Alright. Let's dive into that renal tubule. So you can see in this image on kind of the upper corner of your screen, we've kind of faded out that renal corpuscle. We already know all about that. We've also faded out this limb over here on the right. We're going to learn about that very soon. And what we are focusing on here is this winding tube that makes up the majority of our nephron, and that is our renal tubule. What we are seeing here is basically a very zoomed-in image, looking at the renal tubule that is all color-coded. And we're going to go through what each of those color-coded segments is in this video. So the renal tubule is a winding tube that basically modifies filtrate. And it does that by either conserving or eliminating certain substances. And we're going to talk about the physiology of this tube a ton in upcoming videos. So for now, we're just going to be talking about the anatomy of it. So our renal tubule has 3 main regions, and they each have a unique structure and function. So, first up is our proximal tubule. And proximal just refers to this being the initial or the first segment of our renal tubule. You can see that segment over here in purple. I'm going to label that as one for us, and the proximal tubule is located in the renal cortex.
Now, the proximal tubule is a bit unique because it contains prominent microvilli. And those microvilli are really important because they basically increase the surface area of the proximal tubule, which allows for a very high volume of filtrate to be modified very quickly. And that is important because about 65% of filtrate modification happens in this little tiny part of our tubule, this little purple part. So it has to be very efficient at what it's doing. And those microvilli really help with that. So that is our proximal tubule.
Next up, we have our nephron loop, and the nephron loop is this entire U-shaped loop in our renal tubule. And so our nephron loop is located in the renal cortex. It's always going to start in the renal cortex, but it can dip down into the renal medulla as well. And the nephron loop is divided into 2 limbs, and each limb does have a distinct function. So first, we have our descending limb, which you can see here in green. I'm going to label that as 2a for us. And this is the part of the limb that is basically traveling toward the renal medulla. And then we have our ascending limb, which you can see here in orange. I'm going to label that as 2b. And this is the part of the nephron loop that is traveling toward the renal cortex. And we'll talk about the unique function of those in upcoming videos as well.
And then finally, we have our distal tubule. So this is the final segment of our renal tubule, and you can see it here in blue. We're going to label that as 3 for us. And this is also located in the renal cortex. So typically, our distal tubule and our proximal tubule are going to be about level with each other, approximately. Now, one last structure of note in our renal tubule is the macula densa cells. So the macula densa cells are a group of densely packed cells. So densa literally just means dense here. And they are basically going to be located at the transition point between the ascending limb and the distal tubule. So what we are looking at in this image is basically this location over here. So right where that blue distal tubule is meeting that orange ascending limb of the nephron loop. And you can see, we have our kind of, slightly prominent densely packed, macula densa cells here that we've done in green. So those are the macula densa. And what these cells do is they're going to monitor the sodium chloride content of the filtrate. And that is going to actually play a role in regulating filtration rate as well as blood pressure. And we're going to have a whole video talking about how that happens as well. Alright. So that is our renal tubule, and I will see you guys in our next video. Bye bye.