<prompt> Posterior relation of poal vein1st pa of duodenumHepatic aeryBile ductIVC  <response>: The poal vein usually measures approximately 8 cm in adults. It originates behind the neck of the pancreas and is classically formed by the confluence of the superior mesenteric and splenic veins. ref - BDC 6e vol2 pg282 , researchgate.net 