all right ninine nerds in this video we're going to talk about surface tension and surfactant all right what is surface tension how would you define surface tension so surface tension is really actually better defined when we look at it inside of this actual alviola here but right now we'll put like a little definition for right now surface tension is actually occurring because of two things so surface tension is caused by two things one thing that causes surface tension is there's you know inside of the alviola you have a lot of water like just a little bit you have like nice thin water layer right here and then inside of that you're actually going to have a lot of the air a lot of the nitrogen the oxygen the carbon dioxide molecules which you're going to be in here well there's an interaction an interplay between the water layer and the air layer and we'll talk about it in more detail but because of that interplay between the two there's a certain amount of tension because what happens is the water molecules don't want to interact with the air and they dive deep down closest to the actual alveolar cells type one and type two and because of that it creates this tension because the again the water molecules do not want to interact with the D similar gas molecules okay so it's due to this air gas okay I'm sorry water air water air interaction okay so this air water interaction okay and we'll explain that more detail and the second thing is because of the air water interaction what this causes is whenever the actual water molecules dive down into the deeper layers of the actual water layer it creates the shrinking of the alveoli and when it wants to shrink the alvioli it wants the alvioli to recoil and and collapse and produce the small size possible and so again another thing with surface tension is it tries to promote the actual collapsing of alveoli all right okay so that's how we would define surface tension and again it's you can you can even add on to this it's basically a cohesive interaction between the water molecules so it's a very strong cohesive intermolecular force reaction between the water molecules and then instead of them uh the water molecules acting with the air they react withs and produces a tension and because of that tension it tries to shrink the alvioli and tries to collapse the alvioli and causes them to assume the smallest size possible but for us to better understand this let's take this alvioli and what we're going to do is we're going to take a section of that alvioli so we're going to take this blue part which is the respiratory membrane we're going to look at the um alveolar cells here and then the water and air interaction so let's go ahead and drop down here okay so here we're going to have this blue layer that's basically the basil lamina the basement membrane then we're going to have these alveolar cells now you know alveolar cells there's actually two types of alveolar Cells Two Types there's type one and type two simple as that right so you have what's called type one and if you read them in certain textbooks they also call them num numos sites or I'm just going to call them type one Alvar cells but again you can call them type 1 numos sites or type one alveolar cells and the type one alveolar cells are the ones that are primarily involved in gas exchange so in other words whenever the oxygen is actually moving from what the alveoli into the blood and whenever the CO2 is moving from the blood to the alveoli that's what it's contributing to okay so it contributes in gas exchange all right the second one is type two and type two oh before I do this it's not just important to know their actual their function it's important to know their shape which one of these because obviously I could have said any one of these could be type one and any one could have been type type two the type one are these squamous like epithelial cells the cuboidal like epithelial cells is type two okay and there are more type one than there is type two so the type one or more abundant type two is less abundant so again I should under put under this this is actually squamous epithelial cells epithelial cells okay type two alveolar cells are going to be this cuboidal one and they contribute to a protein lipid complex called surfactant so they play a role in producing this this actual lipid protein detergent complex called surfactant and we'll talk about him and they are cuboidal cuboidal epithelial cells okay okay so now we got all that mumbo jumbo out of the way I want to explain something here okay so bear with me it's kind of a tough topic for some people but I'm going to do my best to explain to you guys I'm going to represent again I told you that there was a water layer right here right so there's a water layer here that's actually interacting between these epithelial cells and the air so let me draw here these circles and what these circles are representing here are they're representing the water molecules now water molecules are interesting because they can interact with one another right and when they interact with one another they exert a certain amount of force it's kind of like an inter intermolecular reaction right so these intermolecular attractions or reactions between each other is very interesting so let me draw a couple more circles here and then we'll see what I'm talking about with these reactions and forces and cohesive interactions okay so we got a lot of water molecules right here all of these brownish colored circles are representing water molecules so it's a thin water layer so this right here is the water layer this is the water layer here's the cell layer and then up here I'll represent it with a couple different types of I'll represent up here you're going to have some oxygen you're going to have some CO2 you're going to have some nitrogen stuff like that this is your gas layer or your air layer right so this is where the air is now here's what's really cool these water molecules exert a force on one another so look at the top the where the surface tension is really taking place is here at the top layer so if you have to remember any of these layers try to remember the top at least first or second layer look what happens here if we go to the second layer and the third layer look at this this guy can exert a force or it can interact it can have intermolecular uh attraction with this water molecule it can have an intermolecular attraction to this water molecule and it could have an intermolecular interaction with this molecule as well as with the one above it same thing for this guy it could react with this guy react with this guy react with this one and react with this one watch here's the problem all of these molecules because of them having this net interaction in other words this one has a nice interaction with this guy nice interaction with this guy nice interaction with this guy and nice interaction with him here's the problem ready look at this guy look at this one on the top he can interact with the guy next to him he can interact with the guy on the side of him and he can interact with the guy below him but he has no interaction with the person above him there's no the actual water molecules do not want to interact with the gas so you know what they do they're very greedy you know about vectors look at this Vector this vector and this Vector they'll cancel each other out so these will cancel each other out if these two vectors cancel each other out where would the net vector be pointing downwards that's where the water molecule is going to want to go it's going to want to interact with the water molecules below and so guess what these water molecules will start doing these water molecules not just this one but this one here this one here this one here if I come over here this one here this one here this one here and you get the point that look at all these net vectors this one's pointing down this one pointing down this one's pointing down and if I even did this one this one's pointing down these water molecules will start diving to the bottom as these water molecules on the top and even some of the actual maybe a layer below as they start diving to the bottom what happens to this layer it gets thinner as this layer gets thinner so watch this let's say that I actually have this layer here I take this layer I put it up here right so now I have here here's my air water interface and again this brown is supposed to represent my actual water molecules right and let's say originally here was actually the water molecules right but what were the water molecules trying to do the water molecules are trying to go and drop down to the lower layers as they try to drop down to the lower layers right so as these water molecules start trying to drop down to the lower layers so for example let's say I take these water molecules they're going to start diving down well they're not going to be here they're going to start trying to move downwards they're going to try get closer to these guys so as they start trying to get closer to these guys they try to pull the water layer down same thing with this one over here these would try to pull the water layer down so as they try trying to pull this water layer down what's happening it's actually shrinking it's actually shrinking and getting smaller and smaller and smaller it's trying to keep dropping and going down to the bottom layer as these water molecules keep trying to go down and drop to the bottom layer it makes this layer thinner okay as this layer gets thinner it actually starts causing the alveoli to develop some type of tension so as this layer gets thinner the alveoli starts actually collapsing and as the alveoli starts collapsing it starts trying to push the air out okay so let me explain one more time because these water molecules right here they have an interaction to the side of of them an interaction to the other side and an interaction below but nothing to interact with above this will not allow for the alveoli to expand because the water layer can't go up okay it has nothing to interact with so because of that because the water does not want to interact with the gases it goes deeper down into the bulk layers of the water down here to the bottom layers as it drops down to the lower layers it makes this layer thinner as the layer becomes thinner it creates a specific type of tension and that tension is called surface tension and as that tension starts increasing it tries to pull on the alveoli tries to make the alveoli collapse now you know there's a guy his name was a lapas and he was working on spheres and he came up with this concept he came up with this concept that we can determine the pressure that whenever whenever the surface tension is increasing there's a certain amount of pressure that's being the Alva is trying to exert and push on the air to push the air out they call it a collapsing pressure he devised this formula which says uh the change in pressure you know this is laplus law here change in pressure is equal to two times the tension and you know what this tension is surface tension let's write that next to it this is specifically the surface tension and then this is going to be over what this will be specifically over radius and we'll represent radius as R okay so p is right here is supposed to represent pressure okay okay but specifically it's a type of pressure what do we say as these layers get thinner because of the water molecules diving to the bottom layers because they have no interaction with the gas molecules above them only the water molecules below them caus this layer to get thinner and as it create caus this layer to get thinner it develops a certain type of surface tension between the water and the air as it does that the alveoli starts trying to collapse as it tries to collapse it tries to push air out that's the whole desire to push air out when it does that the pressure by which it pushes the air out is this pressure so it's called a collapsing pressure okay so we technically all a collapsing pressure okay so let's let's actually explain this a little bit more then let's see how tension can affect is collapsing of pressure so for example let's say that I take this formula and I form two different formulas so I put P here and I put two times the tension over the radius for this one and I put over here in a different color I put this one in this maroonish color I put pressure equals 2 * the tension / the radius so in this situation if the surface tension increases what can we devise from this then if the the surface tension increases okay because of that air water interaction okay because the air water interaction because the water molecules want to dive to the bottom layer it creates a tension what is that going to do to the pressure so an increase in the actual surface tension increases the collapsing pressure of the alvioli increases the collapsing pressure of alvioli what do we say come here surface tension it wants to collapse the alveoli that's all it is and if we understand that what is surface tension is due to the air water interaction and as the water molecules dive to the bottom layer because there's nothing for them to exert their intermolecular force or interaction above they're going to drop down make the layer thinner which is going to create a tension that tension can cause the alveoli to collapse and then in the opposite if you de increase the tension If You by some situation decrease the tension and we'll talk about how we decrease the tension our body has a beautiful way of doing that it's called surfactant if you have the surface tension decreased what is that going to do okay we'll think about the formula if you decrease this number what we'll do to the this number it'll decrease the pressure so it'll actually decrease the collapsing pressure so tension and pressure this collapsing pressure are directly proportional right of the Alvi sweet deal and again whose law was this this was laplus law of a sphere but in this case we're talking about the alveoli okay now you know what since we're here let's see how the radius is affected by it and that's why we have this diagram okay let's say for some situation um you have this alveoli and let's look at the difference look at this one and look at this one let's say that this alveoli by some uh reason isn't getting properly inflated because it has a lot of mucus built up so let's say that this is a mucus plug right here that'd be pretty nasty but you got a big old mucus plug here and this mucus plug is uding or it's uh blocking some of the air flow down into this area so if it's blocking the air flow so air is coming here so flow so air flow as the air is Flowing it's going to want to come down here but there's going to be a lot of uh friction resistance right so this area will become very underinflated it's going to be not very very well inflated so it's going to be you know how they call ventilated if we say ventilated and we actually say it's below the normal ventilation we say it's hypoventilated so we can say that this alvioli is hypo ventilated and let's say that this alveoli it's getting a decent amount of air okay it's getting a decent amount of air so this one let's say for right now it's normally ventilated just for right now and then we'll see something that's really interesting here okay so I say this one's having this mucus plug and this one's normally normally ventilated watch what can happen here look at the radius difference here look at the radius difference look at from this point here so you know how you take you know take radius you take half of the diameter so if we come from here to this point here that's our radius so the radius here and then I come from here and I take the radius here this one must have a much larger radius right let's just say for example this radius is 2 cm even even though that's not it's going to be much smaller than that but anyway this is going to be two I'm sorry this should be let's make this one bigger let's make it two times that let's make it 4 cm let's apply lapis's law to this so lapis's law says that pressure the collapsing pressure is equal to 2 * the tension divided by the radius if this in this situation and let's do this in a different color let's do this one in this blue so pressure is equal to 2 * the tension by the radius in this situation here the radius is very low because it's underventilated if the radius is very very low what does that do to the collapsing pressure it increases the collapsing pressure so the decrease in the radius is going to do what the decrease in the radius of this alveoli is going to increase the collapsing pressure of the alveoli oh that is not good thank goodness our body has different ways of dealing with this you know and I'll explain it in just a second but just for the heck of it look at this radius let's say that this radius is a little bit larger all right it's a little bit larger okay and let's let's say for a second normally our body doesn't do this but it usually we have ways of protecting this if this radius drops down really low and the collapsing pressure of the alveoli becomes too high what would it do to this alveoli collapse it if it collapses this Ali where would the air go it would go over into this guy and as the air starts flowing so normal air is coming this way but then we add in some extra air from this alveoli because this alveoli collapses so if this alveoli collapses it provides some extra air to flow over here so it was normally ventilated but then it gets extra air from this collapsed avoli what would happen to this alveoli it would become above ventilation hyperventilated right so this going to become hyper ventilated all right what happens to the radius then let's say that the radius even increased let's say it was originally four and because of the alveoli emptying some of his actual air in here let's say it went up to like five or something like that let's say not all the air went over and so it goes up to about 5 cm okay if that's the case then we know that the radius is really really what really really high if the radius of this is really really high what is that going to do to the actual colle collapsing pressure it's going to decrease the collapsing pressure so an actual increase in the radius does what to the collapsing pressure increase in the radius of the alvioli decreases the collapsing pressure of alveoli now I told you this normally doesn't happen right it can happen a certain Alvi in the lungs but our body has a way to be able to prevent this from happening in between these alvioli we have these pores that are connecting the adjacent alveoli let's do this in a nice little color let's do this one in this red look at this here's a pore I know I'm I'm really really accentuating the pore here but it's just for you guys to get the point that these two alvioli are connected it's kind of like Gap Junctions in a way so what does that mean then that means that some of the air that's in this alvioli can flow over here right some of the air that's in this alveoli can flow over to this alvioli and some of the air from this alveoli can flow over into this Alvi you know what this helps this helps to maintain proper ventilation normal ventilation between the two alveoli it's amazing I I it just blows my mind so this is actually called the alveolar pores um sometimes they even call it the pores of cone and must have been some dude named con who figured that out but anyway what are these alveolar pores doing they're basically allowing for proper adequate equilibrium of movement between of gases between the two alveoli to maintain a nice alveoli structure right so that there is no collapsing of the alvioli so that's one thing another thing that's also preventing this from happening is surfactin and we'll talk about that one more thing though before we talk about surfactant look at this so if this guy is getting underventilated if you guys remember from the V profusion coupling video look at this let's do this one in this pink marker here remember ventilation was V over q and it was normally equaling to about 08 we solved that what happen what's happening to the ventilation here it's decreasing so if it's decreasing what's that going to mean then okay if it's not getting a lot of air into this area then I'm not going to be able to allow for a proper amount of exchange even though there's no let's say that there's normal perfusion which is representing as our normal profusion coming through here normal amount of blood flow but this thing is it's underventilated it's not going to be able to allow for a proper gas exchange there's not going to be enough oxygen to exchange so what's going to happen here there's going to be an inadequate oxygen Exchange in this situation so inadequate exchange of gases this is super important because if you can't exchange gases you can't get oxygen into the blood and you can't get Co2 across into the lungs to expire which can lead to hypoxia and it can lead to maybe even respiratory acidosis so very s uh serious situation obviously what would happen if this is hypoventilated and you this is decreasing this number is decreasing what do I have to do to fix it remember what we said we would actually decrease the profusion so what would happen to thec capillar here they were constrict if you guys remember opposite scenario if this is hyperventilated apply the formula V over Q is equal to8 what's happening in this one it's over ventilated if it's over ventilated then what's going to happen let's assume here that there is normal perfusion originally we always have to think about things before everything's being compensated but normal perfusion coming through here so the que isn't changing yet but if it's being hyperventilated there's too much oxygen in here to be able to deliver to the actual blood there's not enough blood here to be become adequately oxygenated so if that's the case then because there's not enough red blood cells coming through this area to get oxygenated they'll still get oxygenated but there's still going to be a lot of air here in the lungs so they it gets wasted so because of this there's a lot of air being wasted okay because of this situation whereas in this one if there's an inadequate exchange of gases because there's not going to be enough oxygen and CO2 moving across so in this situation there would be a waste of what the blood coming through that area the blood's going to get wasted because there's going to be no use for it so again that's why just to clarify here again if the ventilation is low what does that mean for the amount of oxygen that's going to be in this alvioli that means that the partial pressure of oxygen is going to be low so if you want if you want blood to come here here it's not going to get properly ventilated so I want to decrease my perfusion to be able to bring it back to normal right so that's why you would actually do what you would constrict these capillaries because if blood flow came through here it would be a waste of the blood you don't want to waste the blood you want to send it to areas where it's properly ventilated so it can actually get enough oxygen okay so in this situation when the partial pressure is low constrict those pulmonary Capers and send it away from that area but again that can cause a lot of problems in the body and in the opposite of this situation it's hyperventilated so what does that mean for the partial pressure of oxygen in this area that means it's high so what are you going to want to do to the actual capillaries here we said if the ventilation is high what do you got to do to the profusion increase the profusion so what would you do to the capillaries you would dilate the capillaries and as you dilate them you'd have more blood flow coming in here so that the air the extra air that you have in here wouldn't go wasted okay all right that takes care of that thing now one last thing before we talk about surfactin there's this really interesting thing that happens if remember how we said that this alvioli if the pressure was really really high it would collapse theoretically right but we do have these mechanisms to try to prevent it but it still can happen if this alveoli collapses because of this increase in surface tension you know what happens as it collapses it it creates like a vacuum like a vacuum and it pulls fluid you know what what's the most abundant fluid inside of the blood plasma water right so there's a lot of water flowing here in the blood plasma when this collapses it creates like a vacuum and pull some of the water out of the pulmonary capillaries and in here into the actual alvioli what does that do as the water is getting pulled into this alvioli you know what it's going to do it's going to put water in here in the alvioli which can affect gas exchange but not only that as water is accumulating what's happening to that respiratory membrane it's getting thicker what did we say was the Rel relationship between a thick respiratory membrane and gas exchange the thicker the membrane the decreased the gas exchange that's another problem so what are the three things that surface tension can really really wreck us up it can cause collapsing of the alvioli if the surface tension is really high right what else could it do it also could create unequal ventilation right of these alveoli and on top of that if these alveoli do collapse what will it do it'll pull water into the alveoli that are actually collapsing and create a lot of pulmonary edema right and that can be a bad thing okay so that takes care of surface tension now the question is how does our body deal with it surfactant okay let's come back over here to this diagram for a second so if we look over here we had these water molecules diving to the bottom well guess what the type two alveolar cells come to the rest SK okay surfactant surfactant let's actually talk about surfactant right over here so surfactant is actually going to be a lipid protein complex right so surfactant is a lipid protein complex now you might ask okay well how much of it is lipid and how much of it is protein don't worry we're getting there all right it's 90% lipids and it's about 10% proteins okay so let's look at before we do anything let's look at the structure of this actual surfactant and then after we talk about the structure let's talk about when it's synthesized okay and then what it does so let's talk about the structure when it's synthesized and what it does okay first off let's look at the lipid component so the lipid component over here let's see let's draw the lipid component in this bluish color here there is actually going to be these two fatty acid tails that are connected and these fatty acids are approximately 16 carbons in length so what do you call these 16 carbon fatty acid structures you know they call it well if it's one you call it the actual what you call it the paleto right it's it's a pile group the other one is going to be another pile group so we call this collectively a d Pyle fatty acid group right so so far we have dtile right then we have another thing we have this next thing right here look at this this right here is actually going to be consisting of a phosphat phospha toile group here so the phosphat group is actually going to be hydrophilic so this part here is actually hydro philic and this part here the diil which is consisting of the fatty acids this is hydro phobic that's going to be super critical here for when we explain this mechanism the last thing is it does have one more thing connected to it it's actually going to have these like uh choline groups which is an essential vitamin like nutrient so they actually completely call this whole name here they call it phosphat [Music] choline so there's this phosphat choline Group which is going to be consisting of this polar head like structure with these actual essential vitamin like nutrient structures called choline but you know that's not it there's proteins many different proteins coming off of this uh sucker here let's show these proteins in let's do these ones in blue here there's actually going to be specifically albumin which is the same albumin that you see within the blood plasma okay there's going to be another one which is going to be IG g a antibodies immunoglobulins right for the passive immunity I mean sorry it's a part of our actual anate immunity like Tye of structure right and then what else are we going to have then we're going to have these APO proteins and there's mainly four four types four types of ail proteins there's actually going to be type A B C and D but we call them surfactant protein type a surfactant protein type B surfactant protein type type c and surfactant protein type D okay now that we have all of this let's go ahead and see the next thing so we said what's the first thing we were going to look at we were going to look at the structure of surfact we know that it's 90% lipids 10% proteins the lipid component is the dtile group which is hydrophobic then what else is it going to have it's going to have these 16 carbon fatty acid change with the dietal group then it's going to have this pink head which is the phospholine group which is hydrophilic it's a little bit more polar then it's going to have these 10% of the proteins right albumin IGA antibodies and apil proteins type A type B type c type D okay what's the next thing we said we said when is it made and how is it like secreted that's the next question so you know in the fetus during the gational period around the 24th week so around the 24th week let's come over here so around the 24th week of gation the the actual fetus starts producing this protein lipid complex called surfactant so around the 24th week of gation the surfactant production begins and it actually is a very slow process very very slow process but by the time the female gets closer to the thir 4th week of gation the surfactant production starts going really high so in the beginning Parts like 24th 25th 26th 27th 28th the actual surfactant production is kind of low but as she starts approaching the 34th to 35th week of gation then the actual surf factum production increases so look let's say right here the surfactive production as we get closer to the 35th week increases so surfactant surfactant production increases right as we get closer to the 34th week now some of you might be like okay well why is it slow in the beginning and then a lot more as we get closer to the 34th week as the female approaches this 34th week getting closer to that she starts producing a hormone you know the hormone within the zone of facula it's called cortisol so you know the woman is actually producing a hormone called cortisol and cortisol you know it's actually it's a glucocorticoid so it's one of the glucocorticoids she can also produce other different types of glucocorticoids cortisol though one of the glucocorticoids can actually help to stimulate this process but primarily it enhances the actual the the cortisol levels become very very high as the female approaches as she starts getting closer to the 34th week so because the cortisol levels start increasing as you get closer to like the 29th 30th 30 1 32nd 33rd 34th week the actual surfactin production starts increasing why is that important because you know in certain people if they actually are prematurely born they aren't able to produce enough surfactant so let's say that the individual is born before the 34th week like maybe like a little bit closer to like I don't know 32nd 31st week that can cause a decreased amount of surfactant available and it can produce what's called infant respiratory distress syndrome we'll talk about why that's important but again I want you to understand when it's produced it's produced during the actual gational period and it's dependent upon hormone levels like cortisol now when this is actually made it's made by the type two alol cells so let's see how it's actually secreted so here's our type two alveolar cells over here these type two alveolar cells when they start making it they store them inside of these actual like large globules inside of our actual alveolar cells and when they're stored in these like look at this I'm going to draw like some circles here they're like these big big GL globules of surfactant this whole big globules of surfactant they look like big old bodies you know what that's called that's called Lamar bodies and then what happens is whenever the actual type two avolar cells exocytose the actual surfactant but specifically it's in this form called Lamela bodies it comes out in like this tubular like fashion and when it comes out in this tubular fashion this tubular like structure here is called tubular milin so what is this here structure called it's called tubular myin so again Lamar bodies is the actual big old globular structure inside of the cell when it's pushed out of the cell by exocytosis when this comes out of the cell by exocytosis it becomes this structure called tubular myON why am I telling you this because tubular myON imagine I take a big old string of tubular milin as I take a big old string of tubular milin let's say I pretend here's a circle here's a circle here's a circle another one another one okay you get it this part of the tubular milin that's a surfactant molecule and that's one two so this would be surfactant one surfactant 2 surfactant three surfactant four surfactant five you get the point this tubular milein structure is consisting of many many surfactant molecules okay so we talk talked about its structure we talked about when it's produced we talked about how it's actually released now let's talk about what it's doing and how it's actually preventing surface tension okay let's bring that molecule and put him right here so now what I'm going to do is I'm going to get rid of these here for a second and now look what happens here I'm going to put this guy right here and I'll put another one right over here let me put another one right over here I'm going to put another one right there now watch what happens this was the phosphole choline group what was coming off of the phosphole choline group you were having the diolo groups right which were the 16 carbon fatty acids and then what's so significant about this all right look at this so as if you guys remember the water molecules what were they doing if we follow this water molecule right here it was exerting a force to the side to the side and down but nothing to exert what above look at this actual guy here this phospholine group it actually can interact with the water molecule what to the side it can interact with the molecule to this side and it can even interact with the water molecule below now you might be saying okay well there's still no there's no no Force upwards guess what yes there is you see this part here what do we say this part was this was the dialetto fatty acid group this dialo fatty acid group is hydrophobic it does not want to be in the water what does that mean it's going to want to be staying out here and because it wants to stay out here it's going to create a force that's trying to pull and Pull and pull this actual surfactant molecule upwards as it does that what happens then as this pulls this upwards it decreases the surface tension because now what's going to happen some of the water molecules might come back up to the surface so as this is pulling this up some of the water molecules might come back up to the surface here what happens to the actual water layer it goes back to its normal thickness when it goes back to its normal thickness because of the surfact what does that due to the tension it decreases the surface tension okay so again surfact molecule here is having interactions with all directions around him and because of the hydrophobic fatty acid Tails it's pulling the surfact molecule upwards as it does that some of these water molecules here on the bottom bulk layers go upwards and draws upwards to interact with the actual surfact molecules as that does that what's it going to do to the cohesive interactions with all of these other water molecules it's going to decrease the cohesiveness it's going to break up those intermolecular forces and it's going to allow for the water molecules to move up to the top and allow for this actual water layer to expand when the water lay expands the surface tension decreases okay now now that we know that let's see really quickly here how this surfactant eliminates all of these problems okay well let's look at this situation right here first surfactant was produced what was the purpose of surfactant to decrease surface tension if it decreases the surface tension what's going to happen here actually wait we already have it right over here we already have it right over here look the surface the actual surface tension decrease what causes this surface tension to decrease surfactant okay and why because surfactant was actually going to be decreasing the cohesiveness of the water molecules and trying to pull the actual water molecules from the bottom upwards to decrease the surface tension and allow for the alveoli to expand so once to decrease the collapsing pressure of the alvioli okay now let's see how this affects the radius okay this one's a little bit more tricky let me do this right over here for a second let me make two small alvioli down here in the BT bottom let me get this out of the way here okay look at this let's say here I have this alveoli here with a small radius and I have this alveoli over here with a really big radius and again what was this layer right here let's say this layer right here I'm going to draw in blue was the water layer this is the water layer right here and that was actually creating that surface tension between the air water interface what did we do to treat this issue we brought in surfactant right as we bring in the surfactant molecules let's say that we show the surfactant in this pinkish color all right so this surfact moleculees to pretend it's actually coding this air water interface and it's coding this air water interface look at what I'm doing what do you notice is different right away you see how this actual surfactant layer is easily coated it's very good it's very nice and dense around all of this air water interface while this one is more distributed has a lot of breaks in certain points of the actual surfact molecules what does that mean then if something has a larger radius a very large radius okay this is diameter but you imagine half of this is the radius here let's just do it anyway let's fix this here this point here this is the radius if you have a large radius the surfactant actual distribution is going to be less if the surfactant distribution is less across this alvioli what does that mean for the actual surface tension there's going to be a little bit more surface tension here so this alveol is going to want to collapse a little bit more even though the radius is much larger isn't that amazing and the last thing if the surfactant is actually if this has a small radius very small radius the surfactant distribution is going to be nice and condensed and concentrated in this area so if that's the case The Sur the actual surface tension is going to decrease and then if you look at this situation now here they had a decrease in radius right if there was a decrease in the radius what did that do decreasing the radius increased the collapsing pressure well if you decrease the radius how can we fix that what did we say surface tension right we actually would do what we would decrease the surface tension that's what we said we would allow for the alvioli to expand and that would help to decrease this collapsing pressure and then what did we say with this last one we said here the radius was really really big big and when the radius is really big what does that want to do to the pressure it decreases the collapsing pressure and whenever you try to decrease this collapsing pressure that's great but let's keep everything even we want equal alveoli so how does that happen What do we do the surface tension what did we do we increase the surface tension because it's not going to be surfactant is not evenly distributed and because of that surface tension increases what does that do to the actual collapsing pressure it brings it up a little bit but tries to bring both of these these two into homeostasis equal amount so there's not we don't want this one to collapse and this one not to collapse we want them to equally have this equal flow of gases between the two okay now that is how the surfactant is working in this situation if this individual is not able to produce surfactin you can imagine how hard it would be for these alvioli to expand if this individual that that little infant who was born prematurely and wasn't able to produce enough surfactant if that infant was born early she doesn't have this surfactant if she doesn't have the surfactant what's the whole thing that's going to happen she doesn't have surfact there's going to be a lot of surface tension what did we say surface tension would do it would want to collapse the alvioli it would create unequal alveoli and it would want to pull water into the alvioli right that's the whole purpose surfact is trying to present prevent all of those things if the baby is born prematurely she doesn't have surfactant and all of those things can happen and in order for this baby to breathe they have to put her on a child on a mechanical ventilator to be able to push air into the baby so that the baby can actually inflate the alveoli because the alveoli constantly want to collapse and when the baby is born you know when the baby is born uh they cut the umbilical cord and then there's decrease in oxygen levels inside of the baby and that triggers hypoxia activates the respiratory centers with inside of the baby and triggers the baby to do what activate some of the muscles right and when the muscles are activated what happens they contract and try to bring air in what is that called it's called the first cry well in this individual it's still going to do the same thing they'll cut the umbilical cord if they have infant respiratory distress syndrome they'll cut the cord they'll still have hypoxia it'll trigger the actual nervous system to trigger inspiration but when they come to inspire the alvioli don't want to open because they have to have so much it takes so much energy and so much work to open up those alveoli the babies have a hard time breathing and they go into distress and they have to put them on a ventilator right last thing I want to mention here is these apil proteins apil protein a and apil protein D are really important because what they help to do is they play a role in your um opsonization reactions so they play a role in opsonization this one here as well as D and if you guys remember what opsonization is it's where you tag these proteins could tag specific types of foreign matter and Trigger them for phagocytosis so pretty cool so there's a little bit of actual immunity component whereas B and C they play a role in the distribution the rate of the distribution in spread of the actual surfactant so they play a role in the spread the rate of which the surfactant is spread so spreading of surfactant all right ners we talked about a lot of information in this video I hope you guys enjoyed I hope it made sense I I really really do um if it did please hit the like button comment down the comment section hit that subscribe button all right ninine ners as always until next time