This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Sphincter of Lutkans seen in 
Select and explain. 
A. Cystic duct, B. Common bile duct, C. Pancreatic duct, D. Ampulla of vater
A: Cystic duct
Answer: A: Cystic duct 
Explanation: The mucosa of the cystic duct is arranged in spiral folds known as the valves of Heister and the wall is surrounded by a sphincteric structure called the sphincter of Lutkens.The mucous membrane contains indentations of the mucosa that sink into the muscle coat; these are the crypts of Luschka.Ref: Bailey and Love 27th edition Pg: 1188