oxygen dissociation is the tendency of oxygen to leave behind uh hemoglobin that's what it means how likely is that to happen and kind of what i want to do here is just kind of show you this graphically okay so we've got we've got this graph here on the x-axis x-axis we've got the partial pressure of oxygen so whether it's kind of you know very high partial pressure to the environment around it and also on the y-axis we've got percentage of hemoglobin saturated with oxygen so the first thing i want you to realize is if i was to sketch a dotted line kind of up here this point here represents what we would call arterial blood okay this is arterial blood now let's just reflect on that for a second what does that mean it is blood that's in the arteries therefore it's oxygenated blood therefore the saturation of hemoglobin is complete it's typically between 97 and 100 we also know that because the saturation is complete it has a very high partial pressure because it has no other it has no partially permeable membrane where it can actually then pass over to another substance so there is effectively a hundred percent partial pressure because there is no other side of the membrane in this case of course the walls of the arteries are in the are themselves uh non-permeable or impermeable now what we're going to do from this point forward is we're going to represent that with what is a very very simple green line what we're saying here is in arterial blood we have 100 partial pressure of oxygen but we also have a 100 hemoglobin saturation now where this gets interesting is where we now this next part of this area here is going to be the arrival of a capillary bed okay so if you can imagine now that what i'm going to do here is i'm going to bring in the next part of the curve here now this here anything after this point here where we get into this purple or this pink this is going to be arrival at the capillary so of course at this point we're starting to get a partial pressure in other words the partial pressure is going down because we've got a partially permeable membrane now what's happening here is that we're starting to now get the dumping or the dissociation of oxygen into those tissues and of course if i was to complete that curve there'd be this little section at the end that's not really important to us now the point i want to make at this is this one if i was to draw another dotted line in here and you know why wouldn't i um if i just draw another dotted line in here i might draw it somewhere like here okay and what we've got now is this is what we would describe as venus blood so this point here this point here represents the saturation of hemoglobin in venus blood the blood in the veins and we're saying it's some x percent over here we've got some percentages that let's call it 70 for argument's sake okay now what that therefore means is that we have now had a delivery of oxygen into the tissue so from here bring that dotted line across this area here this area here represents this area here represents oxygen delivered and i want to be really clear here what i've just drawn in would be at resting levels okay now this is where life gets interesting let me just before we go any further let me just draw back so what we're saying here is that we have arterial blood as the as the blood arrives here at the capillary bed this oxygen is being dumped into let's say the muscle let's say the muscle of the neck as it holds our head up so this this oxygen has been pumped has been dumped into the into the muscle and the other and the other organs and actually until this point this is now what we call the level of venous blood and anything below that of course you know would be it would essentially be unhealthy now this is where it gets where life gets interesting if we start to exercise the following things occur we get around the muscle we get a lower ph we get for example and this contributes of course the presence of co2 we get for example the presence of lactic acid we know for example that we get an increase in temperature now the point i want to make to you about all of those is that these factors what they do is effectively they shift our curve to the right okay so if i now draw this curve we might get something slightly different we might now get something like this my curve now comes like this it comes up it comes up and then it goes in here now the point i want to make we've now got the shift to the right of this curve now the point i want to make now is that this here now this if you look at where our venus blood is here it is at this point here now we've now this now represents our venus but in other words what we've got now is that the quantity of oxygen or the percentage of oxygen which is now being dumped into the muscle is far greater so this is o2 delivered during exercise now this is a really interesting point because what we're saying here is that during exercise conditions if the ph is lower because of the presence of cht and co2 and lactic acid and if the temperature is high which of course is intrinsically going to be the case because we are in an exercise condition we are releasing and transferring that energy therefore that energy is um is exothermic and therefore releases heat what that means is that our blood becomes better able at letting go of oxygen oxygen dissociation it releases more oxygen from hemoglobin and more hemoglobin is passed therefore into the muscle tissue now that is really really useful now we can call this shift the bore shift okay the boar shift and the boar shift explains why during lower ph or more acidic conditions because of co2 lactic acid presence and at higher temperatures the curve shifts to the right and therefore we get a greater delivery of oxygen into the muscle because the oxygen dissociates more readily from the hemoglobin i hope that's clear enough for you thanks for listening