Anatomy of the peritoneum and peritoneal cavity

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Introduction0:00–0:18

At first glance, the peritoneum and peritoneal cavity seem pretty simple, but some aspects, like the peritoneal ligaments, can be a bit confusing.
In order to understand them, we need to go way back to their embryological formation. Once upon a time, in an amniotic galaxy far far away, the embryonic body cavity is lined with mesoderm.

Embryological development0:18–1:17

As the fetus is developing, the embryonic body cavity becomes the primordial abdominal cavity and the mesoderm lining it becomes the parietal peritoneum which is a transparent, serous membrane that helps to form a closed sac, called the peritoneal cavity.
As abdominal organs develop, they protrude into the peritoneum, like pushing your fist into a balloon. Your fist represents the developing abdominal viscera and the balloon represents the parietal peritoneum.
As your fist pushes into the balloon it is lined closely by part of the balloon and this represents the visceral peritoneum.
So, the visceral peritoneum covers the viscera, while parietal peritoneum lines the internal surface of the abdominopelvic wall; and these two layers are continuous with one another.

Peritoneum1:17–1:39

The parietal peritoneum has the same blood and lymphatic supply and the same nerve supply as the region of the wall it lines, meaning it is sensitive to pressure, pain, heat and cold.
The visceral peritoneum, on the other hand, has the same blood, lymphatic, and nerve supply as the viscera it covers, meaning it is sensitive to stretch and chemical irritation.
Depending on their relationship with the peritoneum, abdominal and pelvic organs can be either intraperitoneal, retroperitoneal, or subperitoneal.

Organs in relation to the peritoneum1:39–3:01

Intraperitoneal organs are almost completely covered with visceral peritoneum, but remember they’re not inside the peritoneal cavity.
These organs include the stomach, first part of the duodenum, jejunum, ileum, transverse colon, sigmoid colon, liver and spleen.
Now, the retroperitoneal organs, also known as primarily retroperitoneal, develop posterior to the peritoneal cavity, outside of the peritoneum, so they’re only partially covered with peritoneum.
The retroperitoneal organs include the kidneys, ureters, suprarenal glands, and rectum. There are also secondarily retroperitoneal organs where they begin as intraperitoneal but later on in development become attached to the posterior abdominal wall.
The secondarily retroperitoneal organs include the second to the fourth parts of the duodenum, pancreas, and the ascending and descending colon.
Lastly, the subperitoneal organs, like the urinary bladder, are similar to the retroperitoneal organs, except they are located inferior to the peritoneal cavity, rather than posterior to it.
The peritoneal cavity is a potential space between the parietal and visceral layers of the peritoneum. Keep in mind that the peritoneal cavity has no abdominal organs, it only contains a thin film of fluid that contains water, electrolytes and other substances derived from the interstitial fluid.

Peritoneal cavity3:01–3:31

The peritoneal fluid helps viscera move without friction, allowing for peristalsis, and it also has white blood cells and antibodies to resist infection.
Quick quiz. Can you remember which organs are retroperitoneal and which organs are intraperitoneal?

Quiz3:31–3:43

Now, we are going to look at some of the peritoneal structures in adults. Let’s first start by looking at the omentum, which is a fold of peritoneum.

Omenta3:43–5:13

There’s actually two of them: the greater omentum and the lesser omentum. The greater omentum is a four-layered peritoneal fold that hangs like an apron from the greater curvature of the stomach and the proximal part of the duodenum.
After descending, it folds back and it attaches to the anterior surface of the transverse colon and its mesentery. These four layers fuse with one another.
The lesser omentum is a double-layered peritoneal fold that connects the lesser curvature of the stomach and the proximal part of the duodenum to the liver.
Posterior to the lesser omentum, there’s a space known as the lesser sac or omental bursa, and the rest of the peritoneal cavity is known as the greater sac.
These two spaces communicate through the omental foramen also called the epiploic foramen. Anterior to the omental foramen, there’s the hepatoduodenal ligament, which is the free edge of the lesser omentum that contains the portal triad.
Posterior to the omental foramen, is the inferior vena cava and the right crus of the diaphragm. Superior to the omental foramen is the liver, and inferior to the omental foramen is the first part of the duodenum.
The peritoneal cavity as a whole is divided by the transverse mesocolon into a supracolic compartment and an infracolic compartment.

Transverse mesocolon5:13–5:51

The supracolic compartment contains the stomach, liver and spleen. The infracolic compartment is located posterior to the greater omentum and contains the small intestine, as well as the ascending and descending colon.
Communication between the supracolic and infracolic compartments happens through the paracolic gutters, which are grooves between the lateral aspect of the ascending or descending colon and the posterolateral abdominal wall.

Mesenteries5:51–6:51

Now let’s talk about the mesenteries within the abdomen. Remember that a mesentery is a double layer of peritoneum that occurs as a result of the developing abdominal organs and is continuous with the parietal and visceral layers of peritoneum.
The aorta, inferior vena cava, and the nerves and lymphatics are all posterior to the peritoneum, so the mesenteries allow for passage of neurovasculature from the body wall to and from their respective organs.
The largest mesentery in the body is the mesentery of the small intestine, which is usually just called the mesentery, and connects the posterior abdominal wall to the jejunum and ileum.
Next, is the transverse mesocolon, which connects the transverse colon to the posterior abdominal wall. Then there’s the sigmoid mesocolon, which connects the sigmoid colon to the posterior wall of the abdomen and pelvis .
Finally, there’s the mesoappendix, which connects the ileum to the appendix. Time for a quick break!

Quiz6:51–6:58

How can the peritoneal cavity be divided? Now, let’s switch gears and explore the development to understand how these structures came to be.

Embryologic mesenteries6:58–8:09

Let’s first look at the embryologic mesenteries! Now, the gastrointestinal tract begins as a tube, known as the gut tube.
Initially, it is closely associated with the posterior abdominal wall, but begins to move farther away from it. The gut tube is then suspended from the dorsal wall of the embryo by connective tissue known as the dorsal mesentery and from the ventral wall by the ventral mesentery.
The ventral mesentery is derived from a plate of mesoderm known as the septum transversum and extends from the ventral aspect of the proximal part of the duodenum to the developing liver.
The dorsal mesentery extends from the lower portion of the esophagus to the rectum, attaching it to the posterior body wall and creating a pathway for blood vessels, nerves and lymphatics.
The abdominal organs then continue to get larger as the fetus grows which causes the gut to rotate. The dorsal and ventral mesenteries rotate along with the organs they are attached to, and eventually reach their final destinations.
Let’s look at the ventral mesentery and how it forms. As the liver develops, it protrudes within the ventral mesentery and forms an anterior part, called the falciform ligament and a posterior part, called the lesser omentum.

Ventral mesentery8:09–9:21

Now, the free edge of the falciform ligament contains the umbilical vein, which closes off after birth and remains as the round ligament of the liver.
The lesser omentum is actually made of two ligaments called the hepatoduodenal ligament and the hepatogastric ligament. The hepatoduodenal ligament contains the vessels coming to and from the liver, known as the portal triad, and extends from the proximal part of the duodenum to the liver.
The hepatogastric ligament is the rest of the lesser omentum, connecting from the liver to the lesser curvature of the stomach.
The liver is completely surrounded by ventral mesentery, except on its superior surface, where it is in direct contact with the inferior surface of the diaphragm and this is called the bare area of the liver.
Then there are the coronary ligaments, which are the peritoneum reflection from the inferior surface of the diaphragm.Now that we’ve covered the ventral mesentery, let’s see how the embryonic dorsal mesentery gives rise to adult structures.

Dorsal mesentery9:21–11:18

Due to the rotation of the stomach and the growing pancreas, the duodenum moves from the midline to the right side of the peritoneal cavity.
This pushes the duodenum and pancreatic head against the dorsal body wall, where the right surface of the dorsal mesoduodenum fuses with the posterior abdominal wall peritoneum, making these two organs secondarily retroperitoneal.
However, a small part of the proximal duodenum does remain intraperitoneal, which is the part attached to the stomach.Similarly, the ascending and descending colon will be pushed to either side to push against the posterior abdominal wall where their mesenteries will also fuse with the peritoneum.
However, the appendix and inferior end of the cecum retain a free mesentery. The dorsal mesentery also remains attached to the stomach, known as the dorsal mesogastrium, which continues to grow as the stomach is twisting and bulges out, forming the four layered apron known as the greater omentum.
The dorsal mesentery of the jejunum and ileum is the mesentery proper. Finally, the dorsal mesentery also gives rise to the gastrosplenic and splenorenal ligaments which arise similarly to the falciform ligament and the lesser omentum.
The spleen develops within the dorsal mesentery posterior to the primitive gut tube, creating the gastrosplenic ligament between the spleen and the stomach and the splenorenal ligament between the spleen and the left kidney.
These ligaments allow for the passage of blood vessels, nerves and lymphatics to and from these organs. There is also the gastrophrenic ligament, which connects the stomach to the diaphragm and the phrenicocolic ligament which is located at the left colic flexure and attaches to the diaphragm.
All right, as a quick recap... the parietal peritoneum lines the internal surface of the abdominopelvic wall, while the visceral peritoneum covers the viscera.

Review11:18–13:01

Intraperitoneal organs include the stomach, first part of the duodenum, jejunum, ileum, transverse colon, sigmoid colon, liver and spleen.
Retroperitoneal organs include the kidneys, the ureters, the suprarenal glands and the rectum. Secondarily retroperitoneal organs include the second to the fourth part of the duodenum, the pancreas, the ascending colon and descending colon.
The peritoneal cavity contains no abdominal organs and has peritoneal fluid to help viscera move without friction. The peritoneal cavity is divided into the greater sac and the lesser sac which communicate through the omental foramen.
The peritoneal cavity is divided by the transverse mesocolon into a supracolic compartment and an infracolic compartment.
The mesenteries within the abdomen connect the viscera to the posterior abdominal wall. These include: the mesentery of the small intestine, the transverse mesocolon, the sigmoid mesocolon and the mesoappendix.
The ligaments that derive from the embryological ventral mesentery are: the falciform ligament, the coronary ligaments, the hepatogastric ligament, and the hepatoduodenal ligament.
The ligaments that derive from the embryological dorsal mesentery include: the gastrophrenic ligament, the gastrosplenic ligament, the phrenicocolic ligament, the transverse mesocolon,