USMLE Respiratory 3: Physiology - Lung-Chest Wall Graph and Diffusion
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USMLE Respiratory 3: Physiology – Lung-Chest Wall Graph and Diffusion



this video is to continue our talk on lung physiology we said our previous video your lungs have a tendency to collapse ulam grossly and even small a little alveoli all your low I reveal I want to collapse your alveoli lung collapse and they want to collapse because they're hell s you can also because your alveoli have a little bit of water around them and water groups together surface tension yeah that's why water kind of beads up so I have surface tension how do we get around this again what do we make that stops our alveoli from collapsing our suspecting so our surfactant is this compound that kind of breaks testserver since it kind of lets it extend keep open does not collapse so that's how we stop your alveoli in question but how about your lungs closely how do we stop these giant lungs from wanting to collapse well your chest wall has a natural tendency to expand expand outwards and when it expands outward expands el and when it expands it pulls things out its pull things out probably go back and pass such things out such things out has negative pressure negative pressure that pulls things out pulls things out and what does it pull out well what the test says well how about your pleura your ply opera and in that test your lungs what pulls your lungs out it kind of bounces your lungs desire to collapse your lungs wanting your lungs going to collapse fall in on itself that's positive pressure positive pressure pushing in on itself so you have the negative pressure of your chest wall bouncing with the positive pressure everyone's okay and that's fine balance it allows our lungs to kind of keep inflator you know stay out not collapse on each other so we can draw graphically photographs here's the pressure here zero here's negative pressure here's positive pressure is volume we said your chest wall spends most of his time in the negative zone where every wants to pull things out suck things out and then negative pressure so it's not supposed to hang on the negative side but then spend a little bit time on the other side your lungs on the other hand don't want to go on and think that it basically wants a class myself so it's mostly positive if you balanced until you get a chest wall and lung I think I like a chest wall on one graph you balance it too if you take two the two I combined them they look kind of like this okay so that's just graphically how they I didn't want to demonstrate it now when you're at zero pressure when everything is resting and normal everything's no equal liberated then the lungs are are still and when your lungs are still there's still a little bit of air in them we call it the functional functional residual capacity we're gonna talk about that it won't talking about spirometry a couple videos later budget size mention here alright so that is let's just chest wall lung graph hopefully it has not too bad let's move on to our next topic we said when you breathe air goes in goes into your lungs and that oxygen goes into your blood how does it do that how does it do it well let's just draw out our lung anatomy let's draw some lung Anatomy if you breathe into your trachea you would by the neck branch into your bronchi right the bronchi and your bronchi branch into your son Gary bug eyes tertiary bronchi and secondary tertiary and we'll do your bronchi branch into where's your bucket oh absolutely right my right it's your bum deal than that we can do terminal bronchioles and what your terminal bronchioles become I'm gonna keep repeating this until you get it right okay so I turned into your respiratory bronchioles and your respiratory bronchioles we said we're special did they have the well below and the respiratory bunch over this we became your alveolar sac which had a ton of alveoli and it is that Alvey alive that functional unit that alveoli that comes in contact with blood and exchanges yes you can just guess you breathe in oxygen huh doesn't your blood rushing and you breathe out always probably fixed feel to see you you tell it cuz it all right I'll be like now what factors come into play when we're talking about gas exchange we're talking about diffusion there's a ton of things that come into play how about how big your alveoli is surface area yeah I guess the bigger more than gas exchange will be how about how picture of your life we said well realized and really really thin otherwise cats won't really exchanges be too thick so how thin it is yeah about how about I get the concentration dinner that there's a hundred molecules of oxygen here and a 0 over here don't want to diffuse that's just like that's in physics that's just popular it's like if you have 100 molecules second corner and release all those muscles till one of the fuse out into where there isn't it's a high concentration all right so you have all these Tigers coming in play they're kind of intuitive but the step likes to complicate to deal with anything equation since HR so let's look at the equations for decision equation for diffusion diffusion is just write it out first this so a equal surface area the more surface area you have to diffuse the greater your diffusion this kind of math integrity works this P changing P is the difference in concentration difference in pressure so double eagles difference in pressure later the concentration chi is the thickness we said if there's very very sick you can't diffuse and so if you have a big denominator then mathematically you have a little number you have less the features it's really really thin that's what we want it is really really thin then we have a ton of the fusion all right so T equals thickness and so you can kind of mess around with these variables and kind of mess well with the feeding that hopefully that's not too bad and that's from Magli now i skipped over one thing i skipped over and d what the heck is d gases all different types of gases have their own i guess a natural ability to diffuse some guesses diffuse quicker than the others some guesses the few slower that's just an inherent natural characteristic of the gas and some gases to fuse a lot quicker some diffuse really really slowly let's just take this and look at it in a little bit more detail close your capillary out and i'm blood now some gases like co2 like n2o diffuse immediately diffuse immediately will say you're breathing in 40 molecules every second element we're just making up you hear it well this is as soon as it's such as eat a plate as soon as it touches your capillary and equal liberate equilibrium okay so let us draw it out graphically you start low but then it diffuses immediately and then kinda equilibria the thing that limits how much of these gases games are by it isn't going to be diffusion it diffuses immediately the thing I limited is going to be how much blood we can send over here alright so if we can send more blood and clear more blood out keep sending blood and we can keep picking up molecules immediately we call this profusion limited now some gas is on the other hand don't diffuse don't diffuse immediately some gases like CO she's very very slowly so we taking for debacles it might go zero and I might go to five and then microwave ten so we look at it graphically it looks kind of like this and never reaches equilibrium never reaches equilibrium so how much of this gas again your body is going to depend on diffusion would cause diffusion limited it's not perfusing limited it doesn't matter how much blood you standing there you get that was blood as one but if it's not gonna defuse it's not gonna defuse so we're just waiting on this diffusion to discuss and I were waiting for it to diffuse waiting for it to diffuse and sometimes I'm never ridiculou brain now oxygen kind of splits the difference are good for auction transfers the difference keine almost reaches equilibrium alright so oxygen kind of splits the difference now some things can affect this you can have fibrosis and fibrosis where'd that – what happened to be sticking this membrane will that diffuse quicker diffuse look diffuse lower so how will it look like like this kind look like this right diffuses slower exercise also kind of drops a lot of exercise drop it because because your because the cardiac output increases and there's less time of spins this time blows bends in here to pick up things to grab oxygen so it kind of decreases so our exercise I'll write down five boroughs that is the factors that play into diffusion now our last topic of the day is young beat on dead space when organs in your body like your kidneys don't get enough oxygen what did what is our blood vessel Jim Dave David died late they get larger to try and get more oxygen in yeah yes brain doesn't get enough oxygen it will set the Victor that I try and get more blood in if your your liver doesn't getting the boxing I will be a little bit dilate and try and get more blood in all your organs can do this the one exception is your lungs when there is hypoxia your lungs will basil constrict that's very very important so let's draw our lungs let's say this area has come on a insult and hypoxia and if your lungs will recognize it and say oh no this our lung isn't working anymore as part of the lung isn't working anymore I'm not even going to bother sending blood over there that's not going to work so it will vasoconstrict and shunt blood to the lobes to the bronchopulmonary segments that work yeah it will sell sacrifice itself to send blood elsewhere so this is a very very important distinction in your lungs when there is high possible days of constraint and tense blood elsewhere this part will no longer work what do we call parts of the lungs parts of the respiratory tract that don't take part in the respiration we call those dead space don't we remember how that kind of rude camp recess so this becomes dead space this becomes dead space there's an equation for dead space I'm very very complicated equate and I didn't want you to know I've never actually been tested but okay I want you to know it so that's where my layers we the tidal volume that's how much are you taking – what doesn't partake in gas exchange and that'll be your arterial carbon dioxide – your expired carbon dioxide if there's a difference between carbon dioxide of what you breathe out and how much gets into your pudding no are just the portion of it does not taking place that's not doing gas exchange all right by measuring this we say oh we can find out how much dead space series you can find out how much dead space tricks and that does it for this video the fridge deal in this video we're going to talk about with most video in the next video hope you enjoyed thanks

5 thoughts on “USMLE Respiratory 3: Physiology – Lung-Chest Wall Graph and Diffusion

  1. The Dead space equation at the end of the video should be Tidal volume Multiplied by the CO2 fraction, not subtracted. That's in First Aid and BRS physio at least.

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