What is the hollow space in the abdomen? The peritoneal and retroperitoneal cavities

September 27, 2025 •

3 min read

The abdominal cavity, a large, protective chamber for internal organs, is divided into distinct anatomical areas. These compartments include the peritoneal and retroperitoneal spaces, which together define what is the hollow space in the abdomen, protecting vital viscera and facilitating organ movement.

Quick Summary

The hollow space in the abdomen is not empty but refers to the abdominal cavity, which is primarily divided into the peritoneal and retroperitoneal spaces. This area houses and protects vital organs, lubricates them with fluid, and provides pathways for blood vessels and nerves. Understanding these spaces is key to grasping abdominal anatomy and associated health conditions.

Key Points

The Abdominal Cavity is Not Empty: The "hollow space" in the abdomen is a highly organized cavity filled with organs, separated into distinct compartments by the peritoneum.
Peritoneal vs. Retroperitoneal Spaces: The primary division is between the peritoneal cavity, which contains mobile, mesentery-suspended organs, and the retroperitoneal space, which holds fixed organs behind the peritoneum.
Intricate Organ Placement: Organs are distributed between these spaces; for example, the stomach and liver are intraperitoneal, while the kidneys and pancreas are retroperitoneal.
Lubrication and Protection: The peritoneal cavity contains a lubricating fluid that reduces friction between organs, while the peritoneum and surrounding structures provide protection and support.
Clinical Relevance: A variety of serious conditions, such as peritonitis, ascites, and retroperitoneal bleeding, are directly related to pathologies within these abdominal spaces.
Pain Sensation Differences: Visceral pain originating from organs in the peritoneal cavity tends to be dull and diffuse, whereas parietal pain from the cavity lining is often sharp and localized.

Understanding the abdominal cavity

Contrary to a common misconception, the hollow space within the abdomen is not an empty vacuum, but a partitioned cavity filled with organs, tissues, and fluid. The abdomen is bordered by the diaphragm superiorly and the pelvic inlet inferiorly, supported by abdominal muscles and the vertebral column. The peritoneum, a thin serous membrane, divides this space into intraperitoneal and retroperitoneal areas.

The peritoneal cavity

The peritoneal cavity is the largest abdominal space, located between the parietal peritoneum (lining the walls) and the visceral peritoneum (covering the organs). This cavity is a potential space with a thin film of lubricating serous fluid allowing organ movement.

The greater and lesser sacs

The peritoneal cavity is divided into two main compartments:

The Greater Sac: The main part containing most of the intestines and other structures.
The Lesser Sac (Omental Bursa): A smaller pocket behind the stomach, connected to the greater sac by the epiploic foramen.

Intraperitoneal organs

Intraperitoneal organs are suspended by peritoneal folds called mesenteries, allowing for mobility. These include the liver, stomach, spleen, most of the small intestine, transverse and sigmoid colon, and gallbladder.

The retroperitoneal space

Located behind the peritoneal cavity, this space is between the parietal peritoneum and the posterior abdominal wall. Organs here are fixed, making them less mobile. Retroperitoneal organs can be remembered with the mnemonic SAD PUCKER:

Suprarenal glands (adrenal glands)
Aorta and inferior vena cava
Duodenum (parts 2-4)
Pancreas (except the tail)
Ureters
Colon (ascending and descending)
Kidneys
Esophagus (a small part)
Rectum

Comparison of abdominal spaces


Feature	Peritoneal Cavity	Retroperitoneal Space
Location	Within the abdomen, lined by peritoneum	Behind the peritoneum, against the posterior abdominal wall
Key Characteristic	A potential space containing lubricating fluid	A fixed space containing organs and vessels
Organ Mobility	High, as organs are suspended by mesenteries	Low, as organs are fixed to the posterior wall
Contents Examples	Stomach, liver, spleen, most of small intestine	Kidneys, pancreas, aorta, ureters
Function	Protects and lubricates organs, supports structures	Houses vital organs, major vessels, and lymphatics

Clinical significance of abdominal spaces

Understanding these spaces is vital for diagnosing conditions. Pain from the parietal peritoneum is localized, while visceral pain from organs is often dull and hard to pinpoint. Conditions include:

Ascites: Fluid buildup in the peritoneal cavity, often from liver disease or cancer.
Peritonitis: Inflammation of the peritoneum, usually from infection.
Retroperitoneal hematoma: Bleeding in the retroperitoneal space from trauma or aneurysms.
Internal hernia: Intestine trapped in peritoneal pockets.

Imaging and assessment of the abdominal space

In a healthy state, the peritoneal space is virtual, becoming visible with fluid (ascites), air (pneumoperitoneum), or tumors. Ultrasound and CT scans are used to visualize these spaces and diagnose conditions.

Conclusion

The hollow space in the abdomen consists of the peritoneal and retroperitoneal spaces, housing and protecting vital organs. The peritoneal cavity allows organ movement and is lubricated, while the retroperitoneal space anchors structures like kidneys and the pancreas. The peritoneum acts as both a protective barrier and an anchor. For more information, you can refer to the Cleveland Clinic's page on the peritoneum. Knowledge of this intricate structure is essential for understanding abdominal health and symptoms.

Frequently Asked Questions

The main function is to house and protect vital digestive and urogenital organs. The peritoneal cavity allows for organ movement, while the retroperitoneal space anchors and secures others, all while providing pathways for nerves, blood vessels, and lymphatics.

Yes, an abnormal accumulation of fluid in the peritoneal cavity is known as ascites. This can be a symptom of serious underlying conditions such as liver disease, cancer, or heart failure.

The abdominal cavity is the larger space below the diaphragm that contains all abdominal organs. The peritoneal cavity is a specific, smaller compartment within the abdominal cavity, defined by the peritoneum membrane.

Doctors can use medical imaging such as CT scans and ultrasounds to visualize the organs and detect issues in the retroperitoneal space, such as fluid collections, masses, or bleeding.

In males, the peritoneal cavity is a completely closed space. In females, however, the uterine tubes open into the peritoneal cavity, creating a potential pathway between the female genital tract and the abdominal cavity.

Pain originating from the viscera (internal organs) is often diffuse because the visceral peritoneum has a less concentrated nerve supply. Pain is often perceived as coming from the abdominal midline, even when the organ is located elsewhere.

Peritonitis is the inflammation of the peritoneum, the membrane lining the abdominal cavity. It is a serious medical emergency, typically caused by a bacterial infection or chemical irritation from a ruptured organ leaking into the peritoneal cavity.