Peritoneum

Peritoneum

Also known as: peritoneal cavity, parietal peritoneum, visceral peritoneum

The peritoneum is the largest serous membrane in the body, with an area of about 1.8 m². It lines the abdominopelvic walls as parietal peritoneum and covers the viscera as visceral peritoneum. Between the two is the potential peritoneal cavity, which holds a thin film of fluid.

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Overview

Surface area≈1.8 m² (similar to skin)

Normal fluid<100 mL

The parietal peritoneum lines the inner abdominal and pelvic walls and the underside of the diaphragm. The visceral peritoneum forms the serosa of the organs. The two are continuous through double folds that suspend the organs and carry their vessels and nerves: mesenteries, omenta and peritoneal ligaments. The peritoneal cavity normally contains only a small volume of serous fluid, typically under 100 mL. In males it is closed. In females it communicates with the exterior through the uterine tubes, uterus and vagina, a possible route for infection.

The cavity has two parts. The greater sac is the main compartment. The lesser sac (omental bursa) lies behind the stomach and opens into the greater sac through the omental foramen. The transverse mesocolon divides the greater sac into a supracolic compartment (liver, stomach, spleen, subphrenic and hepatorenal spaces) and an infracolic compartment. The root of the mesentery divides the infracolic compartment into right and left spaces. The paracolic gutters run lateral to the ascending and descending colon and connect the upper abdomen with the pelvis.

Organs are classified by their relation to the peritoneum. Intraperitoneal organs are almost completely covered and usually have a mesentery: stomach, first 2 cm of the duodenum, jejunum, ileum, caecum, appendix, transverse and sigmoid colon, liver, spleen and the tail of the pancreas. Retroperitoneal organs lie behind the peritoneum. Some are primarily retroperitoneal, never having had a mesentery: kidneys, ureters, suprarenals, aorta and IVC. Others are secondarily retroperitoneal, having lost a mesentery by fusion to the posterior wall: duodenum parts 2–4, pancreas, and ascending and descending colon. Subperitoneal organs lie below the pelvic peritoneum, such as the lower rectum and the bladder.

Location: Lines the abdominopelvic cavity and invests the abdominal viscera.

Parts & subdivisions

Greater sac
Main part of the peritoneal cavity, with supracolic and infracolic compartments, paracolic gutters and pelvic pouches.
Lesser sac (omental bursa)
Recess behind the stomach and lesser omentum.
Greater omentum
Apron hanging from the greater curvature of the stomach.
Lesser omentum
Fold from the lesser curvature to the liver.
Mesentery and mesocolons
Suspend the jejunum and ileum, transverse colon, sigmoid colon and appendix.
Hepatorenal pouch (Morison)
Between the liver and right kidney; the lowest point of the abdominal cavity when supine. Fluid collects here (FAST ultrasound view).
Recto-uterine / rectovesical pouch
Lowest point of the cavity when upright.

Anatomy

Innervation: Parietal peritoneum receives somatic innervation from the lower intercostal, subcostal, iliohypogastric and ilioinguinal nerves (anterior wall) and the phrenic nerve (central diaphragm, C3–C5, causing shoulder-tip pain). Its pain is sharp and well localised, with tenderness, guarding and rebound. Visceral peritoneum receives autonomic afferents and is sensitive only to stretch and chemical irritation. Its pain is dull, poorly localised and referred to the epigastrium (foregut), umbilical region (midgut) or hypogastrium (hindgut).
Arterial supply: Parietal peritoneum from the vessels of the body wall; visceral peritoneum from the vessels of the organ it covers.
Histology: Simple squamous mesothelium on a thin layer of connective tissue with blood and lymph capillaries.
Development: The peritoneal cavity comes from the intraembryonic coelom. The gut is suspended by dorsal and ventral mesenteries. The ventral mesentery persists only around the foregut (lesser omentum, falciform ligament). Rotation and fusion produce the lesser sac and the secondarily retroperitoneal organs.

Function

Provides friction-free movement of the viscera.
Suspends organs and carries their vessels, lymphatics and nerves.
Defends against infection (omentum, peritoneal macrophages and lymphocytes) and walls off inflammation.
Acts as a large semipermeable exchange surface, the basis of peritoneal dialysis.
Stores fat (omenta, mesenteries).

Clinical significance

Peritonitis

Inflammation of the peritoneum, usually secondary to perforation of a viscus, appendicitis, diverticulitis or anastomotic leak. It produces a rigid, board-like abdomen with guarding, rebound tenderness and absent bowel sounds, and is a surgical emergency. Spontaneous bacterial peritonitis complicates cirrhotic ascites; it is diagnosed when the ascitic neutrophil count exceeds 250 per mm³.

Ascites

Free peritoneal fluid. A serum–ascites albumin gradient of at least 11 g/L indicates portal hypertension (cirrhosis, heart failure, Budd–Chiari syndrome). A lower gradient suggests peritoneal disease (carcinomatosis, tuberculosis), pancreatitis or nephrotic syndrome.

Spread of fluid and pus

The right paracolic gutter links the pelvis with the hepatorenal pouch and right subphrenic space, which explains subphrenic abscesses after appendicitis. Posterior gastric perforation fills the lesser sac first.

Mnemonics

Retroperitoneal organs: SAD PUCKER

Suprarenals, Aorta/IVC, Duodenum (2–4), Pancreas (except tail), Ureters, Colon (ascending/descending), Kidneys, Esophagus, Rectum (lower two-thirds).

Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.