MyPathologyReport Printed: October 30, 2026

Bile Ducts: Definition

The bile ducts are thin tubes that carry bile from the liver to the small intestine. Bile is a fluid that helps the body digest fat and remove waste. Together, the bile ducts form a branching system called the biliary tree.

This article explains what the bile ducts do, how they connect, which conditions affect them, and what your report may say.

What are the bile ducts?

The bile ducts are a network of tubes that start inside the liver. The smallest ducts lie next to the liver cells that make bile. They join into larger and larger ducts, like the branches of a tree joining a trunk. The largest duct empties into the first part of the small intestine, called the duodenum.

Doctors divide the ducts by location. Intrahepatic ducts lie inside the liver. Extrahepatic ducts lie outside the liver.

What is bile?

Bile is a yellow-green fluid made by the liver. The liver makes about 500 to 600 mL each day. Bile does two main jobs:

Digesting fat. Bile salts dissolve fat from food, along with vitamins that dissolve in fat. This lets the intestine absorb them.
Removing waste. Bile carries cholesterol, bilirubin, and other waste out of the body in the stool. Bilirubin comes from old red blood cells and gives bile its color.

How do the bile ducts connect?

Bile travels through the ducts in a set order:

Intrahepatic ducts. Tiny ducts inside the liver collect bile and join into larger ducts.
Right and left hepatic ducts. These ducts drain the right and left sides of the liver.
Common hepatic duct. The right and left hepatic ducts join to form this duct.
Cystic duct. This duct connects the gallbladder to the common hepatic duct.
Common bile duct. The common hepatic duct and the cystic duct join to form this duct. It passes through part of the pancreas.
Ampulla of Vater. The common bile duct joins the pancreatic duct here and opens into the duodenum. A ring of muscle called the sphincter of Oddi controls the flow.

What does the gallbladder do?

The gallbladder stores bile between meals. When you are not eating, about three-quarters of the bile flows up the cystic duct into the gallbladder. The gallbladder removes water and concentrates the bile. After a meal, the gallbladder squeezes, the sphincter of Oddi relaxes, and bile flows into the duodenum.

What conditions affect the bile ducts?

Several conditions can damage or block the bile ducts. Examples include:

Primary sclerosing cholangitis. In primary sclerosing cholangitis, the immune system attacks ducts inside and outside the liver. It often occurs with ulcerative colitis. It raises the risk of bile duct cancer.
Primary biliary cholangitis. In primary biliary cholangitis, the immune system inflames and slowly destroys the small bile ducts in the liver.
Bile duct adenoma. A bile duct adenoma is a benign growth of small ducts inside the liver. It is not cancer.
Biliary intraepithelial neoplasia. Biliary intraepithelial neoplasia (BilIN) is a precancerous change in the lining of the ducts.
Cholangiocarcinoma. Cholangiocarcinoma is cancer that starts in the bile ducts. It can start inside the liver (intrahepatic cholangiocarcinoma) or outside it (extrahepatic cholangiocarcinoma).
Ampullary tumors. Tumors can also start where the ducts open into the duodenum. Examples include ampullary adenoma and ampullary adenocarcinoma.

How do pathologists examine the bile ducts?

The pathologist examines bile duct tissue from a liver biopsy or surgical specimen. In a liver biopsy, the pathologist checks the small ducts for inflammation, damage, and loss. In a surgical specimen, the pathologist checks the larger ducts for tumors and measures how far any tumor has spread.

What might my report say about the bile ducts?

Reports describe the bile ducts in a few standard ways. Each laboratory phrases them a little differently:

Normal bile ducts. The ducts look healthy.
Bile duct damage. Inflammation is injuring the cells that line the ducts.
Bile duct loss. Some small ducts are missing, often after long-term damage.
Scarring around the ducts. Scar tissue, or fibrosis, surrounds or narrows the ducts.
A tumor involving the bile ducts. The report names the tumor and describes its size and spread.

Questions to ask your doctor

Which bile ducts did my biopsy or surgery include?
Did the pathologist see damage or loss of the bile ducts?
What is causing the changes in my bile ducts?
Do I need blood tests or imaging of my bile ducts?
If the pathologist found a tumor, did it start in the bile ducts?
Do I need to see a liver specialist?