What is the anatomy of the peritoneum?

Anatomy of the Peritoneum

The peritoneum is the largest serous membrane in the body, consisting of a continuous sheet of mesothelial cells on a connective tissue base, which lines the abdominal cavity and covers the visceral organs. 1, 2

Basic Structure and Organization

The peritoneum is divided into two continuous layers:

• Parietal peritoneum: Lines the abdominal wall and accounts for approximately 30% of the total peritoneal surface area 3

  • Receives blood supply from circumflex, iliac, lumbar, intercostal, and epigastric arteries
  • Forms a quadrangular network of large, parallel blood vessels
  • Venous drainage into the inferior vena cava

• Visceral peritoneum: Covers the abdominal organs and accounts for approximately 70% of the total peritoneal surface area 3

  • Receives blood supply from the three major splanchnic arteries: celiac, superior mesenteric, and inferior mesenteric arteries
  • These vessels anastomose extensively
  • Venous drainage into the portal vein

Peritoneal Cavity and Spaces

The peritoneal cavity is a potential space between the parietal and visceral layers containing a small amount of serous fluid. It is divided into:

• Greater sac: Main peritoneal cavity
• Lesser sac (omental bursa): Posterior to the stomach and lesser omentum
• Paracolic gutters: Spaces along the lateral aspects of the ascending and descending colon 4
• Pelvic space: Most dependent part of the peritoneal cavity in the supine position 4

Peritoneal Reflections

The peritoneum forms several important structures:

1. Mesenteries: Double layers of peritoneum that connect the intestines to the posterior abdominal wall

   • Contain blood vessels, lymphatics, and nerves supplying the intestines

2. Omenta:

   • Greater omentum: Hangs from the greater curvature of the stomach, covering the intestines
   • Lesser omentum: Connects the lesser curvature of the stomach to the liver

3. Peritoneal ligaments: Double layers of peritoneum connecting organs to each other or to the abdominal wall

   • Examples include hepatoduodenal, gastrocolic, and falciform ligaments

Microscopic Anatomy

The peritoneum consists of:

• Mesothelial layer: Single layer of flat mesothelial cells with microvilli on their apical surface 5
• Basement membrane: Supporting the mesothelial cells
• Submesothelial connective tissue: Contains blood vessels, lymphatics, nerves, and immune cells

Vascular Supply

• Total effective blood flow to the human peritoneum is estimated between 60-100 mL/min (1-2% of cardiac output) 3
• The anterior abdominal wall peritoneum accounts for only about 4% of the peritoneal surface 3
• The peritoneum has an extensive lymphatic network that plays a crucial role in fluid reabsorption and immune function

Physiological Functions

The peritoneum serves several important functions:

1. Fluid production and reabsorption: Maintains a small amount of lubricating peritoneal fluid
2. Immune defense: Contains macrophages and other immune cells that protect against infection
3. Barrier function: Acts as a selective barrier for fluid and cell transport 5
4. Tissue repair: Participates in wound healing and adhesion formation
5. Prevention of tumor dissemination: Under normal conditions 5

Clinical Considerations

1. Peritonitis Classification 4:

   • Primary peritonitis: Bacterial infection without gastrointestinal tract perforation
   • Secondary peritonitis: Infection resulting from loss of integrity of the gastrointestinal tract
   • Tertiary peritonitis: Recurrent infection occurring >48 hours after apparently successful treatment of secondary peritonitis

2. Surgical Considerations 4:

   • During laparotomy closure, separate closure of the peritoneum is not recommended as it shows no benefit and increases operative time
   • Mass closure (including all layers except skin in a single bite) is preferred over layered closure in emergency settings as it is faster with no difference in complication rates

3. Peritoneal Fluid Flow:

   • In supine position, fluid tends to flow toward the pelvis (most dependent area) 4
   • Trendelenburg position may increase sensitivity for detecting abnormal fluid in the right upper quadrant 4

4. Pathological Processes:

   • Inflammation can induce neoangiogenesis with abnormal vessel formation 3
   • The peritoneum plays a central role in the pathogenesis of conditions like peritonitis and peritoneal carcinomatosis 2

Understanding the complex anatomy and physiology of the peritoneum is essential for comprehending pathophysiological mechanisms and developing effective treatment strategies for peritoneal diseases.