In Situ View – Small Intestine

by James Pickering, PhD

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    00:01 So what does small intestines look like? Well what we can see if we open up the abdomen for the first time. If you are going to the dissecting room and you open up the abdomen and you remove the flaps of anterior abdominal wall. What you met with is actually an apron like structure.

    00:19 An apron like structure which we can see here is and that's hanging down from the transverse colon. Transverse colon would come later on but that's part of the large intestine and actually dangling down from the large intestine is this apron fatty membrane which is known as the greater omentum. We will cover this in more detail.

    00:44 If however we move across onto this diagram on the other side and we have actually elevated the transverse colon and we have elevated the greater omentum we can see we have the coils of intestines.

    01:00 Now here we can't see the duodenum but we can may count the jejunum and we can may count the ileum. The jejunum move in this upper left quadrant and the ileum down in this lower right quadrant as it is continuous with the large intestine. Here we can see the ascending colon and that's going to be taking food up in this direction. So it starts up here where we have got the stomach deep to these elevated structures. And then it’s going to pass generally in this direction towards the large intestine where they are going ascending colon we got the transverse colon that will sweep down towards the rectum we will cover this later on. So we open up the abdomen in the cadaver, and the first thing you see is the greater omentum. Reflex in the greater omentum reveals the small intestine.

    01:49 So if we now look in these cartoons we can see that we have actually mobilized the small intestine.

    01:55 So we have mobilized the small intestine and we have pushed it to the right side on this diagram over here. And on the opposite diagram we can see we moved over to the left hand side and by doing that, we can still see the various features. So over here we can see the ascending colon. We can see the transverse colon and then because we have mobilized it to the right we can see the descending colon and the sigmoid colon. We will cover these in more details in more detail later on.

    02:24 But we can see where we flipped over to the right hand side, we can see the beginning of the jejunum. And this is known as the Duodenojejunal junction.

    02:34 We can see here, we have got the "C" shaped part, this bottom of the "C" shaped, remember the duodenum what we assume in this position, but is posterior to the transverse colon So we can see that the duodenum would be coming around in here. In just in this portion we can see is the horizontal part of the duodenum. This is then going to be continuous with the jejunum and the duodenum is continuous with the jejunum at this region here which is the Duodenojejunal junction.

    03:06 And we can pick that up here. The jejunum is then going to be continuous all the way with the ileum. And then we going to pick the ileum up as it progresses towards the ascending part of the colon, part of the large intestine.

    03:20 So we can see the small intestine, now that we have mobilized it can actually pass from the upper left quadrants all the way down to the lower right quadrant. And what we can see is the small intestine, especially the jejunum and the ileum is mobile.

    03:41 We can actually physically lift it up and move it around the abdomen.

    03:45 We can't do with duodenum. We can't do with the other organs like the pancreas or the kidneys.

    03:51 And that's because the small intestine is suspended within the abdomen by a layer of the peritoneum and this is known as the mesentery.

    04:01 We will cover the peritoneum in later lectures. But for now we can appreciate that the small intestine, the jejunum and the ileum is suspended from the posterior abdominal wall via the mesentery.

    04:17 A layer of peritoneum that extends with the posterior abdominal wall.

    04:23 If we then look at this other picture, we have actually removed the small intestine from the abdominal cavity. You release the majority of the small intestine from the abdominal cavity.

    04:34 And here we can pick up the stomach and then we have got the "C" shaped duodenum.

    04:40 Remember the duodenum is what I said as retroperitoneal? So we have removed the jejunum and the ileum. And when we have passed the large intestine and we can now see the "C" shaped duodenum.

    04:53 We have then got this part of the duodenum which is going to be continuous with the jejunum so there we have the Duodenojejunal junction.

    05:00 This is up in the upper left quadrants of the abdomen. And then we can see this root of the mesentery that's where the mesentry is going to fan out and attach to the small intestine The small intestine is then going to be continuous with the ascending colon over the large intestine. And we can see that on this diagram on the opposite side. We can see the distal ileum is continuous with the large intestine and this occurs at the ileocaecal junction.

    05:31 We can see that the ileum is then progressing and entering into the large intestine through the ileal orifice and there we can see the ileocaecal junction.

    05:42 We can see below the junction, we have the caecum, and then above the junction we have the beginning of the ascending colon.

    05:51 So we can see from the stomach to the duodenum around the jejunum and ileum towards the large intestine. Where the ileum then opens up into the large intestine. The caecum, inferiorly; the ascending colon, superiorly.

    About the Lecture

    The lecture In Situ View – Small Intestine by James Pickering, PhD is from the course Abdomen.

    Included Quiz Questions

    1. Jejunum
    2. Ileum
    3. Ascending colon
    4. Transverse colon
    1. Upper left
    2. Upper right
    3. Lower left
    4. Lower right
    1. Mesentery
    2. Ligament
    3. Greater omentum
    4. Lesser omentum
    5. Fat
    1. Ascending colon
    2. Sigmoid colon
    3. Descending colon
    4. Rectum

    Author of lecture In Situ View – Small Intestine

     James Pickering, PhD

    James Pickering, PhD

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