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Haematopoietic stem cells, coloured scanning electron micrograph (SEM). Stem cells can differentiate into any other cell type. There are three main types of stem cell in mammals: embryonic stem cells, derived from blastocysts; adult stem cells, which are found in some adult tissues; and cord blood stem cells, which are found in the umbilical cord. These cells are destined to become blood cells. During blood cell development in adults, stem cells develop through a process known as haemopoiesis. Blood cells, which have short lifespans, are constantly produced by the bone marrow.
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