The greater omentum is a large, complex organ within the abdominal cavity, often described by surgeons as a fatty apron draped over the intestines. This folded sheet of tissue serves multiple functions, ranging from fat storage to acting as a mobile shield against infection. Despite its importance, the greater omentum remains one of the more misunderstood parts of human anatomy. It lies superficially, covering the delicate organs below, and plays a significant role in maintaining the health of the entire abdominal environment.
Defining the Greater Omentum: Location and Structure
The greater omentum is a large fold of visceral peritoneum, the membrane that lines the abdominal cavity and covers the organs. This tissue is composed of a double layer of peritoneum that folds back on itself, resulting in four fused layers in the adult. It is distinguishable from the smaller lesser omentum, which connects the stomach to the liver, by its extensive reach within the abdomen.
The structure originates from the greater curvature of the stomach and the duodenum, descending downward like a curtain. It can hang as low as the pelvis, covering the small intestines, before looping back up to attach to the transverse colon. In gross appearance, it is characteristically fatty, giving it a yellowish, apron-like look.
The omentum is richly supplied with blood vessels that form an intricate network, ensuring its viability and mobility. This vascularization is accompanied by an extensive lymphatic network. The bulk of the structure is composed of adipose tissue, which provides a significant reservoir for energy storage.
Scattered throughout this adipose tissue are specialized aggregates of immune cells known as “milky spots.” These small, whitish clusters of lymphoid tissue are embedded in the fat. They are dense with various immune cells, including macrophages and lymphocytes, representing a specialized component of the abdominal immune system.
Key Physiological Functions: The Abdominal Policeman
The greater omentum has a remarkable capacity for movement, which is the basis for its historical nickname, the “abdominal policeman.” This moniker recognizes its protective, roving function, as the omentum actively migrates toward any site of inflammation, injury, or trauma within the abdomen.
Upon reaching an injured site, such as a perforated ulcer or a burst appendix, the omentum wraps itself around the damaged area. This action walls off the infection, physically containing the spread of bacteria and inflammatory fluids. By localizing the problem, the omentum prevents the widespread, life-threatening condition known as peritonitis.
The immunological role of the milky spots is directly connected to this protective function. These spots are filtering stations for the peritoneal fluid that bathes the abdominal organs. Macrophages, which are abundant in the milky spots, are professional phagocytes that actively engulf and destroy foreign material and bacteria.
The milky spots are also populated by T and B lymphocytes, which initiate a specific immune response against pathogens. The omentum acts as a localized immune factory, constantly surveying the abdominal environment and mounting a rapid defense. This robust immune activity, combined with its mobile nature, makes it a first line of defense.
The greater omentum also functions as a major site for metabolic energy storage. The significant accumulation of adipose tissue allows it to store large reserves of fat that can be mobilized for energy when the body requires it.
Clinical Implications in Disease and Surgery
The anatomical and immunological properties that make the greater omentum a powerful protector also make it highly susceptible to certain diseases. It is a frequent and preferential site for the metastasis of cancer cells, a process sometimes described as “omental caking.” This occurs most often in advanced cases of ovarian, gastric, and colorectal cancers.
Cancer cells shed into the peritoneal fluid are often filtered by the milky spots, which unfortunately become a fertile ground for tumor growth. The nutrient-rich adipose tissue and the dense vascular supply provide an ideal environment for metastatic colonization. The resulting tumor mass can become thick and hard, posing a significant challenge in cancer treatment.
In acute scenarios, the omentum can undergo omental torsion, where it twists on its own blood supply. Although rare, the twisting cuts off blood flow, leading to tissue death (infarction), which causes sudden and severe abdominal pain. Its rich blood supply, while normally protective, makes it a target for this mechanical complication.
Conversely, the greater omentum is highly valued in modern surgical practice and is frequently utilized as a “pedicled omental flap.” Surgeons detach a segment of the omentum, keeping its blood supply intact, and transpose it to another area of the body requiring repair. This technique is used because its reliable blood supply promotes healing and revascularization.
Omental flaps are used to cover wounds, fill defects, or provide coverage for infected areas, such as deep sternal wound infections. Its high concentration of immune cells and its ability to secrete factors that promote tissue regeneration make it a versatile biological dressing in reconstructive and general surgery.