>> In Dissection 6, we're going to open the abdomen, examine some of the structure
of the peritoneal cavity including the mesenteries.
And also take a look at the inguinal region and the femoral region.
Now the first step in this process is to reflect some of the anterior abdominal wall muscles
such as rectus abdominis that you did in a previous dissection.
And then to make a large X shaped incision through the anterior abdominal wall.
And now we've removed the umbilicus in this cadaver, but make that cut of the X just
above the umbilicus so that, later, we can watch how the umbilical vessels come
to and from the umbilicus.
Now if you reflect these flaps back, you can see that there are 2 layers to the perineal sac,
just like there were up in the chest for the pleural and pericardial sacs.
And we've left a piece of these parietal peritoneum, a nice filmy layer here,
the outer layer of the peritoneal sac, okay?
There is a layer of connective tissue called transversalis fascia
that would bind this parietal peritoneum to all the inner surfaces
of the abdominal and pelvic cavities.
Now if we pull that back, you can appreciate the visceral layer of the peritoneal sac
that is coating all the internal organs.
Now for all these organs to receive their adequate blood supply,
there are structures called mesenteries where the peritoneum is going to form a double layer
that the vessels and nerves can run through to approach all of these organs and provide them
with the innervation and the blood supply that they need.
Now to get better exposure of the abdominal cavity so that you can see in here,
I'm going to do something that's really not part of the dissection,
but will help us expose the abdomen better.
And that is to cut off some of these dangling abdominal wall muscles so that we can see
down inside as we're trying to instruct you how to do the dissection here.
Now that the abdomen is opened well,
we can see some of the derivatives of the embryonic mesenteries.
Remember from the embryology lectures,
that the ventral mesentery only persists in the region of the foregut.
That portion of the digestive tract that continues down through about the, you know,
first or second portion of the duodenum.
So beyond that level, at the levels of the mid and hindguts,
there will be no ventral mesentery.
Now here we can see the adult derivatives
of the ventral mesogastrium or mesentery of the foregut.
I'm pulling back the ventral body wall here and there's a portion of that mesentery
that continues down to the liver.
It's called the falciform ligament.
And there seems to be some scar tissue in this cadaver so that it's shrunken up
and a little bit more tight than it is on most cadavers.
But this falciform ligament would be a portion of the ventral mesentery.
And the liver develops within that ventral mesentery so we'll see another portion
of it spanning between the liver and the main gut tube,
the stomach and the duodenum at this level.
Okay, so this derivative of the ventral mesogastrium is called the lesser omentum.
And I'm sticking my finger through an opening called the epiploic foramen so all the tissue
between my finger, which you can't see,
and right about in here is called the lesser omentum.
And there are 2 segments to it based on the organs that it's attaching to.
Now this is all stomach, okay.
And you can't really see it visually, necessarily,
but the sphincter between the stomach and the duodenum is right about here.
You feel a nice dense thickening of the smooth muscle there in the wall of the organ.
So that this portion of the lesser omentum spanning between the liver
and the stomach is the hepatogastric ligament,
whereas this portion a little bit more toward the right spanning between the liver
and the duodenum is the hepatoduodenal ligament.
And that, in particular, is important because it's got the structures
of the portal triad contained within it, the common bile duct,
the hepatic artery and the hepatic portal vein.
Now the rest of the mesenteries that we're going to see are all derivatives
of the dorsal mesenteries that develop originally.
And there's a very prominent specialization of the dorsal mesentery
of the foregut here, it's called the greater omentum.
It's attached to the greater curvature of the stomach and then balloons out
and forms this apron-like structure hanging down over many of the other abdominal organs, okay?
Among them would be the transverse colon,
part of the large intestine that we see a glimpse of here.
So that, again, by naming these ligaments according to the organs that they attach,
we've got this ligament attaching from the stomach to the transverse colon
and we would call that portion of the greater omentum, the gastrocolic ligament, okay?
Another portion of this dorsal mesentery spans between the stomach
and the spleen which we can see down here.
So, again, by simply naming those organs,
we would have a gastrosplenic ligament in this case.
Now, remember, the reason that these mesenteries persist is because they contain blood vessels
that are supplying the organs that they're passing between.
Now let's pull up the greater omentum and we can catch a glimpse of the transverse colon portion
of the large intestine coming across.
And it's got its own dorsal mesentery.
This would be the mesocolon, transverse mesocolon extending
from the posterior body wall up to the transverse colon.
And in the next dissection, what we're going to find is, as we peel apart the layers
of these different mesenteries, we're going to expose the blood vessels that supply them, okay?
The last major mesentery that you can find within the cadaver is the dorsal mesentery
of the small intestine, the so-called mesentery proper, okay?
And, again, when we peel apart the layers of this mesentery,
we'll see very elaborate blood supply
and nerve supply innervating all of these different organs.
Cut. We're going to take you on a quick tour of the abdominal organs just so you have seen them
and are oriented and find them in your own cadaver.
Of course, we've got the stomach here in the upper left quadrant.
And we've already taken a look at the liver.
And this would be the gallbladder tucked underneath its inferior edge.
Now let's follow along the length of the GI tract and we've got the stomach.
Again, you can't necessarily see it, but you can palpate that pyloric sphincter
that separates the stomach from the duodenum.
And I can follow the duodenum a certain distance, but then it disappears
where it travels right along the posterior abdominal wall
and will cross to the opposite side.
So to find it again, we need to pull the transverse colon out of the way and now here
on the left side, we've got the duodenum coming back into view.
And, as soon as we get a mesentery established, we make the transition from duodenum to jejunum.
So looking at all these loops of small bowel, about half of it is jejunum
and then the second half of it would be the ilium.
And we're not really concerned about looking at these grossly
and making the distinction between ilium and jejunum.
Just realize about half is jejunum, about half is ilium.
Now as you follow the ilium along, you're going to come to an abrupt increase in diameter
where we reach the end of the small intestine
and the beginning of the large intestine or colon.
And where this happens, there's always a segment of the large intestine that hangs down,
or pooches down, a little bit, that's called the cecum.
And, often, this is where you're going
to find the appendix dangling down, right at the ileocecal junction.
Now, from what we've seen, there is no appendix in this cadaver,
but that's where you should expect to find it
if the cadaver's got one that hasn't been removed, okay?
So that would be the home of the appendix.
And now we're going to see that the large intestine travels up along the right side
of the body, this would be the ascending colon.
And then travels across the body as the transverse colon.
And then travels inferiorly, or descends, on the left side of the body as the descending colon.
Now, in this particular cadaver, the descending colon is very small.
It's probably about as big as one of my fingers in diameter.
And, normally, it's at least a couple of inches in diameter.
So there seems to be some obstruction in this cadaver.
You would normally find something larger.
Now notice as I've been flipping organs around here,
some of the organs are really plastered against the posterior body wall.
And these are organs such as the descending colon that have lost their mesenteries
and have become retroperitoneal, or have assumed this position behind the parietal peritoneum.
And, as you go through your dissection, try to identify those organs
that have lost their mesenteries and are now secondarily retroperitoneal.
Following down the descending colon, the next segment that we would find is the sigmoid colon.
And, again, the diameter of the sigmoid colon in this individual seems to be quite reduced, okay?
We do establish a mesentery again with the sigmoid colon.
And then, as that organ straightens out and heads down into the pelvis,
we get to the level of the rectum.
For the next part of dissection 6, we're going to consider descent of the testis and ovary
and how they affect the layers of the anterior abdominal wall.
So, just as a reminder here, the most superficial layer of muscle
that you see would be the external abdominal oblique.
And, if you follow it medially, you see the aponeurosis, that broad,
flat tendon continuing toward the midline, helping to form the rectus sheath
over the rectus abdominous muscle.
Now focus at the inferior edge of this aponeurosis
which is attached to two bony landmarks.
One, the anterior superior iliac spine or ASIS and, medially,
to a bump on the pubis called the pubic tubercle.
And this inferior edge, again, spanning
between those bony landmarks is called the inguinal ligament.
Now examine this aponeurosis carefully and what you'll see is there's a thin spot
down toward the medial inferior edge of it and that is where there's a defect
in the aponeurosis where the spermatic cord passes through.
Now the spermatic cord is a structure that contains vessels, ducts, lymphatics nerves all
that are going to serve the testis,
that were dragged down along during the process of descent.
And a similar process does happen in the female as well.
So this defect in the external abdominal oblique aponeurosis
where the spermatic cord emerges superficially is called the superficial inguinal ring.
And it's literally an opening in the external oblique aponeurosis.
Now if we reflect this layer to examine how the descent process affects the deeper layers
of the abdominal wall, the next layer, of course,
it will encounter is the internal abdominal oblique muscle.
And let's just pull the inguinal ligament down a bit more.
Now we've got the spermatic cord as it's traveling through the body wall
in a structure called the inguinal canal, okay?
As you can see, the inferior edge of the internal oblique muscle is right
about at the level where the descent is occurring.
So a few of the muscle fibers from the internal oblique are dragged along and cover the surface
of the spermatic cord as it continues down toward the testis.
Okay this is called the cremaster muscle.
Now we've reflected the external abdominal oblique aponeurosis and, again,
are looking at the internal oblique.
Now what we can't see from this angle-- .