0:00:11.656,0:00:16.436
>> In Dissection 6, we're going to open[br]the abdomen, examine some of the structure

0:00:16.436,0:00:19.066
of the peritoneal cavity[br]including the mesenteries.

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And also take a look at the inguinal[br]region and the femoral region.

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Now the first step in this process is to reflect[br]some of the anterior abdominal wall muscles

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such as rectus abdominis that[br]you did in a previous dissection.

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And then to make a large X shaped incision[br]through the anterior abdominal wall.

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And now we've removed the umbilicus in this[br]cadaver, but make that cut of the X just

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above the umbilicus so that, later, we[br]can watch how the umbilical vessels come

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to and from the umbilicus.

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Now if you reflect these flaps back, you can[br]see that there are 2 layers to the perineal sac,

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just like there were up in the chest[br]for the pleural and pericardial sacs.

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And we've left a piece of these parietal[br]peritoneum, a nice filmy layer here,

0:01:07.536,0:01:10.316
the outer layer of the peritoneal sac, okay?

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There is a layer of connective[br]tissue called transversalis fascia

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that would bind this parietal[br]peritoneum to all the inner surfaces

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of the abdominal and pelvic cavities.

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Now if we pull that back, you can appreciate[br]the visceral layer of the peritoneal sac

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that is coating all the internal organs.

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Now for all these organs to[br]receive their adequate blood supply,

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there are structures called mesenteries where[br]the peritoneum is going to form a double layer

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that the vessels and nerves can run through to[br]approach all of these organs and provide them

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with the innervation and the[br]blood supply that they need.

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Now to get better exposure of the abdominal[br]cavity so that you can see in here,

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I'm going to do something that's[br]really not part of the dissection,

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but will help us expose the abdomen better.

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And that is to cut off some of these dangling[br]abdominal wall muscles so that we can see

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down inside as we're trying to instruct[br]you how to do the dissection here.

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Now that the abdomen is opened well,

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we can see some of the derivatives[br]of the embryonic mesenteries.

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Remember from the embryology lectures,

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that the ventral mesentery only[br]persists in the region of the foregut.

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That portion of the digestive tract that[br]continues down through about the, you know,

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first or second portion of the duodenum.

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So beyond that level, at the[br]levels of the mid and hindguts,

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there will be no ventral mesentery.

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Now here we can see the adult derivatives

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of the ventral mesogastrium[br]or mesentery of the foregut.

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I'm pulling back the ventral body wall here[br]and there's a portion of that mesentery

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that continues down to the liver.

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It's called the falciform ligament.

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And there seems to be some scar tissue[br]in this cadaver so that it's shrunken up

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and a little bit more tight[br]than it is on most cadavers.

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But this falciform ligament would be[br]a portion of the ventral mesentery.

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And the liver develops within that ventral[br]mesentery so we'll see another portion

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of it spanning between the[br]liver and the main gut tube,

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the stomach and the duodenum at this level.

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Okay, so this derivative of the ventral[br]mesogastrium is called the lesser omentum.

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And I'm sticking my finger through an opening[br]called the epiploic foramen so all the tissue

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between my finger, which you can't see,

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and right about in here is[br]called the lesser omentum.

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And there are 2 segments to it based[br]on the organs that it's attaching to.

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Now this is all stomach, okay.

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And you can't really see[br]it visually, necessarily,

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but the sphincter between the stomach[br]and the duodenum is right about here.

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You feel a nice dense thickening of the[br]smooth muscle there in the wall of the organ.

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So that this portion of the lesser[br]omentum spanning between the liver

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and the stomach is the hepatogastric ligament,

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whereas this portion a little bit more[br]toward the right spanning between the liver

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and the duodenum is the hepatoduodenal ligament.

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And that, in particular, is important[br]because it's got the structures

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of the portal triad contained[br]within it, the common bile duct,

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the hepatic artery and the hepatic portal vein.

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Now the rest of the mesenteries that[br]we're going to see are all derivatives

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of the dorsal mesenteries[br]that develop originally.

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And there's a very prominent[br]specialization of the dorsal mesentery

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of the foregut here, it's[br]called the greater omentum.

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It's attached to the greater curvature[br]of the stomach and then balloons out

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and forms this apron-like structure hanging down[br]over many of the other abdominal organs, okay?

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Among them would be the transverse colon,

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part of the large intestine[br]that we see a glimpse of here.

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So that, again, by naming these ligaments[br]according to the organs that they attach,

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we've got this ligament attaching from[br]the stomach to the transverse colon

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and we would call that portion of the greater[br]omentum, the gastrocolic ligament, okay?

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Another portion of this dorsal[br]mesentery spans between the stomach

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and the spleen which we can see down here.

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So, again, by simply naming those organs,

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we would have a gastrosplenic[br]ligament in this case.

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Now, remember, the reason that these mesenteries[br]persist is because they contain blood vessels

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that are supplying the organs[br]that they're passing between.

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Now let's pull up the greater omentum and we can[br]catch a glimpse of the transverse colon portion

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of the large intestine coming across.

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And it's got its own dorsal mesentery.

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This would be the mesocolon,[br]transverse mesocolon extending

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from the posterior body wall[br]up to the transverse colon.

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And in the next dissection, what we're going[br]to find is, as we peel apart the layers

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of these different mesenteries, we're going to[br]expose the blood vessels that supply them, okay?

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The last major mesentery that you can find[br]within the cadaver is the dorsal mesentery

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of the small intestine, the[br]so-called mesentery proper, okay?

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And, again, when we peel apart[br]the layers of this mesentery,

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we'll see very elaborate blood supply

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and nerve supply innervating[br]all of these different organs.

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Cut. We're going to take you on a quick tour of[br]the abdominal organs just so you have seen them

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and are oriented and find[br]them in your own cadaver.

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Of course, we've got the stomach[br]here in the upper left quadrant.

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And we've already taken a look at the liver.

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And this would be the gallbladder[br]tucked underneath its inferior edge.

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Now let's follow along the length of[br]the GI tract and we've got the stomach.

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Again, you can't necessarily see it, but[br]you can palpate that pyloric sphincter

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that separates the stomach from the duodenum.

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And I can follow the duodenum a certain[br]distance, but then it disappears

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where it travels right along[br]the posterior abdominal wall

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and will cross to the opposite side.

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So to find it again, we need to pull the[br]transverse colon out of the way and now here

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on the left side, we've got the[br]duodenum coming back into view.

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And, as soon as we get a mesentery established,[br]we make the transition from duodenum to jejunum.

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So looking at all these loops of small[br]bowel, about half of it is jejunum

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and then the second half[br]of it would be the ilium.

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And we're not really concerned[br]about looking at these grossly

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and making the distinction[br]between ilium and jejunum.

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Just realize about half is[br]jejunum, about half is ilium.

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Now as you follow the ilium along, you're[br]going to come to an abrupt increase in diameter

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where we reach the end of the small intestine

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and the beginning of the[br]large intestine or colon.

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And where this happens, there's always a[br]segment of the large intestine that hangs down,

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or pooches down, a little[br]bit, that's called the cecum.

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And, often, this is where you're going

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to find the appendix dangling down,[br]right at the ileocecal junction.

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Now, from what we've seen, there[br]is no appendix in this cadaver,

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but that's where you should expect to find it

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if the cadaver's got one that[br]hasn't been removed, okay?

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So that would be the home of the appendix.

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And now we're going to see that the large[br]intestine travels up along the right side

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of the body, this would be the ascending colon.

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And then travels across the[br]body as the transverse colon.

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And then travels inferiorly, or descends, on the[br]left side of the body as the descending colon.

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Now, in this particular cadaver,[br]the descending colon is very small.

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It's probably about as big as[br]one of my fingers in diameter.

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And, normally, it's at least a[br]couple of inches in diameter.

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So there seems to be some[br]obstruction in this cadaver.

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You would normally find something larger.

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Now notice as I've been flipping[br]organs around here,

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some of the organs are really plastered[br]against the posterior body wall.

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And these are organs such as the descending[br]colon that have lost their mesenteries

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and have become retroperitoneal, or have assumed[br]this position behind the parietal peritoneum.

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And, as you go through your[br]dissection, try to identify those organs

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that have lost their mesenteries and[br]are now secondarily retroperitoneal.

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Following down the descending colon, the next[br]segment that we would find is the sigmoid colon.

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And, again, the diameter of the sigmoid colon in[br]this individual seems to be quite reduced, okay?

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We do establish a mesentery[br]again with the sigmoid colon.

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And then, as that organ straightens[br]out and heads down into the pelvis,

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we get to the level of the rectum.

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For the next part of dissection 6, we're going[br]to consider descent of the testis and ovary

0:10:02.706,0:10:06.046
and how they affect the layers[br]of the anterior abdominal wall.

0:10:06.596,0:10:09.536
So, just as a reminder here, the[br]most superficial layer of muscle

0:10:09.536,0:10:12.476
that you see would be the[br]external abdominal oblique.

0:10:12.776,0:10:16.056
And, if you follow it medially, you[br]see the aponeurosis, that broad,

0:10:16.126,0:10:20.306
flat tendon continuing toward the[br]midline, helping to form the rectus sheath

0:10:20.306,0:10:21.936
over the rectus abdominous muscle.

0:10:22.866,0:10:26.286
Now focus at the inferior[br]edge of this aponeurosis

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which is attached to two bony landmarks.

0:10:29.676,0:10:35.756
One, the anterior superior iliac[br]spine or ASIS and, medially,

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to a bump on the pubis called[br]the pubic tubercle.

0:10:39.266,0:10:41.186
And this inferior edge, again, spanning

0:10:41.186,0:10:43.966
between those bony landmarks is[br]called the inguinal ligament.

0:10:45.146,0:10:49.356
Now examine this aponeurosis carefully[br]and what you'll see is there's a thin spot

0:10:49.836,0:10:55.016
down toward the medial inferior edge of[br]it and that is where there's a defect

0:10:55.016,0:10:58.806
in the aponeurosis where the[br]spermatic cord passes through.

0:10:59.446,0:11:04.956
Now the spermatic cord is a structure that[br]contains vessels, ducts, lymphatics nerves all

0:11:04.956,0:11:06.506
that are going to serve the testis,

0:11:06.976,0:11:09.876
that were dragged down along[br]during the process of descent.

0:11:10.476,0:11:13.126
And a similar process does[br]happen in the female as well.

0:11:14.556,0:11:18.776
So this defect in the external[br]abdominal oblique aponeurosis

0:11:19.306,0:11:24.886
where the spermatic cord emerges superficially[br]is called the superficial inguinal ring.

0:11:25.156,0:11:28.466
And it's literally an opening in[br]the external oblique aponeurosis.

0:11:29.636,0:11:35.286
Now if we reflect this layer to examine how[br]the descent process affects the deeper layers

0:11:35.286,0:11:37.796
of the abdominal wall, the[br]next layer, of course,

0:11:37.796,0:11:40.686
it will encounter is the[br]internal abdominal oblique muscle.

0:11:41.486,0:11:45.736
And let's just pull the inguinal[br]ligament down a bit more.

0:11:46.806,0:11:51.206
Now we've got the spermatic cord as[br]it's traveling through the body wall

0:11:51.486,0:11:54.756
in a structure called the inguinal canal, okay?

0:11:54.996,0:12:00.346
As you can see, the inferior edge of[br]the internal oblique muscle is right

0:12:00.346,0:12:02.956
about at the level where[br]the descent is occurring.

0:12:03.276,0:12:09.006
So a few of the muscle fibers from the internal[br]oblique are dragged along and cover the surface

0:12:09.006,0:12:12.266
of the spermatic cord as it[br]continues down toward the testis.

0:12:12.896,0:12:14.856
Okay this is called the cremaster muscle.

0:12:18.956,0:12:23.396
Now we've reflected the external[br]abdominal oblique aponeurosis and, again,

0:12:23.396,0:12:24.896
are looking at the internal oblique.

0:12:25.206,0:12:26.596
Now what we can't see from this angle-- .