The greater omentum (also the great omentum, omentum majus, gastrocolic omentum, epiploon, or, especially in animals, caul) is a large apron-like fold of visceral peritoneum that hangs down from the stomach. It extends from the greater curvature of the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

, passing in front of the small intestines and doubles back to ascend to the transverse colon before reaching to the posterior abdominal wall. The greater omentum is larger than the lesser omentum, which hangs down from the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

to the lesser curvature. The common anatomical term "epiploic" derives from "epiploon", from the Greek ''epipleein'', meaning to float or sail on, since the greater omentum appears to float on the surface of the intestines. It is the first structure observed when the abdominal cavity is opened anteriorly (from the front).

Structure

The greater omentum is the larger of the two peritoneal folds. 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 The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine ...

. They pass in front of the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through t ...

s, sometimes as low as the pelvis, before turning on themselves, and ascending as far as the transverse colon, where they separate and enclose that part of the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans a ...

. These individual layers are easily seen in the young, but in the adult they are more or less inseparably blended. The left border of the greater omentum is continuous with the gastrosplenic ligament; its right border extends as far as the beginning of the

. The greater omentum is usually thin, and has a

perforated A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a ''perforation''. The process of creating perforations is called perfor ...

appearance. It contains some

adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular ...

, which can accumulate considerably in obese people. It is highly vascularised.

Subdivisions

The greater omentum is often defined to encompass a variety of structures. Most sources include the following three: * Gastrophrenic ligament—extends to the underside of the left dome of the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

* Gastrocolic ligament—extends to the transverse colon (occasionally on its own considered synonymous with "greater omentum") * Gastrosplenic ligament (or Gastrolienal) ligament)— extends to the

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

, overlying the kidney The splenorenal ligament (or lienorenal ligament) (from the left

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

to the

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

) is occasionally considered part of the greater omentum. It is derived from the

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesot ...

, where the wall of the general peritoneal cavity comes into contact with the lesser sac between the left

and the

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

; the splenic artery and

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenate ...

pass between its two layers. It contains the tail of the

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an en ...

, the only intraperitoneal portion of the pancreas, and splenic vessels.

Phrenicosplenic ligament

The phrenosplenic ligament (lienophrenic ligament or phrenicolienal ligament) is a double fold of

that connects the

thoracic diaphragm The thoracic diaphragm, or simply the diaphragm ( grc, διάφραγμα, diáphragma, partition), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the ...

and

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

. The phrenicosplenic ligament is part of the greater omentum. Distinctions between the phrenicosplenic ligament and adjacent ligaments, such as the gastrophrenic, gastrosplenic and splenorenal ligaments, which are all part of the same mesenteric sheet, are often nebulous.

Blood supply

The right and left gastroepiploic arteries (also known as gastroomental) provide the sole blood supply to the greater omentum. Both are branches of the celiac trunk. The right gastroepiploic artery is a branch of the gastroduodenal artery, which is a branch of the common hepatic artery, which is a branch of the celiac trunk. The left gastroepiploic artery is the largest branch of the splenic artery, which is a branch of the celiac trunk. The right and left gastroepiploic arteries anastomose within the two layers of the anterior greater omentum along the greater curvature of the stomach.

Development

The greater omentum develops from the

dorsal mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intest ...

that connects the

to the posterior abdominal wall. During its development, the stomach undergoes its first 90° rotation along the axis of the embryo, so that posterior structures are moved to the left and structures anterior to the stomach are shifted to the right. As a result, the dorsal mesentery folds over on itself, forming a pouch with its blind end on the left side of the embryo. A second approximately 90° rotation of the stomach, this time in the frontal plane, moves structures inferior if they were originally to the left of the stomach, and superior if they were originally to the stomach's right. Consequently, the blind-ended sac (also called the lesser sac) formed by the dorsal mesentery is brought inferiorly, where it assumes its final position as the greater omentum. It grows to the point that it covers the majority of the small and large intestine.

Functions

The functions of the greater omentum are: *Fat deposition, having varying amounts of

*Immune contribution, having

milky spots Milky spots are very small white-coloured areas of lymphoid tissue, found in the peritoneal, pleural and pericardial cavities. These are the three coelomic cavities that form as separate compartments from the intraembryonic coelom. More milky spo ...

of macrophage collections *Infection and wound isolation; It may also physically limit the spread of intraperitoneal infections. The greater omentum can often be found wrapped around areas of infection and trauma.

Clinical significance

Surgical removal

Omentectomy refers to the surgical removal of the omentum, a relatively simple procedure with no documented major side effects, that is performed in cases where there is concern that there may be spread of cancerous tissue into the omentum. Examples for this are

ovarian cancer Ovarian cancer is a cancerous tumor of an ovary. It may originate from the ovary itself or more commonly from communicating nearby structures such as fallopian tubes or the inner lining of the abdomen. The ovary is made up of three different ...

and advanced or aggressive

endometrial cancer Endometrial cancer is a cancer that arises from the endometrium (the lining of the uterus or womb). It is the result of the abnormal growth of cells that have the ability to invade or spread to other parts of the body. The first sign is most ...

as well as intestinal cancer and also appendix cancer. The procedure is generally done as an add-on when the primary lesion is removed.

Omental flap

The greater omentum may be surgically harvested for reconstruction of the

thoracic wall The thoracic wall or chest wall is the boundary of the thoracic cavity. Structure The bony skeletal part of the thoracic wall is the rib cage, and the rest is made up of muscle, skin, and fasciae. The chest wall has 10 layers, namely (from ...

. It has also been used experimentally to reinforce bioengineered tissues transplanted to the surface of the heart for cardiac regeneration.

Use in brain surgery

The greater omentum may be surgically harvested to provide revascularization of brain tissue after a stroke.

History

The greater omentum is also known as the great omentum, the omentum majus, the gastrocolic omentum, the epiploon, and the caul. In 1906, the greater omentum was described as the "abdominal policeman" by the surgeon James Rutherford Morrison. This is due to its immunological function, whereby omental tissue seems to "surveil" the abdomen for infection and cover areas of infection when found - walling it off with immunologically active tissue.

Additional images

File:Gray1035.png, Vertical disposition of the

. Main cavity, red; omental bursa, blue. (Greater omentum labeled at left.) File:Sobo 1909 565.png, The greater omentum is attached to the lower portion of the stomach (here the attachment is cut and the stomach is lifted up). File:Gray532.png, The celiac artery and its branches; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed. File:Gray989.png, Schematic figure of the bursa omentalis, etc. Human embryo of eight weeks. File:Gray990.png, Diagrams to illustrate the development of the greater omentum and transverse mesocolon. File:Slide2DDE.JPG, Greater omentum. Deep dissection.

Notes and references

External links

* * * * * ()
Diagram at Tn.edu
* Photo of model at Waynesburg College
digirep/greateromentum
' * Learn about living without an Omentum at The Omentum Project: https://www.theomentumproject.org/ {{Authority control Abdomen

Structure

Subdivisions

Phrenicosplenic ligament

Blood supply

Development

Functions

Clinical significance

Surgical removal

Omental flap

Use in brain surgery

History

Additional images

See also

Notes and references

External links