Lynn Craig, age 14, of Butte, Mont., for her question:

WHERE IS THE GALLBLADDER?

The gallbladder is a muscular organ that serves as a reservoir for bile. In humans, it is a pear shaped membranous sac on the undersurface of the right lobe of the liver just below the lower ribs.

The function of the gallbladder is to store bile, secreted by the liver and transmitted from that organ by way of the cystic and hepatic ducts, until it is needed in the digestive process. The gallbladder is about three inches long, about one inch in diameter at the thickest part and it holds from an ounce to an ounce and a half.

When functioning properly and normally, the gallbladder empties through the biliary ducts into the duodenum to aid digestion by promoting peristalsis and absorption, preventing putrefaction, and emulsifying fat.

The major disorder associated with the gallbladder is the presence of gallstones, varying in shape and size from a pea to a small pear. Accreted from the constituent salts in the bile, they are most common in diabetic patients.