Final answer:
The portal vein carries blood from the gastrointestinal tract to the liver, where nutrients and wastes are processed and excreted.
Step-by-step explanation:
The portal vein transports venous blood from the gastrointestinal tract directly to the liver. The hepatic portal system, which includes the hepatic portal vein, begins at the level of L2 with the confluence of the superior mesenteric and splenic veins. The blood from the GI tract, which is rich in digested nutrients, and spleen, which filters wastes from the blood, then travels to the liver. Here, nutrients can be processed into vital biochemical compounds and wastes can be broken down and excreted. The hepatic portal vein also receives blood from other organs such as the small intestine, two-thirds of the large intestine, and stomach, delivering these materials directly to the liver for processing.