This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Retroperitoneal structure among the following is: 
Select and explain. 
A. Second pa of Duodenu, B. Proximal jejunum, C. Distal jejunum, D. Distal ileum
A: Second pa of Duodenu
Answer: A: Second pa of Duodenu 
Explanation: Duodenum begins at the Duodenal bulb. It travels in the retroperitoneal space around the head of the pancreasIt returns to peritoneal cavity at the ligament of TreitzThe rest of the small intestine is in the peritoneal cavity It is suspended by mesentery, 40% composed by jejunum, 60% by ileum Ref: Sleisenger, E - 9, p - 1615.