The greater omentum and corresponding vasculature is visible covering the intestines (dissection image with liver held out of the way). Label at bottom.
The greater omentum (also the great omentum, omentum majus, gastrocolic omentum, epiploon, or, especially in non-human 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, 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 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).[1]
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.[2]
The two layers of the greater omentum descend from the greater curvature of the stomach and the beginning of the duodenum.[2] They pass in front of the small intestines, 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.[2]
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 duodenum.
The greater omentum is usually thin, and has a perforated appearance. It contains some adipose tissue, which can accumulate considerably in obese people. It is highly vascularised.[3]
Subdivisions
Horizontal disposition of the peritoneum in the upper part of the abdomen (phrenicolienal ligament labeled at bottom left)Diagram to show the lines along which the peritoneum leaves the wall of the abdomen to invest the viscera (phrenicosplenic ligament labeled at center right)
The greater omentum is often defined to encompass a variety of structures. Most sources include the following three:[4][5]
The splenorenal ligament (or lienorenal ligament) (from the left kidney to the spleen) is occasionally considered part of the greater omentum.[6][7] It is derived from the peritoneum, where the wall of the general peritoneal cavity comes into contact with the lesser sac between the left kidney and the spleen; the splenic artery and vein pass between its two layers. It contains the tail of the pancreas, the only intraperitoneal portion of the pancreas, and splenic vessels.One or more of the preceding sentences incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)
Phrenicosplenic ligament
The phrenosplenic ligament (lienophrenic ligament or phrenicolienal ligament) is a double fold of peritoneum that connects the thoracic diaphragm and spleen.[8]
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.[8]
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
Two of the stages in the development of the digestive tube and its mesentery. The arrow indicates the entrance to the bursa omentalis
The greater omentum develops from the dorsal mesentery that connects the stomach 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.
Infection and wound isolation; It may also physically limit the spread of intraperitoneal infections.[9] 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 and advanced or aggressive endometrial cancer 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.[3] It has also been used experimentally to reinforce bioengineered tissues transplanted to the surface of the heart for cardiac regeneration.[10]
Use in brain surgery
The greater omentum may be surgically harvested to provide revascularization of brain tissue after a stroke.[11]
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.[12] 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
Vertical disposition of the peritoneum. Main cavity, red; omental bursa, blue. (Greater omentum labeled at left.)
The greater omentum is attached to the lower portion of the stomach (here the attachment is cut and the stomach is lifted up).
The celiac artery and its branches; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed.
Schematic figure of the bursa omentalis, etc. Human embryo of eight weeks.
Diagrams to illustrate the development of the greater omentum and transverse mesocolon.
1 2 Fayanju, Oluwadamilola M.; Garvey, Patrick Bryan; Karuturi, Meghan S.; Hunt, Kelly K.; Bedrosian, Isabelle (2018). "Surgical Procedures for Advanced Local and Regional Malignancies of the Breast". The Breast. pp.778–801.e4. doi:10.1016/B978-0-323-35955-9.00059-3. ISBN978-0-323-35955-9.
↑ Kuper, C. Frieke; Ruehl-Fehlert, Christine; Elmore, Susan A.; Parker, George A. (2013). "Immune System". Haschek and Rousseaux's Handbook of Toxicologic Pathology. pp.1795–1862. doi:10.1016/B978-0-12-415759-0.00049-2. ISBN978-0-12-415759-0. The omentum helps to restore tissue integrity in the peritoneum by connecting tissue repair with immunological defense. Upon intraperitoneal immunization, follicles and germinal centers can be formed.
The stomach is a muscular, hollow organ in the upper 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 is involved in the gastric phase of digestion, following the cephalic phase in which the sight and smell of food and the act of chewing are stimuli. In the stomach a chemical breakdown of food takes place by means of secreted digestive enzymes and gastric acid.
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 organs, and is composed of a layer of mesothelium supported by a thin layer of connective tissue. This peritoneal lining of the cavity supports many of the abdominal organs and serves as a conduit for their blood vessels, lymphatic vessels, and nerves.
The abdominal cavity is a large body cavity in humans and many other animals that contain organs. It is a part of the abdominopelvic cavity. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm, a thin sheet of muscle under the lungs, and its floor is the pelvic inlet, opening into the pelvis.
In human anatomy, the mesentery, an organ that attaches the intestines to the posterior abdominal wall, comprises the double fold of the peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestines.
The peritoneal cavity is a potential space located between the two layers of the peritoneum—the parietal peritoneum, the serous membrane that lines the abdominal wall, and visceral peritoneum, which surrounds the internal organs. While situated within the abdominal cavity, the term peritoneal cavity specifically refers to the potential space enclosed by these peritoneal membranes. The cavity contains a thin layer of lubricating serous fluid that enables the organs to move smoothly against each other, facilitating the movement and expansion of internal organs during digestion.
In human anatomy, the abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta.
In human anatomy, the splenic artery or lienal artery, an older term, is the blood vessel that supplies oxygenated blood to the spleen. It branches from the celiac artery, and follows a course superior to the pancreas. It is known for its tortuous path to the spleen.
The lesser omentum is the double layer of peritoneum that extends from the liver to the lesser curvature of the stomach, and to the first part of the duodenum. The lesser omentum is usually divided into these two connecting parts: the hepatogastric ligament, and the hepatoduodenal ligament.
In human anatomy, the left gastric artery arises from the celiac artery and runs along the superior portion of the lesser curvature of the stomach before anastomosing with the right gastric artery. It also issues esophageal branches that supply lower esophagus and ascend through the esophageal hiatus to form anastomoses with the esophageal branches of thoracic part of aorta.
The lesser sac, also known as the omental bursa, is a part of the peritoneal cavity that is formed by the lesser and greater omentum. Usually found in mammals, it is connected with the greater sac via the omental foramen or Foramen of Winslow. In mammals, it is common for the lesser sac to contain considerable amounts of fat.
In human anatomy, the greater sac, also known as the general cavity (of the abdomen) or peritoneum of the peritoneal cavity proper, is the cavity in the abdomen that is inside the peritoneum but outside the lesser sac.
The right gastroepiploic artery is one of the two terminal branches of the gastroduodenal artery. It runs from right to left along the greater curvature of the stomach, between the layers of the greater omentum, anastomosing with the left gastroepiploic artery, a branch of the splenic artery.
The left gastroepiploic artery, the largest branch of the splenic artery, runs from left to right about a finger's breadth or more from the greater curvature of the stomach, between the layers of the greater omentum, and anastomoses with the right gastroepiploic.
The foregut in humans is the anterior part of the alimentary canal, from the distal esophagus to the first half of the duodenum, at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the abdominal walls by mesentery. The foregut arises from the endoderm, developing from the folding primitive gut, and is developmentally distinct from the midgut and hindgut. Although the term “foregut” is typically used in reference to the anterior section of the primitive gut, components of the adult gut can also be described with this designation. Pain in the epigastric region, just below the intersection of the ribs, typically refers to structures in the adult foregut.
The gastrocolic ligament is a portion of the greater omentum that stretches from the greater curvature of the stomach to the transverse colon. It forms part of the anterior wall of the lesser sac.
The hepatogastric ligament or gastrohepatic ligament connects the liver to the lesser curvature of the stomach. It contains the right and the left gastric arteries. In the abdominal cavity, it separates the greater and lesser sacs on the right. It is sometimes cut during surgery in order to access the lesser sac. The hepatogastric ligament consists of a dense cranial portion and the caudal portion termed the pars flaccida.
The gastrosplenic ligament is part of the greater omentum extending between the stomach and the spleen. It contains several blood vessels.
The curvatures of the stomach are the long, convex, lateral surface, and the shorter, concave, medial surface of the stomach, which are referred to as the greater and lesser curvatures, respectively. The greater curvature, which begins at the cardiac notch, and arches backwards, passing inferiorly to the left, is four or five times longer than the lesser curvature, which attaches to the hepatogastric ligament and is supplied by the left gastric artery and right gastric branch of the hepatic artery.
In human anatomy, the omental foramen is the passage of communication, or foramen, between the greater sac, and the lesser sac of the peritoneal cavity.
The development of the digestive system in the human embryo concerns the epithelium of the digestive system and the parenchyma of its derivatives, which originate from the endoderm. Connective tissue, muscular components, and peritoneal components originate in the mesoderm. Different regions of the gut tube such as the esophagus, stomach, duodenum, etc. are specified by a retinoic acid gradient that causes transcription factors unique to each region to be expressed. Differentiation of the gut and its derivatives depends upon reciprocal interactions between the gut endoderm and its surrounding mesoderm. Hox genes in the mesoderm are induced by a Hedgehog signaling pathway secreted by gut endoderm and regulate the craniocaudal organization of the gut and its derivatives. The gut system extends from the oropharyngeal membrane to the cloacal membrane and is divided into the foregut, midgut, and hindgut.
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