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Unformatted text preview: rder to maintain a constant number of cells in
adult tissues and organs, cell death must be balanced by cell proliferation.
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© 2009 Sinauer Associates, Inc. 13 UNCORRECTED PAGE PROOFS
14 CHAPTER 17 FIGURE 17.13 Skin fibroblasts
Scanning electron micrograph of a fibroblast surrounded by collagen fibrils.
(© CMEABG-UCBL/Photo Researchers,
Inc.) In order to maintain this balance, most tissues contain cells that are able to
proliferate as required to replace cells that have died. Moreover, in some tissues a subpopulation of cells divide continuously throughout life to replace
cells that have a high rate of turnover in adult animals. Cell death and cell
renewal are thus carefully balanced to maintain properly sized and functioning adult tissues and organs. Proliferation of Differentiated Cells
Most types of differentiated cells in adult animals are no longer capable of
proliferation. If these cells are lost, they are replaced by the proliferation of
less differentiated cells...
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