Greater omentum

At a glance

English

Greater omentum

Latin (TA2)

Omentum maius

System

Digestive

Region

Abdomen

Side

Single, on the midline

About the greater omentum

When the front of the abdomen is opened, the first thing seen is usually the greater omentum, a thin, lace-like sheet draped over the coils of small bowel. It hangs from the stomach's greater curvature and the start of the duodenum, drops down in front of the intestines, sometimes as far as the pelvis, and then folds back up on itself to reach the transverse colon. It is therefore made of four layers of peritoneum: two descending from the stomach and two returning upwards. In children these layers can be told apart; in adults they are largely fused.

The returning layers wrap around the transverse colon and blend with the transverse mesocolon, so the space between the front and back pairs, part of the lesser sac, is usually closed off below the colon. Several named ligaments belong to the same sheet. The gastrocolic ligament joins the stomach to the transverse colon, the gastrosplenic ligament runs from the upper greater curvature to the spleen, and the gastrophrenic ligament reaches the underside of the diaphragm. On the right the omentum ends near the first part of the duodenum; on the left it merges with the gastrosplenic ligament.

The sheet is thin and often perforated, but it holds variable amounts of fat, which increase greatly with obesity. It is richly supplied with blood. Its blood comes entirely from the right and left gastro-omental arteries, which run along the greater curvature and join each other there, sending long branches down into the apron.

The omentum moves freely and tends to stick to inflamed areas, wrapping around an inflamed appendix or a perforated ulcer and walling off infection; for this it was nicknamed the abdominal policeman. Collections of immune cells, the milky spots, support this role. Because it may become a site for spreading cancers, surgeons sometimes remove it (omentectomy) alongside the main tumour. Its good blood supply also makes it useful as a flap to fill defects or cover repairs elsewhere, including the chest wall.

Function and supply

Begins at

Hangs from the stomach's greater curvature and from the first part of the duodenum.

Ends at

After folding back on itself, attaches to the transverse colon and blends with the transverse mesocolon.

Function

Stores fat, contributes immune cells to the peritoneal cavity, and moves to wall off areas of inflammation or injury.

Blood supply

Omental branches of the right gastro-omental artery (from the gastroduodenal artery) and the left gastro-omental artery (from the splenic artery), which join along the greater curvature.