The hepatic portal vein drains blood to the liver from

The hepatic portal system is found in all vertebrates. The flow of deoxygenated blood from the digestive and absorptive parts of the alimentary canal (especially from the intestine) to the liver before returning to the systemic circulation is called hepatic portal circulation. 

The blood which comes from the alimentary canal contains absorbed food such as glucose, amino acids. The excess of glucose is converted into glycogen and is stored in the liver for later use.