Lecture 4 - Respiratory System I

Hinzugefügt: 2026-05-14

[00:00:00]hi everyone welcome back this week we're going to be moving on to chapter 19 where we take a look at the respiratory system we'll be spending the next two weeks looking at this system before we move into our midterm review before the midterm exam this week's focus is primarily going to be looking at the overall organization of the respiratory system we're going to spend a lot of our time looking at the structure and how that structure leads to the specific function one of the first things we need to do is to define the difference between ventilation and respiration now ventilation is essentially just the movement of air into and out of the lungs so i want you to think of a patient who is on a ventilator okay what is that ventilator doing for them it's simply pumping that air into them it's not forcing anything into their bloodstream ultimately it's just simply supplying their lungs with the air that they would normally be taking in on their own so when we breathe in through inspiration inhalation we're taking that air from the external environment into our lungs and when we expire through exhalation that's when we are breathing out in that air okay so with ventilation think bulk flow now comparing ventilation then to respiration two very different physiological activities here with ventilation we're simply increasing the volume of our thoracic cavity so that we draw air into our lungs during inspiration and then with expiration we're decreasing the volume to force air out when we look at respiration we're focusing on the gases that are going to be diffusing from the external environment into our bloodstream and vice versa from our bloodstream out to the external environment now there are two main types of respiration that we're going to be looking at external respiration and internal respiration internal respiration is also known as cellular respiration we focused on this in biology last semester where we looked at how our cells take up the oxygen that was delivered to them by our systemic arteries and how the cells then utilize that oxygen to make atp to make the usable energy so that the cells can function the process by which oxygen moves from our blood into the cells is known as internal respiration now external respiration occurs between the most terminal portions of our bronchial tubes known as the alveoli and we've talked about alveoli specifically because they are made up of simple squamous epithelial tissue and so they are very thin to allow for gases to be able to diffuse across those cells so external respiration looks at the air that we've drawn in to those alveoli ultimately the oxygen in that air is going to be capable of diffusing into the capillaries that surround these structures and so the movement of oxygen from within our lungs into our bloodstream that is external respiration and internal respiration is the process by which oxygen is capable of moving into our body's cells here's a diagram to help give a bit of a visual there with external respiration we're simply drawing air in remember through ventilation that oxygen will get to those terminal portions of our bronchial tree once in the alveoli oxygen can then diffuse from the alveoli into the surrounding capillaries that is external respiration with internal respiration that oxygen that got into our capillaries is then going to be sent back to the heart through the pulmonary veins into the left atrium left ventricle out through the aorta and then transferred somewhere throughout the body once in the blood capillaries within our tissues that oxygen is able to then move into the cells where the cells can use the oxygen to be able to make atp through aerobic respiration all right so external respiration is the exchange of gases between the alveoli and the capillaries surrounding them and internal respiration is between the blood capillaries and the tissue cells so one of the obvious functions that we are going to spend more time next week talking about is the ability for a respiratory system to take oxygen in from the external environment into our blood and then ultimately remove carbon dioxide from our blood so that we can ultimately breathe it out secondly because carbon dioxide is so closely connected with overall proton levels within our blood and therefore acidity we're able to regulate our overall blood ph by either increasing or decreasing the amount of carbon dioxide that we remove from our blood also the paranasal sinuses that connect to the nasal cavity they're responsible for warming and moistening that inhaled air as well we have the ciliated cells that line our upper respiratory tract that are responsible for filtering particles from the air that we inhale we also have the olfactory nerve endings that are located within that nasal epithelium and those nerve endings are what give us the ability to be able to smell and then lastly here within the larynx we have what's known as the glottis and that's where our vocal cords are located so when we speak it's the air that's moving past these vocal cords with specific tensions on them which then vibrate at specific frequencies and give us our voice so in order for us to discuss the respiratory system we need to review the body cavity in which the main respiratory organs are located that would be the thoracic cavity if you recall the thoracic cavity is one of our ventral body cavities right located in the anterior portion the thoracic cavity is divided into three main sections the two lateral cavities are known as the pleural cavities and the pleural cavities house our lungs now the mediastinum is also important to the respiratory system because this is where our trachea ultimately enters into the thoracic cavity and then splits into two primary bronchi and it's the primary bronchi that are the tubes that ultimately feed in to each of our lungs now if you recall all of these body cavities they are all lined by specific types of serous membranes we just looked at the pericardium which is the double layered serous membrane that surrounds the heart well the double layered membrane that surrounds the lungs is known as the pleura and the pleura like all serous membranes is a double layered serous membrane with two layers and a space between and in that space between these two layers we have a specific type of serous fluid which is known as pleural fluid now the two layers recall the innermost layer is known as the visceral pleura and that is the layer that contacts the lungs directly and then we have the outer layer which connects to the inner part of the rib cage and that is known as the parietal layer of the pleura now the pleural fluid within this intrapleural space is responsible for helping to decrease friction by increasing lubrication and so as we breathe in and we breathe out these two layers the parietal and the visceral should be able to move against each other very smoothly without a lot of friction in this image here we are looking at a cross section you can see that we are looking in the thoracic cavity obviously because we have the presence of ribs as well anteriorly you can see part of the sternum here we are looking at the heart and you can see that we are here you can see the heart located within the mediastinum specifically within the pericardial cavity and then you can see the presence of two lungs within the pleural cavities now if you recall the heart sits towards the left of the midline so if you're trying to figure out are we looking from the top down or from inferior to superior perspective the heart sits towards the left of the midline also you're going to see that the left lung is also much smaller than the right and so we know this would be the individual's left side okay so in this case here we're looking at a cross section from an inferior to a superior perspective over here you can see labeled the parietal pleura which would be contacting the thoracic cage itself and then you see the visceral layer would be the layer contacting the lungs specifically and so the intrapleural space would be this dark space located between the visceral and the parietal pleura now we're going to take a look at the organization of the respiratory system from both a structural perspective dividing into upper and lower portions and then we're going to take a look at the functional divisions of the respiratory system i.e where is air simply just passing through and then where is respiration actually taking place so we're going to start here looking at the structural divisions of the respiratory system we have an upper portion to the respiratory system and a lower portion to the respiratory system the dividing portion here occurs at the larynx anatomically this portion right here where you have the opening of your glottis which is the opening into your trachea that typically defines the boundary between upper and lower but for our purposes we are going to use the larynx as that defining boundary between the upper and the lower respiratory system all right so if you were to take a breath in if it's cold outside remember we talked about this you should probably not breathe directly in through your mouth why because there is going to be less ability for your body to be able to warm that air up so it's best and less painful for you to be able to then slowly breathe in through your nose taking that air in and as those nasal concha are able to circulate that air the air is going to be warmed and moistened as it passes through the nasal cavity so it's important to remember though both the oral cavity as well as the nasal cavity are both conduits through which we can enter into the respiratory system so we're going to follow through here through the nose into the nasal cavity finally back to the posterior aspect of the nasal cavity where we enter into the nasopharynx the pharynx has three portions nasopharynx oropharynx and laryngopharynx air is then going to move anteriorly into our larynx and then through the larynx we now have passed through the entire upper respiratory system from the larynx we then pass directly into the trachea which you'll notice here is supported by a number of cartilaginous rings i get to take a look at those in a little bit more detail but most of this is supported by cartilage why well we want to be able to hold this whole windpipe open if it weren't supported by cartilage any of these larger tubes would be more prone to collapsing anytime we breathe out and then we'd be starting all over again trying to completely inflate the tube so these cartilaginous structures they keep the overall bronchial tubes open now from the trachea the trachea bifurcates here into left and right primary bronchi and the primary bronchi are the structures that are ultimately going to be feeding each of our lungs okay so you have two primary bronchi a left and a right then we have further divisions of those primary bronchitis into secondary and tertiary bronchi those ultimately terminate into bronchioles and the bronchioles are the first structures that do not have any cartilaginous support to them instead they have smooth muscle that surrounds them and that allows them to be able to bronchodilate and bronco constrict and then lastly we end up in the alveoli and those are those terminal portions i was speaking of before they're like grape-like clusters at the ends of all of your respiratory bronchioles and that is the site where gas exchange will take place so remember the larynx that is the terminal portion of the upper respiratory system past the larynx we move into the lower respiratory system so we move from the trachea into the primary bronchi secondary tertiary into the bronchioles and finally the alveoli now from a functional perspective we also need to divide the respiratory system into two main components we have the conducting zone which is where ventilation is going to be taking place okay remember ventilation is looking just at bulk flow of air and so ultimately here the conducting zone runs all the way from the nose or your mouth all the way through the nasal and oral cavities until we get to the pharynx larynx trachea primary secondary even tertiary bronchi bronchioles and the final portion of the conducting zone are the terminal bronchioles and this is very important for you to highlight the terminal bronchioles mark that final portion of the conducting zone before we move in to the respiratory zone and you'll notice if you follow through the terminal bronchioles which mark the end of the conducting zone they are located here before the respiratory bronchioles okay so it's important to remember why they are terminal because they mark the end of the conducting zone past the terminal bronchioles the terminal bronchioles branch into respiratory bronchioles the respiratory bronchioles alveolar ducts and alveoli are all sites where respiration is able to take place and so the conducting zone all the way through the larynx into the trachea primary bronchi secondary bronchi tertiary bronchi bronchioles terminal bronchioles marks the end of the conducting zone and in the respiratory zone we have the respiratory bronchioles alveolar ducts feeding into the alveoli so now we're going to spend some time looking at all of these various parts of the respiratory system in more detail we're going to start off here looking at the nasal cavity to begin with now a main function of the nasal cavity is to be able to draw air in and circulate that air in order to warm and moisten it within that environment you'll remember that we have a mucous membrane that lines the inner nasal mucosa and that lines all of these nasal conchae and it's the nasal concha that are ultimately going to be creating turbulence within the nasal cavity which is going to help to further warm the air as it passes through the olfactory nerve also sends fibers directly innervating that nasal mucosa where we are capable of sensing smells within our environment and then lastly the nasal cavity also provides us with a resonance chamber specifically the sinuses themselves if you have a sinus infection you notice that your voice sounds significantly different if i just simply plug up my nose right now my voice becomes very congested and plugged up okay so we rely on our nasal cavity and the paranasal sinuses to be able to give us that resonance of our voice now bounding the nasal cavity we have the external nares which are our nostrils internally we have our internal nerves now remember the nasal cavity itself is divided by the nasal septum which is made up of the perpendicular plate of the ethmoid bone and the vomer this can give you a perspective here from the external nerves through the nasal cavity to the internal nerves and the internal nerves marks that boundary from the nasal cavity to the nasal pharynx and it's within the nasal pharynx here as we move further into the respiratory tract that you'll see that these eustachian tubes open into the nasal pharynx and the eustachian tubes are connected directly to our middle ear and they're responsible for helping to equal liberate pressure within our middle ear in infants eustachian tubes tend to be more horizontal anatomically and also there can be variants from individual to individual where some infants would have more horizontal eustachian tubes as you can see as we get older because our anatomy further develops the eustachian tubes are then more angled as we age which enables us to be able to drain fluid a lot easier from that middle ear this is where middle ear infections can be very prevalent amongst young infants because just due to the morphological structure of the eustachian tube being more horizontal infants can be more prone to poor drainage and as a result you're more prone to middle ear infections now as mentioned before we have the nasal conchae the superior middle and inferior remember the superior and the middle are part of the ethmoid bone whereas the inferior nasal concha is its own facial bone now all of these are then lined by the olfactory mucosa what is mucosa mucosa is that lining that mucous epithelium that lines our upper respiratory tract and so when those conchae are lined by the epithelial tissue they are then each known as a superior middle and inferior meatus now the olfactory mucosa plays a huge role in being able to provide us with protection from external pathogens as well as other foreign particulate ciliated refers to the fact that there are those little tiny hairs on the surface and what do we know about ciliated epithelium they all contain goblet cells and so the olfactory mucosa is set up so that it is lined by all of these ciliated epithelial cells that produce mucus so producing over half a cup of mucus per day we are capable of ultimately purifying the air that's going to enter into our lower respiratory tract by trapping a lot of those irritants and foreign pathogens within the mucous lining of our olfactory mucosa and then ultimately the cilia are going to beat in that one direction which are going to help to then propel that mucus up and out of our bodies if you recall of four bones that contain the paranasal sinuses or the craniofacial bones the frontal bone the maxillary bone the ethmoid which you can see here located more anteriorly and the sphenoid sinus now the paranasal sinuses they act to decrease the overall weight of the skull bones but also lined with mucous epithelium they're capable of further trapping foreign particles and be able to prevent them from entering into the deeper portions of a respiratory system ultimately any of the mucus that's produced in these sinuses will all drain back into our nasal cavity now from the external nares through the nasal cavity internal nerves we then enter into the pharynx and the pharynx you can think of as your throat all right so whether air is coming in through the nasal cavity or oral cavity it'll ultimately enter into the pharynx at some point now the pharynx is located superior to the larynx but also anterior to the cervical vertebrae of the neck now the three main divisions of the pharynx are most superiorly the nasal pharynx the oral pharynx and then most inferior the laryngopharynx now if you take a look at these prefixes they all describe to you specifically which cavity that part of the pharynx is connected to so let's look here the nasal pharynx is connected directly to the nasal cavity the oral pharynx is connected to the oral cavity and the laryngopharynx is connected directly to the larynx okay so always look back to your prefixes suffixes root words because they will usually help you in identifying the structures maybe associations or even locations now when we look at the digestive system we're going to see how when we swallow this soft palate lifts up and blocks the nasal pharynx so ultimately food that's brought in through the mouth will be pushed back to the oral pharynx and move inferiorly that's great because we really don't want to be spraying out any kind of fluids from our noses but ultimately the pharynx acts as a passageway for food through the oropharynx laryngopharynx liquid as well oro and laryngopharynx or air which can then pass through the nasal oroluringo or from the oral cavity directly to the oro and laryngopharynx now some structures also located within the pharynx specifically within the nasal and oral pharynx are our tonsils within the nasal pharynx we have what are known as our adenoids and those adenoids are specifically called pharyngeal tonsils now you'll notice here in this diagram that we've had a bit of a portion of our soft palate removed from this diagram because typically you would like to see the uvula that would be hanging down here from the soft palate now we'll get into talking more about the uvula in the digestive system and its function but the reason why it's been cut away here is to be able to show you the pharyngeal tonsils that are located superior to the soft palate within that nasopharynx and so if we look at this image here you can see there's your soft palate and there is your nasal pharynx there are the pharyngeal tonsils located superior to the soft palate within that nasal pharynx now when you open your mouth and you say ah and you're looking to the back of your throat those large masses of lymphoid tissue that you see are the tonsils those are the ones that you would think of as the tonsils whenever you talk about them these are specifically known as the palatine tonsils why because they are closely associated with the soft palate and then at the base of your tongue much harder to see there are the lingual tonsils so ultimately between the nasal pharynx and the oral pharynx we have three sets of tonsils and the tonsils as we talked about in the lymphatic system last week tonsils are responsible for providing us with immune support right they are lymphoid tissue specifically lymphatic nodules and we see them here to provide us with immune support because our oral cavity nasal cavity are exposed to the external environment now some of you may have had your palatine tonsils or your pharyngeal tonsils you may have had your adenoids removed and you might be wondering okay so what kind of immune support do i have there well limited but you still do have lymphatic nodules there at the base of your tongue lingual tonsils and typically palatine tonsils as well as the pharyngeal tonsils are removed because either through chronic recurrent infections um and or the fact that they swell to a point at which they start to block the airway typically your doctor is wanting to see that there is some sort of compromise that could actually prove to be more of a life-threatening issue and so here you can see again the adenoids the pharyngeal tonsils located in the nasopharynx and then here associated with the soft palate the palatine tonsils and at the base of your tongue you have the lingual tonsils now moving inferiorly from the oral pharynx we're moving into the laryngopharynx and the laryngopharynx is located at the same level as the hyoid bone remember this is that floating bone that was part of the axial skeleton that we took a brief look at back when we looked at skeletal anatomy and then really haven't talked about it since it's located at the same level as the hyoid and you can see here that the laryngeal pharynx actually connects directly to the esophagus and then anteriorly connects to the larynx and so when we swallow food the food bolus is pushed back by our tongue and ultimately is going to be more likely to want to move posteriorly down the esophagus and when we breathe in we're actually drawing that air in and so it's more likely to be able to move anteriorly now the larynx runs from your c4 to your c6 cervical vertebrae and the larynx is an incomplete cartilaginous structure it's made of a number of paired and unpaired pieces of cartilage that are all held together by various ligaments and those cartilaginous structures are the thyroid cartilage cricoid cartilage epiglottis the arytenoid as well as the corniculate cartilage now if you all go to the anterior portion of your neck you should hopefully be able to feel the adam's apple that prominence typically larger in males but females should be able to palpate theirs as well that structure is known as the laryngeal prominence the laryngeal prominence is located on the thyroid cartilage now the thyroid cartilage is the largest of the cartilaginous structures that make up the larynx it is unpaired so there's only one and it is open posteriorly the reason that it's named the thyroid cartilage is because our thyroid gland sits directly in front of it now a lot of these cartilaginous structures are all made up of hyaline cartilage which you will remember is somewhat flexible but is really good at holding its shape and it's the thyroid that connects superiorly to the hyoid bone now moving inferiorly from the thyroid cartilage we have the cricoid cartilage so if you just run your fingers down a little bit or even if you place your fingers on your laryngeal prominence and if you swallow move your fingers down a little bit you should feel a bit of a ridge that will move up and down as you swallow well that ridge further down that is your cricoid cartilage the cricoid cartilage is another unpaired so there's only one of them and it is a ring-like structure that expands posteriorly now we've been looking in anatomical position if we were to turn around and look from a posterior view you would see here that the thyroid cartilage is open posteriorly and the cricoid cartilage expands posteriorly to form a complete ring the last of the unpaired cartilaginous structures is the epiglottis and in any of these lateral views when we viewed the epiglottis you saw it as this flap right here this is the epiglottis itself and this is its ligamentous attachment directly to the hyoid now the epiglottis is responsible for closing off our airway whenever we swallow so as i mentioned as food or liquid passes through the oral cavity into the oral pharynx laryngopharynx the epiglottis is going to close and it is going to shut off the glottis and our windpipe so ultimately food is forced posteriorly now this is where if you're talking and eating all at the same time that's confusing things for the epiglottis and so this is where you can be more prone to than choking because the epiglottis may be up because you're talking and trying to get air out but then also at the same time food is moving downwards and so is more likely to then bypass the epiglottis and cause you to choke now moving on the two final paired cartilaginous structures that we have are the arytenoid cartilage as well as the corniculate cartilage that sits on top of the arytenoid cartilages now the arytenoids are paired and they are located superior to the cricoid they're important because they attach the true vocal cords and pharyngeal musculature and so when we alter the way in which we speak it's contraction of specific muscles that causes those arytenoids to either tighten the vocal cords or loosen them to allow us to be able to produce the sound of our voice and finally here you can see the corniculates that sit directly on top of the arytenoids and the arytenoids attach directly to the vocal ligament the vocal ligament then is surrounded by tissue and the tissue is what's going to be vibrating at a specific frequency as the air passes through our opening which is known as the glottis and so let's take a look here at the glottis specifically at the corniculate and arytenoid cartilaginous structures and how they attach to those vocal ligaments and can tighten or loosen our vocal cords allowing us to change the pitch and sound of our voice so here we are looking from a superior to an inferior view okay so we're looking top down you can see here we have the thyroid cartilage remember the thyroid anterior prominence is known as the laryngeal prominence and we know it is open in the back so this must be the posterior surface and this must be the anterior surface this ring-like structure that is the cricoid cartilage you can see how it's thicker posteriorly than it is anteriorly now the arytenoid cartilaginous structures these are the arytenoids and then sitting on top of the arytenoids we have the corniculate cartilage okay so the arytenoids and the corniculates they are paired okay which means there's two of each now as mentioned before the arytenoids they have little muscles that attach to them and at the other end they have the vocal ligament attached to them and ultimately there this is what forms the opening which is our glottis and so here you can see the glottis is almost closed and here you can see the glottis is open and so it's the alternation of the contraction of different muscles that coordinate the movement of those arytenoid cartilages and then cause them to pull on the vocal ligaments and so ultimately if the vocal ligaments are tighter the frequency of the sound waves is going to be much higher and if the vocal ligaments are a lot looser then you're going to end up with larger wavelengths so lower frequencies i would highly recommend at this point that you take a look at the video that takes an endoscopic approach to looking at a number of operatic singers as they sing to see how their glottis changes shape to be able to produce the various pitches that you hear them singing so remember now we are moving from the upper respiratory tract from a structural perspective into the lower respiratory tract and the trachea conducts air from the larynx superiorly all the way through the mediastinum remember that central cavity located in the thoracic cavity and the trachea ends here at this bifurcation known as the carina and the corina divides then into primary bronchi remember the primary bronchi are the tubes that ultimately supply the lungs with air okay so we have one of each one on the left one on the right now the trachea runs from about c6 the inferior portion of the larynx all the way down to t5 which is the level of the carina it's located anterior to the esophagus and it's composed of these cartilaginous structures that keep it open now something you may have not been able to appreciate when looking from an anterior perspective is that these cartilaginous structures are c-shaped and because they are c-shaped they are open posteriorly now there is a muscle that runs posteriorly and connects these to one another which is known as the trachealis muscle now besides preventing the trachea from collapsing and keeping it open when we're breathing out it also allows for the esophagus to be able to expand anteriorly i'm sure we've all been in that boat where you've just been eating really fast you're not chewing your food you're loving what you're eating and all of a sudden you can feel your food move all the way down your esophagus and it feels like it's never going to pass through until finally it empties into your stomach because the trachea is supported by these c-shaped cartilages the esophagus is capable of being able to expand into the trachea ever so slightly so when you're feeling that kind of discomfort it's likely that you're stretching the esophagus to a point where it's starting to put pressure now on the other structures in the area now the inner layer of the trachea is lined by the respiratory mucosa and the respiratory mucosa is similar to the olfactory mucosa where we have pseudostratified epithelial tissue containing both goblet cells as well as cilia and so they are going to be doing the same job as our olfactory mucosa was doing we are producing mucus so that we're trying to trap foreign particulates as well as foreign pathogens and then the cilia are going to be beating in this upward direction to try to keep the mucus up and out of our lungs ultimately removing it from the body now the middle layer as we've mentioned is made up of 16 to 20 c-shaped cartilaginous rings and the trachealis muscle that runs posteriorly and then finally all of this is held together by the external layer that's made out of fibrous connective tissue now it's important to note that the respiratory mucosa as well as olfactory mucosa lined by that pseudostratified ciliated epithelial tissue the cilia can be destroyed by smoking and so ultimately that's where smokers can develop a smoker's cough because the cilia are no longer able to do the job of keeping mucus up and out of the lungs and so they rely on the coughing reflex to do so now the positive here is that the cilia are capable of being able to regenerate themselves as well now from an external perspective we've already covered the carina which occurs here at the level of t5 from an anatomical landmark here we can see it at the sternal angle and then where the primary bronchi left and right enter into the lung this region of the lung is known as the hilum in addition to the primary bronchial structures that enter into an individual hylus at this point you're also going to have those pulmonary arteries and veins entering the lungs and exiting from the lungs you'll also notice here that the left lung is slightly smaller as we mentioned previously and this is partially due to the fact that we have the heart sitting within the mediastinum slightly towards the left of the midline and because this all exists within this enclosed thoracic cavity that is contained by our rib cage there are limitations with space and so ultimately the left lung has this cardiac notch which provides extra space in order for the heart to be able to fit and sit towards the left of the midline and to review remember we have the lungs sitting within the pleural cavities and the pleural cavities are lined by the pleural membranes and the pleural membranes are serous membranes that contain a parietal pleura that lines the inner portion of the ribcage and a visceral pleura that contacts the lungs directly and between the visceral and the parietal pleura we have the pleural cavity which contains the pleural fluid we're now going to move into focusing on all of the bronchial structures here that feed the lung and then we're going to take a look at the anatomy of each of our lungs both left and right so from larynx we've moved into the lower respiratory tract through the trachea down to the carina at the level of t5 where we have a split into primary bronchi the left primary bronchi supplies the left lung entering here at the hilus the right primary bronchi enters the high list of the right lung to supply it with oxygenated air now when the primary bronchi enter the lung they then divide into secondary bronchi and there is one secondary bronchi that is dedicated to each lobe of the lung and you'll see here looking at the right lung we have a horizontal fissure and an oblique fissure and that horizontal and oblique fissure divide the right lung into three separate lobes when looking at the left lung you can see here that we only have the left oblique fissure which then divides the left lung into only two lobes and so the left lung has two lobes it's smaller the right lung has three lobes therefore the left lung has two secondary bronchi supplying each of those lobes and the right lung has three secondary bronchi supplying each of those lobes secondary bronchi then split into tertiary bronchi and you'll notice that the bronchial system is set up like an inverted tree where the trachea is similar to the trunk of a tree and then you have your primary bronchi or the larger branches and then you get smaller branches the secondary bronchi the secondary bronchi then split into tertiary bronchi and then we're going to look further and further as we get into the bronchioles and finally the alveoli so from the primary secondary tertiary bronchi tertiary bronchi ultimately branch into bronchioles and the bronchioles split into smaller terminal bronchioles and remember it's the terminal bronchioles that mark the end of the conducting zone now in the bronchioles there's also the replacement of smooth muscle remember before we had cartilaginous ring structures that were supporting the trachea the primary bronchi secondary bronchi even tertiary bronchi once we get into the bronchioles the bronchioles then replace that cartilage with smooth muscle and the smooth muscle allows for them to be able to dilate and constrict so remember we looked at the blood vessels we refer to that as vasodilation in vasoconstriction well now we're in bronchial structures so we're referring to this as bronchodilation and bronchoconstriction okay similar phenomenon happening when the smooth muscle contracts around the bronchioles they will bronchoconstrict and when the smooth muscle relaxes they will bronchodilate now at the terminal bronchioles we then are at the end of the conducting zones the terminal bronchioles are then going to branch into the respiratory bronchioles now here's a different perspective looking at the different lobes of the lungs you'll recall on the right hand side we had three separate lobes and on the left we had two separate lobes we have an oblique fissure on both it's the presence of the horizontal fissure on the right that gives us that additional third lobe so you'll see here that we have superior lobes for both left and right we have inferior lobes for both left and right the additional lobe in the right lung is known as the middle lobe now on the next slide you're going to see further lung lobe divisions because what we're going to do now is break these lobes down into smaller and smaller pieces until we ultimately have your smallest functional unit which is known as a lobule and each lobule contains a lymphatic vessel an arteriole and a venule so obviously a capillary bed and then a branch from terminal bronchiole so the way that we find these smaller subdivisions is by first off finding a lobe okay so let's take a look at the right lung and let's choose the superior lobe if we take this superior lobe which is supplied by a secondary bronchus and we divide it let's just do this and divide it into four okay so we divide into four pieces each of these four pieces those smaller segments they would all be supplied by a tertiary bronchus the secondary is going to connect to the lobe and then ultimately the secondary bronchus is going to split into smaller tertiary bronchi in each of those let's just say four for simplicity's sake each of those four are going to supply one of those smaller components of the lobe now if we take one of those quadrants that we divided the lobe into and we divide it into smaller little pieces each of those compartments is going to be supplied by its own lymphatic vessel arterial venule and its own terminal bronchiole and those smallest segments are known as lobules okay so you can define the lobule as that smallest sort of functional unit of your lung okay so from a functional perspective we have the conducting zone and the respiratory zone so we've looked through the trachea bronchitis primary secondary tertiary bronchi and it's the tertiary that are going to supply those smaller segments of the lobes and then finally we have further divisions into bronchioles and terminal bronchioles and it's the terminal bronchioles that are ultimately going to be supplying the lobules those smallest functional compartments that we've divided the lobe into and along with the terminal bronchiole the lobule is also going to be supplied by the lymphatic vessel arterial venule now all of those structures then are going to feed into this respiratory zone because remember it's at the level of the respiratory zone where you're going to want to have the capillaries surrounding these structures why because these are the structures through which gas exchange can occur respiratory bronchioles alveolar ducts and finally the alveoli they are all capable of gas exchange now because the alveoli are so thin the overall surface area of them is very large and that allows us to be able to really rapidly exchange a lot of oxygen and carbon dioxide through diffusion if you were to take all of that simple squamous epithelial tissue that makes up your alveoli and you were to spread that out it would roughly cover the size of a tennis court so again we're looking at another example of how the smallest smallest thinnest structures have such huge surface areas to allow for a lot of transport across those surfaces to take place so we're going to zoom in here on this terminal portion of the respiratory zone at the alveoli and take a look at the two different types of cells that make them up and so here you can see the alveoli are made up of a number of layers of simple squamous epithelial cells the cells that actually make up the alveolar walls those are known as type 1 aviolar cells and so here you can see this would be one type one alveolar cell this would be another and this another okay here zooming out that would be another that would be another that would be another that would be another okay so all of the simple squamous epithelial cells that make up the actual structure of the alveoli those are known as type 1 alveolar cells now remember if the alveolar are made up of simple squamous epithelium and they're surrounded by capillaries remember the capillaries are made up of a single layer of simple squamous epithelium known as endothelium and so we have about 0.2 microns between the capillary and the alveoli that oxygen and carbon dioxide have to diffuse across in order for oxygen to diffuse from our alveoli into our bloodstream and for carbon dioxide to be able to diffuse from our bloodstream out into our avioli now what allows us to be able to keep these alveoli open even when we are breathing out are the type 2 alveolar cells so here you can see an example of one of those type 2 alveolar cells the reason that these are so crucial is because they secrete a substance that's known as surfactant and surfactant is a substance that helps to decrease the surface tension of all of the opposing layers of this one aviola you have to remember if this is all very very very thin simple squamous epithelial tissue when you breathe out and they start to deflate what's keeping them from just totally sticking together well it's the surfactant that's secreted by the type two alveolar cells that lines all of these inner portions of the alveoli that helps to keep them open and inflated when we inhale and finally when we exhale i want you to think of the example again of going to the grocery store and trying to separate those produce bags you know how difficult that is especially in the winter when your hands are dry everything's dry and everything clings together the same idea goes for the alveoli if we did not have the surfactant being produced by the type 2 alveolar cells they would be likely to simply collapse and it would be difficult for us to inflate the alveoli and harder for us to get air down into those regions next week we're going to get to take a look at infant respiratory distress syndrome where when you have a premature infant that is not yet producing surfactant they require oxygen to be delivered to them because they're unable to simply breathe on their own okay and that brings us to the end of part one of the respiratory system so next week we're going to be taking a further look now at more of the functional perspective of the respiratory system we're going to take more of a specific look at how oxygen is capable of being able to diffuse into our bloodstream and then once it's in our bloodstream how it's transported by hemoglobin as well as being dissolved in our plasma to all of the tissue cells in our body and then we're also going to take a look at then how carbon dioxide is picked up from our tissue cells delivered back to the lungs so we can then breathe it out so if you have any questions in the meantime please feel free to reach out otherwise i look forward to seeing you all in tutorial next week take care