as we move through the lower respiratory tract the trachea becomes the paired primary bronchi which become lobe our bronchi segmental bronchi smaller and smaller we go as we're delivering atmospheric air to the a violist these sac-like structures at the very end now we've learned some things about this lower respiratory tract already but what I wanted to focus on is the changes that occur to the cells as we move through this conducting zone and into what's known as the respiratory Zone so these are going to branch smaller and smaller 23 orders of magnitude in some cases getting smaller and smaller until we feed what's known as a single lobule now lobules of the lung are shaped like hexagons actually they may be a octagons I'm not sure but they're about the size of a Eraserhead so yeah approximately that size these are the smallest structures that we can see with the unaided eye when you look at lung tissue you can actually see these little lobules within the lobes now as the respiratory bronchioles are getting smaller and smaller there are some changes taking place now if we consider the trachea the trachea has a large lumen or opening relative to the thickness of the wall this is to hold it open and the amount of cartilage is quite substantial now the backside of this cartilage has some smooth muscle and connective tissue in it that interestingly is all soft tissue unlike the firmer cartilage and this allows the esophagus which is posterior to the trachea to actually flex into the back of the trachea as food or a bolus when we put a chunk of apple maybe goes by so as a piece of food goes by it can flex into the back of that trachea but the trachea is designed to have an open airway to keep that opening patent and what allows that is the amount of cartilage we find a high amount of cartilage in this trachea now the relative amount of smooth muscle is quite low because smooth muscle would let us alter the diameter and we don't want that we want this stained open for air to feed our entire lung volume now the amount of epithelium relative to the cartilage is quite low and the epithelial type in that trachea is going to be the tall ciliated pseudostratified columnar epithelium so the amount of cilia is actually quite high but as we move from that trachea into the primary bronchus or the main bronchus the cartilage begins to break up a little bit the lumen size becomes smaller now still the relative amount of cartilage is quite high but it's gotten to be less the amount of smooth muscle decreases in absolute term we don't have that large amount of muscle of the neck and whatnot but the relative amount of smooth muscle relative to how much cartilage there is has actually increased a little bit so this makes up about half these aren't exact numbers this makes up about half of this column right here whereas here it's a bit less than half there's more of it than here but the relative amount in this has actually increased a little bit now the epithelial cells are still there I'll be at less and the amount of cilia is actually going to start to decrease I let's do 5 here I'm gonna do 4 here this epithelial cells start to become shorter there's still columnar and they're still ciliated pseudostratified : are but the height of them is starting to shorten we're losing the character of something that absorbs and secretes inks and increases surface area to be able to with those silly of being able to run the ciliary escalator all these things we're losing that character and we're actually moving more towards cuboidal or squamous let's go to the secondary promise or the low bar well the amount of cartilage becomes even less the openings become even less the relative amount of smooth muscle though far less in absolute terms is relatively more and the squamous cells have become shorter or the the epithelial cells have become this local um Mar with even less cilia we did three my apathy liam is thinning my smooth muscle is actually becoming less but in relative terms it's actually more compared to the cartilage that's holding things open let's go into segmental or tertiary bronchi well now the lumens even smaller cartilage is less absolute amount of smooth muscle is less but the relative amount relative to the luminal diameter is actually more the epithelium is thinning and the amount of cilia is decreasing we're now it kind of be is key boydle cells with just a couple cilia 23 orders of magnitude approximately depending on the segment in the lobe we get smaller and smaller so smaller and smaller bronchi we get even less cartilage relatively more smooth muscle but in absolute terms not very much then epithelium things are truly cuboidal now with just a little bit of sparse vasilia but that relative amount of smooth muscle compared to the wall is quite a bit in relative terms now terminal arterioles the last one is kind of like a a terminal arteriole in the vascular system these are terminal long guy okay these are approximately a millimeter in diameter they don't have or very little if any if any cartlidge a considerable amount of smooth muscle sorry I can't draw it anymore any smaller without your not being able to see it the relative amount of smooth muscle is very high this gives us control kind of like in an arterial of closing off when people have asthma and these smooth muscles of the airway get excited they feel tightness in their chest they're not struggling to breathe here there's no way this a little bit about a little bit of smooth muscle here is going to or the little bit of the say biro sternothyroid muscle passing by it's going to close this off but down here down here we can actually close things off they feel like an elephant is sitting on their chest and that's because this amount of smooth muscles able to shut that opening and the epithelium has moved from this cuboidal to squamous cells and the amount of it is minimal silly has disappeared now what patrols to keep this area clean is in macrophage the macrophage is going to patrol this area to help keep it clear so as we go from the trachea to the terminal bronchi which is known as the respiratory zone of the lower respiratory tract and if we add on that nasal cavity the needs of pharynx the oral pharynx the hypopharynx the larynx we have the full respiratory zone which is approximately 150 milliliters in volume as we move through this the amount of cartilage decreases the absolute amount of muscle decreases but when we compared to the cartilage the relative amount of smooth muscle actually increases the epithelium thins and the cilia become less and less prevalent as we go from this tall ciliated pseudostratified columnar epithelium to lower and then low columnar tall cuboidal cuboidal may be low cuboidal and then squamous epithelium and when we reach that squamous epithelium we've gone smaller and smaller as the cartilage disappears and now we reach those terminal arterioles with they're thick muscle but that epithelium has thinned and now we reach the terminal arterial but sorry the terminal bronchial and we move into the respiratory bronchus and the respiratory bronchioles are the first place that we're going to actually see these little ovular sacs they'd then go through a duct this is all just a single cell layer thick of epithelium with a little bit of supporting connective tissue but essentially no smooth muscle this is going to be our respiratory zone and the respiratory bronchials these are less than a millimeter in diameter these ones were a millimeter these are less than a millimeter and it's going to feed into our first air sacs getting more and more of them until we reach these ducks and each one of these ducks are going to feed a lobule a lobule is fed by one of these ducks and in the lobule we'll find many of these air filled sacs throughout it being fed by some of these ducks now I want to get back to blue a little bit this is just all epithelium and I want to look at one of these a violist an AB ulis is made up of all these little air filled sacs some of us and this is where gas exchange is going to be able to occur this is like a bunch of grapes that you would see on a dinner table and if we cut them in half we would see the inside of each of these individual grapes okay this is the ovule or sack that are made up of many a viola and if I just look at one a violist that was cut in half it would be a lot like looking at a soccer ball cut in half well on this edge I'd see epithelial cells like so but from a frontal view as I move closer and closer to the middle I'd start to see the cells tipped a little bit these are still just epithelial cells there's a big guy these are just the edges of another epithelial cell and then tipping it more I'm looking straight on to these guys and then I'm looking straight on at that guy okay there's a couple different cell types as these ducts lead into these air filled sacs along the edges here we're going to find cells known as tight to nuuma sites these are going to be type 2 Numa sites kind of here at the entrance and type 2 Numa sites make something called surfactant surfactant is like a soap that can break hydrogen bonding because all this epithelium this is a mucosa makes water and water has let's see when we bring one molecule towards a similar molecule that would be cohesion or cohesive forces and that soap that these make break the hydrogen bond the hydrogen bonds that cause the cohesive forces and water when you put a drop of water on a freshly waxed car that water wants to move towards other water and then run off together when you put a little bit of water between two pieces of cellophane they're going to tend to stick because of those cohesive forces we need to interrupt these cohesive forces with soap a lipid and now we can actually fill the space with air coming in through that duct coming in from the conducting zone and then the respiratory zone okay these are tight to ovular cells or tight to pneumo sites and they make surfactant this is the part in a premature baby that hasn't wrapped up the process yet and that's why it's really a challenge to get their lungs inflated and why they're often underdeveloped in their lung tissue and on respirators initially but we also have a type 1 name aside a type 1 Yuma site and these are the actual or type 1a b ol are cells these are the actual epithelium cells they give the structure along with those types unit NUMA sites to the air-filled sac and remember we're looking inside that airfield zach now surrounding each sack is going to be blood capillaries here's a arteriole that comes in and it sends capillaries all around these we sectioned this one this way all around these so if I drop from the outside if we saw this one from the outside we would just see all these capillary beds surrounding it they called this the respiratory zone because this is the first place where we can actually move air from the ductwork into the bloodstream into the bloodstream you call that external respiration moving the air into or out of the bloodstream from the lungs or into the one's all these little capillary beds now these have a tendency to collapse that's the default and they have a tendency to collapse because of elastic fibers and elastic fibers run all around each of these a viola or the heavy Olas and it helps shrink this size down now when we pull on it with our muscle tissue on that pleura will expand and draw air in but the default is actually to recoil back to a smaller space now these elastic fibers can only recoil so much but this is why exhalation or expiration is a passive process it's just we pulled and expanded these and now they want to collapse back down so we have elastic fibers we have blood capillaries we have type 1 Numa sites type 2 Numa sites and then we have the occasional macrophage crawling around in here and patrolling and they can get from a Buehler sac to another alveolar sac through these little pores they connect this ovular sac to this alveolar sac and it can go in there and patrol and clean up material and then when it needs to get into the next one that's right next door there's a little opening or break in the tight junctions between these epithelial cells and it can squeeze through and that macrophage can go clean up a bit in the adjacent Abiola sac one kind of next door here okay all right so that's kind of an overview of the micro anatomy and the different cell types that we find in the respiratory zone and the changes that occur through the conducting zone let me see is there anything else I want to talk about now with any of this I don't think so not that I can do it