in this particular tutorial you folks have the dubious pleasure of watching what i'm going to loosely refer to but as a bit of jimbo drawing now i can't draw for toffee and you might be wondering what the hell is that that you've just just drawn you might be thinking it's a very poorly drawn golf club head for example but no this is in fact an alveolus and if you're wondering why i haven't said alveoli it's because i've drawn one of these so it's an alveolus so of course if we were to sort of follow this line up and out would eventually get to the nose and the mouth right where air is coming in and out of our respiratory system and this is sort of the end of that particular line we cannot let me sort of illustrate that with arrows in and arrows out and do it that way now the other thing we might be able to sort of quickly summarize here is what we have inside this alveolus once we've of course inspired or breathe in we have what we describe as an up arrow or high conc o2 and conch means concentration so in the air we breathe in there's quite a high concentration of oxygen around about 20 but there is also a low conc or low concentration of co2 there is whatever it is 0.04 of the air we breathe in from an external air environment at sea level in being breathed into the alveolus right so we've got a high concentration of oxygen in that mixture of gases we've got a low concentration of co2 now this alveolus does not exist on its own running near it in fact running right alongside it is this little structure and by the way there would be many hundreds of thousands of them around this alveolus and what we've got here is we have a capillary now please please don't think i'm drawing these to scale i am absolutely not but there's my capillary there and of course as my capillary passes by here this capillary is going to have a line of red blood cells and you guys who are studying biology or maybe you just recall it from gc biology you should be able to tell me that these red blood cells are exactly seven micrometers in diameter just as a capillary is seven micrometers in diameter that's not what we're interested in today but the point i want to make about these um red blood cells here that of course have a very of very many million hemoglobin proteins that are associated with them what we find in here is that here we have a low concentration of o2 and we have let's see if i can get the same pink a high concentration of co2 now before we get into what we call our diffusion gradient i want you to realize that the cell wall of the alveolus and the cell wall of the capillary they are both what we refer to as partially permeable membranes now i know that's not news to you because i happen to know for a fact that you studied that in your gcse biology course and of course all that means is there are gaps in those what we refer to as epithelial cells that are big enough to allow gases to move along molecular gases to move between them so in other words these gases which are in high concentration the alveolus of oxygen low concentration of oxygen in the capillary they can move backwards and forwards um therefore what we have is a diffusion so we have a diffusion gradient now when we have a diffusion gradient on either side of a partial permeable membrane what do we experience in that in that event we get a net movement of gas from high to low concentration from high upper from h to l concentration so what are we going to find that happens here well of course by definition we're going to find that the high concentration of co2 is going to move net in that direction and the high concentration of o2 compared to in the capillary is going to move net in this direction and that is what we refer to as the exchange of gases down the concentration gradient down the concentration gradient so i'm really going to stress that point down from high to low the concentration or diffusion gradient okay so of course the greater that gradient the faster the diffusion itself okay so that's a really nice sort of comprehensive idea here of what's going on in this particular environment of course i'm not getting really really technical here we're looking at the big picture type scenario but what we can certainly say is that the the higher this arrow goes so the grade to the concentration of oxygen which we can't really change because the air is at the concentration is unless we take some kind of face mask and take on extra oxygen which does happen in certain sporting conditions especially recovery phase but if the concentration of oxygen in the blood gets even lower perhaps because we're utilizing more when we're exercising then we're going to get a greater diffusion gradient and a greater net movement of gases along that gradient same with co2 being produced if we've got more co2 being produced because we're exercising for example aerobically we're going to get a greater diffusion greater more co2 breathe out now this is all well and good that's at the alveolus but let me give you a possibly an even worse drawing because we're now going to talk about the muscle so let me go see if you recognize this here's my first structure for you guess what this is it's 7 micrometers in diameter it is the exact diameter of these little lined up chain of red blood cells in here and of course these are the capillaries so i've got a capillary there but i want you to imagine and then trust me it ain't green i don't imagine that now what we've got is we've got muscle tissue so my green box here very unrepresentative this is muscle tissue and what we've got here of course especially when we're exercising let me just check which colors i use so here here what we've got is we've now got a high conch of oxygen in the capillary and we've got a low conch concentration of course of co2 in the capillary but in the muscle especially during oxygen especially during exercise we've got a low concentration of oxygen in the muscle and we have a high concentration of co2 muscle because we're exercising and of course we produce that aerobically through the aerobic system we've got a high concentration of co2 so what do we get we get a net movement of gases down the concentration gradient down the concentration gradient and that of course defines diffusion down the concentration gradient so what do we what would we expect to hear well in broad terms in net terms the oxygen in the capillaries will go into the muscle as a net movement and the co2 which is within the muscle will leave the muscle and it will depart in a couple of different ways actually one is as carb amino hemoglobin attached to red blood cells but it also dissolves in the plasma so we've got the net movement of oxygen in the net movement of co2 out and therefore we equip the muscle to respire aerobically because of course oxygen is one of the reactants of the aerobic system and co2 of course is one of the products now that in a simple nutshell sense is how diffusion takes place how gay exchange takes place now i want to add a little bit of extra detail here for you okay if we exercise so if let's say we go for a 20 minute jog or something like that if we exercise size what can we expect well we would expect that the diffusion gradient increases both for co2 and oxygen now what this means is that if we get an up arrow increase in diffusion gradient okay which of course we're saying we would do um in exercise we would expect that we would get an increased rate of diffusion increased rate of two so actually you know the rate in which gas is exchanging are increased and that causes an increase and this is the point i've been getting that all along an increase in net diffusion of gases so therefore during exercise conditions we are able to diffuse more gas both into the capillary via the alveolus and from the capillary into the muscle uh at the working muscle for example and of course co2 is being processed in the opposite direction now we're going to go further we're going to look at potentially depending on which course you're on we're going to look at oxygen dissociation how that works as a process but here these are the basic mechanics of gas exchange and diffusion guys can i leave you with a thought if you're sitting there wondering well why do these gas molecules do that please go back to your physics in your in your year 9 year 10 and go and have a look at kinetic theory because that is the answer to why do they do it because the thing is these gas molecules are just bouncing around randomly and it's probability that causes this to happen in other words this concentration gradient just i know i'm a danger potentially confusing here but it's not like we've only got co2 going in that direction there is also some co2 going in that direction but the total the net movement is there is there okay because these gases are bouncing around randomly that's what we mean by kinetic theory so we get a net movement of gases from high to low so if you want to get back into your 9 physics it may just be helpful in this context thanks