Embryology | Development of the Respiratory System

all right ninja nerds in this video today we're going to be talking about the development of the respiratory system before we get started please make sure you guys continue to support us by hitting that like button commenting down in the comment section and please subscribe also down in the description box we have a link to our facebook instagram patreon go check that out all right engineers let's get into it all right ninja nurse when we talk about the development of the respiratory system let's start again understanding how we get the respiratory system we actually develop the respiratory system from two germ layers one is going to be the endoderm and the other one's going to be the mesoderm so first thing we have to talk about is going from our bilemminer disc to our trial liner disc do a quick folding process in both the lateral folding process and craniocaudal folding process and then we'll talk about some of the structures that are developing from these layers that being the larynx the trachea and the lungs all right so first things first start up here at the top we have our bilemeter disc right which is around week two right so this is going to be made up of our epiblast layer on the top at the blast layer and the epiblast layer remember above that is going to be the amniotic cavity right and then below the epiblast layer is going to be the hypoblast layer and then below the hypoblast is going to be like the little yolk sac layer right what happens is you guys remember you develop a nice primitive streak right but in the epiblast layer some of those epiblast cells move through the primitive streak and convert the hypoblast layer into the new endoderm layer this bottom green layer so here's your endoderm then more epiblast cells move through that primitive streak as it moves through the primitive streak it forms a new layer between this new endoderm and this epiblast layer what is this called that's called your mesoderm and then we also know that this little black dot here is your nodochord that's from the epiblast cells moving through the primitive node and then you go through the process of what's called neurulation and you make this maroon color structure called your neural tube then finally the epiblast cells start differentiating themselves and turning into ectoderm and we should all know what this process is called where we take a bilaminar disc and turn into a triliminer disc we have done this at least a million times this is called gastrulation and if you guys remember what else do we have kind of happening at this process here as well besides making two layers to three layers we also developed the nodochord so there's also this notogenesis that's also occurring all right sweet now we have our three layers now it just looks like a nice little pancake right we need to look at this kind of in a three-dimensional way so what we're going to do now is i want you guys to imagine that we're going to fold this pancake in two directions one is we're going to fold this this is a cross section i'm going to fold this in a lateral type of way and bring this together or you can only see you can't really see it in this view but if i were to pull out from this point here would be the top of the embryo or the cranial portion and going back into the world would be the caudal portion it's going to fold this way which is called craniocaudal folding so we're going to go through the two folding processes here one is going to be the lateral folding right and then the other one is going to be the cranio caudal folding process and what this does is this kind of just gives us a little bit of an idea of more of the anatomy and kind of how these layers will derive into the structures that look familiar to us in the adult all right beautiful so this top one is the after lateral folding and this bottom one is after craniocaudal folding now what you guys need to remember here is this structure here remember i told you that there's two things that are making up your respiratory system two germ layers your endoderm and your mesoderm all right so this first thing here is this green layer what is that called your endoderm now this endoderm you guys need to remember that the endoderm is basically going to give way to what's called your gut tube the epithelial lining and the glands of your gi tract right so it's going to make that thing called your gut tube and there's different portions of the gut tube we'll talk about that it's easier to see in the cranial caudal section the other thing that we need to know is this mesoderm now you guys remember one of the mesoderm layers this one closest to the neural tube is called your par axial mesoderm you guys are going to be pros at this right par axial mesoderm then after that a little bit more lateral is your intermediate mesoderm and then the ones that we care about you have the two layers here right this one that's closest to the ectoderm what do we call this one that is your somatic layer of the lateral plate mesoderm we're just going to abbreviate that lateral plate mesoderm and then this one here closest to the endoderm or the gut tube is going to be your splanchnic layer of we're going to abbreviate lateral plate miser the two layers i really want you guys to remember here is the endoderm that's going to make the epithelial lining of the respiratory tract in this case which we're going to talk about larynx trachea and what else lungs and the splanchnic layer of the lateral plate mesoderm is going to help to make some of the cartilage the muscle and the connective tissue around the larynx and the trachea and the lungs we'll get a little bit more detail on the larynx because that's a little bit different for but for the most part endoderm is going to make the epithelial lining and the splenk nuclear is going to make the cartilage muscle and connective tissue of the respiratory tract now let's come down here and look at this craniocaudal type of fold all right beautiful so we've seen this in the lateral type of process the lateral folding to make this nice cross-sectional diagram so we kind of have an idea of what layers are going to give us most of the respiratory system we'll we'll get a little bit more specifics but for right now just understand those two things are going to make up most of the respiratory system now this sagittal view after craniocaudal folding also gives you a really nice representation of kind of where the respiratory system is coming from so if you guys remember this green tube here is your gut tube we only see it at one section for example i maybe i just took it at that section we're only seeing a portion of it but i want you to remember that there is three portions of it you have the four gut here the mid gut here and the hindgut here we don't really care about the mid gut in the hind gut we really only care about this foregut and then at the top of this endodermal tube we're going to see that there's like these little pouches that are part of your pharyngeal apparatus and these are also the structures that we care about so we care about two layers of this endoderm the foregut and this area we're going to just denote it as the primitive pharynx but that's going to be the pharyngeal apparatus and we'll talk about it a little bit later all right so this is a beautiful view to kind of give you an idea so what i want us to know here is what are the three structures we are going to make from this endoderm and from that splanctic layer of the lateral plate mesoderm you're gonna make the larynx okay you're gonna make the trachea and you're going to make the lungs okay these are the three structures now just for the basics we'll talk about a little bit more the larynx is going to have two layers they're all going to have two layers if you will an endoderm layer and a mesoderm wear layer which mesoderm layer though the splanchnic layer of the lateral plate mesoderm so they all have this what i want you to understand is what they give rise to okay that's kind of the big thing here so first things first when we talk about the larynx i really this is really the one that i kind of want to focus on because we're going to talk about this next the endoderm is actually going to be particularly coming from a structure called the pharyngeal pouch okay it's going to be coming from a structure called the pharyngeal pouches we'll talk about the fourth and sixth pharyngeal pouches okay these are the ones that are really going to give rise to the epithelial lining of the larynx the mesoderm is going to come from the part of the pharyngeal arches the fourth and sixth mesoderm component of pharyngeal arches the rest of all of this stuff is endoderm from what this is endoderm from the foregut and we'll talk about how it actually buds off the foregut and then the mesoderm is still that lateral plate mesoderm the lateral plate mesoderm lateral plate mesoderm which component the splanchnic layer of the lateral museum so that's why i wanted to just specify a little bit more here on the endoderm and mesoderm portion for the larynx the trachea in the lungs all right so now we got to do is we have to take and make the larynx then make the trachea then make the lungs let's go through the larynx first all right so now that we've kind of built the foundation for developing our respiratory system let's go by each component first so we're going to develop the larynx then we'll do the trachea in the lungs so first things first we got to take a look here at a nice little sagittal section of the embryo this kind of gives us a really good kind of start for the development of the larynx what we're going to do is we're going to take here remember we had four gut up here we had your mid gut and you got that good old hindgut right and right here you have these kind of like your pharyngeal apparatus if you will right what i want us to do is to take a nice little section kind of like this here and take a look at the layers right starting with the endoderm mesoderm and ectoderm of this good old pharyngeal apparatus okay so this is going to be kind of our pharyngeal apparatus all right sweet deal so first thing i want us to go through is obviously start here at the top this is your buccopharyngeal membrane right so the buccal pharyngeal membrane is what will become the mouth now the inner portion here the green portion is the endoderm but we give this kind of portion a little bit of a special name so this inner portion here this green portion this green portion of the endoderm right this portion here we actually call this the pharyngeal pouches so this is going to give way to what's called your pharyngeal pouches okay and this is going to make the epithelium and the glands in this case of the larynx the next thing is in between that you have this next layer this red layer and this red layer here is your mesoderm right so this right here is your mesoderm and the mesoderm is a part of this pharyngeal arches right so this would be your first fringe arch second third fourth you sometimes your fifth either develops um and then it actually digresses over time or doesn't develop at all so we don't even consider the fifth one and then your six pharyngeal arch the core of these pharyngeal arch is made up of mesoderm and this is what gives way to like muscle right this is going to give way to your connective tissue give way to your cartilage all that good stuff right and then the outer part here of this pharyngeal apparatus you have this blue portion which is your ectoderm and we actually kind of give these kind of like little things here these little divots we call it the pharyngeal clefs so the ectoderm we give a nice special name and we call that your pharyngeal clefs but what i really want us to focus on here is again what did we say were the two components that make up the respiratory system the endoderm particularly the pharyngeal pouches and the mesoderm which is going to make the muscle the connective tissue and the cartilage but here's the next part that we got to build on what portion of this pharyngeal apparatus is actually making the larynx that's what's important and it's really the fourth and sixth pharyngeal arch okay so now what we're going to do is we're going to take this fourth and sixth french arch and zoom in on it approximately around week five okay so somewhere around week five within that fourth and sixth pharyngeal pouch you develop a little cavity okay you develop a little cavity here and we call that cavity the laryngeal orifice so you develop a cavity around week five called the laryngeal orifice now here's what's really cool within that orifice some of this endodermal tissue within these actual pharyngeal pouches start invading into this laryngeal orifice and after it kind of invades into the laryngeal orifice guess what it makes guess what that endodermal lining makes it makes your vocal cords so the vocal cords will develop from endodermal cells invading into the laryngeal orifice pretty cool right all right what else happens around week six that mesoderm right around week six that mesoderm starts forming cartilage and muscles that are surrounding this portion of the larynx and it starts to make these swellings if you will so you start to develop these swellings around the orifice okay so around the orifice what are these swellings that you start to see all right one of the swellings let's do it here in this blue color develops on the top of the laryngeal orifice and this swelling here is called the epiglottic swelling so the first swelling that you'll have here develops above the laryngeal orifice this is called the epiglottic swelling then below you're going to develop another swelling that comes like this and what is this swelling here called this is called your arytenoid swelling okay so this is called your arytenoid swelling eventually over time and over time that mesoderm is continuing to make more cartilage the endoderm is continuing to invade into laryngeal orifice and again help those pharyngeal pouches to make a nice little epithelial lining of the larynx at around week 12 we finally make somewhat of our mature type of larynx so now we're going to come down here to about week 12. but along the way here's what i want you to know so our week 12 will make kind of our somewhat mature larynx okay along the way that we develop some things here's what i want you to remember the endoderm okay the endoderm portion is going to give way to what the epithelial lining of the larynx what is the epithelium of the larynx you know there's a particular type of epithelium that develops within the larynx this is called we're going to abbreviate it because there's no way in heck i'm going to spell this the pseudostratified ciliated columnar epithelial tissue all of that is derived from the actual endoderm the other thing is it's going to help with making your good old vocal cords and the other thing i want you to remember is that laryngeal orifice eventually becomes what's called the laryngeal inlet so the laryngeal orifice becomes a laryngeal inlet next thing i want you to remember is the mesoderm we talked about how the mesoderm becomes muscle it becomes cartilage it becomes connective tissue it's going to give way to a bunch of different cartilage all right all that laryngeal cartilage and i know you guys probably know that right what are all those cartilage i'm not going to name them all i'm not going to write them all but i'm going to name them let's see if you guys remember you have your thyroid your cricoid then you have your arytenoid cartilage you have your cuny form cartilage and your corniculae cartilage so all of that is going to be derived from the mesoderm but it's also going to make some of those laryngeal muscles the laryngeal muscles right so all of those cricoarytenoids all your cricothyroid muscles all that good stuff one more thing what's the nerve that comes down and supplies the larynx because it's one of the things that are derived from the french arches your vagus nerve right so you also have to remember that your vagus nerve is also going to be derived from the fourth and sixth pharyngeal arches and that's going to be actually supplying what these laryngeal muscles that's pretty cool as well as giving sensory information to the epithelial lining of the larynx pretty darn cool all right so now at around week 12 we develop somewhat of what looks like our nice mature larynx you start to see here you have the epithelial lining of the larynx here nice epithelial lining remember what happens to the laryngeal orifice the laryngeal orifice becomes what becomes the laryngeal inlet and also what else starts to form here okay so you have the the epithelium you have your vocal cords the laryngeal orifice becomes the laryngeal inlet you even get some of your epiglottic folds here and then you get all the cartilage around what was the cartilage made from the mesoderm then you get your muscles the critical retinoids the cricothyroids right then you have your vagus nerves supplying those muscles and what else can the vagus nerve do depending upon which portion it is it can also penetrate through here and give sensory information to the actual laryngeal epithelium boom we have our mature larynx now that we've made our larynx let's go on to making the trachea in the lungs all right engineer so we've we've actually made our larynx now let's go ahead and start making that trachea those lungs all that good stuff all right you guys remember we got that nice good old sagittal section here so again what do we have here we have that four gut we got that mig good we got that hang good right and we already went over this top portion here if i were to draw like a little bit of a little like sakis here right we already went through that pharyngeal apparatus up there which made our larynx all right so now we're going to do here is we're going to take a portion of the foregut so i'm going to go through a portion of the mesoderm and i'm going to go through a portion of the mesoderm here and just focus on this portion of the foregut and look at it okay so this is going to be looking at it from the side and this is going to be looking at it kind of from the front end okay so you're looking at this from the front and you're looking at this gut tube from the side what is happening to the foregut okay that's helping us to develop our trachea and lungs around week four so sometime around that week four period off of the fore gut so here's your foregut tube right so i'm gonna abbreviate this foregut tube here's your foregut coming off of that some of the endodermal cells start kind of coming out and budding off of the foregut and as they start budding off of the foregut they make this tiny little bud pretty straightforward right they make a tiny little bud called the lung bud so they make a bud called the lung butt around week four now that's what you can see from the side view from the frontal view or anterior view something else is kind of important to define here you see how coming off of this we're going to draw this in blue some of the endodermal cells come out here into this bud and create kind of this nice little long bud here well they create a little groove if you will that goes into this anterior lung blood what is this groove here called this is called it's a heck of a thing it's called the tracheo esophageal groove or ridge and this is basically going to be where the endodermal cells are kind of coming out and forming that nice little long bud okay now here's the next thing i want you guys to understand we're just looking at that gut tube but again what is wrapping around that gut tube what is this red layer here can't forget that what is this red layer here called that's your mesoderm what part of the mesoderm that's your lateral plate mesoderm what part of the lateral plate measure your splank nuclear of the ladder plate mesoderm what does that become cartilage connective tissue and muscle what does the endoderm become epithelial lining of the tracheal lungs beautiful we have an idea here as we continue to grow from week four all the way down to here about week five we're going to continue to kind of see some small changes happen here so we had that lung blood coming off of the lung butt it starts to continue to replicate replicate replicate and buds off into these two little sacks here okay then what happens is if you look here the lumber creates one little bifurcation right there and we call this now went from a lung bud to what's called a bronchial bud to what's called a bronchial bud and we can see that very nicely from this side view but if you look here in the frontal view remember how we had those tracheoesophageal grooves or ridges look what happened to them they completely come together and meet in the middle and whenever they do that they form a nice little septum between the anterior lung bud and the posterior foregut which become in this case the esophagus so now not only do we have a groove kind of coming together and closing that creates that nice little septum so now we have what's called the tracheo esophageal septum and that is beautiful because what it does is is it starts helping us to separate the foregut right from the diverticulum coming off of it which is going to be that respiratory diverticulum which will become the trachea and we know where's the trachea with respect to the esophagus anterior beautiful as we continue continue down what happens is that tracheoesophageal septum will completely close and separate posteriorly what's going to be posteriorly here so whenever we have this continuously happening here that lung bud will continue to grow and what it'll do is it'll create a nice separation between what it'll create a separation and anteriorly you're going to have your lung bud which will give way to your trachea and then eventually your lungs and then posteriorly you're going to have what that is going to give you your foregut in this case this is actually going to become the esophagus again to kind of in this kind of giving you guys an idea here so we continue to repeat it the endoderm which came from that actual gut tube will invade into this actual lung bud and bronchial blood and make what structures here the endoderm will give way to the epithelium and the glands and then what will that lateral plate mesoderm become that lateral plate mesoderm will give way to the muscle right so the bronchial smooth muscle that you'll start to have there the trachealis muscle the the connective tissue and the cartilage beautiful we now have an understanding here how we started to make what the beginning of our trachea and lungs now let's continue so we're at about where have we finished here from week four at this point where we completely separate the anterior lung but from the posterior fore gut tube which will become the esophagus we're around week five so now we have to do is go from week five all the way till birth actually even eight years of age and start really developing all the intricacies of the respiratory system boom got it all right all right so we now have our bronchial buds and our lung buds which came off of the foregut so we have an idea where the origin of the trachea and the lungs are coming from now let's keep building that trachea and lungs so if we start up here we're at where we ended which was again starting at week four where we developed the long bud to where we developed the bronchial buds and the separation of the lung developing lung away from the foregut so we're around week five so we're gonna start here at week five with our which portion here the top portion coming off of the foregut was our lung bud and then here we're going to have the bronchial buds all right beautiful so now what we're going to do is we're going to go through these stages this is a lot this is sometimes asked a lot in questions on your exam so let's start with the first stage the first stage we're going to go with continuing to build from these bronchial buds is going to be what's called the pseudo-glandular stage so this is called your pseudo glandular stage the pseudoglandular stage starts at around week five and continues to occur till about week 16. okay so about week five to week 16. what we're going to do is we're after we continue to keep growing and growing growing we get a structure somewhat like this so if we start here we have our trachea that came off of that foregut right from the lung bud now we're going to do is here was the beginning of the bronchial buds they're going to continue to keep growing and growing growing outwards and downwards so let's start here kind of color coding them and then naming them the bronchial buds as they grow the first thing that they're going to make is these primary bronchi so the first thing you're going to develop is a right and left primary bronchi beautiful then these primary bronchi are going to bifurcate all right so we have our right and left primary bronchi these are going to split now it's important to remember that within the adult lung generally you have about three lobes in the right lung and two lobes in the left lung so that means that this primary bronchi on the right side is going to have to split into how many low bar it's going to have to split into one two three low bar bronchi on the right so on the right side you're gonna have right on that one you're gonna have three low bar or also called secondary bronchi on the left side it's only going to split into two because we only have two lobes on the left side so you're gonna have on the left side you're gonna have two low bar or secondary bronchi beautiful then what happens is those secondary bronchi break up even more and they break up into a ton of these actual small little bronchial bronchi so we're gonna have a ton of these here and what i want you to know is that these next ones here are called your tertiary and for the tertiary bronchi that you actually make here you're going to have about 20 in the right lung and about 18 in the left lung so on the right side you're going to have a total of 20 tertiary bronchi and then on the left side you're gonna have about 18 tertiary bronchi beautiful then these tertiary bronchi feed into even smaller bronchi but now we actually like to call these small bronchi bronchioles so then you have to see these little squiggly guys here these little squiggly guys that are going to be fed by the tertiary bronchi here these are going to be called your terminal bronchioles so all of these little guys here are called your terminal bronchioles so then you're going to have your nice good old terminal bronchials all right so what i want you guys to take away from the pseudoglandular stage is we start week 5 216 you start with that lung blood bronchial blood and by the end what have you made right and left primary bronchi you've made three low bar on the right side two lobar on the second side on the left side 20 tertiary bronch on the right side 18 on the left side and then you've even fed into these small little guys called terminal bronchioles that happens to about week 16. then we go into the next stage and the next stage here is called the canalicular stage so we call this stage here the canalicular stage and this continues at week 16. so the canal liqueur stage goes from about week 16 to about week and what happens here is let's continue off with our actual terminal bronchioles so now we're just taking this section here and looking at it so this right here is going to be our terminal bronchials from the terminal bronchioles we're going to continue to keep making more and more structures what are these neck structures that we're going to make coming off of this you're going to have these little guys here so then the terminal bronchioles will break into what's called respiratory bronchioles so they're going to make these neck structures here called respiratory bronchials and these are very very little special things because what they do is they break off into smaller little things called alveolar ducts so then they're gonna break off into about three to six of these things called alveolar ducts so then the respiratory bronchials will give way to what's called alveolar ducts the alveolar ducts though are very interesting because what they do is they feed into what's called a little primitive alveolar kind of sac if you will so they're going to feed into this next structure here which is called your primitive alveoli so it's called your primitive alveoli now here's what i want you guys to remember the primitive alveoli are very interesting and the reason why is if you were to actually kind of cut open the primitive alveoli and look at them they're actually just made up of cuboidal cells so that's not really good for gas exchange process because they're too thick that's a lot of cytoplasm for the respiratory gases like oxygen and co2 to have to move across so at this stage these primitive alveoli it's very important to remember that they are very immature they're not very good at their job yet so we're going to have to continue to keep growing and developing off of that okay so now the next thing that happens here is after we have these primitive alveoli some pulmonary capillaries start kind of growing here so you see how you have these like little structures that start growing around these primitive alveoli that's the next structure so the next structure here is you start forming what structure here your pulmonary capillaries all right beautiful so now at this point we have an idea of what's starting to kind of develop into our respiratory system now we're going to do is is we're going to take these actual primitive alveoli and continue to keep going with them so now if we take and continue to keep going through this process here we've got to take a cut one of these actual primitive alveoli and zoom in on them there's a reason why when you look at this primitive alveoli cutting into it and zooming in on it at this stage it's very immature and the reason why it's very immature is if you look at this it's only cuboidal cells so this is a primitive or immature alveoli that we formed by the end of that kind of canalicular stage now when you look at this what you see is a lot of cuboidal cells and why is that why is that important to understand that cuboidal cells are not good at gas exchange okay so this is going to have very little uh function with gas exchange so there's a decreased ability for gas exchange in this process so what we need to start doing in the next stage is kind of changing some of these cuboidal cells to make them smaller so make some of them smaller so that they'll be easier for that gas exchange process to occur so that leads us into the next stage so over the next following weeks from about week 26 to about birth we go to the third stage what is this third stage this third stage here is called the saccular stage so we call it the sacular stage at the terminal sac stage doesn't really matter it's generally about week 26 to around the time of birth and what happens here is very important obviously you make more respiratory bronchioles because you're going to continue to increase the number of alveoli right so one thing that's happening here is we're increasing the number of alveoli so if you're increasing the number of alveoli you're also respectively going to have to fill more air into the alveolar ducts and more more alveoli so there's also going to be an increase in the number of respiratory bronchioles so increasing number of alveoli and increased number of respiratory bronchioles there's also going to be another thing here you see how we have this brown structure here forming around this actual kind of primitive but somewhat differentiated alveoli this brown tissue here is called your basement membrane so you're also going to start forming a basement membrane around that actual primitive alveoli we're going to increase the number of pulmonary capillaries so we're going to increase the number of pulmonary capillaries beautiful now here's what i want you guys to really take away from the sacular stage so from the canalicular stage we more made more primitive alveoli more respiratory bronchioles but something else happens to these alveoli that i really want you to distinguish this stage from the other one and this is it remember at the primitive this canalicular stage this is what our alveoli looked like so the canalicular sage was all cuboidal cells as we went into the sacular stage now look what happens to this alveoli this alveoli is a little bit more mature not completely but it's starting to become a little bit more mature from the canalicular stage to the saccular stage how look at the cell difference here used to be all cuboidal but now we went from all cuboidal so it was all cuboidal to two different types of cells one is these little fat little flat squamous cells and the flat cells are called your type 1 cells your type 1 pneumocytes these are the ones where guess what happens between them gas exchange occurs so in other words oxygen will move across these cells and then co2 will move across these cells and it's much easier for the gases to move across these flat cells than it would be across these cuboidal really big cells so that's one kind of phenotypic change the other thing is that some of these cuboidal cells they stay cuboidal but they come a little bit more specialized and these cuboidal cells that kind of remain cuboidal become a little bit more specialized and they're called type 2 pneumocytes or type 2 alveolar cells and you know what these guys do they're very very special and they make a kind of protein and lipid kind of complex here that coats the inner surface of the alveolar membrane you know what this is called surfactant and that surfactant is super important uh whenever the baby's born because if there's a decreased number of surfactant guess what hap guess what surfactant does it prevents the alveoli from collapsing keeps them open reducing surface tension if there's less surfactant whenever the baby's born guess what happens those alveoli naturally want to collapse it's really hard for the baby to bring in air because it has to pop open already collapsed alveoli so that's why this is important so big thing to take away here is between canalicular stage and sacular stage is not only is the number of primitive alveoli increasing and making a basement membrane and making more capillaries but the alveoli are becoming more specialized and differentiated beautiful now let's go to the last stage of lung development all right so the last stage here is the probably one of the cooler stage i think is very interesting about this stage this is kind of the alveolar stage so we're really kind of zooming in and looking at that alveoli and seeing what's happening because we've already seen one thing already right one of the things that we've already kind of noticed here is that the cell change that was a big one right what happened to the cells we formed type one allele cells in type two alveolar cells that was a big thing that happened within that saccular stage well you're going to continue to make more primitive alveoli in the alveolar stage but here's what else is happening something that's very very important so not only are we increasing the number of the alveoli right the primitive alveoli converting more of those primitive alveoli into having type 1 and type 2 pneumocytes but you see what else is different here remember how this was just one big cavity one big alveoli we start to form a little septa or partition within the alveoli and that really helps with kind of increasing the surface area so one of the things that's going to be changing here in the alveolar stage is you're increasing the septa or the partition within these alveoli and one of the things that helps to do is it really helps to increase the surface area and that's very important when it comes to gas exchange it also just helps to mature so this again just contributes to the maturation process okay now that's the big thing that happens within the alveolar station big thing to take away from the alveolar stage is obviously you're making more alveoli differentiating them into type 1 type 2 from just straight cuboidal and then forming septa to increase surface area the other thing is again it's pretty obvious here we're kind of thickening that basement membrane again so we're making a good old basement membrane that we're going to have here and the other thing is we're really kind of helping with those pulmonary capillaries as well so again we're kind of increasing the number of the pulmonary capillaries as well all right the next thing that we need to go through here is actually not only just to talk about the alveolar stage but we should denote on how long this stage actually occurs which is very interesting because you would think oh by the time you're born your lungs are pretty much perfect no so the alveolar stage generally starts around week 36 and this kind of occurs around the same time as the saccular stage but it extends very very far past birth eight years of age to about eight years of age now here's the big thing i want you guys to understand at birth you have a decent number of alveoli you know how many alveoli you have around by birth time to give you kind of an understanding of this around birth you start off with approximately maybe close to a hundred million of those primitive alveoli but by the time you get to about eight years of age guess what happened you increased the number of alveoli to about 300 million that is insane so that kind of just gives you an appreciation of what's happening even after birth so again alveoli number goes from 100 million at birth to about 300 million alveoli by about eight years of age and again this is because you're continuously going through this alveolar stage forming septations increasing the number of alveoli and making them specialized making more basement membranes and more pulmonary capillaries beautiful we're not done here though what i want to do now is i want to talk about what happens as you go through the birthing process whenever they're basically in utero to the point of birth and what happens if you don't have that surfactant all right so now what i want us to go through is let's say that we're before birth right so we're basically before the birthing process okay before birth the baby does have a little bit of fetal breathing movements and the purpose of this fetal breathing movements is to allow for the lungs and the muscles of the respiratory system to kind of work with one another right but generally before birth okay the baby is in amniotic fluid so whenever the baby breathes guess what the baby actually breathes in the baby breathes in amniotic fluid so that amniotic fluid from the amnion will actually come into the baby's alveoli and kind of cover all of this area whenever it's in utero before the birthing process and again what is the purpose of this it's to kind of allow for some to have the lungs and muscles work together okay to really kind of strengthen up that actual uh baby's lungs or whenever it is born it can help with bringing in air from that first cry now once birthing process actually occurs what happens so at the time of birth what happens is the amniotic fluid gets sucked up into the pulmonary capillaries so all that amniotic fluid that was in the pulmonary capillaries gets sucked in all the actual amniotic fluid in the alveoli gets sucked into the pulmonary capillaries then after that happens do you guys remember what those type 2 alveolar cells were secreting it was secreting that surfactant and after the amniotic fluid is removed all that's pretty much remaining here should be surfactant and why is that important because again what does surfactant help us to do reduce surface tension and keep those alveoli stented if the baby is born premature right if the baby's born premature what can happen let's say it's born a little bit earlier before you know like maybe week 26 maybe week 27 something around that time the type 2 alveolar cells haven't had time to really produce enough surfactant so if there's very little surfactant what's going to happen to the surface tension it's going to increase as surface tension increases what happens to the collapsing pressure it increases and now the baby's alveoli will collapse so whenever it's born it has to take in its first breath push the amniotic fluid into the pulmonary capillaries leave a layer of surfactant that surfactant layer is very thin and because of that alveolar collapse whenever it tries to breathe it has to take in so much more air than it even has the ability to take in to open up those already collapsed alveoli what is that condition called it's called infant respiratory distress syndrome so whenever there is significantly decreased surfactant related to what kind of a premature birth this can lead to infant respiratory distress syndrome sometimes referred to as the highland membrane disease but again what are the stages that are happening at birth to kind of recap here at birth baby takes in air so it takes air in as it takes the air in what happens the amniotic fluid gets absorbed and surfactant layer remains and this helps to reduce surface tension to allow for the baby to breathe and take in air without a lot of effort that is the process of the development of the respiratory system all right engineers so in this video we talk about the development of the respiratory system i hope it helped and i hope you guys enjoyed it all right ninja nerds as always until next time [Music] you

Channel: Ninja Nerd

Views: 245,317

Keywords: Ninja Nerd Lectures, Ninja Nerd, Ninja Nerd Science, education, whiteboard lectures, medicine, science, Embryology, lung embryology, lungs, lung development, Respiratory system, respiratory embryology, usmle, development of the respiratory system, bronchi, trachea, anatomy

Id: 00jgSl0FHNE

Length: 45min 11sec (2711 seconds)

Published: Tue Feb 02 2021