If an injury occurs to a human body, the tissue regenerates over time as new cells replace the injured ones, and non-injured skin tissue regenerates within two weeks. Humans can regenerate the liver if a part of it is lost or injured. It regenerates itself back to its original size though not shape. Many liver transplants are done where a part of the donor's liver grows into the receiver's body and functions normally. Our skin constantly renews itself by shedding old cells.