The digestive and excretory systems
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Kidney function and anatomy
Voiceover: The kidneys are pretty crazy. They can hold about 22 percent of your entire blood supply at any time. I've heard somewhere that you can have about 1.1 liters per minute of your blood flow through. And in a normal person, that's got about 5 liters of blood, that means that within 5 minutes all of your blood will pass through your kidneys, that's crazy. So, I think we should investigate further into how our kidneys work, and we'll start in this video with a brief overview before going into the specific parts of what are involved. So, with these two kidneys right here, we're going to take in some blood, that will come in through our renal artery and come out at the end through our ureters right there to produce urine. So, that's sort of the overview look of what we're going to be doing here, and the reason why we do this is because there are cells in our body produce waste products or change up the acidity or the osmolality of our blood. We've heard these terms before. And it's very important for us to regulate what is the pH of our blood or how acidic it is or how many osmoles we have or things that dictate where ions or water flows. And our kidneys make sure that that's at a set level. So going into the details, when blood comes into our kidneys, they enter through the renal artery, so I've got two renal arteries right here, one right there, one right there, and as you can see, it's going to go branch off and have a whole bunch of other networks that are going to be disseminated from here, and I'll talk a little more about that in a separate video. But what happens is that we're going to have filtration of our blood, and from that filtrate that comes out, we're going to process it and reabsorb some ions and water. And as we reabsorb the things that are important, we are going to collect it into our renal vein. So here are two blue renal veins right here for each of our kidneys. Our renal veins are going to take the returned or reabsorbed nutrients back into our blood and send it on its way. All right, very cool. So now we know sort of how the blood enters and leaves. Now, let's talk about the two main functions our kidneys are responsible. What are the two main functions that they need to carry out in order for us to filter our blood? So, the first function you probably guessed is filtration. We take our blood and we filter it out, so we have all our waste products and some important molecules like ions or amino acids or glucose that end up in a filtrate that then passes through the kidneys. So somethings in that filtrate, we want to get rid off, all the wasty stuff that we don't need, and so another or the second very important function of our kidneys is collection, and between these two jobs, the kidney will take our blood and put out some urine. Now, at this point, I should also mention that there is a single functional unit, and so when we talk about our functions, there is a unit that we can talk about. The single smallest functional unit of a kidney is called the nephron, the nephron, and the nephron is responsible for filtration and collection. We'll talk about some other structures in a minute that are only responsible for collection, but the nephron is charged with filtration and collection, so it's got two hats on. And the nephron is sort of situated in two parts of the kidney. The first part is sort of this outside area right here. You can kind of see that it's the shell of the kidney right, and as a shell, we call it the renal cortex. Cortex is a term you probably heard of before right. Cerebral cortex, adrenal cortex. Cortex just means the shell, so that's this light tan part on the outside. These darker parts inside right here, there is a couple of them that you can see. This is sort of in the middle and so we call that the renal medulla, the renal medulla, and medulla you might have heard of like the adrenal medulla or the medulla oblongata, it just means the middle, okay the middle, so it's inside the cortex. So, our nephron is situated between the cortex and the medulla, it sort of starts up here and squiggles around and then it dips into your medulla and then it jumps back out over here and then it dips in again. And so I'll draw that in a separate video, sort of all the separate parts of the nephron, but just understand that it dances between your cortex and your medulla. And where it's dancing determines whether it wants to reabsorb important things or allow some stuff to be collected into the urine. Now, for the collection process, we have these little tips that are kind of kissing our renal medulla, right, so these little tips right here that collect the urine in the first place, the first point that urine sort of presents itself. This is called the renal calyx, the renal calyx. And if we've got a whole bunch of these, we call them the renal calyces, the renal calyces. And so that's the first part you're going to have urine be present. There is a whole bunch of these guys that meet together and then you've got this central area right there. That central area is called the renal pelvis, the renal pelvis, and that's just where all your calyces collect together, and once you've got urine in your renal pelvis, it's going to go out this tube right here, and that's where urine is going to exit our kidneys. This tube right there is just called the ureter, the ureter, and we've got two ureters right here. That's going to send urine away from the kidneys, and as we'll talk about in a separate video, into the bladder. And now that we've talked about the ureter, this is a pretty good time to mention what these three guys make together. Whatever you've got in organ like our kidney right here, I'll sort of highlight that. That's your kidney, and then there are some things that are coming out of your kidney, these three guys right there. We call the place where we've got tubes or vessels coming out, the hilum, the hilum, and if we've got more than one of them, we can call them the hila, but we've got a renal artery, a renal vein, and a ureter coming out of the renal hilum over here. All right, and so that's the anatomical structure of our kidneys. Now, why don't we take a step back and let me make a philosophical note if I may. What's the point of the kidney even doing this? Why should we even filter and collect urine? What's the whole purpose of this altogether? Well, the kidneys are actually a very important organ for maintaining something that's called homeostasis, and you've probably heard of this term before. It's a big buzz word in biology. Homeostasis just means the way things are, the status quo, which can mean things like what the pH in your blood is. So your kidneys maintain the pH in your blood by regulating the amount of hydrogen ions that are there. It could also mean blood pressure because when you've a lot of salt ... And you've probably heard this from doctors. If you've a lot of salt intake, you're going to have high blood pressure, so your kidneys make sure you excrete the right amount of sodium and chloride ions to make sure that you don't have high blood pressure, but there are other things here that the kidney also maintains homeostasis of. And that could be things like osmolality, and of course the main thing that we're going to talk about in an upcoming video, is just the excretion of waste products of getting rid of the extra materials that we have, and one of the main waste products that the kidney gets rid off is something that's called urea. And we'll touch on urea in a little bit, but this just goes to show you how important your kidneys really are. There is a lot at stake here, and so it's very important to have these guys filtering your blood to produce urine to maintain homeostasis.
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