hi everybody Dr Mark here in this video we're taking a look at an overview of respiratory physiology [Music] now we need to keep in mind that the fact that the whole purpose or the primary purpose of our respiratory system is to bring oxygen in from the external atmosphere take that oxygen into our lungs transfer it from our lungs into our bloodstream and allow for the bloodstream to transfer that oxygen to the tissues of the body then at the tissues of the body we take the byproduct of creating ATP or energy the exhaust of our cells which is going to be carbon dioxide take that from the cells into the blood take it now in Reverse from the blood to our lungs throw it into our lungs and then we exhale the carbon dioxide so it's a two-purpose system bringing in oxygen and removing carbon dioxide and the way that this works is because the respiratory system focuses on playing around with pressures so we need to take a look at pressures and there's actually three gas laws that we need to have a look at today that explain exactly how the respiratory system works from start to finish the first thing we need to look at is the atmosphere itself the fact that I'm standing here at approximately sea level so I live in Queensland Australia and we are very close to sea level what we're going to find is that if I take a look so I'm at sea level right here and I'm standing here a very skinny stick figure looking person with a smile on my face if I stand here and notice that if I were to draw a tube around me that goes all the way up into the sky and capture the various gas particles within that tube what I'm going to find is that those gas particles will be exerting a particular amount of pressure onto me now we've spoken that pressure before in our cardiovascular system lectures and we've spoken about blood pressure so blood pressure is the force that the blood places on the walls of the vessels gas pressure is the force that the gases place on the walls of a container for example now I've said to you that the blood pressure is 120 millimeters of mercury at least when the heart contracts it's 120 millimeters of mercury that's enough pressure to squirt blood about one and a half meters right now here's the thing that's 120 millimeters of mercury the pressure that right now at sea level that gases are placing upon me is actually 760 millimeters of mercury that's far greater that's almost seven times greater than the blood pressure now the question you might ask is I don't feel that pressure right why not what's because simply we were born into this right we're born into this atmosphere and we feel it the only times that we feel it is when it's different so for example if I decided to then climb Mount Everest and I'm now standing on top of a mountain up here and if I were to just remove this 760 for a second now I put a tube around me going up to the same height and think about all the gas particles inside there's going to be fewer gas molecules inside of that tube now remember all pressure is is the force that these gas molecules place on the walls of a tube for example because there's fewer gas molecules the pressure is going to be lower so here at sea level it might be 760 millimeters of mercury worth of pressure but here it might be significantly lower it might be something like let's say 600 millimeters of mercury now the reason why this is important is this the gas molecules that are surrounding me right now is a mixture of different gases and now we're going to start talking about something called Dalton's law Dalton's law basically states that in a mixture of gases the total pressure so in this case 760 millimeters of mercury is equal to the sum of all the individual pressures so for example in this case we are surrounded by three major types of gases so the first gas that we need to talk about that we are surrounded by is that of nitrogen then there's oxygen then there's carbon dioxide and then the rest is what we call Trice gases so nitrogen for example 78 percent of our atmosphere is nitrogen 78 of all the gases around us is nitrogen but we never talk about our body using nitrogen I can talk about that shortly oxygen is 21 of the entire atmosphere and carbon dioxide is 0.03 percent now the remaining of what we call Trace gases like argon for example we don't need to talk about those these are the three main gases in the atmosphere now the thing with Dalton's law is that it states that this 760 millimeters Mercury of pressure of the gas around us is simply each of these gases added up so you can do a simple you can take your calculator out take your phone out and go okay what's 78 of 760 and you'll find it's going to be something around 593 millimeters of mercury so in the atmosphere at sea level you have 593 millimeters of mercury worth of nitrogen pressure being placed to upon you oxygen being 21 this is going to be around about 160 millimeters of mercury worth of pressure and if you have a look at the carbon dioxide you're going to find this is going to be around about 0.3 millimeters of mercury worth of pressure if you add them up it's going to be 760-ish millimeters of mercury worth of pressure this is Dalton's law that the total mixture of gases is simply the added up of each partial pressure of the gases so what we term this is the partial pressure partial pressure this is a really important concept for you to get your head around first of all is the partial pressure because we're going to State very soon another law which talks about the fact that each gas only moves down its own pressure gradient down its own pressure gradient we've spoken about diffusion before which is the concentration of things like solute right and those solutes will only move down their own concentration gradient so for example if we've got a lot of if we've got a cell for example right if I've got a cell and I've got a lot of sodium outside the cell and I've got a lot of potassium inside the cell the sodium will move down its own concentration gradient and go inside and the potassium will move down its own concentration gradient and go outside gases are exactly the same they will only move down their own pressure gradient and a take-home point that you must understand is gases will only ever move down their own pressure gradient gases will always move from a high pressure to a low pressure that's why when you watch the weather it says a high pressure system is moving in it's always going from high to low think about going down a slide we'll go back to this concept shortly so now we've got this Dalton's law we understand it this is what's out in the atmosphere next is I want to have a look at the lungs itself and how we take these individual gases and bring them in firstly I want to take these two because they're the major gases we are dealing with oxygen and carbon dioxide so let's draw them up here we'll have oxygen here and we'll have carbon dioxide here and we know that the partial pressure of oxygen in the atmosphere at sea level is 160 millimeters of mercury and carbon dioxide is around about 0.3 millimeters of mercury how do we bring the gas that's outside into our lungs I know that seems weird but how do we do it no one's pushing it in our lungs aren't a vacuum cleaner there's no engine or motor that's whirling to be able to bring it in so how does it work this is where we need to talk about the second gas law which is called Boyle's Law now Boyle's law states Boyle's law is a really interesting little super important to understand Boyle's law states that there is an inverse or opposing relationship between the volume of a container and the pressure inside of that container what does that mean let's think about this I've got a small container here and I've got a larger container here now let's just say I had five one two three four five oxygen gas molecules present in that small container and I have the same number present in this one one two three four five so both have five oxygen molecules present within each now remember molecules are constantly moving and shaking and they move through something called Brownian motion which is this random Motion in which they basically just bounce off things and continue to move along this is what the gases are doing so these oxygen molecules will be bouncing off the walls as they move around the pressure that these gas molecules exert inside the box is directly relevant to how often will they bounce off the walls right so here in a smaller box these five gas molecules are constantly bouncing off the walls so the pressure is going to be quite high so even though the volume of this box is quite low the pressure is going to be higher right in this larger box with the same number of gas molecules they're less likely to bounce off the wall because it's further away right and because there's so few gas molecules it's rarely going to happen and so the pressure in this one even though the volume is higher the pressure is lower so you can see that there's an inverse relationship between the volume of a container and the pressure in that container another great way another great example that demonstrates this is using a syringe right so we can take a syringe here so let's just take a syringe there we go there's our syringe there's the plunger and let's just say we've plunged it about halfway right now and we're going to have let's just say one two three four five gas molecules inside of that syringe what happens when I would if I were to pull down on that syringe and increase the volume inside right well you know that when we pull on the barrel of the syringe things get drawn in gases fluids get drawn in why because we change the pressure because we changed the volume so if I were to pull back on that and increase the volume what we're going to find is that the pressure is going to change so now it's been drawn all the way back to there now even though one two three four five one two three four five the volume is greater but the pressure has gone down right just like those boxes we drew now remember if the pressure is lower from here to here from inside to outside gases want to move down their pressure gradient so if the pressure out here is higher now than it is in there what do you think it wants to do once the balance it out so gas molecules will move in until it's balanced out this is how a respiratory system works we need to change the volume of our what we call our thoracic cavity and when we do that we change the pressure and when we change the pressure if the pressure is lower inside than it is outside things will move down its pressure gradient the if we decrease the volume things will want to move out because now it's a higher pressure inside than outside and things move out that is Boyle's Law the inverse relationship between the volume of a container and the pressure inside that container once you understand that and you know that all gases will move down their pressure gradient well that's important because they will then you will then know which direction there traveling Perfect all right so let's now take this how do we get these gases from here to here I've just told you we need to apply Boyle's Law we need to increase the volume of this thoracic cavity how do we do this well first thing is that at the very bottom of where our lungs are we've got this muscle and this muscle is called the diaphragm right now you know what I want to draw before I draw that diaphragm I want to draw up a really important structure called the pleural cavity let's draw that up because that's super important to understand before we even go into the diaphragm and everything like that so let's take a look at drawing up the pleural cavity so what I've drawn up as you can see is that there is now a cavity a two membrane cavity here that surrounds the lungs again this is called the pleural cavity and it's got two membranes right one membrane is most adherent to the lungs that's called the visceral pleura that's this one here and then the one that's attached to the thoracic wall the wall of our thoracic cavity that's called the parietal pleura so it's going to be attached to our thoracic cavity and we know that we have our ribs now here so let's draw those ribs back up one two and we're just going to draw an arbitrary amount of ribs we don't need to draw the exact amount of ribs let's draw it up over here as well all right there's our ribs now let's draw that diaphragm up under here perfect now outside I said the pressure overall cumulatively including all the gases is 760 millimeters of mercury at rest inside of our lungs it's also 760 millimeters of mercury it's the same so where are they get where's the gas going to go in this scenario nowhere the amount of gas going in is going to equal the amount of gas going out there's basically no net movement at rest now here's the thing if I were to now measure pressure inside this pleural cavity right it's going to be around about negative four to five millimeters of mercury more than those inside and outside right this is means it's going to be 756. millimeters of mercury oh think about that now what does this mean higher pressure here higher pressure here lower pressure it's like a sandwich where two slices of bread or a higher pressure and the meat in the middle is a lower pressure that's the pleural cavity that's the lower pressure what does that mean I said High pressures want to move to low pressures so that means that the lung tissue itself wants to stick to the pleural cavity I'll draw that the wrong direction once the stick to the pleural cavity and the external atmosphere places pressure on the pleural cavity as well so that means this pleural cavity is stuck together like that luckily they release a fluid in between so that it's lubricated but the lungs want to stick to it and the external atmosphere is pushing down onto it as well the reason why this is important is because the lungs are adherent to the pleural cavity which means wherever the pleural cavity goes the lungs will follow because it's stuck to it because of again the pressure difference the high pressure wants to go towards that low pressure so again how do we bring these gases in to the lungs we need to increase we need to apply Boyle's Law increase the volume of this thoracic cavity there is a couple of ways we can do it the first primary way we do it is we take this dome-shaped diaphragm muscle and we contract it when we contract the diaphragm we bring it from a dome-shaped shape to a flattened shape and because the diaphragm is pulling down on the pleural cavity and I said the lungs are stuck to the pleural cavity the lungs come with it what we've just done is we've now increased the volume of the thoracic cavity because now we've increased the volume here what do you think happens to that pressure it goes down it goes from 760 lower and that then allows for this gas to go oh there's now a pressure gradient I want to balance that out and this gas will brush in now that's if we want to take a small breath in what if we want to take a really deep breath in well we need to now recruit what we call accessory muscles additional muscles to help further increase the volume of our thoracic cavity this is where the rib cage comes into play and we've got two muscles that join our ribs together we've got the external intercostals these are the ones on the outside and we've got the internal intercostals the ones on the inside right now they're on both sides but just so I don't make it messy I won't drop the whole thing but you've got the external on the outside and internal on the inside here we're Contracting the external intercostal muscles and what they do is they bring the rib cage up and out that's what these external intercostal muscles do look at that the diaphragm pulls it down making the thoracic cavity larger the external intercostals pull it up and out and we further increase the volume which means now this pressure inside here it's going to be dropping precipitously which means now even more gases come in perfect right so that means we're now bringing that oxygen and carbon dioxide in to our lungs in through the Airways into our lungs all right let's take a look at this now as this gas comes in what you're going to find interestingly so we're now going to pretend that we are now into the LVL line right this is this site of gas exchange if we are now in the lvo line what we need to understand is that the lvolite are going to be in close proximity to that of the bloodstream of the capillary network of the respiratory system foreign so once the oxygen is in so let's draw oxygen up here let's draw carbon dioxide here here's the interesting thing once it goes from outside in the environment into the alveoli here the oxygen goes from 160 to 104 and the carbon dioxide goes from 0.3 40. Hmm this is interesting how does this happen how do we lose oxygen by getting into the alveoli how do we gain carbon dioxide well remember that you've got a blood stream here which basically is circulating around the entire body I'm just going to draw it like that to make it easier so that's the entire circulation going to the body remember this as the oxygen comes in the Airways the respiratory tract it has three major roles right regardless of the temperature of this air and the humidity of the air by the time it gets here it will be 37 degrees Celsius it will be 100 percent humidified and hopefully it's cleaned right that's its process as it travels through the respiratory tract it's the humidification this is where we add water molecules to the gas molecules and sometimes what can happen is the oxygen that travels in gets actually pulled into the water molecules so we lose oxygen by throwing it into some of the water molecules that are present throughout the respiratory tract so that's how we drop down that a little bit but the other thing is remember here at the alveoli oxygen what it wants to do is jump into the bloodstream so when losing oxygen straight away because it wants to jump into the bloodstream that's why it's 104 millimeters of mercury here now carbon monoxide goes from 0.3 millimeters of mercury to 40. it goes up why well the major reason is because we know the bloodstream here is throwing carbon dioxide out that's why it goes up all right here's another point this is now where we apply the third law called Henry's law Henry's law basically is referring to the fact that each gas will move down its own pressure gradient right through a fluid and so if you've got a bit of fluid or liquid the thing that determines the thing most important that determines whether a gas dissolves and diffuses through that liquid is its partial pressure gradient from one side to the other so what we need to imagine is that here we have water and we do we've got water in our alveoli your alveoli is actually covered with water right and this is important because water is really sticky and people don't necessarily realize this and it's a little bit of an aside but remember water is made up of H two two hydrogen and one oxygen in a boomerang shape fashion the hydrogen is slightly positive charge and the oxygen is slightly negative charge this makes water a polar molecule polar means it's charged right the great thing about this is water likes to be attracted to other charged things like sodium and potassium and chloride and magnesium and they're all got charges the positive is associated with the negative the negative becomes associated with the Positive they like shifting each other around the body that's super important but the other thing you need to recognize here is that the hydrogen the positive hydrogen will love other oxygen molecules which are negatively charged which means water attracts water that's what makes water sticky to itself now on the macro level we think about water more so as something that's slippery as a lubricant but on the micro scale water is very sticky and adhesive and the reason why this is important is because if you think about inside of our alveoli they're like little Bunches of grapes right if they are filled with if they got water lining their surface which they do right this helps facilitate gas exchange into the bloodstream that's moving past that's good but you take a breath in they expand great you take your breath out they shrink now if they shrink so much that the water on this side comes into contact with the water on this side what do you think the alveoli does it collapses and if you've ever had something like a glass chopping board or a glass flat thing and you put water on it and put it flat on your stone bench top it's nearly impossible to pull off you have to slide it off right you will not be strong enough to pull off same thing here if those those alveoli collapse because of the water sticking together you do not have enough muscles in your body to be able to physically open those LVL light back up so what do we do well luckily our body has these type 2 pneumocytes or type 2 alveoli cells that are present inside of our alveoli and they secrete something called surfactant and what the surfactant does is it breaks the surface tension of the water so if you break the surface tension of the water it's less sticky right remember if if you have a glass right get a glass fill it up with water from the tap and you'll find that the water tends to form a meniscus layer so it goes above the lip yet it doesn't tip over the edge why because all the water molecules are sticking to them themselves right like that sticking into the middle but if you were to pour detergent on it or an oil or something like that tends to break the surface tension and it falls down and that's what the surfactant does that's released by the alveoli breaks that surface tension so that's a little bit of an aside but it's very important because babies born prior to six months of age can't make surfactant and they need artificial surfactant delivered to them otherwise they cannot breathe they take their first breath in that's great they take the first breath out Airways collapse so we need to give them surfactant all right remember we're now applying Henry's law about the fact that in order for oxygen to go in that direction what does the pressure the partial pressure remember that's the term is what does the partial pressure of oxygen we can write PP if you like what does the partial pressure of oxygen need to be here in the bloodstream that's remember the blood's moving in this direction right and down here we're going to the tissues so they're individual cells the tissues of the body right what does the partial pressure need to be in this bloodstream going past well the oxygen partial pressure needs to be lower right needs to be lower because it has to be like a slide things will go from the top of the slide down to the bottom of the slide because it's going from high to low it costs no energy same with pressure so we need to think about what the partial pressure here is interesting it's going to be at around about the partial pressure of oxygen 40 millimeters of mercury I won't draw in that because it's going to take up too much room but it's 40. so we're going from up here 104 millimeters of mercury this is for oxygen going down the slide all the way down to 40. down the slide great okay carbon dioxide in order to go from In the Blood Out it needs to go down its pressure grain so the partial pressure of carbon dioxide in the blood needs to be higher than outside and it is so the partial pressure of carbon dioxide here at the blood in the pulmonary vessels is 45 millimeters of mercury so 45 down to 40. again it's going down so we can draw that slide up we've got 45 going to 40 and this is carbon dioxide going down now important point have a look at the gradient of the slide going from 104 to 40 is pretty steep but going from 45 to 40 isn't that steep yet we exchange an equivalent amount of these gases here at the Airways at the alveoli at the what we call the respiratory membrane how well it's because carbon dioxide carbon dioxide is around about 20 times more soluble than water that means it's easier for carbon dioxide to mix in with this gas so it's a lot easier for carbon dioxide to move through so the pressure doesn't need to be as steep think about it like this if somebody doesn't want to go through a doorway and you give them a push if they really don't want to go through that doorway you've got to give them a hard push oxygen doesn't really want to go through so it needs a very hard push right carbon dioxide wants to go through the door you don't really have to push it much he goes that's okay I want to get through so you don't need much of a push to move it through but both are still going down their own concentration gradient now that makes sense so now in the bloodstream we've got 40 millimeters of mercury of oxygen moving through and 45 of carbon dioxide let's first focus on the oxygen let's bring it down here so we've got the partial pressure of oxygen now here's the thing sorry let me just take one step back it's going from 104 down to 40 which means we're now going that's going to be a higher number right it's 40 as it's coming in but now we're adding gas so what we're going to find that the partial pressure of oxygen is coming through is a hundred and four millimeters of mercury in the blood right the carbon dioxide it's losing some so it's not going to be 45 it's going to be 40. so the partial pressure of carbon dioxide is going to be 40. millimeters of mercury now this is important because we want to deliver oxygen from the bloodstream to the tissues right that's its job and we want to take carbon oxide from the tissues and throw it into the blood again so we can throw it back out so again the partial pressures what are they for the oxygen here the partial pressure needs to be lower here and it is the partial pressure of oxygen in the tissues is around about 40 millimeters of mercury the partial pressure of carbon dioxide in the tissues is higher because they're producing carbon dioxide and it's 45 so it's going down from here to here perfect it's going down from here to here perfect all of this has to do with an application of Henry's law right going down its own partial pressure gradient all right if we take a look at the fact that we've got got four different phases here right first phase is bringing gases into and out of the lungs this process of bringing things into and out of the lungs is termed ventilation ventilation that's bringing gases into and out of lungs it's not called respiration it's called ventilation then we've got the exchange of gases here at the respiratory membrane this is called external respiration external respiration then we've got gas transport happening here and that's exactly what it's called it's called gas transport right so this part is gas transport and then we've got the exchange here from the blood to the tissues and this is called internal respiration now your question might be but both external and internal respiration are happening inside the body yes but if you've got a tube that enters from the outside of the body and that tube goes all the way down you could still say that that's the external aspect of the Body for example following the digestive tract inside the esophagus and the stomach and the gastrointestinal tract can actually be referred to as external right so this is external respiration that's internal respiration so what's the difference between the term ventilation and respiration ventilation is simply moving gas into and out of the Airways respiration is gas exchange exchanging gas across membranes very important and how did we bring it all in by changing the pressures all right the question now is how do we get these gases out because we want to Exhale that carbon dioxide out well we apply Boyle's Law we need to do something that decreases the volume of the thoracic cavity how do we do that well remember originally we had the diaphragm contracted we now simply relax the diaphragm it snaps back we relax the external intercostals they can relax back and because the Airways are filled with elastic tissue they snap back as well decreasing the volume because you decrease the volume you increase the pressure in here and they want to go down there pressure gradients they're higher pressure in here than outside it rushes out but what if you want to forcefully exhale well that's when you start recruiting those internal intercostal muscles and they pull the rib cage down and in down and in right you can contract the abdominal muscles that will be here and they push it up and in right the abdominal muscles up and in again further decreasing the volume increase in the pressure and gases Escape final point I want to add because I've spoken about a lot is I told you that you've got a lot of elastic tissue inside of your Airways and this is important so we've got the trachea and let's now say it branches into the bronchi and let's now say it branches out into all of these various bronchioles so I want to draw this up like this let's highlight these tubes like that the elastic tissue that's present hold on to the tubes right like that and attach to the lungs now what this means is that while the elastic tissue when you take a breath in they stretch and when you relax they snap back perfect they hold on to the Airways and they keep the Airways open that's important the elastic tissue keeps the Airways open when you smoke cigarettes the cigarettes tend to destroy this elastic tissue right now what do you think that means it's two things one you'll take your breath in in the Airways and the lungs get larger but it won't snap back as well so an emphysema which is a disease State generally caused by cigarette smoking where these elastic tissues destroyed in emphysema the air the lungs expand but they don't snap back because the elastic tissue isn't there right so they remain hyperinflated and so they can't get rid of that carbon dioxide because they can't decrease the volume so what do you think they do they recruit all those accessory muscles the abdominal muscles they recruit the internal intercostal muscles and they try to forcefully exhale out problem with forcefully exhaling is that the elastic tissue which is now gone can't keep the Airways open and the Airways will collapse and so in emphysema it's very common for their airways to collapse so what they need to do is they take a breath in which isn't too bad right because it's easy to open the lungs up but they don't snap back so they stay hyperinflated so they try and forcefully force it out but they don't want their airways to collapse so they burst their lips and try and control the forceful breath out so it's not one big forceful breath and everything collapses so they go and you'll see that they purse their lips the term that's sometimes used and historically used was pink puffers which is a horrible term but they're pink because they're exhausted they're using a lot of energy to breathe because it's difficult and they're puffing because they're trying not to collapse their airways so there's a clinical application of understanding this so that was a whirlwind tour of an overview of respiratory mechanics and respiratory physiology I'm Dr Mike hi everyone Dr Mike here if you enjoyed this video please hit like And subscribe we've got hundreds of others just like this if you want to contact us please do so on social media we are on Instagram Twitter and Tick Tock at Dr Mike tadarovich at d-r-m-i-k-e-t-o-d-o-r-o-v-i-c speak to you soon