CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Human stem cells. Artwork of human stem cells being cultured in a petri dish (left) and differentiating into different cell types (right). Stem cells are undifferentiated cells that can produce other types of cell when they divide. There are three main stem cell types in mammals: embryonic stem cells, derived from blastocysts; adult stem cells, which are found in adult tissues; and cord blood stem cells, which are found in the umbilical cord. The cell types (some shown at right) include smooth muscle cells, skin cells, liver cells, heart cells, nerve cells and red blood cells.
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