in the previous video we were talking about the concept of excretion together with homeostasis but I told you that um there was a particular chemical known as ammonia produced by your liver and your liver will convert ammonia into Uria and these two substances are referred to as nitrogenous wastes so even though your body has now produced UA it is still circulating inside the blood that is where the other organ comes in to remove the Ura from the body and that organ is known as the kidney in this video we are going to be just focusing a little bit on the anatomy of the kidney just a little bit not too advanced by the way but we have to focus on kidneys when we are covering homeostasis why do we have to talk about the kidney well because the kidney first carries out excretion the kidney is a bean-shaped organ and how it carries out excretion to put it very simply is They will receive blood through a blood vessel represented by the red arrow the arrow shows the blood entering the kidney and the blood going into the kidney will usually have a high concentration of Uria which is a waste product they have salts like minerals uh minerals ions or salts such as sodium ions uh chloride ions potassium ions calcium ions and such which you get from your diet and you also Al have lots of water now the problem is I told you Ura is a nitrogenous waste we have to remove it from the body salts are important like sodium ions potassium ions and such but to much of salts can also be detrimental to the body and I've also mentioned that water is important but too much of water can also cause harm it may cause your cells to swell and burst so here's the interesting thing when the blood goes into the kidney represented by the red line another blood vessel comes out of the kidney and that blood vessel represented in the blue line it will have a lower amount of Uria salt and water so where did the uh UA salt and water go to so the kidney removes that excess UA salts and water from the blood and they will form this liquid that we all know known as urine or P so urine is just a liquid or a solution that contains means water salts and UA not needed by our body anymore and subsequently we will remove the Ura from our body that's how it works so the kidney carries out excretion by filtering the blood and producing urine that's the first thing that the kidney does the second thing that the kidney also does is it helps with homeostasis what is homeostasis by the way homeostasis is maintaining the optimal internal environment in your body for example if you drink too much water a bucket of water over that that's so huge compared to the size of your body but if you drink too much water that's not good so the kidney produces more urine so you will pee more you will urinate more to remove that excess water from your body so this Returns the amount of water in your blood back to Optimum conditions but if you sweat too much the kidney produces less urine and it reabsorbs water so it retains more water inside your body so that is how kidney does both things excretion and homeostasis in reality by the way does the kidney actually just do these two functions excretion and H homeostasis in reality no the kidney also has some other extra functions but we're not going to talk about them well I guess we are not going to talk about them at all so there's no point bringing it up so moving on let's look at the structure of the urinary system the urinary system in most cases is made out of two kidneys yes there have been instances where the person is born with only one kidney or five kidneys that are quite rare news of these things happening if you see the arrow the red color Arrow where it's pointing downwards uh that one is the blood vessel going into the kidney that's known as the renal artery and the blood vessel with the arrow pointing upwards that's the renal vein that is just to represent the blood supply in and out of the kidney and another set of tubes are going downwards and that set of tubes are connected to another pouch known as the bladder so we have the kidney urer and bladder all right and if we were to take the kidney out uh and if we were to cut it into halves to see the inside of the kidney we are able to see that the kidney actually has a few sections the sections of the kidney are as follows the outermost section which is the capsule the slightly inner part cortex which is important the medula which is important and also the pelvis the reason why the cortex and medula are important is because internally a lot of important structures are running through those two layers and we will cover that in a while so in the exam usually they may give you the section of the kidney over here and they may just ask you to label those parts cortex Pula and pelvis now in terms of excretion and homeostasis the kidney has this extremely important structure and this is the one that causes the most amount of pain for students and that thing is known as a nefron a nefron is a structure that produces urine in the kidney and it's made out of a few important parts or portions known as The Bowman capsules and tubules tubules are just small tubes and if you notice the tubules I've I've blanched out the tubules by showing PCT Loop of Handley DCT and collecting that so collecting duct not duck okay but yeah um so when I use the word duck or duct you know it's just pronunciation issues anyway so what I'm doing here is I'm drawing out the structure of the Nephron in most cases in the exam they will not ask you to draw out the structure of the nefron what they're going to give you is um they'll give you the image of the Nephron and they may ask you to label it now the nephron looks like this weird looking it looks weird okay it looks like this coiled snake of sorts it does look like a weird mutated snake doesn't it um but the good news about the nephron is it has a beginning part and the ending part the initial portion or the beginning of the nefron is always represented by that cup like structure and that cup like structure structure is known as the bbman capsule all right and then we also have the second part which is attached to the bbman capsule known as the proximal convoluted tubule now I know what you're thinking do I have to memorize the full name of PCT the good news is you don't have to all right you can just call it the PCT in the exam or if they ask you to label it the word proximal just means in this this case it is nearer to the center or the um beginning of a structure so the beginning of the structure is the Bowman's capsule so proximal just means it's nearer okay to the Bowman's capsule convoluted as a word just means Twisted so as you can see that portion that it looks like you know it's quite coiled in a complicated manner tubule like I said to you is just small tubes so the proximal convoluted tubule at this small Twisted tubes nearest to the Bowman's capsule that's what it means they're not going to ask you the meaning of it I'm just explaining it is named as such then we also have the this part where it is like a u shape okay Loop of Henley and then we have the distal convoluted tubule con again tubule small tubes convoluted complicated or coiled and distal meaning to say further away from the Bowman's capsule so that's why it's called distal convoluted tub in the exam DCT is good enough and the DCT will then attach to something known as the collecting duct that's what it means so do you have to know the names of all this structure yes you do there is no ifs ends or butts about it so you know just take a deep breath and be like yeah okay I need to know this now and it's about to get a little bit more complicated one of the most important questions that I love to ask my students is this when you look at this overall structure of the nefron is it a large structure within the kidney or is it a small structure within the kidney so most students will be like uh I don't know some students will say well it's large some students will say well it's small but when you look at the structure of the kidney over here the section uh where's the nephron you don't see the ne that all do you okay you can only just see the cortex medula and pelvis now what I'm going to tell you here is you don't have to memorize this part but I'm going to tell you that each kidney usually has about 1 million nephrons 1 million of these structures are found inside each kidney so that should give you an idea as to whether the nephrons are small or large so obviously if the kidney can fit 1 million or so nephrons the structure of the Nephron is very small so in reality the nephrons are quite microscopic but of course in this case I'm just making it as slightly larger and this is how the nephrons are fitted inside the kidney so so you're like ah okay that's how it looks like I'm throwing out one nephron over there another nephron here uh I'm just drawing on as you can see we just drawing on a couple of nephrons here as follows and I'm also going to just put in the layers of the kidney the cortex medula and pelvis right so if you notice there certain parts of the nephrons are only found in the cortex certain parts of the nephrons are only found in the medula and certain parts of the nephrons are only found in the pelvis as an example as you can see over here look at the parts where I'm circling it shows you that the Bowman's capsule PCT and DCT and also part of the collecting duck are located at the cortex but the loop of Henley extends down to the Jula as you can see over there I've highlighted that in yellow however the collecting duct goes all the way until the pelvis so you need to know these parts as well because you need to know the locations they may ask you where's the in the kidney where's the Bowman capsule located then you have to say ah it's located in the cortex what about PCT and DCT they are also in the cortex Loop of henle is located usually in the uh we yes I know part of the loop of Handley is in the cortex but we always say that the loop of Handley is in the medula and the collecting duct extends all the way down to the pelvis of the kidney so this is the introduction to the part of the kidney first that we have to know