biliary system
Meaning of biliary system: A branching drainage network that carries a digestive fluid one way and, when it blocks, turns the skin yellow.
Definition of biliary system
The biliary system is the network of organs and ducts that produces, stores and delivers bile to the small intestine. It begins with tiny channels between the liver cells, which merge into progressively larger ducts, joins the gallbladder through a side branch, and ends where the common bile duct empties into the duodenum alongside the pancreatic duct.
What does bile do?
Two jobs at once, one digestive and one excretory. Bile salts act as detergents, breaking dietary fat into droplets small enough for enzymes to work on, and without them fat and the vitamins dissolved in it pass through largely unabsorbed. At the same time the fluid is a disposal route: the liver uses it to eliminate bilirubin from broken-down red cells, excess cholesterol, and processed drugs and toxins that are too large to leave through the kidneys.
How is the flow controlled?
Between meals a muscular ring at the outlet stays shut, so bile backs up and diverts into the gallbladder, which concentrates it several-fold by absorbing water. When a fatty meal reaches the duodenum, the intestinal lining releases a hormone that makes the gallbladder squeeze and the ring relax together, delivering a concentrated pulse just as it is needed. Most bile salts are then reabsorbed lower down the intestine and returned to the liver for reuse, a recycling loop that runs several times during a single meal.
What goes wrong with it?
| Problem | What obstructs or inflames |
|---|---|
| Gallstones | Concentrated bile crystallizes in the gallbladder |
| Cholecystitis | A stone blocks the gallbladder outlet |
| Obstructive jaundice | A stone or tumor blocks the common duct |
| Cholangitis | Bacteria infect bile trapped behind a blockage |
| Sclerosing cholangitis | Progressive scarring narrows the ducts |
Why does blockage turn the skin yellow?
Bilirubin is a yellow pigment that the liver processes and then discards into bile. If the exit is blocked, the processed pigment has nowhere to go and returns to the bloodstream, staining the skin and the whites of the eyes. Two further signs follow from the same cause: stool loses its brown color because the pigment never reaches the intestine, and urine darkens because the kidneys begin excreting what the bile ducts cannot. Itching is common and is thought to arise from other bile components that also accumulate.
Also known as
Used in a sentence
Imaging of the biliary system showed dilated ducts above the level of the obstruction.
Good to know
The yellow skin, pale stool and dark urine of obstruction share one cause: processed bilirubin cannot reach the intestine and returns to the blood for the kidneys to excrete.
Word origin
Where “biliary system” comes from
Biliary comes from the Latin bilis, meaning bile or gall.