 Hello, my little cutelets. So today we get to talk about one of my favorite body systems. I'm pretty sure that every body system that I talk about is my favorite body system, but the kidneys really are like one of my very favorite body systems. Maybe good for you, maybe not so good for you. Today's conversation is going to focus on the anatomy of the kidney and not so much how it does its job. We'll save that for physio, and you will get lots of doses of how the kidney does its job. Before we dive into the anatomy, though, we kind of need to look at an overview of what the kidney does because its job is really important. If you remember, the kidneys are actually retroperitoneal. They're in the abdominal cavity, and you can see that here. You can see my diaphragm up here defining the superior border of the abdominal cavity. And you remember that the peritoneal cavity sits inside the abdominal cavity. The peritoneal cavity contains many digestive organs. Not all of them, though. And part of, for example, the duodenum is retroperitoneal, the pancreas, retroperitoneal, behind the peritoneal cavity. Those structures that are retroperitoneal are definitely included in the abdominal cavity. The kidneys are an example of that. When we look at our cadavers, if you don't remove the peritoneal cavity, like break through the peritoneal cavity, you can't see the kidneys. Like, it doesn't even look like you have kidneys. It looks like you just reached the back of the body wall, and it's just this smooth back wall. But if you go in there and kind of poke around, you'll see that the kidneys are back there, and thankfully they're back there. So let's talk about what they do. Their primary purpose, like, really, if you think about it, all of us, all critters really are just giant bags of saltwater. Now think about that for a second. I'm going to draw you. Okay. There you are. Actually, I should probably make a little mouth and a little digestive system and a little anus. Okay. But then the rest of this, all of this part that is not the inner tube, all the rest of this stuff, it's cells. And your cells are filled with salty water. Each cell is, that's the cytoplasm of the cell. And the cells are surrounded by salty water. Blood. If there's blood flowing through here, then, oh, we already know, yes, indeed, there is. And look, I'm making a little vessel right here just for the fun of it. I didn't connect my vessel to anything, which is a very bad thing. But the blood is salty water that cells are floating through. The kidneys work with the circulatory system to basically remove the garbage produced during metabolism. The job of the kidney, okay, I'm going to draw one here for you. There's a kidney. This is not anatomically correct. The job of the kidney is to take all your blood and filter it. Because as you metabolize, as you go through processes of life, you make garbage. Think about just cellular respiration. Think about the process, the cellular mechanism that results in ATP, which is the energy currency required for almost all cellular processes. Just making ATP that your muscles can use and your neurons can use and whatever, you make carbon dioxide as a byproduct. And carbon dioxide is bad news. Like if you keep carbon dioxide in your blood, you will get acidic blood. And if your blood gets too acidic, your blood, all the proteins in your system will stop working. That's a bad situation. Like let's try to avoid that. So your kidneys do all this work to get garbage out and to make sure and to monitor the qualities of this fluid that surrounds everything in your body. Okay. Monitoring qualities. Like what kind of qualities are we monitoring? The kidneys help address pH. They help maintain ion concentrations. For example, they maintain sodium ions, potassium ions, bicarbonate ions. These are just examples. We'll talk a ton about this. The kidneys help maintain glucose concentration. The way a kidney works is it filters out all of the blood and then functions to modify this. The kidneys also maintain, like, I don't know if there's a better way to say this, but the amount of water in your system, the kidneys monitor how concentrated your blood is. If it's too concentrated, the kidneys send messages that say, dude, we need more water. Let's make our blood less concentrated. So reabsorb more water from the system and maybe even go get some water and drink it. They're involved in all sorts of homeostatic processes. I think where we're going to start is we're going to look at the gross anatomy of a single kidney and then we're going to look in at the cellular pieces in our kidney that are functioning as filters. All right. Gross anatomy first. Here we go.