Primary Biliary Cirrhosis
Primary Biliary Cirrhosis (PBC) Overview
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? Bile ducts are small tubes that transport bile from the liver to the larger hepatic ducts and into the gallbladder where bile is stored until a person eats. Bile is then released from the bladder through the common bile ducti into the small intestine where it breaks down food for absorption. Nutrients are then absorbed in the small intestine for the body's use.
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.
Medically Reviewed by a Doctor on 1/9/2014
John M. Vierling, MD, FACP
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