Peritoneum and peritoneal cavity

Structure and layers of the peritoneum

The peritoneum consists of the propria layer (lamina propria), serous membrane, and superficial mesothelium. In anatomy, this membrane is conventionally divided into two layers:

• Parietal peritoneum (peritoneum parietale) — it closely adheres to the inner walls of the abdominal cavity.
• Visceral peritoneum (peritoneum viscerale) — it covers the surface of internal organs.

Passing from the walls to the organs or between the organs themselves, the serous membrane forms ligaments (ligamenta), folds (plicae), and mesenteries (mesenteria).

The slit-like space between the parietal and visceral layers is called the peritoneal cavity (cavitas peritonealis). Inside it is a small amount of serous fluid (liquor peritonei) that acts as a lubricant. In females, this cavity has an opening to the outside through the uterine tubes, uterus, and vagina.

Organ relations to the peritoneum

The degree to which organs are covered by the serous membrane varies. Based on this feature, three groups are distinguished:

1. Intraperitoneal organs — covered by the peritoneum on all sides. These include the small intestine, cecum, and vermiform appendix. Typically they have a mesentery (e.g., the appendix is fixed by the mesoappendix), but the cecum lacks a mesentery.
2. Mesoperitoneal organs — covered on three sides (ascending and descending colons).
3. Retroperitoneal and extraperitoneal organs — contact the peritoneum on only one side or lie outside of it.

The parietal peritoneum of the posterior wall separates the main cavity from the retroperitoneal space (spatium retroperitoneal), where retroperitoneal organs are located. Extraperitoneal cellular spaces also include spatium extraperitoneale and spatium retrorubicum.

Mesenteries and division into floors

Mesentery (mesenterium) is a duplication (duplicature) of the peritoneum. It not only anchors the intestine to the posterior abdominal wall but also serves as a pathway for vessels and nerves. The site of its 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 cavity into two floors:

• Upper floor includes the subhepatic and subphrenic recesses, as well as the omental bursa.
• In the lower floor, the mesentery of the small intestine forms the right and left mesenteric sinuses. The right sinus is bounded by the ascending colon, and the left by the descending colon.

Omenta and omental bursa

Greater omentum (omentum majus) is an expanded dorsal mesentery of the stomach that hangs down, covering the intestines anteriorly. The presmental space remains between it and the anterior abdominal wall. Lesser omentum (omentum minus) is formed by two ligaments: the hepatogastric and hepatoduodenal ligaments. The portal triad—portal vein, common bile duct, and proper hepatic artery—is enclosed within the latter.

Behind the stomach lies the omental bursa (bursa omentalis). It can be entered from the general cavity through the omental foramen (foramen epiploicum), located posterior to the hepatoduodenal ligament.

Walls of the omental bursa:

• Anterior: posterior wall of the stomach, lesser and partially greater omenta.
• Posterior: parietal peritoneum over the aorta, inferior vena cava, left kidney, left adrenal gland, and pancreas.
• Superior: caudate lobe of the liver.
• Inferior: transverse colon with its mesentery.

The narrowed part of the bursa between the caudate lobe and the duodenum is called the vestibule (vestibulum).

Recesses, fossae, and relief of the anterior wall

The peritoneal cavity abounds with various recesses (recessus) that are of great clinical significance.

• In the cecal region there are ileocecal folds and recesses (superior and inferior), as well as the retrocecal recess.
• In the duodenal region the paraduodenal fold, paraduodenal, and retroduodenal recesses are distinguished.
• Between the curves of the sigmoid colon hides the intersigmoid recess.

Beneath the visceral surface of the liver lie the right subphrenic and subhepatic recesses, which together form the hepatic bursa. The subphrenic pockets themselves are separated by the falciform ligament.

On the anterior abdominal wall, the parietal layer lies over vessels and ducts, forming umbilical folds: median (covers the obliterated urachus), medial (obliterated umbilical arteries), and lateral (inferior epigastric vessels). Between these folds, supravesical fossae, as well as medial and lateral inguinal fossae, are formed.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Detailed topography of the omental foramen and the vestibule of the omental bursa
• Boundaries of the right and left mesenteric sinuses
• Fossae of the anterior abdominal wall as weak spots and pathways for inguinal hernias
• Anatomy of the hepatic bursa and subphrenic spaces

Other topics in "Splanchnology / Digestive System"

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