Peritoneum Anatomy Notes

Peritoneum

• Peritoneum is covered by mesothelium, a layer of simple squamous epithelial-like cells with a supportive layer of connective tissue.
• It has two layers:
  • Parietal: lines the abdominal wall/peritoneal cavity.
  • Visceral: reflects onto and covers organs.

Peritoneal Cavity

• The peritoneal cavity lies between the parietal and visceral layers of the peritoneum.
• It consists of two sacs:
  • Greater sac: extends from the diaphragm to the pelvis.
  • Lesser sac: located behind the stomach.
• These sacs communicate at the epiploic foramen (foramen of Winslow).

Peritoneum - Organs

• The abdominal viscera are divided based on their relationship to the peritoneum into:
  • Intraperitoneal organs: enveloped by visceral peritoneum, covering them both anteriorly and posteriorly. Examples: stomach, liver, and spleen.
  • Retroperitoneal organs: not associated with visceral peritoneum; only covered in parietal peritoneum on their anterior surface.
    • Primarily retroperitoneal organs: developed and remain outside the parietal peritoneum. Examples: esophagus, rectum, and kidneys.
    • Secondarily retroperitoneal organs: were initially intraperitoneal but became retroperitoneal during embryogenesis as their mesentery fused with the posterior abdominal wall. Only their anterior surface is covered with peritoneum. Examples: ascending and descending colon.

Mnemonic for Retroperitoneal Organs: SAD PUCKER

• S = Suprarenal (adrenal) Glands
• A = Aorta/IVC
• D = Duodenum (except the proximal 2cm, the duodenal cap)
• P = Pancreas (except the tail)
• U = Ureters
• C = Colon (ascending and descending parts)
• K = Kidneys
• E = Esophagus
• R = Rectum

Peritoneal Cavity - Specializations

• Mesenteries:
  • Double layer of peritoneum that reflects away from the abdominal wall.
  • Connects organ to body wall (suspends viscera).
  • Contains vessels and nerves.
• Reflections:
  • Bends in the parietal peritoneum.
• Recesses:
  • Spaces created by the parietal peritoneal reflections.
• Fold:
  • Peritoneum raised from the body wall by vessels and ducts.

Peritoneal Folds

• Folds:
  • Median Umbilical Fold:
    • Apex of bladder to umbilicus.
    • Covers median umbilical ligament (remnant of embryonic urachus/allantois).
  • Medial Umbilical Folds:
    • Cover 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 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.
     • Gastrophrenic ligament.
     • Gastrosplenic ligament.
     • Gastrocolic ligament.
  2. Lesser omentum:
     • 2 layers or peritoneum.
     • Lesser curvature of stomach & proximal duodenum to liver.
     • Hepatogastric ligament.
     • Hepatoduodenal ligament.
     • Contains portal triad.
  • Falciform ligament:
    • Contains round ligament of the liver.
    • a.k.a. ligamentum teres hepatis.
    • Remnant of umbilical vein.

Peritoneal Cavity – Divisions

• Greater Sac:
  • Main portion of cavity.
  • Greater Sac divided by transverse colon.
    • Supracolic:
      • Stomach, liver, spleen.
    • Infracolic:
      • Posterior to greater omentum.
      • Small intestines, ascending and descending colon.
      • Right and left infracolic space divided by the principle mesentery.
    • Paracolic gutters:
      • Right is lateral to ascending colon.
      • Left is lateral to descending colon.
• Lesser Sac (omental bursa):
  • Posterior to stomach and lesser omentum.
• Omental foramen:
  • Anterior: hepatoduodenal ligament.
  • Posterior: Retroperitoneal IVC & R crus of diaphragm.
  • Superior: Liver.
  • Inferior: Superior or 1st part of duodenum.
  • a.k.a. epiploic foramen/ Foramen of Winslow.