Primary Biliary Cirrhosis
(PBC)
Medical Author: John M. Vierling, MD, FACP
Medical Editor: Leslie J. Schoenfield, MD, PhD
What is PBC?
Primary biliary cirrhosis (PBC) is a chronic (long duration) disease
characterized by progressive inflammation and destruction of the small bile
ducts within the liver. What are the bile ducts and what do they do? Lined with
cells named biliary epithelial cells, the bile ducts are tubules that make up a
plumbing system for the liver. The bile ducts along with the gallbladder are
part of what is called the biliary tract.
The plumbing system begins in the liver with very small caliber ducts that
connect to increasingly larger caliber ducts, like a tree in which twigs connect
to small branches that connect to larger branches. In fact, this system is often
referred to as the biliary tree. The large right and left bile ducts, still
within the liver, connect to an even larger common bile duct that runs outside
the liver to the small intestine just beyond the stomach. The common bile duct
connects by the cystic duct to the gallbladder. The gallbladder is a
pear-shaped, expandable, sac-like organ in the biliary system. The branching
bile ducts course through special tissue in the liver, called portal tracts,
which act like conduits for the ducts. In fact, the branching portal tracts
containing the bile ducts also contain the blood vessels that enter and leave
the liver.
The bile ducts carry bile, a fluid that is produced by the liver cells
(hepatocytes) and modified by the biliary lining (epithelial) cells as it flows
through the ducts to the small intestine. Bile contains substances required for
digestion and absorption of fat called bile acids, as well as other compounds
that are waste products, such as the pigment bilirubin. (Bilirubin is a
yellow-orange compound produced by the breakdown of hemoglobin from old red
blood cells.) Bile is stored in the gallbladder between meals and discharged
into the small intestine during digestion of the meals.
The inflammation in PBC starts in the liver's portal tracts and involves
the small bile ducts in these areas. The destruction of the small bile ducts
blocks the normal flow of bile into the gut. The medical term for decreased flow
of bile is cholestasis. (Chole means bile and stasis means failure to flow.)
Cholestasis is a very important aspect of this disease. As the inflammation
continues to destroy more of these bile ducts, it spreads to destroy nearby
liver cells (hepatocytes). As the inflammatory destruction of the hepatocytes
proceeds, scar tissue (fibrosis) forms and spreads through the areas of
destruction.
The combined effects of progressive inflammation, scarring, and toxicity of
bile trapped within hepatocytes (liver cells) culminates in cirrhosis. Cirrhosis
is defined as the stage of disease when there is both widespread scarring of the
liver and clusters (nodules) of hepatocytes reproducing (regenerating)
themselves within the scars. Since cirrhosis occurs only in the later stage of
PBC, the name primary biliary cirrhosis is actually a misnomer for patients in
the earlier stages of the illness. The more technically correct and ponderous
term for PBC, chronic non-suppurative destructive cholangitis, however, has
never been widely used and is unlikely to replace PBC.
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