so now let's look at some body cavities and body cavities as the name implies or spaces or holes within the body and we can divide them into posterior or dorsal body cavities and ventral anterior or ventral body cavities and we're going to look first at the dorsal body cavities and we have two cavities that we're going to consider the cranial cavity which is contained within the skull the part of the skull that holds your brain is the cranial cavity so this is the cranial cavity and then we have the vertebral canal also known as the spinal cavity and it is continuous with the cranial cavity and so here what we've done on this model is we have taken the posterior part of the vertebral column and cut off the posterior part of each vertebra so that you can see inside and you can see the spinal cord and we have one vertebra here that we can pull out and we can see within at the spinal cord so the spinal cavity or a vertebral canal contains the spinal cord and if we take the spinal cord out you can see that each vertebra has a little hole called the vertebral foramen and this is the hole through which the spinal cord passes and the vertebral canal continues the length of the vertebral column and this contains the spinal cord and that's this yellow thing right here so you can see it contained within the vertebra here and so those are our two posterior or dorsal body cavities we have a few other body cavities that we can consider they're sort of minor or smaller body cavities one of which is the body cavity in which we find the eye and that's called the orbital cavity because it's contained within the orbit of the skull so this is the orbital cavity you can also see it here on the skeleton the orbital cavity and you'll find the eyes within the orbital cavity then we have the oral cavity which is contains the mouth or I should say is within the mouth we have the nasal cavity we have the middle ear cavity what you can't see here it's sort of interior but it's where you have the tympanic cavity which is part of the auditory system and this is where you have what are called auditory ossicles and these are three bones that are very important for the transduction of sound and your middle ear cavity would be contained within the temporal bone of the skull now we can look at our ventral body cavities so I'm going to go over to this model for that and really you could consider the orbital cavity the nasal and the the oral cavity on the ventral aspect because they're on the anterior part of the body but they're not part of the major body cavities when we consider the ventral body cavities proper we're really talking about the thoracic cavity and the abdominal pelvic cavity so here we have our model and we can consider first the thoracic cavity and that's everything contained within the chest so the thoracic cavity is bounded by the rib cage so the rib cage contains the thoracic cavity and the thoracic cavity is bounded on the inferior portion by a sheet of muscle called the diaphragm and that would be this sheet right here and this is a muscle important for breathing so the diaphragm denotes the lower most part of the thoracic cavity or you should say the floor of the correct thoracic cavity and all of the organs are within the thoracic cavity we then have the abdominal pelvic cavity which is everything from below the diaphragm into the floor of the pelvis so we can further divide the abdominal pelvic cavity into the abdominal cavity and the pelvic cavity and before we get into the abdominal pelvic cavity I'm going to focus a little bit more on the thoracic cavity so the thoracic cavity contains within it several other cavities and these cavities are associated with certain organs so we have our lungs in our heart here's our heart here we have some lungs and these organs are going to be surrounded by a very specialized membrane and the membrane that we're talking about is called a serous membrane so to demonstrate a serous membrane I'm going to use this freezer bag because it is a two-sided or I should say double-sided membrane if we treat it like this we can consider this freezer bag our membrane that wraps around the organs and it's called a serous membrane because it has between the two layers it has a very thin film of fluid called serous fluid and the serous fluid is important because it allows the two sides of this membrane to slide over one another and that allows there to be some freedom of movement so when we consider that an organ is covered with a serous membrane we have the inner layer of the serous membrane that would be flush against the organ and that is called me this roll layer because you can think of this rug being the organ and the visceral layer being flush up against the organ then you have the outer layer which is called the parietal layer and between the visceral and parietal layer you have this very very thin space between which really isn't a space at all it's where you find the serous fluid and this acts as a kind of lubricant to allow the two layers of the membrane to slide over one another very easily and when you consider that the fact that the heart is contained within a serous membrane called the pericardium and peri means around and cardia has to do with heart so you've heard of cardio that has to do with the heart so the pericardium surrounds the heart we have a similar serous membrane that surrounds the lung and it is called the pleural membrane and again it's a two-sided membrane that has a visceral layer and a parietal layer and between the two layers you have this very slick serous fluid which allows the layers to slide over one another and when you consider the action of the heart beating is a pump and you consider the action of the lungs inhaling and exhaling you can see that there's quite a bit of change of shape in these organs and they have to be able to slide over one another without generating friction and so this is what your membrane is important and the serous fluid is what allows that to happen now another important thing to understand is that the potential space where we find this fluid is what we call the particular cavity so what I mean by that is when we have our pericardial membranes here the pericardial space is the space between the two sides of the pericardial membrane so the pericardium is the serous membrane that surrounds the heart the pericardial space is the space between the visceral and parietal layers so when we say that the heart is surrounded by the pericardial cavity we mean exactly that we mean that the heart is actually surrounded by it not within it technically if the heart world within the pericardial cavity would be inside the bag which it is not it is surrounded by it and the same is true with the lungs so the pleural cavity is a cavity that surrounds the lung now both of these things both of these membranes can become in flames you could have an accumulation of fluid or you could have an infection inside the membrane that could then impinge upon the function of the organ or basically impede it and this is a situation that when we see it around the heart it's called pericarditis when we see it around the long as it's called pleurisy and pleurisy can be quite painful it's difficult to breathe because it feels like someone's holding your lungs so keeping the serous membrane intact and functioning correctly now while we're in the thoracic cavity we should look at this section right here which is called the mediastinum which is the central part of the thoracic cavity that contains things like the esophagus if you could see it we would have the thymus in here as well it contains the heart within the pericardium so I should put my pericardial member and the pericardial cavity but the the mediastinum itself is not a cavity it is just a collection of tissues and organs within the center of the thoracic cavity on either side of the mediastinum we have the lungs and each lung is contained within its own pleural cavity so I should say each lung is surrounded by its own pleural cavity so you have your left and right pleural cavities you have your pericardial cavity which surrounds the heart and the heart itself including the pericardium is contained within the mediastinum so these are the things that you find within the thoracic cavity and the subdivisions of the thoracic cavity now we can look at the abdominal pelvic cavity and that is everything from the diaphragm all the way to the pelvic floor so the abdominal cavity contains most of our digestive organs it's going to contain our liver our gallbladder here our stomach our pancreas our kidneys our small intestine large intestine and so forth many of these organs are also surrounded by a serous membrane and this serous membrane sort of interdigitate sand wraps around a lot of these organs and it is called the peritoneum and so if I put my stomach back in here we would see the peritoneum basically wrapping around the organs an inner did you around the organs like this so these organs a lot of your digestive organs are surrounded by the peritoneal cavity the interesting thing is not all organs are surrounded by the peritoneum we have some organs that are behind it these organs are called retro peritoneal because they're not surrounded by it but they are locked into the back body wall and the peritoneum touches them but it does not surround them in this case for example the pancreas and the kidneys are both what we call retroperitoneal and they're anterior surface here will be in contact with the parietal part of the peritoneum the cause once again they are not within the peritoneum but they are behind it organs that are surrounded by the peritoneum are called intraperitoneal organs now let's have a little bit more of a look at the divisions between the abdominal cavity and the pelvic cavity so as we know the abdominal pelvic cavity is this entire space from here to here so the abdominal cavity contains most of our digestive organs and the pelvic cavity contains the reproductive organs the rectum the bladder and so forth so if we want to look at the pelvic cavity a bit more closely we can sort of get our landmarks from this pelvis here so here we have a pelvis and you can see hello represent the iliac crest so this is the Ilia each one of these is an ilium which are make up some of the bones within the pelvis this whole thing is the pelvis now this part of the pelvis right here is called the pelvic Inlet and from the pelvic Inlet to the floor would be our pelvic cavity so everything pretty much from here to the floor once again that's going to contain most of our reproductive organs the rectum and the bladder a lot of these organs are what we call infra peritoneal because the parietal portion of the peritoneum overlies them but once again the peritoneum does not surround them so we see that the peritoneum spans most of the abdominal cavity and part of the pelvic cavity so you can find the peritoneum within both now let's sort of put everything back together again so once again our pelvic cavity is here and we can start to put our organs back now we can see here our small intestine framed within the large intestine here then we have our stomach which is going to be anterior to or in front of the pancreas here and the kidneys we also have our liver in our gallbladder that's going to be here then we're going to have our diaphragm which is that sheet of muscle that separates the thoracic cavity from the abdominal pelvic cavity and then within the thoracic cavity we're going to have our mediastinum which is going to contain the heart surrounded by the pericardium we're also going to have on either side of the mediastinum we're going to have our two lungs each of which is within its own pleural cavity sometimes putting these things back together it can be quite the task I'm gonna have to take the diaphragm out for just a moment to get the one back in there and like put this back and sometimes these models can be quite the thing to put together and take apart and I like to put our heart back in and our other long and that concludes our introduction to the body cavities