The figure below summarizes the blood flow to and from the liver. As mentioned above, the liver receives a dual blood supply. The portal vein supplies blood (from the portal system, the network of veins and capillary beds draining the intestines and spleen) that is rich in nutrients and absorbed dietary substances but poor in oxygen. This provides 75% of the liver's blood supply. The hepatic artery supplies oxygenated blood from the systemic circulation (aorta) and provides the remaining 25% of the liver's blood supply.
 

Within the liver, both the portal vein and the hepatic artery branch within the lobes and eventually converge together into tunnels, or sinusoids , that run parallel to rows of hepatocytes (liver cells). Sinusoids allow the exchange of substances between the blood and hepatocytes and merge to form central veins, which drain blood from the liver into the hepatic vein and then back to the right heart and lungs via the inferior vena cava. 

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