So there are two parts to the lesser omentum, you've got a medial and a lateral part.
The medial part is called the hepatogastric ligament.
This runs between the stomach and the liver.
So hepato- is liver; -gastric is stomach.
The lateral part is called the hepatoduodenal ligament.
So hepato- is liver; -duodenal is referring to duodenum.
So this passes between the duodenum and the liver.
So I'll just switch back to this diagram and I'll show you what we've just talked about.
We've got the liver at the top.
We've got the attachment to the inferior surface of the diaphragm.
This is the superior lobe, the coronary ligament and you've got this attachment a little bit
further down on the posterior aspect of the liver.
This is the inferior layer of the coronary ligament, which attach it to the diaphragm
above.
And these are the peritoneal reflections from the diaphragm.
So at the porta hepatis, the peritoneum meets.
The visceral peritoneum meets and it forms this double layer of peritoneum which runs
to the stomach, to the lesser curvature of the stomach.
This is the lesser omentum.
So at the stomach, the double layer of peritoneum splits.
So one side of the peritoneum goes around one side of the stomach and the other side
goes around the other side of the stomach to completely enclose the stomach in peritoneum.
So coming back to this 3D model, we've got the liver enclosed in peritoneum except for
the bare area on the posterior surface.
I've just drawn the falciform ligament and the coronary ligament at the top.
And then the peritoneum meets at the porta hepatis and extends to the lesser curvature
of the stomach.
It splits around the stomach to completely enclose the stomach.
So the stomach is completely enclosed in peritoneum.
And then the two layers of peritoneum which split at the lesser curvature that encapsulate
the stomach meet again at the greater curvature.
They form this double layer of peritoneum again.
So this is called the greater omentum.
This attaches to the greater curve of the stomach.
This great omentum hangs down like an apron and it covers the intestinal loops.
So it hangs down like this, covering the intestinal loops.
It's called the great omentum.
So just to show you in diagrammatic form.
The greater omentum is this bit here which hangs down in front of the loops of the intestine,
the small intestine.
And again, it's this double layered fold of peritoneum.
So we've got the lesser omentum up here, which is a double fold.
It splits around the stomach.
It encapsulates it completely.
And then you've got the greater omentum coming from the greater curvature hanging down in
front of the loops of the small intestine and it folds back in on itself and upwards
and it wraps around the transverse colon.
So behind the lesser omentum in the stomach, you've got this thing called the lesser sac
or the omental bursa.
This is shaded in blue in this diagram.
So this lesser sac extends downwards behind the stomach and between the layers of this
greater omentum.
So you've got this anterior fold of the greater omentum (double fold) and you've got this
u-bend and it rises up again.
And you've got this posterior fold which attaches around the transverse colon.
So the lesser sac extends between these two folds of greater omentum.
So I've switched over to another diagram, a horizontal section and this shows the boundaries
of the lesser sac.
So we're looking superiorly down at a cross-section.
You can see the stomach here.
And to the left, you've got the spleen and slightly posteriorly.
So the lesser sac is this bit outlined in blue sitting behind the stomach.
And you can see that on the left, the left margins of the lesser sac are made up by these
attachments between the stomach and the spleen and also between the spleen and the posterior
abdominal wall.
So this peritoneal attachment between the spleen and the stomach, which makes up the
left wall of the lesser sac is called the gastrosplenic ligament or the gastrolienal
ligament.
This attaches the greater curvature to the hilum of the spleen.
At the back, you've got the lienorenal ligament.
This attaches the hilum of the spleen back to the posterior abdominal wall.
So it just covers a bit of the surface of the kidney.
So you've got the gastrosplenic or the gastrolienal ligament and you've got the lienorenal ligament,
which form the left wall of the lesser sac (the lesser sac here in blue).
The lesser sac actually communicates with the greater sac via a little foramen called
the foramen of Winslow or the epiploic foramen.
So you can see the area where this foramen is located.
Anterior to the foramen of Winslow, you've got the lesser omentum.
It contains the portal triad.
The portal triad consists of the hepatic artery, the bile duct and the portal vein.
And just behind the foramen of Winslow, you've got the inferior vena cava.
And then, inferiorly, you've got the first part of the duodenum and superiorly, you've
got the caudate process of the liver (which isn't shown on this particular diagram).
So coming back to the transverse colon which is where we left off, it's encapsulated by
peritoneum.
The greater omentum splits and surrounds the transverse colon.
The transverse colon is tethered to the posterior abdominal wall by a double fold of peritoneum
called a mesentery.
A mesentery is a double fold of visceral peritoneum, which anchors a viscera to the posterior abdominal
wall.
So you can see this double fold towards the posterior abdominal wall like this.
So when this mesentery reaches the posterior abdominal wall, the upper part and lower part
separate so the upper part splits and passes superiorly and reflects back again onto the
liver like so.
And the lower part passes inferiorly on the posterior abdominal wall.
So this mesentery which attaches the transverse colon to the posterior abdominal wall is called
the transverse mesocolon.
As we follow the peritoneum inferiorly, there's another mesentery which encapsulates the small
intestines.
This mesentery is called the mesentery of the small intestine.
So this mesentery wraps around the small intestine from the duodenojejunal flexure down to the
ileocecal junction.
And this mesentery suspends the small intestine in the peritoneal cavity.
And then you've got a fine mesentery which surrounds the sigmoid colon.
This is called the sigmoid mesocolon.
It's not shown in this model, but it's further down and it suspends the sigmoid colon within
the visceral peritoneum.
So these mesenteries together with the greater and lesser omenta carries vascular supply
and lymphatic drainage to the viscera and from the viscera.
So what we've looked at is we've taken a trip through the peritoneal cavity looking at the
peritoneal attachments.
We've seen how the liver is attached to the anterior abdominal wall by the falciform ligament.
We've seen how the parietal peritoneum surrounds the whole peritoneal cavity.
And at the top, we looked at how the peritoneum reflects from the inferior surface of the
diaphragm onto the liver via these coronary ligaments.
So you've got an upper/superior/anterior coronary ligament and a lower/inferior/posterior coronary
ligament, which reflects from the diaphragm and surrounds the liver in this peritoneum.
And then we saw how the peritoneum meets at the porta hepatis to form this double fold
which forms the lesser omenta and joins the liver to the lesser curvature of the stomach.
We saw how the stomach was entirely encapsulated by this fold of peritoneum.
And at the greater curvature, the peritoneum really fuses again to form another double
fold called the greater omentum which loops down and covers the intestinal loops in this
double fold.
And then it joins on to the transverse colon and surrounds that in a layer of peritoneum.
The transverse colon is then suspended in the peritoneal cavity by a mesentery.
The mesentery attaches the transverse colon to the posterior abdominal wall.
The upper part of the mesentery passes back up and reflects back onto the liver.
The lower part passes inferiorly on the posterior abdominal wall and forms other mesenteries.
It forms the mesentery of the small intestine and it forms the mesentery of the sigmoid
colon.
So behind the peritoneum, you've got structures like the pancreas and you've got the second
to fourth parts of the duodenum which are retroperitoneal.
So only one part of their surface is in contact with the peritoneum.
So other retroperitoneal structures are the ascending colon and the descending colon.
And also, you've got the kidneys which are retroperitoneal structures.