Okay, so this is a tutorial on the peritoneum and the peritoneal cavity.
The peritoneum is a thin serous membrane, which lines the abdominal cavity and a lot of the vessels within it. It’s kind of similar to the pleura and the serous pericardium. A serous membrane is one which produces serous fluid.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. We’ll switch over to a diagram and we'll talk about the peritoneum and the peritoneal cavity.
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.
We’re looking, here, at the sagittal section, which I just described to you. 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.
The peritoneum is this membrane, which surrounds the abdominal cavity and the abdominal organs. 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.
The parietal peritoneum lines the abdominal cavity. I'm going to draw this on in red, so I'm drawing on the parietal peritoneum. 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. I'm going to draw this on in blue.
Now we've got the red parietal peritoneum and we've got the blue visceral peritoneum. It’s one continuous layer, but where it surrounds the organs, it's called the visceral peritoneum.
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. You can see, in this red shading in this diagram and this blue shading, this is the peritoneal cavity.
It’s this potential space between the visceral peritoneum and the parietal peritoneum. The peritoneal fluid contained in this space, inside the peritoneal cavity, helps to lubricate the movement and expansion of the gut.
You can see there are also these double folds. 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.
The doubling up of the visceral peritoneum between the stomach and other organs is called omenta. 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.
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.
It’s important also to understand the difference between a retroperitoneal and an intraperitoneal organ.bAn 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.
The cavity - the peritoneal cavity - lies outside the visceral peritoneum, between the visceral peritoneum and the parietal peritoneum. The intraperitoneal organs are just wrapped entirely in visceral peritoneum and suspended into this peritoneal cavity.
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.
Retroperitoneal organs are organs which lie behind the peritoneum or just have one surface covered by peritoneum. You can see the pancreas here and the duodenum.
These lie behind the peritoneum, so they've only got one surface covered by the parietal peritoneum; so they're called retroperitoneal organs.
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.
The peritoneal cavity is divided into a greater sac and a lesser sac. 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.
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.
Behind the stomach and the liver and shaded in blue in this diagram is the lesser sac. 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.
This is shaded in red, and this starts all the way up at the diaphragm. You can see this bit of shading in red above the liver. It starts above, at the diaphragm, and extends all the way down to the pelvic cavity. That’s the greater sac.
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.
Okay, so we've talked about a little bit of the basics of the peritoneal cavity and the peritoneum and what the visceral and parietal peritoneum are and the divisions of the actual cavity, so the greater and lesser sacs. now, we'll just have a guided tour through the peritoneal cavity. We'll start off at the liver and look at some of the peritoneal attachments in a bit more detail. I'll start at the top and we'll work our way down.
The liver has various ligaments which attach from its surface to the diaphragm and also to the anterior abdominal wall. These ligaments aren't like ligaments in joints which connect bones to bones. These ligaments are folds of peritoneum and they anchor the liver into place.
The liver is this organ here in the right upper quadrant of the abdomen. It sits just underneath the diaphragm like this. We'll just take a look at some of the peritoneal attachments of the liver. I'll just isolate it and I'll show you some of the ligaments that we have.
We’re looking at the anterior surface of the liver. We've got a ligament which separates the right from the left lobes. this is called the falciform ligament. I'm drawing this on in yellow. This runs up the middle of the liver.
This ligament attaches the liver to the anterior abdominal wall. It attaches it to the inner surface of the rectus sheath. it attaches behind the rectus sheath as low as the level of the umbilicus. It's a remnant of the umbilical vein of the fetus.
In its base, at the base of this ligament, the falciform ligament, in the free margin, you've got a ligament called the round ligament. I'm drawing this little round ligament on in blue. That's contained within the falciform ligament in the free margin at the base of the falciform ligament. The round ligament passes into the groove between the quadrate and left lobe.
Remember, above the liver, you've got the diaphragm. I'm drawing the diaphragm on here. This is the diaphragm in red. Reflecting off the diaphragm, you've got folds of peritoneum. These folds of peritoneum reflect off the inferior surface of the diaphragm and attach onto the liver. You’ve got these reflections from the inferior surface of the diaphragm which reflect onto the liver.
This ligament here is called the coronary ligament. You've got upper and lower coronary ligaments. This one here is the upper coronary ligament. You'll be able to see the lower coronary ligament or posterior coronary ligament on the posterior surface of the liver. Where the anterior and posterior coronary ligaments meet, you get the triangular ligament. You've get this triangular ligament at this side. this side is the left triangular ligament. And on the other side, you've got the right triangular ligament where the upper and lower coronary ligaments meet.
What I'm going to do is show you a diagram to make this a bit clearer than my silly scriblings. If we rotate the liver around, we're going to take a look at the superior surface of the liver. imagine looking at this view.
We’re looking at the same view I just showed you in the model. We're looking superiorly at the liver. We've got the right lobe here, the left lobe on this side, we've got the inferior vena cava posteriorly and you can see the ligament that I drew on before.
You’ve got the falciform ligament coming up here separating the right and left lobes. It goes off to attach to the anterior abdominal wall. And then you've got the coronary ligaments which come down from the diaphragm. And then you've got the left triangular ligament and right triangular ligament.
Just coming back to this 3D model. We're looking at an anterior view here. What I'm going to do is we're going to rotate it around to the back and we'll look at a diagram of this sort of posterior and inferior surfaces of the liver.
We’re looking at the inferior and posterior surface of the liver. You can see the coronary ligament here. This is a reflection of peritoneum which attaches the diaphragm (the inferior surface of the diaphragm) to the liver.
You can see the coronary ligament here running round. And then at the bottom, you can see this lower part. this is the lower part of the coronary ligament which you can see on the posterior surface.
This coronary ligament demarcates an area of the liver, which is not peritoneal. there is a bare area on the liver where there is no peritoneum. This is called the bare area of the liver. This part of the liver is in direct contact with the diaphragm.
The right triangular ligament is formed in this lower extremity of the bare area of the liver where these two layers of the coronary ligaments fuse and this right triangular ligament passes to the diaphragm.
The peritoneum covers the whole liver except for this area (which I'm showing you) at the back of the liver called the bare area. The majority of the liver is covered in peritoneum, which reflects off the diaphragm.
And then you've got this fissure here, which is called the fissure for the ligamentum venosum. the ligamentum venosum is a fibrous remnant of the ductus venosus. Just below it, just here on the side of the quadrate lobe, you can see where the round ligament comes into the back of the liver. remember, I showed you the round ligament passing in the margin of the falciform ligament. It passes to the posterior surface and runs along here.
From the ligamentum venosum and the porta hepatis, you get the lesser omentum, which connects the liver to the lesser curve of the stomach and to the first part of the duodenum. the peritoneum which encloses the liver meets to form this double layer of peritoneum at the porta hepatis. And it connects the porta hepatis to the lesser curvature of the stomach and the first part of the duodenum. this is called the lesser omentum.
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. Hepato- is liver; -gastric is stomach. The lateral part is called the hepatoduodenal ligament. Hepato- is liver; -duodenal is referring to duodenum. This passes between the duodenum and the liver.
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.
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.
At the stomach, the double layer of peritoneum splits. 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.
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. 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. 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. It hangs down like this, covering the intestinal loops. It's called the great omentum.
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.
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.
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. This lesser sac extends downwards behind the stomach and between the layers of this greater omentum.
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. The lesser sac extends between these two folds of greater omentum.
I've switched over to another diagram, a horizontal section and this shows the boundaries of the lesser sac. 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. 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.
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. It just covers a bit of the surface of the kidney.
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. 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).
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. You can see this double fold towards the posterior abdominal wall like this.
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. 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. 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.
These mesenteries together with the greater and lesser omenta carry vascular supply and lymphatic drainage to the viscera and from the viscera.
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. 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.
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. Only one part of their surface is in contact with the peritoneum.
Other retroperitoneal structures are the ascending colon and the descending colon. And also, you've got the kidneys which are retroperitoneal structures.
Which organs are intraperitoneal? We've got the liver, the spleen, the stomach, the first part of the duodenum. We've got the jejunum and ileum. All these loops of intestine. Then the transverse colon is obviously intraperitoneal. We've got the sigmoid colon, which is intraperitoneal. And the superior parts of the rectum are also intraperitoneal.
The retroperitoneal organs are the kidneys at the back. You can see the kidneys here. And the adrenal glands which sit on top are retroperitoneal. We've got the head and the body of the pancreas, which are retroperitoneal (the tail is actually intraperitoneal). And then we've got the second to fourth parts of the duodenum, so the bits between the duodenojejunal flexure. We’ve got the second to fourth parts of the duodenum which are retroperitoneal. And then you've got the ascending and descending parts of the colon, which are retroperitoneal.