we're going to start this tutorial with a brain and a heart it's almost a metaphor for life you young people but actually this isn't about the heart today it's about the output of the heart and i want to remind you before we go any further that our heart here's yours metaphorically represented it is emitting and ejecting blood and of course from the aorta here which we've sliced we have got a certain amount of blood that's leaving here and of course typically it's going to be going on to the rest of the body it's going to go down to the working muscles whatever happens to be and the main point i want to get across to you first of all is where that blood is destined for what's the destination for that blood and the big idea of this is that the blood is the delivery mechanism of resources around the body you've studied in biology for example that um multicellular organisms like human beings they need delivery networks to get resources to all cells right but of course that's what's the blood what the blood's doing so where is this blood going to once it departs the heart and we're going to look first of all at rest kind of meant to be yellow we're going to first of all look at rest conditions at rest where is this blood going so first things first i want to consider the notion that let me use a bit less of a dark color than that one i want to consider the notion of other organs and let me be clear what we mean by this we are talking about other organs being the liver the kidneys the skin the brain how much of this blood of the stroke volume leaving the heart per minute cardiac output how much of it is going to these collective organs in other words other than the muscles and i'm going to stress to you that at rest this is 80 to 85 now if you consider there's about five liters of blood at rest now we've got you can calculate that if you want to we've got that notion of about four liters of that is going to um it's going forth to 4.25 liters is going to other organs not the muscles and if we then consider the muscles and specifically i want to consider the working muscles we can determine that some bunch of this is going to those muscles and we're saying here it's 15 to 20 now you might be thinking well at rest what are the working muscles well they're your postural muscles they're your breathing muscles they're for example the muscles in your neck that hold up the posture of your head these are working they are aspiring and they're doing that work now this is where life gets interesting we'll look at the how of this in a second what happens during exercise now i am going to mention exercise generically and of course the more it moves towards maximal the more this would be the case so if we look at the other organs now we're going to argue that they are going to receive in the region of 20 of that blood okay so from 80 to 85 the vast majority during exercise now they're going to receive as little as 25 20 and our working muscles let's say our rectus femoris muscles our gastroenterous as we're running that's going to receive 80 so this blood here which is departing our our left ventricle and going out of the aorta during exercise it's going from it's going from 20 at rest to eighty percent of it being being delivered to muscle so therefore we must ask the question how does that happen okay and there's actually two stages to how we're gonna answer that the first one is that we have blood vessels who are specialized in the uh in the achievement of this so if i'm just going to switch to here and i'm going to go into my circle little what i'm going to do here for you folks i'm going to draw a blood vessel and i want you to be aware that this blood vessel here as i draw it in this blood vessel here is its outer layer now what we're going to do is we're going to draw this little bit here this is the muscle and we'll do one more time a little bit and this is going to be like the inner layer please notice the inner layer is not actually green but the point i want to make to you folks is that if i fill this layer up here that layer there that layer there that is what we would describe as smooth muscle let me use a different color to annotate that that there is smooth muscle okay so that smooth muscle has a capacity to vaso dilate and it has a capacity to vasoconstrict okay so if you consider and by the way if the level of constriction dilation how tight the muscle is this is what we refer to as vaso motor towing the level of that okay vasomotor tone it's a nice word for you to include now the point i want to make is that of course when the when the smooth muscle vaso dilates it relaxes and moves outwards in this direction what that means then is that the lumen becomes wider and that wider lumen has a lower resistance to blood flow and blood will flow through that passageway more to have a higher tendency to do so so can you recognize that these arterioles which means nothing more than a smaller artery can you recognize that these arterials at rest leading to the other other organs are vasodilated well what about here to the working muscles well what we'd find here is they would have a higher level of constriction so if i was to just bring my circle tool back in for a second if i was just to bring my circle tool back where's it going there it is and i was to say right okay we're going to put that we're going to put that here and we're going to sort of bring it in what we'd be saying now is that we would now have i didn't mean to do that we would just bear with me a second i didn't actually draw that one out so let me draw that in blue there we go so let me draw that in and i'm going to fill that up so what we're saying now is that that smooth muscle has now contracted inwards so effectively what's happened there is the smooth muscle is constricted inwards the lining of course would go with it and now we've got effectively a smaller lumen we've got a greater resistance to blood flow and therefore we've got vasoconstriction so what we're saying here is that this would be an example of vasoconstriction now when we start to exercise i'll explain how this happens in a second exactly the opposite happens we get vasoconstriction leading to the other organs increasing pressure decreasing blood flow and we get vasodilation to the working muscle so more of cardiac outcome can be distributed or redistributed to that environment and that simply happens through the dilation and constriction of these arterials now that's all well and good but there's another side to the story as well and that is that these arterials they lead somewhere and effectively these arterials lead to capillary beds so imagine that this is an arterial bringing blood in this way here's our capillary bed going in here and then it kind of branches into all kinds of branches here in the actual capillary bed and then eventually these capillaries they deoxygenate and then over here now we're getting effectively we're getting the leading in of this blood now into into what we call a venule now a deoxynated blood leaving now notice here that what we've got is we've got a tissue we've got a capillary bed we've got a capillary bed and of course what's happening is that the oxygen of the oxygenated blood is being dropped off at the actual capillary bed of let's say the liver of let's say the muscle if that's in the skin but this is the really important point folks these capillaries have circular muscles around them here here here here here here now what the way this works is if these circular muscles if they constrict inwards then what happens is our blood flow all it can do is go through the central avenue through here and then out and back through the through the the venule to the veins and then back to the heart in other words we get far less exchange taking place here because the blood is shunted through okay the blood is shunted through and this happens these circular muscles here these are called pre capillary sphincter muscles they're circular hence the word sphincter you probably know that there's other sphincter muscles in the body at the bum hole for example around your eyes for example they're circular muscles they can effectively constrict and dilate but of course what's happening here then is that effectively these ones here would block off it would block it would block it would block it would block it will block it will block and the blood will simply run through the what's called the central uh capillary rather than the peripheral capacitance that pushes the blood round faster so that is actually the arterials and pre-capillary sphincters is how we do this is how we do that all well and good now james why on earth did you have a brain at the top you haven't even mentioned it yet well the point i want to make about the brain is a very very simple one we have what's referred to as a vaser motor control center here we're going to call it the vcc vaser motor control center and of course it is positioned in your medulla oblongata and if you've looked at the control of heart rate you've probably already got a good idea of what's going on here now what happens is that this system if i was to draw let's say an arterial down here this has the capacity to do what we call sympathetic stimulation and it has the capacity to do parasympathetic stimulation of that arterial or pre-capillary sphincter sympathetic and what that means is that sympathetic stimulation effectively it will increase vasomotor tone it will cause the arterial to squeeze inwards whereas parasympathetic stimulation will cause vasodilation so it's actually this vasomotor control center which is controlling the level of vasomotor tone in these areas and the points i want to make to you again is that the information that this vcc receives they tend to be or is of neural nature so this is going to be coming from chemoreceptors telling the vcc receptors telling the vcc that let's say ph has gone down and exercise is occurring it's going to be receiving information from baroreceptors saying that blood pressure has risen and exercise is happening and it's going to receive information also from proprioceptors in the muscle in the tendon saying that muscle tension and tendon tension is increased and exercise is happening or indeed it's ended and therefore sympathetic during exercise and parasympathetic during um recovery can happen to the working muscles now of course it reverses the other way around when we stop exercising so that is the how with vascular shunted vasomotor control but just be reminded that we get this redistribution we get this redistribution of blood as a result of the vasoconstriction phasor dilation of pre-capillary fingers and arterials leading to the relative working muscles or areas of activity and inactivity thanks