Peritoneum

The peritoneum is a thin, serous membrane that lines the abdominal cavity and covers most of the abdominal organs. It provides support, facilitates movement of organs, and plays an important role in immune defense and fluid balance. Understanding its anatomy and function is essential for both clinical and surgical practice.

Anatomy of the Peritoneum

Structure and Layers

The peritoneum consists of two continuous layers:

• Parietal peritoneum: Lines the internal surface of the abdominal and pelvic walls, sensitive to pressure, pain, and temperature.
• Visceral peritoneum: Covers the external surfaces of most abdominal organs and is less sensitive to pain.

Both layers are composed of a single layer of mesothelial cells supported by connective tissue containing blood vessels, lymphatics, and nerves. The space between these layers is the peritoneal cavity, which normally contains a small amount of lubricating peritoneal fluid to allow smooth movement of organs.

Peritoneal Reflections and Ligaments

The peritoneum forms various reflections, folds, and ligaments that connect and support abdominal organs:

• Mesentery: Double layer of peritoneum suspending the intestines from the posterior abdominal wall and providing a conduit for vessels and nerves.
• Omenta: Greater and lesser omenta that connect the stomach and other organs, providing fat storage, cushioning, and immune functions.
• Peritoneal ligaments: Connect organs to each other or to the abdominal wall, such as the falciform ligament of the liver.
• Folds and pouches: Includes peritoneal recesses like the rectovesical pouch in males and rectouterine pouch in females, which may collect fluid or become sites of pathology.

Peritoneal Compartments

The peritoneal cavity is divided into compartments that facilitate the organization and movement of abdominal organs. These compartments are clinically significant as they influence the spread of infections or fluids within the abdomen.

• Supracolic compartment: Located above the transverse colon and includes the liver, stomach, and spleen.
• Infracolic compartment: Located below the transverse colon and contains the small intestine and ascending and descending colon.
• Right and left subphrenic spaces: Located between the diaphragm and liver, often involved in abscess formation.
• Right and left paracolic gutters: Channels along the lateral sides of the ascending and descending colon that allow fluid movement within the peritoneal cavity.

Embryology and Development

The peritoneum develops from the lateral plate mesoderm during early embryogenesis. As the embryo folds, the mesoderm splits into two layers, forming the parietal and visceral peritoneum.

• Origin: Lateral plate mesoderm gives rise to the connective tissue and mesothelial lining of the peritoneum.
• Development of peritoneal layers: The parietal layer lines the body wall while the visceral layer envelops the developing gut and organs.
• Rotation and fixation of the gut: During embryogenesis, the gut undergoes rotation and fixation, creating peritoneal folds, mesenteries, and recesses essential for adult anatomy.

Physiology and Functions

Secretion and Lubrication

The peritoneum secretes a small amount of serous fluid into the peritoneal cavity, which lubricates the surfaces of the abdominal organs. This fluid allows organs to move smoothly against each other during digestion, respiration, and changes in posture.

Support and Suspension of Organs

The peritoneum, through its ligaments, mesenteries, and omenta, provides structural support for abdominal organs. These structures help maintain organ position while allowing necessary mobility for physiological function.

Immune Defense

The peritoneum contains immune cells, including macrophages and lymphocytes, that detect and respond to pathogens. It plays a crucial role in local defense mechanisms, helping to contain infections and facilitate wound healing.

Absorption and Transport

The peritoneal membrane facilitates absorption of fluids, solutes, and certain medications, making it a key component in peritoneal dialysis. It also allows movement of peritoneal fluid throughout the cavity, aiding in the distribution of nutrients and immune factors.

Clinical Significance

Peritoneal Diseases

Various conditions can affect the peritoneum, ranging from infections to neoplastic processes:

• Peritonitis: Inflammation of the peritoneum, which can be infectious, chemical, or secondary to organ perforation.
• Ascites: Accumulation of fluid within the peritoneal cavity, often due to liver disease, heart failure, or malignancy.
• Peritoneal Carcinomatosis: Dissemination of malignant cells throughout the peritoneal cavity, commonly from gastrointestinal or ovarian tumors.
• Mesothelioma: Rare malignancy arising from the peritoneal mesothelium, associated with asbestos exposure.

Peritoneal Access and Procedures

The peritoneum is utilized in several medical and surgical interventions:

• Peritoneal Dialysis: A renal replacement therapy that uses the peritoneal membrane to filter waste products from the blood.
• Laparoscopy: Minimally invasive surgical technique accessing the peritoneal cavity for diagnosis or surgery.
• Peritoneal Lavage and Drainage: Procedures to remove blood, pus, or other fluids from the cavity in trauma or infection.

Trauma and Injury

The peritoneum can be affected by both blunt and penetrating abdominal trauma, which may lead to significant morbidity if not promptly recognized.

• Blunt Trauma: Motor vehicle accidents or falls can cause peritoneal contusions, lacerations, or internal bleeding.
• Penetrating Trauma: Stab or gunshot wounds may perforate the peritoneum, resulting in hemoperitoneum or peritonitis.
• Hemoperitoneum: Accumulation of blood within the peritoneal cavity, often requiring urgent surgical intervention.
• Visceral Injuries: Damage to abdominal organs can compromise the integrity of the peritoneum and lead to infection or adhesions.

Imaging and Diagnostic Techniques

Ultrasound Evaluation

Ultrasound is a first-line imaging modality to assess peritoneal structures and detect fluid collections. It is useful for identifying ascites, abscesses, or organ injury within the peritoneal cavity.

CT and MRI

Computed tomography (CT) provides detailed visualization of the peritoneum and associated organs, helping diagnose trauma, tumors, or infectious processes. Magnetic resonance imaging (MRI) offers superior soft tissue contrast and is particularly useful in evaluating peritoneal malignancies or complex fluid collections.

Diagnostic Laparoscopy

Direct visualization of the peritoneum through laparoscopy allows accurate diagnosis of peritoneal diseases. It is both a diagnostic and therapeutic tool, enabling biopsy, fluid drainage, and treatment of adhesions or localized infections.

References

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