Okay, so this is a tutorial on the peritoneum and the peritoneal cavity.
So, the peritoneum is a thin serous membrane, which lines the abdominal cavity and a lot
of the vessels within it.
So it's kind of similar to the pleura and the serous pericardium.
So, a serous membrane is one which produces serous fluid.
So, we're looking, here, at a model of the abdominal organs.
And what I'm going to do is I'm going to take a cross-section right down the middle here.
So we'll switch over to a diagram and we'll talk about the peritoneum and the peritoneal
cavity.
So we're just going to slice right down the liver, the stomach, the pancreas behind the
stomach, the colon, the intestines, the rectum, the uterus, and the bladder.
So, we're looking, here, at the sagittal section, which I just described to you.
So we've got the liver at the top.
We've got the stomach that was sliced through.
The transverse colon.
The small intestine.
One of the loops of the small intestine.
We've got the sigmoid colon.
Rectum down here.
The uterus and the bladder at the bottom.
So the peritoneum is this membrane, which surrounds the abdominal cavity and the abdominal
organs.
So the bit which surrounds the abdominal cavity is called the parietal peritoneum.
And what you've got to remember is that the parietal peritoneum and the visceral peritoneum
are one continuous sheet.
They're not separate things.
This is what confused me when I was learning about it.
So the parietal peritoneum lines the abdominal cavity.
So I'm going to draw this on in red, so I'm drawing on the parietal peritoneum.
So we've got the parietal peritoneum in red and you can see it lined the outside, so it
lines the abdominal cavity.
And then, where the peritoneum surrounds the viscera, so the organs within the cavity,
it's called the visceral peritoneum.
So I'm going to draw this on in blue.
So now we've got the red parietal peritoneum and we've got the blue visceral peritoneum.
So it's one continuous layer, but where it surrounds the organs, it's called the visceral
peritoneum.
So there's a potential space between the parietal peritoneum and the visceral peritoneum, and
this is called the peritoneal cavity and this contains peritoneal fluid.
So, you can see, in this red shading in this diagram and this blue shading, this is the
peritoneal cavity.
So, it's this potential space between the visceral peritoneum and the parietal peritoneum.
So the peritoneal fluid contained in this space, inside the peritoneal cavity, helps
to lubricate the movement and expansion of the gut.
So you can see there's also these double folds.
So, where the visceral peritoneum doubles up -- so, you can see between the liver and
the stomach, there's this doubling up of the visceral peritoneum.
It's given a special name.
So, the doubling up of the visceral peritoneum between the stomach and other organs is called
omenta.
So, you've got a greater omentum and a lesser omentum.
And where the visceral peritoneum doubles up around other organs and attaches it to
the posterior abdominal wall, it's called a mesentery.
So you can see this doubling up of the visceral peritoneum surrounding the transverse colon
and attaching it to the posterior abdominal wall, and you can also see it surrounding
the small intestine and attaching it to the posterior abdominal wall.
This is called a mesentery.
So it's important also to understand the difference between a retroperitoneal and an intraperitoneal
organ.
So, an intraperitoneal organ is an organ that is almost fully covered by a layer of visceral
peritoneum.
And these organs are not actually -- there's no organ which is actually inside the peritoneal
cavity, but some of these organs are suspended by mesenteries or by the doubling up of the
visceral peritoneum so that they are kind of within the peritoneal cavity, but they
are not truly within the cavity.
So, the cavity - the peritoneal cavity - lies outside the visceral peritoneum, between the
visceral peritoneum and the parietal peritoneum.
So, the intraperitoneal organs are just wrapped entirely in visceral peritoneum and suspended
into this peritoneal cavity.
So, you can see these organs, which are suspended by mesenteries from the posterior abdominal
wall, are completely encapsulated in visceral peritoneum and suspended into the peritoneal
cavity, but they are not literally within the peritoneal cavity, if that makes any sense.
So, retroperitoneal organs are organs which lie behind the peritoneum or just have one
surface covered by peritoneum.
So you can see the pancreas here and the duodenum.
So, these lie behind the peritoneum, so they've only got one surface covered by the parietal
peritoneum; so they're called retroperitoneal organs.
So, intraperitoneal organs are completely or almost completely surrounded by visceral
peritoneum, but the retroperitoneal organs only have a part of their surface covered
by peritoneum.
So, the peritoneal cavity is divided into a greater sac and a lesser sac.
So, remember I mentioned omentum.
There's a lesser and a greater omentum, and the lesser omentum connects the lesser curvature
of the stomach to the porta hepatis of the liver.
So, this bit here - these double folds of visceral peritoneum connecting the liver to
the lesser curvature of the stomach is called the lesser omentum.
And connecting the greater curvature of the stomach to the transverse colon is this fold
of peritoneum called the greater omentum.
And this loops down over the small intestines and curves back up to attach to the transverse
colon.
So, behind the stomach and the liver and shaded in blue in this diagram is the lesser sac.
So this is a part of the peritoneal cavity, which lies behind the stomach and the liver.
And the greater sac is the larger part of the peritoneal cavity and makes up most of
the cavity.
So, this is shaded in red, and this starts all the way up at the diaphragm.
So, you can see this bit of shading in red above the liver.
So it starts above, at the diaphragm, and extends all the way down to the pelvic cavity.
So that's the greater sac.
So, next what we'll do is we'll take a look in a bit more detail at some of the peritoneal
attachments and we'll trace their path through the peritoneal cavity so we can get a better
understanding of where these attachments are and what organs are retroperitoneal and which
organs are intraperitoneal.