Printer friendly format! | Email to a friend!

WHAT ARE GALLSTONES AND GALLBLADDER DISEASE?
Gallstones are small, hard pellets that can form in the gallbladder, a sac-like organ that lies under the liver in the right side of the abdomen. Most people with gallstones don't even know they have them. But in some cases a stone may cause the gallbladder to become inflamed, resulting in pain, infection, or other serious complications.

Bile and the Gallbladder
The formation of gallstones is a complex process that starts with bile, a fluid composed mostly of water, bile salts, lecithin (a fat known as a phopholipid), and cholesterol. (Most gallstones are formed from cholesterol.)

• Bile is important for the digestion of fat. It is first produced by the liver and then secreted through tiny channels that eventually lead into a larger tube called the common bile duct, which leads to the small intestine.

• Only a small amount of bile drains directly into the small intestine, however. Most flows into the gallbladder through the cystic duct, which is a side extension off the common bile duct. (This system of ducts through which bile flows is called the biliary tree).

• The gallbladder is a four-inch sac with a muscular wall that is located under the liver. Here, most of the bile fluid (about two to five cups a day) is removed, leaving a few tablespoons of concentrated bile.

• The gallbladder serves as a reservoir until bile is needed in the small intestine to digest fats. This need is triggered by a hormone called cholecystokinin, which is released when food enters the small intestine.

• Cholecystokinin signals the gallbladder to contract and deliver bile into the intestine. The force of the contraction propels the bile back down the common bile duct and then into the small intestine, where it emulsifies (breaks down) fatty molecules.

• This part of the digestive process enables the emulsified fat, along with important fat-absorbable nutrients (e.g., vitamins A, D, E, and K), to pass through the intestinal lining and enter the blood stream.

Formation of Gallstones (Cholelithiasis)
Gallstones can range from a few millimeters to several centimeters in diameter. Most are formed from cholesterol. The other most common gallstone is known as a pigment stone. Patients can also have mixture of these two. Another 15% are known as pigment stones and are formed from a brown-colored substance called calcium bilirubinate.

Cholesterol Stones. Although cholesterol makes up only five percent of bile, about three-quarters of the gallstones found in the US population are formed from this substance. Cholesterol gallstones typically form in the following way:

• Cholesterol is not very soluble, so in order to remain suspended in fluid it must be transported within clusters of bile salts called micelles. If there is an imbalance between these bile salts and cholesterol, then the bile fluid turns to sludge. This thickened fluid consists of a mucus gel containing cholesterol and calcium bilirubinate.

• If the imbalance worsens, cholesterol crystals form (calledsupersaturation), which can eventually form gallstones.

• This process of gallstone formation is referred to as cholelithiasis. It is very slow and most often painless.

Supersaturation and cholelithiasis can occur as a result of various abnormalities, although the cause is not entirely clear. Events that may promote cholelithiasis include the following:

• The liver secretes too much cholesterol into the bile.

• The gallbladder may not be able to empty normally, so that the bile becomes stagnant.

• The cells lining the gallbladder may not be able to absorb cholesterol and fat from bile efficiently.

Pigment Stones. Pigment stones are composed of calcium bilirubinate, or calcified bilirubin. Bilirubin is a substance normally formed by the breakdown of hemoglobin in the blood and is excreted in bile. Pigment stones can be black or brown.

• Black stones form in the gallbladder and are the more common type. In fact, they represent 20% of all gallstones in the US. They are more likely to develop in people with hemolytic anemia (a relatively rare anemia in which red blood cells are destroyed) or cirrhosis (a scarred liver).

• Brown pigment stones are more common in Asian populations. They contain more cholesterol and calcium than black pigment stones and are more likely to occur in the bile ducts. Infection plays a role in the development of these stones. One report suggests that bacteria or other microorganisms may trigger oxidation -- a damaging chemical process in the body -- that in this case causes changes that lead to pigment stone formation.