Anatomy of the Large Intestine (Nursing)

by Darren Salmi, MD, MS

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    00:01 But the large intestine on the other hand is quite different from the small intestine.

    00:07 And this terminal portion of the digestive tract isn't really absorbing nutrients anymore that was really carried out by the small intestine.

    00:14 What the large intestine is doing at this point is just reabsorbing waters and salt and then propelling the leftovers which are feces out towards the anus.

    00:25 So if we sort of fade out the jejunum, we can again see where the terminal ileum begins.

    00:31 And the large intestine is gonna be everything from the end of that terminal ileum all the way down to the anus.

    00:40 The first part is this blind pouch called the cecum.

    00:44 And coming off of the cecum is this tiny little thing called the vermiform appendix.

    00:51 And the appendix is sort of an enigma.

    00:52 It's something that we don't necessarily need and is commonly removed in appendectomies.

    01:00 Coming upward from the cecum is the ascending colon along the right side of the abdominal cavity.

    01:07 Then it makes a sharp turn and goes transversely as the tree transverse colon, before taking another sharp turn on the left side of the abdomen and going down as the descending colon.

    01:19 The ascending and descending colons are actually attached to the posterior body wall.

    01:24 So they don't have much movement.

    01:26 So they're also something that we will call retroperitoneal.

    01:30 After the descending column, it takes something of an S shaped turn, hence the term sigmoid colon before becoming straight again as the rectum and that's what rectum means. rectum means straight.

    01:44 Then the distal most portion is going to be the anal canal, which is going to be continuous with the outside world.

    01:52 Where we have these turns, get their special names, we have the right colic flexure, where the ascending becomes the transverse colon.

    02:01 And because this is in the right upper quadrant, where the liver is sometimes also called the hepatic flexure.

    02:07 Similarly, where the transverse turns to become the descending colon, it's the left colic flexure, but that's also where the spleen is.

    02:14 And so that's also called a splenic flexure.

    02:19 Now, as I mentioned, jejunum from ileum is a very subtle distinction.

    02:24 But the large intestine versus small intestine is not.

    02:28 There are features you can see superficially on the surface of the large intestine that tell you it's large intestine, as opposed to small intestine.

    02:38 For starters, there are these three bands around the outside of the large intestine called taenia coli.

    02:46 And what these taenia coli are, is not something new in the GI tract, it's actually just the longitudinal muscle that's been there throughout the GI tract.

    02:56 But instead of being evenly distributed around the large intestine, it coalesces into three bands.

    03:03 We only see one in this particular view.

    03:06 And that contraction of that longitudinal muscle in the taeniae coli creates circulations called haustra throughout the large intestine that give it a very distinct appearance.

    03:21 And finally, there are these little bits of fat, not related to the mesentery, which is a wide sheet of fat, but just individual pieces of fat called fat tags, or epiploic appendages, which something that you don't see on the small intestine.

    03:38 Now, if we look at the distal most portion of the large intestine, began, we have the portion that becomes straight again after the sigmoid and that is the rectum.

    03:48 And then down around the area of the surrounding sphincters, we have the anal canal.

    03:56 So the anal canal is a pretty short portion, but it's an important portion.

    04:00 It's an important portion embryologically, because it's the union of two very different types of precursors, namely between mesoderm and endoderm.

    04:10 And therefore, there's going to be a lot of differences and transitions throughout the anal canal.

    04:16 For example, in venous drainage or lymphatic drainage or nervous supply.

    04:22 But what we see surrounding the anal canal are two sets of sphincters.

    04:27 We have an internal anal sphincter, which is under involuntary control.

    04:34 An external anal sphincter, which is under voluntary control.

    04:41 And this anal canal, eventually that mucosa will become continuous with the surrounding perianal skin.

    04:47 And essentially, that's the end of the GI tract.

    04:54 So we can actually go through the anal canal and up into the various portions of the large intestine through colonoscopy.

    05:05 And that colonoscopy, much like endoscopes from the other side can give us access to the mucosal surface and help us identify any areas that need to be biopsied.

    About the Lecture

    The lecture Anatomy of the Large Intestine (Nursing) by Darren Salmi, MD, MS is from the course Anatomy of the Gastrointestinal System (Nursing).

    Included Quiz Questions

    1. Cecum
    2. Appendix
    3. Ascending colon
    4. Transverse colon
    5. Descending colon
    1. Longitudinal muscles
    2. Circumferential muscles
    3. Longitudinal connective tissues
    4. Circumferential connective tissues
    5. Nerve sheaths
    1. The external anal sphincter is under voluntary control.
    2. The internal anal sphincter is under voluntary control.
    3. The internal anal sphincter is controlled by the nervous system.
    4. The external anal sphincter is controlled by the nervous system.
    5. The internal anal sphincter assists with defecation.

    Author of lecture Anatomy of the Large Intestine (Nursing)

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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