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Omental bursa

Omental bursa in situ with stomach reflected.

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Transcript

Hey everyone! This is Nicole from Kenhub, and welcome to our tutorial on the anatomy of the omental bursa. In this tutorial, we're going to be discussing what the omental bursa is, what it contains, as well as its anatomical relationships. Here we see the omental bursa highlighted in green. This is a cavity within the abdomen formed between the dorsal abdominal wall and the viscera and omental membranes that are suspended from it. So it would be very difficult to understand the omental bursa without a proper understanding of the anatomy of the abdominal viscera.

So before we begin describing the borders and walls of the bursa, we're going to first review the main viscera of the abdominal cavity associated with it and we'll start by looking at the organs of the digestive tract and then move on to looking at the organs of the abdomen from left to right. Once we've done that, then we'll move on to describing the omental bursa and its contents in detail.

Let’s start with the posterior part of the stomach. The posterior part of the stomach which is the back side of the stomach forms part of the anterior wall of the omental bursa and you can see the posterior part of the stomach here highlighted in green. The stomach contains an acidic fluid which helps digest and disinfect food boluses it receives from the esophagus then promotes these boluses into the duodenum.

Next here, we see we have the descending part of the duodenum and as we've already discussed, the duodenum receives food boluses from the stomach. The descending part of the duodenum is an important part of the digestive tract as it is the location where bile and pancreatic fluids meet with food boluses and help further digest them into absorbable materials. It is also important to note that the descending part of the duodenum is a retroperitoneal structure and is not involved in the formation of any border of the bursa located outside the bursa. And as this is a tutorial focused on the omenta bursa, the remaining parts of the small bowel are omitted.

So the next part of the digestive tract we're going to discuss is the ascending colon, and this part of the colon promotes fecal content upwards while absorbing some last traces of water and it's not involved in the formation of any of the walls of the bursa. This part of the colon is located outside the omental bursa and you can later see that the colon bend to form the right colic flexure.

So let's move a little bit further up and have a look at this structure highlighted in green – the right colic flexure. And the right colic flexure is a curvature of the colon in the right upper quadrant of the abdomen. It's also known as the hepatic flexure due to its position in relation to the liver and it marks an anatomical transition point between the ascending and transverse colon.

So where now looking at the transverse colon and it should be noted that the transverse colon is suspended from the dorsal surface of the abdomen by the transverse mesocolon while it also attaches to the greater omentum. And these anatomical attachments place the transverse colon at the lowermost border of the omental bursa, or to say it in a better way, the transverse colon forms the inferior margin of the omental bursa. Yet despite those attachments, it is considered one of the most mobile parts of the digestive tract.

So if you look to the left right behind the greater omentum, you'll see the left colic flexure also known as the splenic colic flexure, and this part of the colon is a transition point between the transverse and the descending colon. And finally, let's have a look at the descending colon. So here we can see the descending colon highlighted in green, and the main function of this part of the colon is to store digested food for emptying through the rectum.

Okay, so now that we've clarified the major parts of the digestive tract related to the omental bursa, let's shift our attention to the other structures.

So here we see the liver highlighted in green and as you can see, it can be found in the right upper quadrant of the abdomen and just below the diaphragm. The liver is a vital organ responsible for a wide range of metabolic functions. So keep in mind that the liver is retracted in this image to reveal structures normally lying underneath it. And as far as the omental bursa is concerned, it should be noted that the liver forms its superior margin and that its quadrate lobe marks the superior anterior margin of the bursa.

This vesicular structure found below the liver is the gallbladder, and the gallbladder stores bile, a fluid produced by the liver to aid digestion. It contracts rhythmically under the control of cholecystokinin which is a hormone produced when fat-containing foods into the digestive tract. And these contractions push the bile to flow up towards the duodenum where it emulsifies liquids present in food.

So while we're still on the right side, let's have a look at the right kidney. So the right kidney can be seen behind the descending part of the duodenum and below the liver. In reality, it's a retroperitoneal structure just like the descending part of the duodenum. At the same coronal level as the right kidney and the descending part of the duodenum, we're going to find the pancreas.

And the pancreas is another retroperitoneal organ which performs both endocrine and exocrine functions. Its exocrine function is to secrete proteolytic enzymes to the descending part of the duodenum while its endocrine function is to produce and secrete insulin and glucagon – two hormones largely implicated in the regulation of blood sugar levels. And as far as the omental bursa is concerned, the pancreas forms its lower posterior margin.

Moving on now to the left and just behind the pancreas, we’ll find the left kidney seen here highlighted in green. So notice that its margins are not clearly defined and that's because the left kidney is not only located in the retroperitoneal space like the pancreas, but it's also covered by a layer of retroperitoneal fat. It should be noted that just like the pancreas, the left kidney is retroperitoneal.

The left adrenal gland is located just above the kidney as its name suggests and it forms part of the left border of the omental bursa. And this is a very vital endocrine gland and it's responsible for producing steroid hormones and catecholamines. And the first category induces a wide variety of effects in the body from helping regulate blood pressure to controlling growth and development of gender to enabling our body to withstand stressful environmental situations. And the second category is more strictly implicated in the fine tuning of our body to potentially hazardous situations by causing redistribution of blood to the heart, brain, and kidneys and by increasing heart rate and glucose availability.

Finally moving more to the left, we'll find the spleen, and unlike the kidneys and the pancreas, the spleen is not a retroperitoneal organ and the spleen acts like a blood filter removing old and decayed red blood cells from circulation while also assisting the body in its immune response.

Okay so now that we've completed our review on the viscera of the abdomen related to the omental bursa, let's move on now to discuss the membranous parts of the abdominal cavity that are related to the bursa, and we’ll be momentarily shifting to a view where the bursa is closed up as it normally is.

So now we're looking at the lesser omentum, and notice that the stomach is not retracted, but that it's in its true anatomical location and the structure highlighted is the lesser omentum which also happens to be the roof of the omental bursa. And we can also see the foramen of Winslow marked with the arrow. And do note that the lesser omentum forms part of the anterior wall of the omental bursa and we’ll be opening up the bursa and retracting the stomach again to better explore its relationship with the membranous structures of the peritoneum.

Okay, so in this image, we’ve sliced through the greater omentum which is a fold of visceral peritoneum attached to the transverse colon and the stomach, and a particular part of the greater omentum we have divided to reveal the space is known as the gastrocolic ligament, and this division is done in surgery to provide access to the pancreas or the back of the stomach.

The gastrocolic ligament is a part of the greater omentum that connects the greater curvature of the stomach to the transverse colon and this ligament is also important because it forms part of the anterior margin of the omental bursa. And let's now examine other ligaments at the sides of the bursa.

So we're now moving to the left compartment of the wall of the omental bursa and this consists of the gastrosplenic ligament which as its name suggests connects the stomach to the spleen. And this ligament contains the short gastric vessels and the left gastroepiploic vessels.

Let’s now shift our attention to the right side of the omental bursa to the hepatoduodenal ligament. This ligament forms a bridge of connective tissue between the liver and the duodenum as its name suggests, and it's actually a portion of the lesser omentum that folds around structures collectively known as the portal triad. And these structures are the proper hepatic artery, the portal vein, and the common bile duct. This ligament is a very important structure in our discussion about the omental bursa because it forms the anterior border of the epiploic foramen. And the epiploic foramen is the sole route of communication between the omental bursa and the peritoneal cavity proper.

So most of the floor of the omental bursa consists of parietal peritoneum as the organs you can see inside the bursa are located beneath the parietal peritoneum in the retroperitoneal space. However, some of the floor of the bursa consists of a free-hanging membrane – the transverse mesocolon. And the transverse mesocolon extends from the lower margin of the pancreas to the transverse colon and separates the omental bursa from the peritoneal cavity proper below.

So now that we're familiar with most abdominal viscera and their relationship to the omental bursa, let's start putting what we've learned in order. So, first of all, let's try to define what the omental bursa is and, as you may have guessed, the bursa is an almost completely closed cavity within the peritoneal cavity proper. Its upper surface is walled off by the lower surface of the liver, the front of the bursa is demarcated by the quadrate lobe of the liver upwards, the transverse colon in its lowermost part while the lesser omentum and the gastrocolic ligament fill in the regions in between. So the inferior part of the bursa is covered by the transverse mesocolon which suspends the transverse colon and the posterior inferior margin of the bursa is the pancreas and the left kidney.

And moving now to the medial and lateral borders of the bursa, its medial border consists of the foramen of Winslow – an opening beneath the hepatoduodenal ligament – and its lateral or left border consists of the left kidney and adrenal and the gastrosplenic ligament.

Okay, having clarified the anatomical relationships of the bursa, it's now time to move on to discuss the vasculature present within this region. So, we're going to be starting with the celiac trunk, which is the first solitary branch to sprout from the abdominal aorta, and the celiac trunk gives off three main branches, all of which can be found by exploring the omental bursa. So the celiac trunk is located in the retroperitoneal space.

The left gastric artery is one of the branches of the celiac trunk and it supplies the lesser curvature of the stomach and you can see the artery moving upwards to be distributed to that region. The common hepatic artery is a branch of the celiac trunk responsible for supplying the liver, the duodenum, and the other surrounding structures, and we're going to be exploring its branches later in this tutorial.

The splenic artery can be seen coursing on the superior margin of the pancreas and this artery supplies the body and the tail of the pancreas and the spleen. The gastroduodenal artery is one of the branches of the common hepatic artery and it supplies blood to the proximal part of the duodenum and the head of the pancreas, and this artery has two major branches which we'll look at now.

So the first branch of the gastroduodenal artery which you can see here highlighted in green is the right gastroomental artery and this artery supplies the greater curvature of the stomach and the gastrocolic ligament and it runs from left to right in the gastrocolic ligament and anastomosis with the left gastroomental artery of the splenic artery.

The next branch of the gastroduodenal artery is the superior pancreaticoduodenal artery, and this particular branch of the gastroduodenal artery supplies the head of the pancreas and the proximal part of the duodenum. It divides two posterior and anterior branches as it descends which anastomose with the respective branches of the inferior pancreaticoduodenal artery of the superior mesenteric artery.

Let’s move on now to the other branch of the common hepatic artery – the proper hepatic artery. And this artery arises from the common hepatic artery and is the artery we've already discussed as running along the common bile duct and the portal vein within the hepatoduodenal ligament, and it supplies the liver and the gallbladder.

The artery highlighted right now is the middle colic artery and this artery is a branch of the superior mesenteric artery, and as you can see, it supplies the transverse colon and it's located in the transverse mesocolon along with the middle colic vein. So, here we see the middle colic vein highlighted in green and this vein drains into the superior mesenteric vein and runs within the transverse mesocolon alongside the middle colic artery.

So now that we've talked about all the varying parts of the omental bursa, let's take a few minutes to discuss some pathology.

So there are many pathologies that may affect the omental bursa, and the most common condition one can encounter in this area is an abscess or a pseudocyst which often arise as complications of acute pancreatitis. So, acute pancreatitis is the acute inflammation of the pancreas where digestive pancreatic enzymes turn against the pancreatic parenchyma. Symptoms of this condition can range from a transient abdominal pain to a life-threatening pancreatic necrosis. And it's often possible for these same digestive enzymes to gradually break down the parietal peritoneum covering the pancreas and let all the digestive juices and liquefied parenchyma enter into the omental bursa, and this is what we call a pseudocyst. And if that pseudocyst becomes infected, then it turns into a collection of pus and it becomes an abscess.

So lots of fluid is considered to be lost in acute pancreatitis especially when vessels are eroded and bleeding is involved, so one of the first steps in the management of acute pancreatitis is early aggressive fluid resuscitation targeted at maintaining an adequate urine output. So patients are directed to avoid feeding by mouth since that way of feeding may lead the damaged pancreas to secrete more digestive fluids, and since this condition tends to be rather painful in hospitalized patients, it is often treated with opioid analgesics – and this is a pretty strong class of pain medication.

Pseudocysts may develop about a month after the initial attack and they usually resolve spontaneously so unless they begin to cause problems, there's no real need to aspirate them. And occasionally these cysts become infected and they turn into abscesses in which case patients should be administered antibiotics and have the abscess drained usually by CT-guided aspiration.

Okay, so we're at the end of our tutorial now but before I leave you, let's just go over what we talked about today.

So first let's recount the anatomical borders of the omental bursa. So the superior border is created by the lower surface of the liver. The left border is created by the left kidney, left adrenal gland, and the gastrosplenic ligament. The inferior border is created by the transverse mesocolon. The anterior border is occupied by many structures – superiorly, there's the quadrate lobe of the liver, inferiorly the transverse colon and the main anterior area is occupied by the gastrocolic ligament and the lesser omentum. And finally on the right there's no border, but we have the foramen of Winslow.

Of the arteries we find in the omental bursa, you should be able to recognize the celiac trunk and its three main branches – the left gastric artery, the common hepatic artery, and the splenic artery. And, finally, you should be able to remember two other visible arterial branches – the gastroduodenal artery and, its branch, the gastroomental artery.

Alright, so that's the end of our tutorial for today. Thanks for watching. Happy studying!

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