The peritoneum is a layer of serous membrane that constitutes the inner lining of the abdominopelvic cavity. 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.
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.
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 and 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. 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 epiploic foramen is hiatus in the peritoneum that can be found just below the neck of the gallbladder. It is divided into both a supracolic and an infracolic compartment. It is bordered 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 and inferiorly by the proximal part of the duodenum, the portal vein, the hepatic artery and the bile duct. 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 which 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, while the splenorenal or lienorenal ligament runs between the spleen and the left kidney. The stomach has three ligaments that directly relate to it including the gastrophrenic ligament which runs from the stomach to the inferior surface of the diaphragm, the gastrosplenic ligament which was previously mentioned in the list of splenic ligaments and finally the gastrocolic ligament which is also known as the greater omentum and links the stomach to the transverse colon. Lastly, the hepatic ligaments or ligaments of the liver. The falciform ligament attaches the liver to the anterior abdominal wall, while 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.
Intraperitoneal and Retroperitoneal Organs
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 and the superior rectum.
The retroperitoneal organs are subcategorized into primarily 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, however the other organs in this subcategory are the adrenal glands, the pancreas, the rest of the duodenum, the ascending colon and the descending colon.