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Greater omentum

Overview of the greater omentum and neighbouring abdominal viscera.

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Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial on the greater omentum. In the following image, we can see the greater omentum here and some associated structures such as the small and large intestine, the stomach and the liver. In this illustration which is an anterior view of the abdominal cavity, the layers of the anterior abdominal wall including skin, fat and muscles have been dissected away. This has been done to reveal the membranes and organs within the abdominal cavity.

One of the structures that's been dissected away is the parietal peritoneum which is highlighted here in green. The parietal peritoneum is a serous membrane that lines and attaches to the abdominal wall. It's considered to be the outer layer of the peritoneum whereas the inner layer is known as the visceral peritoneum and wraps around the visceral organs. Between these two layers, there's a potential space known as the peritoneal cavity which contains a small amount of serous fluid that lubricates the visceral peritoneum.

The peritoneum also consists of many folds and ligaments. Peritoneal ligaments consist of two layers of peritoneum that connect to organs to each other or attach an organ to the body wall. One of these is the falciform ligament of the liver, a thin peritoneal fold which we can see here just inferior to the parietal peritoneum. This structure is known as a ligament because it connects the liver to the anterior abdominal wall.

To the right of the falciform ligament, we can see another peritoneal ligament which is the round ligament of the liver. It's also commonly known as the ligamentum teres. This is a cord-like ligament that is actually the remnant of the fetal left umbilical vein which normally deteriorates soon after birth. If we take a look at the liver on its own, we can see these two ligaments more clearly. The falciform ligament is highlighted in green and we can see that it's both a broad and thin ligament separating the right lobe of the liver from the left lobe. At the base of the falciform ligament which is often referred to as a free edge, we can see the round ligament.

The largest fold of visceral peritoneum in the abdominal cavity is the greater omentum which we can see here highlighted in green. It's also known as the epiploon which is derived from the Greek word "epipleo" meaning floating on the surface of something which in this case is the surface of the intestines.

The greater omentum is a large apron-like fold of visceral peritoneum that hangs inferiorly from the greater curvature of the stomach. An important thing to remember is that the greater omentum is considered a double sheet as in two sheets that are folded back on each other. So, if you look at it side on in the sagittal plane, it would appear similar to the letter U. each sheet consists of two layer of peritoneum, therefore, the greater omentum has four layers in total. An interesting fact about the greater omentum is that it often adheres to inflamed visceral organs within the abdomen which is thought to limit the spread of infection. This is why it's commonly called the policeman of the abdomen.

The anterior sheet of the greater omentum originates from the stomach and passes inferiorly before it folds upon itself to form the posterior sheet. The posterior sheet then passes superiorly to attach to the structure here – the transverse colon.

Let's move on to look at some relations of the greater omentum. Knowing the relations of the greater omentum is really important in clinical practice when palpating the abdomen and even more so in abdominal surgery. Located to the right of the greater omentum is the ascending colon. The ascending colon is the second part of the large intestine and it ascends from the lower right quadrant of the abdomen to the upper right quadrant.

Superior to the greater omentum, we can see the right lobe of the liver. The right lobe of the liver is located in the right upper quadrant of the abdomen also known as the right upper hypochondrium. If we look at the liver on its own, we can clearly see that the right lobe is the larger of the two lobes. Another relation of the greater omentum is the gallbladder which we can see here in yellow lying in a shallow fossa under the right lobe of the liver. In this image on the right, the liver has been reflected upwards to give us a complete view of this organ.

To the left hand side for the liver and functionally separated from the right lobe is, of course, the left lobe of the liver. The left lobe is located in the epigastrium and towards the upper left hypochondrium. As we just mentioned, the left lobe is the smaller of the two lobes. If we zoom in, we can see a structure highlighted in green to the left of the greater omentum and in continuation with the transverse colon. This structure is named the left colic flexure. This is also known as the splenic flexure because, as you can see in the image on the right, this flexure is in close proximity to the spleen.

In this illustration, the greater omentum and several organs have been dissected away to give us a better view of the left colic flexure. The left colic flexure is the point that the transverse colon turns downwards to form the descending colon.

Inferior to the greater omentum, we can see the ileum – the third part of the small intestine. In the next illustration, we can see that most of the ileum is covered by the greater omentum and we can only see the inferior portion. Superior to the ileum, we can see the jejunum. It's the second part of the small intestine and is located proximal to the ileum. It occupies the central part of the abdominal cavity and is normally completely covered by the greater omentum which has been reflected upwards in this image.

Inferior to the ileum and moving downwards towards the lower abdomen, we can see the urinary bladder. The urinary bladder stores urine transported by the kidneys before it leaves the body via the urethra. The bladder has a capacity to hold between 300 and 500 milliliters of urine. So let's also have a quick look at two vessels that we find in close proximity with the greater omentum.

Running within the transverse mesocolon, we can see the middle colic artery. The middle colic artery is a branch of the superior mesenteric artery and it supplies the transverse colon. Immediately inferior to the middle colic artery is the middle colic vein, a tributary of the superior mesenteric vein. The middle colic vein drains the transverse colon and follows the path of the middle colic artery.

Now we've looked at some of the related vasculature of the greater omentum, you're probably wondering which vessels actually supply and drain this structure. We'll move on to discuss these vessels before we conclude our tutorial.

The blood supply of the greater omentum is derived from these arteries here – the gastroepiploic arteries. These arteries run along the greater curvature of the stomach to anastomose with one another within the anterior sheet of the greater omentum. They give off many omental branches that travel the length of the greater omentum supplying it with oxygenated blood. The venous drainage of the greater omentum mirrors that of the arterial supply draining into these veins here – the gastroepiploic veins.

So that concludes our tutorial on the greater omentum. I hope you enjoyed it and thank you for listening.

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