The majority of the blood flow to the liver comes from the portal vein. This situation is somewhat unique as that most organs receive their blood supply from an artery. The reason for this is that the digested nutrients from the small intestine and most of the colon drain directly into veins which connect into the portal vein. Therefore nutrients as well as the breakdown products of digestion that need to be filtered flow to the liver as a first stop before going to the rest of the organs.
The liver plays an important role in the digestion and processing of proteins, fat and sugar. The liver helps create some of the building blocks of proteins needed for the body known as amino acids. The liver plays an important role in fat digestion as well as the production of fats needed for the function of different organs of the body.
Simple sugars are created in the liver by breaking down both proteins as well as more complex sugars known as glycogen. The liver can also convert simple sugar into glycogen which is better for storage. In this way the liver acts as an energy center for the body. It controls the balance of simple and complex sugar storage and releases sugar stores when needed for energy.