Peritoneum

Overview

The peritoneum is a continuous, thin, and transparent serous membrane that lines the walls of the abdominal cavity and covers most of the abdominal organs. It forms a complex, slippery surface that facilitates movement, supports organs, and serves as a conduit for blood vessels, lymphatics, and nerves. The peritoneum is divided into two main layers: the parietal peritoneum and the visceral peritoneum.

Location

The peritoneum resides in the abdominal and pelvic cavities. It:

• Parietal peritoneum: Lines the internal surface of the abdominal wall

• Visceral peritoneum: Covers the outer surfaces of most abdominal organs, including the stomach, intestines, and liver

• Encloses the peritoneal cavity, a potential space between the two layers filled with a small amount of lubricating serous fluid

It creates structures such as the mesentery, omentum, and ligaments that suspend and connect organs.

Structure

The peritoneum is made up of:

• Mesothelium: A single layer of flat, squamous epithelial cells that secrete serous fluid

• Underlying connective tissue: Contains blood vessels, lymphatics, and nerves

• Two continuous layers:

  • Parietal peritoneum: Sensitive to pressure, pain, and temperature; innervated by somatic nerves

  • Visceral peritoneum: Less sensitive; innervated by autonomic nerves and sensitive to stretch or ischemia

The peritoneal cavity is a closed sac in males and open to the external environment in females via the uterine tubes.

Function

The peritoneum serves several vital roles:

• Lubrication: Secretes serous fluid to reduce friction between moving organs

• Support: Helps maintain the position of abdominal organs

• Pathway for neurovascular supply: Blood vessels, nerves, and lymphatics travel within peritoneal folds to reach the organs

• Fat storage: Especially in the greater omentum, which contains abundant adipose tissue

Physiological Role(s)

The peritoneum plays dynamic physiological roles:

• Immunologic function: Contains macrophages and lymphocytes that respond to infection or inflammation

• Absorptive properties: Can absorb fluids, drugs (e.g., via peritoneal dialysis), and local inflammatory mediators

• Barrier function: Localizes infections (e.g., in appendicitis) by forming adhesions and walls off affected areas

• Healing response: Supports rapid tissue repair following injury or inflammation

Clinical Significance

The peritoneum is frequently involved in various clinical conditions:

• Peritonitis: Inflammation of the peritoneum, usually due to infection (e.g., ruptured appendix); can be life-threatening and requires urgent treatment

• Ascites: Accumulation of fluid in the peritoneal cavity, commonly seen in liver cirrhosis, malignancy, or heart failure

• Peritoneal carcinomatosis: Widespread cancer spread within the peritoneum, often from gastrointestinal or ovarian cancers

• Adhesions: Fibrous bands formed after surgery or inflammation, which can cause bowel obstruction

• Peritoneal dialysis: A treatment for renal failure where the peritoneum acts as a semipermeable membrane for waste exchange

• Hernias: Protrusion of abdominal contents through weak spots in the abdominal wall, often involving peritoneal sacs

The peritoneum is visualized and assessed using imaging modalities like ultrasound, CT, and diagnostic laparoscopy, especially in abdominal emergencies or oncologic evaluations.