so what does the filtrate look like so the composition of filtrate is very similar to tissue fluids there's not any proteins the big ones there's not any blood cells because those things can't get through a cell membrane they can't get through the capillary bed but the problem with the filtrate the reason we can't call it urine is there's too much good stuff in there all based on the idea that cardio is flying in and out of there the blood is flying in and out of there so fast that we only have a limited amount of time to clean so we're gonna grab a lot of good stuff water vitamins ions nutrients things we never had any intention of getting rid of but we just grabbed it at Bowman's really quickly so this is an illustration of if we let the kidneys win like the last PowerPoint was about the kidneys want to make a hundred and eighty liters of filtrate in 24 hours so picture a two-liter bottle of soda picture 90 of those bad boys can you imagine peeing that and today obviously you did be dead but that's how ambitious the kidneys want to be a hundred and eighty liters of filtrate so you only make on average and this is really hard to Ballpark because everybody's so different like some people drink a ton of water some people exercise some people you know work outside roofing where it's really hot but we say about two liters to beer in a day is what most people make so two liters is what you make versus 180 is what the kidneys want to make so obviously you are reabsorbing almost everything so filtration remember is going from the blood to the urine reabsorption is going back into the blood so if we do not pull stuff back into the blood especially a lot of water we'll be peeing ourselves to death but with the hundred and eighty liters these are not numbers you have to know but your blood volume is about five liters you have about five liters of blood so you're basically about three liters of that five is the plasma of your blood which is what you're cleaning basically you're filtering your blood about 60 times a day you're cleaning your blood about 60 times a day which is really impressive so filtration is going from the blood to the urn for focus on reabsorption so once the substances are in Bowman's capsule and in the proximal convoluted tubule once they're in somewhere in that nephron they are destined to be peed you are destined to make up make these put them in your urine so we have to reabsorb we have to bring things from the urinary system back into the blood all that good stuff that we had no intention of getting rid of so I shop at my own garage sale because I had no intention of getting rid of that stuff anyway I accidentally grabbed it remember we can easily put it back into the blood because wrapped around the nephron are the peritubular capillaries and they're just sitting there ready to take back any good stuff you want to give them so the peritubular capillary is highly adapted for reabsorption that's why it's laying there it's laying there because it's there in my picture anyway if there's something in the purple which is the nephron that guy is destined to exit your body so if there's something good in that purple we want to put it back into the blood so the good stuff has to go through the kidney tubule the purple into the interstitial fluid which is just the fluid around the tube you'll the space and then into the peritubular capillary so reabsorption is selective so this is a crucial point filtration if you remember was non selective when I go in and clean my closet because I'm in a mood I'm not being choosy I'm just grabbing everything I hate but when I stare at that big pile that's on my bedroom floor and I have to decide what to put back in my closet then I think about it then I sit there and think well I kind of like that or maybe a you know I'll need that for a party or whatever so you're more choosy when you put it back in your closet than you were when you took it out because when you took it out you were spring cleaning it was a frenzy so it's the same thing here when you take skank out of the blood at Bowman's capsule it's a frenzy because you're just grabbing things really quickly but now if I am making the decision to put it back into the blood I'm gonna be picky right I'm gonna be selective so I'm gonna choose just the good stuff and put it back in so filtration fr-s filtration is non-selective are the ribs fortune is selective we are choosing now what to put back into the blood so this is how we're separating the good stuff from the waste so Perry again meaning around tubular we're around the renal tube here capillaries have very low this has a very low blood pressure we're pretty far from the heart the blood is slowing down because it's you know spread around that tube very permeable remember capillaries have the fenestrations they have the holey holes a very very high colloid osmotic pressure in the peritubular capillary that's because a lot of fluid has already been filtered out so the the fluid that's in the peritubular capillary we've lost a lot of water so the percentage of protein is really really high what we're creating in the peritubular capillary with these first three characteristics is if something wants to come back into the capillary its gonna really really want to so reabsorption is selective but we still have to like encourage it so all the all these things encourage things to move back into the capillary so almost all of your reabsorption immediately takes place in the proximal convoluted tubule so that's why the proximal convoluted tubule is so twisty and gnarly if you think of this like a river the twisty gnarly part is gonna slow the river down right well it's the same thing here this filtrate is gonna slow down it's gonna wind its way around we've it's way way around the proximal convoluted tubule giving plenty of time for your body to decide is there something in that filtrate that I'd rather put back into the blood so almost all of my changing my mind occurs that first night I clean my cloth it and then I stare at the pile and the pile probably goes down by half because I put it right back into my closet so almost all of our changing our mind occurs right away once I have bagged it up and put it in my car to take it to the Soviet Salvation Army I don't change my mind but initially when it's still in the pile on my floor I changed my mind so almost all of our reabsorption occurs right away we never meant to get rid of that stuff anyway so how do we reabsorb these things through mechanisms we've seen before so some substances move passively if you're a passive person you go with the flow passive people are awesome because it doesn't take any energy to get them to do anything they're willing to do whatever I have a friend like this I'm like where do you want to go to dinner I don't care well good cuz I always care or what movie do you want to see I don't care like their effortless right so this is diffusion so passive transport is diffusion the fact that things go from high concentration to low concentration nothing likes to be crowded right so a lot of things are gonna move because they're very crowded where they are and they'd rather be where they're not crowded so we're gonna see that other substances are active transport so this is going to require some energy so if you remember when we talked about diffusion and active transport before ok active transport is like force seeing things to swim upstream so this is something like sugar so when you get sugar in the filtrate we don't want it there we do not want a peashooter right we need sugar to make ATP plus we don't want sugar in the urine because it'll lead to yeast infections so there's no benefit to having sugar in the urine but if you compare the urine or the filtrate to the blood there's more sugar in the blood than in the filtrate so if you look at it from the sugars perspective the sugar does not want to leave the urinary system to go back into cardio that's like your number 5 in line and they want you to move to the line that has 10 people you're not gonna go willing so they could bribe you right Nikki give you a coupon well how are we gonna bribe sugar well we're gonna have to use ATP and force it another thing with these is a lot of these have to go through those protein doors so if you remember the cell membrane if you're on waters team you can just come right through the cell membrane but remember most things are on proteins team and have to go through a protein door so again with sugar insulin is the protein door well if I have tons and tons of sugar in the filtrate I'm not going to be able to put it all back in the blood I'm gonna be limited by how much insulin I have so because it has to go through a protein door you're limited by how many doors you have it's just like a classroom when class is over and you have to exit through a door well sometimes there's like a bit of a line because you have to wait in line to go through the door you can't go through the walls so we can actually max out on how much we can pull out of the year and because we only have a certain amount of doors for certain substances but if you can just go right through the cell membrane you're good to go because that's just simple diffusion but otherwise some substances have to go through these doors but it's sometimes we don't need to use energy sometimes we do so diffusion does not require any energy but to bring sugar to bring amino acids to bring vitamins we're gonna have to use some ATP but that's okay I mean we make 17.5 pounds of ATP every hour I mean that's what it's for so it's not like active transports back it's just gonna take more work so this whole maxed out thing is called renal plasma threshold so a threshold is like a maximum right like you cross a threshold it's like a goal so this is the level at which you cannot reabsorb you cannot get it back into the blood so you're just gonna lose it in the urine so again glucose is the classic example here because insulin is the door so normally if you have a normal healthy body you have enough insulin to for whatever sugar that escapes into the filtrate you can pull it back into the blood no problem but diabetics which we've talked about before if you're diabetic you do not have enough insulin so one of the indicators of being diabetic is you'll have glucose in your urine glucose Surya because you don't have enough insulin to reabsorb that glucose and so there's not enough doors to pull the sugar back into the peritubular capillary so it stays in the filtrate another indicator is you're peeing all the time that's because if there's a lot of sugar in the filtrate the water inside the capillary bed the water inside the glamourous is going to be really attracted to the filtrate and so normally water follows solute right right normally that wouldn't happen but because you'd have so much extra solute you'd have so much extra sugar in the urine it would actually cause you to pee more it will actually cause you to filter more so renal plasma threshold is just the moment where you can't reabsorb again it's limited by how many doors you have so most of us we don't have we don't reach threshold with sugar but diabetics would reach threshold with sugar because they don't have enough doors to pull it back in sugar will stay in the urine sodium has a role just like it did with digestion so if you remember in the large intestine the goal was to suck the water out of the fecal matter so you don't have squirty duties so we absorbed sodium because water follows solute or water follow salt is a way to think about it and so the more sodium you reabsorb the more sodium you bring back into your bloodstream the more water you're gonna pull back into your bloodstream we want this right because we can't pee 180 liters of urine we just can't so we need to make sure that a lot of that water is getting put back into the bloodstream so in the proximal convoluted tubules and in the descending limb of the nephron loop we are going to pull sodium back into the blood this is gonna take some ATP because the sodium doesn't want to do that remember things like to go from where they're crowded to where they're not well in this case the sodium is not crowded in the urine he's not gonna want to go back into the blood so we just make him so active transport again we're using some ATP but if we force sodium back into the blood water is gonna follow like the puppy so we absorb the sodium chlorine is going to be attracted to that because I mean that's all table salt is right is NaCl so that's a passive process the more sodium we pull the more chlorines gonna follow also so again creating water follow solute more water's going to follow so the more sodium that we pull into the peritubular capillary the more the blood the more hypertonic the blood but is going to become so remember hypertonic is a lot of dissolved stuff not a lot of water so water is always gonna go from hypotonic hypertonic so water has always been attracted to the blood but if I am pumping all of the ions into the blood I am making the ion the blood even more hyper Ratanak which means even more water is going to want to go back to the blood because of osmosis showing water okay this is the whole thing we're trying to see this water reabsorption so I need to get the water out of the urinary system I want the the urinary system to win I want to pee the two liters a day not the hundred eighty liters a day so the proximal tubules which is shown in this picture you can see all those ions well if I start putting those back into the blood you can see how the blood is getting full of ions well as we move through this proximal tubule once all those ions have pumped into the blood once we've made the blood extremely hypertonic the water is going to want to follow so the whole thing with sodium is to trick the water back into the blood it was the same thing with the digestive system so we didn't have squirty duties we wanted to get the sodium back in to the blood so water would follow you this is very very wordy so this is where you may want to get your drawing again so you can have something to kind of look at or at least a picture of enough Ron if you didn't draw it so I wrote it all out because it is it is complicated so I'm going to talk it out but then I wrote it out here okay so is the fill tree is going down the descending limb okay we are pulling tons and tons of water out we're pulling the ions we're pulling the sugar we're pulling all the good stuff and water's falling like a puppy so if you go back to your drawing remember how we did the dash line halfway down water is able to leave because the the left side of our drawing was permeable to water so if I was water and I was in the proximal convoluted tubule or the descending limb I was free to leave and go back into the look at the concentrated filtrate goes up the a sending limp the rules change so again if you look at your drawing the right side height of your - line remember that tube is impermeable to water so the water can't leave so the filtrate becomes more hypotonic because there's more water because the water can't leave whereas the peritubular capillary is becoming hypertonic because we pumped all those I ion's into it you - that hypertonic hypotonic thing that was just kind of a introduction with it okay but caffeine a lot of people think that caffeine makes you pee more and that is true if you have up to seven cups of coffee a day which this is marca so a lot of us get especially these crazy energy drinks that have like an insane amount of caffeine so they call this osmotic diuresis there's a diuretic we've had that word before like antidiuretic hormone is water loss so if you have lots and lots of caffeine it can dehydrate you otherwise so if you're just having a little bit of caffeine a day like a couple cups of coffee or tea or soda this isn't good do this but seven cups of coffee a day isn't unrealistic for people that are really into coffee so why do you pee more if you drink a lot of caffeine well caffeine stops you from absorbing that reabsorbing that sodium so if you're not pulling sodium into the blood you're not gonna the water's not going to follow so more water is gonna stay in the filtrate and then you're gonna pee more because you're not putting as much water back into the blood so caffeine affects your ability to pull sodium which was what these last couple slides have been all about when you pull sodium back into the blood water follows because water will always go from where it's crowded to where it's not it will always be a track it to the solute