In Isolation – Large Intestine

by James Pickering, PhD

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    00:01 So here we have got the diagram of the large intestine which has been removed from the abdomen. We are looking at in the isolation. Again we can pick up the ileocecal junction and then we can see food, the indigestible parts of food, is going to be running in this direction. We can see now the various parts really clearly.

    00:21 Inferior to the ileocecal junction, we finally have got the cecum. Attached to the cecum we find this blind ended pouch, which is the appendix.

    00:31 And then above the ilocecal junction we find the ascending colon, remember this is heading up towards the liver so we have the right colic flexure also known as the hepatic flexure which we can see here. So liver would be positioned around about in this direction. So there would be where the liver is. So we have the hepatic flexure. Then running transversely from right to left we have the transverse colon heading towards the spleen, so here we have the spleen and so that would be the splenic flexure. And that's where the transverse colon now runs down this left side. It descends down this left side of the abdomen as the descending colon.

    01:13 Descending colon continues with the sigmoid colon, so descending colon with the sigmoid colon which is continuous with the rectum.

    01:22 The sigmoid colon travels towards the midline, so starting in this left inguinal region, the sigmoid colon migrate via the sigmoid mesocolon, it's a mesentery. It passes through the midline where that is in continuous with the rectum. On here, on this diagram, you can see there is a whole series of external features.

    01:44 And that's what we can explore in the next slide. This is just the small section of large intestine specifically the colon really that we have removed.

    01:54 And we have opened up a window, and we've reflected these flaps.

    01:57 Now what we can see on the large intestine are features that can distinguishable from the small intestine. Now you should be able to notice the small intestine by it's location. It sometimes throughout life various things can happen and the position of organs in the abdomen can become distorted. But here we can see there is a series of distinguishable features that make the large intestine standout from the small intestine.

    02:28 We have, what are known as taenia coli. These taenia coli here are bands of longitudinal muscle. When we looked at the small intestine we saw that the longitudinal muscle that went in the same direction is the small intestine. When there was the complete band that went all the way around be like my sleeve completing covering the small intestine running in this longitudinal direction. But for the large intestine you only have three bands this is incomplete sleeve. You just have three bands that are going around, going alongside the large intestine and these are called taenia coli. Now because these contract, they create these pouches or haustra. And as these muscles contract they have to shuffle the indigestible, the faeces along the large intestine and the constriction of these taenia coli, these three bands of longitudinal muscle create these pouches which we known as the haustra. We have three taenia coli which we will, three different types of taenia coli which we will explore in the next slide.

    03:40 And here we can see we also have some omental appendices or appendices epiploica. And these are just fatty tags that are attached to the colon. You don't find them in the small intestine. They are just attached to the large intestine. These peritoneal sacs that are filled with fats, these omental appendices. If we open up the large intestine we can see that where we have these kind of pouches, the constriction of these pouches on the inside leads us to what we knows as the semilunar folds.

    04:14 And that gives us the appearance internally of these regions where the taenia coli longitudinal bands of muscle have in-fact shortened the large intestine somewhat.

    04:27 We can see if we returned to taenia coli that we have three types of taenia coli. We have the taenia coli which is known as the omental taenia.

    04:35 And this the part that attaches to the greater omentum. So the greater omentum hanging down from the transverse colon will actually be attached to the omental taenia. The mesocolic taenia is where the transverse mesocolon attaches to. So the transverse mesocolon is coming up from the posterior abdominal wall in-line with the pancreas.

    05:01 And it passes up towards the transverse colon and it attaches to the transverse colon where this taenia is, where this mesocolic taenia is located this specific band of longitudinal muscle. The greater omentum extends from the omental taenia coli band. And then the final one is this free taenia coli which doesn't have any omental or mesocolon attached to it.

    05:27 And here we can see we have got some details of what I just explained. We have got the three different bands of taenia coli: the mesocolic, the omental, the free.

    05:38 We have got these longitudinal bands of muscles creating these haustra, the sacculations and internally creating these semilunar folds.

    05:47 And also I mentioned the small fatty tags, these omental appendices.

    05:51 Another clear way to distinguish the large intestine from the small intestine is it's greater diameter. The greater diameter compared to that of the small intestine So apart from the obvious position of the small intestine, you should be out to work how, where the large intestine is and due to this inverted "U" shape around the lateral aspects of the abdomen. Also via these three clear distinguishable features.

    About the Lecture

    The lecture In Isolation – Large Intestine by James Pickering, PhD is from the course Abdomen.

    Included Quiz Questions

    1. Villi
    2. Three bands of tenia coli
    3. Haustrations
    4. Omental appendices
    5. Semilunar folds
    1. Omental tenia
    2. Haustra
    3. Omental appendices
    4. Mesocolic tenia
    5. Free tenia
    1. Ascending, transverse, descending and sigmoid
    2. Transverse, descending, ascending and sigmoid
    3. Sigmoid, transverse, ascending and descending
    4. Descending, transverse, sigmoid and ascending
    5. Sigmoid, ascending, transverse and descending

    Author of lecture In Isolation – Large Intestine

     James Pickering, PhD

    James Pickering, PhD

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