Unformatted text preview: ced as a programmed response to
stimuli such as infection or DNA damage, which also induce apoptosis.
Under these conditions, regulated necrosis may provide an alternative
pathway of cell death if apoptosis does not occur. For example, if apoptosis
is inhibited, stimulation of the TNF receptor leads to cell death by necrosis.
The importance of both autophagy and necrosis as alternatives to apoptosis
remains to be fully explored, not only in normal cells but also in diseases
such as cancer, heart disease, and neurodegeneration, which involve abnormalities of cell survival. Stem Cells and the Maintenance
of Adult Tissues
Early development is characterized by the rapid proliferation of embryonic
cells, which then differentiate to form the specialized cells of adult tissues
and organs. As cells differentiate, their rate of proliferation usually
decreases, and most cells in adult animals are arrested in the G0 stage of the
cell cycle. However, cells are lost either due to injury or programmed cell
death throughout life. In o...
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