A model for gallbladder function and cholesterol gallstone formation.

An analysis of fluid mechanics and diffusion in the gallbladder predicts that there is a thin layer of high bile-constituent concentration near the gallbladder wall. Cholesterol may precipitate in this layer, even when the average cholesterol concentration in the gallbladder is below saturation. The amount precipitated increases with time, with increased average cholesterol concentration, and with decreased average lecithin concentration. If the gallbladder does not empty completely, the precipitated cholesterol particles may grow over many cycles of gall bladder filling and emptying. The analysis explains why cholesterol-gallstone formation is not correlated with bile-constituent concentration alone, why a flaccid, noncontractile, gallbladder has a greater chance of forming gallstones, why small stones are frequently found near the gallbladder wall, and why stones may be found in only one limb of a double gallbladder.