The omentum is a unique and complex anatomical structure that resides within the abdominal cavity, often described as a large, curtain-like sheet of tissue. It is a fold of the peritoneum, the membrane that lines the abdominal wall and covers most of the internal organs. Although it may appear to be a simple, fatty drape, the omentum possesses a surprisingly sophisticated biological nature. It has been recognized for centuries as an abdominal guardian, hinting at its profound, yet often unseen, functions within the body.
Anatomical Structure and Position
The omentum is divided into two distinct components: the Greater Omentum and the Lesser Omentum, each with specific attachments and positions within the abdomen.
Greater Omentum
The Greater Omentum is the larger and more prominent component, visualized as a large, apron-like fold that hangs down from the stomach. This structure originates from the greater curvature of the stomach and the beginning of the duodenum, descending inferiorly to drape over the small intestine. It then folds back on itself and ascends to attach to the transverse colon, creating a structure that is four layers thick. This arrangement means the Greater Omentum physically covers and protects the majority of the intestines. Its tissue composition is a rich mix of fat, giving it a yellowish, lacy appearance, along with an extensive network of blood vessels and lymphatic channels.
Lesser Omentum
The Lesser Omentum is significantly smaller and takes a more localized position in the upper abdomen. It is a double-layered sheet of peritoneum that connects the lesser curvature of the stomach and the first part of the duodenum to the liver. This structure forms the anterior boundary of a space behind the stomach known as the lesser sac. The Lesser Omentum primarily serves as a conduit, housing important elements like the hepatic artery, portal vein, and bile duct at its free edge.
Essential Biological Functions
The omentum is crucial for immune surveillance, earning it the historical nickname, the “abdominal policeman.” This protective ability is attributed to specialized structures called “milky spots,” which are clusters of immune cells embedded within the fatty tissue. These milky spots actively filter the fluid circulating in the peritoneal cavity, collecting antigens and pathogens to mount a localized immune response.
The omentum also exhibits a remarkable ability to migrate quickly within the abdomen to any site of injury or infection. When an organ is perforated or inflamed, the omentum adheres to the damaged area, walling it off with its immunologically active tissue to limit contamination.
The omentum functions as a large site for visceral fat storage, providing an energy reserve. The tissue is highly vascularized and capable of promoting the growth of new blood vessels, known as neoangiogenesis. This rich blood supply is crucial for its healing and regenerative potential at sites of abdominal trauma or inflammation.
Clinical Relevance in Health and Disease
The unique combination of mobility, immune function, and rich vascularity makes the omentum highly relevant in both pathology and surgical practice. Unfortunately, its function as a filter means it can be a common site for the metastasis of abdominal cancers, particularly those originating from the ovaries or stomach. Malignant cells often preferentially lodge in the milky spots, leading to the formation of tumor deposits that can spread across the entire sheet.
The omentum is also susceptible to a rare but acute condition called omental torsion, where the tissue twists upon itself. This twisting cuts off the blood supply, causing acute abdominal pain that often requires surgical intervention.
Despite these vulnerabilities, surgeons frequently utilize the omentum’s natural healing capabilities in various medical procedures. Its ability to provide a new blood supply and seal off defects makes it invaluable for reconstructive surgery. For instance, a piece of the omentum can be used as a patch to close perforations in the gastrointestinal tract, a procedure known as omentoplasty. The tissue can also be transposed, or moved, to cover damaged organs or to reinforce surgical connections, leveraging its angiogenic properties to enhance healing and reduce infection risk.