The Immune System

In this episode, we learn about the Immune System, focusing on the branches of the immune system, different immune cell types, MHC classes, and more! If you have any questions, suggestions, or corrections, please email themcatquizshow@gmail.com

Transcript

SPEAKER_00 0:08

But you may want to stop changing your way. Or changing your name.

SPEAKER_02 0:30

Thanks for the intro, Pat Collins. Welcome everyone to the MCAT quiz show. I'm Eric Cartman, and joining me today, as always, is my favorite podcast host, Isa Huck. Let's not waste any time and get right into the episode. But first, if you haven't listened to the intro episode yet, make sure you do that first. So today's topic is the immune system.

SPEAKER_03 0:53

Yep. Thanks for the intro, Cartman. Let's get started. Round one. And just a quick heads up: if the audio sounds different, that's because I am in a different recording studio. So I hope everyone can hear me clearly. Okay, first question. Which vessels converge at the thoracic duct, which travels up the spine and into the circulatory system through the left subclavian vein? It's a pretty complicated question to start, but if you want to make it simplified, it's which vessels converge at the thoracic duct? And the hint is what the topic of today is. And that would be the lymphatic vessels, very important to the immune system. Where are white blood cells made? They are made in the lymph nodes. Lymph nodes. The lymph from the upper right side of the body is drained by what duct? So your upper right side is, you know, your right shoulder area, right arm, right side of your head. That is drained by what duct? And that's the lymphatic duct. How would the lymph from the left side and bottom of the body? Which duct is that drained by? That's drained by the thoracic duct. So that's everywhere else on your body is the thoracic duct. Okay. The lymphatic system plays a role in transporting fat for the use of what in the small intestine? For the use of lacteals. So lacteals help transport fat. What kind of immunity reacts quickly? Because it targets all foreign invaders in a generic way. And this is called innate immunity. So I would highly recommend looking up a tree of the immune system. There's gonna be different categories, different subcategories, different cell types. It's helpful to know what cell types are in which type of immunity. Gives you an overall better understanding of the immune system. So, in terms of innate immunity, what is it also known as? It's known as non-specific immunity, right? We said it's targeting things in a generic way. How about what kind of immunity reacts slowly? Because it targets pathogens using specific mechanisms made for that specific pathogen. And this would be called adaptive immunity. And what's another name for adaptive immunity? So if it's not non-specific, adaptive immunity is specific immunity. Pretty intuitive. Okay, all cells with a nucleus display which MHC class on their cell surface. And MHC stands for major histocompatibility complex. It's an important cluster of genes for the adaptive immune system. But anyways, back to the question. All cells with a nucleus display which MHC class on their cell surface? This would be MHC class one. So what are the only cells to display MHC class two on their cell surface? These would be phagocytic cells. If you see an antigen on MHC class one, what does that mean? That means that the cell is infected by a foreign invader. MHC class one, cells infected by a foreign invader. What happens if you see MHC class two? An antigen on MHC class two. What does that mean? That means the cell has killed a foreign invader. So MHC class one means the cell is infected, MHC class two means the cell has killed. So I like to think of um you know antigens as these little sort of tags, kind of sticky notes. So you're in the immune system and an antigen, a little sticky note, gets put on MHC class one. So now we know that this cell that has a sticky note on it is infected by a phone invader. I'm not sure if you guys played this game Agario growing up or Slaterio. Fun game when I was growing up, but there's these little balls floating around in this map. And if the ball, which is the cell, you get a little sticky note on it, which is the antigen, on MHC class one, it's letting everyone else in the immune system know that that guy is infected. And what do we do to infected beings? I mean, we just had COVID. I don't know when you're listening to this episode, but we had COVID about five years ago and six years ago. And if someone was infected, especially the initial phases, we put them on quarantine. And we said, stay away from us, we don't want this. And that's kind of the same idea, is we're tagging the cell as you're infected, you need to be quarantined. And unfortunately, in the case of your immunity, you actually kill that cell. So the cell gets infected, and we say, we don't quarantine them and let them live, we actually say you need to die because it's better off for our immune system just to get rid of that one infected cell rather than risk infection to other cells. Right? So that's what MHC class one does. But let's say, for example, we see an antigen or a sticky note on MHC class two. Okay, that means, like we said, the cell has killed a pathogen. It gets a badge of honor, and it also presents this pathogen to other immune cells, letting everyone know, yo, look what I just did. So you can imagine that when you when you kill your enemy, you know, sometimes back in the day, they would take their head and they would hold their head up and say, look who I just killed. And imagine that was your enemy. Let's say, for example, you're attacking, I'm not gonna name any countries, don't want this to get political, but let's say we're attacking Kingdom Y. We don't like Kingdom Y. And we kill one of their guys and we hold up their head, and he's got like a big chain on, and it says like Kingdom Y, and we're like, look who we just got, we just killed Kingdom Y. We're letting everyone else know, yo, Kingdom Y is low-key in our castle. We need to do something about it. You're letting the other immune cells get ready for war. And these might sound crazy, but I just like making analogies, helps it stick better. I like picturing the immune system as a big defense. You have your kingdom, we'll call it Kingdom X, and you are defending yourself against Kingdom Y. Kingdom Y are foreign invaders, not to be xenophobic, but they're attacking our kingdom. And everything in the immune system is the defense. So all your different types of cells, these are just different types of military units, and they're all working together to notify each other to build up this response to defeat the enemy. So imagine it whatever way you want, but that's the way it works for me. And that's the way actually most people teach the immune system. Okay, that was a long side tangent. Let's get back to the main content. So MHC class one antigens are developed through what pathway? And they are developed through the endogenous pathway, MHC class one. So intuitively, MHC class two antigens are developed through which pathway? I mean, we went over this in pretty good detail. This is the exogenous pathway. Okay, moving on. The antibacterial enzymes on the skin are called what? These are called defensins. Defensins. How about the antibacterial enzymes in the mouth? These are called lysozymes. Pathogens are removed from the lungs through what process? And this is called the mucociliary escalator. Muco is mucus ciliary cilia. Those two things work together to get rid of pathogens from your lungs. In the bloodstream, which system has proteins that punch holes through the cell walls of bacteria? And these are this is called the complement system. And just remember that the MCAT is not going to go super in-depth for anything, but if there's something that you're not too familiar with, because you know I can't explain every single concept in great detail. For example, you're not as familiar with the complement system, just look it up, right? No harm in that. This podcast is supposed to help you identify gaps and you need to touch up on. But for the most part, remember, don't go too in-depth with anything. Just skim the surface and know everything. And focus more on practice questions, focus more on your understanding, uh, your thought process, your critical thinking, and don't focus too much on tiny details. Okay, in the bloodstream, what proteins prevent replication of nearby cells to prevent the spread of viruses? And these are called interferons. Interferons. What kind of cells include macrophages and natural killer cells? These are called agranulocytes. Agranulocytes? So all these next questions are basically asking about cell types, and they're all gonna be on that immune system tree, like I was talking about. So please look this up and take a look after so you can get a picture of where everything stands on this tree. What kind of cells include eosinophils, basophils, and neutrophils? And these are called granulocytes. What are the large phagocytic cells that display MHC class two called? These are called macrophages. What kind of cells destroy cells that do not display MHC class one? And these are called natural killer cells. What kind of cells release histamine when an allergen or parasite is detected? And these are called eosinophils. What kind of cells release histamine in the bloodstream? These are called basophils. And how about the cells that release histamine in the tissues? And these are called mast cells. So eosinophils, basophils, and mast cells all release histamine? Just different areas. What kind of phagocytic cells detect bacteria through chemicals or opsonization? And these are called neutrophils. What is the phenomenon where white blood cells sense and follow the chemicals released by bacteria? This is called chemotaxis. What is the process when a pathogen has been marked with antibodies by the adaptive immune system? And this is called opsonization. Tumoral immunity is mediated by which cells? These are B cells. How about cell-mediated immunity? Which cells is that mediated by? And those are by T cells. B cells mature in what? They mature in the bone marrow. And how about T cells? Maturation, where is that? That would be in the thymus. So we know that B cells are matured in the bone marrow, but where are they activated? And that would be in the spleen or lymph nodes. What is the process where many B cells are made that each respond to a different antigen, but only those with a high affinity to the antigen survive? And this is called clonal selection. What kind of B and T cells have not been exposed to an antigen on an MHC class II? And these would be called naive B and T cells. What kind of B cells produce a large quantity of antibodies? And these are plasma B cells. Antibodies are also known as what? They're also known as immunoglobulin or Ig. Can you describe what antibodies look like? What are they made up of? So to start, they have two identical heavy chains. Those are in the middle. It's kind of like a Y shape. So two Y chains. And two identical light chains. And the light chains are located on the outside of the heavy chains. You can look this up, but it's a Y with the heavy chains on the inside, the light chains on the outside, and they have disulfide bonds holding everything together. What kind of B cells stay in the lymph nodes waiting for re-exposure? And these are called memory B cells. During what kind of selection do the T cells that cannot recognize MHC undergo apoptosis? This would be called positive selection. So the T cells that can't recognize MHC, they undergo apoptosis. During negative selection, what happens? And this time the T cells that react against one's own body undergo apoptosis. So what's the difference? In positive, the T cells that can't recognize MHC undergo apoptosis, but in negative selection, the T cells that react against one's own body undergo apoptosis. So what's a word for that? What is reacting against one's own body called? That's called autoimmunity. So if you heard about an autoimmune disorder, that's what's happening. What kind of T cells respond to MHC class II antigens by using chemicals called lymphocines to recruit other immune cells to help destroy the pathogen? Key word there was help, so they're called helper T cells. Helper T cells are also known as what? They're also known as C D4 plus T cells. What kind of T cells respond to MHC class 1 antigens from infected cells by killing the infected cells through the use of toxic chemicals that cause apoptosis? Gave you a lot of hints there. These are called cytotoxic T cells. And what are cytotoxic T cells also known as? And these guys are called C D eight plus T cells. So C D4 plus are helper T cells, and C D eight plus are cytotoxic T cells. What kind of T cells tone down the immune response to prevent issues with autoimmunity? And these are called regulatory T cells. What kind of T cells are also known as regulatory T cells? And these are called suppressor T cells. What kind of T cells are stored away waiting for re-exposure? We kind of hinted at this earlier. These are called memory T cells. So we have memory B cells that stay in the lymph nodes waiting for re-exposure. We also have memory T cells that are stored away waiting for re-exposure. What is the specialized macrophage that the skin has that destroys pathogens? And these are called Langerhan cells. What kind of cells in the epidermis interact with sensory neurons to provide the sensation of touch? And these are called Merkle cells. The inner layer of the skin is called what? And this is called the dermis. And under the skin is which layer? And that would be the subcutaneous layer. And you may be thinking, like, why are those questions being asked? I thought this is about immunity. And you're right, but these parts of the skin are definitely involved in immunity. And while that was the last question, that's just a quick preview as to what we're going to look at in the musculoskeletal and skin system podcast. But like I said before, there's going to be overlap in questions, and I want you to start recognizing that where there's overlap in topics. Keep that in mind because the MCAT is going to throw so much overlapping content at you. So I just threw a couple of skin questions there at the end. Help you connect that to the immune system because it does. It's very much related to immunity. But also it's a preview to our podcast episode that will be coming out in a bit from now. But regardless, that was the last question. So I wanted to thank you for paying attention, hopefully, to this podcast. I mean you're still here. So I also hope you enjoyed and learned something new or refreshed your current understanding. And as always, please feel free to email me if you have any questions, corrections, or suggestions. And with that, I'll pass the mic back to Cartman for a final message.

SPEAKER_02 21:24

Thanks, Isa. I learned a lot from this episode. If you guys also benefited from this podcast, please feel free to leave us a review as it helps us reach more students. And for all the listeners out there, you got this. And I'm not just your butters, I'm HIV positive. Being a still not is sweet because you make a lot of money. And don't you know the first law of physics? Anything that's fun costs at least $8. Love is like taking a dump butter. Sometimes it works itself out, but sometimes you gotta give it a nice hard slimy push. Shut up, fat boy! I'm not fat! I'm festively pump! I made you eat your parents. Great, you guys. I'm going home. Words cannot express how much I hate you guys. As we find our way northward into the great unknown, only that one thing remains certain. That I hate you guys with every tired muscle in my Confederate body. I'm a cop, and you will respect my authority.