 Let's draw a picture of the renal corpuscle. First of all, renal rener, renal corpuscle equals glomerulus, capillaries, plus, and I apologize profusely for this, because I can't do anything but Bowman's capsule, even though I'm supposed to call it the glomerular capsule. The glomerulus, this is just easier for me. So Bowman's capsule is the nephron piece. The glomerulus is the blood piece. Together, they make up the renal corpuscle. The renal corpuscle is where filtration occurs. It's where blood and nephron come together to allow filtration, so that's why it's significant. Really? And you can commit this to memory. This is the only place where filtration occurs. Filtration only happens from the glomerulus into Bowman's capsule. How? Why? Well, there's a couple of... We'll look at the mechanics of filtration in the next section, but the anatomy of this is extremely important. First of all, let's talk about the glomerulus. Glomerular capillaries are not normal capillaries. They're called fenestrated capillaries. And basically, it just means that they're holy. They're holy capillaries. They're leaky capillaries. They have fenestrations or slits in them or holes in them. They're like leaky colanders, which isn't normal. If all of your capillaries were as leaky as the glomerular capillaries, you really would be like a giant blueberry of swollen edema. So thank you for that not being the case. They're fenestrated capillaries that are surrounded by Bowman's capsule, and it also has some unique characteristics. Remember how I showed you Bowman's capsule looked like this? It had the two layers, and anatomy humans know that this is the parietal layer of Bowman's capsule, and this would be the visceral layer of Bowman's capsule. And the visceral layer is tight because it is not of fenestrated capillaries. So the visceral layer of Bowman's capsule is unique, and I have to draw it for you. This is how my brain works. Learned something new about me every day. I'm drawing the cells of the visceral layer of Bowman's capsule. They're normal. They're not normal. They're epithelial cells. However, they have these bizarre, they're called podocytes. The cells are called podocytes, and they've got these pedisols that reach out. Like, here's my nucleus, and I'm not very excellent at drawing these. But do you see how they've got... Okay, let's label these. This whole thing is a podocyte. And this part is a pedisol. And these podocytes are like squished on top of my glomerular capillaries, my fenestrated capillaries. But here's the cool thing. The podocytes interdigitate. What? Okay, look, because I don't think I can explain that. Here's another podocyte, and it's little... Okay, this looks like an extremely spastic starfish. Okay, look at my interdigitation. That's what I'm trying to show you. The pedisols interdigitate, but there are spaces in between. And deep in here, like, I'm just going to put a little smiley face in there, that's the glomerular capillaries of fenestrated leaky. Really? Okay. I'm calling it good, except I'm going to show you a picture that actually is what I'm trying to explain to you right here. So look at this. Yay. See, there's my podocyte. See all those little interdigitated little pedisols. And see how they can... Here's another podocyte with its little pedisols that are interdigitating. And this is covering... The podocytes are covering the glomerular capillaries. See, if you cut in there, you can see that there's a capillary in there and there's blood cells in there. But there's spaces in between. This isn't like the blood-brain barrier where astrocytes are covering the capillaries and creating an extra layer of stuff, a barrier between the blood and the brain. It's not like that. There's lots of spaces. Combine that with the fact that the capillaries themselves, look, you can actually see holes. In this picture right here, you can see holes in the walls of these capillaries, which is indicating the capillaries are fenestrated. This was my visceral layer of Bowman's capsule. Here is my parietal layer. You get a very nice sense of this space. This is a space in here. And we're going to filter into this space. Now look, who's this? Proximal convoluted tubule in the house. And that's... you can see that my filtrate, whatever I can collect in Bowman's capsule, can then proceed into the lumen of the proximal convoluted tubule. Why do we care? We care because the fenestrated capillaries plus these weird pedestals create a very leaky environment. Out here, the parietal layer of Bowman's capsule, that isn't leaky. It is simple squamous epithelium, but it isn't leaky. It's going to allow... It's going to collect the fluid that we filter out. Okay, are you ready to talk about filtration? There are some significant concepts there that are important. Filtration coming up.