Urinary System Part 4

Summary

In the fourth part of Larry Young's urinary system series, the video explores the intricacies of homeostasis in relation to reabsorption and secretion along various parts of the nephron, including the proximal convoluted tubules, the loop of Henle, and the distal convoluted tubules. The video dives into the mechanisms of tubular reabsorption and different transport methods, like symport and antiport, and explains the importance of maintaining osmotic and electrical balance for efficient kidney function. Young uses detailed explanations and diagrams to illustrate these complex processes, from the role of sodium in transport mechanisms to the phenomenon of solvent drag and the role of hormones in secretion and reabsorption. The lecture also highlights the efficiency of the kidneys in filtering blood and the precise balance required to maintain homeostasis and proper kidney function.

Highlights

• Larry Young explains complex kidney processes via reabsorption and secretion mechanisms in this detailed video. 🎥
• Tubular reabsorption involves the exchange of molecules and ions through mechanisms like solvent drag, symport, and antiport. 🔄
• Solvent drag pulls dissolved ions with water from the tubules into bloodstream, ensuring vital components aren't lost! 🌊
• Counter-current multiplier mechanism in the loop of Henle optimizes water reabsorption with salt concentration gradients. 🌀
• Regulatory hormones like ADH play crucial roles in targeting areas for water reabsorption or secretion, maintaining balance. 🧪
• Secretion processes occur mostly in the distal tubule, regulating the excretion of drugs, waste, and balancing pH. ⚗️

Key Takeaways

• The nephron's reabsorption process ensures only 1-2 liters of urine from 180 liters of filtrate a day. Wow, efficient! 🤯
• Solvent drag is water's sneaky way to bring friends into the bloodstream—like sodium, vitamins, and more! 💦
• Counter-current multiplier mechanism is like a seesaw balance of salt and water for perfect reabsorption. Balance game strong! ⚖️
• Tubular secretion ensures finer adjustments by getting rid of excess ions like hydrogen, bicarbonate, or even drugs. 💊
• Hormones like ADH and aldosterone are the kidneys' secret sauce for water and salt management. 🍯

Overview

The video delves into the reabsorption and secretion processes within the nephron, a key component of the urinary system. Larry Young takes viewers on a journey through the microscopic world of the kidneys, elucidating how various parts like the proximal and distal convoluted tubules and the loop of Henle collaborate to maintain bodily homeostasis. The focus is on understanding the movement of water and solutes, and the multiple pathways and mechanisms, such as solvent drag, that facilitate these essential kidney functions.

Through in-depth discussion about the counter-current multiplier mechanism, the video illustrates how the loop of Henle manages to efficiently reabsorb water and salts. This segment underscores the vital role of concentration gradients in the kidney's work, optimizing water reabsorption using the balance between descending and ascending limb activities. Viewers get insight into how this balance ensures maximum reabsorption with minimum energy.

Moreover, the video sheds light on the role of hormones in kidney function. Hormones like ADH and aldosterone are pivotal in regulating urine concentration and volume. Larry Young explains how these hormones influence kidney function, affecting water reabsorption and solute balance. Additionally, the video covers tubular secretion roles, highlighting how kidneys finetune blood composition by secreting waste and adjusting pH balance when needed.

Chapters

• 00:00 - 00:30: Introduction The chapter titled 'Introduction' begins with a welcome message for the fourth part of a series on the urinary system. It promises to explore the processes of homeostasis with particular focus on reabsorption and secretion. The discussion will navigate through the proximal convoluted tubules, the loop of Henle, the distal convoluted tubules, and down into the collecting ducts.
• 00:30 - 05:30: Basic Terminology and Tubular Reabsorption The chapter covers basic terminology and the concept of tubular reabsorption. It emphasizes the importance of understanding these terms to grasp the overall process effectively. The presenter aims to provide a detailed yet concise explanation to ensure comprehension without overwhelming the audience.
• 05:30 - 13:00: Reabsorption Diagrams and Mechanisms The chapter discusses the processes occurring in the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule in relation to tubular reabsorption. It highlights the movement involved in these processes, building on concepts introduced in a previous video.
• 13:00 - 28:00: Details of the Proximal Convoluted Tubule The chapter discusses the proximal convoluted tubule, focusing on the movement of filtrate from inside the tubule back into either the peritubular capillaries or the Vasa recta, particularly around the loop of Henle. It explains the process of water reabsorption from the lumen of the tubule into the capillaries. The water movement can occur through a transcellular route or a paracellular route, with 'transcellular' referring to movement through the cells.
• 28:00 - 39:00: Loop of Henle Mechanisms and Reabsorption The chapter "Loop of Henle Mechanisms and Reabsorption" explores the pathways through which substances move in the renal system. It discusses the movement of substances, particularly water, through the cytoplasm and epithelial layers of blood vessels. It explains the concept of paracellular transport, where molecules pass between cells, as opposed to through them. This is illustrated with the example of fenestrated capillaries, which have spaces that allow water to move between them, contributing to the overall reabsorption process in the kidneys.
• 39:00 - 65:00: Countercurrent Multiplier and Water Reabsorption The chapter titled 'Countercurrent Multiplier and Water Reabsorption' discusses the concept of solvent drag, where substances dissolved in water, the solvent, are carried along during the process of reabsorption.
• 65:00 - 73:00: Tubular Secretion and Hormonal Regulation This chapter discusses the process of tubular secretion and its role in the renal system. It explains how ions, molecules, and vitamins dissolved in water are reabsorbed as water moves from the lumen of the tubule into the capillaries of the peritubule or vasa recta. The concept highlights the phenomenon where water, the solvent, carries with it various dissolved substances, demonstrating the intricate mechanisms involved in fluid and electrolyte balance in the body.
• 73:00 - 75:00: Summary and Conclusion The chapter explains various mechanisms of transport from the Lumen into the capillary, including symport and antiport. In symport, sodium and other materials are transported together, while antiport involves pumping sodium.

Urinary System Part 4 Transcription

• 00:00 - 00:30 hello and welcome back for part four of our look at the urinary system during this video we will look at the processes of homeostasis as it relates to both reabsorption and secretion so moving through the proximal convoluted tubules moving through the loop of henle and moving through the distal convoluted tubules down into the collecting ducts this
• 00:30 - 01:00 might be a little bit of a lengthy presentation but I don't want to break this up into two because all of this kind of flows together you know pun intended um so I'm going to try to keep this as concise as I can but yet give you the detail that you need and not make it too overwhelming and too long as we move through this so let's go ahead and get started on this slide here this is just some basic terminology that
• 01:00 - 01:30 you need to be mindful of as we go through and look at the processes that are going to be occurring through the again proximal convoluted tubule the loop of henle and the distal convoluted tubule um when we talk about tubular reabsorption we are talking about um the movement once again we kind of touched on this in the last video the
• 01:30 - 02:00 movement from the filtrate inside of the tubule back into either the peritubule capillaries or the Vasa recta down around the loop of henle and the way and as that water is being reabsorbed from the Lumen of the tubule into the capillary that water can move either through what we call a trans cellular root or a paracellular root trans cellular means
• 02:00 - 02:30 it's actually going through the cytoplasm and passing into the epithelia of the blood vessels paracellular means in between the cells so uh going back to those fenestrated capillaries that are lining the uh the the capillaries themselves and so um water can also go into the capillaries in between those fenestrated uh spaces that we talked about in the
• 02:30 - 03:00 last video um as that water is moving whether it is trans cellular or paracellular there is something that is referred to as solvent drag and I think this is a term that I have mentioned previously solvent drag is exactly what it sounds like things that are dissolved in water water being the solvent becomes dragged along for reabsorption
• 03:00 - 03:30 so if there are ions dissolved in the water if there are molecules if there are vitamins that are in the water anything whatever might be dissolved in that water is that water moves from the Lumen of the tubule into the capillary of the peritubule or the vassarecta all of that's going to go with it as the water moves so the water being the solvent drags with it whatever is
• 03:30 - 04:00 dissolved in it um there are other ways in which we can transport material from the Lumen into the capillary as well and that's what those last three terms are that you see there symport is where you are transporting sodium and something else and so something else is going to be attached to the sodium and it goes along for a ride antiport is where you are pumping sodium
• 04:00 - 04:30 into the cell and by into the cell we're talking about from the filtrate into the capillary uh and at the same time we actually pump hydrogen out um and we'll talk about why that makes sense again this is a topic that we've kind of visited when we looked at um buffering systems in the blood uh which we talked about in the
• 04:30 - 05:00 respiratory system this plays along those same lines as what was happening there and then we've also talked about the sglts before as well sodium glucose transport proteins and this is where we're using glucose that is bound to sodium and it's removed again from the filtrate and it goes back into the capillaries in this case here uh we're talking about the Peri uh capillary tube or the um the
• 05:00 - 05:30 peritubule capillaries because this is mainly happening within the proximal convoluted tubule and so when we're looking at reabsorption a lot of this is also enhanced or driven by the fact that you have large amounts of microvilli that are present along the surface of the tubules more so within the proximal convoluted tubules as opposed to the distal but the distal does still have some that are present
• 05:30 - 06:00 and so this diagram here shows and explains visually everything that we just talked about in the previous slide and so the previous slide was the verbal and this here is the visual and so again what you're seeing all right in
• 06:00 - 06:30 here right what you're seeing all right in here this would be the the trans cellular transportation all right this is trans cellular everything that you see happening here this here would be the Lumen of the tubule this here would be the cuboidal cell this here would be the uh the tissue fluid uh and then this here would of course be the peritubule capillary just
• 06:30 - 07:00 as it is outlined for us and so trans cellular again is going from the Lumen of the tubule into the capillary this is paracellular all right this is paracellular because it's going in between the cells right and notice that this is where that solvent drag is going to be occurring to pay close attention to
• 07:00 - 07:30 pay close attention to this right here all right water urea uric acid sodium potassium chloride magnesium calcium and inorganic phosphates which we know is important in the formation of ATP all of these substances can get called up and transported through solvent drag solvent drag is less restrictive
• 07:30 - 08:00 in other words more things get reabsorbed through solvent drag trans cellular is a lot more selective because uh it's a it's a it's a balancing act of trying to maintain homeostasis inside of this cuboidal cell and so what gets moved is a little bit more selective and so understand that um trans cellular I'm sorry paracellular is
• 08:00 - 08:30 less restrictive and so you get a lot more things that are reabsorbed trans cellular is more restrictive and so you have a little bit more of a regulatory mechanism here and so when we're looking at trans cellular reabsorption all right let's kind of go through and look at all of the factors that are happening now within this area so let's start with the Sodium and hydrogen ion anti-transport
• 08:30 - 09:00 all right so sodium gets reabsorbed right and this happens both in the distal and the convoluted or the distal and the proximal convoluted tubules which is what we're more concerned with right now and really if we wanted to be a little bit more precise precise we're really dealing with proximal convoluted tubules at this point in time and so sodium very often gets reabsorbed in the
• 09:00 - 09:30 proximal convoluted tubule and as that happens we're coming in from the again filtrate and that sodium is collecting now inside of the cuboidal cell now it doesn't stay there long because as we move from the cuboidal cell into the peritubal capillary we can see that we have sodium potassium pumps that regulate that
• 09:30 - 10:00 um we'll get to that here in a few minutes so as sodium is coming from the filtrate into the cuboidal cell we have to pump hydrogen ions out and so hydrogen ions that are stored in the cuboidal cell gets pumped into the tubule fluid why
• 10:00 - 10:30 homeostatic balance if you just moved sodium in and that was it you're super charging if you would um the intracellular or the intercellular environment of that cubital cell cuboidal cell you're making two you're making it too much positively charged and that can throw off the balance of everything else and so what we do is to maintain
• 10:30 - 11:00 the electrical charge of the cell as we pump the sodium in at the same time we're removing hydrogen ions and that again helps to maintain the the balance of the charge and by pumping the hydrogen ions out you're also helping to regulate pH balance inside of the cell so that is your antiport all right this happens
• 11:00 - 11:30 um uh without the use of cellular energy right that is different than what is happening on this side as we move from the cuboidal cell into the peritubule capillary where we have sodium potassium pumps that are doing the same thing but notice as we pump that sodium now into the capillary right now we're getting rid of those positive charges and so we have to balance that back out by bringing some
• 11:30 - 12:00 potassium back in this is energy intensive right so this here is using energy as does the um completely lost my train of thought the sglt pumps as well the sodium glucose transport pumps they're also using sorry that's over here this is also energy required as well
• 12:00 - 12:30 so that reabsorption of sodium is really what is driving everything that you see going on in here all right you also see some calcium chloride symports going on here so if we are absorbing too many positive ions we can actually then turn around and pump the potassium out and as we do that we're also going to be dragging some chloride ions out which again helps to maintain the balance
• 12:30 - 13:00 because on the flip side we have chloride ions that are being pumped in and so we can sometimes get that collection of over collection of negative charges um but because we we have so much movement of sodium we can afford to pump the potassium back out to again equalize the charge now the transport of chloride ions which is
• 13:00 - 13:30 negatively charged from the um Lumen of the tubule into the cell and then from the cell into the capillary is independent of is not dependent of the transportation of the sodium ions and so that's why you see redundancy here within the movement of the potassium ions we're both pumping potassium in to maintain a positive environment but then if we get too much
• 13:30 - 14:00 we can pump that potassium out and drag the chloride ions with it as needed and so they are two separate processes that are going on all right um and so what we're really doing is we're creating an environment of osmotic and electrical balance osmotic from the perspective of um uh balance of solutes that are in there
• 14:00 - 14:30 all right so think of Osmosis all right so we've got to keep osmotic balance because if we get too many positive ions or too many negative ions that are in there you're going to throw the balance of water reabsorption off so you have to keep that stable in order to keep the water moving in the right direction um and the flip side to that is the electrical gradients because if you have an imbalance in
• 14:30 - 15:00 the distribution of the ions you throw off the electrical charge which then can halt this entire system as well when we're talking about trans cellular so sodium concentration in the tubular fluid is about 140 um what we what we refer to as molar equivalent per liter that meq stands for molar equivalent
• 15:00 - 15:30 meq right here stands for molar equivalent all right and then in the cytoplasm of the epithelial cells of the cuboidal cells
• 15:30 - 16:00 that sodium concentration is about 12 molar equivalents per liter so you can see that there is a dramatic drop there um the molar equivalent is defined as the amount of a substance which will either react with or Supply one mole of hydrogen ions within an acid base reaction
• 16:00 - 16:30 um and so this is one way in which we can go ahead and regulate um pH and that's kind of what we were talking about with the Sodium and hydrogen ion anti-antiport and so again the molar equivalent is defined as the amount of a substance which will either react with or Supply one mole of hydrogen ions in an acid-base reaction
• 16:30 - 17:00 or we'll Force the movement of sodium molecules into a cell so that sodium doesn't build up uh due to sodium potassium pumps so you can again see what is happening on this side meets the first criteria for molar equivalent all right and then what is happening on
• 17:00 - 17:30 this side meets the second criteria for molar equivalent um and so uh we try to balance out how much sodium is there to be able to maintain pH and to be able to maintain um the concentration of sodium being diffused back into the peritubule capillaries by the way for those who have not had chemistry all right what is a mole a mole is not
• 17:30 - 18:00 the furry thing that digs in your digs holes and tunnels into your ground that's not what we're talking about here mole is the quantity of anything gummy bears earthworms sodium ions whatever it is that has the same
• 18:00 - 18:30 number of um particles found in 12 grams of carbon and we Define that as being 6.02 times 10 to the 23rd those who
• 18:30 - 19:00 would have had chemistry have heard of Avogadro's number and that is what Avogadro's number is so um 6.02 times 10 to the 23rd molecules of sodium equals one mole um 6.02 times 10 to the 23rd
• 19:00 - 19:30 um uh sugar molecules equals one mole all right so there so everything is that is that constant back to one mole so on a daily basis you are actually filtering uh producing about 180 liters of filtrate
• 19:30 - 20:00 per day that is happening within the um within the glomerulus in the renal corpuscle and that is through the tubules through the proximal convoluted tubule the loop of Henley and the distal convoluted tubule that is whittled down to about one to two liters a day of actual urine that is produced right so 180 liters of
• 20:00 - 20:30 filtrate produced per day but that it only amounts to about one to two liters of urine that is actually excreted and the reason for that is because about 99 of the water that is actually removed in the filtrate is going to be reabsorbed um and so reabsorption is key in the process there's another video here for you to kind of review all of this with and you have access to that in canvas
• 20:30 - 21:00 and I encourage you to if you want to stop this video hop into canvas and take a listen all right and kind of watch that and then maybe come back in and finish this video um and so a little bit more on reabsorption uh we got to talk a little bit more about pressure here and why reabsorption works um so
• 21:00 - 21:30 uh what we end up seeing Happening Here is we if you remember in the renal corpuscle it's more specifically in the glomerulus blood hydrostatic pressure was equal to 60 millimeters of mercury and that was
• 21:30 - 22:00 maintained all through the glomerulus well once you enter into the peritubule capillaries once you enter into the peritubule capillaries that pressure now drops down to about eight millimeters of mercury so you've got low pressure in the capillaries you've got low pressure within the capillaries now remember all of these
• 22:00 - 22:30 proteins have stayed in the capillary the red blood cells have stayed in the peritubal capillaries the white blood cells have stayed in the peritubule capillaries large negatively charged molecules have stayed in the peritubular capillaries so you end up with very low blood hydrostatic pressure but you end
• 22:30 - 23:00 up with extremely high colloid osmotic pressure all right not to mention that you also have very high tubule hydrostatic pressure in other words you've got very high pressure in the proximal convoluted tubule because that's where all the fluid that's where
• 23:00 - 23:30 all the filtrate now is so low blood hydrostatic pressure high colloid osmotic pressure in the peritubular capillary coupled with very high tubule hydrostatic pressure drives reabsorption because that water wants to go from an area of low solute concentration to an area of high solute concentration that solute is your colloids that's that suspended
• 23:30 - 24:00 material that is Left Behind in the peritubular capillaries and so that water is like I've got all of this pressure that I'm exerting on this wall of this of this of this proximal convoluted tubule there's not a whole lot of solute in here compared to what is over there in the peritubular capillary and so that water is forced it's driven from the filtrate back into that peritubular capillary forcing reabsorption all along
• 24:00 - 24:30 the proximal convoluted tubule all right so again the factors that are contributing to reabsorption through the proximal convoluted tubule is a low blood hydrostatic pressure inside the peritubal capillary an extremely high colloid osmotic pressure inside the peritubular capillary with a high tubule hydrostatic pressure inside the proximal
• 24:30 - 25:00 convoluted tubule and that drives reabsorption that drives the movement of water from the proximal convoluted tubule into the peritubule capillary and in the proximal convoluted capillaries we have something that is
• 25:00 - 25:30 referred to um I'm sorry and within the proximal convoluted tubules we have transport proteins all right um that have a limit to what they can actually transport so the rate at which we go ahead and we move through trans cellular transportation those molecules um from the cuboidal cells into the
• 25:30 - 26:00 peritubule capillaries is based on the number of transporters or receptors that we have and we refer to that as the transport maximum all right or the TM the rate the maximum rate at which you can reabsorb uh solutes uh that are within the tubule so and each solute has its different has its own number all right each solute has its own
• 26:00 - 26:30 um TM right or transport maximum uh glucose is probably the most important one because all of glucose gets reabsorbed within the proximal convoluted tubule and so the TM the transport maximum for glucose is 320 milligrams per minute of glucose even after a heavy meal where typically we are reabsorbing glucose right around about 125 milligrams per minute of glucose so we don't even come close to
• 26:30 - 27:00 the glucose maximum or I'm sorry the transport maximum for for glucose um in individuals who are diabetic all right what happens is that glucose is not being reabsorbed inside of the cells inside of the tissues for the use of cellular respiration and so that glucose is all getting excreted into the filtrate and at that point in time you do exceed
• 27:00 - 27:30 the TM you do exceed the transport maximum for glucose and so not all of that glucose can be absorbed because the body is not sufficiently using it um and so when that happens you have glucose that's left in the urine and that is why when you do a a a chem stick test right or the the the p-test and you'd stick the dipstick into the urine sample and it comes up positive for urine or for glucose this is why
• 27:30 - 28:00 because you've exceeded the TM within the proximal convoluted tubule back in the day back in the 1600s um Physicians would actually diagnose diabetes by taking a urine sample handing it off to the the um the uh the intern and saying taste this and if the urine was sweet it indicated that the glucose was still in the urine it wasn't being reabsorbed and they would actually diagnose those individuals usually with
• 28:00 - 28:30 um diabetes all right okay so now that was all proximal convoluted tubule aren't you glad we're uh we're doing this all right let's take a take a few minutes to talk about what is happening in the loop of Henley because in the loop of Henley we
• 28:30 - 29:00 see the other 24 or so of water being reabsorbed remember about 75 percent of the water is being reabsorbed in the um proximal convoluted tubule and the remainder of that water almost there all of the remainder of that water is going to be reabsorbed in the loop of henle and so how this happens is through using what we call the counter current
• 29:00 - 29:30 multiplier mechanism all right or the counter current mechanism counter current multiplier and I'll Define that a little bit more for you here in a little bit um and so we can go ahead and we can increase the water reabsorption in the loop of henle through this mechanism that we're going to spend some time talking about the other way that we can go ahead and
• 29:30 - 30:00 um regulate the reabsorption of water is within the distal convoluted tubule and that's done through antidiuretic hormone and we'll talk about that next but the countercurrent mechanism creates and maintains a an osmotic flow by basically swapping salt for water and this is where the medulla of the of the kidneys that the renal pyramids become such a vital
• 30:00 - 30:30 role and this is why that Loop of henle dips down into uh the medulla so let's go ahead and jump into this um by the way let me just Define real quick here for you all right m-o-s-m which is a milli um osmo Emily osmo and this is simply the number
• 30:30 - 31:00 of moles of a solute that contributes to the osmotic pressure
• 31:00 - 31:30 of a solution all right so the miliosmol is the number of moles of a solute that contributes to the osmotic pressure of a solution as you increase osmotic pressure you can increase the rate of water reabsorption and as you decrease osmotic pressure you decrease the rate of water reabsorption and so when you talk about balancing the the solute concentrations we can do that
• 31:30 - 32:00 through the regulation of water and that's exactly what the character currents multiplier mechanism does and um what we see here is uh we see basically a two-step process sodium chloride is actively reabsorbed into the interstitial fluid now that interstitial fluid that interstitial fluid is
• 32:00 - 32:30 that interstitial fluid is the renal pyramid right or the medulla all right so what we're doing is we're super concentrating with salt the renal pyramids and in doing that you create a hypertonic environment that the water in
• 32:30 - 33:00 the filth trait coming down into that Loop of henle is then forced to move into the interstitial fluid and then and then as it dilutes the salt it that water then moves back into the Vasa recta which again is the capillaries that are surrounding that Loop of henle so we remove salt
• 33:00 - 33:30 actually on the ascending Loop or the ascending branch of the loop of henlee it super concentrates the medulla of the renal pyramid which draws the water out of the filtrate coming through the loop of henle that decreases the solute concentration within the medulla and then allows the water to be moved into the Vasa rectum and so we therefore reabsorb that water
• 33:30 - 34:00 and it kind of looks like this all right so step one all right here's step one this is the ascending Branch right here all right the salt the sodium chloride has a higher concentration here in the ascending Loop than in the surrounding uh renal pyramid and so that salt is
• 34:00 - 34:30 moved from this area of low concentration I'm sorry from this area of high concentration to this area of low concentration that salt just moves and as it does that it super concentrates the renal pyramid and as it super concentrates this renal pyramid it drives the water out of the filtrate coming down the descending
• 34:30 - 35:00 Loop and down into this Loop of Henley um and so then that water is then reabsorbed and then you have your peritubule capillaries that are right here this is the counter current part of it because your filtrate get a load of this is why I love this stuff hold on one second your filtrate is moving in this direction your filtrate is moving in this
• 35:00 - 35:30 direction but your peritubule capillaries I'm sorry your Vassar recta is moving in this direction so it's counter current it's counter current and it's a multiplier because you're super concentrating the sodium on the descending Branch from removing it from the ascending branch and so you're pulling that much more water out of the
• 35:30 - 36:00 uh the descending limb where the where the loop is here and you can also see that you actually constrict your diameter of the loop decreases and so this thinner Loop that's actually made of simple squamous for easy diffusion of water all right easy diffusion of water because remember you have simple squamous epithelium
• 36:00 - 36:30 all right allows for diffusion of water okay and so that water just comes right on out the vasor recta again moving in the opposite direction of the filtrate is there to go ahead and just reabsorb that water all right and so that's what you're seeing on this slide right here now you're seeing the addition of the
• 36:30 - 37:00 vasarecta right here let me just come over and so your Vasa recta is moving in this direction here's your proximal convoluted tubule down into the descending Branch down
• 37:00 - 37:30 into the loop which is made up of simple squamous and then up here and so watch Watch What Happens you concentrate you concentrate the little balls that you see there are salt all right so this is the salt and so you're super concentrating the osmolarity of the salt and then as it comes up into this ascending Loop uh it just goes ahead and just explodes outward
• 37:30 - 38:00 all right um and as you're doing that as you're doing that that salt is then being again reabsorbed and it's going into the interstitial here which is going to draw water out but it's also being sucked up and brought into the Vasa recta over here and so you go from in the vassarecta 300 millimoles of salt 600 because now it's starting to be drawn from the ascending Loop 900
• 38:00 - 38:30 1200 millimoles of sodium chloride in the Vasa recta all right at the same time at the same time you're super concentrating here in the interstitial as well which is now drawing that water out and that water is now being reabsorbed into the vasarecta up here all right and so you're super concentrating this whole area which is
• 38:30 - 39:00 forcing water this way and on this side you have a little bit of water that's moving out not much you're not losing much but you've got a lot of sodium that's coming in and being reabsorbed on this side so it's a fascinating fascinating dichotomy that happens with this counter current multiplier you're just it's it's efficient um and it's it's really simplistic and ingenious in how we use the molarity to
• 39:00 - 39:30 go ahead and drive the osmosis and so um there's a again a short video uh that is on that uh all right secretion spend a few minutes talking about that I promise We're Not Gonna belabor this too much
• 39:30 - 40:00 um but tubular secretion um happens in Reverse so we're going from the capillary inch back into the filtrate uh and so that's just in case we have excess waste that has now been removed and reabsorbed and we need to balance it out a little bit more um and so what are some of the things that might be included in that urea and uric acid that we would have accidentally reabsorbed through solvent drag in the proximal convoluted tubule you might have some more ammonia in
• 40:00 - 40:30 there catecholamines epinephrine uh norepinephrine um um and dopamine right prostaglandins which are inflammatory hormones uh creatinine once again you might have more acid-base balance that needs to go on within the blood and so you might be secreting um hydrogen ions if the blood is too acidic or you might be secreting
• 40:30 - 41:00 bicarbonate ions if the blood is too basic and so um you have all of that that's happening within again this is primarily within the distal convoluted tubule um the other thing that will be secreted in the distal convoluted tubule are drugs um and so any kind of medication that you may be taking even if it's Tylenol or aspirin the
• 41:00 - 41:30 metabolites of those will be go ahead and we'll be uh gotten rid of within the distal convoluted tubulin added to the filtrate we Define this as renal clearance every drug has a renal clearance or a rate by which the drug will be filtered out using the kidneys and this is why sometimes drugs have to be taken or medications have to be taken three or four times a day because of that rate of renal clearance
• 41:30 - 42:00 and So within the within the distal convoluted tubule um hormone regulation again aldosterone which we've already talked about helps in um salt uh reabsorption or retaining so
• 42:00 - 42:30 it's a salt retaining hormone so we're going to go ahead and we're going to keep that salt uh again secrete it back into um I'm sorry try that again um aldosterone is salt retaining and so that's going to reabsorb it from the filtrate back into the vasarecta and again that typically happens in the distal convoluted tubule and we know that that happens in response to a drop in pH
• 42:30 - 43:00 all right because that's going to drive water reabsorption once we get into the collecting duct atrial natural uretic peptides is a hormone that's secreted from within the heart and that causes the excretion of excess salt all right so if you have too much salt in the blood you'll go ahead and you'll get rid of that and so that's the secretion hormone ADH we already know uh
• 43:00 - 43:30 antidiuretic hormone um when it is secreted reduces uh or I should say uh it reduces the amount of urine that is produced all right so it causes for water reabsorption if we inhibit ADH then we go ahead and we can actually increase the rate of urine production and uh parathyroid hormone also has some regulatory effects here in the distal
• 43:30 - 44:00 convoluted tubule all right again here's another little video here for you for you to go ahead and kind of review reabsorption and secretion within the distal convoluted tubule you got a pretty little diagram here for you that kind of uh summarizes for you uh where reabsorption and secretion is happening and what exactly is moving and
• 44:00 - 44:30 where and then the collecting duct and really it is the lower end of the collecting duct that is actually in the renal pyramid where we're going to go ahead and see water reabsorption uh occur and again this here just kind of summarizes everything force a little bit
• 44:30 - 45:00 more on these two slides here and you have those slides in the PowerPoint and so that brings us to the end of the urinary system and so I encourage you to go back and review this jot down questions that you may have we can bring them into our uh class time and feel free to ask um questions all right for clarification
• 45:00 - 45:30 and so with that um happy studying happy happy reviewing um happy thinking and uh I will see you guys on the flip side