The Anatomy of the Biliary System

The biliary system, also called the biliary tract or biliary tree, is a system of ducts (narrow tubular structures), organs (including the liver, gallbladder, and pancreas), and associated structures that function to produce, store, secrete, and transport bile.

Bile

Bile is a greenish-brown, thick substance produced in the liver and stored in the gallbladder. Bile’s function is to be released into the small intestine when a fatty meal is ingested to help break down fats for absorption.

Once food has gone through the initial process of digestion in the stomach, it moves into the duodenum (the first segment of the small intestine). Bile and other digestive secretions travel into the duodenum via the biliary tract's system of bile ducts. These continue the digestive process by breaking down food so its nutrients can be absorbed.

Terms

To fully understand how the biliary system works, it’s important to know the definition of some related medical terms, including the following.

Duodenum: This is the first of three sections of the small intestine, and receives food from the stomach and digestive juices from the liver, gallbladder, and pancreas via the biliary tract. This is the part of the small intestine that is primarily involved in breaking down food so that nutrients can later be absorbed in the jejunum (middle section of the small intestine).

Liver: A large glandular organ that performs many vital metabolic functions, such as the digestion of fats to make energy in the body. The liver cells make bile.

Bile: A thick, greenish-brown substance made in the liver and stored in the gallbladder, bile is comprised of water, bile acids, cholesterol, phospholipids, bile pigments (such as bilirubin), and electrolytes. It is important in enabling the body to digest and absorb fats and fat-soluble vitamins, such as vitamins D and K.

Bile duct: This is a small, hollow tube that functions to transport bile. The biliary system is comprised of a system of these ducts, which flow from the liver to the gallbladder for storage and then into the small intestine (duodenum).

Gallbladder: A pear-shaped organ located in front of the duodenum, just underneath the liver, the gallbladder's main function is to store bile. It connects to the cystic duct.

Pancreas: A large gland located behind the stomach, the pancreas secretes pancreatic enzymes (such as lipase, which breaks down fats) into the biliary system via the pancreatic duct.

Gallstone: Abnormal, small, hard masses comprised of bile pigments, cholesterol, and calcium salts, gallstones can cause a blockage of bile ducts, a condition called cholestasis.

Biliary System Anatomy

The organs, ducts, and other structures of the biliary system are located in the upper-right abdominal quadrant, while the gallbladder is located just below the liver.

Connected to the liver and gallbladder are the extrahepatic ducts, located outside of the liver, which function to transport bile. Note that some bile ducts are also located inside the liver. These function to drain bile out of the organ and are called intrahepatic ducts.

Structure

The biliary system is comprised of a series of ducts, organs, and other structures responsible for producing, storing, and transporting bile. The bile is made in the cells of the liver and travels to the gallbladder to be stored for later use.

When a fatty meal is ingested, the bile is released and travels to the small intestine through this system of ducts to its final destination, the duodenum.

Bile Flow Through the Biliary System

Through the system of ducts and other structures of the biliary system, bile travels in a controlled manner.

• From the liver, where bile is made in the liver cells, next it flows into a system of ducts located inside and outside of the liver. These ducts function to collect the bile. Once collected, the bile travels to the right and left hepatic ducts.
• From the right and left hepatic ducts, bile then flows into the common hepatic duct.
• The common hepatic duct joins the cystic duct, where the bile then flows.
• The cystic duct is connected to the gallbladder. Bile flows from the cystic duct into the common bile duct.
• The common bile duct (CBD) is located where the common hepatic duct and the cystic duct join. The CBD runs from the liver to the duodenum, where bile is excreted through a muscular opening called the sphincter of Oddi.
• The common bile duct passes through the pancreas before it empties into the duodenum. The lower portion of the CBD joins the pancreatic duct before entering the duodenum. This is where pancreatic juices (containing digestive enzymes) enter the biliary system.
• The sphincter of Oddi relaxes to allow bile to enter the duodenum. Once the bile enters the duodenum, it begins to break down ingested fats. Only half of the bile ends up in the duodenum, while the other half travels into the gallbladder.
• The gallbladder receives half of the bile that flows through the common bile duct, where it is stored in the gallbladder for future use.
• Once bile is stored in the gallbladder, it isn’t released until a large meal is eaten and a hormone named cholecystokinin gets secreted. This hormone stimulates the release of bile, which travels to the duodenum through the cystic duct and into the common bile duct to begin the process of breaking down fats.

Anatomical Variations

Aberrant ducts are a common variation from the normal anatomy that comprises the biliary system. Aberrant ducts are not anatomically structured the way they should be. For example, the ducts may abnormally join the wrong ducts, so that bile does not flow properly.

In fact, according a study published in Liver and Biliary Tract Surgery, “50% of patients presenting with gallbladder stones or common bile duct stones show a significant variation from what is generally considered as the expected normal pattern.”

A 2011 study discovered as many as 22 variations of bile ducts in 59.5% of the study participants who had liver surgery. These included an extra right hepatic duct (in which a cystic duct drained) and five other abnormalities that had never been described before.

Variation from the normal anatomy of the bile ducts is a primary reason the ducts get inadvertently injured during some types of surgery.

Function of the Biliary System

There are three important functions of the biliary system:

• Draining the waste products from the liver (into the duodenum)
• Secreting bile in a controlled-release manner
• Transporting bile and pancreatic juices to help break down food in the small intestine

Associated Conditions

Biliary disease describes any condition that affects the gallbladder, bile ducts, and other structures needed to produce and transport bile. Common maladies of the biliary system include gallbladder disease, biliary colic, and bile duct obstruction.

Gallbladder Disease

Gallstones are the most common gallbladder condition, but tumors and acute acalculous cholecystitis (sudden, severe inflammation of the gallbladder without gallstones) are other common types of biliary disease.

Biliary Colic

Biliary colic is intermittent pain in the upper-right quadrant of the abdomen or above the stomach (epigastrium). Caused by a temporary obstruction of the cystic duct (this is usually secondary to a gallstone that is trapped in the cystic duct), the pain resulting from this condition can range from mild to severe.

If the obstruction is not removed or the gallstone doesn’t pass on its own, it results in cholecystitis (an acute inflammation of the gallbladder).

Bile Duct Obstruction

Also known as biliary obstruction, this is the blockage of any of the ducts in the biliary system. This condition most commonly occurs from a gallstone, but can also be caused by a tumor or another underlying cause.

Treatment

 Treatment for biliary disease may include:

• Medications to increase the flow of bile from the liver
• Antibiotics to treat an infection
• Hepatoportoenterostomy: A surgical procedure to drain bile from the liver when bile ducts are blocked
• Endoscopic retrograde cholangiopancreatography: A minimally invasive surgical procedure performed by a gastroenterologist, who uses an endoscope (a flexible tube with a light and a camera) to locate and remove gallstones from the bile duct
• Cholecystectomy: Surgical removal of the gallbladder

Tests

Several types of tests are done to diagnose abnormalities and diseases of the biliary system.

• Liver function tests: A blood sample is taken, and a lab test is performed to evaluate certain enzymes and protein levels to see how the liver is functioning.
• Endoscopic ultrasound: This is the use of an endoscope, which is inserted through the mouth into the digestive tract; high-energy sound waves (ultrasound) are bounced off the endoscope, creating an image of body tissues.
• Computed tomography (CT) scan: CT Involves taking a series of images at different angles inside the body.
• Magnetic resonance imaging (MRI): MRI uses radio waves and magnetic fields to create a series of detailed images inside of the body.
• Endoscopic retrograde cholangiopancreatography: Used for treatment (see above), this procedure is also used to diagnose problems in the biliary system. It is sometimes combined with MRI, in a procedure called magnetic resonance cholangiopancreatography, to detect gallstones and diagnose the cause of other obstructions in the biliary tract.
• Liver biopsy: This procedure involves the removal of a very small portion of liver tissue, which is examined in the lab for signs of disease or damage.