Peritoneum and peritoneal cavity

Peritoneal Basics - The Body's Saran Wrap

• Peritoneum: A large, continuous serous membrane lining the abdominopelvic cavity, forming a potential space-the peritoneal cavity.
• Layers:
  • Parietal: Lines the internal abdominopelvic walls. Receives somatic innervation (sharp, localized pain).
  • Visceral: Invests the organs. Receives visceral innervation (dull, poorly localized pain).
• Function: The thin layer of peritoneal fluid lubricates organ movement and provides immune defense via leukocytes and antibodies.

⭐ The greater omentum ("policeman of the abdomen") can migrate to wall off infections.

Cavity Subdivisions - Abdominal Real Estate

• Greater Sac: The main, larger area of the peritoneal cavity.
• Lesser Sac (Omental Bursa): A smaller cavity posterior to the stomach and lesser omentum.
• Communication: The sacs connect via the Foramen of Winslow (Omental Foramen).

Key Gutters & Recesses

• Paracolic Gutters: Channels alongside the ascending/descending colon.
• Clinically Significant Pouches (Gravity-Dependent):
  • Morison's Pouch (Hepatorenal Recess): Between the liver and right kidney; the most dependent area when supine.
  • Pouch of Douglas:
    • Rectouterine Pouch (Females)
    • Rectovesical Pouch (Males)

⭐ In a supine patient, fluid from a perforated ulcer often collects in Morison's Pouch.

Organ Relations - The In vs. Out Crowd

• Intraperitoneal: Organs suspended in the peritoneal cavity by a mesentery; almost completely covered by visceral peritoneum.
• Retroperitoneal: Organs outside the peritoneal cavity, with only their anterior surface covered by parietal peritoneum.

⭐ The duodenum is a transition organ: its first part is intraperitoneal, while the 2nd, 3rd, and 4th parts are secondarily retroperitoneal.

Peritoneal Folds - Gut's Supporting Cast

• Mesentery: Double layer of peritoneum connecting an intraperitoneal organ to the posterior abdominal wall.
• Omentum: A double-layered extension of the peritoneum passing from the stomach and proximal duodenum to adjacent organs.
  • Greater Omentum: Hangs from the stomach's greater curvature. The "policeman of the abdomen" due to its ability to migrate to inflamed areas.
  • Lesser Omentum: Connects the stomach's lesser curvature and duodenum to the liver.
• Peritoneal Ligament: Folds of peritoneum that connect organs to one another or to the abdominal wall.
  • Hepatoduodenal Ligament: Free edge of the lesser omentum. 📌 Mnemonic DAV: Duct (bile), Artery (hepatic), Vein (portal).
  • Other Ligaments: Falciform, Gastrosplenic, Splenorenal.

⭐ The hepatoduodenal ligament contains the portal triad (proper hepatic artery, portal vein, common bile duct). A Pringle maneuver involves clamping this ligament to control hepatic bleeding.

High‑Yield Points - ⚡ Biggest Takeaways

• The peritoneum consists of a parietal layer (lining the abdominal wall) and a visceral layer (covering the organs).
• Intraperitoneal organs are suspended by a mesentery, while retroperitoneal organs are fixed behind the peritoneum.
• The lesser omentum is a crucial structure as it contains the portal triad (portal vein, hepatic artery, bile duct).
• The greater omentum acts as the "policeman of the abdomen" by walling off infections.
• Ascites is the pathologic accumulation of fluid within the peritoneal cavity.