1. Peritoneum & Peritoneal Cavity
Abdomen, Pelvis & Perineum Unit Lecture 4
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2. Peritoneum
It is a thin serous membrane that lines walls of abdominal and pelvic cavities (parietal peritoneum) & covers viscera (visceral peritoneum). Peritoneal cavity is a potential space between parietal and visceral layers. In males, this is a closed cavity, but in females, there is a communication with the exterior through the uterine tubes, uterus, and vagina. Peritoneum secretes a small amount of serous fluid (peritoneal fluid), which lubricates surfaces of peritoneum and allows free movement between viscera. Extraperitoneal tissue is a layer of connective tissue between fascial lining of abdominal and pelvic walls and parietal peritoneum; near the kidneys this tissue contains a large amount of fat, which supports the kidneys.

3. Embryology of peritoneal cavity
Embryonic Primordial abdominal cavity is lined with mesoderm (parietal peritoneum). The lumen of peritoneal sac is the peritoneal cavity. As the organs develop, they invaginate (protrude) into peritoneal sac, acquiring a peritoneal covering, visceral peritoneum. Some organs such as kidney, pancreas and ascending and descending colons protrude only partially into peritoneal cavity (Retroperitoneal). Other viscera, such as stomach, jejunum, ileum and spleen, protrude completely into peritoneal sac and are almost completely invested by visceral peritoneum (Intraperitoneal). These viscera are connected to abdominal wall by a mesentery (two layers of peritoneum with a thin layer of loose connective tissue between them).

4. Folds of the peritoneum
They are folds of peritoneum that develops from the original embryonic ventral and dorsal mesentery of the abdomen and connect the abdominal organs to each other or to abdominal walls. Some of these folds (peritoneal ligaments, omenta or mesenteries) permit blood, lymph vessels, and nerves to reach the viscera. Peritoneal Ligaments: two-layered folds of peritoneum that connect solid viscera to abdominal walls. Liver is connected to diaphragm by falciform ligament, coronary ligament, and right & left triangular ligaments. Omenta: (omentum=single) They are two-layered folds of peritoneum that connect stomach to another viscus. Mesenteries: are two-layered folds of peritoneum connecting parts of the intestines to posterior abdominal wall:

5. Omentum
two-layered folds of peritoneum connecting stomach to another viscus. Lesser omentum extends from lesser curvature of stomach and first part of duodenum to fissure of ligamentum venosum and porta hepatis on undersurface of liver. It is divided into two parts: Medial hepatogastric ligament Lateral hepatoduodenal ligament Greater omentum connects greater curvature of stomach and first part of duodenum to transverse colon. It hangs down like an apron in front of coils of small intestine and is folded back on itself to be attached to transverse colon. Gastrosplenic omentum (ligament) connects stomach to the hilum of spleen.

6. Mesenteries
Mesentery of small intestine: is a large, fan-shaped, double-layered fold of peritoneum that connects jejunum and ileum to posterior abdominal wall. Its superior attachment is at duodenojejunal junction (to the left of upper lumbar part of vertebral column). It passes obliquely downward and to the right, ending at ileocecal junction near upper border of right sacroiliac joint. It contain aa, vv, nn & lymp.vv. Transverse mesocolon: is a fold of peritoneum that connects transverse colon to posterior abdominal wall. It is originated from posterior abdominal wall across anterior surface of head and body of pancreas and pass outward to surround transverse colon. Sigmoid mesocolon: is an inverted, V-shaped peritoneal fold that attaches sigmoid colon to abdominal wall. Apex of the 'V' is near the division of left common iliac artery into its internal & external branches. Sigmoid and superior rectal vessels, along with the nerves and lymphatics associated with the sigmoid colon, pass through this peritoneal fold.

7. Subdivisions of Peritoneal Cavity
The peritoneal cavity is the largest cavity in the body. It is divided into two parts: Greater sac & Lesser sac (omental bursa). The greater and lesser sacs are in free communication with one another through an oval opening of lesser sac, or epiploic foramen.
Lesser Sac: lies behind stomach &
lesser omentum. The Boundaries are:
Superiorly: diaphragm
Inferiorly: extend till layers of
greater omentum fuse together.
Left margin of the sac is formed by
spleen and gastrosplenic omentum &
splenicorenal ligament.
Right margin opens into the greater sac
through opening of lesser sac (epiploic foramen)

8. Subdivisions of Peritoneal Cavity
Greater Sac: is the main and larger part of peritoneal cavity and extends from diaphragm down into pelvis. Transverse mesocolon (mesentery of transverse colon) divides abdominal cavity into: A. Supracolic compartment, containing stomach, liver, and spleen, B. Infracolic compartment, containing small intestine and ascending and descending colon. The infracolic compartment lies posterior to the greater omentum and is divided into right & left infracolic spaces by mesentery of the small intestine. Free communication occurs between supracolic and infracolic compartments through paracolic gutters, grooves between lateral aspect of ascending or descending colon and posterolateral abdominal wall.

9. Epiploic foramen: Boundaries:
Anteriorly: Free border of lesser omentum which contain hepatic triad (bile duct & hepatic artery anteriorly, and portal vein posteriorly)
Posteriorly: Inferior vena cava
Superiorly: Caudate process of the caudate lobe of the liver
Inferiorly: First part of the duodenum

10. Subdivisions of Peritoneal Cavity
Duodenal Recesses: (Superior duodenal, Inferior duodenal, Paraduodenal & Retroduodenal recesses). They are four small pocket-like pouches of peritoneum close to duodenojejunal junction: Cecal Recesses: (superior ileocecal, inferior ileocecal, and retrocecal recesses). They are folds of peritoneum close to cecum and produce three peritoneal recesses. Intersigmoid Recess: is situated at apex of inverted, V-shaped root of sigmoid mesocolon; its mouth opens downward. Subphrenic Spaces: Right & left anterior subphrenic spaces lie between diaphragm and liver, on each side of falciform ligament. Right posterior subphrenic space lies between right lobe of liver, right kidney, and right colic flexure. Right extraperitoneal space lies between the layers of the coronary ligament and is therefore situated between the liver and the diaphragm.

11. Subdivisions of Peritoneal Cavity
Paracolic Gutters: 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.

12. Nerve Supply of the Peritoneum
A: Parietal peritoneum: is sensitive to pain, temperature, touch, and pressure.
Parietal peritoneum lining anterior abdominal wall is supplied by lower 6 thoracic & first lumbar nerves.
Central part of diaphragmatic peritoneum is supplied by Phrenic nerves;
Peripheral part of diaphragmatic peritoneum is supplied by lower 6 thoracic nerves.
Parietal peritoneum in the pelvis is mainly supplied by Obturator nerve, a branch of the lumbar plexus.
B: Visceral peritoneum is sensitive only to stretch and tearing, but not sensitive to touch, pressure or temperature. It is supplied by autonomic afferent nerves that supply the viscera or are traveling in the mesenteries. Over-distention of a viscus leads to the sensation of pain.

13. Functions of the Peritoneum
1- Secretion of peritoneal fluid to lubricate and glide mobile viscera easily on one another. 2- Peritoneal coverings of intestine tend to stick together in the presence of infection. Greater omentum, which is kept constantly on the move by peristalsis of neighboring intestinal tract, may adhere to other peritoneal surfaces around a focus of infection. therefore, many of intraperitoneal infections are sealed off and remain localized by greater omentum which is called Watch dog or policeman of the abdomen. 3- Peritoneal folds (mesenteries) play an important part in suspending various organs within peritoneal cavity and serve as a means of conveying blood vessels, lymphatics, and nerves to these organs. 4- Large amounts of fat are stored in the peritoneal ligaments and mesenteries, and especially large amounts can be found in the greater omentum.

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