Omentum: Definition, Types, Structure, Subdivisions and Functions

It is a large expanse of fatty tissue that envelops the liver, intestine and stomach.

It is a curtain of fatty tissue that hangs from our stomach and liver and wraps around the intestines, and is known to play a role in immune responses and metabolism, although exactly how that happens is barely understood.

Most of the action in the omentum takes place in groups of white blood cells, officially known as ” milky spots “, which dot the organ. They serve as a kind of filter for the abdominal fluid that circulates through the omentum and play a role in controlling the immune response to bacteria in the intestine.

When a harmful microbe is detected, milky spots initiate the release of inflammatory molecules that mount a defense. If a microbe arrives in peace, the omentum can signal the bowel to withdraw.

The omentum also plays a role in metabolism. There is evidence that the excessive accumulation of fatty tissue from which it is made can contribute to metabolic diseases, such as diabetes.

Some cells included in the omentum help to digest fatty acids, in addition to their immune responsibilities. The loss of these cells has been correlated with an increase in some types of obesity and insulin sensitivity.

The omentum is divided into greater omentum and minor omentum. The greater omentum is larger than the lesser omentum, which hangs from the liver to the lesser curvature.

The greater omentum

It is a large fold of visceral peritoneum similar to an apron hanging from the stomach. It extends from the greater curvature of the stomach, passing in front of the small intestine and bends backwards to ascend to the transverse colon before reaching the posterior abdominal wall.

The greater omentum is usually thin and has a perforated appearance. It contains some adipose tissue, which can accumulate considerably in obese people.

Structure

It consists of a double sheet of peritoneum, folded on itself so that it has four layers.

The two layers of the greater omentum descend from the greater curvature of the stomach and the beginning of the duodenum. They pass in front of the small intestine, sometimes as low as the pelvis, before turning on themselves, and ascend to the transverse colon, where they separate and enclose that part of the intestine.

These individual layers are easily seen in young people, but in adults they are more or less inseparably mixed.

The left edge of the greater omentum is continuous with the gastroesplenic ligament; its right edge extends to the beginning of the duodenum.

Subdivisions

The greater omentum is often defined to encompass a variety of structures. Most sources include the following three:

  • Gastroprine ligament: extends to the lower part of the left dome of the diaphragm.
  • Gastrocolic ligament: extends to the transverse colon (sometimes, by itself, is considered synonymous with “greater omentum”.
  • Gastrosplenic ligament (or Gastroliennial): extends to the spleen, covering the kidney.

The splenorenal ligament (from the left kidney to the spleen) is occasionally considered part of the greater omentum.

Functions

The functions of the greater omentum are:

  • Fat deposition: that has variable amounts of adipose tissue.
  • Immune contribution: that has milky spots of collections of macrophages.
  • Infection and wound isolation: can also physically limit the spread of intraperitoneal infections. The greater omentum can often be found wrapped around areas of infection and trauma.

Minor omentum

The lesser omentum (small omentum or gastrohepatic omentum) is the double layer of the peritoneum that extends from the liver to the lesser curvature of the stomach (hepatogastric ligament) and the first part of the duodenum (hepatoduodenal ligament).

Divisions

Anatomically, the lesser omentum is divided into ligaments, each beginning with the prefix “hepato” to indicate that it connects to the liver at one end.

Most sources divide it into two parts:

  • Hepatogastric ligament: the portion that connects with the lesser curvature of the stomach.
  • Hepatoduodenal ligament: the portion that connects to the duodenum.

In some cases, the following ligaments are considered part of the lesser omentum:

  • Hepatophernic ligament:  the portion that connects to the thoracic diaphragm.
  • Hepatosophageal ligament: the portion that connects to the esophagus.
  • Hepatocolic ligament: the portion that connects to the colon.