Okay. So let's dive into the reabsorption in the distal tubule and the collecting duct, which, in my opinion, is the coolest type of reabsorption. Though, one thing to note is that reabsorption in the proximal tubule and the nephron loop tends to occur at a pretty constant rate. Now, it just kind of is what it is, but the distal tubule and the collecting duct kinda shake things up a little bit. The reabsorption in these locations actually varies depending on your body's need. So, there are actually 4 main hormones that can influence the rate at which certain substances are going to be reabsorbed within our distal tubule and our collecting duct. So I always think of these as kind of like our little urine customization sections of our nephron where, like, you know, maybe your body needs a little more water to be retained. They can handle that. Maybe you have to get rid of some salt. Maybe you have to reabsorb some calcium, you know, who knows? Your distal tubule knows, which is like so cool, right? So we're gonna go over these 4 hormones and we'll talk a little bit about what they each do. So first up, we have our old friend aldosterone. Remember him from the renin-angiotensin-aldosterone system mechanism. So this is our salt-retaining hormone, remember, and it's going to increase the rate of sodium reabsorption. So it's making sure that sodium is leaving the filtrate and getting put back into the blood. And this can actually create an osmotic gradient that will also increase water reabsorption via osmosis. Remember that from the renin-angiotensin-aldosterone mechanism. So the aldosterone itself specializes in salt retention and salt reabsorption, but it can have the indirect effect of more water reabsorption as well. So if you look at our image here, number 1, I'm gonna label this as aldosterone flora. And you can see we've got sodium channels over here on the apical membrane. We've got sodium potassium pumps here on the basolateral membrane, and a whole bunch of sodium reabsorption is going on in that image there.
Alright. Next up, we have our atrial natriuretic peptide or ANP. And this is basically the opposite of Aldosterone. So it's going to actually reduce the rate of sodium reabsorption. Which just means that sodium is going to be staying in the filtrate and it will end up in the urine. So if you look down at our image, you see number 2. We have our atrial natriuretic peptide there. I mean, we've got all these little sodium ions just hanging out and they're not really doing anything. They're not getting reabsorbed. They're just kinda sitting in that filtrate and they're gonna end up in the urine. And I always remember that this one deals with salt because I look at that NA in natriuretic, and I think NA means sodium. So that's how I remember that one.
Next up, moving on from sodium, we have an antidiuretic hormone or ADH. And an antidiuretic hormone is pretty intuitive based on its name. So it's going to reduce the volume of urine by increasing the rate of water reabsorption. Of course, a diuretic would put more water into the urine and it would increase urine volume, and so our antidiuretic is doing the opposite. It's helping us reabsorb water, and then it's reducing the urine volume, through that reabsorption because it's all ending up back in our blood. So looking at our image on number 3, we have our antidiuretic hormone, and you can see we've got little aquaporin here, and they are helping water get reabsorbed and put back into the blood.
And then finally, we have our parathyroid hormone or PTH, and this will be stimulating calcium reabsorption specifically in the distal tubule. So if you look down at our last image, we have our parathyroid hormone, and you can see we have all of our little triangular calcium ions there and they are getting reabsorbed and put back into the blood. Alright. So those are kind of the 4 main hormones that work in our distal tubule and our collecting duct, and that is how they kind of customize our urine which is so neat, Alright. So I'll see you guys in our next video. Bye bye.