Gallstone formation as an example of the two-step space confined aggregation process.

Gallstone disease and in particular its cholesterol type is one of the most common diseases of the digestive system. More than 10% of the population is affected by this disease and in the case of Native Indians of Peru and Chile this rate reaches as much as 100%. While the disease is well-researched from a medical point of view, the two-step mechanism of formation of gallstones is not well studied. In this work the first stage gallstone formation namely cholesterol crystallization in the bilayer of the phospholipid vesicles has been described as space confined aggregation process. The formula for the growth rate of the cholesterol crystal has been proposed. It takes into account two competing factors: first is a supersaturation factor and the other is a geometrical stipulation. Depending on the prevailing factor different kinetics can be obtained. Some hypothetical limitations for the second stage of gallstone formation have been proposed.