the paracortex. But in the spleen, they are in the periarteriolar lymphatic sheath. That's why I came up with this crazy mnemonic: The T is always in the P.
And this is the lovely comparison from the previous video. B lymphocytes versus T lymphocytes. Origin: bone marrow for either one. Primary maturation: B cell in the bone marrow, T cell in the thymus. Secondary maturation: B lymphocytes are in follicles. If your lymph nodes, follicles. If you are on the spleen, of course, this is still in the white pulp. How about T lymphocytes? Well, my secondary maturation is always in a P, such as paracortex in lymph node and periarteriolar lymphatic sheath in the white pulp of the spleen. Together, all of your lymphocytes make around 33% of your total leukocytic count, which is the total white blood cell count in your blood.
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