What is the function of the peritoneum?

Functions of the Peritoneum

The peritoneum is a metabolically active serous membrane that serves multiple critical physiological functions including fluid exchange and absorption, immune surveillance and inflammatory response, friction reduction for organ mobility, and regulation of intraperitoneal homeostasis. 1, 2

Structural Composition and Basic Characteristics

The peritoneum is the largest serous membrane in the human body, consisting of a layer of mesothelium supported by thin connective tissue containing hyaluron, collagen, proteoglycans, and interstitial cells (endothelial cells, fibroblasts, and pericytes). 3 It forms a continuous sheet creating two layers with a potential space between them—the peritoneal cavity—which contains small amounts of serous fluid. 4

Primary Physiological Functions

Fluid Exchange and Regulation

• The peritoneum facilitates bidirectional fluid exchange between the peritoneal cavity and systemic circulation, maintaining intraperitoneal homeostatic equilibrium. 1, 5
• The peritoneal vasculature plays a pivotal role in fluid dynamics, with the membrane contributing to absorption and drainage mechanisms. 5
• Small amounts of serous fluid (normally present) facilitate frictionless movement of mobile intraabdominal viscera. 4

Immunologic and Inflammatory Response

• The peritoneum functions as an immunologic niche controlled by diverse signaling networks, serving as a key element in regulation of inflammatory responses. 3, 1
• The peritoneum responds to insult through complex immunologic and inflammatory cascades involving cytokine production (IL-6, IL-1β, IL-8, TNF-α) and other biomediators. 3, 2
• Cavity-resident macrophages within the peritoneum maintain homeostasis through GATA6-mediated mechanisms and participate in immune surveillance. 3
• The peritoneal inflammatory response increases with duration and extent of injury, manifesting through systemic effects and local neural pathways via the neuro-immuno-humoral axis. 2

Prevention of Adhesion Formation

• The peritoneum plays a central role in prevention of fibrotic adhesions in the abdominal cavity under normal physiological conditions. 1
• Disturbance of normal peritoneal mechanisms can lead to generation of fibrotic adhesions following injury or inflammation. 1

Barrier and Compartmentalization Function

• The peritoneal reflections forming ligaments, mesenteries, and omenta serve as boundaries for disease processes and determine routes of intraperitoneal fluid flow. 6
• These anatomical arrangements create compartmentalized spaces that can contain or direct the spread of pathological processes. 6

Clinical Implications of Peritoneal Function

Response to Pathological Conditions

• When peritoneal homeostasis is disturbed, serious conditions can develop including production of large amounts of ascites, inflammatory peritonitis, and peritoneal carcinomatosis. 1
• The accumulation of intraperitoneal inflammatory mediators during sepsis can be removed by percutaneous drainage or negative pressure therapy to mitigate bio-mediator effects causing distant organ failure. 3
• Increased levels of both systemic and peritoneal cytokines are associated with post-operative complications and can discriminate survivors from non-survivors. 3

Diagnostic Utility

• The peritoneum's fluid-containing potential space allows for diagnostic procedures such as peritoneal lavage, which can detect as little as 20 mL of intra-peritoneal blood. 3
• Peritoneal fluid analysis provides diagnostic information for conditions like spontaneous bacterial peritonitis (neutrophil count >250/mm³) and secondary peritonitis. 7

Common Clinical Pitfalls

A critical caveat is that the peritoneum is a dynamic organ capable of adapting its structure and functions to various physiological and pathological conditions, meaning normal baseline function can be significantly altered in disease states. 1 Clinicians must recognize that peritoneal dysfunction in conditions like severe intra-abdominal hypertension (IAH ≥15 mmHg) can decrease intestinal microcirculatory blood flow, increase bowel wall permeability, and induce bacterial translocation leading to multi-organ dysfunction. 3