107
CHAPTER THREE
Cells
one or more steps
Sperm
Egg
Fertilized
egg
Stem cell
Stem cell
Progenitor cell
Progenitor
cell
Progenitor
cell
Progenitor
cell
Progenitor
cell
Progenitor
cells
Blood cells and platelets
Fibroblasts (a connective tissue cells)
Bone cells
Progenitor
cell
Progenitor
cell
Astrocyte
Neuron
Skin cell
Sebaceous
gland cell
produces another stem cell
(self-renewal)
Progenitor
cell
Progenitor
cells
FIGURE 3.41
Cells specialize along cell lineage pathways. All cells in the human body ultimately descend from stem cells, through the processes
of mitosis and diF
erentiation. This simpliĀ±
ed view depicts a few of the pathways that cells follow, grouping the cell types by the closeness of their
lineages. A progenitor cell may yield daughter cells of the same type, such as bone cells, or daughter cells of diF
erent types, such as a neuron and an
astrocyte. Imagine the complexity of the lineages of the more than 260 human cell types!
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