Large Intestine in Isolation

00:01 So let's now have a look at the large intestine really in isolation and look at any distinguish or features that we can really have to differentiate the large intestine from the small intestine. And it couldn't be relatively straightforward. The large intestine by it's very name is much more substantial than the small intestine. But it does have some key standout features. One of them is here, these little fatty tanks which we call epiploic appendages and these really are just fatty tanks, the little accumulations of fat in little packets of peritoneum that are coming off the structure of the large intestine here.

00:36 We also have 3 bands of longitudinal muscle. Now, all over the colon we have circular muscle that goes around it in a circumferential manner. But here we also have longitudinal muscle, but it's not a continuous layer. It splits into 3 very discrete bands and you can see one here; the omental taenia which is part of the greater omentum. So the greater omentum which we'll talk about in a moment or two is coming off the transverse colon in this green position. We also have the mesocolic taenia which is on the more posterior aspect of the colon and this is where the mesocolon attaches to the large intestine. You also in blue have 3 taenia and this is really where no omentum or mesentery is attached to and is essentially just a free-forming longitudinal band of muscle. The natural constriction, the basal tone of this longitudinal muscle leads to what are known as haustra. These are the punchings that you can see within the large intestine. And then by opening up the wall of the large intestine, we can see the various folds, those semilunar folds. So here if we have a look at the taenia coli in a little bit more detail, this is the free one. So on the left hand side, you can see the anterior view. On the right hand side, the posterior view. Other thing it's worth getting to hang up on these necessarily but it is important to recognize their location both in these different views. So you can see here highlighted in blue the various aspects there of the free taenia. So this is the location of the free taenia coli of the large intestine. So this doesn't have any attachment of the mesentery or the greater omentum. If we then move on to the omental taenia, this is where the greater omentum comes from. We can see it very much in this anterior view, a right lateral and the left lateral view. We can bring up the locations in which the omental taenia are located. And this is the position where the greater omentum would come from. So this is the attachment site of that greater omentum, but again it is highly variable and most of the times you'll see it coming from the aspect around the transverse colon. The final one that we mentioned is the mesocolic taenia and this is what helps to suspend parts of the large intestine to the posterior abdominal wall. And again, part of it is very much based on some embryological remnants here because during embryology the large intestines actually push laterally on this ascending and descending parts and it fuses with the posterior abdominal wall. And the only really free mobile parts of the large intestine is the transverse colon And the only really free mobile parts of the large intestine is the transverse colon and this is where it's suspended by the transverse mesocolon at the mesocolic taenia in that location. So here we can then just see the rectum and we've got the recto-sigmoid junction, the continuation of the large intestine, the sigmoid colon specifically passing into the rectum. Just to remind ourselves the haustrations of the colon, these are only covered by circular muscle. So you got circular muscle going around the large intestine and then you have these 3 bands of longitudinal muscle and it's the basal tone of these longitudinal muscles that cause these haustrations to occur. You may also find at various locations typically towards the descending and the sigmoid colon, so the latter aspects of the large intestine.

03:53 You may find these diverticulum and these are kind of outpouchings of the wall of the large intestine due to increases in intraluminal pressure within the actual space occupied by the colon.

04:07 And this is thought to be considered to perhaps an unhealthy diet about as much wheat passing in. The large intestine is important in absorbing water from the ingested food and if you have a lot of wheat in your diet and that retains some of the water and it helps to aid the feces being removed from the large intestine. If you don't have a lot of wheat, it doesn't retain that water. Large intestine takes much more of the water out and you need to do apply much more internal pressure to remove the feces from the body and that can cause the slight elevations in the wall of these diverticula due to increased pressure in the luminal space. The problem with this is that it can accumulate pieces of feces and they become infected and you can have an inflammation there as well so it's important to as ever maintain that healthy diet to help protect the structure of the large intestine.