Learning Objective

By the end of this section, learners should be able to:

Define the peritoneal cavity and describe its function.
Differentiate between the greater sac and the lesser sac.
Describe the supracolic and infracolic compartments.
Explain sex-based anatomical differences in the pelvic peritoneal cavity.
Discuss key clinical correlations, including ascites and peritonitis.

Anatomy of the Peritoneal Cavity

The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum. It normally contains only a thin film of peritoneal fluid, which consists of water, electrolytes, leukocytes, and antibodies. This fluid acts as a lubricant, enabling free movement of the abdominal viscera, and the antibodies in the fluid fight infection.

While the peritoneal cavity is ordinarily filled with only a thin film of fluid, it is referred to as a potential space because excess fluid can accumulate in it, resulting in the clinical condition of ascites.

Subdivisions of the Peritoneal Cavity

The peritoneal cavity can be divided into the greater sac and the lesser sac. The greater sac comprises the majority of the peritoneal cavity. The lesser sac (also known as the omental bursa) is smaller and lies posterior to the stomach and the lesser omentum.

The greater sac is further divided into two compartments by the transverse mesocolon:

Supracolic compartment – lies above the transverse mesocolon and contains the stomach, liver, and spleen.
Infracolic compartment – lies below the transverse mesocolon and contains the small intestine, ascending colon, and descending colon. The infracolic compartment is further divided into left and right infracolic spaces by the mesentery of the small intestine.

The supracolic and infracolic compartments are connected by the paracolic gutters.

Lesser Sac (Omental Bursa)

The lesser sac lies posterior to the stomach and the lesser omentum, allowing the stomach to move freely against posterior structures. The omental bursa is connected with the greater sac through an opening – the epiploic foramen (of Winslow).

Pelvic Structure of the Peritoneal Cavity

Due to different pelvic organs, the peritoneal cavity differs between sexes. The primary difference is the location of the most distal portion of the cavity.

Male

In males, the rectovesical pouch is a double fold of peritoneum located between the rectum and the bladder. The peritoneal cavity is completely closed.

Female

Important pouches in females:

Rectouterine pouch (of Douglas) – between the rectum and the posterior wall of the uterus.
Vesicouterine pouch – between the bladder and the anterior surface of the uterus.

The peritoneal cavity is not completely closed, as the uterine tubes open into the peritoneal cavity, providing a potential pathway for infection.

Activity

Clinical Relevance

Ascites: Accumulation of excess fluid within the peritoneal cavity, typically caused by portal hypertension, malignancy, malnutrition, heart failure, or trauma. Symptoms include abdominal distension, discomfort, nausea, and dyspnea.
Peritonitis: Infection and inflammation of the peritoneum, often secondary to GI tract perforation or surgery. Presents with pain, tenderness, guarding, fever, nausea, vomiting; patients may flex their knees to relax abdominal muscles.
Subphrenic abscesses: Pus accumulation between the diaphragm and liver, more common on the right side.
Paracentesis: Procedure to drain fluid from the peritoneal cavity.
Culdocentesis: Extraction of fluid from the rectouterine pouch via the posterior vaginal fornix.