Anatomy of the Large Intestine (Nursing)

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.