DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Differentiating stem cell (CD34+) from umbilical cord blood, coloured scanning electron micrograph (SEM). Shown here is the first stage of a CD34+ stem cell differentiating in to another blood cell type. Note the new protoplasmic bulge forming at one position on the CD34+ stem cell periphery; this new growth extension of the cell is the first morphological sign of the stem cell developing in to another cell type. CD34+ stem cells are normally found in the umbilical cord and bone marrow as hematopoietic stem cells. They are multipotent because they differentiate to produce precursor (progenitor) cells of any of the body's blood cell types. This process of stem cell differentiation in the circulatory system is called hemopoiesis. CD34 is a cluster differentiation molecule present on undifferentiated stem cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. Magnification: x2,600 when shortest axis.
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