[Music] in this video we're going to look at the role of the kidneys and see how they regulate the levels of waste products ions and water in the bloodstream we'll also cover the role of adh in fine tuning those water levels now the main job of the kidneys is to filter the blood and remove all of the waste that we don't want the main waste product you need to know about is urea which is made in the liver during the process of deamination which is where excess amino acids that we don't need anymore are converted to fats and carbohydrates for storage the kidneys other job is to regulate the levels of useful things like ions and water which we need to keep at the right levels we get ions like sodium and potassium ions from our diet and we need them for all sorts of things in the body however if the levels get too high or too low it can start to damage our cells and cause problems so we have to keep them just perfect we lose some ions naturally during sweating which is why sweat tastes a bit salty but the main way we regulate our ions is through our kidneys now water regulation is a bit more complex we gain water from the foods and drinks that we consume and we lose it partly from our skin when we sweat and our lungs when we breathe but really most of the water has to be lost from the kidneys in the form of urine the reason why water regulation is so important is that our cells will lose or gain water through osmosis depending on how much water there is in the body for example if you have too much water in your body the water will diffuse into your cells by osmosis causing them to swell and possibly burst while if you have too little water your cells could lose their water and shrink so far in this video we've seen that the main roles of the kidneys are to remove waste products like jubilee and regulate other substances like ions and water next up we need to look at how the kidneys actually do all of this stuff inside each of our two kidneys are around a million of these structures called nephrons we're not going to cover all the details in this video but this yellow tube-like thing is called a tubule and as blood passes through the kidneys these kidney tubules absorb anything small so water glucose amino acids urea pretty much everything except the really large things like proteins and cells and we call this process filtration then as all this stuff makes its way through the kidney tubules we reabsorb all the things that we want to keep for example because glucose is always useful we reabsorb all the glucose whereas we only reabsorb some of the water and we don't reabsorb any urea because we're selectively reabsorbing only those bits that we want we call this process selective reabsorption to use an analogy you can kind of think about it like cleaning out your house by first of all throwing everything outside and then only bringing back inside those bits that you want to keep and in the kidney version all those things that we don't want is what forms the urine the last thing we need to cover is how water levels are regulated in the body inside the brain there's a structure called the hypothalamus which detects the concentration of water in the bloodstream if it detects that the water levels in the body are too low like if we're dehydrated then it sends a signal to the pituitary gland which sits just in front of the brain behind our eyes the signals tell the pituitary gland to release a hormone called adh or antidiuretic hormone into the bloodstream and as the adh travels around the body it reaches the kidneys and tells the tubules to reabsorb more water into the blood meaning that the amount of water in the bloodstream increases and as a result we produce less urine so basically if we have too little water we produce more adh which tells the kidneys to reabsorb more of the water and so we produce less urine however if this process goes too far or we drink too much water and the level of water in the bloodstream gets too high then the hypothalamus will stop sending signals to the pituitary gland and so it won't release as much adh because of this less adh will travel to the kidneys and to the tubules will reabsorb less water into the blood this means that more water will stay in the tubules and so the kidneys will have to produce more urine to get rid of the extra water now one last thing we need to mention is that this whole process of water regulation is an example of a negative feedback loop because the body is constantly monitoring our water levels and adjusting them to make them balance so if the water levels get too high then the body will bring them back down and if the water levels get too low then the body will bring them back up and so overall the body manages to keep our water levels almost perfectly balanced all the time and that's everything for this video so cheers for watching and we'll see you again soon you