The peritoneum is a layer of serous membrane that constitutes the inner lining of the abdominopelvic cavity. It covers most of the abdominal organs, which are therefore called intraperitoneal. Only a few are left out, and they referred to as the retroperitoneal organs. Histologically, it falls to the category where the all the other serous membranes do - built of the layer of the mesotelial cells.
Peritoneum is very important for keeping the organs alligned and stacked up just the way they are supposed to, while at the same time, the peritoneum protects the organs from the outer mechanical factors.
|Structure||Outer layer - parietal peritoneum - attached to the abdominal and pelvic walls
Inner layer - visceral peritoneum - wrapped around visceral organs; the duplicature of the visceral peritoneum around gastrointestinal tract is the mesentery
Space between the layers - peritoneal cavity that is subdivided to the lesser sac (consists of the greater and lesser omentum) and greater sac (cavity inside peritoneum but outside the lesser sac)
Greater omentum: extends from the greater curvature of the stomach -> passes in front of the small intestines -> turns on itself and ascends to the transverse colon -> attaches to the posterior abdominal wall and encloses that part of the intestine
Left border - gastrosplenic ligament; Right border - beginning of the duodenum
Contains right and left gastroepiploic vessels
Lesser omentum: extends from the liver to the lesser curvature of the stomach and the first part of duodenum
Left border - hepatoduodenal ligament; Right border - hepatogastric ligament
Contains portal vein, bile duct, lymph nodes and the lymph vessels, hepatic plexus of nerve
|Greater sac||Communicates with the lesser sack via omental foramen|
|Mesentery||Part of peritoneum through which most abdominal organs are attached to the abdominal wall; it contains nerves, blood and lymph vessels. Divisions:
Mesentery proper - from small intestine to the posterior abdominal wall (contains superior mesenteric artery and accompanying veins)
Transverse mesocolon - from transverse colon to the posterior abdominal wall (contains middle colic artery)
Sigmoid mesocolon - from the sigmoid colon to the pelvic wall (contains sigmoid arteries and superior rectal artery)
Mesoappendix - from the mesentery of the ileum to the appendix (contains appendicular artery)
Gastrosplenic - stomach -> spleen (contains short gastric and left gastroepiploic artery)
Splenorenal - spleen -> kidney (splenic artery, tail of pancreas)
Gastrophrenic - stomach -> diaphragm (left inferior phrenic artery)
Gastrocolic - stomach -> transverse colon (right gastroepiploic artery)
Falciform - liver -> thoracic diaphragm, anterior abdominal wall (round ligament of liver, paraumbilical veins)
Hepatogastric - stomach -> liver (right and left gastric arteries)
Hepatoduodenal - duodenum -> liver (hepatic artery proper, portal vein, bile duct, autonomic nerves)
Intraperitoneal: liver, spleen, stomach, proximal duodenum, jejunum, ileum, transverse colon, sigmoid colon, superior rectum
Retroperitoneal: the kidneys (primary); small intestine, adrenal glands, pancreas, distal duodenum, ascending colon, descending colon (secondary)
|Clinical significance||Peritoneal dialysis, peritonitis, primary peritoneal carcinoma|
This article will highlight the main anatomical features of the peritoneum and its subdivisions, the omenta, the mesenteries, the peritoneal ligaments and the epiploic foramen.
Anatomy of the Peritoneum
It consists of two inseparable layers of mesothelium that are known as the parietal peritoneum and the visceral peritoneum. The parietal peritoneum covers the internal abdominal walls and is supplied by the regional neurovasculature. The visceral peritoneum encapsulates the individual abdominal organs and is supplied by the organ it is closest to.
The peritoneal cavity is a theoretical space that exists between the two layers of the peritoneal mesothelium. This space is filled with a thin fluid film that helps prevent friction between the tightly packed organs. It should be noted however, that no organs actually lie within this potential space. In males, the peritoneal cavity is completely closed off, but in females however, it communicates with the exterior body via the female sexual organs and genitalia.
Greater and Lesser Sacs
There are two peritoneal subdivisions, known as the greater and lesser sacs. The greater sac consists of the main peritoneal cavity, while the lesser sac or omental bursa is situated posterior to the stomach and can be directly seen through the lesser omentum.
The lesser sac communicates with the greater sac via the epiploic foramen of winslow, which is a hiatus in the peritoneum that can be found just below the neck of the gallbladder. It is bordered as follows:
- anteriorly by the hepatoduodenal ligament
- posteriorly by the inferior vena cava and the right crus of the diaphragm
- superiorly by the caudate lobe of the liver
- inferiorly by the proximal part of the duodenum, the portal vein, the hepatic artery and the bile duct
The lesser sac also has a superior and an inferior recess. The superior recess is an actual cavity and is bordered superiorly by the diaphragm and the coronary ligament of the liver, while the inferior recess is the theoretical space between the layers of the greater omentum.
Greater & Lesser Omentum
The omentum is the double layered fold of the peritoneum which is apparent when it turns back upon itself. The lesser omentum is fixed to the lesser curvature of the stomach, the proximal duodenum and the adjacent surface of the liver. It is comprised of both the hepatogastric ligament and hepatoduodenal ligament of the liver.
The greater omentum is the corresponding peritoneum that is fixed to the greater curvature of the stomach as well as the opposite side of the proximal duodenum. It creates a hanging curtain of peritoneal tissue that folds back on itself and attaches inferiorly to the transverse colon.
The mesentery is a double peritoneal layer that is created by an invagination of the tissue as it tightly packs itself around the organs. Its main function is to prevent any friction between the different visceral surfaces and to carry the neurovasculature as well as house the lymphatic system and various amounts of fat padding for that particular region. It is known as the mesentery on the small intestine and the mesocolon on the large intestine, including the transverse and sigmoid mesocolon.
The greater sac is divided into both a supracolic and an infracolic compartment. The supracolic compartment is comprised of the greater sac above the transverse mesocolon and contains the stomach, the liver and the spleen. The infracolic compartment is comprised of the greater sac below the transverse mesocolon and contains the small intestine, the ascending colon and the descending colon. The mesentery of the small intestine subdivides this area into left and right sides. The paracolic gutter allows the two compartments to directly communicate.
A ligament is described as a double layer of peritoneum that can connect an organ to either another organ or to the internal lining of the abdominal wall. These anatomical structures create stability within the abdomen and prevent the organs from moving around too much. They can also carry important nerves, vessels or lymph nodes to and from different regions. The ligaments are categorized according to the organs from which they arise. The notable ligaments include those of the liver, the stomach and the spleen.
- The phrenicocolic ligament or sustentaculum liens is not directly considered a ligament of the spleen, however it stretches between the left hepatic flexure of the transverse colon up to the diaphragm and acts as a hammock of support for the spleen.
- The gastrosplenic ligament links the hilum of the spleen to the stomach
- The splenorenal or lienorenal ligament runs between the spleen and the left kidney.
- The gastrophrenic ligament connects the stomach to the inferior surface of the diaphragm.
- The second ligament attaching to the stomach is the gastrocolic ligament, also known as the greater omentum, which runs to the transverse colon. (The third one is the gastrosplenic ligament mentioned earlier).
There are three major ligaments originating from the liver:
- The falciform ligament attaches the liver to the anterior abdominal wall.
- The gastrohepatic ligament forms a portion of the lesser omentum by running from the lesser curvature of the stomach up to the liver
- The hepatoduodenal ligament forms a communication between the liver and the proximal part of the duodenum. On the right side it forms a thick edge layer of the lesser omentum and contains the portal triad.
The intraperitoneal organs are those that are considered to be almost completely covered by the mesothelial layer of the visceral peritoneum. It is important to recognize that these organs are not actually inside the peritoneal cavity, however they do project into it. They are held in place via ligaments that attach them to the internal abdominal wall and by the mesenteries where they are present.
The list of viscera for this particular categorization includes
- the liver
- the spleen
- the stomach
- the proximal part of the duodenum
- the jejunum
- the ileum
- the transverse colon
- the sigmoid colon
- the superior rectum
The retroperitoneal organs are subcategorized into primary retroperitoneal and secondarily retroperitoneal organs. The primary organs are those that develop and remain beneath the parietal peritoneum. Until now, the kidneys are the only organs that fall into this category and are therefore an exception to the general term retroperitoneal.
The secondary organs are those that develop with a short mesentery and end up communicating with the body wall in order for other organs to develop. The mesentery fuses with the parietal peritoneum lining the internal abdominal wall and forms a type of fusion fascia. Since the parietal peritoneum only covers the anterior aspect of these organs and they can be freed along their lateral aspects where the plane of fusion fascia can be seen, they are classified as secondarily retroperitoneal. This occurs primarily with:
- the small intestine
- the adrenal glands
- the pancreas
- the rest of the duodenum
- the ascending colon
- the descending colon
The peritoneum is a layer of serous membrane that constitutes the inner lining of the abdominopelvic cavity. It consists of two inseparable layers of mesothelium that are known as the parietal peritoneum and the visceral peritoneum. The peritoneal cavity is a theoretical space that exists between the two layers of the peritoneal mesothelium. This space is filled with a thin fluid film that helps prevent friction between the tightly packed organs.
There are two peritoneal subdivisions, known as the greater and lesser sacs. The greater sac consists of the main peritoneal cavity, while the lesser sac or omental bursa is situated posterior to the stomach. The two sacs communicate with each other via the epiploic foramen of Winslow.
The omentum is the double layered fold of the peritoneum which is apparent when it turns back upon itself. It consists of the lesser and greater omenta. The mesentery is a double peritoneal layer that is created by an invagination of the tissue as it tightly packs itself around the organs. The greater sac is divided into both a supracolic and an infracolic compartment, with a paracolic gutter establishing the communication between the two compartments.
A ligament is described as a double layer of peritoneum that can connect an organ to either another organ or to the internal lining of the abdominal wall. These anatomical structures create stability within the abdomen and prevent the organs from moving around too much. The notable ligaments include those of:
- the liver, (falciform, gastrohepatic and hepatoduodenal ligaments)
- the stomach and (gastrophrenic ligament, gastrocolic ligament)
- the spleen. (phrenicocolic, gastrosplenic, splenorenal ligaments)