biliary tract
Meaning of biliary tract: The plumbing that carries bile from liver to gut, and the route gallstones, tumors and infection take to cause jaundice.
Definition of biliary tract
The biliary tract is the system of ducts and the gallbladder that collects bile from the liver, stores it and delivers it to the small intestine. Fine channels between liver cells join into progressively larger ducts, which merge and leave the liver as the common hepatic duct. A side branch leads to the gallbladder, and the final common duct empties into the duodenum.
What does bile actually do?
It does not digest anything. Bile contains no enzymes at all. What it carries are bile salts, which act like detergent: they break a large blob of dietary fat into a suspension of tiny droplets, vastly increasing the surface the pancreas can work on. The enzymes that split fat come from the pancreas, not from the liver. Bile has a second job that has nothing to do with digestion. It is the drain through which the body sheds worn-out red blood cell pigment, surplus cholesterol and many processed drugs, all of which leave in the stool and give it its color.
How is the tract laid out?
| Segment | Runs from | Runs to |
|---|---|---|
| Intrahepatic ducts | Between liver cells | Right and left hepatic ducts |
| Common hepatic duct | Union of right and left | Junction with the cystic duct |
| Cystic duct | Gallbladder | Common hepatic duct |
| Common bile duct | That junction | Duodenum, through the pancreas head |
The gallbladder hangs off this line as a side pocket rather than sitting in the main flow. Between meals a valve at the far end stays shut, so bile backs up and fills it, and there it is concentrated. A fatty meal makes the gallbladder squeeze and the valve open together.
Why does a blockage turn the skin yellow?
The final duct runs through the head of the pancreas and shares its outlet with the pancreatic duct, an arrangement that leaves it vulnerable. A stone slipping out of the gallbladder, a tumor of the pancreatic head, or scarring can plug it. Pigment then has no exit, backs up into the blood and stains the skin and eyes yellow, while the stool loses its color and the urine darkens. Stagnant bile also breeds bacteria, so a blocked duct can become an infected one. Blockage low down affects the flow of digestive juice into the intestine as well.
Also known as
Used in a sentence
Imaging showed dilated ducts throughout the biliary tract.
Good to know
Bile contains no digestive enzymes; it emulsifies fat into droplets that pancreatic enzymes then break down, and it also serves as the exit route for red cell pigment, surplus cholesterol and many processed drugs.
Word origin
Where “biliary tract” comes from
Latin bilis, bile, gives biliary; tract comes from Latin tractus, a drawing out or stretch, used for a run of connected passages.