M01.06.003 The Peritoneum

The peritoneum is a continuous serous membrane that lines the abdominal cavity and envelops the abdominal organs (viscera). It plays a crucial role in supporting the organs and providing pathways for blood vessels, lymphatics, and nerves.

This article covers the anatomy of the peritoneum, including its structure, relationship with abdominal organs, and clinical relevance.

Structure of the Peritoneum

The peritoneum consists of two layers that are continuous with each other:

1. Parietal Peritoneum

• Lines the internal surface of the abdominopelvic wall.
• Derived from somatic mesoderm.
• Innervated by somatic nerves, making it sensitive to pain, pressure, temperature, and laceration.
• Pain is well localized.

2. Visceral Peritoneum

• Covers the majority of the abdominal viscera.
• Derived from splanchnic mesoderm.
• Innervated by autonomic nerves, making it sensitive to stretch and chemical irritation.
• Pain is poorly localized and is referred to dermatomes corresponding to the affected organ.

Peritoneal Cavity

• The potential space between the parietal and visceral peritoneum.
• Normally contains a small amount of lubricating fluid.

Peritoneal Adhesions

Damage to the peritoneum due to infection, surgery, or injury can lead to fibrous adhesions, which may:

• Cause pain.
• Lead to volvulus (twisting of intestines), potentially causing bowel obstruction.

Intraperitoneal & Retroperitoneal Organs

The abdominal viscera are categorized based on their relationship to the peritoneum.

1. Intraperitoneal Organs

• Completely enclosed by visceral peritoneum.
• Suspended by mesentery.
• Examples:
  • Stomach
  • Liver
  • Spleen
  • Small intestine (jejunum, ileum)
  • Transverse and sigmoid colon

2. Retroperitoneal Organs

• Only covered by the peritoneum anteriorly.
• Lack of a mesentery.
• Can be further classified as: a) Primarily Retroperitoneal
  • Developed outside the peritoneal cavity.
  • Examples:
    • Esophagus
    • Rectum
    • Kidneys
  b) Secondarily Retroperitoneal
  • Initially intraperitoneal during embryonic development but became retroperitoneal.
  • Examples:
    • Ascending & Descending Colon
    • Duodenum (except the first part)
    • Pancreas (except tail)

Mnemonic: SAD PUCKER

Helps recall retroperitoneal structures:

• S = Suprarenal (adrenal) glands
• A = Aorta/IVC
• D = Duodenum (except first 2 cm)
• P = Pancreas (except tail)
• U = Ureters
• C = Colon (ascending & descending)
• K = Kidneys
• E = Esophagus
• R = Rectum

Peritoneal Reflections

The peritoneum is highly folded and forms various structures:

1. Mesentery

• A double layer of visceral peritoneum that connects an organ to the posterior abdominal wall.
• Provides a passage for blood vessels, lymphatics, and nerves.
• Examples:
  • The Mesentery (for small intestine)
  • Transverse mesocolon
  • Sigmoid mesocolon
  • Mesoappendix

2. Omenta

• Large folds of peritoneum that extend from the stomach and duodenum.

a) Greater Omentum

• Four-layered fold hanging from the greater curvature of the stomach.
• Functions:
  • Fat storage
  • Immune defense (acts as the “abdominal policeman” by migrating to sites of infection/inflammation).

b) Lesser Omentum

• Double layer of peritoneum extending from the lesser curvature of the stomach to the liver.
• Contains two ligaments:
  • Hepatogastric ligament (connects the liver to the stomach).
  • Hepatoduodenal ligament (contains the portal triad: hepatic artery, portal vein, bile duct).

3. Peritoneal Ligaments

• Double layers of peritoneum connecting organs or to the abdominal wall.
• Example:
  • Hepatogastric ligament (liver to stomach).

Clinical Relevance – Referred Pain

Pain from the peritoneum varies based on its source:

1. Visceral Peritoneum

• Pain is poorly localized.
• Referred to dermatomes based on the embryological origin of the affected organ: RegionOrgansReferred Pain AreaForegutEsophagus, stomach, pancreas, liver, gallbladder, proximal duodenumEpigastric regionMidgutDistal duodenum to proximal 2/3 of transverse colonUmbilical regionHindgutDistal 1/3 of transverse colon to upper anal canalSuprapubic region
• Retroperitoneal organs (e.g., kidneys, pancreas) may present as back pain.
• Diaphragmatic irritation (e.g., gallbladder or liver inflammation) can result in shoulder tip pain.

2. Appendicitis

• Early stage: Referred pain in the umbilical region (visceral peritoneum irritation).
• Late stage: Localized pain in the right lower quadrant (parietal peritoneum irritation).

Summary Table: Peritoneum Key Points

Points to Remember

• Parietal peritoneum has somatic innervation → localized pain.
• Visceral peritoneum has autonomic innervation → referred pain.
• Greater omentum acts as the abdominal policeman.
• SAD PUCKER mnemonic helps recall retroperitoneal organs.
• Appendicitis pain migrates from the umbilical region to → right lower quadrant.

Bibliography & References

1. Moore, K.L., Dalley, A.F., & Agur, A.M.R. (2018). Clinically Oriented Anatomy (8th ed.). Lippincott Williams & Wilkins.
2. Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2020). Gray’s Anatomy for Students (4th ed.). Elsevier.
3. Standring, S. (2020). Gray’s Anatomy: The Anatomical Basis of Clinical Practice (42nd ed.). Elsevier.
4. TeachMeAnatomy – The Peritoneum. Available at: https://teachmeanatomy.info