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quote:The liver is among the few internal human organs capable of natural regeneration of lost tissue; as little as 25% of remaining liver can regenerate into a whole liver again. This is predominantly due to the hepatocytes acting as unipotential stem cells (i.e. a single hepatocyte can divide into two hepatocyte daughter cells). There is also some evidence of bipotential stem cells, called oval cells, which can differentiate into either hepatocytes or cholangiocytes (cells that line the bile ducts).
quote:Regeneration is a form of tissue repair. The restoration of lost or damaged tissues, organs or limbs. When tissue is damaged, it will be either regenerated or replaced by connective tissue. Regeneration is common in invertebrates but far more limited in most vertebrates, where usually only certain kinds of tissue can regenerate if the damage is not too substantial. Nevertheless, even humans are capable of some degree of regeneration. Humans can regenerate finger tips (distal to the last joint). It can occur throughout the human lifetime, but it is generally best in young children. The human liver also retains its ability to regenerate throughout a person's lifetime. Other tissues, such as the epidermis, blood vessels and peripheral nerves also regenerate under many conditions. Regeneration of some tissues, such as the epidermis, is related to the fact that these tissues are continuously being replaced throughout life. Regeneration of a lost limb occurs in two major steps, first de-differentiation of adult cells into a stem cell state similar to embryonic cells and second, development of these cells into new tissue more or less the same way it developed the first time. Some animals like planarians instead keep clusters of non-differentiated cells within their bodies, which migrate to the parts of the body that need healing.
quote:Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a "type". The morphology of a cell may change dramatically during differentiation, but the genetic material remains the same, with few exceptions.A cell that is able to differentiate into many cell types is known as pluripotent. These cells are called stem cells in animals and meristematic cells in higher plants. A cell that is able to differentiate into all cell types is known as totipotent. In mammals, only the zygote and early embryonic cells are totipotent, while in plants, many differentiated cells can become totipotent with simple laboratory techniques.
quote:Stem cells in people are primal undifferentiated cells that retain the ability to produce an identical copy of themselves when they divide (clone) and differentiate into other cell types. In higher animals this function is the defining property of the deleted cells. Stem cells have the ability to act as a repair system for the body, because they can divide and differentiate, replenishing other cells as long as the host organism is alive.