 Hey everybody, Dr. O here. In this video, we're going to talk about the peritoneal cavity. So just like the pleural cavity, which we talked about with the lungs and the pericardial cavity with the heart, this is going to be a double layered cavity, one of your ventral body cavities. So that's going to be this blue-green or green structure that you see here. So the peritoneal cavity is going to be made up of the visceral peritoneum, which is right on the organs that envelopes the organs themselves and the parietal peritoneum which lines the cavity, the abdominal wall here. And between those, you're going to have that watery cirrus fluid, quite a bit of it, there's going to be a larger space here than the other ones, and that's going to reduce friction. So as your internal organs are moving around, as materials are being moved to your GI tract, there's no friction and there's no pain. So that's going to be, so the lubrication is still the primary function here. But a couple more things. Number one, you'll notice that not all these structures are actually inside this greenish peritoneal cavity. So during embryonic development, some structures stayed behind this peritoneal cavity. The key ones you can see here are going to be the kidneys and the pancreas. Those would be the two key, what are known as retroperitoneal organs. But if you want the complete list of the structures that are either completely or partially behind the peritoneal cavity or retroperitoneal or outside of it anyways, it would be the duodenum, the first portion of the small intestine. We said the pancreas already. So those are going to be structures that would be considered completely or partially retroperitoneal. These kind of structures though, they're going to be basically held in place by some other tissue or else attached directly to the posterior abdominal wall. Because these structures have to stay still. And that's why another very, very important term is the mesentery. So the double layers, so we said each of these layers of peritoneum is already two layers. But if you double that up, you're going to see that the peritoneal cavity that you double that up, these double layers of peritoneum that are in your abdominal cavity called the mesentery, they're primary job. They're actually anchored to your spinal column and they're going to anchor almost all the small intestine. That's very, very important. You have this long tube inside of you. Think about what happens if you throw your phone charger in your bag, it's all knotted up. The mesentery is this double layer of peritoneum that's holding your intestinal contents, most importantly, the small intestine in place. So they don't just all fall based on gravity. They don't get all knotted up, leading to potentially fatal bowel obstructions. All right, so that's the peritoneal cavity. But I would say most importantly is this idea of the mesentery. And then lastly, why some of your structures are going to be called, some of your organs are going to be called retroperitoneal. I hope this helps. Have a wonderful day. Be blessed.