Mednotes.

Peritoneal Cavity, Mesentery, Omentum, and Ligaments

Summary

  • Peritoneum
    • Membrane
    • Contents
    • Structures
  • Mesentery
  • Omentum
  • Peritoneal ligaments

Peritoneum

  • Serous membrane with 2 layers
    • Parietal peritoneum – lines the abdominal wall
    • Visceral peritoneum  – lines the viscera
      • Intraperitoneal organs are simply organs that are covered with visceral peritoneum
        • Will be connected to the body wall/parietal peritoneum via ligaments, omentum, or mesentery (except liver which is kind of directly connected)
      • Extraperitoneal organs lie between the parietal peritoneum and the abdominal wall – therefore will usually have a surface covered in peritoneum
Key peritoneal features.
  • Certain aspects of the peritoneum also contain fat – this provides protection to the organs within
  • There are several types of peritoneal folds
    1. Mesentery – between posterior abdominal wall and organ
    2. Ligament – between two organs
    3. Omentum – between stomach and another organ
Abdominal structures are either intraperitoneal or extraperitoneal (retroperitoneal/subperitoneal). Table from Wikipedia

 

Subdivisions of the peritoneal cavity
  • There are two main divisions of the peritoneal cavity
    1. The Greater Sac
    2. The Lesser Sac (Omental Bursa) 
      • This is a potential space
      • Boundaries:
        • The lesser sac lies posterior to the hepatoduodenal ligament, lesser omentum, and stomach
        • Superiorly limited by the diaphragm
        • Inferiorly limited by the fused greater omentum/transverse mesocolon
      • Clinically relevant due to various pathologies that can affect it
  • Both of these communicate via the (omental) epiploic foramen 
    • The boundaries of this are clinically important in surgery
      • Anterior: portal triad/hepatoduodenal ligament
      • Posterior: peritoneum covering IVC and right crus of diaphragm
      • Superior: caudate lobe of liver
      • Inferiorly: Superior duodenum + portal triad

        The epiploic foramen and greater sac (red) vs lesser sac (blue)

The Mesentery

  • = ‘Middle Intestine’
    • This is a double layer of the peritoneum which connects the organ/visceral peritoneum to the posterior abdominal wall’s peritoneum. 
    • Developed when an (intraperitoneal) organ invaginates the peritoneum
      • Therefore it is essentially a kind of stalk.
  • Embryologically, all of the GIT is intraperitoneal when it first develops and suspended by the dorsal mesentery.
    • However, some parts (the descending/ascending colon) are pushed out of the peritoneum and become secondarily retroperitoneal
  • The mesentery communicates nerves and vessels
  • It is actually quite fragmented depending on the organs it contains
  • 2 main bits
    • Mesentery proper – Jejunum and ileum
      • This is what is usually referred to as ‘the mesentery’
    • Mesocolon – covers parts of the large intestine
      1. Transverse mesocolon
      2. Sigmoid mesocolon
      3. Mesoappendix – mesentery covers the ideal aspect of the appendix
      4. Mesorectum – attaches to upper third of rectum
      • NB the ascending and descending colon, and middle 1/3 of rectum are fixed to the body wall

Omentum

  • This is a double layer of peritoneum extending from the stomach
  • Lesser omentum – lesser curvature of stomach to the liver
    • Also attaches to the greater curvature
  • Greater omentum – hangs down the greater curvature of the stomach.
    • This is the largest peritoneal fold
    • Folds back to become continuous with the transverse mesocolon
    • Contains the left and right gastroepiploic arteries (which anastamose to form the epiploic arterial arc)
  • The omenta can contain within them some ligaments as well
  • Fat contained within here provides protection from trauma (as does the peritoneum as a whole)

Peritoneal Ligaments

  • A peritoneal double layer/fold that connects an organ to another organ
    • 3 hepatic and 3 gastric ligaments + splenorenal ligament
    1. Hepatic ligaments:
      1. Falciform ligament : Connects liver -> anterior abdominal wall
        • Attaches from umbilicus to below the ribs
        • Divides the left and right hepatic lobes
      2. Gastrohepatic ligment:  Liver -> stomach (part of lesser omentum)
      3. Hepatoduodenal ligament: Liver -> duodenum (free edge of lesser omentum)
        • This conducts the portal triad and divides the greater and lesser sacs

 

 

  • Gastric ligaments:
    • Gastrophrenic ligament: Stomach -> Diaphragm
    • Gastrosplenic ligament: Stomach ->  Spleen
    • Gastrocolic ligament: Stomach -> Transverse Colon (part of greater omentum)
    • Gastrohepatic ligament – see above