hi welcome to our quick discussion of the body cavities the body itself is the ultimate cavity it's filled with cells and tissues and organs they all have a specific job or function to keep the body running and working well but when we look inside the body it's not just one big open sac with all the organs crammed in there the body is actually very well organized it's separated into smaller compartments that we call body cavities and these body cavities or compartments each house specific organs this is kind of like your house right think about your house you have this nice strong wall that forms the outer barrier for your house provides a lot of protection maybe it keeps the good stuff in and it keeps the bad stuff out now when you go inside your house there are typically additional walls that separate the house into separate rooms and each room has its own designated function for example in the bathroom you go to the restroom or shower in the kitchen you cook food right each of those separate compartments has its own separate function now in the body again it's the same way we see the outer barrier of our body but if you section the body and look inside you'll see that there are smaller barriers or walls that divide the body up into body cavities now there are multiple functions of the body cavities the most obvious of these is that if the body cavities provide protection for our organs if there are additional or extra walls surrounding the organs that are frequently tough in nature fibrous and strong and that provides extra protection for the organs inside for example will see that the chest cavity here is called the thoracic cavity and there's this strong wall that surrounds the thoracic cavity it has bones like the bones on your ribs right that's your thoracic cage and there are muscles layered there provides a strong wall or barrier around to the thoracic cavity to protect the organs that are inside the body cavities also gives the organs space it gives the organs the room that they need to change in size and shape as they function if you imagine if we just had all of our organs crammed in here and we just let them all sit the organs would all drop down towards the bottom and hables wash each other everything would be able to squish together and it they wouldn't be able to function because many of our organs actually change in size and shape as they work for example think about your heart um the heart's job is to contract right to squeeze and that pumps blood through the body if you've ever seen a beating heart for example like on a TV show or on the internet the heart moves quite a bit as it contracts and beats it needs space to do that if all of the other organs were just cramped all around it it wouldn't have the room that it needs to contract so it has its own little space its own cavity that gives it the room it needs to function the lung is for example as the lungs inhale or pull air in and then exhale to push air out that is intimately related to changes in the size and shape of the body cavities we have multiple organs that change size as they fill and empty the stomach for example the stomach stretch is quite a bit as we put a meal in it right we don't eat little tiny bits of food all day long we don't graze all day we sit down and we eat a nice sizable meal well when we put that meal in the stub the stomach expands or stretches out it needs space to do that can you think of another organ that stretches and expands as we fill it up the bladder may be right we can hold a lot of urine in the bladder at one time but that means that the bladder needs space to expand as it fills with that urine so body cavities provide protection for our organs and if they give the organs the space that they need to function properly when we look at body cavities as well as the organs that are inside of them we see that the cavities and the organs are lined by what we call serous membranes a membrane is like a lining in serous membranes specifically are very thin smooth linings that have the ability to produce fluid so these serous membranes will align the body cavity and the lined organs that are inside and they produce a serous fluid and they fill the body cavity they fill the space that surrounds the organs with serous fluid now this fluid is important because it provides lubrication as the organs move we don't want them to be rubbing up against the body wall or the cavity wall in generating friction if you rub your hands together you know really fast your rub against your I'm really really fast it gets hot very quickly and it starts to hurt you start to wear away at the tissue so imagine an organ like your heart it beats all day every day for your entire life if it was generating friction every time and tracked you would damage the heart tissue very fast so having these really smooth slick moist membrane and having this lubricating fluid serous fluid surrounding the organ allows for the organ to slide and glide against the cavity wall without generating any friction now when we look at these membranes there are different serous membranes lining each of the cavities and associated with each of the organs the three serous membranes that we'll look at are the pericardium the pleura and the peritoneum the pericardium is the membrane that's associated with the heart now when you look at that word pericardium you can see cardio in the middle and if you think back to chapter 1 where we learned word roots you guys should note that the root cardio means heart so pericardium is the membrane that's associated with the heart surround the heart the pleura is the membrane that's associated with the lungs and the peritoneum is the membrane that's associated with the abdominal organs or you could say the digestive organs now each of these membranes the pericardium the pleura and the peritoneum each of them has two layers there are two layered membranes the two layers are called the parietal layer and the visceral layer so that means there's a parietal pericardium and a visceral pericardium these two layers are they're named according to whether they're lining the the organ itself or they're lining the body cavity the cavity wall so the parietal lair this is the outer layer the layer that's lining the actual cavity wall then the parietal layer curves inward and it's continuous with the visceral layer the visceral layer is the inner layer that lines our covers the actual organ itself if this sounds confusing don't worry just go with me I'm gonna show you a lot of examples as we go so we're gonna go through all of the body cavity is now and as we go through the cavities we'll look at the organs that are in each cavity and the membranes that line the cavities when applicable so the body cavities are kind of like you know those those nesting dolls where you just see you know one wooden doll and you open it and then there's a smaller one and you open that and there's a smaller one and you open that and there's a smaller one the body cavities are kind of the same way so the body itself is like the ultimate cavity but then when we look inside we see that the body is divided up into two smaller cavities the dorsal cavity and the ventral cavity and then if you open those you see there are even smaller cavities right you open those and there are even smaller cavities you get the point so first we're gonna look at the two large body cavities that are present the dorsal cavity and the ventral cavity from our directional terms you guys should know that dorsal pertains to the back remember on like a shark or a dolphin the dorsal fin is the big fin that sticks off of the back the one that you see is sticking up so dorsal pertains to the back so the dorsal body cavity is the cavity and it runs down the back it starts up here in the skull and then continues down the vertebrae though the bones that form your spine down your back so all of that circled everything in orange is the dorsal body cavity now the dorsal body cavity can be separated in two smaller cavities which you see here the dorsal cavity includes the cranial cavity and the vertebral cavity now cranial cavity you see up top here cranial refers to the skull so the cranial cavity is the cavity within the skull now what organ do you think is inside the cranial cavity hopefully you said the brain the brain is inside the cranial cavity now the membranes that surround the brain are a little bit different than the other membranes the membranes that surround the brain are called the meninges and we'll talk about those a lot more at the very end of a semester when we talk about the brain but the meninges are the the membranes that surround the brain specifically the cranial meninges the vertebral cavity you see going down all of the vertebrae you there's a hole in the center of each of the vertebrae and the holes all line up to create like a canal that goes up and down the back inside the vertebral cavity we have the spinal cord the spinal cord is very similar to the brain and the membrane that surrounds the spinal cord we also refer to as meninges there are multiple layers we refer to them as the meninges but in this case it's the spinal meninges so the dorsal cavity includes the cranial cavity which houses the brain and is lined by the cranial meninges the vertebral cavity houses the spinal cord and that's lined by the spinal meninges that's it for the dorsal body cavity it's pretty simple the ventral body cavity on the other hand is quite a bit more complex so we'll spend a lot more time talking about the ventral body cavity ventral remember refers to the belly side right the front side of the body the ventral body cavity includes everything you see over here so all of these other colors here everything essentially in front of the spinal cord urn in front of the divertible canal you have the ventral body cavity now the ventral body cavity is divided into top or superior and bottom or inferior portions and it's divided by the diaphragm the diaphragm is a huge dome shaped muscle it was a big muscle that kind of curves like this and it almost completely separates the chest from the abdomen there's only a couple little things that go through the diaphragm it's a really big muscle that separates that the top of the ventral body cavity from the bottom of the ventral body cavity everything above the diaphragm is in the thoracic cavity the thoracic cavity referre is what we would refer to as the chest cavity he it's all of this stuff that's inside your ribcage so in purple in this picture here you see the thoracic cavity in a second will look inside the thoracic cavity and will look at all of the other stuff that's inside for now just understand that above the diaphragm is the thoracic cavity below the diaphragm is referred to as the abdominal pelvic cavity in the picture here you see two subdivisions or two parts of the abdominal pelvic cavity the top of it is the abdominal cavity that's what you see in pink the bottom is the pelvic cavity that's what you see in green but the whole area together right all of this that's below the diaphragm is all together called the abdominal pelvic cavity and you see where the name comes from right abdominal pelvic because it's abdominal and pelvic alright guys so we're gonna look in more detail at the thoracic cavity or the chest cavity remember that the thoracic cavity is the area above the diaphragm so if you look at this picture down here this tissue this is all showing you the diaphragm so it's a big dome shaped muscle that forms a big barrier between the chest cavity and the abdominal cavity the thoracic cavity is all of this so all of this tissue up here about the diaphragm is included in the thoracic cavity and then when we open up the thoracic cavity we'll see that it's got numerous cavities within it it's separated into multiple other areas so we'll start by looking at the pleural cavities inside the thoracic cavity on either side so on the outer sides there's a right and a left pleural cavity and these pleural cavities house the lungs so the Wrights pleural cavity has the right lung the left pleural cavity has the left lung and down here again the picture you can see the the lungs themselves so this here is the right lung this one over here is the left lung keep in mind that right and left are always the subjects right and left with the patient's right and left not yours so like when I look at this I have to go crisscross in order to get the patient's right and left you'll notice that in between the lungs right here you guys see the heart in a second we'll look at the heart in the pericardial cavity but right now we'll focus on the lungs on either side remember that the lungs and the pleural cavity has a membrane present and that membrane is called the pleura these words pleural cavity and pleura are very similar to each other so don't mix those up pleural cavity pleura when we look at the pleura the membrane remember that there are two layers there's a visceral layer that's actually on the lungs and then there's a parietal layer or an outer layer that's lining the actual egg body wall so let's look at the way that those kind of work the visceral pleura again is the layer that's actually on the surface of the lungs forgive my terrible drawing but this is supposed to be lining the lungs right so that would be in green the visceral pleura and then that visceral pleura curves around and continues as an outer layer called the parietal pleura you'll notice that they leave a space between them make the visceral pleura and the parietal pleura there's a little bit of space between them it's shown in light blue on this picture and the space right here that's the actual pleural cavity that's the actual space that the lung has to function also you'll notice that that's filled with fluid remember we said that each of the cavities is filled with serous fluid and that that fluid provides lubrication in this case because the fluid is in the pleural cavity we call it pleural fluid if you look over here at this picture the the pleura the membranes aren't shown but you can kind of imagine the visceral pleura would be coating the surface of the log itself so it's a really thin delicate layer that covers the entire surface of the lung and then the parietal pleura comes out and it lines the body wall and then in between them is where we have the space or a nice coating a nice layer of pleural fluid moving on in the thoracic cavity we said that on either side of the thoracic cavity we have the pleural cavities in the lungs the area in between the lungs right the area in the middle is referred to as the mediastinum or mediastinal and just look at that word right look this first part here it looks very similar to the word medial and if you remember from your directional terms medial is towards the midline of the body the mediator number mediastinum is the area in the middle right along the midline so this area here in between the lungs is referred to as the mediastinum now the superior mediastinum which superior is like the top has a lot of kind of random structures passing through it and then the inferior portion or the bottom of the mediastinum houses the pericardial cavity so let's just really quickly talk about the superior mediastinum and then we'll talk about the pericardial cavity in the superior portion we have a lot of really large blood vessels that are going in and out of the heart because the heart remember is right down here so there's large vessels like this is the superior vena cava dumping blood into the heart there's the aorta which is a huge artery bringing blood out of the heart all of the big vessels that are attached to the top of the heart are present in that superior mediastinum the trachea is also present the trachea is the windpipe or the airpipe that brings air down into the chest the esophagus passes through the esophagus is a tube that brings up food from the throat down to the stomach the thymus is also present the thymus is a lymphatic organ where some of our immune system cells go to mature so there's structures from all different body systems we've got the cardiovascular system the respiratory system the digestive system and the lymphatic system so a lot of kind of randomness then in the inferior or the bottom portion of the mediastinum we have another body cavity the pericardial cavity again cardio means heart so the pericardial cavity is the cavity around the heart so again the heart is located within the pericardial cavity and you guys know that there should be another serous membrane here and the serous membrane is called the pericardium the pericardium just like with the the pleura the pericardium has two layers the visceral layer and a parietal layer if you look here this picture you can see the heart itself in the center and then there's this layer that's kind of peeled back that's showing you the parietal pericardium so this anthers there's also a strong fibrous pericardium that forms like the strong part of the sac but don't worry about that right now we'll do that in anp2 when we do cardiovascular so this right here again we're pulling back the parietal pericardium and then the visceral pericardium is a really thin delicate layer that's actually on the surface of the heart if you look at this picture here you can see the way that the two layers are associated with each other again the visceral pair Guardium is the inner layer that actually touches the surface of the heart and then that curves around to form the parietal pericardium and that's the one that's gonna be lining this strong like the strong wall that's protecting the heart you'll notice the space between the two layers is the pericardial cavity and what do you guys think we fill this space with you think it's empty filled with air solid fat what hopefully you guys said that that is filled with serous fluid or in this case we could call it pericardial fluid and what is that fluid there for lubrication now we're gonna move down below the diaphragm and remember below the diaphragm we have the abdominal pelvic cavity so above the diaphragm is the thoracic cavity below the diaphragm is the abdominal pelvic cavity now the abdominal pelvic cavity is then further separated into multiple cavities on the next slide we'll see the abdominal cavity and then the pelvic cavity but within the abdominal pelvic cavity there's another kind of like sub cavity or another like sac that's covered or surrounded by a serous membrane we refer to this area as the peritoneal cavity so the peritoneal cavity is a chamber within the abdominal pelvic cavity now the peritoneal cavity goes through most of the abdomen and then it dips down and goes through part of the pelvic cavity but it doesn't cover it doesn't include every organ that's present in the abdomen or the pelvic cavity the peritoneal cavity is associated with the serous membrane again called the peritoneum and that has two layers so the parietal peritoneum is the outer layer that lines the body wall so that's lining the internal body wall like the inside of our our abdominal wall where your abs are where your your abdominal muscles are the inside of that abdominal wall is lined with the parietal peritoneum then the parietal peritoneum curves around informs the visceral layer the visceral peritoneum is the inner layer that actually covers the organs themselves right so this lines the organs that are present in the peritoneal cavity and this includes a lot of different digestive organs or organs that are part of the digestive tract like the intestines for example this visceral peritoneum actually forms something called the serosa and the serosa is the outer most layer of the GI tract that I just subtract now of course this is only present in parts of the digestive tract that are down in the peritoneal cavity so parts of the digestive tract like the esophagus for example that's up here in the thoracic cavity so that does not have this visceral peritoneum or serosa present now I said that the peritoneal cavity does not include all organs in the abdomen there are some organs in the abdomen and in the pelvis that are not included in the peritoneal cavity this space that's present behind the peritoneal cavity is referred to as the retro peritoneal space retro is in behind or posterior to the peritoneal space the peritoneum so this retroperitoneal space again the area posterior to are behind the peritoneum and anterior into the muscular to the muscular body wall so this is like saying be high into the peritoneum and in front of the muscular wall the back of the back so let's look at this really quick this picture right here this is the front of the body okay so like this is the belly your abdominal muscles and this is the back of the body so these this body wall these are your back muscles the peritoneal cavity is in the front so all of this in yellow this is all showing you the peritoneal cavity again there's a lot of digestive organs in there a lot of your digestive tract is present in that peritoneal cavity but notice that the peritoneum right the membrane that surrounds this does not go all the way back to the back right it stops and then all this back here this entire area in the back that's the retroperitoneal space that's the space that has some organs that are not included in the peritoneal cavity so for example the pancreas the kidneys which are in your lower back there your readers these are the tubes that carry urine down into the bladder some parts of the digestive tract are located retroperitoneal a writer behind the peritoneal cavity in this picture that we were just looking at these for example are your kidneys so you notice that your kidneys are located right up against the muscular butt wall of the back-pay and they're in the retroperitoneal space they're outside of the peritoneal cavity in this picture here don't get confused because it's kind of flip-flopped this is the front of the picture right here these are you excuse me these are what you can see is like your dominoe muscles right in the body wall comes around and then you've got these back muscles back here so this is the back you can see the this shows you a little bit better it shows you like kind of the space of the peritoneal cavity so there's the layer the the parietal peritoneum that lines the body wall and then it curves in and the visceral layer covers the organs in themselves so the visceral layer it's kind of complex like as it um as it wraps around so wraps around here the visceral layer rubs around here and then you notice the space in between those two layers so all this space there's space this space that's all the peritoneal cavity the area back behind the peritoneal cavity so this is retro peritoneal when you look at this picture over here the peritoneal cavity is like inside this red line so you see it covers most of the stuff in the abdominal cavity and then it drops down and it covers some stuff down in the pelvic cavity but not everything now the abdominal pelvic cavity we said could also be separated into the abdominal cavity cavity and the pelvic cavity and these are a little bit easier to understand than the peritoneal cavity the abdominal cavity the abdominal portion is that superior or the top portion of the abdominal pelvic cavity it's from the diaphragm which remember the diaphragm was this big dome shaped muscle so the abdominal cavity extends from the diaphragm down to the top of the pelvic bones or the top of the hippos so with all of this that you see in light blue that's the abdominal cavity and it contains most of the digestive organs so the organs involved in digestion would include things like the stomach most of the small intestine the liver the pancreas parts of the large intestine Hey most digestive organs are present in the abdominal cavity just the very end of the digestive tract goes down into the pelvic cavity the pelvic cavity then is just the inferior portion or the bottom portion it's the area that's located within the pelvic bones or within the hips and this contains the reproductive organs so and men this would be like the prostate gland the seminal glands and women this would include things like the uterus and the ovaries it also includes the rectum the rectum is the very end of the GI tract so this is like the last five inches or so of the GI tract where the feces or poop goes before it exits the body and then also the urinary bladder where our urine is stored alright guys that is it hopefully you are super comfortable with the body cavities our next discussion will go ahead and talk about some other ways that we can divide up the abdominal pelvic region thank you so much shoot me an email if you have any questions