Transcript for:
Venous Return Mechanisms

big idea of venus return and that is essentially what we refer to as starling's law now it's got nothing to do with little speckled birds what this does have to do with is that stalin's law states that stroke volume in other words the amount of blood leaving the heart per contraction is equal to venous return okay so i'm going to refer to that as vr so this venous return the amount of blood returning to the heart specifically the right atrium it's very important because it's only that blood which is then available to be ejected from the heart and therefore when we're under things like exercise conditions we need to make this as high as possible so that we are delivering oxygen and other resources to the cells to respire and for other processes so how is it that we can get this venous return during exercise and up it the amount of blood returning to the right atrium how can we up it and what mechanisms does the body have to achieve that well here's the first one and it's a very very simple one it's the idea folks of gravity now i'm not going to draw the body and gravity i've drawn a little apple here to give us memories of newton but what we can say here is that gravity helps blood return to the heart depending on the position of the body and depending on where the blood is so for example if we have got blood in what we call our superior superior vena cava and this is the vena cava that's coming from the upper body let's describe it as the arms the shoulders the head this means that that blood will fall back to the heart with the support of gravity effectively we can talk about our mechanics it will produce a weight force mass times gravity and it will fall back to the heart through those veins now obviously that doesn't work effectively from the legs unless we invert the body and by the bite invert the body i mean you know switch it to be upside down so think about images of athletes maybe between full time and a period of extra time in let's say a rugby match or a hockey match and they are literally lying on their backs with someone shaking their legs to encourage that blood back to the heart increased venus return and that's one mechanism which we've got now that of course is almost an accidental mechanism so let's have a look at things which are a little bit more specific biological this here folks is a vein okay now what i've drawn enough because i've drawn these things in fact what i've drawn here is specifically a vein and that vein containing what we refer to as smooth muscle and i do want to sort of first of all highlight which layer is the smooth muscle is this red let me do that again actually i wasn't specific enough it's this red layer here this red layer here this is smooth muscle now i have to say i've drawn the vein here in a very kind of structural format veins are actually much looser not very often kind of circular in their structure because they don't have as much smooth muscle but the nature of this smooth muscle is very interesting it is capable of pulsing so its vasomotor tone increases which squeezes in and this vase motor tone decreases and then it kind of relaxes out should have chosen a different color for that but anyway it relaxes out it relaxes out it dilates out and this is what we would refer to as the pulsing of smooth muscle of course pulsing of smooth muscle will increase blood pressure and let me maybe describe in here we'd also get lumen reducing lumen reducing you know during the actual contractile phase of that and of course this is happening rhythmically so as blood is trying to return back to the heart this pulsing smooth muscle is supporting that process and by the way i apologize for that little tingle in the background obviously something i meant to turn off that i didn't never mind okay let's move on i'd now like to talk to you about a really remarkable structure they are called pocket valves and you know again excuse my somewhat shaky drawing i thought it'd be better to do them in advance than you watch me draw these things but we are talking about pocket valves and pocket valves you can see one of them exactly here the pocket valves are featured in veins only i mean we could say venuals as well but veins is where we want to sort of put our focus and what do these do as blood is pushed upwards through this vein of through this vein of course the the actual valve will open but once that sort of systole that pressure deceases and the blood falls backwards this valve will close and why is that important it will prevent backflow that is the role of valves you've probably come across these valves in other areas for example the structure of the heart but their job is essentially to prevent the backflow of blood so the blood can only move in one direction because the valves prevent any sort of movement backwards and remember this is particularly important during diastole of the heart okay as the heart is in a relaxation phase the blood will actually begin to fall backwards the valves prevent that from happening so it's a really really important um process and by the way you get more of them more of them in what we call distal valves now distal is not a particularly important key term for us but what i mean by this is that the further this is away from the left atrium in like the loop circuit of the systemic circuit the more valves are actually featured in other words the lower the pressure the more the valves that helps us to maintain and increase our venous return now my favorite mechanism of this return i bet you guys don't even have a favorite mechanism of venus return do you but my favorite mechanism of venus return is what's called the skeletal muscle pump and i've got it illustrated here i'm very happy with my drawing here actually this is going to show us the skeletal muscle pump now what you will notice is that i've got a vein in the middle of the shot right it's the same vein right apart we've got a couple of valves as opposed to one right we've got a couple of that so the blood is effectively moving up this way pushing through these valves but you'll also notice that around this uh this vein we have got two skeletal muscles we have got probably more likely what we'd say is two motor two separate motor units of a skeletal muscle so what we've actually got here is the idea that veins run through muscles or skeletal muscles i mean write it in properly skeletal muscles they actually or we are evolved developed in a way that those veins will run through those gluteal muscles so of course if you're performing in your barrington match in your dance routine whatever it happens to be and these muscles are actually contracting and relaxing they're shortening and fattening guess what is the impact on here and i've actually drawn this in for us that is the impact as these muscles as these muscles short and contract you can now see that effectively blood is squeezed we get an increase of pressure and this allows better venous trauma now can i just ask for you to start to consider why this might be relevant well think about something like an active recovery can you see now why an active recovery is more effective than a non-active recovery could you see now where let's say you're playing in a rugby match and the ball goes out of play for a set player line out whatever you might want to jog rugby i don't need to run hit me right rugby there jog back into position so rather than sort of ambling back into position it's helpful to keep moving so athletes will often do that sort of like little side steps jogging back into position movement because it maintains the pressure through these veins because the muscles let's say the gastrocnemius let's say if the rectus femoris are contracting and forcing blood back to the heart itself so that's my favorite one you can come up with your own favorite if you really want to but i think that's a really interesting one and then finally are very much on the same lines we're going to talk about our fifth mechanism here where are we there we are and we have got obviously here what is a very shaky drawing of the ribs and the thoracic cavity now i'm going to tell you that this mechanism is what we refer to as the respiratory pump and of course as you are exercising or as a performer is exercising we are getting greater depth and ultimately uh frequency of breathing so what then happens is as blood i'll also draw blood in a color that blood definitely isn't let me choose white for example as blood starts to kind of return into this hot into this area via let's say the vena cava and of course it's going to come back into here these are terrible drawings by the way and here's our heart just here awful drawing what we're getting here is as the thoracic cavity as it falls and moves in during expiration as it rises and moves out during inspiration of course we're getting a change in pressure in this respiratory environment and this is effectively from respiratory muscles contracting think about the diaphragm i've actually got that almost illustrated here respiratory muscles are contracting and they are better able now in this area to increase the pressure within the veins and therefore squeeze that blood back to the heart so one last thing you see that the more we exercise the more let me change that the more intensity that we exercise with can you see actually how this would operate more the ribs would be moving up and down with more force more rapidly and this respiratory pump would therefore have more impact this is how we ultimately maintain or increase venous return that relationship with stroke volume means that we've always got blood to be ejected through systole from the heart that is the big picture of venus return thank you