hi everyone and welcome to chapter 14 on osmo regulation as you can see here osmoregulation has a lot to do with the kidney and urine formation so before we go into the actual osmoregulation parts we really need to know how is uriform and urea is a major component in actual urine okay how the kidney and the nephron structure is like and then only look at the mechanism of excretion kidney and based on that talk about osmo regulation so there are a few uh topics here to talk about yeah so anyways let's talk about excretion first now the idea of exclusion is really the removal of unwanted products of metabolism that if not removed will be toxic poisonous and will cause damage to tissues now the main excretory products here besides urea is actually carbon dioxide and this is something you have learned already now we learned that carbon dioxide is actually a product of aerobic respiration and um how is it excreted it's not true the kidneys right like urea but more of the bloodstream and the lungs now this is a as sort of information you can refer to chapter 8 to check out how carbon dioxide is transported out from respiring cells to the lungs via the bloodstream think hydrogen carbonate ions think carbon amino hemoglobin anyways that's carbon dioxide here we really like to focus on urea which is a nitrogenous waste form in the liver from excess amino acids and then the liver will process that and then it will be excreted via the kidneys through urine okay so it is urea but as um this is only one of the few nitrogenous waste this is just the main nitrogenous phase actually there's two more that you just need to know the names of briefly number one is creatinine which is also nitrogenous waste but only produced from certain amino acids it's most of them is used in energy storage in muscles and very few of it very little amount of it is excreted by other kidneys so that's creatinine the next one is uric acid which is also a nitrogenous waste it is produced from excess purines of nucleotides i don't know if you realize but urea creatinine your acid are all produced in the liver and excreted via the kidneys through urine but you can forget about creatinine and uric acid a little bit and let's just focus on urea as we said is the main nitrogenous waste in the body it is formed from excess amino acids so excess protein from food will be broken down in the liver and converted to urea now how does that work step one is deamination so here we can see a structure of the amino acid okay this is chapter two stuff you should remember this there's a central carbon and it's connected to a hydrogen group a hydrogen atom sorry an nh2 which is an amine group a carboxylic acid group as well as an r group okay the first step is deamination and the idea is to remove this amine group and a hydrogen atom from the amino acid forming ammonia ammonia is toxic to the body it will be toxic if it's allowed to accumulate so in the urea cycle aka the argentine cycle okay i'll just stick to your real cycle because that's easier so ammonia is toxic right so in the ural cycle ammonia gets converted to urea with the addition of co2 so nh3 plus co2 carbon dioxide will be converted into urea and then this product will then be excreted through the kidneys now what remains here the carboxylic acid group the r group here in the central carbon is that it becomes something called we call keto acid it can be respired or converted to glucose and then respired or converted to storage molecule in the form of glycogen and fat so you can see here this amino acid one the amine group becomes ammonia and the rest of the stuff becomes keto acid now before we go on to how urine is excreted exactly using the kidney it gets in the urine let's talk a bit about the structure of kidney and how it works so this is a kidney here you can see the main arteries going in it's called the renal artery so think renal as anything related to kidney so when you see the white renal it's anything made of kidney think urinal but without the u and spelled with e so renal artery supplies blood into the kidneys and renal vein removes the deoxygenated blood what comes out of the kidney is the urethra the ureter brings the urine out from the kidney to the urinary bladder and then the urethra would take the urine out from the urinary bladder so when the urinary bladder is full when your blood is full there will exert a slam pressure and you will need to go pee and the urine comes out from the urethra that's the general idea so kidney ureter goes down to the bladder which is the bottom here comes out through the ueetra focusing back on the kidney and the internal structures of it so the kidney has a few layers the entire outside layer is called capsule it's a tough protective layer for the kidney inside the kidney there are three main regions the cortex the medulla and its pelvis cortex sounds like cover so it's on the outside medulla sounds like middle which is in the middle and then at the base of it is called a pelvis now in the cortex and medulla in between them okay spanning here and this area right here there are tiny tubes called nephrons and this is the functional unit of the kidney there are many many of these nephrons in the cortex and medulla which looks something like this let's look at each and every part of the nephron starting with the bowman's capsule the woman's capsule looks like a little cup here okay there is another name for it renal capsule again we know is anything to do with the kidney and then it goes into the proximal convoluted tubule so these are all tubes yeah so the tube is called proximal convoluted tubule proximal means close by like in proximity so it is it comes first right after the moment's capsule after that we have the loop of henle and then um the distal converted tubule the loop of henle is two parts okay it's subdivided into a descending limb which is the limb that goes down and the ascending limb then only digital convoluted tubule this is a converted tubule starts with the word distal which sounds like distance which means it's the second one that comes after super family okay proximal distal proximal comes first right after that there is a collecting duct which extends into the medulla and is connected to the pelvis where a urethra is present okay so again bowman's capsule proximal covalent tubule the loop of henle this tubule and the collecting duct make sure you familiarize with this structure before you move on the next thing i want to point out to you is the presence of this blue line right here as we said just now nephrons are present in the cortex and medulla it actually spans across both of them this blue line here is a boundary of where the cortex ends and where the medulla begins so everything above this line is in the cortex so moments capsule the cortex proximal convoluted tunes on the cortex and this will convert the tubule into the cortex by the medulla there's a loop of henle and the collecting duct now this is actually a simplification of the structure of the nephron real nephrons probably look more like this not exactly but more so it's cubes that are windy and there's also capillaries that go in there now now um we did say that in the kidney there is a renal artery right now the renal artery is going to be branching out into different efferent arteriole efferent a comes first before e so we they got efferent efferent arterial carries the blood and um branches out into a tangle of capillaries called glomerulus you hear this word a lot global rules is actually capillaries inside the bowman's capsule so all the capillaries inside is called glomerulus after that it part the blood would go into the efferent arteriole okay efferent arterial so e starts after a so it comes after right so efferent dominus efferent and after that it actually goes into a network of blood capillaries we already have a particular name for them but you can see that they are actually surrounding the rest of the nephron so actually almost every part of the nephron is very close in proximity very close in distance to capillaries why this is so that whatever nutrients or whatever useful substances that are in the urine can be returned into the blood very quickly and whatever waste products that have not been filtered out can then enter into the nephron and become and be excreted via urine so the proximity close distance between capillaries and the tubes really really help anyways these capillaries they also supply some oxygen to the cells there some of the blood will become deoxygenated and this would connect to a branch of the renal vein so yeah that's the structure of a nephron now let's look at some pictures of the cortex and try to spot the nephron so it's very hard to spot the distal tubule actually and the other tubes but it's a very easy to spot the bowman's capsule because it has this like cup like structure and if you cut it because this is a transverse section uh you will see something like this this white area here is the bowman space so it's inside the moment's capsule and then this bunch of random stuff inside is actually the glomerulus which is the network of capillaries inside that cup okay or moment's capsule you can see woman's capsule again here and here and here and here and all these round things that are arranged rings these are all tubes very nice the ones that are longer we can identify them as a distal distal converted tubule or the proximal converted tubules one of them because this is the cortex right so it has to be one of them so yep this might be um this can be a question in your structured questions they can show you a picture of this and ask you to identify the bowmen space so it's good to know and finally we can talk about the mechanism of excretion in kidneys now if you're not familiar with the structure of the nephron yet it's probably a good idea to pause and go and memorize the names now okay pause but if you have already not memorized names let's talk about mechanism right now so in general there are two stages in general one is ultra filtration and the other is selective reabsorption ultra filtration is the filtering of small molecules including urea out of the blood okay so filter everything out at the moment's capsule and then selective reabsorption is where all the useful molecules in the fluid let's say glucose that is not used amino acids and other useful molecules can be reabsorbed from that fluid the rest of the stuff that is not re-absorbed will end up in the urine so two stages ultra filtration and selective reabsorption let's talk about ultra filtration first ultra filtration again is the filtering of small molecules including urea out of the blood in the glomerulus okay so remember ultra filtration happens in the bowman's capsule which is the little cup here glomerulus is a blood capillaries in the cup in the bowen's capsule now there are blood it's capillary so there are blood inside there okay and um all the other stuff besides the red blood cells white blood cells will become filtrate and pass into the woman's capsule space okay or the lumen of the woman's capsule and then end up flowing along the entire nephron method so this is the first stage before we talk about the process of things we need to understand the structure so this is a zoom in picture of and the um bowman's capsule so you can see here caffeine lary and natalia so this is the endothelium layer of the glomerulus between that there's a basement membrane and portal sites here actually make up part of the bowman's capsule okay so let's start by practicing cutting them down one by one breaking them down again so blending gumballs is separated from the lumen of the woman's capsule okay lumen is here on this side of the cell this is the blood they are separated by three layers one is the endothelium layer of the blood capillaries so here are the anatomy layers is one cell thick okay these are capillaries they have actually a lot of gaps again capillaries remember they have gaps between the cells so that substances can pass through the next one next layer is the basement membrane basin membrane actually is made out of collagen and glycoprotein so a lot of protein and cup protein there it actually acts as a main selective barrier or filter so this is actually the filter that stops some substances from passing through it's selective means it's semi-permeable number three okay the third layer here is the podocytes which are actually epithelial cells of the moment's capsule the final layer before it reaches the lumen of the moment's capsule it is a linear inner lining okay and actually these cells wrap around the capillaries of the glomerulus what does this mean okay so what's the name actually prototypes actually mean feed cells cells we feed pod means feet like food f-o-t like kaki okay so um these prototypes actually have all these legs and you can see here it's called food processors and these food processors are actually really long and wrap around so like wraps around if this is capillary it's gonna wrap around the capillary like this my fingers are those food processors you see quite interesting we have a picture later on don't worry now they have many finger-like projections or the proper term here is food processors that forms gaps and filtration slits later on in order for the filtered substances to get into the lumen so as mentioned there are three layers again that is the endothelial of the blood capillaries the total cells there's a basement membrane and there's a protocytes now a microscope image will look something like this whoops right we have again this is the capillary here you can see a red blood cell hanging out here um you can see one cell take endothelial layer a basement membrane and a protocyte same thing here capillary lumen this is a neutral cell a basement membrane and a protocyte in a bowman's space same thing here and this picture here is just to show you how the prototypes actually wrap around the capillaries of the glomerulus so yeah that is how the structure looks like so what actually happens how is the structure adapted adapted for ultra filtration so as we mentioned just now there are actually many large gaps in the capillary and the thorium and there's also filtration slits between food processors of the podocytes and these gaps are there for a reason it is to allow substances to move from the blood into the bowman capsule lumen so this is the lumen here in beige okay there is one secondly you need those large gaps you also need some pressure and this pressure is due to the diameter of the arterioles interesting right so as i said the efferent arterials come first afferent arterial has a bigger lumen than the efferent arteriole so diameter of the lumen of afferent arterial is wider than efferent arterials this leads to a pressure difference it leads to a very high hydrostatic pressure in the glomerulus itself therefore forcing the fluid from the glomerulus from the capillaries here into the bowman's capsule so some gaps some pressure the next one is a filter a filter is needed now what's the filter needed for is to prevent certain things from passing through so regular cells white blood cells and large plasma protein that has the molecular mass of above 68 000 deltons this is a unit for mass those things cannot pass through so it won't end up in the global ruler in the bowman capsule lumen what is in the lumen or become well it will be um soluble molecules such as water amino acids glucose urea inorganic ions including sodium potassium chloride ions uric acid creatinine which are another nitrogenous waste and some vitamins so everything except no cells and no large proteins with pressure with the gaps and with the basement membrane as a filter this glomerular filtrate will pass through the gaps and into the renal capsule okay or the bowman's capsule and result in the renal fluid this fluid here containing all this will be passed on to the proximal convoluted tubule where the next stage will happen selective reabsorption okay so selective reabsorption is a necessary process to reabsorb essential substances from the filtrate we filter everything out now we need to reabsorb back what can be reused okay back into the blood just a reminder that blood capillaries are very close to all these tubes so that scientific absorption is really much easier now what are scientifically if we absorb for example there's glucose amino acids there are vitamins that can be reused as well as ions and water and this occurs throughout the rest of the nephrons let's talk about what happens at the proximal convoluted tubule first this is the first place that the government lura filtrate ends up after the bowman's capsule okay so before we go into any further let's give you a little introduction about the pct now pct is actually the main site for glucose or amino acid reabsorption as well as vitamin chlorides it also is the main site of water reabsorption but this is not shown in diagram here walls are actually made out of single cuboidal epithelial cells which you can see here looks something like this now all the diagrams i'll show you will look something like this again reminding just a reminder that again the tubes are very close to capillaries so you will see here there's a lumen okay it's the inside of the tube this is the outside of the tube this is a pct cell and then right next to that is a capillary so imagine an endothelial layer endothelium of the capillary here and the blood going inside so when you want to reabsorb stuff okay like glucose and amino acid you really want it to come out from the lumen and go to the bloodstream but of course this is a levels it ain't gonna be so simple but there are three steps which are not that complicated okay so let's look at step number one to get glucose from the lumen of the proximal tubule into the bloodstream the first step here is actually active transport of sodium ions this is done via a sodium potassium pump as you can see here and this pumps sodium ions from the pct cell into the blood and capillary okay so there's a sodium potassium pump here pumping the sodium from inside against the concentration into the outside into the bloodstream now this causes the sodium ion concentration to be lower in the pct cell and higher in the bloodstream the b c cells concentration is also lower than the lumen so there's a concentration gradient that is the second thing that happens as a result of that is that sodium ions in the pca lumen will diffuse into the pct cell why concentration is lower here so this is diffusion down its gradient but when it diffuses into the cell okay there's actually a special protein involved it's called a core transporter carrier protein when the sodium ion diffuses down the co-transported protein it brings a long amino acid of glucose sodium ions are co-transported with these molecules and these molecules end up in the cell okay now it's just a matter of getting this into the blood and that's easy because we're just gonna take glucose and amino acid and they are going to diffuse down the concentration gradient again by facilitate diffusion into blood via the transport protein number one pumping uh pumping or active transport of sodium ions into the blood from the pct cells number two is the core transport of sodium ions and amino acids or glucose from the lumen into pct cell number three is the facet diffusion of amino acid and glucose down its concentration gradient from the pct cell into the bloodstream so now you can see the bloodstream what have been reabsorbed sodium ions amino acid and glucose the result that process is that glucose in the lumen of the pct is all actively reabsorbed into the blood so there's no glucose in urine at this point if you are a healthy individual amino acids vitamins and chloride ions are also actively reabsorbed in the states using the mechanism we just described water and urea a large portion is absorbed passively but um not all so just some large portion by just some uric acid and creatinine however are waste products and not be absorbed okay at all why are they not reabsorbed because they are the waste material as we just said it has to end up in the urine creatinine is actually actively secreted or transported from the blood into the lumen of the pct to make sure that all the creatinine in the blood is excreted now you might be wondering why urea is here why is urea reabsorbed isn't urea a waste material as well and you're absolutely right urea is a waste material but it will be returned into the renal fluid or the filtrate later on okay so moving on um before we move on we need to talk about the adaptations the pct cells actually have for this process we just talked about there is a few okay it's important to realize that pt pct cell again is facing the lumen one side and on the other side it is facing the capillaries on one side there is the microvilli facing the lumen which provides a large surface area for absorption and i forgot to pair this up but what happens is because there's a large surface area there's a presence of different transport proteins in the membrane for example cold transporters pumps aquaporins when there is space you can place more proteins there secondly is the high density of mitochondria again the first stage of absorption in the pct cells require active transport of sodium out of the pct cell so mitochondria is needed to provide atp there's also foldings at the basal membrane so these are the surface that is facing the blood capillaries that's high in folding for what well again always related to how many transport proteins you can put at the membrane now besides all of that there is another point here tight junctions holding adjacent cell together tight junction is actually a specialized term for a complex substance that holds the cell together so these tight junctions actually separate proteins in the front and basal membrane so the front membrane is a microvilli the basal membrane is the one facing the capillaries right proteins carrier proteins tend to diffuse laterally if you remember the fluid exact mosaic model they actually can move around if you have that tight junction okay that substance just hanging out between cells they actually separate proteins from front and the basal membrane so they don't allow those proteins to diffuse and change places which is other hydrogen also ensures that fluid cannot pass between cells freely but substances must pass through cells so the cells can regulate what's getting absorbed and what does not get reabsorbed and that's pretty much what happens in the proximal convoluted tubule and how the structure is adapted to its function now we are at the loop of henle on the loop of henle something different happens there is not a lot of glucose or amino acid reabsorption here but what is most reabsorbed here is water you will see low of henle is actually located at the medulla so it's long it cut it bears down okay um and there are two parts remember there's a descending limb and that's the ascending limb different limbs have different traits so descending limb which has this blue wall is actually permeable to both water sodium and chloride ions so it's permeable to all of that therefore it's in blue but ascending limb have different properties the ascending limb the wall is permeable impermeable sorry to water and only permeable to sodium and chloride ions so sodium chloride ions can move out but water cannot move out or in so how does this work this is slightly unusual but we're going to follow numbering here and start at the us ascending limb it will make sense later okay so slightly ascending limb so remember the ascending limb is impermeable to water and only permeable to sodium and chloride ions this is where sodium and chloride ions move out of the tube it moves out of the ascending limb by active transport so this process requires atp into the tissue fluid of the medulla space as a result of that active transport of sodium chloride ions you expect a high concentration of sodium and chloride ions in the medulla space so again loop of hennes medulla medulla is the one in the space outside here okay so high concentration and that become very important later on but right now we know that hey this also means that the renal fluid is more dilute because you have removing all these solutes right and this fluid here is that more than you you um we know fluid can then pass into the distal converted tubule and be processed further now it's important to realize that hey a longer loop here actually can result in higher concentration of solute build up in the mandular space because the more the longer it is the more surface area for this active transport to occur so more carrier proteins more active transport for sodium and chloride ions and therefore more concentrated medulla space and actually it results in more water reabsorption and results in more concentrated urine how is that let's look at the next section so as we said just now we ended a conversation with a high concentration in the medulla space now in the descending limb which is permeable to both water and sodium and chloride ion right there is renal fluid and because it is less concentrated then the medulla space outside water moves out into the medulla tissue fluid on the medulla space with typo there this is true a process of osmosis of course and this actually is a reabsorption of water so water moves out of the renal fluid which will eventually become urine into the body also sodium chloride ions and as well as urea okay this is where the urine diffuses back diffuses back into the descending limb resulting in a con small concentrated fluid here as it moves down the loop if we look at the interstitial osmolarity which is really a measure of concentration okay don't worry about it too much this is concentration we will see that it changes in the descending limb and the ascending name so in the descending limb we talked about how water moved out right from down the water potential gradient from the inside the renal fluid to the metadata space this results in the increase in solute concentration and doesn't help that sodium and chloride ions diffuse back into the descending limb as well so this results in a higher concentration of fluid as we go along so here is 300 but after a while it's 12 is 1200 i mean 1200 here so you can see here at the base there is a highest solute concentrated concentration the renal fluid is most concentrated at the base of the loop but as it moves up the ascending limb sodium and chloride ions are being removed and moved into the medulla space so you can see here that renal fluid again decreases in solid concentration and increases in water potential but by the time the renal fluid passes through the acidic limb a lot of the water has already been reabsorbed and cannot diffuse back into the snail at all so i hope you understand now how this works and why a longer loop of handling will result in more concentrated urine because the longer it is the more salts can be ions can be transported out of the ascending limb resulting in more concentrated medullary space more water will be removed from the descending limb resulting in less volume of water in the renal fluid overall so we're done with the pct we're done with the loop of henle what happens at the dct the distal convoluted tubule and this is surprisingly easy why because it separated the two okay the first part of the dct is pretty similar to the loop of henle more water is reabsorbed whatever um the second part of the city is similar to collecting dark so it doesn't really have much in um much unique features okay half of it half of it inside the cotting duck the only difference is that there is potassium ions and hydrogen ions and urea that is reabsorbed from the blood sorry what we absorb but remove from the blood and move into the filtrate or the renal fluid moving on to the collecting duct the cooling duct is located in medulla it moves down here right and at this point after so much processing and selective absorption tissue fluid of the medulla has a very high concentration of solutes this is also because more water is reabsorbed at the collecting down okay so this here the clogging duct and the desoto tubule is where we can finally talk about osmoregulation which is our main point here the rate of water reabsorption is actually controlled by adh the anti-diuretic hormone so let's talk about respiratory regulation and how it affects the collecting duct it all starts at the hypothalamus so also regulation as you know is a control of water potential of body fluids the stimulus okay so we're using negative feedback mechanism here the stimulus is when the water potential of the blood is low there's a change in water potential the receptor which are osmore receptors at the hypothalamus can detect this water potential decrease and therefore the hypothalamus will be able to synthesize adh okay how does it do this they have something called neural secretary cells your secret cells sends a nerve impulse to posterior pituitary glands so if you don't know what i'm talking about this is the brain your hypothalamus is the center of it center of it is connected to this little butt right here called the pituitary and there is a anterior pituitary and a posterior so the one in front the one behind so at first it's the hypothalamus okay neural secretory cells here sends enough impulse to the posterior pituitary glands these are very important terms hypothalamus produces the adh the posterior pituitary actually releases it into the bloodstream where does it go that's in your brain it will go through the distilled converted tubule or the collecting duct of the kidneys what is the response and what occurs at the kidney exactly so what happens is the adh which was secreted from the posterior pituitary gland of the brain it actually binds to receptors on the plasma membrane of the collecting duct okay this is a common tubule half of it functions like chlorine that that's why the name is here so at the adh binding receptors on plasma membrane okay so imagine this is blood binds to receptors and this actually cause a series of enzyme control reactions remember adh is a hormone and remember in last in a s chapter four you learn about how an enzyme cascade works so radiation hormone binds to receptor it activates an enzyme cascade you don't need to know the details here just the enzyme cascade happens and this actually results in the production of an active phosphorylase enzyme this enzyme will cause the vesicle containing aquaporins which are carrier protein channel proteins for water to fuse with the plasma membrane on the lumen side so you can see here the vesicle containing those proteins move fuse and result in more aquaporins residing at the lumen side of the collecting duct the result is increased membrane permeability so adh will increase the membrane permeability of the colliding duct this increases water reabsorption as the medulla is very concentrated with a lot of solutes right we've established that previously so more water moves out of the cotton duct into the blood into the medulla space around it so as a result smaller volume of more concentrated urine is produced all this water is returned into the body therefore water potential of blood increases and returns to the norm or set point that is when the water potential is low in the blood all right but what if there is an increase in water potential of the blood how does the cells decrease the water potential then so when there's an increase of water potential in the blood osmo receptors are no longer stimulated everything happens in reverse neurons stop secreting adh alcohol problems move out of the cell surface membrane back into the vesicles in the cytoplasm so that's interesting everything moves in reverse cutting dark is less permeable in water and therefore more urine is produced more dilute urine is produced as well so that there is a decrease of water potential in blood resulting a return to the set point or norm you realize that the term return to set point or norm happens and occurs a lot as long as well as the terms used to describe a negative feedback mechanism because these are the main key words so here's a summary of what went down in the nephron the moment's capsule there's ultra filtration remember that capillaries in there are called glomerulus the specifics of this process is pretty important the proximal tubule the main process here is the reabsorption of glucose and amino acids mainly there's also the reabsorption of water but it's a passive process look of henle mostly the reabsorption of water and salts caulking duct is mostly involved in osmoregulation and water reabsorption actually is very affected by the hormone called adh that is produced when the blood pretend water potential is low so water is reabsorbed in back into our blood and therefore more concentrated urine is formed the distilled tubule here is half half half like the loop of henle half hydrocollecting down all these processes of reabsorption is called selective reabsorption you can watch this video down here if you would like to hear another voice repeat the same concepts to you now the next slide is a graph that also acts as like a little summary of what is re-absorbed where so you can see the x-axis is different parts of the nephron and on the y-axis is the concentration of these different molecules so why is glucose amino acids decreasing so rapidly in approximately convoluted tubules this is because glucose amino acids are reabsorbed there in the loop of henle water moves out in the descending limb and in the ascending limb sodium and potassium a sodium and chloride ions move out sorry not potassium so water move out resulting in increase in concentration but when sodium ions and chloride ions move out this causes a decrease in concentration and a more dilute renal fluid urea on the other hand increases in concentration constantly because it's always a waste product you can see that all these curves are increasing especially right at the end here in the dark and this is due to water reabsorption so this these waste products become even more concentrated in the urine so that's pretty much it for this video i hope you learned something it is a little confusing at first but after a while it makes a lot of sense so i'll see you next time bye