41. Immune System
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foreign invaders that will call pathogens. These can be things like bacteria, viruses or other microorganisms like single celled eukaryotic for example. The thing they all have in common is that they cause disease that's kind of what defines a pathogen. It's something that's bad for us. I mean really you can just think of this. There's germs their germs. Now the immune system is the defense network against pathogens that animals have and it is comprised of lots of different cells and various tissues and it is actually incredibly complicated and sophisticated here we're really just trying to get an introduction. So there's two main types of immunity that we are going to talk about innate immunity and adaptive immunity, innate immunity is going to be able to mount the fastest response And that's because these are non specific defenses and the responses as I said are rather generic so they're not going to be specific to the exact type of pathogen. That's the job for the adaptive immune system. The innate immunity is really just like your first line of defense, adaptive immune system is an acquired specific defense that will be mounted against specific pathogens. And what's really cool is this actually confers long term immunity. That's why for example once you get a certain virus that virus won't get you sick again even if you know it gets into your body because you have this long term immunity against it Thanks to the adaptive immune or the adaptive aspect of the immune system. Now the reason we need an immune system is because there are germs everywhere. There's germs on everything Our bodies are constantly being assaulted by germs. It is an unrelenting onslaught. In fact H. G. Wells basically said that we've earned our place in the natural world by constantly battling against pathogens here. You can see a nice microscopic photograph of red blood cells and some white blood cells mixed in there. Remember there will be white blood cells moving around in the blood. Just a very small percentage of course that percentage is going to increase when you are fighting and actively fighting an infection. Now here we are looking at a cell from the innate immune system and it is basically munching down these bacteria. The innate immune system. Cell is in yellow. The bacteria is an orange and you can see that the yellow immune cell is consuming it. This is actually a process known as fado psychosis and this is going to be a common tactic employed by cells of the immune system to deal with these foreign invaders. These germs, fagot psychosis, it's kind of like cell eating but I don't really want to call it eating because it gives the wrong impression. This isn't necessarily how cells are trying to obtain nutrition which is the purpose of eating right. Some cells will do fado psychosis to obtain nutrition in our immune system. That's not the goal. The goal is to basically break down the particle as you can see happening here and to create some chunks of the pathogen that can be recognized by the adaptive immune system. And we'll talk more about that in a second. So with faye go psychosis, the important thing I want you to note is that yes, it happens with the cell engulfing a particle as you see the cells like reaching out its membrane and wrapping this pathogen right here. But the reason it's doing that is because there is a response between ligand binding and receptors on the surface of the cell performing fabio psychosis. So this is a ligand receptor interaction That leads to this response. And that's what I really want you to take note of that, that uh this is being carried out by a signal that's being passed from Ligon two receptors. And yes, our immune cells will have receptors that can detect Liggins on the surface of pathogens. And you'll see that that is going to actually be an idea that we evolve later. Now another thing that cells of the immune system are going to do is release cytokines. These are signaling molecules that help recruit other immune cells to help mount an immune response. And it's sort of like um putting a lure somewhere in the body for these immune cells to come. So whereas for example, hormones, signal by being spread out into the body, immune cells will come uh release cytokines in a specific area where there's an infection and this will cause other immune cells to go to that area and to mount an immune response there. So it recruits immune cells by attracting them like a lure to a specific place. Now the real magic of the immune system happens with antigen presentation. This is going to be the thing that makes adaptive immunity such an amazing process. So what's going on there? Well, basically immune cells will present pieces of pathogens membrane that contain recognizable proteins. That is stuff that another immune cell is able to look at recognize and mount a specific response for. So what these cells are really presenting are called antigens. This is any molecule really that induces an immune response. Our adaptive immune system is going to build antibodies to those antigens. These are basically molecules produced by the immune system that recognize those specific antigens and this is how our adaptive immune system learns to recognize specific pathogens and mount specific defenses. So here you can see some examples of antigens, right? They come in different shapes and colors and sizes and antibodies are going to be specific to an antigen. So you can see here at our antigen binding site right here it is of a shape that is specific to binding this particular antigen. Right, so antibodies are going to be specific to antigens. And behind me is an example of antigen presentation, we have an antigen presenting cell. It has an antigen here. Well now it's a blue dot this is the antigen and it's going to present it on its surface two. an immune system cell in this case we're looking at a T cell and this T cell is going to be able to recognize that antigen or take that antigen and create a specific response for it. So this is just sort of a general idea, general overview of antigen presentation. When we talk about the adaptive immune system we will go into much more detail. I just want you to get the general sense of how our immune cells deal with stuff. Right. This fagot psychosis there's literally consuming it, bringing it into a cell, getting it out of an area where it can do harm and there's signaling to other immune cells. But most importantly is this antigen presentation thing right, presenting recognizable components of pathogens to cells that can create specific responses to those antigens with that. Let's flip the page.
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the lymphatic system plays an important role in the immune system. Now the lymphatic system is a network of lymphatic vessels which carry lymph towards the heart. It's similar in a way, to the circulatory system, which has blood vessels that carries blood around the body. Lymph, however, is a clear fluid, and it forms from the interstitial fluid. That fluid that is outside of cells in tissues now limp will pass through these lymphatic vessels and get to what are called lymph nodes. These are, uh, places that filter the lymph and clean it before it mixes in with blood, which is what some of this fluid is going to do. And these lymph nodes will actually house, um, house Some Lucas cites a type of immune cell, and they are going thio those immune cells. They're going to help clean the lymph fluid and ensure that, you know, cleaned stuff is making it back into the blood. Nothing that's contaminated is going to get back into the blood. And so here you can see in green the diffuse network of the lymphatic system. All the little dots are lymph nodes, so they're basically all over your body and Here's a zoomed in image of lymph node, and you can see that it has a Lots of little tubes or fluid will enter. It has a tube, we're fluid, will exit, and you can see in this zoomed in image. If I get out of the way, you can see there are lymphocytes that are flowing around in their lymphocytes are a type of immune cell, and you can also see that there are lymphocytes flowing around here in the outside of the lymph node in the lymph vessel. So these guys air cleaning out the limp so that it is uncontaminated and can return to the blood. And also this is a way of identifying infections, now their various organs involved in the lymphatic system as well. There are the tonsils, which are found in the throat and have some involvement in T cell development. It's not super well understood as of yet. Thean Yoon system super complicated, and there's still a ton to be learned to be known about it. Be learned. That's a oh, it's good for a teacher toe. Speak such good English, right? Well, the thinus there's another organ of the lymphatic system and This is a gland where T cells, which is type of immune cell, learn more about, go to mature and develop, and you can see the thymus gland is sort of in this area, kind of like in the upper chest area, the tonsils in the back of the throat. And if we move down a little bit, you can see the spleen, the organ with a really selling name that has a super important job. It filters blood and red blood cells or anthrocytes. It actually is super important Oregon in maintaining our blood. However, its involvement in the immune system is that it stores Lucas sites those white blood cells and produces options. A type of protein will learn more about that. Has an immune function swelled? Antibodies now not pictured here because it's kind of diffuse. You know, it's all around the gut, and in the respiratory system is the stuff called mucosal associated lymphoid tissue or malt. And there's a bunch of different types golf, salt. I'm not gonna list them all. You don't need to really worry about knowing all of it. Just know that there's this lymphoid tissue that you will find in the gut in the respiratory system, and it produces mucous. Hence the name and that mucus is going to be really useful for trapping stuff that's trying to make it into the body. Right? Uh, through your digestive tract, like by taking in food that has pathogens in it. You know, those They're gonna find their way to the gut and breathing in pathogens. Those pathogens, they're gonna find their way to the respiratory system. So this mucosa mucus producing tissue is sort of a measure to try to stop them before they really get in and do some serious damage. So with that, let's flip the page.
Immune System Cells
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thes cells of the immune system as well as red blood cells, are produced in bone marrow, which is a tissue that contains stem cells and is found in the core of bones. You can see some marrow inside this bone right here. Now these cells of the immune system are called Lucas sites, and they're broadly grouped into two categories of granule sites and a granule sites. However, I should warn you right now that classification of immune cells is a crapshoot. I mean, there's many ways to classify them. Some involved form, some involved function, the one that I've chosen to mention involves form. You don't need to worry about knowing the groupings of these guys. It z really complex and convoluted and just way beyond what you need to understand. An intro bio, which is really just an introduction to how the immune system works. So let's start talking about some of the cells some of the players were gonna meet in the immune system. You sign a fills are these, uh, cells, which will be involved in innate defense, and they're going to attack large foreign particles and release harmful chemicals to destroy them. So they're going Thio, You know, basically try to hunt down pathogens and destroy them chemically. Neutrophils are going to perform fag aceto sys, which we talked about before. And also macrophages and monos sites are gonna perform faggot site ASUs. However, they're going to be involved in antigen presentation now, mast cells and base of fills are different types of cells, but they have very similar functions which is releasing signaling molecules like histamine to stimulate the inflammatory response macrophages and Monta sites that I just mentioned. I want to say, uh they're fairly similar. For our intents and purposes, you could just think of them is the same thing, Really. Macrophages developed from monos sites, but we're not really going to differentiate between them much, So don't worry about the distinction there. Just know that they perform faggots, ketosis and antigen presentation. However, the main antigen presentation cells are going to be these dendritic cells and they present antigens to t cells. And this is going to be what connects innate and adaptive immunity, right? It's going to connect the innate and adaptive immune systems because picking up those antigens is going to be part of the innate immune system and coming up with specific responses against them is the job, the adoptive immune system. And we'll talk about the innate and adaptive immune system in more detail later. Now, I just want to give you a general sense of what all the cells dio so lymphocytes are a type of cell found in lymph. They're found other places to but because they're the main cell type of cell found in lymph, they're named lymphocytes. Don't worry about memorizing that name and just want you to know the types of lymphocytes that there are, which include natural killer cells, great name, great name, absolutely savage sounding. And these guys are They provide a rapid response to viral infected cells as part of the innate immune system. And these guys are just killer. They go in, destroy stuff and in a NY ideal world, prevent the spread of the infection and mitigate, you know, the hold it takes on the body. Now these guys T and B cells, these air the major cells of adaptive immunity. These are going to be super important. We're going to talk about them in great detail for now. All I want you to know is that he sells are involved in cell mediated response, which is a type of response will see in the adaptive immune system. And B cells are gonna be what produce antibodies, and they're involved in the other type of response of the adaptive immune system. Hugh. Moral response. So these two things are part of the adaptive immune system, and we'll learn more about those later. Now. T cells get their name because they mature in the theme Ast's faint mature in ah, the famous B cells mature in the bone marrow. So let me just do you t and be now other immune cells will mature in the bone marrow. However, uh, T and B cells are the ones I really want you to know about. Here, you can see this very complicated chart that shows you how all of these various cells of the immune system and some other blood cells developed from stem cells Don't worry about memorizing all of this. Really. All I want you thio get out of this is a that you know there is a relation. Thio, uh, wreath recites and these were going to be, um, turned into platelets and, you know I just want you to see the connection between the types of blood cells and see that there's just a ton of different types of immune cells. That's why I say that it gets very complicated very quickly. But we're going to go into the details of the process of innate immunity and adaptive immunity and learn about the specifics, the specific roles of all of these cells. So with that, let's call it a day. I'll see you guys next time.
Additional resources for Immune System
PRACTICE PROBLEMS AND ACTIVITIES (3)
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