Abdominal cavity

The abdominal cavity is a major internal body cavity found in humans and in many other vertebrate animals. Forming the upper portion of the abdominopelvic cavity, it lies below the thoracic cavity and above the pelvic cavity. Its superior boundary is created by the dome-shaped thoracic diaphragm, a muscular sheet that separates abdominal organs from the lungs and heart, while its inferior limit is the pelvic inlet, which opens into the pelvis. The cavity houses numerous vital organs essential for digestion, metabolism, detoxification, and excretion, and is lined by a specialised serous membrane that supports and protects its contents.

Structure and Location

The abdominal cavity occupies the central portion of the trunk and, together with the pelvic cavity, comprises the abdominopelvic cavity. It is enclosed by the abdominal walls, the diaphragm above, and the pelvic structures below. Because of its size, the abdominal cavity provides space for many visceral organs, ensuring that systems involved in digestion and metabolism have sufficient room to function and move.
This cavity sits in a region where pressure changes occur regularly through breathing, digestion, and posture. Its structural arrangement allows for organ expansion, displacement during movement, and protection through layers of muscle and connective tissue.

Major Organs

The abdominal cavity contains many of the body’s significant organs. These include:

• Stomach, responsible for the mechanical and chemical breakdown of food.
• Liver, a crucial metabolic organ involved in detoxification, nutrient storage, and bile secretion.
• Gallbladder, which stores and concentrates bile.
• Spleen, part of the immune system and involved in blood filtration.
• Pancreas, with both endocrine and exocrine functions, contributing to digestion and hormone regulation.
• Small intestine, the primary site of nutrient absorption.
• Large intestine, responsible for water reabsorption and faecal formation.
• Kidneys, which filter blood and produce urine.
• Adrenal glands, endocrine glands involved in stress and metabolic regulation.

Although the kidneys and adrenal glands are functionally related to abdominal organs, they lie behind the peritoneal lining, in the retroperitoneal space rather than within the cavity proper.

Peritoneum

The abdominal cavity is lined and protected by the peritoneum, a specialised serous membrane that facilitates organ movement and provides structural support. It has two main layers:

• Parietal peritoneum, which lines the inside of the abdominal wall.
• Visceral peritoneum, which covers the surfaces of most abdominal organs.

Between these layers lies the peritoneal cavity, a potential space containing a thin film of peritoneal fluid. This fluid reduces friction, allowing free movement of organs such as the stomach and intestines during digestion and respiration.
The peritoneum also forms multiple compartments and recesses within the abdominal cavity. A notable example is the lesser sac, situated behind the stomach and connected to the larger peritoneal space—the greater sac—via the foramen of Winslow. These compartments help organise and stabilise abdominal contents.
Some organs are attached to the abdominal walls through peritoneal folds and ligaments, which consist of thickened peritoneum. Examples include the gastrocolic ligament linking the stomach to the colon, and the splenocolic ligament connecting the spleen to the colon. Other ligaments, such as the round and triangular ligaments of the liver, take their names from their shape or structure.

Mesentery

Mesenteries are broad folds of visceral peritoneum that suspend portions of the gastrointestinal tract from the posterior abdominal wall. They completely enclose the organs they support and are well supplied with blood vessels, nerves, and lymphatics.
Key mesenteries include:

• The mesentery of the small intestine, which anchors the jejunum and ileum.
• The transverse mesocolon, supporting the transverse colon.
• The sigmoid mesocolon, which enfolds the sigmoid colon.

These mesenteries provide mobility while preventing torsion and maintaining an organised arrangement for blood supply and innervation.

Omenta

The abdominal cavity contains two major omenta, specialised fatty folds of peritoneum with protective and immune functions:

• The greater omentum, descending from the greater curvature of the stomach and draping over the intestines before attaching to the transverse colon.
• The lesser omentum, spanning between the liver and the stomach.

Rich in blood vessels, nerves, and lymphatics, the omenta are important in limiting the spread of infection. The greater omentum in particular can adhere to inflamed areas, forming a natural protective barrier.

Clinical Significance

AscitesAscites refers to the pathological accumulation of fluid within the abdominal cavity. This condition often develops gradually and may go unnoticed until the abdomen becomes visibly distended. The increased fluid volume exerts pressure on abdominal organs, veins, and even the thoracic cavity. Common causes include liver cirrhosis, portal hypertension, lymphatic leakage leading to chylous ascites, and heart failure. Management focuses on treating the underlying condition and, where necessary, reducing portal pressure or repairing damaged lymphatic vessels.
PeritonitisPeritonitis is inflammation of the peritoneum and may result from infection, trauma, surgical complications, or organ perforation. It can be acute or chronic, localised or generalised, and may originate from various sites, most commonly the gastrointestinal tract. Without treatment, infection can spread rapidly throughout the cavity. The omenta can offer short-term containment, but medical management with antibiotics and surgical or percutaneous drainage is usually required to resolve abscesses and prevent systemic illness.