Re: what causes an enlarged gallbladder
I'm not sure what your term "enlarged gallbladder" means. The gallbladder can become filled with gallstones, in a few cases with stones as large as golf balls. Would this stretch the gallbladder, perhaps.
You also have situations where the walls of the gallbladder become thicker and less flexible due to inflammation or disease. Causes of gallbladder disease can include low fat diets, high fat diets, a family history.
Basically, your liver produces cholesterol and bile which then travels to the the gallbladder where it is concentrated. When your digestive system sends a message for the gallbladder to contract it releases concentrated bile to help with digesting fat. As the bile sits in the gallbladder it can precipitate out and start forming stones.