Peritoneum Anatomy Notes

Peritoneum

  • Layer of simple squamous epithelial-like cells with supportive layer of connective tissue.
  • Two Layers:
    • Parietal: Lines the abdominal wall/peritoneal cavity.
    • Visceral: Reflects onto and covers organs.
  • Peritoneal fluid exists between the parietal & visceral layers of the peritoneum.

Organ Relationships to Peritoneum

  • Intraperitoneal organs: Nearly completely covered by visceral peritoneum.
  • Extraperitoneal organs: External to parietal peritoneum, partially covered with visceral peritoneum.
    • Developing organs protrude into the peritoneal sac and acquire visceral peritoneum covering.
  • Retroperitoneal organs: Posterior to parietal peritoneum, against the posterior abdominal wall.
    • Typically, one surface (usually the anterior) is covered by parietal peritoneum.
  • Subperitoneal organs: Inferior to parietal peritoneum.
    • The superior surface of the organ is covered by parietal peritoneum.

Peritoneal Contents

  • Esophagus
  • Liver
  • Gallbladder
  • Stomach
  • Colon
  • Jejunum
  • Appendix
  • Small Intestine
  • Rectum

Peritoneal Cavity

  • Mesenteries
    • Double layer of peritoneum.
    • Connects organ to body wall, suspending viscera.
    • Contains vessels and nerves.
  • Reflections
    • Bends in the parietal peritoneum following the conical structure of the abdomen.
  • Recesses
    • Spaces created by the parietal peritoneal reflections.

Peritoneal Folds and Fossae

  • Folds:
    • Median Umbilical Fold
      • Apex of the bladder to the umbilicus.
      • Covers the median umbilical ligament (remnant of embryonic urachus/allantois).
    • Medial Umbilical Folds
      • Cover the medial umbilical ligaments (occluded umbilical arteries).
      • Median and medial umbilical folds are separated by supravesical fossae.
    • Lateral Umbilical Folds
      • Cover inferior epigastric vessels.
  • Fossae:
    • Supravesical fossae
      • Median to medial umbilical folds.
    • Medial inguinal fossae (inguinal triangles or Hesselbach triangles)
      • Medial to lateral umbilical folds.
      • Site of direct inguinal hernias.
    • Lateral inguinal fossae
      • Lateral to the lateral umbilical folds and contain the deep inguinal ring.
      • Common site of indirect inguinal hernias.

Peritoneum – Innervation & Blood Supply

  • Parietal Peritoneum
    • Blood supply from branches of body wall vessels.
    • Somatic afferents from associated spinal nerves.
    • Sensitive to interior body wall pressure, pain, heat and cold, and laceration.
    • Well-localized pain.
  • Visceral Peritoneum
    • Blood supply same as viscera.
    • Visceral afferents accompanying autonomic nerves (sympathetic and parasympathetic).
    • Not sensitive to touch, heat and cold, and laceration.
    • Stimulated by stretching and chemical irritation.
    • Referred discomfort (non-specific localization).

Mesenteries & Ligaments

  • Double layer of peritoneum connecting viscera to peritoneal wall.
  • Some ligaments connect viscera to one another.
  • Mesenteries contain neurovasculature.
  • Major mesenteries:
    • Small intestines – principle mesentery – “the mesentery”.
    • Vermiform appendix - mesoappendix.
    • Transverse colon – transverse mesocolon.
    • Sigmoid colon – sigmoid mesocolon.
  • Omenta
    • Pass between stomach and other organs and contain neurovasculature.
    1. Greater omentum
      • 4 layers of peritoneum.
      • Greater curvature of stomach & proximal duodenum.
      • Folds back to attach to transverse colon and transverse mesocolon.
      • Ligaments associated: Gastrophrenic, Gastrosplenic, Gastrocolic.
    2. Lesser omentum
      • 2 layers of peritoneum.
      • Lesser curvature of stomach & proximal duodenum to liver.
      • Ligaments associated: Hepatogastric, Hepatoduodenal.
        • Hepatoduodenal ligament contains the portal triad.
      • Falciform ligament
        • Contains the round ligament of the liver.
      • Round ligament of liver
        • a.k.a. ligamentum teres hepatis
        • Remnant of the umbilical vein.

Peritoneal Cavity – Divisions

  • Greater Sac
    • Main portion of the cavity.
    • Divided by the transverse colon into:
      • Supracolic: Contains the stomach, liver, spleen.
      • Infracolic: Posterior to the greater omentum; contains the small intestines, ascending and descending colon.
        • Right and left infracolic spaces are divided by the principle mesentery.
    • Paracolic gutters:
      • Right: Lateral to the ascending colon.
      • Left: Lateral to the descending colon.
  • Lesser Sac (omental bursa)
    • Posterior to the stomach and lesser omentum.
    • Omental foramen (a.k.a. epiploic foramen/ Foramen of Winslow):
      • Anterior: Hepatoduodenal ligament.
      • Posterior: Retroperitoneal Inferior Vena Cava (IVC) & Right crus of the diaphragm.
      • Superior: Liver.
      • Inferior: Superior or 1st part of the duodenum.