 So in this section, let's start looking at fluid shifts. Now before we look into what happens in microgravity, let's just consider what happens to us here on Earth. We stand up straight and we know that due to gravity a lot of the blood pulls into the dependent parts and especially in the lower extremities. So much that at the level of the heart, let's just say if the pressures there are an average 100 millimetres of mercury in the head, it can be a lot less, let's just say about 80 and it can definitely be a lot more down in the feet. And we have mechanisms in the capillary bed and in the arterioles to maintain tone and to keep the blood flowing so that all of it at least doesn't pull and just distains the vessels until they rupture. So that certainly doesn't happen under normal circumstances. Now we go lie supine and we are now lying down. What happens now? And we think well the same sort of thing should now happen when we go into microgravity. So what's going to happen there? This is an enormous pool of blood which now gets redistributed and what we would net immediately if for a 70 kilogram man if you had about 75 millilitres per beat ejection fraction as the ventricles contract that's the ejection fraction that is the volume of blood that gets ejected it will now go up to about 95 millilitres per beat. Okay because that heart distains and what is going to happen? Well there's better receptors and we spoke about the better receptors they can to notice. Well there's more. There's more pressure and there's more distention. So what are we going to have with those better receptors? Well first of all there's going to be some sympathetic effects and the first thing you'll notice is that the heart rate goes down because we're going to have some form of cardiac output and remember that will be my beats per minute my millilitres per beat and my beats per minute so that will give me millilitres per minute so it's actually going to be liters because it goes over over a thousand. Okay let's just do that mathematics so cardiac output is going to be the strength volume times the heart rate if you think about that just a bit of simple mathematics strength volume so that's going to be millilitres per beat per beat times beats per minute so those two are going to cancel and I'm left with millilitres per minute with cardiac output so it can't just increase out of bounds with cardiac output so as this goes up this is going to tend to fall and do that for yourself if you're in a treadmill or you've just jumped or you've just been on a training bike and you've got a heart rate monitor on you'll have certain beats per minute now just as it's quite high 130, 140, 150 go lying down to do some push-ups or sit-ups and look on your heart rate monitor you'll notice that your heart rate comes down quite a bit you are lowering this part just to compensate so the cardiac output doesn't go it doesn't go too high so you can see this decrease in heart rate and then through the other sympathetic pathways specifically to the kidneys you're going to have suppression of your renal angiotensin-aldosterone system definitely going to have the renal levels go down and the downstream effects of that as you try and compensate for this volume that is now pushed into the central section you're also going to have a decrease in your antidiuretic hormone central antidiuretic hormone through reflex pathways antidiuretic hormone that's going to keep volume back but now you lower that and because of the tension in the heart itself you're going to increase your ANP ANF depending on where you live anti-natriuretic peptide so that's going to increase and all of this together will give you a higher urinary output as you now try and get rid of this excess volume that is now being pushed central as you lie down you're going to have to get this sodium and water as water follows it is going to be excreted due to all at least to these mechanisms so that's what happens when you lie down for a while and it's tested for you to simulate on earth have people bed bound for some considerable time and you notice all these things but does this indeed happen in microgravity? that's the question