Answer:
The hepatic portal vein is created by the anastamoses between the superior mesenteric vein and spleinc vein. It is arguable that the inferior mesenteric vein joins at this same anastomoses but generally it actually joins the splenic vein which then meats the sup. mesenteric vein as stated above. The veins that drain into the portal vein (ie above the ansastmoses between the splenic and sup. mesenteric) are the cystic vein, the right gastric vein and the posterior-superior part of the pancreaticoduodenal vein.