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Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial on the gallbladder. This tutorial will mainly focus on the gallbladder – a small organ in the abdomen which is in close rela... Read more
Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial on the gallbladder. This tutorial will mainly focus on the gallbladder – a small organ in the abdomen which is in close relation with the liver. However, we'll also look at some other structures that are neighboring the gallbladder such as the duodenum and the sphincter of Oddi as well as the pancreas and the pancreatic duct.
Before we begin this tutorial, I just want to get familiar with the orientation of this illustration. So here we have an anterior view of the body and we're looking at the right hand side of the body. Here we can see the right lobe of the liver which has been reflected upwards to reveal the entirety of the gallbladder, whereas when the liver is in its normal anatomical position usually only the fundus of the gallbladder is visible as it projects from the inferior border of the liver.
If we zoom in on this image, we can get a better look at the gallbladder which is highlighted here in green. The gallbladder is hollow and is located just inferior to the liver. It is usually about 8 centimeters in length and 4 centimeters in diameter when it's fully distended. The main function of the gallbladder is to store bile that it receives from the liver where the bile is produced. During storage in the gallbladder, the bile is concentrated by removing some water and electrolytes.
Anatomically, the gallbladder can be divided into four different parts. The first part which we can see here highlighted in green is called the fundus. This part is usually located adjacent to the anterior abdominal wall behind the ninth costal cartilage on the right hand side of the body. Because this part may project from the inferior border of the liver, when there's a suspicion of an enlarged gallbladder on clinical examination, this is usually the location used for palpation.
The next part of the gallbladder we'll be looking at is the body of the gallbladder. The body is the largest part of the gallbladder and is this portion we can see here highlighted in green. Unlike the fundus, the body normally lies in contact with the liver surface. Towards its proximal end, the body narrows into the third part of the gallbladder which is called the infundibulum. The infundibulum is considered to be this tapering area between the body and the neck of the gallbladder. The most proximal and narrow part of the gallbladder is called the neck. The neck consists of a few folds which give it this twisted shape.
Continuous with the neck of the gallbladder is the cystic duct. Bile can either travel through this duct to the gallbladder or in the opposite direction out of the gallbladder. This duct is about 3 to 4 centimeters long and contains between 5 and 12 folds giving it a twisted appearance like the neck of the gallbladder. The cystic duct joins the common hepatic duct to form a structure called the common bile duct.
Okay, now we move on to talk more about bile and its pathway through the different ducts in the abdomen looking at the structures involved along the way. Bile is a dark green fluid that's secreted in the liver. It is produced by the hepatocytes and is modified downstream towards the gallbladder by the bile duct epithelium. The bile that's produced here in the liver by the hepatocytes is referred to as liver bile.
The left hepatic duct and the right hepatic duct transfer bile from the liver. These ducts are formed by the intrahepatic ducts and are part of the ductal system that leads to the gallbladder. So, basically, bile will exit the liver through one of two possible ducts. The first duct is the right hepatic duct which is the shorter of the two ducts. Bile from the right functional lobe usually exits the liver via this duct. The other pathway that bile can exit the liver is via the left hepatic duct. This duct is a bit longer than the right one and contains bile from the left functional lobe of the liver.
The right and left hepatic ducts join together to form the common hepatic duct. This duct continues for about 3 centimeters before it joins the cystic duct to form the common bile duct. At this point, the bile usually travels through the cystic duct to the gallbladder to be stored and concentrated. This bile is now considered to be gallbladder bile. So these arrows represent bile entering and exiting the gallbladder. So bile enters the gallbladder and is stored and concentrated, then after eating it leaves towards the cystic duct and into the common bile duct.
The common bile duct is about 6 centimeters long and descends downwards before curving slightly to the left. It's about 6 millimeters in diameter and it's sometimes embedded in the tissue of the pancreas. As it veers towards the left, it passes under the duodenum and joins up with the pancreatic duct.
In the next illustration, we can see part of the pancreas. The pancreas is an organ with both endocrine and exocrine function. The exocrine part of the pancreas is responsible for secretion of fluids that contain essential enzymes for digestion. These enzymes help break down proteins, carbohydrates and lipids. So how did these secreted fluids leave the pancreas and where do they travel to? The pancreatic juices leave the exocrine part of the pancreas via this duct here which is the pancreatic duct. In most people, this is the only duct carrying juices from the pancreas and this duct is related at its proximal end to the common bile duct that we mentioned earlier.
After the common bile duct and pancreatic duct join, they enter the duodenum which is part of the small intestine and they do this via the major duodenal papilla. This papilla is located at the level of the second or third lumbar vertebrae. It's important to remember that this papilla is surrounded by a muscular valve which regulates the flow of bile and pancreatic fluids in the duodenum. This valve is known as the sphincter of Oddi. Once the bile and pancreatic enzymes enter the duodenum, they can begin the digestion process. Bile is responsible for emulsifying lipids otherwise known as fats. This process results in a mixture of bile and lipids. This mixture is known as micelle and increases the surface area for digestion by pancreatic enzymes.
Now let's go over some important clinical notes to finish off this tutorial. The most common problem to affect the gallbladder is of course gallstones. Gallstones are hardened deposits of bile and calcium salts usually saturated with either cholesterol or bilirubin. Bilirubin is a breakdown substance of haem molecules from haemoglobin.
A gallstone is also known as a cholelith and they usually cause no symptoms when staying in the bile duct. This is known clinically as cholelithiasis. However, gallstones can potentially block the gallbladder and most commonly they occlude the neck or the cystic duct. When the duct is occluded, this can lead to inflammation of the gallbladder which is called cholecystitis. When this occurs, there is also a risk of a bacterial infection due to the obstruction of the flow of the bile outside the gallbladder. This can result in fever and pain in the upper right quadrant of the abdomen.
Cholecystitis can be differentiated from other causes of upper right quadrant pain such as pyelonephritis by trying to elicit Murphy's sign. This sign is very important in clinical practice especially in the differential diagnosis of acute abdominal pain and is tested by first asking the patient to breathe out. A hand or fingers are then placed below the costal margin on the right mid-clavicular line – the approximate location of the gallbladder. The patient is then asked to breathe in and if they wince in pain, this is considered a positive test. However, this must be confirmed by ensuring the same maneuver doesn't cause pain on the left hand side.
Cholecystitis is often treated with antibiotics and pain relief, however, if this doesn’t improve the patient's symptoms or the patient has recurrent gallstones, removal of the gallbladder may be indicated. Removal of the gallbladder is called cholecystectomy.
Gallstones may also occlude the common bile duct. This condition is known as choledocholithiasis. This can result in jaundice which is yellowing of the skin as well as liver damage. Choledocholithiasis is often differentiated from cholecystitis by a negative Murphy's sign. Gallstones are usually diagnosed by ultrasound or by a procedure known as ERCP which stands for Endoscopic Retrograde Cholangio-Pancreatography. ERCP can also be used as a treatment for choledocholithiasis by removing gallstones from the common bile duct.
So while gallstones may cause a lot of different conditions with difficult names that are hard to remember, the most important thing to take away is that they are usually asymptomatic and don't cause any problems in over 70% of people.
So that brings us to the end of this tutorial on the gallbladder. I hope you enjoyed it and thank you for listening.
Now that you just completed this video tutorial, then it’s time for you to continue your learning experience by testing and also applying your knowledge. There are three ways you can do so here at Kenhub. The first one is by clicking on our “start training” button, the second one is by browsing through our related articles library, and the third one is by checking out our atlas.
Now, good luck everyone, and I will see you next time.