peritoneum

General organization of the peritoneum

The peritoneum is a thin serous membrane that lines the walls of the abdominal and pelvic cavities and clothes the viscera. The peritoneum can be regarded as a balloon against which organs are pressed from outside.
General Arrangement

Sagittal section of the female abdomen showing the arrangement of the peritoneum

The parietal peritoneum lines the walls of the abdominal and pelvic cavities, and the visceral peritoneum covers the organs. The potential space between the parietal and visceral layers, which is inside space of the balloon, is called the peritoneal cavity.
Parietal peritoneum
Visceral peritoneum


In males, this is a closed cavity, in females, there is communication with the exterior through the uterine tubes, the uterus, and the vagina.


Between the parietal peritoneum and the fascial lining of the abdominal and pelvic walls is a layer of connective tissue called the extraperitoneal tissue; in the area of the kidneys this tissue contains a large amount of fat, which supports the kidneys.

The peritoneal cavity is the largest cavity in the body and is divided into two parts: the greater sac and the lesser sac. The greater sac is the main compartment and extends from the diaphragm down into the pelvis. The lesser sac is smaller and lies behind the stomach.
Greater sac
lesser sac



Sagittal section through the entrance into the lesser sac showing the important structures that form boundaries to the opening
The greater and lesser sacs are in free communication with one another through an oval window called the opening of the lesser sac, or the epiploic foramen. The peritoneum secretes a small amount of serous fluid, the peritoneal fluid, which lubricates the surfaces of the peritoneum and allows free movement between the viscera.


An organ is said to be intraperitoneal when it is almost totally covered with visceral peritoneum. The stomach, jejunum, ileum, and spleen. Retroperitoneal organs lie behind the peritoneum and are only partially covered with visceral peritoneum. The pancreas and the ascending and descending parts of the colon.
Intraperitoneal and Retroperitoneal Relationships


Note the position of the peritoneal reflections, the bare areas, and the peritoneal ligaments
Peritoneal Ligaments Peritoneal ligaments are two-layered folds of peritoneum that connect solid viscera to the abdominal walls. The liver, is connected to the diaphragm by the falciform ligament, the coronary ligament, and the right and left triangular ligaments.

Omenta

Omenta are two-layered folds of peritoneum that connect the stomach to another viscus. The greater omentum connects the greater curvature of the stomach to the transverse colon.
Note that the greater omentum hangs down in front of the small and large intestines


It hangs down like an apron in front of the coils of the small intestine and is folded back on itself to be attached to the transverse colon.
Greater Omentum

Lesser omentum

Greater omentum
The lesser omentum suspends the lesser curvature of the stomach from the fissure of the ligamentum venosum and the porta hepatis on the undersurface of the liver.

The gastrosplenic omentum (ligament) connects the stomach to the hilum of the spleen.

Mesenteries
Mesenteries are two-layered folds of peritoneum connecting parts of the intestines to the posterior abdominal wall,

for example, the mesentery of the small intestine, the transverse mesocolon, and the sigmoid mesocolon. The peritoneal ligaments, omenta, and mesenteries permit blood, lymph vessels, and nerves to reach the viscera.
Peritoneal recesses (arrows) in the region of the cecum and the recess related to the sigmoid mesocolon.

Peritoneal Pouches, Recesses, Spaces, and Gutters

The lesser sac lies behind the stomach and the lesser omentum.
The arrow indicates the position of the opening of the lesser sac.
Lesser Sac
Lesser sac



It extends upward as far as the diaphragm and downward between the layers of the greater omentum. The left margin of the sac is formed by the spleen and the gastrosplenic omentum and splenicorenal ligament.
Transverse section of the lesser sac showing the arrangement of the peritoneum in the formation of the lesser omentum, the gastrosplenic omentum, and the splenicorenal ligament. Arrow indicates the position of the opening of the lesser sac.


The right margin opens into the greater sac through the opening of the lesser sac, or epiploic foramen. The opening into the lesser sac (epiploic foramen) has the following boundaries: Anteriorly: Free border of the lesser omentum, the bile duct, the hepatic artery, and the portal vein Posteriorly: Inferior vena cava Superiorly: Caudate process of the caudate lobe of the liver Inferiorly: First part of the duodenum
Sagittal section through the entrance into the lesser sac showing the important structures that form boundaries to the opening.

Duodenal Recesses

Close to the duodenojejunal junction, there may be four small pocketlike pouches of peritoneum called the superior duodenal, inferior duodenal, paraduodenal, and retroduodenal recesses
Peritoneal recesses, which may be present in the region of the duodenojejunal junction. Note the presence of the inferior mesenteric vein in the peritoneal fold, forming the paraduodenal recess.

Cecal Recesses

Folds of peritoneum close to the cecum produce three peritoneal recesses called the superior ileocecal, the inferior ileocecal, and the retrocecal recesses.
Peritoneal recesses (arrows) in the region of the cecum

Intersigmoid Recess

The intersigmoid recess is situated at the apex of the inverted, V-shaped root of the sigmoid mesocolon; its mouth opens downward.
the recess related to the sigmoid mesocolon

Subphrenic Spaces

The right and left anterior subphrenic spaces lie between the diaphragm and the liver, on each side of the falciform ligament. The right posterior subphrenic space lies between the right lobe of the liver, the right kidney, and the right colic flexure. The right extraperitoneal space lies between the layers of the coronary ligament and is therefore situated between the liver and the diaphragm.

Paracolic Gutters

The paracolic gutters lie on the lateral and medial sides of the ascending and descending colons, respectively. The subphrenic spaces and the paracolic gutters are clinically important because they may be sites for the collection and movement of infected peritoneal fluid.

Nerve Supply of the Peritoneum The parietal peritoneum is sensitive to pain, temperature, touch, and pressure. The parietal peritoneum lining the anterior abdominal wall is supplied by the lower six thoracic and first lumbar nerves. The central part of the diaphragmatic peritoneum is supplied by the phrenic nerves; peripherally, the diaphragmatic peritoneum is supplied by the lower six thoracic nerves. The parietal peritoneum in the pelvis is mainly supplied by the obturator nerve, a branch of the lumbar plexus. The visceral peritoneum is sensitive only to stretch and tearing and is not sensitive to touch, pressure, or temperature. It is supplied by autonomic afferent nerves that supply the viscera or are traveling in the mesenteries. Overdistention of a viscus leads to the sensation of pain. The mesenteries of the small and large intestines are sensitive to mechanical stretching.


Functions of the Peritoneum The peritoneal fluid, which is pale yellow and somewhat viscid, contains leukocytes. It is secreted by the peritoneum and ensures that the mobile viscera glide easily on one another. As a result of the movements of the diaphragm and the abdominal muscles, together with the peristaltic movements of the intestinal tract, the peritoneal fluid is not static. It seems that intraperitoneal movement of fluid toward the diaphragm is continuous, and there it is quickly absorbed into the subperitoneal lymphatic capillaries.
Normal direction of flow of the peritoneal fluid from different parts of the peritoneal cavity to the subphrenic spaces


This can be explained on the basis that the area of peritoneum is extensive in the region of the diaphragm and the respiratory movements of the diaphragm aid lymph flow in the lymph vessels. The peritoneal coverings of the intestine tend to stick together in the presence of infection. The greater omentum, which is kept constantly on the move by the peristalsis of the neighboring intestinal tract, may adhere to other peritoneal surfaces around a focus of infection. In this manner, many of the intraperitoneal infections are sealed off and remain localized. The peritoneal folds play an important part in suspending the various organs within the peritoneal cavity and serve as a means of conveying the blood vessels, lymphatics, and nerves to these organs. Large amounts of fat are stored in the peritoneal ligaments and mesenteries, and especially large amounts can be found in the greater omentum.

Clinical NotesThe Peritoneum and Peritoneal Cavity

Movement of Peritoneal Fluid The peritoneal cavity is divided into an upper part within the abdomen and a lower part in the pelvis. The abdominal part is further subdivided by the many peritoneal reflections into important recesses and spaces, which, in turn, are continued into the paracolic gutters.
Direction of flow of the peritoneal fluid. 1. Normal flow upward to the subphrenic spaces. 2. Flow of inflammatory exudate in peritonitis. 3. The two sites where inflammatory exudate tends to collect when the patient is nursed in the supine position. 4. Accumulation of inflammatory exudate in the pelvis when the patient is nursed in the inclined position.



The attachment of the transverse mesocolon and the mesentery of the small intestine to the posterior abdominal wall provides natural peritoneal barriers that may hinder the movement of infected peritoneal fluid from the upper part to the lower part of the peritoneal cavity.

Greater Omentum

Localization of Infection The greater omentum is often referred to by the surgeons as the abdominal policeman. The lower and the right and left margins are free, and it moves about the peritoneal cavity in response to the peristaltic movements of the neighboring gut. In the first 2 years of life it is poorly developed and thus is less protective in a young child. Later, however, in an acutely inflamed appendix, for example, the inflammatory exudate causes the omentum to adhere to the appendix and wrap itself around the infected organ. By this means, the infection is often localized to a small area of the peritoneal cavity, thus saving the patient from a serious diffuse peritonitis.
A. The normal greater omentum. B. The greater omentum wrapped around an inflamed appendix. C. The greater omentum adherent to the base of a gastric ulcer. One important function of the greater omentum is to attempt to limit the spread of intraperitoneal infections.

Peritoneal PainFrom the Parietal Peritoneum

Abdominal pain originating from the parietal peritoneum is therefore of the somatic type and can be precisely localized. An inflamed parietal peritoneum is extremely sensitive to stretching. Pressure is applied to the abdominal wall with a single finger over the site of the inflammation. The pressure is then removed by suddenly withdrawing the finger. The abdominal wall rebounds, resulting in extreme local pain, which is known as rebound tenderness. It should always be remembered that the parietal peritoneum in the pelvis is innervated by the obturator nerve and can be palpated by means of a rectal or vaginal examination. A pelvic examination can detect extreme tenderness of the parietal peritoneum on the right side.
Some important skin areas involved in referred visceral pain.


From the Visceral Peritoneum The visceral peritoneum, including the mesenteries, is innervated by autonomic afferent nerves. Stretch caused by overdistension of a viscus or pulling on a mesentery gives rise to the sensation of pain. Because the gastrointestinal tract arises embryologically as a midline structure and receives a bilateral nerve supply, pain is referred to the midline. Pain arising from an abdominal viscus is dull and poorly localized.


Peritoneal Dialysis Because the peritoneum is a semipermeable membrane, it allows rapid bidirectional transfer of substances across itself. Because the surface area of the peritoneum is enormous, this transfer property has been made use of in patients with acute renal insufficiency. Internal Abdominal Hernia Occasionally, a loop of intestine enters a peritoneal pouch or recess (e.g., the lesser sac or the duodenal recesses) and becomes strangulated at the edges of the recess.

Embryologic Notes

Development of the Peritoneum and the Peritoneal Cavity Once the lateral mesoderm has split into somatic and splanchnic layers, a cavity is formed between the two, called the intraembryonic coelom. The peritoneal cavity is derived from that part of the embryonic coelom situated caudal to the septum transversum. In the earliest stages, the peritoneal cavity is in free communication with the extraembryonic coelom on each side. Later, with the development of the head, tail, and lateral folds of the embryo, this wide area of communication becomes restricted to the small area within the umbilical cord.
Ventral and dorsal mesenteries and the organs that develop within them



Early in development, the peritoneal cavity is divided into right and left halves by a central partition formed by the dorsal mesentery, the gut, and the small ventral mesentery. However, the ventral mesentery extends only for a short distance along the gut, so that below this level the right and left halves of the peritoneal cavity are in free communication. As a result of the enormous growth of the liver and the enlargement of the developing kidneys, the capacity of the abdominal cavity becomes greatly reduced at about the sixth week of development. It is at this time that the small remaining communication between the peritoneal cavity and extraembryonic coelom becomes important.


Formation of the Lesser and Greater Peritoneal Sacs The extensive growth of the right lobe of the liver pulls the ventral mesentery to the right and causes rotation of the stomach and duodenum. By this means, the upper right part of the peritoneal cavity becomes incorporated into the lesser sac. The right free border of the ventral mesentery becomes the right border of the lesser omentum and the anterior boundary of the entrance into the lesser sac. The remaining part of the peritoneal cavity, which is not included in the lesser sac, is called the greater sac, and the two sacs are in communication through the epiploic foramen.
The rotation of the stomach and the formation of the greater omentum and lesser sac