Structure and Layers of the Peritoneum
The peritoneum consists of a lamina propria, a serous membrane, and a surface mesothelium. In anatomy, this membrane is divided into two continuous layers:
- Parietal peritoneum (peritoneum parietale) — lines the inner surface of the abdominopelvic walls.
- Visceral peritoneum (peritoneum viscerale) — reflects onto and covers the internal organs.
As the serous membrane transitions from the walls to the organs or between organs, it forms ligaments (ligamenta), folds (plicae), and mesenteries (mesenteria).
The slit-like potential space between the parietal and visceral layers is called the peritoneal cavity (cavitas peritonealis). It contains a small amount of serous fluid (liquor peritonei) that acts as a lubricant. In females, this cavity has an opening to the exterior via the uterine tubes, uterus, and vagina.
Peritoneal Relationships of Organs
The degree to which organs are covered by the serous membrane varies. Based on this, organs are divided into three groups:
- Intraperitoneal organs — completely surrounded by visceral peritoneum. These include the small intestine, cecum, and vermiform appendix. They typically possess a mesentery (e.g., the appendix is anchored by the mesoappendix), although the cecum lacks a true mesentery.
- Mesoperitoneal organs — covered by peritoneum on three sides (e.g., ascending and descending colons).
- Retroperitoneal and extraperitoneal organs — contact the peritoneum on only one side or lie entirely outside the peritoneal cavity.
The parietal peritoneum of the posterior abdominal wall separates the main cavity from the retroperitoneal space (spatium retroperitoneale), where retroperitoneal organs reside. Extraperitoneal cellular spaces also include the spatium extraperitoneale and spatium retrorubicum.
Mesenteries and Compartments of the Peritoneal Cavity
A mesentery (mesenterium) is a double layer of peritoneum (duplication). It not only suspends the intestines from the posterior abdominal wall but also serves as a pathway for vessels and nerves. The line of attachment to the abdominal wall is called the root of the mesentery (radix mesenterii).
At the level of the second lumbar vertebra, the transverse mesocolon divides the peritoneal cavity into two main compartments:
- Supracolic compartment contains the subphrenic and subhepatic recesses, as well as the omental bursa.
- Infracolic compartment is divided by the mesentery of the small intestine into right and left mesenteric sinuses. The right sinus is bounded by the ascending colon, and the left by the descending colon.
Omenta and the Omental Bursa
The greater omentum (omentum majus) is an elongated dorsal mesentery of the stomach that hangs down like an apron, covering the intestines anteriorly. A potential space between the greater omentum and the anterior abdominal wall is the presmental space.
The lesser omentum (omentum minus) is formed by two ligaments: the hepatogastric and hepatoduodenal ligaments. The hepatoduodenal ligament encloses the portal triad: portal vein, proper hepatic artery, and common bile duct.
Posterior to the stomach lies the omental bursa (bursa omentalis). It communicates with the greater sac through the epiploic foramen (foramen epiploicum), located posterior to the hepatoduodenal ligament.
Walls of the omental bursa:
- Anterior: posterior wall of the stomach, lesser omentum, and part of the greater omentum.
- Posterior: parietal peritoneum overlying the aorta, inferior vena cava, left kidney, left adrenal gland, and pancreas.
- Superior: caudate lobe of the liver.
- Inferior: transverse colon and its mesocolon.
The narrowed portion of the bursa between the caudate lobe and the duodenum is called the vestibule (vestibulum).
Recesses, Folds, and Anterior Abdominal Wall Relief
The peritoneal cavity contains various recesses (recessus) of significant clinical importance:
- Cecal region features superior and inferior ileocecal folds and recesses, as well as a retrocecal recess.
- Duodenal region includes the paraduodenal fold, paraduodenal recess, and retroduodenal recess.
- Sigmoid colon folds form the intersigmoid recess.
Beneath the visceral surface of the liver lie the right subphrenic and subhepatic recesses, which together form the hepatic pouch. The subphrenic spaces are separated by the falciform ligament.
On the anterior abdominal wall, the parietal peritoneum drapes over underlying vessels and remnants, forming umbilical folds: median (covering the obliterated urachus), medial (covering the obliterated umbilical arteries), and lateral (covering the inferior epigastric vessels). These folds create supravesical, medial, and lateral inguinal fossae.