The human liver can grow back to its full size from just one-quarter of its original mass.

The liver begins the repair process within hours of an injury or surgery. It does not grow back into its original shape. Instead, the remaining parts of the liver expand until the organ reaches its normal weight.In living-donor transplants, surgeons can remove up to 70% of a healthy person's liver. Both the donor and the person receiving the organ will have full-sized livers within 4 to 6 weeks. This rapid growth is controlled by specific proteins and chemicals in the blood.Growth factors like Hepatocyte Growth Factor signal liver cells to start dividing. Other chemicals called cytokines help manage this process. These signals tell the cells when to start growing and when to stop once the liver is the right size.The liver continues to work while it is growing. It still produces bile and stores energy without stopping. This makes it the only internal organ in humans that can fully regenerate itself.