hi everybody and welcome back to miss Angler's biology class I am Miss angler in today's video we are going to be looking at the Loop of Henley and its role in maintaining osmo regulation in the kidney we are going to focus specifically on structures and how they do their jobs but if you are looking for the sodium potassium pump explanation that is in a separate video because it requires a little bit more detail than I'm going to include in this introduction to how the loop of Hindi does its job now if you are new here don't forget to give this video a thumbs up and make sure you are subscribed because I post every Tuesday and Thursday for grade 10 to 12 Life Sciences if you are in grade 11 and you're thinking about improving your marks before exams and tests you should also think about getting a copy of my cheat sheet study guide which is available on missangler.co.za it covers all the years worth of work it makes learning and studying so easy and easy to remember for those exams so let's get into the video now and I want to just recap some of the things we've already gone over starting off with the nephron which we're looking at right now in previous videos we would have covered what happens over here in the glomerulus which is glomerular filtration we then also had a video on the proximal convoluted tubule where we looked at um reabsorption of nutrients and now what we're going to focus on is this region down here the loop of Henley and the loop of Henley has a really important process called Oslo regulation but before we get into osmoregulation there's a couple of things I want to explain to you first so that you understand them really really well now to fully understand osmoregulation or the regulation of water in the loop of her name we actually need some diffusion or osmosis knowledge and we need to unpack the word osmolarity because I'm going to use it quite regularly through this explanation and I need you to understand what it means so essentially when we talk about osmolarity we are talking about these solutes which in this case is often salts and how many there are dissolved in the liquid in other words does it have a high solute and if it has a high solute that means it has high osmolarity so that's how those two things work together and so osmolarity refers to the solute content now if we use this little diffusion diagram below um touching in on our grade 10 knowledge what we look at here is we've taken some dye and we have dropped it into a beaker of water now this region over here where there is a lot of dye particles this is technically an area of high osmo clarity in other words the there is a high concentration of our dye molecules versus this area over here which would have a low osmolarity now why is this important to know high and low osmolarity well through the laws of diffusion and osmosis substances are always going to move from a high to a low and we can see that in the second diagram over here our dye particles are slowly diffusing throughout the space until eventually they equal a dynamic equilibrium or it basically means that we have an even distribution of water to die now how does this factor into the loop of Henley well the loop of Henley runs on osmolarity in other words making water move depending on where the solute concentration is now the other thing that we must remember when we speak about osmolarity is when we talk about the water Movement we talk about it as osmosis and osmosis is water moving passively the thing is water moves passively but solutes don't move passively they move actively in other words they need energy to move now we are going to talk more about this active movement in the sodium potassium pump instead we're going to just focus in on the general idea of how we move water out of the loop of henle using the idea of osmolarity that solutes are going to try and distribute themselves and they're always going to move from a high to a low now one other thing that we must not forget that we also learned in grade 10 was the words hypotonic and hypertonic and so I'm just going to go over them again if a solution is high per tonic what that means is it has a high amount of solutes and a low amount of water now together this indicates to me that the osmolarity is high how do I know it's high well osmolarity remember is linked to the amount of solutes so if there is a high amount of solutes there is a high amount of osmolarity if a solution is hypotonic this means that there is a low level of solutes and a high level of water and we would describe this situation as being a low osmolarity now that we have a basic understanding of what osmolarity is we can now apply it to osmo regulation now osmoregulation is the way in which the loop of Henley regulates how much water but also how much salt is in the bloodstream and so we've got to remember that when we talk about osmoregulation we're not just talking about regulating water we're also talking about regulating salt now some Anatomy breakdown on this Loop of henle is that the left hand side of the loop of Henley is what we call the descending limb which is the side that's going down and on the right hand side here we have the Earth sending limb which is the side of the loop of Henny going up and so essentially what's happening is the filtrate is entering at the top here and exiting on the other side on the earth ending bit now for me to explain osmolarity and what's actually happening very well here I'm going to use some numbers to try and explain what's happening I want you to know that these numbers are not specific they are arbitrary I'm I'm making them up so that I can explain this idea to you so what are these numbers well let's say the filter enters at the top of the tube here and the filtrate has a concentration level of 300. what does that represent that represents the osmolarity of the filtrate of the fluid it starts off at 300 and as we go down it becomes 600 then 900 and in the middle here it is now 1200. now this represents the concentration and you'll notice it's getting more concentrated the main thing I want you to take away from here is that I'm not adding any extra salts to make it more concentrated I'm actually taking water away so what's happening is water is leaving the loop of Henley as we go down until we get to the bottom here when it's at its highest point and water is leaving and this is because the descending limb of the loop of Henley is permeable to water now what does that mean permeable be forgotten permeable means substances can move through it now water is permeable which means it's leaving and the only way I can describe this to you in like a everyday example would be like imagine you made a glass of oros juice you put too much water in now you want to take the water out hypothetically that is actually possible where you can take the water out and you can make it more concentrated again you would do this by like dehydrating the the concentration removing the water now that means the descending limb is permeable to water but it is not permeable to salts in other words salts cannot leave or solutes cannot leave on the descending limb so that means as the filtrate moves down through the descending limb its osmolarity is increasing it's getting higher now to fully understand this we need to also know one other important piece of information and that is that the loop of Henley is actually divided into two zones the left hand zone is permeable to water and the tissues around the loop of henle they are high per tonic whereas the solutions on the right hand side are high pose tonic now again this is important to know because if you've learned anything from grade 10 you will know that solutions that are hypertonic are high in solutes Schultz in this instance which is going to attract the water out of the loop of Henley so that it will enter the surrounding tissue on the other hand on the earth sending side we have a solution that's sitting around the loop of Henley that is hypotonic now because it's hypotonic it means the water levels are high and the salt levels are low now this is where it gets interesting when we look at the ascending limb the limb that's going up in the loop of Henley we will notice that the numbers start to decrease again and by quite a lot now what's interesting on this side is we are now actually not moving any water this time round we are actually moving solutes or salts so what's coming out on this side is going to be all of your solutes like sodium and chloride potassium they are all leaving on this side of the loop of henle and that is because the ascending side of the loop of Henny is permeable to salts but it is not permeable to water now this is very interesting and I know you're probably sitting here thinking okay so one side lets water out and the other side let's salt it out yes that is what is happening now why do we do it that way well we have to maintain a concentration gradient we always have to be moving water from a high concentration in the tube to a low concentration outside the tube into the surrounding tissue and eventually into the bloodstream now the only way to do that is to consistently put salts out of the loop of Henley so what I'm saying is where we drew here in green these are all the salts that are leaving and they leave so much so that even on the other side they start to drift into this area over here and now this area here becomes salty and this area here and all around here becomes salty hence the description of hypotonic and as we learned before water goes wherever salt goes so if the area is salty water will follow I want to also say that this section is very difficult and there is a lot of moving pieces to osmoregulation what we are going to do in the upcoming video for sodium potassium pump is I'm going to go over this again and actually show you how does the salt get out of the tube that then makes the surrounding tissue salty which then attracts the water I'm going to clarify that for you so if you're still not so certain I suggest you go on to watch the that video next now as always I like to finish off my lessons with a terminology recap and you can use all of these terms to create flashcards with starting off with the terminology around the actual physical structure of the loop of hilly we have the descending limb and the ascending limb the descending limb is the limb that is going down and the Earth sending means it's going up it is important to know that it's not just about the names but also what happens in each remember in the descending limb we are going to absorb water only back into the blood whereas the Earth sending limb is only going to be able to absorb salts back into the surrounding tissue and in doing so it allows for water to then also leave as well now speaking of salt and water we can't not speak about osmolarity osmolarity is the amount of solutes that are in a liquid in other words it references the concentration and osmolarity is really important when it comes to maintaining the water level in the bloodstream particularly in the loop of Henley osmolarity is linked to osmoregulation because if there is a high osmolarity in the blood which means the blood is very salty we need to put more water out of the loop of Henley and back into the bloodstream speaking of that the only way we are able to get blood into the bloodstream is through permeability and something that is permeable means it allows substances to move through it remember earlier that the descending limb is permeable to water but not to Salt whereas the Earth sending limb is permeable to Salt but not to water because they have opposite functions the one limb allows the other limb to do its job much better why because wherever salt goes water follows which brings me to the word osmo regulation it is the regulation of water through salts and a lot of people don't understand that you have to regulate the salt first before you can regulate water it's also important to go and watch my video on how ADH and aldosterone function as they are the two main hormones that regulate water and regulate salt and those videos are already up on my playlist last but not least the words hypotonic and hypertonic hypotonic refers to a solution that is low in solutes but high in water hypertonic means that the solution is high in solutes but low in water now if you like this video don't forget to give it a thumbs up and make sure you're subscribed because I post every Tuesday and Thursday and I'll see you all again soon bye