Biliary system: anatomy, functions, general conditions


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


Bile is a thick, greenish-brown substance that is produced in the liver and stored in the gallbladder. The role of bile is to be released into the small intestine when fatty foods are eaten to help break down fats for absorption.

After food has gone through the initial digestion process in the stomach, it travels to the duodenum (the first segment of the small intestine). Bile and other digestive secretions enter the duodenum through the biliary tract and bile ducts. They continue the digestive process by breaking down food so that its nutrients can be absorbed.


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

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

Liver – A large glandular organ that performs many vital metabolic functions, such as digesting fat for energy in the body. Liver cells produce bile.

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

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

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

Pancreas : The pancreas, a large gland located behind the stomach, secretes pancreatic enzymes (such as lipase that breaks down fats) into the biliary system through the pancreatic duct.

Gallstones – Abnormal, small, hard formations made of bile pigments, cholesterol, and calcium salts, gallstones can cause bile duct obstruction, a condition called cholestasis .

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Anatomy of the biliary system

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

Associated with the liver and gallbladder are extrahepatic ducts located outside the liver and used to transport bile. Note that some bile ducts are also within the liver. They serve to drain the bile from the organ and are called intrahepatic ducts.


The biliary system consists of a series of ducts, organs, and other structures responsible for the production, storage, and transport of bile. Bile is produced in liver cells and travels to the gallbladder where it is stored for later use.

When fatty foods enter the body, bile is secreted, and through this system of ducts, it enters the small intestine to its final destination: the duodenum.

Bile outflow through the biliary system

Bile passes through the duct system and other structures of the biliary system in a controlled manner.

  • From the liver , where bile is produced in liver cells, it travels to the duct system in and out of the liver. These ducts collect bile. The collected bile is sent to the right and left hepatic ducts.
  • From the right and left hepatic ducts , bile enters the common hepatic duct.
  • The common hepatic duct connects to the cystic duct, through which bile 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 at the junction of the common hepatic duct and the cystic duct. CBD travels from the liver to the duodenum, where bile is excreted through a muscular hole called the sphincter of Oddi.
  • The common bile duct passes through the pancreas before entering the duodenum. The lower part of the CBD joins the pancreatic duct before entering the duodenum. This is where the pancreatic juices (which contain digestive enzymes) enter the biliary system.
  • The sphincter of Oddi relaxes, allowing bile to enter the duodenum. As soon as bile enters the duodenum, it begins to break down fats. Only half of the bile enters the duodenum, while the other half enters the gallbladder.
  • The gallbladder receives half of the bile, which passes through the common bile duct, where it is stored in the gallbladder for future use.
  • Once bile builds up in the gallbladder, it is not secreted until a large meal is eaten and a hormone called cholecystokinin is released. This hormone stimulates the secretion of bile, which travels to the duodenum through the cystic duct and to the common bile duct to begin the process of breaking down fat.

Anatomical variations

Aberrant ducts are a common deviation from the normal anatomy of the biliary system. Aberrant ducts do not have the anatomical structure that they should. For example, ducts can join abnormal ducts abnormally, causing bile to not flow properly.

In fact, according to a study published in the journal Liver and Binary Tract Surgery , "50% of patients with stones in the gallbladder or common bile duct show significant deviations from what is generally considered normal."

A 2011 study found 22 bile duct variants in 59.5% of study participants who underwent liver surgery. These include the accessory right hepatic duct (into which the cystic duct is drained) and five other abnormalities that have never been described before.

Deviation from the normal anatomy of the bile ducts is one of the main causes of inadvertent damage to the ducts during some surgical procedures.

Function of the biliary system.

The biliary system has three important functions:

  • Elimination of waste products from the liver (in the duodenum)
  • Controlled release bile flow
  • Transport of bile and pancreatic juice to break down food in the small intestine.

Related conditions

Biliary tract disease describes any condition that affects the gallbladder, bile ducts, and other structures necessary for the production and transport of bile. Common diseases of the biliary system include gallbladder disease, biliary colic, and bile duct obstruction.

Gallbladder disease

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

Biliary colic

Biliary colic is a recurring pain in the right upper quadrant of the abdomen or above the stomach (epigastrium). Caused by temporary obstruction of the cystic duct (usually a secondary stone lodged 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 does not pass on its own, cholecystitis (acute inflammation of the gallbladder) occurs .

Bile duct obstruction

Also known as biliary obstruction, it is a blockage in any of the ducts of the biliary system. This condition is most often due to a gallstone, but it can also be caused by a tumor or other underlying cause.

Watch out

  Treatment of the biliary tract may include:

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


To diagnose abnormalities and diseases of the biliary system, various types of tests are performed.

  • Liver function tests : A blood sample is taken and a laboratory test is performed to evaluate specific enzymes and protein levels to see how the liver is working.
  • Endoscopic ultrasound : it is the use of an endoscope that is inserted through the mouth into the digestive tract; High-energy sound waves (ultrasound) are reflected back to the endoscope, creating an image of body tissue.
  • Computed Tomography (CT) : CT involves taking a series of images from different angles within the body.
  • Magnetic Resonance Imaging (MRI) : MRI uses radio waves and magnetic fields to create a series of detailed images inside 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 an MRI in a procedure called magnetic resonance cholangiopancreatography to look for gallstones and diagnose the cause of another biliary obstruction.
  • Liver biopsy : This procedure involves the removal of a very small piece of liver tissue, which is examined in a laboratory for signs of disease or damage.

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