When you think about it, your body is just a squishy meat sack. You might have some muscles and bones that let you move around, but otherwise, all of human life can be reduced to fluid-filled bundles of cells. And some of those bundles do useful things and make for really fun dissections, but otherwise, there's a bunch of empty space around the body. Our bodies take advantage of those empty spaces, or body cavities, by filling them with some important, squishy organs. So today, we're going to learn about body cavities, the organs that fill them, and all the membranes that wrap up and protect them. What's up, everybody? My name is Pat Kelly, back with a new semester of videos. Super excited to have you with us today. We're talking about body cavities because I wanted to teach about the container before we teach the stuff that fills it. So the human body isn't just a meat sack, it's an organized meat sack. And learning about these cavities can help us understand what's sitting next to what during normal, healthy conditions, or maybe what's impeding something else during pathological conditions. You have a few different empty pockets throughout your body. I'd break them up into either sinuses, Or cavities. Usually these sinuses are empty. No organs, just mucus, fluid, or air. Those sinuses can fill up though, like you've felt if you've ever gotten a sinus headache, or sprained your ankle and experienced swelling in the sinus tarsi. But we care more about body cavities because of what they contain. So to get us started, I want you to picture looking at someone from a lateral view, or looking at them from the side. That's where you'll find our first two cavities. The dorsal cavity in the back, and the ventral cavity towards the front. The dorsal cavity is fairly straightforward. It holds the two important pieces of the central nervous system, the brain and the cranial cavity of the skull, and the spinal cord and the vertebral cavity within the vertebral column of the spine. Now, if our brain and spinal cord only had these two bony layers for protection, they'd be pretty uncomfortable. Kind of like how bike helmets have a hard outer shell, but they also have extra soft padding on the inside. These structures are wrapped in three layers of meninges and some liquid cerebrospinal fluid for extra protection. And that's a great feature for the dorsal cavity to have. These are very delicate structures, and you want to keep them protected. On the flip side, the ventral cavity has very few bony structures and lots of padding. This is where you'll find your lungs, liver, intestines, and reproductive organs, among others. And this less rigid, more malleable structure is a great feature to have for these particular organs. Like, your lungs change size and shape every few seconds, and your spleen can enlarge if you get sick, and, you know, a baby can start growing in a uterus from time to time. But some organs need a bit more protection and separation, so we organize again. We can divide the ventral cavity further into two smaller cavities, the thoracic cavity and abdominopelvic cavity. which are separated by the big, muscly diaphragm. When we zoom into the thoracic, we'll see two big organs and two more cavities. The pericardial cavity, which holds the heart, which is not a huge surprise considering it has the word cardial in it. We also have the pleural cavity, which holds our two lungs. Coincidentally, that's how I remembered this one, because we don't have singular lung, we have pleural lungs. Inferior to the diaphragm, we have the abdominal pelvic cavity, where we'll find all the fun stuff. Most of the digestive system and some key players in the immune system. What beginner anatomy students forget, though, is that this cavity extends all the way down into the pelvis. They know the abdomen is somewhere from rib cage to waistline, but by including the pelvis in this body cavity, we're including contents that go all the way down to your pelvic floor muscles. Finally, there are technically a few other body cavities, like your orbital cavities that house your eyes, or your oral cavity with your tongue and chompers in them. Otherwise, that's it. Those are the traditional body cavities. And with all the stuff that we need to fit into those cavities, it really pays off to minimize friction of organs rubbing up against organs. It's like a really terrible nightclub. It's dark, cramped, sticky, and you're not sure what liquid just touched your leg, but you don't like it. That's where serous membranes come in, layers of epithelial tissue wrapped around major organs that give the organs some kind of lubrication. So, each of these serous membranes will have a few different layers which contain a very small amount of serous fluid, a fluid with similar consistency to blood serum, which is where this fluid and these membranes get their name from. And they have a few different layers. Starting with an empty cavity, say the abdominal pelvic cavity, you'll want to line that with parietal membrane. Parietal comes from the word for wall. Which I remember because you'd want to decorate the walls before a party. Look, it's a stretch, but it works. Under that, you'll find some connective tissue and serous fluid, then another membrane called the visceral membrane, which wraps individual organs. Since this membrane wraps individual organs, I like to imagine somebody saying, hey, which serol is it? Visceral. These are the memory devices you're subscribed for, right? Speaking of names, depending on the cavity and the organ of interest, some of these membranes get unique names, like the epicardium around the heart or the pleura around the lungs. But each of those structures does the same thing. They either line a body cavity or an organ within it. All things considered, the heart has a similar setup to the abdomen. A parietal layer, some space for a few milliliters of serous fluid, and a visceral layer. Then, you throw on a tough, fibrous outer layer, and that's really the only additional structure. Yes, these layers get fancy names, like the visceral layer is often called the epicardium, but the structure is still similar to the other body cavities and membranes. All of those membranes wrap around heart muscle or myocardium, which is a special type of muscle tissue. But otherwise, the same concepts of layers of serous membranes still apply. You just have to put a little bit more work into naming conventions. During this video, I mentioned a few types of tissue, like epithelial tissue and connective tissue. I want to do a deeper dive into those types of tissues, so I dedicated an entire video to it, which you can click on right here. Otherwise, if you want some more basics of anatomy style videos, click on this playlist right here. Otherwise, if you liked the video, make sure to leave a thumbs up down there, subscribe if you haven't already, and make sure to hit the bell so you get notified when I post new videos. Thanks for Have fun, be good, I'll see you next time.