Innate Immunity | Immune System

hi everybody Dr Mike here in this video we're taking a look at the immune system specifically we're focusing on one division of the immune system called the innate division now to begin with we need to talk about the differences between the Adaptive arm and the innate arm of the immune system firstly the Adaptive arm of the immune system is a specific response division so it responds specific or specifically to what pathogen I what bacteria or virus or fungi is targeting the body for attack and it responds in very specific ways to target attack and destroy

that pathogen now the innate division is non-specific it really doesn't care what is trying to attack and harm us it will respond the same way regardless so the Adaptive side it responds specifically depending on what type of pathogen is attacking us the innate really doesn't care a nice analogy I like to use is that of a house so if somebody's trying to get into our house attack us inside the house well it needs to get through the first line of defense it needs to get through the walls it needs to get through the doors it

needs to get through the windows it needs to get through the roof now walls doors window roof doesn't really care what type of intruder is trying to get in it's going to stop it the same way that is the innate division of the immune system but if we think about what the Adaptive site is that is like us hiring guards to walk around the premises of the house these guards know how to respond depending on the type of attacker does that attacker have a knife or a gun their response will be specific to that so

that is the analogy that I like to use between innate and adaptive let's focus on the innate a little bit more that's going to be the focus of today's lecture like I said it's non-specific but a couple of other things that help us classify the innate system is it's not just non-specific it has no memory now what does that mean once it has targeted and attacked a pathogen whether it's a bacteria or a virus or a fungi or some sort of microbial agent once it's attacked it and destroyed it it doesn't remember it which means

it can't adapt itself so that next time it comes along it's more efficient at targeting and killing it so it has no memory of what it's killed the other thing is that it's the first line of defense and this makes total sense especially when we think about the analogy I just used walls doors windows roof and so forth they're the first line of defense so let's now focus a little bit more on the innate system because there's two more arms of the innate system that we should focus on so the first of which is the

external division and so the external division primarily includes things like skin and mucous membranes so let's write that down the external division is mainly skin and mucous membranes now this is going to be different to the other arm of the innate which is the internal division and we'll get to that in a second but again both of these external internal they're still our first line of defense and they're still non-specific and they don't have a memory so let's focus on the external skin mucous membrane so firstly is our skin we know that when you're looking

at me and I'm looking at you I'm looking at your epidermis now your epidermis is the most superficial layer of your skin and it's made up of epithelia so let's write this down so we've got our epidermis and our epidermis is made up of epithelia remember the four tissue types of the body your whole body is made up of only four tissue types epithelia connective nervous and muscle and so our skin made of epithelia specifically it's a type of epithelia called stratified squamous epithelia stratified means many layers squamous means squished so these cells are actually

many layers of these squished dead pancake looking cells makes total sense they're dead which means that it doesn't matter if they get damaged or they Slough away that's the term we use and there's many layers so that it protects what's underlying perfect so that's first line right that's the very first thing but that's not all we have for our skin our skin has oil glands so we've also got what's called sebaceous oil glands and these sebaceous oil glands release an oil and importantly this oil has two important properties that make it protective for us against

microbial agents these properties include things like it is filled with unsaturated fatty acids now what's that got to do with anything that is a poor energy source for microbes viruses bacteria fungi really don't like using unsaturated fatty acids for energy so it's not a great environment for them to grow and thrive on the other thing is that our sebaceous oil glands they have a pH of around about three to five which again makes it an inhospitable environment for microbes so that's our sebaceous oil glands but we know our skin also secretes sweat now what's the

benefit of sweating well we don't sweat necessarily to get rid of microbes we sweat to cool us down through conduction so we have sweat and we release mostly water and a bit of salt onto our skin and as the breeze comes through it takes the heat away and we cool down but when we do sweat it allows one it's a salty environment so again not great for microbes and two it helps wash away any microbes that may be on the skin so sweat's important too we have hair and this hair we know we have on

our head our eyelashes and our nasal cavity as well and allows for us to trap particles because with hair often comes mucus as well so we've got mucus and other various secretions and some of these secretions for example include secretions of our tears and our saliva now what's important about these secretions of tears and saliva is they have enzymes enzymes called defensins and enzymes called lysozymes simply put these enzymes just tear apart any invading pathogens and kill them so that protects our eyes protects our nasal cavity it protects our oral cavity but if we do

tend to inhale something luckily for us in our Airways we have little hairs called cilia foreign is different to the hair on her head eyelashes and nose cilia can actually move they beat now when you inhale particles or pathogens it gets caught in the mucus in our Airways and the Cilia can move these pathogens caught in the mucus we can cough it up or we can swallow it down Aaron's esophagus into our stomach and you might be thinking wait that's bringing it more internally but that's okay and I'll tell you why is because in our

stomach we have gastric secretions of a pH of one to three and that pH will denature it basically unfolds the proteins that comprise those bacteria viruses fungi or whatever microbial agents they are so luckily for us our external defenses here now first line of defense is quite extensive now this is external what if it starts to get more inside so let's think of our bloodstream for example well what can happen here is once it's inside there's three more divisions or three more different ways that we can using our innate immune system attack and Destroy these

invading pathogens let's take a look so we have a way to use our cells so we have cellular defenses we have in addition to cells we have chemicals and we have physiological responses so once it's inside we have cellular responses chemical responses physiological responses let's focus on the cells so firstly what we have are cells called phagocytes phagocytic cells so phagocytes so let's have a look at this word phage phage means to eat sight is a cell these are cells that eat so we've got a couple of different types of phagocytic cells that we should

talk about here that's part of the innate immune system we have neutrophils and we have macrophages so let's first look at neutrophils neutrophils are one of our white blood cells do you remember the way to remember your white blood cells remember never let monkeys eat bananas remember that mnemonic never let monkeys eat bananas now you can get rid of the end of those words and what do we have we've got neutrophils we've got lymphocytes we've got monocytes we've got eosinophils and we've got basophils look at that and the great thing is it also shows us

these white blood cells in most abundant to least abundant so neutrophils are our most abundant white blood cell so it is a phagocytic cell it targets engulfs so takes this pathogen in now the thing with neutrophils is the pathogen is usually bacterial so it usually not always but usually it's bacterial that's what it engulfs and it digests it inside of it so that's what the neutrophils do they are the very first white blood cell that gets to the site of infection so it's the first there it's the first one that arrives and again targets attacks

engulfs and gets rid of that pathogen generally bacteria macrophages work similarly so both undergo phagocytosis phagocytosis is the targeting they're grabbing a hold of the engulfing and the destruction inside of whatever that pathogen may be macrophages include you've got something called wandering macrophages and fixed macrophages so let's write this down you've got wandering macrophages and you have fixed macrophages so wandering macrophages are the macrophages floating through our bloodstream these are like the monocytes so a monocyte is an example of a Wandering macrophage and have a look here is the monocytes we spoke about neutrophils both

are phagocytic cells but monocytes floating through our bloodstream when there's an infection it goes to that area and once it jumps out of the bloodstream to go to the damaged tissue it turns into a macrophage and it can engulf and destroy that whatever that pathogen may be but here's the other thing you might be thinking well what's the difference then between neutrophils and macrophages why isn't a neutrophila macrophage neutrophils generally attack bacteria and engulf and Destroy what macrophages can do is in addition to not all of them do this but what they can do once

they ingest and Destroy they can pull off parts of the pathogen generally proteins that I use like flags for these pathogens that say Hey I don't belong to you I'm a virus I belong to me and not belong to you so it can take that antigen and present it to its surface and these are called antigen presenting cells apcs so macrophages can become a PCS antigen presenting cells and to present these antigens allows for the Adaptive immune system the tmb cells to go hey I recognize that you don't belong here I'm going to attack and

Destroy so that's perfect so you've got wandering macrophages like monocytes floating through the bloodstream and you've got fixed macrophages that sit in the tissues and they don't move so for example there's a whole bunch of different types so you've got histiocytes so histiocytes are in our connective tissue right you've got cut for cells and cup for cells are in our liver you've got alveolar cells they're in our lungs you got micro glia and microglia are in our nervous system so there's heaps of different types of fixed macrophages again they identify things that shouldn't be there

in Golf and destroy but there's other types of cells so while we have these ones the phagocytic cells the other type you should know is called NK cells so we've also got n K cells now these are called natural killer cells what a name natural killer cells how tough does that sound now these natural killer cells what they can do is a couple of different things again they target and Destroy they don't care what it is they target and Destroy really and have a think what they do is this they can release a couple of

things they can release something called performance or performance and they can release something called grandsons now if it releases perforins it perforates it just puts holes in the cell that's invading the body the pathogen puts a hole in it now if there's a hole in it there's going to be a concentration difference from inside that cell to the fluid of the body and usually that cells far more concentrated so fluid rushes into that cell it swells and bursts so that's how NK cells can kill some pathogens granzymes a little bit different granzymes enter that cell

and they trigger that cell to undergo apoptosis they trigger that invading cell to undergo apoptosis they're apoptosis is a programmed cell death so program cell death means it triggers a couple of important chemicals and proteins to say hey it's time to die and what it does is the cell membrane of that cell remains intact and the inside just degrades and destroys itself it's a clean way of a cell to trigger a cell to die this is different to necrosis in necrosis where a cell is dying the walls are destroyed and the cell sort of just

falls apart into the environment apoptosis is not the case this is a Greek term which means when the leaves fall off the trees in autumn which is quite beautiful but it's saying it's time to die so that's apoptosis and that's what these NK cells can perform so they're the cells now let's take a look at the chemicals inside of our body so the chemicals inside of our body can include our complement proteins so we can release something called complement proteins now these complement proteins there's like 30 of them around about 30 complement proteins and the

way that it works is when one complement protein is released it triggers the release and activation of the next protein which triggers the release and activation of the next and the next and the next and the next and it's this cascading effect what do these complement proteins do they complement aspects of the innate division of the immune system so that means they complement phagocytic cells to do their job like macrophages they complement what we're going to talk about here which is the process of inflammation so basically complement proteins complement or support innate immune responses another

group of chemicals that are important here are the cytokines cytokines and there's a couple of different types of cytokines this isn't an extensive list but things like interleukins and interferons I mean there's heaps tumor necrosis factors and things like that what do they do so cytokines also complement the immune system so you might be thinking how they different all right here's the difference complement proteins are proteins cytokines aren't just proteins which they can be they can be glycoproteins so proteins with sugars attached to them but the big difference is this cytokines don't just complement the

innate immune system they also complement the Adaptive immune system so for example interleukins inter means between Lucan means white blood cell so interleukins when they're released they basically call upon the white blood cells and say hey I need a hand for example and I'll rub it off the lymphocytes so you've got your B cells for example your B lymphocytes it can which are part of the Adaptive immune system it can call them in and say hey I need your help here to Target and destroy this part so that's interleukins part of cytokines interferons are interesting

they're released by cells that are I'll actually write this down right so the interleukins they call upon white blood cells interleukins are actually released when a cell is attacked by a virus and it says hey I'm attacked by a virus and then that calls in the T cells to come which is Again part of the Adaptive immune system to attack and destroy that cell that's invaded by the virus so these are just cytokines so these are some of the chemicals of the internal defenses let's now focus on the physiological responses which this Prime primarily two

associated with the innate immune system we have inflammation and we have fever now I'm just having a look where I can draw some stuff because I want to draw the process of inflammation so let's have a look so inflammation is this uh the way I like to explain it to my students is inflammation is like when a friend is coming over to visit it's great in the short term it's horrible in the long term you're like okay you're getting annoyed now you need to go away so inflammation is a good thing short term long term

you need to get rid of it because it can lead to damaged cells over time and that's not a good thing so let's focus on what happens during inflammation so what I might do is I'm just going to very quickly wipe off this internal part here and draw it up in this little spot right here so what I have is a blood vessel and I'm going to have some cells associated with that blood vessel all right inflammation by definition is damage that occurs to vascularized tissue here's some tissue it's got a dedicated blood supply you

can call this vascularized tissue if tissue that doesn't have a dedicated blood supply is damaged inflammation probably won't occur and you might think well what tissue of the body is has no dedicated blood supply cartilage cartilage has no dedicated blood supply superficial layers of our epithelia notice how you don't get inflammation if you have very superficial scratches because it doesn't have a dedicated blood supply but if it scratches deeper then you've damaged vascularized tissue inflammation occurs right so cartilage avascular no dedicated blood supply therefore when cartilage is damaged inflammation rarely occurs not never occurs rarely

occurs but that also means it's really hard it takes a long time for that tissue to repair and fix because inflammation is an important part of attacking destroying invading pathogens but also triggering the Regeneration and fixing of damaged tissue so here's a blood vessel here's some vascularized tissue this vascularized tissue is now damaged because something has happened whether it be some trauma or whatever so it's damaged what happens is these cells release important chemicals so some of the chemicals it can release include prostaglandins this is a really important one which I've done multiple lectures on

prostaglandins and the use of non-steroidal anti-inflammatory drugs that Target prostaglandins and it can also trigger the release of histamine and you know what there's one more we should probably say that it triggers the release of Brady cannons these are probably three of the most important pro-inflammatory chemicals released during the process of inflammation what all three of these chemicals do now again prostaglandins are released by damaged cells it's made from the cell membranes of broken cells histamine is released by mast cells generally when there's some allergen or some immune particle that's triggered that Mast Cell to

release histamine and bradykinins are triggered to be released when any vascularized tissue is damaged but all of them do similar or overlapping jobs that you need to be aware of when it comes to inflammation so one of the things that they do is they trigger the blood vessel to dilate so now this blood vessel is dilating so I'll get rid of that and now you've got this widened blood vessel so one it's triggered dilation so I'm just going to take inflammation here I'll get rid of fever for a sec I'll write it up in a

second so it triggers vascular dilation known as vasodilation what does that mean now vasodilation means more blood can go to this area where do our white blood cells sit in our blood so that means more blood cells white blood cells immune cells can come to this area to target attack destroy any invading pathogens and fix the area beautiful the other thing that these things do is they make the blood vessel really permeable so increases vascular permeability increases vascular permeability why is that important so that the white blood cells like the monocytes and the macrophages and

the neutrophils for example so they can leak out so they can get out of the blood vessel to the tissue to attack and Destroy so these chemicals vasodilate and increase vascular permeability every time you get inflammation what do you always find associated with inflammation called the cardinal signs of inflammation you get redness hate Pine and swelling redness because more blood is going to the area hate because blood carries the heat of the body to that area pain for a couple of different reasons if it's swelling in this area there's going to be pressure put on

our nociceptors our pain receptors that are going to be located in tissue so there's going to be pain receptors here the pressure of the fluid buildup or the direct damage can trigger that plus prostaglandins histamines and bradykinins can directly stimulate nociceptors because it's good to say hey this area is in pain don't use it we need to fix it right and you've got swelling again because of all the fluid that's leaking out so this is inflammation a lot of the drugs that we take Target for inflammation that is Target these things so NSAIDs Target prostaglandins

antihistamines Target histamine for example and there's not a lot for bradycardins but there are some things all right so that's one of the physiological responses the second is fever let's talk about fever very quickly so we've got fever as another physiological response fever's super interesting right what happens with fever is that you've got things called pyrogens Pyro give it the term pyro if have you ever called somebody a pyro pyromaniac someone who loves fire who loves heat okay pyrogen is something that stimulates Heat and pyrogens can be actual uh pathogens themselves or they can be

cytokines and when they're released they travel to the hypothalamus so they travel to the hypo Thelma's do you remember what the hypothalamus is hypothalamus is base of the brain it is the control center of the autonomic nervous system so fight or flight rest and digest and the endocrine system to release a whole cascading array of hormones it also sets our temperature level our thermostat remember our thermostat is set generally at 38 degrees Celsius but if a pyrogen is present again whether it's a virus or bacterial maybe it's a cytokine it takes this thermostat and goes

38 is not right let's bump it up to 40 41 degrees Celsius now what does that mean your body now thinks that 40 41 degrees is the normal body temperature which means if you're now if you're at 38 but it thinks 40 41 is what we should be at 38 is now cold because it goes well that's lower than it should be that's cold so you should be cold which means start shivering so you start to shiver even though your body temperature is starting to go what does shivering do tells the muscles to contract relax

contract relax contract relax you release hate you'll you get warmer what's the other thing that happens your blood vessels and your periphery constrict pulling all the heat from your blood deep into your body again increasing your body temperature you start to get really hot but you feel cold what's the benefit of all this couple of things one is that the benefit of fever is that it makes our immune cells better at functioning immune cell so increases immune cell function the warmer the temperature the better they function the other thing is that it decreases the ability

of uh pathogens to divide decreases pathogen reproducibility amazing so it's to our benefit but again like inflammation to a point people always ask is fever something that we should always try and get rid of as soon as we have it or should we keep it well it depends and I know that's a horrible answer but it's like inflammation sometimes inflammation is good sometimes it's not same way as sometimes fever is good sometimes it's not all right so what we've got here and I'm going to get out the road so you can see it is this

is our summary of the innate division of the immune system so I hope you enjoyed that I'm Dr Mike hi everyone Dr Mike here if you enjoyed this video please hit like And subscribe we've got hundreds of others just like this if you want to contact us please do so on social media we are on Instagram Twitter and Tick Tock at Dr Mike tadarovich at d-r-m-i-k-e-t-o-d-o-r-o-v-i-c speak to you soon