hi everybody Dr Mike here in this video we're taking a look at how our kidneys can help regulate acid base balance let's take a [Music] look so to begin we need to talk about that beautiful equation the bicarbonate buffer equation which I'm sure you're familiar with you know that all the cells of our body that undergo metabolism need to create ATP energy and they do this by taking proteins fats and carbohydrates right proteins and carbohydrates are all made up of carbons hydrogens and oxygens and the process of metabolism is pretty much about stealing the hydrogens to give to the electron transport chain to make ATP but what we're left with is carbons and oxygen that's carbon dioxide that is the exhaust fumes of the body we need to get rid of it so all the cells of our body are making CO2 making carbon dioxide to get it to the lungs to get rid of as an exhaust it needs to jump into the blood and we know that most of our blood is made up of water and in doing so they combine to form an acid this acid is called carbonic acid which is H2 CO3 there's the two hydrogen there's the one carbon there's the three oxygen definition of an acid at least my definition is it hates itself so it splits itself apart and it produces hydrogen ions and bicarbonate ions and we've spoken about in a previous video the respiratory regulation of acidbase balance which has to do with this end obviously our lungs deal with carbon dioxide so our lungs deal with this side of the equation so think about it like this just as a quick preface if you increase your carbon dioxide levels it binds to more water pushes the equation in that direction and will ultimately produce more hydrogen ions making your blood more acidic this can happen in situations where you retain carbon dioxide and can't breathe it out things like empyema for example all right or if we think about the opposite if we blow out too much carbon dioxide we might be anxious or stressed and hyperventilate if we breathe out all of our carbon dioxide it binds to less hydrogen ions less less so so the equation is pushed in this direction where whatever hydrogen ions we have remaining will bind to the bicarbonate to try and reestablish our carbon dioxide but that means our hydrogen ion levels drop so we become more alkalin if we get rid of our carbon dioxide so importantly this side of the equation is dealt with by our lungs and it can regulate our hydrogen ion concentration what we want to talk about now is this side of the equation the bicarbonate can be handled by our kidney and again increasing or decreasing the amount of bicarbonate so think about it like this for example what if something happens to introduce too many hydrogen ions into the blood so let's just say you do a lot of vigorous exercise and you produce lactic acid by definition an acid hates itself and releases hydrogen ions into the solution now that means we're becoming too acidic but luckily for us the bicarbonate in our blood will bind to it push it in this direction and hopefully we what happens when you do a lot of vigorous exercise and you produce a lot of acid you produce a lot of carbon dioxide and you hyperventilate to get rid of the excess acid so luckily we've got our respiratory system working here but if that wasn't working very well this side would need to compensate and so if the hydrogen ion levels go up here we would need to produce more bicarbonate and so the question is how do we produce more bicarbonate and this is where our kidneys come into play so our kidneys can actually do three things to help regulate this acid base balance it can one reabsorb bicarbonate we can reabsorb bicarbonate so our kidneys filter everything that's small enough right and then reabsorbs pretty much all of it back into the body it can manage our pH by excreting that means peeing out hydrogen ions and the third thing that it can do is it can generate new bicarbonate generate new bicarbonate if we needed so that's how the kidneys can regulate our acid base balance this is not the short term lungs shortterm right now if I hyperventilate I could tweak my blood pH if I held my breath I could tweak my blood pH short term this is hours to days is the way that the kidney regulates it so you can do these three things let's take a look at how it does it so first thing you need to understand if you haven't done rol yet which I assume that you have but let's just as a quick preface if you've got your kidneys right you've got anatomically the cortex of the kidney and the medala of the kidney and you've got blood entering you've got your abdominal aoda and then you're going to have your renal Branch right so you got your renal artery blood entering the kidneys now it branches multiple times I've done a video on the renal arteries it branches multiple times and ultimately the blood will go into the cortex in the cortex we have our filtration unit called our nephron and our nefron is like a little snake there's the snake head and it's its body that goes like that now effectively this blood vessel will go in and form a little capillary called a glus that goes in and it filters and moves all the substances through these tubules of the Nephron and whatever ends up at the very end here will move through and exit as P right so if I were to just make that a little bit bigger right make this whole thing a little bit bigger have a look at this nefron in a bit more detail let's just say there's the Pac-Man head or the head of the snake and let's just say there's part of the body right the tubules you've got let's say the blood's entering here so we've got blood entering here forms a capillary bed and exits and here we filter anything small enough gets pushed through this capsule and will move through this tubal right if it keeps moving through the tubal it exits as P now the thing is we filter 180 L of blood per day now we don't want to so we make 180 L of filtr rate every single day we don't pee out 180 L what do we pee out 1.8 L per day that's only 1% which means we need to throw 99% back into the body how do we do it we've got cells that line these tubules and luckily for us this blood vessel that leaves is intimately related to these tubular cells so of pretty much 99% of everything that gets filtered we need to take from here and throw it into the tubular cell and then take it from the tubular cell and throw it into the blood vessel because then that goes to the body so that what we need to look at now so when we're talk about sodium sorry bicarbonate reabsorption all the bicarbonate gets filtered but we want to reabsorb all of it so let's talk about and show you how that happens so we're going to draw it up like this we're going to have a tubul we're going to have a tubular cell and we're going to have the blood vessel and we're going to draw that up three times okay let's take a look first one we want to look at the reabsorption of bicarbonate how do we reabsorb bicarbonate so here's the tubu right here's the tubu whatever comes out the end here it will become P this is the blood vessel whatever moves through the end here goes back to the body and that's the tubular cell now 80% % of our bicarbonate gets reabsorbed at the proximal convoluted tubule so for those of you that know if this is the nefron you got the proximal convoluted tubule descending limb ascending limb distal convoluted tubule and collecting duct 80% of bicarbonate gets reabsorbed there at the proximal convoluted tubule so what happens is we are filtering into our tub carbon dioxide cuz it's a gas it's easy to get filtered but because it's a gas it's easy to get thr back into the tubular cell the other thing is every cell that's living needs to undergo some degree of metabolism so it will produce carbon dioxide itself so not only does it get absorbed into the cell it's producing carbon dioxide now as you know because of the equation that carbon dioxide will bind with water and it will produce carbonic acid H2 CO3 and that carbonic acid because it hates itself splits itself apart to produce bicarbonate and hydrogen ions now these hydrogen ions actually get thrown back or get thrown into the tubal and it does this because something very important you know the sodium pottassium pump I told you it's my favorite enzyme it is an enzyme in the body what it does is it's located on the basil lateral side of every cell in our body and what the sodium potassium pump does is it takes three sodium and throws it out of the cell and takes two potassium and throws it into the cell and it does this using ATP that means this cell is deficient or mostly void of sodium that's important because it means now that the sodium that's being filtered by our kidneys and entering this tubu it actually has a concentration gradient that it can move down and just gets thrown back into the tubal to replenish it but it's also then going to be thrown out via the sodium potassium pump when it comes in it actually exchanges for hydrogen ions because we like to maintain some degree of balance if a positive thing goes in we swap it for a positive thing going out now what do you think happens to the hydrogen ions here we can't just pee out hydrogen ions because it changes the pH of that urine so much we really don't want our urine we don't want our urine to be less than 4.5 pH if so it's very disruptive and can be a problem and so to if we want to maintain a urine a urine pH greater than 4.5 and still just pee out free hydrogen ions we'd need to pee out over a liter 1,000 lers every day not possible so we need to buffer that hydrogen ion in order to get rid of it right and we do that by binding it to surprise to surprise the bicarbonate that's being filtered so the bicarbonate that's been filtered will enter and that bicarbonate will bind to the hydrogen ions unsurprisingly it forms h23 carbonic acid which splits itself apart to form carbon dioxide and water and that water gets peed out effectively the hydrogen ions get peed out as water wonderful and the carbon dioxide re-enters now have a look at this what happens to the bicarbonate the bicarbonate gets sent back into the body and it does this by piggy backing now sodium can be thrown through the sodium pottassium pump or it can go through a sodium bicarbonate simpa Channel all right now there's another way the bicarbonate can move across it's through another Channel which is a chloride Channel I think this is called a pendrin right so the bicarbonate can also move through this way and it does it by swapping it with chloride because negative thing going out negative thing must go in right here negative thing going out balanced by a positive thing if a negative thing goes out we need to balance it with a negative thing here okay easy so this bicarbonate can then get thrown back into the body how wonderful now look at this we've just reabsorbed bicarbonate how let's first look at the sodium we've reabsorbed sodium look at it sodium comes in jumps in jumps back out reabsorb sodium directly but the bicarbonate is different the bicarbonate goes in then gets altered chemically turns into carbon dioxide which binds with water reformed and then thrown out again so even though we've taken that car bicarbonate and reabsorbed it back into the body it's not a direct reabsorption this is where the textbooks make it tricky because unlike sodium which is a direct reabsorption it's still a one for one reabsorption here it's just being rearranged now the other really important Point here is this for every bicarbonate that we've reabsorbed we've excreted a hydrogen ion in the form of water it's a one: one ratio of reabsorption of bicarbonate to hydrogen excretion so at the same time that we reabsorb bicarbonate we are excreting hydrogen ions so we've just ticked off the first two in that process and that's how we manage the pH at the kidneys using this under normal physiological conditions now think about this what if we have too many bicarbonate ions this is when it's a perfect scenario right so if I've got just as a r sorry as a random unit five units of B carbonate five units of hydrogen ions they perfectly match and go through this process but what if we have 10 bicarbonate and five hydrogen well they bind to each other so that five disappears but we've got five bicarbonate remaining so we've got an alkalosis happening here we've got too many bicarbonate ions so what happens well that bicarbonate can just be peed straight out easy we've just reestablished our pH through excretion of bicarbonate we just don't reabsorb it but what happens if it's the opposite we've got 10 units of hydrogen and five of bicarbonate they bind we get rid of the bicarbonate but we've got five units of hydrogen remaining okay this is actually what happens every single day every single day we produce hydrogen ions through our carbon dioxide but luckily we can breathe most of it out so this um uh equation here accounts for most of the hydron management or pH management in the body but we still have some excess hydrogen being produced and then the question is how do we manage it I said you can't just pee hydrogen directly like we can by carbonate because it makes it too acidic that's a problem so we need a new buffer to buffer that hydrogen out in order to be able to pee it out and this is going to be this third part generating new bicarbon you might think wait a minute that's not what we're talking about yes it is let's have a look right we've got excess hydrogen ions so where do we start we start where we began last time we've got carbon dioxide it gets thrown back in this cell also produces its own carbon dioxide and that binds with water that then produces h2co3 carbonic acid splits itself apart to produce bicarbonate and hydrogen ions those hydrogen ions get thrown into the tubular cell in exchange for sodium but I said to you in this scenario we've used all our bicarbonate we've got excess hydrogen so unlike here where we can just bind to bicarbonate we can't do that and we can't just pee out that hydrogen we need a new buffer so for example one buffer that we can use is the phosphate buffer a very important chemical buffer it's really important as an intracellular buffer and as a renal tubal buffer like in this scenario so what happens is H p42 NE hydrogen phosphate is its name binds to hydrogen produces dihydrogen phosphate also known as phosphoric acid and that can get peed out beautiful now in this instance have a look in the process of buffering the hydrogen ions through another buffer that's not a bicarbonate buffer we've actually produced generated new bicarbonate we've just generated new bicarbonate through the buffering of hydrogen using another buffer so when we've got excess hydrogen ions in the body and this buffer can't deal with it the kidneys go don't stress I'll use the phosphate buffer not only will I get rid of that hydrogen iion dropping it and helping reestablish pH but I'll even make new B carbon to throw back into the body to try and level it out again beautiful right now that's not the only way that it can do it another way that it can do it is through glutamine so glutamine is an amino acid that the liver can produce if there's too many hydrogen ions glutamine can help bind hydrogen ions up that's important and sends them to the kidneys and what happens is the glutamine the glutamine that enters will actually get absorbed into the tubule and glutamine can break up it breaks up into two bicarbonate and breaks up into two ammonia so we have glutamine breaking up into two bicarbonate and two ammonia now a couple things can happen in this instance remember I said we've got carbon dioxide carbon dioxide binding to water producing carbonic acid that produces bicarbonate and hydrogen ions well couple things can happen one the hydrogen combined with the ammonia and it produces nh4 positive which can be thrown in to the tubal that's called ammonia ion ammonium ion and that can be peed out let's just write this down for you right NH3 is ammonia and nh4 positive is ammonium ion right so that can they can bind and ped out or the NH3 can move here and bind with hydrogen in the tubule cuz we know that that hydrogen also gets absorbed by swapping for sodium and then forms the same thing and can be peed out so through glutamine we and again we generate even more bicarbonate through glutamine so the generation new bicarbonate so this is how the kidneys help manage our pH when it comes to reabsorbing bicarbonate excreting hydrons and generating new bicarbonate I hope that makes sense hi everyone Dr Mike here if you enjoyed this video please hit like And subscribe we've got hundreds of others just like this if you want to contact us please do so on social media we are on Instagram Twitter and Tik Tok at Dr Mike todorovich at d m i k t o d o r oov i c speak to you soon