Poal vein is formed by the union of
The poal vein is usually formed by the confluence of the superior mesenteric and splenic veins and also receives blood from the inferior mesenteric, gastric, and cystic veins. Ref - BDC 6e vol2 pg282
Splenic and inferior mesentric veins
Splenic and superior mesentric veins
Right and left hepatic veins
Hepatic and splenic veins
Abdomen and pelvis