Peritoneal Compartments

Peritoneal cavity divided into compartments
- Supracolic
- Infracolic
- Pelvic
Dividing line between Supracolic and Infracolic compartments
- Attachment of the Transverse Mesocolon to the posterior abdominal wall

Lesser Sac

Anterior Wall:
- Posterior layer of Lesser Omentum
- Peritoneum over the posterior aspect of the Stomach
- Posterior of the two anterior layers of the Greater Omentum
Posterior Wall:
- Anterior of the two posterior layers of the Greater Omentum
  - Adheres to but is surgically separable from the anterior surface of the Transverse Colon and Transverse Mesocolon
- Peritoneum that covers:
  - Front of the neck and body of Pancreas
  - Upper part of Left Kidney
  - Left Suprarenal Gland
  - Commencement of Abdominal Aorta
  - Coeliac Artery (Plexus and Nodes)
  - Part of the Diaphragm
    - NB: Common Hepatic Artery also in the posterior wall
Upper border
- Narrow and located at the right side of the abdominal Oesophagus
- Where the peritoneum of the posterior wall is reflected anteriorly on the inferior aspect of the diaphragm to form the posterior layer of the Lesser Omentum
Lower border
- Theoretically can extend down between the anterior two layers and the posterior two layers of the Greater Omentum
  - However, fusion of the two layers of the Greater Omentum means the lesser sac does not extend much below the Transverse Colon
- Lesser sac extends behind the first 2.5cm of Duodenum
Left border
- Formed by the Splenorenal and Gastrosplenic ligaments at the tail end of the Pancreas

Definition
- Two layers of peritoneum extending between the Liver and the Lesser Curvature of the Stomach
  - A.k.a. Gastrohepatic Omentum
Attachments
- Extends from right side of the abdominal Oesophagus and along the Lesser Curvature to the first 2cm of the Duodenum
- Liver attachment is ‘L’ Shaped to the Fissure for the Ligamentum Venosum and the Porta Hepatis.
  - NB: There is NO attachment to the fissure for the Ligamentum Teres
Superior extension
- Two layers enclose the Liver and then spread onto the diaphragm and anterior abdominal wall as the Coronary, Triangular and Falciform Ligaments
  - Anterior layer continuous with the posterior layer of the Left Triangular Ligament
Inferior extension – Two layers become the Greater Omentum
NB: Derived from the Ventral Mesogastrium

Double fold of peritoneum
Passes from Transverse Colon to the front of the 2nd part of the Duodenum and to front of Head and Body of the Pancreas
- Adherent to the posterior surface of the Greater Omentum

Attachments of Liver to the Diaphragm and abdominal wall define the subdivisions of the Supracolic compartment
Falciform Ligament – divides the Left and Right Subphrenic (Subdiaphragmatic) spaces
- Two spaces closed above by the superior layer of the Coronary Ligament and the anterior layer of the Left Triangular Ligament
Right Subhepatic Space (Hepatorenal Pouch of Morrison)
- Behind the right lobe of the Liver and in front of the Right Kidney
- Superiorly, space closed above by the inferior layer of the Coronary Ligament and the small right Triangular Ligament
- To the right, bounded by the abdominal surface of the Diaphragm
- To the left, the space communicates through the Epiploic Foramen with the Lesser Sac or Left Subhepatic Space
- Inferiorly, it is continuous with the Right Paracolic Gutter
When supine, Hepatorenal pouch is the lowest part of the peritoneal cavity (with the sole exception of the pelvis)
- Thus, area of intraperitoneal fluid accumulation

Divided into two by the attachment of the Root of the Mesentery of the Small Bowel
To the right of the Mesentery: Right Infracolic space
- Triangular
- Apex at the Ileocaecal Junction
- Right side: Ascending Colon
- Upper border: Attachment of the Transverse Mesocolon
To the left of the Mesentery: Left Infracolic space
- Quadrilateral
- Widens below where it is continuous across the Pelvic Brim with the pelvic cavity
- Left side: Descending Colon
- Upper border: Attachment of the Transverse Mesocolon

Small Bowel Mesentery

Course: Passes down from left to right at an angle of about 45°, begins at the Duodenojejunal Junction ⇒ Crosses 3rd part of the Duodenum where the Superior Mesenteric Vessels enter between its two layers ⇒ Continues downwards across the Aorta, Inferior Vena Cava, Right Psoas Muscle, Right Ureter ⇒ Reaches Right Iliac Fossa
- NB: Root of the Mesentery also related posteriorly to the Right Gonadal Vessels
Length of attachment: 15cm
Depth of mesentery (from root to gut): 20cm at its deepest (i.e. in the central part)

Numerous Pacinian Corpuscles are located in the retroperitoneal tissue in the region of the Mesentery Root – tension and traction on peritoneal folds in the upper abdo cause a drop in blood pressure by undue stimulation of these encapsulated mechanoreceptors

Lateral to the Descending Colon
Limited above by the Phrenicocolic Ligament (small transverse fold of peritoneum between the Splenic Flexure and Diaphragm
Traced downwards – left attachment of the lateral limb of the Sigmoid Mesocolon at the Pelvic Brim

Upside-down V-Shape
Two limbs diverge from each other at the bifurcation of the Common Iliac Vessels on the Pelvic Brim over the Left Sacroiliac Joint
Left Ureter lies over the bifurcation of the Common Iliac Artery
Inferior Mesenteric Vessels lie medial to the Left Ureter
Inferior Mesenteric Vein lies between the Inferior Mesenteric Artery and the Left Ureter
Lateral limb
- Passes forwards along the Pelvic Brim over the External Iliac vessels halfway to the Inguinal Ligament
Medial limb
- Slopes down into the hollow of the Sacrum
- Reaches the midline in front of S3 at the commencement of the Rectum

Partial Peritoneum supplied segmentally by spinal nerves innervating adjacent muscles
Diaphragmatic Peritoneum supplied centrally by the Phrenic Nerve (C4)
Remainder of Parietal Peritoneum supplied segmentally by Intercostal and Lumbar Nerves
In pelvis, Obturator nerve is the chief source of supply
Visceral Peritoneum – innervated by afferent nerves which travel with the autonomic supply to the viscera
- Pain from diseased viscera due to ischaemic, muscle spasm and stretching of the visceral peritoneum (including mesenteric folds) or involvement of the parietal peritoneum