Human Anatomy Dissection 06 (part 1 of 2) Peritoneal Cavity

peritoneal cavity, mesenteries, inguinal region

>> 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-- .