Introduction

Gallstones are small, hard pellets that can form in the gallbladder, a sac-like organ that lies under the liver on 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

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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 phospholipid), 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).

Click the icon to see an image of the biliary tree.

• The gallbladder is a 4-inch sac with a muscular wall that is located under the liver. Here, most of the bile fluid (about 2 to 5 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.

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