Peritoneal Cavity

• The Peritoneal Cavity is a potential space in the abdomen and pelvis, lined by a serous membrane called the peritoneum.
• It contains a small amount of lubricating fluid, which reduces friction between organs.
• The peritoneum consists of two layers: parietal (lining the abdominal wall) and visceral (covering organs).
• It supports and suspends many abdominal organs, allowing for their mobility.
• The cavity is involved in fluid exchange and immune responses within the abdomen.

What is the Peritoneal Cavity?

The Peritoneal Cavity refers to the potential space located within the abdomen and pelvis, situated between the parietal and visceral layers of the peritoneum. It is not an empty space but rather a thin, fluid-filled area that allows organs to move freely against each other without friction. Understanding the peritoneal cavity definition is fundamental to grasping abdominal anatomy and physiology, as it outlines the boundaries and contents of this critical region.

The peritoneum itself is a serous membrane, similar to the pleura around the lungs or the pericardium around the heart. It secretes a small amount of serous fluid, typically less than 50 milliliters, which acts as a lubricant. This lubrication is essential for the smooth gliding of abdominal organs, such as the intestines, during digestion and body movements.

Anatomy of the Peritoneal Cavity

The anatomy of peritoneal cavity is intricate, defined by the extensive folding of the peritoneum. This membrane is divided into two main layers:

• Parietal Peritoneum: This layer lines the inner surface of the abdominal and pelvic walls, including the diaphragm. It is sensitive to pain, temperature, touch, and pressure, receiving its innervation from the somatic nervous system.
• Visceral Peritoneum: This layer covers the external surfaces of most abdominal organs. It is generally insensitive to touch, temperature, and cutting, but stretching and chemical irritation can cause pain, which is poorly localized and referred to dermatomes.

The space between these two layers constitutes the peritoneal cavity. Organs are classified based on their relationship to the peritoneum. Intraperitoneal organs are almost completely covered by visceral peritoneum and are suspended within the cavity by mesenteries. Examples include the stomach, spleen, liver, gallbladder, jejunum, ileum, and parts of the large intestine. Retroperitoneal organs, conversely, lie behind the peritoneum and are only covered on their anterior surface; these include the kidneys, adrenal glands, pancreas, aorta, and inferior vena cava.

The peritoneum also forms specialized folds and structures, such as the mesenteries, which are double layers of peritoneum that connect organs to the posterior abdominal wall, providing pathways for nerves, blood vessels, and lymphatics. The omenta, such as the greater and lesser omentum, are also peritoneal folds that play roles in fat storage and immune response.

Functions of the Peritoneal Cavity

The peritoneal cavity function is multifaceted, contributing significantly to abdominal health and organ integrity. One of its primary roles is lubrication. The serous fluid within the cavity minimizes friction between mobile abdominal organs, allowing them to slide past each other smoothly during digestive processes and body movements. This prevents damage and ensures efficient organ operation.

Beyond lubrication, the peritoneal cavity offers a degree of protection to the abdominal viscera. The fluid and the membrane itself can act as a barrier against the spread of infection within the abdomen, often localizing inflammation. The greater omentum, a large peritoneal fold, is particularly noted for its “abdominal policeman” role, migrating to areas of inflammation or injury to wall off infections.

Furthermore, the peritoneum is involved in fluid and electrolyte exchange. Its large surface area allows for the rapid absorption and secretion of fluids, which is critical in conditions like peritonitis or during peritoneal dialysis, where the peritoneum is used as a semi-permeable membrane to filter waste products from the blood.