The adult human body consists of 100 trillion cells and over 200 different cell types. All these cells have the same genetic material, but they differ in terms of their external characteristics and function. However, the human body does not have this variety of specialists from the outset. At the beginning of individual development, there is always a single unspecialized cell: the fertilized egg cell. In the course of embryonic development, the entire body, with all of the specialized cell types, develops from this original cell (a single-cell embryo) by means of cell division. This characteristic is known as totipotency (Latin: abilityfor all). Not only is the single-cell embryo totipotent, but it is assumed that, up to the eight-cell stage, every cell of the human body has the potential to produce a complete organism.
Stem cells, which form the basis for all organs and tissues in the human body, are crucial for this development of the organism. However, stem cells play an important role not only in embryonic developmentbut throughout our lives. They maintain the functioning of tissues and organs by regularly supplying specialized (differentiated) cells and replacing damaged or dead cells. For example, the body can produce new blood, skin, hair, etc.