This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gallbladder, Subject name: Surgery
[{'content': 'All of the following are essential for formation of gallstones except: \nSelect and explain. \nA. Bile stasis, B. Nucleation, C. Crystallization, D. Lithogenic bile', 'role': 'user'}, {'content': "Answer: C \nExplanation: Factors Responsible for Formation of Gallstones Lithogenic bile Nucleation Stasis or GB hypomotility Increased Biliary Cholesterol: - Obesity - Cholestrol rich diet - Clofibrate therapy Cholesterol monohydrate crystal agglomerate to become macroscopic crystal by nucleation Pro-nucleating Factors: - Mucin - Non-mucin glycoprotein - Infection Anti-nucleating Factors: Apolipoprotien A-1 and A-2 Excess of pro-nucleating factors or deficiency of anti-nucleating factors results in formation of gallstones Prolonged TPN Prolonged fasting Pregnancy Octreotide OCPs Massive burns Decreased Bile Acids: - Primary biliary cirrhosis - OCP's - Mutation of CYP7A1 gene - Impaired enterohepatic circulation of bile acids:Ileal disease or resection, cholestyramine or colestipol (bile acid sequestrants) Decreased Biliary Lecithin: - MDR-3 gene mutation leads to defective lecithin secretion in bile", 'role': 'assistant'}]