Stem Cell|醫療線上App不用買-HotApp4Game

The human body is made up of billions of cells, each one ofwhich is derived from a single fertilised 'egg cell'.However, the body's cells are not all identical. There areat least two hundred distinct cell types, all with differentfeatures and functions, such as neurons (nerve cells), livercells, skin cells, and so on. These specialised cells arethe body's mature or fully differentiated, cells, all ofwhich are derived from their common ancestors, stem cells.Stem cells are a class of undifferentiated cells that areable to differentiate into specialized cell types. Commonly,stem cells come from two main sources:1. Embryos formed during the blastocyst phase ofembryological development (embryonic stem cells) and 2.Adult tissue (adult stem cells).Both types are generally characterized by their potency, orpotential to differentiate into different cell types (suchas skin, muscle, bone, etc.).Stem cells have the remarkable potential to develop intomany different cell types in the body during early life andgrowth. In addition, in many tissues they serve as a sort ofinternal repair system, dividing essentially without limitto replenish other cells as long as the person or animal isstill alive. When a stem cell divides, each new cell has thepotential either to remain a stem cell or become anothertype of cell with a more specialized function, such as amuscle cell, a red blood cell, or a brain cell.Stem cells are distinguished from other cell types by twoimportant characteristics. First, they are unspecializedcells capable of renewing themselves through cell division,sometimes after long periods of inactivity. Second, undercertain physiologic or experimental conditions, they can beinduced to become tissue- or organ-specific cells withspecial functions. In some organs, such as the gut and bonemarrow, stem cells regularly divide to repair and replaceworn out or damaged tissues. In other organs, however, suchas the pancreas and the heart, stem cells only divide underspecial conditions.