This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
Brunner's glands are seen in: 
Select and explain. 
A. Jejunum, B. Upper duodenum, C. Lower duodenum, D. Appendix
B: Upper duodenum
Answer: B: Upper duodenum 
Explanation: An extensive array of compound mucous glands, called Brunner's glands, is located in the submucosa of the first few centimeters of the duodenum, mainly between the pylorus of the stomach and the papilla of Vater These glands secrete large amounts of alkaline (pH 9) mucus.