The peritoneum is a thin, transparent, serous membrane that lines the abdominal cavity and covers most of the abdominal organs. It consists of two layers: the parietal peritoneum, which lines the inner walls of the abdominal and pelvic cavities, and the visceral peritoneum, which envelops the surfaces of the abdominal organs. The space between these two layers is called the peritoneal cavity, filled with a small amount of lubricating serous fluid to reduce friction during organ movement. The peritoneum provides structural support, facilitates organ mobility, and plays a role in immune defense within the abdominal cavity.
Structure and Layers
The peritoneum is a bilayered serous membrane composed of connective tissue and a surface layer of mesothelium, which is a simple squamous epithelium. It is divided into two distinct layers based on its anatomical relationship with the abdominal cavity and organs.
Parietal Peritoneum
- Location: Lines the inner surface of the abdominal and pelvic walls.[6]
- Composition: Rich in pain-sensitive nerves that respond to mechanical, chemical, or thermal stimuli.
- Attachment: Firmly adheres to the abdominal wall, diaphragm, and pelvic cavity.
Visceral Peritoneum
- Location: Covers the outer surfaces of most abdominal organs, such as the stomach, intestines, and liver.
- Composition: Less sensitive to pain but responsive to stretching or chemical irritation.
- Attachment: Adheres tightly to the organ surfaces and blends with their connective tissue coverings.
Peritoneal Cavity
- Description: A potential space between the parietal and visceral layers.
- Content: Contains a small amount of serous fluid that reduces friction and allows free movement of the abdominal organs during digestion, respiration, and other activities.
Specialized Structures
- Mesenteries: Double layers of peritoneum that attach the intestines to the posterior abdominal wall and provide pathways for blood vessels, lymphatics, and nerves.
- Omenta: Folds of the peritoneum, such as the greater and lesser omentum, that connect the stomach to other organs.
- Ligaments: Peritoneal folds that connect organs to each other or to the abdominal wall, such as the falciform ligament of the liver.[4]
Location
The peritoneum is located within the abdominal and pelvic cavities, forming a continuous, protective membrane that lines the internal surfaces of these cavities and envelops the abdominal organs. Its location is defined by the two primary layers:
Parietal Peritoneum
- Found lining the inner surface of the abdominal wall, the pelvic cavity, and the undersurface of the diaphragm.
- It is attached to the surrounding musculoskeletal structures and maintains the cavity’s shape and integrity.
Visceral Peritoneum
- Covers the external surfaces of most abdominal organs, including the stomach, liver, intestines, and spleen.
- It is closely associated with the organs, blending seamlessly with their outer connective tissue coverings.
Peritoneal Cavity
- The space between the parietal and visceral layers of the peritoneum.[1]
- It extends throughout the abdominal and pelvic regions, accommodating organs such as the stomach, intestines, liver, and reproductive organs in females.
Abdominal and Pelvic Organs
- Some organs, such as the stomach and intestines, are fully enclosed by the peritoneum (intraperitoneal organs).
- Others, like the kidneys and pancreas, are located outside the peritoneal cavity and are only partially covered by the peritoneum (retroperitoneal organs).
Types of Peritoneum
The peritoneum is classified into two main types based on its anatomical location and relationship with the abdominal cavity and organs:
Parietal Peritoneum
- Description: This layer lines the inner walls of the abdominal and pelvic cavities.
- Location: It is attached to the diaphragm, abdominal wall, and pelvic cavity.
- Innervation: Supplied by somatic nerves, making it sensitive to pain, pressure, and temperature changes.
- Function: Provides structural support and acts as a barrier between the abdominal organs and the body wall.
Visceral Peritoneum
- Description: This layer covers the external surfaces of most abdominal and pelvic organs.
- Location: Adheres tightly to the organs such as the stomach, intestines, and liver.
- Innervation: Supplied by autonomic nerves, making it less sensitive to pain but responsive to stretching and chemical irritation.
- Function: Protects the organs and allows smooth movement by reducing friction.
Peritoneal Cavity
The peritoneal cavity is a potential space between the parietal and visceral layers of the peritoneum. It is filled with a small amount of serous fluid that allows the abdominal organs to move smoothly against each other without friction.
Location
- The peritoneal cavity lies within the abdominal and pelvic regions.
- It is bounded by the parietal peritoneum on the abdominal walls and the visceral peritoneum covering the organs.[8]
Divisions
The peritoneal cavity is divided into two compartments:
- Greater Sac:
- The main portion of the peritoneal cavity.
- Extends from the diaphragm down to the pelvic cavity.
- Lesser Sac (Omental Bursa):
- A smaller, enclosed space located behind the stomach and the lesser omentum.
- Communicates with the greater sac through the epiploic foramen (Foramen of Winslow).
Serous Fluid
- The cavity contains a thin layer of serous fluid produced by the mesothelium of the peritoneum.
- This fluid acts as a lubricant, reducing friction during the movements of the organs, such as during digestion and respiration.[7]
Gender Differences
- In males, the peritoneal cavity is completely closed.
- In females, the peritoneal cavity communicates with the external environment via the openings of the fallopian tubes, uterus, and vagina.
Function
The peritoneum performs several vital functions that are essential for the proper functioning of the abdominal cavity and its organs. Its structure allows it to support, protect, and facilitate movement within the abdominal region.
Protection and Support
- The peritoneum provides a protective layer around the abdominal organs, shielding them from mechanical injury.
- It helps anchor the organs in place, preventing displacement during movement or changes in body position.
- Peritoneal folds, such as mesenteries and omenta, support organs while allowing flexibility.
Lubrication
- The peritoneum secretes serous fluid into the peritoneal cavity, reducing friction between abdominal organs.[5]
- This lubrication allows the smooth movement of organs during digestion, respiration, and other activities.
Pathway for Vessels and Nerves
- The peritoneum forms structures like mesenteries and omenta, which act as conduits for blood vessels, lymphatics, and nerves.
- These pathways ensure proper nourishment and innervation of the abdominal organs.
Immune Defense
- The peritoneum contains immune cells that help detect and respond to infections or injuries in the abdominal cavity.
- The greater omentum, often referred to as the “policeman of the abdomen,” plays a role in isolating infections and facilitating immune responses.
Storage of Fat
The peritoneum, particularly the omenta, stores adipose tissue, which serves as an energy reserve and provides insulation for the abdominal organs.[3]
Fluid Absorption
The peritoneum can absorb excess fluid or waste products from the peritoneal cavity, contributing to homeostasis.
Clinical Significance
The peritoneum is essential for abdominal health, and its involvement in various conditions highlights its clinical importance. Peritonitis, an inflammation of the peritoneum caused by infection or perforation, is a life-threatening condition requiring urgent intervention. Ascites, the accumulation of fluid in the peritoneal cavity, is commonly associated with liver cirrhosis or cancer and can lead to discomfort and complications. The peritoneum is also involved in cancer spread, as in peritoneal carcinomatosis, which signifies advanced malignancy.
Post-surgical or inflammatory changes can lead to adhesions, causing bowel obstruction or pain. Additionally, the peritoneum is used in peritoneal dialysis for kidney failure patients, leveraging its semi-permeable properties.[2] Gender-specific conditions like pelvic inflammatory disease can arise due to the peritoneum’s communication with the reproductive tract in women. These conditions emphasize the peritoneum’s vital role in health and disease management.